Regulation of vascular endothelial growth factor expression by homeodomain-interacting protein kinase-2

<p>Abstract</p> <p>Background</p> <p>Homeodomain-interacting protein kinase-2 (HIPK2) plays an essential role in restraining tumor progression as it may regulate, by itself or within multiprotein complexes, many proteins (mainly transcription factors) involved in cell growth and apoptosis. This study takes advantage of the recent finding that HIPK2 may repress the β-catenin transcription activity. Thus, we investigated whether HIPK2 overexpression may down-regulate vascular endothelial growth factor (VEGF) levels (a β-catenin target gene) and the role of β-catenin in this regulation, in order to consider HIPK2 as a tool for novel anti-tumoral therapeutical approaches.</p> <p>Methods</p> <p>The regulation of VEGF expression by HIPK2 was evaluated by using luciferase assay with VEGF reporter construct, after overexpression of the β-catenin transcription factor. Relative quantification of VEGF and β-catenin mRNAs were assessed by reverse-transcriptase-PCR (RT-PCR) analyses, following HIPK2 overexpression, while β-catenin protein levels were evaluated by western immunoblotting.</p> <p>Results</p> <p>HIPK2 overexpression in tumor cells downregulated VEGF mRNA levels and VEGF promoter activity. The VEGF downregulation was partly depending on HIPK2-mediated β-catenin regulation. Thus, HIPK2 could induce β-catenin protein degradation that was prevented by cell treatment with proteasome inhibitor MG132. The β-catenin degradation was dependent on HIPK2 catalytic activity and independent of p53 and glycogen synthase kinase 3β (GSK-3β) activities.</p> <p>Conclusion</p> <p>These results suggest that VEGF might be a target of HIPK2, at least in part, through regulation of β-catenin activity. These findings support the function of HIPK2 as tumor suppressor and hypothesise a role for HIPK2 as antiangiogenic tool in tumor therapy approaches.</p

HIPK2 modulates p53 activity towards pro-apoptotic transcription

<p>Abstract</p> <p>Background</p> <p>Activation of p53-mediated gene transcription is a critical cellular response to DNA damage and involves a phosphorylation-acetylation cascade of p53. The discovery of differences in the response to different agents raises the question whether some of the p53 oncosuppressor functions might be exerted by different posttranslational modifications. Stress-induced homeodomain-interacting protein kinase-2 (HIPK2) phosphorylates p53 at serine-46 (Ser46) for p53 apoptotic activity; p53 acetylation at different C-terminus lysines including p300-mediated lysine-382 (Lys382) is also required for full activation of p53 transcriptional activity. The purpose of the current study was to evaluate the interplay among HIPK2, p300, and p53 in p53 acetylation and apoptotic transcriptional activity in response to drug by using siRNA interference, p300 overexpression or deacetylase inhibitors, in cancer cells.</p> <p>Results</p> <p>Knockdown of HIPK2 inhibited both adriamycin-induced Ser46 phosphorylation and Lys382 acetylation in p53 protein; however, while combination of ADR and zinc restored Ser46 phosphorylation it did not recover Lys382 acetylation. Chromatin immunoprecipitation studies showed that HIPK2 was required <it>in vivo </it>for efficient p300/p53 co-recruitment onto apoptotic promoters and that both p53 modifications at Ser46 and Lys382 were necessary for p53 apoptotic transcription. Thus, p53Lys382 acetylation in HIPK2 knockdown as well as p53 apoptotic activity in response to drug could be rescued by p300 overexpression. Similar effect was obtained with the Sirt1-inhibitor nicotinamide. Interestingly trichostatin A (TSA), the inhibitor of histone deacetylase complexes (HDAC) did not have effect, suggesting that Sirt1 was the deacetylase involved in p53 deacetylation in HIPK2 knockdown.</p> <p>Conclusion</p> <p>These results reveal a novel role for HIPK2 in activating p53 apoptotic transcription. Our results indicate that HIPK2 may regulate the balance between p53 acetylation and deacetylation, by stimulating on one hand co-recruitment of p300 and p53Lys382 on apoptotic promoters and on the other hand by inhibiting Sirt1 deacetylase activity. We attempted to reactivate p53 apoptotic transcriptional activity by rescuing both Ser46 and Lys382 modification in response to drug. Our data propose combination strategies for the treatment of tumors with dysfunctional p53 and/or HIPK2 that include classical chemotherapy with pharmacological or natural agents such as Sirt1-deacetylase inhibitors or zinc, respectively.</p

Homeodomain Interacting Protein Kinase 2: A Target for Alzheimer's Beta Amyloid Leading to Misfolded p53 and Inappropriate Cell Survival

BACKGROUND: Homeodomain interacting protein kinase 2 (HIPK2) is an evolutionary conserved serine/threonine kinase whose activity is fundamental in maintaining wild-type p53 function, thereby controlling the destiny of cells when exposed to DNA damaging agents. We recently reported an altered conformational state of p53 in tissues from patients with Alzheimer's Disease (AD) that led to an impaired and dysfunctional response to stressors. METHODOLOGY/PRINCIPAL FINDINGS: Here we examined the molecular mechanisms underlying the impairment of p53 activity in two cellular models, HEK-293 cells overexpressing the amyloid precursor protein and fibroblasts from AD patients, starting from recent findings showing that p53 conformation may be regulated by HIPK2. We demonstrated that beta-amyloid 1-40 induces HIPK2 degradation and alters HIPK2 binding activity to DNA, in turn regulating the p53 conformational state and vulnerability to a noxious stimulus. Expression of HIPK2 was analysed by western blot experiments, whereas HIPK2 DNA binding was examined by chromatin immunoprecipitation analysis. In particular, we evaluated the recruitment of HIPK2 onto some target promoters, including hypoxia inducible factor-1alpha and metallothionein 2A. CONCLUSIONS/SIGNIFICANCE: These results support the existence of a novel amyloid-based pathogenetic mechanism in AD potentially leading to the survival of injured dysfunctional cells

Zinc Downregulates HIF-1α and Inhibits Its Activity in Tumor Cells In Vitro and In Vivo

Hypoxia inducible factor-1α (HIF-1α) is responsible for the majority of HIF-1-induced gene expression changes under hypoxia and for the "angiogenic switch" during tumor progression. HIF-1α is often upregulated in tumors leading to more aggressive tumor growth and chemoresistance, therefore representing an important target for antitumor intervention. We previously reported that zinc downregulated HIF-1α levels. Here, we evaluated the molecular mechanisms of zinc-induced HIF-1α downregulation and whether zinc affected HIF-1α also in vivo.Here we report that zinc downregulated HIF-1α protein levels in human prostate cancer and glioblastoma cells under hypoxia, whether induced or constitutive. Investigations into the molecular mechanisms showed that zinc induced HIF-1α proteasomal degradation that was prevented by treatment with proteasomal inhibitor MG132. HIF-1α downregulation induced by zinc was ineffective in human RCC4 VHL-null renal carcinoma cell line; likewise, the HIF-1αP402/P564A mutant was resistant to zinc treatment. Similarly to HIF-1α, zinc downregulated also hypoxia-induced HIF-2α whereas the HIF-1β subunit remained unchanged. Zinc inhibited HIF-1α recruitment onto VEGF promoter and the zinc-induced suppression of HIF-1-dependent activation of VEGF correlated with reduction of glioblastoma and prostate cancer cell invasiveness in vitro. Finally, zinc administration downregulated HIF-1α levels in vivo, by bioluminescence imaging, and suppressed intratumoral VEGF expression.These findings, by demonstrating that zinc induces HIF-1α proteasomal degradation, indicate that zinc could be useful as an inhibitor of HIF-1α in human tumors to repress important pathways involved in tumor progression, such as those induced by VEGF, MDR1, and Bcl2 target genes, and hopefully potentiate the anticancer therapies

Targeting Hypoxia in Cancer Cells by Restoring Homeodomain Interacting Protein-Kinase 2 and p53 Activity and Suppressing HIF-1α

BACKGROUND:The tumor suppressor homeodomain-interacting protein kinase-2 (HIPK2) by phosphorylating serine 46 (Ser46) is a crucial regulator of p53 apoptotic function. HIPK2 is also a transcriptional co-repressor of hypoxia-inducible factor-1alpha (HIF-1alpha) restraining tumor angiogenesis and chemoresistance. HIPK2 can be deregulated in tumors by several mechanisms including hypoxia. Here, we sought to target hypoxia by restoring HIPK2 function and suppressing HIF-1alpha, in order to provide evidence for the involvement of both HIPK2 and p53 in counteracting hypoxia-induced chemoresistance. METHODOLOGY/PRINCIPAL FINDINGS:Upon exposure of colon and lung cancer cells to hypoxia, by either low oxygen or cobalt, HIPK2 function was impaired allowing for increased HIF-1alpha expression and inhibiting the p53-apoptotic response to drug. Cobalt suppressed HIPK2 recruitment onto HIF-1alpha promoter. Hypoxia induced expression of the p53 target MDM2 that downregulates HIPK2, thus MDM2 inhibition by siRNA restored the HIPK2/p53Ser46 response to drug. Zinc supplementation to hypoxia-treated cells increased HIPK2 protein stability and nuclear accumulation, leading to restoration of HIPK2 binding to HIF-1alpha promoter, repression of MDR1, Bcl2, and VEGF genes, and activation of the p53 apoptotic response to drug. Combination of zinc and ADR strongly suppressed tumor growth in vivo by inhibiting HIF-1 pathway and upregulating p53 apoptotic target genes. CONCLUSIONS/SIGNIFICANCE:We show here for the first time that hypoxia-induced HIPK2 deregulation was counteracted by zinc that restored HIPK2 suppression of HIF-1 pathway and reactivated p53 apoptotic response to drug, underscoring the potential use of zinc supplementation in combination with chemotherapy to address hypoxia and improve tumor treatment

Inhibition of HIF-1alpha activity by homeodomain-interacting protein kinase-2 correlates with sensitization of chemoresistant cells to undergo apoptosis

<p>Abstract</p> <p>Background</p> <p>Homeodomain-interacting protein kinase-2 (HIPK2), a transcriptional co-repressor with apoptotic function, can affect hypoxia-inducible factor 1 (HIF-1) transcriptional activity, through downmodulation of its HIF-1α subunit, in normoxic condition. Under hypoxia, a condition often found in solid tumors, HIF-1α is activated to induce target genes involved in chemoresistance, inhibition of apoptosis and tumor progression. Here, we investigated whether the HIPK2 overexpression could downregulate HIF-1α expression and activity in tumor cells treated with hypoxia-mimicking condition, and evaluated whether HIPK2-dependent downregulation of HIF-1α could sensitize chemoresistant tumor cells to adriamycin (ADR)-induced apoptosis.</p> <p>Methods</p> <p>Tumor cell lines carrying wild-type p53, siRNA p53, or mutant p53 were overexpressed with HIPK2 (full length or catalytic inactive mutant) and treated with cobalt chloride (CoCl₂) to mimic hypoxia, in the presence or absence of ADR treatment. HIF-1α expression was measured by semiquantitative reverse-transcriptase (RT)-PCR and Western immunoblotting and HIF-1 activity was evaluated by luciferase assay using reporter plasmid containing hypoxia response elements (HREs) upstream of luciferase gene. HIF-1 target genes, including multidrug resistance 1 (MDR1) and the antiapoptotic Bcl2 were determined by RT-PCR. Cell survival and apoptosis were measured by colony assay and cleavage of the caspase-3 substrate PARP, respectively.</p> <p>Results</p> <p>Overexpression of HIPK2 resulted in downmodulation of cobalt-stabilized HIF-1α protein and HIF-1α mRNA levels, with subsequent inhibition of HIF-1 transcriptional activity. MDR1 and Bcl-2 gene expression was downmodulated by HIPK2 overexpression in cobalt-treated cells. Inhibition of HIF-1 transcriptional activity was dependent on HIPK2 catalytic activity. HIPK2 overexpression did not induce per se apoptosis of cobalt-treated cells, on the contrary it sensitized cobalt-treated cells to ADR-induced apoptosis, regardless of their p53 status.</p> <p>Conclusion</p> <p>The ability of HIPK2 to restore the apoptosis-inducing potential of chemotherapeutic drug in hypoxia-mimicking condition and therefore to sensitize chemoresistant tumor cells suggests that HIPK2 may induce fundamental alterations in cell signaling pathways, involving or not p53 function. Thus potential use of HIPK2 is promising for cancer treatment by potentiating cytotoxic therapies, regardless of p53 cell status.</p