Gene Summary

Gene:HIPK2; homeodomain interacting protein kinase 2
Aliases: PRO0593
Summary:This gene encodes a conserved serine/threonine kinase that is a member of the homeodomain-interacting protein kinase family. The encoded protein interacts with homeodomain transcription factors and many other transcription factors such as p53, and can function as both a corepressor and a coactivator depending on the transcription factor and its subcellular localization. Multiple transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Nov 2011]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:homeodomain-interacting protein kinase 2
Source:NCBIAccessed: 15 March, 2017


What does this gene/protein do?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 15 March 2017 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 15 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (4)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: HIPK2 (cancer-related)

Haque M, Kendal JK, MacIsaac RM, Demetrick DJ
WSB1: from homeostasis to hypoxia.
J Biomed Sci. 2016; 23(1):61 [PubMed] Free Access to Full Article Related Publications
The wsb1 gene has been identified to be important in developmental biology and cancer. A complex transcriptional regulation of wsb1 yields at least three functional transcripts. The major expressed isoform, WSB1 protein, is a substrate recognition protein within an E3 ubiquitin ligase, with the capability to bind diverse targets and mediate ubiquitinylation and proteolytic degradation. Recent data suggests a new role for WSB1 as a component of a neuroprotective pathway which results in modification and aggregation of neurotoxic proteins such as LRRK2 in Parkinson's Disease, via an unusual mode of protein ubiquitinylation.WSB1 is also involved in thyroid hormone homeostasis, immune regulation and cellular metabolism, particularly glucose metabolism and hypoxia. In hypoxia, wsb1 is a HIF-1 target, and is a regulator of the degradation of diverse proteins associated with the cellular response to hypoxia, including HIPK2, RhoGDI2 and VHL. Major roles are to both protect HIF-1 function through degradation of VHL, and decrease apoptosis through degradation of HIPK2. These activities suggest a role for wsb1 in cancer cell proliferation and metastasis. As well, recent work has identified a role for WSB1 in glucose metabolism, and perhaps in mediating the Warburg effect in cancer cells by maintaining the function of HIF1. Furthermore, studies of cancer specimens have identified dysregulation of wsb1 associated with several types of cancer, suggesting a biologically relevant role in cancer development and/or progression.Recent development of an inducible expression system for wsb1 could aid in the further understanding of the varied functions of this protein in the cell, and roles as a potential oncogene and neuroprotective protein.

Schulten HJ, Hussein D, Al-Adwani F, et al.
Microarray Expression Data Identify DCC as a Candidate Gene for Early Meningioma Progression.
PLoS One. 2016; 11(4):e0153681 [PubMed] Free Access to Full Article Related Publications
Meningiomas are the most common primary brain tumors bearing in a minority of cases an aggressive phenotype. Although meningiomas are stratified according to their histology and clinical behavior, the underlying molecular genetics predicting aggressiveness are not thoroughly understood. We performed whole transcript expression profiling in 10 grade I and four grade II meningiomas, three of which invaded the brain. Microarray expression analysis identified deleted in colorectal cancer (DCC) as a differentially expressed gene (DEG) enabling us to cluster meningiomas into DCC low expression (3 grade I and 3 grade II tumors), DCC medium expression (2 grade I and 1 grade II tumors), and DCC high expression (5 grade I tumors) groups. Comparison between the DCC low expression and DCC high expression groups resulted in 416 DEGs (p-value<0.05; fold change>2). The most significantly downregulated genes in the DCC low expression group comprised DCC, phosphodiesterase 1C (PDE1C), calmodulin-dependent 70kDa olfactomedin 2 (OLFM2), glutathione S-transferase mu 5 (GSTM5), phosphotyrosine interaction domain containing 1 (PID1), sema domain, transmembrane domain (TM) and cytoplasmic domain, (semaphorin) 6D (SEMA6D), and indolethylamine N-methyltransferase (INMT). The most significantly upregulated genes comprised chromosome 5 open reading frame 63 (C5orf63), homeodomain interacting protein kinase 2 (HIPK2), and basic helix-loop-helix family, member e40 (BHLHE40). Biofunctional analysis identified as predicted top upstream regulators beta-estradiol, TGFB1, Tgf beta complex, LY294002, and dexamethasone and as predicted top regulator effectors NFkB, PIK3R1, and CREBBP. The microarray expression data served also for a comparison between meningiomas from female and male patients and for a comparison between brain invasive and non-invasive meningiomas resulting in a number of significant DEGs and related biofunctions. In conclusion, based on its expression levels, DCC may constitute a valid biomarker to identify those benign meningiomas at risk for progression.

Di Rocco G, Verdina A, Gatti V, et al.
Apoptosis induced by a HIPK2 full-length-specific siRNA is due to off-target effects rather than prevalence of HIPK2-Δe8 isoform.
Oncotarget. 2016; 7(2):1675-86 [PubMed] Free Access to Full Article Related Publications
Small interfering RNAs (siRNAs) are widely used to study gene function and extensively exploited for their potential therapeutic applications. HIPK2 is an evolutionary conserved kinase that binds and phosphorylates several proteins directly or indirectly related to apoptosis. Recently, an alternatively spliced isoform skipping 81 nucleotides of exon 8 (Hipk2-Δe8) has been described. Selective depletion of Hipk2 full-length (Hipk2-FL) with a specific siRNA that spares the Hipk2-Δe8 isoform has been shown to strongly induce apoptosis, suggesting an unpredicted dominant-negative effect of Hipk2-FL over the Δe8 isoform. From this observation, we sought to take advantage and assessed the therapeutic potential of generating Hipk2 isoform unbalance in tumor-initiating cells derived from colorectal cancer patients. Strong reduction of cell viability was induced in vitro and in vivo by the originally described exon 8-specific siRNA, supporting a potential therapeutic application. However, validation analyses performed with additional exon8-specific siRNAs with different stabilities showed that all exon8-targeting siRNAs can induce comparable Hipk2 isoform unbalance but only the originally reported e8-siRNA promotes cell death. These data show that loss of viability does not depend on the prevalence of Hipk2-Δe8 isoform but it is rather due to microRNA-like off-target effects.

Conrad E, Polonio-Vallon T, Meister M, et al.
HIPK2 restricts SIRT1 activity upon severe DNA damage by a phosphorylation-controlled mechanism.
Cell Death Differ. 2016; 23(1):110-22 [PubMed] Free Access to Full Article Related Publications
Upon severe DNA damage a cellular signalling network initiates a cell death response through activating tumour suppressor p53 in association with promyelocytic leukaemia (PML) nuclear bodies. The deacetylase Sirtuin 1 (SIRT1) suppresses cell death after DNA damage by antagonizing p53 acetylation. To facilitate efficient p53 acetylation, SIRT1 function needs to be restricted. How SIRT1 activity is regulated under these conditions remains largely unclear. Here we provide evidence that SIRT1 activity is limited upon severe DNA damage through phosphorylation by the DNA damage-responsive kinase HIPK2. We found that DNA damage provokes interaction of SIRT1 and HIPK2, which phosphorylates SIRT1 at Serine 682 upon lethal damage. Furthermore, upon DNA damage SIRT1 and HIPK2 colocalize at PML nuclear bodies, and PML depletion abrogates DNA damage-induced SIRT1 Ser682 phosphorylation. We show that Ser682 phosphorylation inhibits SIRT1 activity and impacts on p53 acetylation, apoptotic p53 target gene expression and cell death. Mechanistically, we found that DNA damage-induced SIRT1 Ser682 phosphorylation provokes disruption of the complex between SIRT1 and its activator AROS. Our findings indicate that phosphorylation-dependent restriction of SIRT1 activity by HIPK2 shapes the p53 response.

Valente D, Bossi G, Moncada A, et al.
HIPK2 deficiency causes chromosomal instability by cytokinesis failure and increases tumorigenicity.
Oncotarget. 2015; 6(12):10320-34 [PubMed] Free Access to Full Article Related Publications
HIPK2, a cell fate decision kinase inactivated in several human cancers, is thought to exert its oncosuppressing activity through its p53-dependent and -independent apoptotic function. However, a HIPK2 role in cell proliferation has also been described. In particular, HIPK2 is required to complete cytokinesis and impaired HIPK2 expression results in cytokinesis failure and tetraploidization. Since tetraploidy may yield to aneuploidy and chromosomal instability (CIN), we asked whether unscheduled tetraploidy caused by loss of HIPK2 might contribute to tumorigenicity. Here, we show that, compared to Hipk2+/+ mouse embryo fibroblasts (MEFs), hipk2-null MEFs accumulate subtetraploid karyotypes and develop CIN. Accumulation of these defects inhibits proliferation and spontaneous immortalization of primary MEFs whereas increases tumorigenicity when MEFs are transformed by E1A and Harvey-Ras oncogenes. Upon mouse injection, E1A/Ras-transformed hipk2-null MEFs generate tumors with genetic alterations resembling those of human cancers derived by initial tetraploidization events, such as pancreatic adenocarcinoma. Thus, we evaluated HIPK2 expression in different stages of pancreatic transformation. Importantly, we found a significant correlation among reduced HIPK2 expression, high grade of malignancy, and high nuclear size, a marker of increased ploidy. Overall, these results indicate that HIPK2 acts as a caretaker gene, whose inactivation increases tumorigenicity and causes CIN by cytokinesis failure.

Kwon MJ, Min SK, Seo J, et al.
HIPK2 expression in progression of cutaneous epithelial neoplasm.
Int J Dermatol. 2015; 54(3):347-54 [PubMed] Related Publications
BACKGROUND: Homeodomain-interacting protein kinase 2 (HIPK2) is responsible for a DNA damage response, centrally regulating p53. The aberrant HIPK2 expression is known to be involved in carcinogenesis in several malignancies. However, the correlation of HIPK2 expression along with progression of cutaneous epithelial neoplasm has not been investigated.
METHODS: Using immunohistochemistry and real-time reverse transcription-polymerase chain reaction, we examined the correlation between HIPK2 and HIPK2-related protein expressions and the progression of some cutaneous epithelial neoplasms (i.e., actinic keratosis, Bowen's disease, keratoacanthoma, squamous cell carcinoma, and basal cell carcinoma).
RESULTS: HIPK2 expression was distinct between preinvasive and invasive lesions: the expression decreased in keratoacanthoma (none of eight) and squamous cell carcinoma (five of 35) compared to actinic keratosis (12 of 19) and Bowen's disease (10 of 23) (P < 0.001). HIPK2 expression was also negatively correlated with aggressiveness of basal cell carcinoma; high-risk subtypes showed lower HIPK2 expression than did low-risk subtypes (P < 0.001). HIPK2 mRNA expression of each tumor group was significantly higher than that of normal skin. HIPK2 mRNA expression of each tumor group was not correlated with the relevant HIPK2 protein expression, which was consistent with previous studies.
CONCLUSIONS: HIPK2 expression tends to be decreased along tumor progression and may be involved with the invasive potential, suggesting a possible tumor suppressor role for HIPK2.

Zhou L, Feng Y, Jin Y, et al.
Verbascoside promotes apoptosis by regulating HIPK2-p53 signaling in human colorectal cancer.
BMC Cancer. 2014; 14:747 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: We investigated the role of the HIPK2-p53 signaling pathway in tumorigenesis and resistance to the drug Verbascoside (VB) in colorectal cancer (CRC), using in vivo and in vitro experiments.
METHODS: Primary human CRC samples and normal intestinal tissues from patients were analyzed for HIPK2 expression by immunohistochemistry (IHC) and its expression was correlated against patients' clinicopathological characteristics. Human CRC HCT-116 cells were implanted in BALB/c nude mice; mice with xenografted tumors were randomly administrated vehicle (control), 20, 40, or 80 mg/mL VB, or 1 mg/mL fluorouracil (5-FU). HIPK2, p53, Bax, and Bcl-2 expression in these tumors were determined by IHC. In vitro effects of VB on CRC cell proliferation and apoptosis were measured by CCK-8 assay and flow cytometry; HIPK2, p53, p-p53, Bax, and Bcl-2 were measured by western blot.
RESULTS: IHC analysis for 100 human CRC tumor samples and 20 normal intestinal tissues, showed HIPK2 expression to inversely correlate with Dukes stage and depth of invasion in CRC (P<0.05). In vivo, the inhibition rates of 20, 40, and 80 mg/mL VB on CRC xenograft tumor weight were 42.79%, 53.90%, and 60.99%, respectively, and were accompanied by increased expression of HIPK2, p53, and Bax, and decreased Bcl-2 expression in treated tumors. In vitro, VB significantly inhibited proliferation of CRC cell lines HCT-116, HT-29, LoVo, and SW620, in a time- and dose-dependent manner. The apoptosis rates of 25, 50, and 100 μM VB on HCT-116 cells were 10.83±1.28, 11.25±1.54, and 20.19±2.87%, and on HT-29 cells were 18.92±6.12, 21.57±4.05, and 25.14±6.73%, respectively. In summary, VB treatment significantly enhanced the protein expression of pro-apoptotic HIPK2, p53, p-p53, Bax, and decreased anti-apoptotic Bcl-2 expression in CRC cells.
CONCLUSIONS: HIPK2 protein modulates the phosphorylation status of p53, and levels of Bax and Bcl-2 in CRC. We also found that VB effectively activated the HIPK2-p53 signaling pathway, resulting in increased CRC cell apoptosis.

Lin J, Zhang Q, Lu Y, et al.
Downregulation of HIPK2 increases resistance of bladder cancer cell to cisplatin by regulating Wip1.
PLoS One. 2014; 9(5):e98418 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: Cisplatin-based combination chemotherapy regimen is a reasonable alternative to cystectomy in advanced/metastatic bladder cancer, but acquisition of cisplatin resistance is common in patients with bladder cancer. Previous studies showed that loss of homeodomain-interacting protein kinase-2 (HIPK2) contributes to cell proliferation and tumorigenesis. However, the role of HIPK2 in regulating chemoresistance of cancer cell is not fully understood. In the present study, we found that HIPK2 mRNA and protein levels are significantly decreased in cisplatin-resistant bladder cancer cell in vivo and in vitro. Downregulation of HIPK2 increases the cell viability in a dose- and time-dependent manner during cisplatin treatment, whereas overexpression of HIPK2 reduces the cell viability. HIPK2 overexpression partially overcomes cisplatin resistance in RT4-CisR cell. Furthermore, we showed that Wip1 (wild-type p53-induced phosphatase 1) expression is upregulated in RT4-CisR cell compared with RT4 cell, and HIPK2 negatively regulates Wip1 expression in bladder cancer cell. HIPK2 and Wip1 expression is also negatively correlated after cisplatin-based combination chemotherapy in vivo. Finally, we demonstrated that overexpression of HIPK2 sensitizes chemoresistant bladder cancer cell to cisplatin by regulating Wip1 expression.
CONCLUSIONS: These data suggest that HIPK2/Wip1 signaling represents a novel pathway regulating chemoresistance, thus offering a new target for chemotherapy of bladder cancer.

Tan M, Gong H, Zeng Y, et al.
Downregulation of homeodomain-interacting protein kinase-2 contributes to bladder cancer metastasis by regulating Wnt signaling.
J Cell Biochem. 2014; 115(10):1762-7 [PubMed] Related Publications
Homeodomain-interacting protein kinase-2 (Hipk2) has been shown to have important regulatory roles in cancer biology, such as cancer cell proliferation, cell cycle, and cell invasion. However, the contributions of Hipk2 to bladder cancer metastasis remain largely unknown. In the current study, we assayed the expression level of Hipk2 in bladder cancer tissues by real-time PCR, and defined its biological functions. We found that Hipk2 levels were downregulated in most bladder cancer tissues compared with adjacent normal tissues, and Hipk2 levels were remarkably decreased in metastasized tumor tissues when compared with primary tumors. SiRNA-mediated Hipk2 silencing increased bladder cancer cell invasion. Hipk2 knockdown resulted in decrease of E-cadherin expression and increase of N-cadherin and fibronectin expression, indicated that epithelial-mesenchymal transition (EMT) was induced. We further demonstrated that Hipk2 knockdown induced Wnt signaling activation and β-catenin nuclear localization. Finally, we confirmed that Hipk2 inhibition promoted EMT and subsequent cell invasion, at least in part by activating Wnt signaling. These data suggest an important role of Hipk2 in regulating metastasis of bladder cancer and implicate the potential application of Hipk2 in bladder cancer therapy.

Fleischmann KK, Pagel P, Schmid I, Roscher AA
RNAi-mediated silencing of MLL-AF9 reveals leukemia-associated downstream targets and processes.
Mol Cancer. 2014; 13:27 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The translocation t(9;11)(p22;q23) leading to the leukemogenic fusion gene MLL-AF9 is a frequent translocation in infant acute myeloid leukemia (AML). This study aimed to identify genes and molecular processes downstream of MLL-AF9 (alias MLL-MLLT3) which could assist to develop new targeted therapies for such leukemia with unfavorable prognosis.
METHODS: In the AML cell line THP1 which harbors this t(9;11) translocation, endogenous MLL-AF9 was silenced via siRNA while ensuring specificity of the knockdown and its efficiency on functional protein level.
RESULTS: The differential gene expression profile was validated for leukemia-association by gene set enrichment analysis of published gene sets from patient studies and MLL-AF9 overexpression studies and revealed 425 differentially expressed genes. Gene ontology analysis was consistent with a more differentiated state of MLL-AF9 depleted cells, with involvement of a wide range of downstream transcriptional regulators and with defined functional processes such as ribosomal biogenesis, chaperone binding, calcium homeostasis and estrogen response. We prioritized 41 gene products as candidate targets including several novel and potentially druggable effectors of MLL-AF9 (AHR, ATP2B2, DRD5, HIPK2, PARP8, ROR2 and TAS1R3). Applying the antagonist SCH39166 against the dopamine receptor DRD5 resulted in reduced leukemic cell characteristics of THP1 cells.
CONCLUSION: Besides potential new therapeutic targets, the described transcription profile shaped by MLL-AF9 provides an information source into the molecular processes altered in MLL aberrant leukemia.

Tong Y, Li QG, Xing TY, et al.
HIF1 regulates WSB-1 expression to promote hypoxia-induced chemoresistance in hepatocellular carcinoma cells.
FEBS Lett. 2013; 587(16):2530-5 [PubMed] Related Publications
WSB-1 is involved in DNA damage response by targeting homeodomain-interacting protein kinase 2 (HIPK2) for ubiquitination and degradation. Here, we report that hypoxia significantly up-regulates the expression of WSB-1 in human hepatocellular carcinoma (HCC) cells. We also provide evidence that WSB-1 is a target of hypoxia-inducible factor 1 (HIF-1). Silencing the expression of HIF-1α in HCC cells by RNA interference abolishes hypoxia-induced WSB-1 expression. Using chromatin immunoprecipitation and luciferase reporter assays, we identified a HRE of the WSB-1 gene. Moreover, silencing the expression of WSB-1 by RNA interference rescues HIPK2 expression in hypoxic HCC cells and promotes etoposide-induced cell death in hypoxic HCC cells. Taken together, these data shed light on the mechanisms underlying hypoxia-induced chemoresistance in HCC cells.

Saul VV, Schmitz ML
Posttranslational modifications regulate HIPK2, a driver of proliferative diseases.
J Mol Med (Berl). 2013; 91(9):1051-8 [PubMed] Related Publications
The serine/threonine kinase homeodomain-interacting protein kinase (HIPK2) is a tumor suppressor and functions as an evolutionary conserved regulator of signaling and gene expression. This kinase regulates a surprisingly vast array of biological processes that range from the DNA damage response and apoptosis to hypoxia signaling and cell proliferation. Recent studies show the tight control of HIPK2 by hierarchically occurring posttranslational modifications such as phosphorylation, small ubiquitin-like modifier modification, acetylation, and ubiquitination. The physiological function of HIPK2 as a regulator of cell proliferation and survival has a downside: proliferative diseases. Dysregulation of HIPK2 can result in increased proliferation of cell populations as it occurs in cancer or fibrosis. We discuss various models that could explain how inappropriate expression, modification, or localization of HIPK2 can be a driver for these proliferative diseases.

Kurokawa K, Akaike Y, Masuda K, et al.
Downregulation of serine/arginine-rich splicing factor 3 induces G1 cell cycle arrest and apoptosis in colon cancer cells.
Oncogene. 2014; 33(11):1407-17 [PubMed] Related Publications
Serine/arginine-rich splicing factor 3 (SRSF3) likely has wide-ranging roles in gene expression and facilitation of tumor cell growth. SRSF3 knockdown induced G1 arrest and apoptosis in colon cancer cells (HCT116) in association with altered expression of 833 genes. Pathway analysis revealed 'G1/S Checkpoint Regulation' as the most highly enriched category in the affected genes. SRSF3 knockdown did not induce p53 or stimulate phosphorylation of p53 or histone H2A.X in wild-type HCT116 cells. Furthermore, the knockdown induced G1 arrest in p53-null HCT116 cells, suggesting that p53-dependent DNA damage responses did not mediate the G1 arrest. Real-time reverse transcription-polymerase chain reaction and western blotting confirmed that SRSF3 knockdown reduced mRNA and protein levels of cyclins (D1, D3 and E1), E2F1 and E2F7. The decreased expression of cyclin D and E2F1 likely impaired the G1-to-S-phase progression. Consequently, retinoblastoma protein remained hypophosphorylated in SRSF3 knockdown cells. The knockdown also induced apoptosis in association with reduction of BCL2 protein levels. We also found that SRSF3 knockdown facilitated skipping of 81 5'-nucleotides (27 amino acids) from exon 8 of homeodomain-interacting protein kinase-2 (HIPK2) and produced a HIPK2 Δe8 isoform. Full-length HIPK2 (HIPK2 FL) is constantly degraded through association with an E3 ubiquitin ligase (Siah-1), whereas HIPK2 Δe8, lacking the 27 amino acids, lost Siah-1-binding ability and became resistant to proteasome digestion. Interestingly, selective knockdown of HIPK2 FL induced apoptosis in various colon cancer cells expressing wild-type or mutated p53. Thus, these findings disclose an important role of SRSF3 in the regulation of the G1-to-S-phase progression and alternative splicing of HIPK2 in tumor growth.

Imberg-Kazdan K, Ha S, Greenfield A, et al.
A genome-wide RNA interference screen identifies new regulators of androgen receptor function in prostate cancer cells.
Genome Res. 2013; 23(4):581-91 [PubMed] Free Access to Full Article Related Publications
The androgen receptor (AR) is a mediator of both androgen-dependent and castration-resistant prostate cancers. Identification of cellular factors affecting AR transcriptional activity could in principle yield new targets that reduce AR activity and combat prostate cancer, yet a comprehensive analysis of the genes required for AR-dependent transcriptional activity has not been determined. Using an unbiased genetic approach that takes advantage of the evolutionary conservation of AR signaling, we have conducted a genome-wide RNAi screen in Drosophila cells for genes required for AR transcriptional activity and applied the results to human prostate cancer cells. We identified 45 AR-regulators, which include known pathway components and genes with functions not previously linked to AR regulation, such as HIPK2 (a protein kinase) and MED19 (a subunit of the Mediator complex). Depletion of HIPK2 and MED19 in human prostate cancer cells decreased AR target gene expression and, importantly, reduced the proliferation of androgen-dependent and castration-resistant prostate cancer cells. We also systematically analyzed additional Mediator subunits and uncovered a small subset of Mediator subunits that interpret AR signaling and affect AR-dependent transcription and prostate cancer cell proliferation. Importantly, targeting of HIPK2 by an FDA-approved kinase inhibitor phenocopied the effect of depletion by RNAi and reduced the growth of AR-positive, but not AR-negative, treatment-resistant prostate cancer cells. Thus, our screen has yielded new AR regulators including drugable targets that reduce the proliferation of castration-resistant prostate cancer cells.

Wang Y, Liu F, Mao F, et al.
Interaction with cyclin H/cyclin-dependent kinase 7 (CCNH/CDK7) stabilizes C-terminal binding protein 2 (CtBP2) and promotes cancer cell migration.
J Biol Chem. 2013; 288(13):9028-34 [PubMed] Free Access to Full Article Related Publications
CtBP2 has been demonstrated to possess tumor-promoting capacities by virtue of up-regulating epithelial-mesenchymal transition (EMT) and down-regulating apoptosis in cancer cells. As a result, cellular CtBP2 levels are considered a key factor determining the outcome of oncogenic transformation. How pro-tumorigenic and anti-tumorigenic factors compete for fine-tuning CtBP2 levels is incompletely understood. Here we report that the cyclin H/cyclin-dependent kinase 7 (CCNH/CDK7) complex interacted with CtBP2 in vivo and in vitro. Depletion of either CCNH or CDK7 decreased CtBP2 protein levels by accelerating proteasome-dependent CtBP2 clearance. Further analysis revealed that CCNH/CDK7 competed with the tumor repressor HIPK2 for CtBP2 binding and consequently inhibited phosphorylation and dimerization of CtBP2. Phosphorylation-defective CtBP2 interacted more strongly with CCNH/CDK7 and was more resistant to degradation. Finally, overexpression of CtBP2 increased whereas depletion of CtBP2 dampened the invasive and migratory potential of breast cancer cells. CtBP2 promoted the invasion and migration of breast cancer cells in a CCNH-dependent manner. Taken together, our data have delineated a novel pathway that regulates CtBP2 stability, suggesting that targeting the CCNH/CDK7-CtBP2 axis may yield a viable anti-tumor strategy.

Song H, Boo JH, Kim KH, et al.
Critical role of presenilin-dependent γ-secretase activity in DNA damage-induced promyelocytic leukemia protein expression and apoptosis.
Cell Death Differ. 2013; 20(4):639-48 [PubMed] Free Access to Full Article Related Publications
Promyelocytic leukemia (PML) is a major component of macromolecular multiprotein complexes called PML nuclear-bodies (PML-NBs). These PML-NBs recruit numerous proteins including CBP, p53 and HIPK2 in response to DNA damage, senescence and apoptosis. In this study, we investigated the effect of presenilin (PS), the main component of the γ-secretase complex, in PML/p53 expression and downstream consequences during DNA damage-induced cell death using camptothecin (CPT). We found that the loss of PS in PS knockout (KO) MEFs (mouse embryonic fibroblasts) results in severely blunted PML expression and attenuated cell death upon CPT exposure, a phenotype that is fully reversed by re-expression of PS1 in PS KO cells and recapitulated by γ-secretase inhibitors in hPS1 MEFs. Interestingly, the γ-secretase cleavage product, APP intracellular domain (AICD), together with Fe65-induced PML expression at the protein and transcriptional levels in PS KO cells. PML and p53 reciprocally positively regulated each other during CPT-induced DNA damage, both of which were dependent on PS. Finally, elevated levels of PML-NB, PML protein and PML mRNA were detected in the brain tissues from Alzheimer's disease (AD) patients, where γ-secretase activity is essential for pathogenesis. Our data provide for the first time, a critical role of the PS/AICD-PML/p53 pathway in DNA damage-induced apoptosis, and implicate this pathway in AD pathogenesis.

Veschi V, Petroni M, Cardinali B, et al.
Galectin-3 impairment of MYCN-dependent apoptosis-sensitive phenotype is antagonized by nutlin-3 in neuroblastoma cells.
PLoS One. 2012; 7(11):e49139 [PubMed] Free Access to Full Article Related Publications
MYCN amplification occurs in about 20-25% of human neuroblastomas and characterizes the majority of the high-risk cases, which display less than 50% prolonged survival rate despite intense multimodal treatment. Somehow paradoxically, MYCN also sensitizes neuroblastoma cells to apoptosis, understanding the molecular mechanisms of which might be relevant for the therapy of MYCN amplified neuroblastoma. We recently reported that the apoptosis-sensitive phenotype induced by MYCN is linked to stabilization of p53 and its proapoptotic kinase HIPK2. In MYCN primed neuroblastoma cells, further activation of both HIPK2 and p53 by Nutlin-3 leads to massive apoptosis in vitro and to tumor shrinkage and impairment of metastasis in xenograft models. Here we report that Galectin-3 impairs MYCN-primed and HIPK2-p53-dependent apoptosis in neuroblastoma cells. Galectin-3 is broadly expressed in human neuroblastoma cell lines and tumors and is repressed by MYCN to induce the apoptosis-sensitive phenotype. Despite its reduced levels, Galectin-3 can still exert residual antiapoptotic effects in MYCN amplified neuroblastoma cells, possibly due to its specific subcellular localization. Importantly, Nutlin-3 represses Galectin-3 expression, and this is required for its potent cell killing effect on MYCN amplified cell lines. Our data further characterize the apoptosis-sensitive phenotype induced by MYCN, expand our understanding of the activity of MDM2-p53 antagonists and highlight Galectin-3 as a potential biomarker for the tailored p53 reactivation therapy in patients with high-risk neuroblastomas.

Cheng Y, Al-Beiti MA, Wang J, et al.
Correlation between homeodomain-interacting protein kinase 2 and apoptosis in cervical cancer.
Mol Med Rep. 2012; 5(5):1251-5 [PubMed] Related Publications
Homeodomain-interacting protein kinase 2 (HIPK2) is a serine/threonine nuclear kinase that is involved in apoptosis and cell growth, and is also thought to play a role in the process of tumorigenesis. The purpose of this study was to identify the role of HIPK2 in cervical cancer. HIPK2 expression was examined in normal and cervical cancer tissues at the mRNA and protein levels by quantitative real-time PCR and western blotting. To investigate the mechanism of action of HIPK2 in cervical cancer, RNA interference was used to analyze the effect of HIPK2 on apoptosis and cell growth in cervical cell lines. The results showed that HIPK2 expression was significantly higher in the cervical cancer tissues compared to the normal cervical tissues, both at the mRNA and protein level. Moreover, inhibition of HIPK2 promoted cell growth and decreased the rate of cell apoptosis in cervical cell lines. Taken together, these results indicate that HIPK2 expression is higher in cervical cancer tissues and has a positive correlation with cervical cancer. HIPK2 may be important in the development of cervical cancer.

Das Purkayastha BP, Roy JK
Molecular analysis of oncogenicity of the transcription factor, BRN3A, in cervical cancer cells.
J Cancer Res Clin Oncol. 2011; 137(12):1859-67 [PubMed] Related Publications
OBJECTIVE: The host cellular transcription factor, BRN3A, has been observed to play a vital role in cancer of the uterine cervix. BRN3A possesses multipartite functions, which include transcription of the genes of the high-risk HPVs and mediation of cellular changes in the host. In this study, we made an effort to decipher the regulation of BRN3A in cervical cancer cells by studying its interaction with different components of the cell.
METHODS: In cervical cancer cells, the endogenous HIPK2 was induced through cisplatin treatment, and then, its subsequent effect on BRN3A was primarily investigated through co-immunostaining and western blotting as HIPK2 has been observed to act as a co-repressor of Brn3a. The physical interaction of the two proteins was analyzed through co-immunoprecipitation. We resorted to chromatin immunoprecipitation in order to testify the autoregulatory pathway of BRN3A in cervical cancer cells. Interaction of BRN3A with cellular components, p73 and active form of JNK, was also studied through co-immunostaining.
RESULTS: We observed that BRN3A is independent of the regulative activity of HIPK2 and undergoes positive autoregulation in cervical cancer cells. Interestingly, during the study, it was revealed that BRN3A is unaffected by the treatment of cisplatin. Interaction of BRN3A with p73 and phosphorylated JNK in cervical cancer cells, observed in the present study, would help in understanding the molecular mechanism directed by BRN3A.
CONCLUSIONS: BRN3A possesses anti-apoptotic property, and considering the above results, it may be regarded as the key component in promoting tumorigenic growth in the uterine cervical cells.

Mougeot JL, Bahrani-Mougeot FK, Lockhart PB, Brennan MT
Microarray analyses of oral punch biopsies from acute myeloid leukemia (AML) patients treated with chemotherapy.
Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2011; 112(4):446-52 [PubMed] Related Publications
OBJECTIVE: Understanding the pathogenesis of chemotherapy-induced oral mucositis (CIOM) is vital to develop therapies for this common, dose-limiting side effect of cancer treatment. We investigated molecular events in CIOM from buccal mucosa tissue collected before and 2 days after chemotherapy from patients with acute myeloid leukemia (AML) and healthy controls by microarray analysis.
METHODS: Microarray analysis was performed using Human Genome U133 Plus 2.0 Array on buccal mucosa punch biopsies from patients with AML before (n = 4) or after chemotherapy (n = 4), and from healthy controls (n = 3). Following Robust Multichip Average (RMA) normalization, we applied Linear Models for Microarray data (LIMMA) and Significance Analysis of Microarrays (SAM) for data analysis using the TM4/TMeV v4.5.1 program.
RESULTS: LIMMA and SAM identified genes potentially affected by the presence of AML, including homeodomain-interacting protein kinase 1 (HIPK1), mex-3 homolog D (MEX3D), and genes potentially affected by chemotherapy, including argininosuccinate synthase 1 (ASS1), notch homolog 1 (NOTCH1), zinc transporter ZIP6 (SLC39A6), and TP53-regulated inhibitor of apoptosis 1 (TRIAP1). The expression of 2 genes with potential biological significance in oral mucositis, ASS1 and SLC39A6 (alias LIV-1), was confirmed by quantitative real-time reverse transcriptase-polymerase chain reaction (qRT-PCR).
CONCLUSIONS: Our results suggest that AML-specific deregulated immune responses and inflammatory tissue damage to the oral mucosa caused by chemotherapy may not be overcome by the natural cellular repair processes and therefore contribute to CIOM.

Lavra L, Rinaldo C, Ulivieri A, et al.
The loss of the p53 activator HIPK2 is responsible for galectin-3 overexpression in well differentiated thyroid carcinomas.
PLoS One. 2011; 6(6):e20665 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Galectin-3 (Gal-3) is an anti-apoptotic molecule involved in thyroid cells transformation. It is specifically overexpressed in thyroid tumour cells and is currently used as a preoperative diagnostic marker of thyroid malignancy. Gal-3 expression is downregulated by wt-p53 at the transcriptional level. In well-differentiated thyroid carcinomas (WDTCs) there is an unexplained paradoxical concomitant expression of Gal-3 and wt-p53. HIPK2 is a co-regulator of different transcription factors, and modulates basic cellular processes mainly through the activation of wt-p53. Since we demonstrated that HIPK2 is involved in p53-mediated Gal-3 downregulation, we asked whether HIPK2 deficiency might be responsible for such paradoxical Gal-3 overexpression in WDTC.
METHODOLOGY/PRINCIPAL FINDINGS: We analyzed HIPK2 protein and mRNA levels, as well as loss of heterozygosity (LOH) at the HIPK2 locus (7q32-34), in thyroid tissue samples. HIPK2 protein levels were high in all follicular hyperplasias (FHs) analyzed. Conversely, HIPK2 was undetectable in 91.7% of papillary thyroid carcinomas (PTCs) and in 60.0% of follicular thyroid carcinomas (FTCs). HIPK2 mRNA levels were upregulated in FH compared to normal thyroid tissue (NTT), while PTC showed mean HIPK2 mRNA levels lower than FH and, in 61.5% of cases, also lower than NTT. We found LOH at HIPK-2 gene locus in 37.5% of PTCs, 14.3% of FTCs and 18.2% of follicular adenomas. To causally link these data with Gal-3 upregulation, we performed in vitro experiments, using the PTC-derived K1 cells, in which HIPK2 expression was manipulated by RNA interference (RNAi) or plasmid-mediated overexpression. HIPK2 RNAi was associated with Gal-3 upregulation, while HIPK2 overexpression with Gal-3 downregulation.
CONCLUSIONS/SIGNIFICANCE: Our results indicate that HIPK2 expression and function are impaired in WDTCs, in particular in PTCs, and that this event explains Gal-3 overexpression typically observed in these types of tumours. Therefore, HIPK2 can be considered as a new tumour suppressor gene for thyroid cancers.

Soubeyran I, Mahouche I, Grigoletto A, et al.
Tissue microarray cytometry reveals positive impact of homeodomain interacting protein kinase 2 in colon cancer survival irrespective of p53 function.
Am J Pathol. 2011; 178(5):1986-98 [PubMed] Free Access to Full Article Related Publications
The human p53 gene is a tumor suppressor mutated in half of colon cancers. Although p53 function appears important for proliferation arrest and apoptosis induced by cancer therapeutics, the prognostic significance of p53 mutations remains elusive. This suggests that p53 function is modulated at a posttranslational level and that dysfunctions affecting its modulators can have a prognostic impact. Among p53 modulators, homeodomain interacting protein kinase (HIPK) 2 emerges as a candidate "switch" governing p53 transition from a cytostatic to a proapoptotic function. Thus, we investigated the possible prognostic role of HIPK2 on a retrospective series of 80 colon cancer cases by setting up a multiplexed cytometric approach capable of exploring correlative protein expression at the single tumor cell level on TMA. Crossing the data with quantitative PCR and p53 gene sequencing and p53 functional assays, we observed the following: despite a strong impact on p21 transcription, the presence of disabling p53 mutations has no prognostic value, and the increased expression of the HIPK2 protein in tumor cells compared with paired normal tissue cells has a strong impact on survival. Unexpectedly, HIPK2 effect does not appear to be mediated by p53 function because it is also observed in p53-disabling mutated backgrounds. Thus, our results point to a prominent and p53-independent role of HIPK2 in colon cancer survival.

Puca R, Nardinocchi L, Porru M, et al.
Restoring p53 active conformation by zinc increases the response of mutant p53 tumor cells to anticancer drugs.
Cell Cycle. 2011; 10(10):1679-89 [PubMed] Related Publications
Absence of p53 expression or expression of mutant p53 (mtp53) are common in human cancers and are associated with increased cancer resistance to chemo- and radiotherapy. Therefore, significant efforts towards pharmaceutical reactivation of defective p53 pathways are underway. We previously reported that, in HIPK2 knockdown background, p53 undergoes misfolding with inhibition of DNA binding and transcriptional activities that correlate with increased chemoresistance, and that zinc rescues wild-type p53 activity. Zinc has a crucial role in the biology of p53, in that p53 binds to DNA through a structurally complex domain stabilized by zinc atom. In this study, we explored the role of zinc in p53 reactivation in mutant p53-expressing cancer cells. We found that zinc re-established chemosensitivity in breast cancer SKBR3 (expressing R175H mutation) and glioblastoma U373MG (expressing R273H mutation) cell lines. Biochemical studies showed that zinc partly induced the transition of mutant p53 protein (reactive to conformation-sensitive PAb240 antibody for mutant conformation) into a functional conformation (reactive to conformation-sensitive PAb1620 antibody for wild-type conformation). Zinc-mediated p53 reactivation also reduced the mtp53/p73 interaction restoring both wtp53 and p73 binding to target gene promoters by ChIP assay with in vivo induction of wtp53 target gene expression, which rendered mutant p53 cells more prone to drug killing in vitro. Finally, zinc administration in U373MG tumor xenografts increased drug-induced tumor regression in vivo, which correlated with increased wild-type p53 protein conformation. These results show that the use of zinc might restore drug sensitivity and inhibit tumor growth by reactivating mutant p53.

Huang Y, Chuang A, Hao H, et al.
Phospho-ΔNp63α is a key regulator of the cisplatin-induced microRNAome in cancer cells.
Cell Death Differ. 2011; 18(7):1220-30 [PubMed] Free Access to Full Article Related Publications
Head and neck squamous cell carcinoma (HNSCC) cells exposed to cisplatin (CIS) displayed a dramatic ATM-dependent phosphorylation of ΔNp63α that leads to the transcriptional regulation of downstream mRNAs. Here, we report that phospho (p)-ΔNp63α transcriptionally deregulates miRNA expression after CIS treatment. Several p-ΔNp63α-dependent microRNA species (miRNAs) were deregulated in HNSCC cells upon CIS exposure, including miR-181a, miR-519a, and miR-374a (downregulated) and miR-630 (upregulated). Deregulation of miRNA expression led to subsequent modulation of mRNA expression of several targets (TP53-S46, HIPK2, ATM, CDKN1A and 1B, CASP3, PARP1 and 2, DDIT1 and 4, BCL2 and BCL2L2, TP73, YES1, and YAP1) that are involved in the apoptotic process. Our data support the notion that miRNAs are critical downstream targets of p-ΔNp63α and mediate key pathways implicated in the response of cancer cells to chemotherapeutic drugs.

de la Vega L, Fröbius K, Moreno R, et al.
Control of nuclear HIPK2 localization and function by a SUMO interaction motif.
Biochim Biophys Acta. 2011; 1813(2):283-97 [PubMed] Related Publications
The serine/threonine kinase HIPK2 regulates gene expression programs controlling differentiation and cell death. HIPK2 localizes in subnuclear speckles, but the structural components allowing this localization are not understood. A point mutation analysis allowed mapping two nuclear localization signals and a SUMO interaction motif (SIM) that also occurs in HIPK1 and HIPK3. The SIM binds all three major isoforms of SUMO (SUMO-1-3), while only SUMO-1 is capable of covalent conjugation to HIPK2. Deletion or mutation of the SIM prevented SUMO binding and precluded localization of HIPK2 in nuclear speckles, thus causing localization of HIPK2 to the entire cell. Functional inactivation of the SIM prohibited recruitment of HIPK2 to PML nuclear bodies and disrupted colocalization with other proteins such as the polycomb protein Pc2 in nuclear speckles. Interaction of HIPK2 with Pc2 or PML in intact cells was largely dependent on a functional SIM in HIPK2, highlighting the relevance of SUMO/SIM interactions as a molecular glue that serves to enhance protein/protein interaction networks. HIPK2 mutants with an inactive SIM showed changed activities, thus revealing that non-covalent binding of SUMO to the kinase is important for the regulation of its function.

Li Z, Hu S, Wang J, et al.
MiR-27a modulates MDR1/P-glycoprotein expression by targeting HIPK2 in human ovarian cancer cells.
Gynecol Oncol. 2010; 119(1):125-30 [PubMed] Related Publications
OBJECTIVE: MicroRNAs (miRNAs) are non-coding, single-stranded small RNAs that regulate gene expression negatively, which is involved in fundamental cellular processes and the initiation, development and progression of human cancer. In this study, we investigated the role of miR-27a in the development of drug resistance in ovarian cancer cells.
METHODS: Expression of miR-27a in ovarian cancer cell lines A2780 and A2780/Taxol were detected by stem-loop real-time PCR. A2780 and A2780/Taxol cells were transfected with the mimics or inhibitors of miR-27a or negative control RNA (NC) by Lipofectamine 2000. The expression levels of MDR1 mRNA, P-glycoprotein (P-gp) and Homeodomain-interacting protein kinase-2 (HIPK2) proteins were assessed by real-time PCR and western blot respectively. Drug sensitivity was analyzed by MTT assay while apoptosis and the fluorescence intensity of intracellular Rhodamine 123 (Rh-123) were measured by FACS.
RESULTS: The expression levels of miR-27a and P-gp were up-regulated in paclitaxel-resistant ovarian cancer cell line A2780/Taxol as compared with its parental line A2780. Transfection of A2780/Taxol cells with the inhibitors of miR-27a decreased the expression of MDR1 mRNA and P-gp protein, increased HIPK2 protein expression, enhanced the sensitivity of A2780/taxol cells to paclitaxel, increased paclitaxel-induced apoptosis and the fluorescence intensity of intracellular Rh-123. Expression of MDR1 mRNA was increased while the sensitivity to paclitaxel was decreased in A2780 cells management with the mimics of miR-27a.
CONCLUSIONS: The deregulation of miR-27a may be involved in the development of drug resistance, regulating the expression of MDR1/P-gp, at least in part, by targeting HIPK2 in ovarian cancer cells.

Esposito F, Tornincasa M, Chieffi P, et al.
High-mobility group A1 proteins regulate p53-mediated transcription of Bcl-2 gene.
Cancer Res. 2010; 70(13):5379-88 [PubMed] Related Publications
We have previously described a mechanism through which the high-mobility group A1 (HMGA1) proteins inhibit p53-mediated apoptosis by delocalizing the p53 proapoptotic activator homeodomain-interacting protein kinase 2 from the nucleus to the cytoplasm. By this mechanism, HMGA1 modulates the transcription of p53 target genes such as Mdm2, p21(waf1), and Bax, inhibiting apoptosis. Here, we report that HMGA1 antagonizes the p53-mediated transcriptional repression of another apoptosis-related gene, Bcl-2, suggesting a novel mechanism by which HMGA1 counteracts apoptosis. Moreover, HMGA1 overexpression promotes the reduction of Brn-3a binding to the Bcl-2 promoter, thereby blocking the Brn-3a corepressor function on Bcl-2 expression following p53 activation. Consistently, a significant direct correlation between HMGA1 and Bcl-2 overexpression has been observed in human breast carcinomas harboring wild-type p53. Therefore, this study suggests a novel mechanism, based on Bcl-2 induction, by which HMGA1 overexpression contributes to the escape from apoptosis leading to neoplastic transformation.

Puca R, Nardinocchi L, Givol D, D'Orazi G
Regulation of p53 activity by HIPK2: molecular mechanisms and therapeutical implications in human cancer cells.
Oncogene. 2010; 29(31):4378-87 [PubMed] Related Publications
The p53 protein is the most studied tumor suppressor and the p53 pathway has been shown to mediate cellular stress responses that are disrupted when cancer develops. After DNA damage, p53 is activated as transcription factor to directly induce the expression of target genes involved in cell-cycle arrest, DNA repair, senescence and, importantly, apoptosis. Post-translational modifications of p53 are essential for the activation of p53 and for selection of target genes. The tumor suppressor homeodomain-interacting protein kinase-2 (HIPK2) is a crucial regulator of p53 apoptotic function by phosphorylating its N-terminal serine 46 (Ser46) and facilitating Lys382 acetylation at the C-terminus. HIPK2 is activated by numerous genotoxic agents and can be deregulated in tumors by several conditions including hypoxia. Recent findings suggest that HIPK2 active/inactive protein can affect p53 function in multiple and unexpected ways. This makes p53 as well as HIPK2 interesting targets for cancer therapy. Hence, understanding the role of HIPK2 as p53 activator may provide important insights in the process of tumor progression, and may also serve as the crucial point in the diagnostic and therapeutical aspects of cancer.

Nardinocchi L, Puca R, Givol D, D'Orazi G
HIPK2-a therapeutical target to be (re)activated for tumor suppression: role in p53 activation and HIF-1α inhibition.
Cell Cycle. 2010; 9(7):1270-5 [PubMed] Related Publications
Oncosuppressor p53 is often inactivated by either mutations or deregulation of regulatory proteins. These include the homeodomain-interacting protein kinase 2 (HIPK2) that, by phosphorylating p53 at Ser46 modulates p53 response to DNA damage by inducing pro-apoptotic transcription. There is compelling evidence that HIPK2 is also involved in the response to hypoxia by acting as co-suppressor of hypoxia inducible factor 1α (HIF-1α), a major factor in cancer progression that activates the transcription of genes involved in angiogenesis, glucose metabolism and invasion. Hence conditions that induce HIPK2 deregulation would end up in a multifactorial response leading to tumor chemoresistance by affecting p53 activity on one hand and to angiogenesis and cell proliferation by affecting HIF-1 activity on the other hand. For these reasons, HIPK2 protein is a promising target for anti-cancer therapies. HIPK2 can be inhibited by hypoxia. In this respect, we have recently shown that hypoxia-driven HIPK2 downregulation is not irreversible. We found that, zinc supplementation reactivates the hypoxia-inhibited HIPK2, leading to repression of the HIF-1 pathway and restoration of p53Ser46 apoptotic activity. Here, we discuss about these findings and the potential relevance of zinc supplementation to chemotherapy in cancer treatment. The results will be also discussed in light of recent findings showing that cancer treatment with antiangiogenic agents may result in hypoxia and selection of cancer cells with increased tumor aggressiveness and metastasis.

Yang LH, Xu HT, Han Y, et al.
Axin downregulates TCF-4 transcription via beta-catenin, but not p53, and inhibits the proliferation and invasion of lung cancer cells.
Mol Cancer. 2010; 9:25 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: We previously reported that overexpression of Axin downregulates T cell factor-4 (TCF-4) transcription. However, the mechanism(s) by which Axin downregulates the transcription and expression of TCF-4 is not clear. It has been reported that beta-catenin promotes and p53 inhibits TCF-4 transcription, respectively. The aim of this study was to investigate whether beta-catenin and/or p53 is required for Axin-mediated downregulation of TCF-4.
RESULTS: Axin mutants that lack p53/HIPK2 and/or beta-catenin binding domains were expressed in lung cancer cells, BE1 (mutant p53) and A549 (wild type p53). Expression of Axin or AxinDeltap53 downregulates beta-catenin and TCF-4, and knock-down of beta-catenin upregulates TCF-4 in BE1 cells. However, expression of AxinDeltabeta-ca into BE1 cells did not downregulate TCF-4 expression. These results indicate that Axin downregulates TCF-4 transcription via beta-catenin. Although overexpression of wild-type p53 also downregulates TCF-4 in BE1 cells, cotransfection of p53 and AxinDeltabeta-ca did not downregulate TCF-4 further. These results suggest that Axin does not promote p53-mediated downregulation of TCF-4. Axin, AxinDeltap53, and AxinDeltabeta-ca all downregulated beta-catenin and TCF-4 in A549 cells. Knock-down of p53 upregulated beta-catenin and TCF-4, but cotransfection of AxinDeltabeta-ca and p53 siRNA resulted in downregulation of beta-catenin and TCF-4. These results indicate that p53 is not required for Axin-mediated downregulation of TCF-4. Knock-down or inhibition of GSK-3beta prevented Axin-mediated downregulation of TCF-4. Furthermore, expression of Axin and AxinDeltap53, prevented the proliferative and invasive ability of BE1 and A549, expression of AxinDeltabeta-ca could only prevented the proliferative and invasive ability effectively.
CONCLUSIONS: Axin downregulates TCF-4 transcription via beta-catenin and independently of p53. Axin may also inhibits the proliferation and invasion of lung cancer cells via beta-catenin and p53.

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