Updates on HIPK2: a resourceful oncosuppressor for clearing cancer

Exosomal miR-3174 induced by hypoxia promotes angiogenesis and metastasis of hepatocellular carcinoma by inhibiting HIPK3

Hepatocellular carcinoma (HCC) is a highly malignant tumor with rich blood supply. HCC-derived exosomes containing hereditary substances including microRNAs (miRNAs) were involved in regulating tumor angiogenesis and metastasis. Subsequently, series experiments were performed to evaluate the effect of exosomal miR-3174 on HCC angiogenesis and metastasis. HCC-derived exosomal miR-3174 was ingested by human umbilical vein endothelial cells (HUVECs) in which HIPK3 was targeted and silenced, causing subsequent inhibition of Fas and p53 signaling pathways. Furthermore, exosomal miR-3174 induced permeability and angiogenesis of HUVECs to enhance HCC progression and metastasis. Under hypoxia, upregulated HIF-1α further promoted the transcription of miR-3174. Moreover, HNRNPA1 augmented the package of miR-3174 into exosomes. Clinical data analysis confirmed that HCC patients with high-level miR-3174 were correlated with worse prognosis. Thus, exosomal miR-3174 induced by hypoxia promotes angiogenesis and metastasis of HCC by inhibiting HIPK3/p53 and HIPK3/Fas signaling pathways. Our findings might provide potential targets for anti-tumor therapy.

miR-147b is an oncomiR acting synergistically with HIPK2 to promote pancreatic carcinogenesis

MicroRNAs (miRs, miRNAs) are known players in the regulatory network of pancreatic tumorigenesis, but the downstream effectors remain poorly characterized. This study addressed this issue based on in silico prediction, in vitro experiments, and in vivo validation. The differentially expressed PCa-related miRNAs and bioinformatics tools predicted downstream regulators. The expression of miR-147b was examined in PCa cell lines. Putative targets of miR-147b were predicted by a publicly available database and confirmed by luciferase activity assay. Mimic/inhibitor, siRNA/overexpression plasmid, or pifithrin-α (p53 inhibitor) were delivered into PCa cells to assess the effect of miR-147b, HIPK2, and p53 on malignant phenotypes of PCa cells. AntagomiR-147b and shRNA targeting HIPK2 were introduced to xenograft-bearing nude mice for in vivo experiments. The expression of miR-147b was significantly increased in PCa cell lines. Ectopic expression of miR-147b promoted the malignant phenotypes of PCa cells and inhibited their apoptosis. HIPK2 was confirmed as a target gene of miR-147b. Inhibiting miR-147b could promote HIPK2 expression and potentially activate the p53 pathway, inhibiting PCa cell growth. In vivo experiments suggested that miR-147b inhibition suppressed the growth of xenograft tumors in nude mice, while HIPK2 knockdown counteracted its effect. Collectively, our work reveals a novel miR-147b-mediated carcinogenic regulatory network in PCa that may be a viable target for PCa treatment.

New Copper-Based Metallodrugs with Anti-Invasive Capacity

While metal-based complexes are deeply investigated as anticancer chemotherapeutic drugs, fewer studies are devoted to their anti-invasive activity. Herein, two copper (Cu)(II) tropolone derivatives, [Cu(Trop)Cl] and [Cu(Trop)Sac], both containing the N,N-chelated 4,4'-bishydroxymethyl-2,2'-bipyridne ligand, were evaluated for their anticancer and anti-invasive properties. RKO (RKO-ctr) colon cancer cells and their derivatives undergoing stable small interference (si) RNA for HIPK2 protein (RKO-siHIPK2) with acquisition of pro-invasive capacity were used. The results demonstrate that while [Cu(Trop)Sac] did not show cytotoxic activity, [Cu(Trop)Cl] induced cell death in both RKO-ctr and RKO-siHIPK2 cells, indicating that structural changes on substituting the coordinated chloride ligand with saccharine (Sac) could be a key factor in suppressing mechanisms of cellular death. On the other hand, both [Cu(Trop)Sac] and [Cu(Trop)Cl] complexes counteracted RKO-siHIPK2 cell migration in the wound healing assay. The synergic effect exerted by the concomitant presence of both tropolone and saccharin ligands in [Cu(Trop)Sac] was also supported by its significant inhibition of RKO-siHIPK2 cell migration compared to the free Sac ligand. These data suggest that the two Cu(II) tropolone derivatives are also interesting candidates to be further tested in in vivo models as an anti-invasive tumor strategy.

Potential roles of exosomes in the initiation and metastatic progression of lung cancer

Lung cancer (LC) incidence and mortality continue to increase annually worldwide. LC is insidious and readily metastasizes and relapses. Except for its early diagnosis and surgical resection, there is no effective cure for advanced metastatic LC, and the prognosis remains dismal. Exosomes, a class of nano-sized extracellular vesicles produced by healthy or diseased cells, are coated with a bilayer lipid membrane and contain various functional molecules such as proteins, lipids, and nucleic acids. They can be used for intracellular or intercellular signaling or the transportation of biological substances. A growing body of evidence supports that exosomes play multiple crucial roles in the occurrence and metastatic progression of many malignancies, including LC. The elucidation of the potential roles of exosomes in the initiation, invasion, and metastasis of LC and their underlying molecular mechanisms may contribute to improved early diagnosis and treatment.

Activating transcription factor 4 drives the progression of diabetic cardiac fibrosis

AIMS

Diabetic cardiomyopathy (DC) is one of serious complications of diabetic patients. This study investigated the biological function of activating transcription factor 4 (ATF4) in DC.

METHODS AND RESULTS

Streptozotocin-treated mice and high glucose (HG)-exposed HL-1 cells were used as the in vivo and in vitro models of DC. Myocardial infarction (MI) was induced by left coronary artery ligation in mice. Cardiac functional parameters were detected by echocardiography. Target molecule expression was determined by real time quantitative PCR and western blotting. Cardiac fibrosis was observed by haematoxylin and eosin and Masson's staining. Cardiac apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labelling. Activities of superoxide dismutase, glutathione peroxidase, and levels of malonic dialdehyde and reactive oxygen species were used to assess oxidative stress damage. Molecular mechanisms were evaluated by chromatin immunoprecipitation, dual luciferase assay, and co-immunoprecipitation. ATF4 was up-regulated in the DC and MI mice (P < 0.01). Down-regulation of ATF4 improved cardiac function as evidenced by changes in cardiac functional parameters (P < 0.01), inhibited myocardial collagen I (P < 0.001) and collagen III (P < 0.001) expression, apoptosis (P < 0.001), and oxidative stress (P < 0.001) in diabetic mice. Collagen I (P < 0.01) and collagen III (P < 0.01) expression was increased in MI mice, which was reversed by ATF4 silencing (P < 0.05). ATF4 depletion enhanced viability (P < 0.01), repressed apoptosis (P < 0.001), oxidative damage (P < 0.001), and collagen I (P < 0.001), and collagen III (P < 0.001) expression of HG-stimulated HL-1 cells. ATF4 transcriptionally activated Smad ubiquitin regulatory factor 2 (Smurf2, P < 0.001) to promote ubiquitination and degradation of homeodomain interacting protein kinase-2 (P < 0.001) and subsequently caused inactivation of nuclear factor erythroid 2-related factor 2/heme oxygenase 1 pathway (P < 0.001). The inhibitory effects of ATF4 silencing on HG-induced apoptosis (P < 0.01), oxidative injury (P < 0.01), collagen I (P < 0.001), and collagen III (P < 0.001) expression were reversed by Smurf2 overexpression.

CONCLUSIONS

ATF4 facilitates diabetic cardiac fibrosis and oxidative stress by promoting Smurf2-mediated ubiquitination and degradation of homeodomain interacting protein kinase-2 and then inactivation of nuclear factor erythroid 2-related factor 2/heme oxygenase 1 pathway, suggesting ATF4 as a treatment target for DC.

HMGB1-induced activation of ER stress contributes to pulmonary artery hypertension in vitro and in vivo

BACKGROUND

HMGB1 and ER stress have been considered to participate in the progression of pulmonary artery hypertension (PAH). However, the molecular mechanism underlying HMGB1 and ER stress in PAH remains unclear. This study aims to explore whether HMGB1 induces pulmonary artery smooth muscle cells (PASMCs) functions and pulmonary artery remodeling through ER stress activation.

METHODS

Primary cultured PASMCs and monocrotaline (MCT)-induced PAH rats were applied in this study. Cell proliferation and migration were determined by CCK-8, EdU and transwell assay. Western blotting was conducted to detect the protein levels of protein kinase RNA-like endoplasmic reticulum kinase (PERK), activating transcription factor-4 (ATF4), seven in absentia homolog 2 (SIAH2) and homeodomain interacting protein kinase 2 (HIPK2). Hemodynamic measurements, immunohistochemistry staining, hematoxylin and eosin staining were used to evaluate the development of PAH. The ultrastructure of ER was observed by transmission electron microscopy.

RESULTS

In primary cultured PASMCs, HMGB1 reduced HIPK2 expression through upregulation of ER stress-related proteins (PERK and ATF4) and subsequently increased SIAH2 expression, which ultimately led to PASMC proliferation and migration. In MCT-induced PAH rats, interfering with HMGB1 by glycyrrhizin, suppression of ER stress by 4-phenylbutyric acid or targeting SIAH2 by vitamin K3 attenuated the development of PAH. Additionally, tetramethylpyrazine (TMP), as a component of traditional Chinese herbal medicine, reversed hemodynamic deterioration and vascular remodeling by targeting PERK/ATF4/SIAH2/HIPK2 axis.

CONCLUSIONS

The present study provides a novel insight to understand the pathogenesis of PAH and suggests that targeting HMGB1/PERK/ATF4/SIAH2/HIPK2 cascade might have potential therapeutic value for the prevention and treatment of PAH.

HIPK2 in the physiology of nervous system and its implications in neurological disorders

HIPK2 is an evolutionary conserved serine/threonine kinase with multifunctional roles in stress response, embryonic development and pathological conditions, such as cancer and fibrosis. The heterogeneity of its interactors and targets makes HIPK2 activity strongly dependent on the cellular context, and allows it to modulate multiple signaling pathways, ultimately regulating cell fate and proliferation. HIPK2 is highly expressed in the central and peripheral nervous systems, and its genetic ablation causes neurological defects in mice. Moreover, HIPK2 is involved in processes, such as endoplasmic reticulum stress response and protein aggregate accumulation, and pathways, including TGF-β and BMP signaling, that are crucial in the pathogenesis of neurological disorders. Here, we review the data about the role of HIPK2 in neuronal development, survival, and homeostasis, highlighting the implications in the pathogenesis of neurological disorders, and pointing out HIPK2 potentiality as therapeutic target and diagnostic or prognostic marker.

HIPK2 in Angiogenesis: A Promising Biomarker in Cancer Progression and in Angiogenic Diseases

Angiogenesis is the formation of new blood capillaries taking place from preexisting functional vessels, a process that allows cells to cope with shortage of nutrients and low oxygen availability. Angiogenesis may be activated in several pathological diseases, from tumor growth and metastases formation to ischemic and inflammatory diseases. New insights into the mechanisms that regulate angiogenesis have been discovered in the last years, leading to the discovery of new therapeutic opportunities. However, in the case of cancer, their success may be limited by the occurrence of drug resistance, meaning that the road to optimize such treatments is still long. Homeodomain-interacting protein kinase 2 (HIPK2), a multifaceted protein that regulates different molecular pathways, is involved in the negative regulation of cancer growth, and may be considered a "bona fide" oncosuppressor molecule. In this review, we will discuss the emerging link between HIPK2 and angiogenesis and how the control of angiogenesis by HIPK2 impinges in the pathogenesis of several diseases, including cancer.

HIPK2 as a Novel Regulator of Fibrosis

Fibrosis is an unmet medical problem due to a lack of evident biomarkers to help develop efficient targeted therapies. Fibrosis can affect almost every organ and eventually induce organ failure. Homeodomain-interacting protein kinase 2 (HIPK2) is a protein kinase that controls several molecular pathways involved in cell death and development and it has been extensively studied, mainly in the cancer biology field. Recently, a role for HIPK2 has been highlighted in tissue fibrosis. Thus, HIPK2 regulates several pro-fibrotic pathways such as Wnt/β-catenin, TGF-β and Notch involved in renal, pulmonary, liver and cardiac fibrosis. These findings suggest a wider role for HIPK2 in tissue physiopathology and highlight HIPK2 as a promising target for therapeutic purposes in fibrosis. Here, we will summarize the recent studies showing the involvement of HIPK2 as a novel regulator of fibrosis.

Single-Cell and Transcriptome-Based Immune Cell-Related Prognostic Model in Clear Cell Renal Cell Carcinoma

Traditional studies mostly focus on the role of single gene in regulating clear cell renal cell carcinoma (ccRCC), while it ignores the impact of tumour heterogeneity on disease progression. The purpose of this study is to construct a prognostic risk model for ccRCC by analysing the differential marker genes related to immune cells in the single-cell database to provide help in clinical diagnosis and targeted therapy. Single-cell data and ligand-receptor relationship pair data were downloaded from related publications, and ccRCC phenotype and expression profile data were downloaded from TCGA and CPTAC. Based on the DEGs of each cluster acquired from single-cell data, immune cell marker genes, and ligand-receptor gene data, we constructed a multilayer network. Then, the genes in the network and the genes in TCGA were used to construct the WGCNA network, which screened out prognosis-associated genes for subsequent analysis. Finally, a prognostic risk scoring model was obtained, and CPTAC data showed that the effectiveness of this model was good. A nomogram based on the predictive model for predicting the overall survival was established, and internal validation was performed well. Our findings suggest that the predictive model built and based on the immune cell scRNA-seq will enable us to judge the prognosis of patients with ccRCC and provide more accurate directions for basic relevant research and clinical practice.

ASH2L Aggravates Fibrosis and Inflammation through HIPK2 in High Glucose-Induced Glomerular Mesangial Cells

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease and continues to be a threat to patients with diabetes. Dysfunction of glomerular mesangial cells (GMCs) is the main contributing factor to glomerulosclerosis, which is a pathological feature of DN. The epigenetic factor ASH2L has long been thought to be a transcriptional activator, but its function and involvement in diabetic nephropathy is still unclear. Here, we investigated the effect of ASH2L on the regulation of fibrosis and inflammation induced by high glucose in mouse mesangial cells (mMCs). We observed that ASH2L expression is increased in high glucose-induced mMCs, while loss of ASH2L alleviated fibrosis and inflammation. Furthermore, ASH2L-mediates H3K4me3 of the homeodomain-interacting protein kinase 2 (HIPK2) promoter region, which is a contributor to fibrosis in the kidneys and promotes its transcriptional expression. Similar to loss of ASH2L, silencing HIPK2 also inhibited fibrosis and inflammation. In addition, ASH2L and HIPK2 are upregulated in the kidneys of both streptozocin-induced and db/db mouse. In conclusion, we uncovered the crucial role of ASH2L in high glucose-induced fibrosis and inflammation, suggesting that ASH2L regulation may be an attractive approach to attenuate the progression of DN.

TRAF2 regulates the protein stability of HIPK2

A nuclear serine/threonine kinase homeodomain-interacting protein kinase 2 (HIPK2) is a critical regulator of development and DNA damage response. HIPK2 can induce apoptosis under cellular stress conditions and thus its protein level is maintained low by constant proteasomal degradation. In the present study, we present evidence that TNF receptor-associated factor 2 (TRAF2) regulates the protein stability of HIPK2. Overexpression of TRAF2 decreased while its knockdown increased the HIPK2 protein level. The TRAF2-mediated decrease in HIPK2 protein expression was blocked by proteasomal inhibitor. In addition, TRAF2 decreased the protein half-life of HIPK2. We found that HIPK2 and TRAF2 co-immunoprecipitated. Interestingly, the co-immunoprecipitation was reduced while HIPK2 protein level increased following TNFα treatment, suggesting TNFα induced dissociation of TRAF2 from HIPK2 to accumulate HIPK2. Inhibition of HIPK2 partially suppressed TNFα-induced cell death, indicating that the accumulated HIPK2 may contribute to the TNFα-induced cell death. Our results suggest that TRAF2 can regulate proapoptotic function of HIPK2 by promoting proteasomal degradation.

MiR-221-3p targets HIPK2 to promote diabetic wound healing

Diabetic foot ulcer is a severe complication of diabetes and is prone to being a chronic non-healing wound. We previously demonstrated that endothelial progenitor cell-derived exosomes, which contain miR-221-3p, alleviate diabetic ulcers. Here, to explore the mechanisms underlying this wound healing, we investigated the potential angiogenic effects of miR-221-3p in vitro using cultured human umbilical vein endothelial cells (HUVECs) and in vivo using a streptozotocin-induced mouse model of diabetes. We found that miR-221-3p promoted HUVEC viability, migration, and capillary-like tube formation. HUVECs cultured in high glucose showed up-regulated expression of homeodomain-interacting protein kinase 2 (HIPK2), a predicted target of miR-221-3p that may decrease angiogenesis. Knockdown of HIPK2 enhanced high glucose-suppressed HUVEC viability, migration, and tube formation, counteracting the effects of high glucose. Using a dual luciferase reporter assay, we found that HIPK2 was indeed a direct target of miR-221-3p. Subcutaneous injection of miR-221-3p agomir into diabetic mice promoted wound healing and suppressed HIPK2 expression in wound margin tissue. These findings indicate that HIPK2, as a direct target of miR-221-3p, contributes to the regulatory role of miR-221-3p in diabetic wound healing and may be a novel therapeutic target for diabetic foot ulcer.

HIPK2 cooperates with KRAS signaling and associates with colorectal cancer progression

HIPK2 is an evolutionary conserved kinase that has gained attention as a fine tuner of multiple signaling pathways, among which those commonly altered in colorectal cancer (CRC). The aim of this study was to evaluate the relationship of HIPK2 expression with progression markers and mutational pattern and gain insights into the contribution of HIPK2 activity in CRC. We evaluated a retrospective cohort of CRC samples by immunohistochemistry for HIPK2 expression and by NGS for the detection of mutations of cancer associated genes. We show that the percentage of HIPK2 positive cells increases with tumor progression, significantly correlates with TNM staging and associates with a worse outcome. In addition, we observed that high HIPK2 expression significantly associates with KRAS mutations but not with other cancer related genes. Functional characterization of the link between HIPK2 and KRAS show that activation of the RAS pathway either due to KRAS mutation or via upstream receptor stimulation, increases HIPK2 expression at the protein level. Of note, HIPK2 physically participates in the active RAS complex while HIPK2 depletion impairs ERK phosphorylation and the growth of tumors derived from KRAS mutated CRC cells. Overall, this study identifies HIPK2 as a prognostic biomarker candidate in CRC patients and underscores a previously unknown functional link between HIPK2 and the KRAS signaling pathway. Implications: Our data indicate HIPK2 as a new player in the complex picture of the KRAS signaling network, providing rationales for future clinical studies and new treatment strategies for KRAS mutated CRC.

MiR-423-5p activated by E2F1 promotes neovascularization in diabetic retinopathy by targeting HIPK2

BACKGROUND

Diabetic retinopathy (DR) is a diabetic complication and the primary cause of blindness in the world. However, the treatments of DR are challenging given its complicated pathogenesis. Here, we investigated the molecular mechanisms of DR by focusing on the function of E2F1/miR-423-5p/HIPK2/HIF1α/VEGF axis.

METHODS

Cultured retinal endothelial cells (hRMECs, hRECs) were treated with 25 mM glucose to mimic the high glucose-induced DR in vitro. Streptozotocin (STZ) was injected into mice to induce DR in mice. qRT-PCR, western blotting, immunohistochemistry, and ELISA were employed to measure levels of E2F1, miR-423-5p, HIPK2, HIF1α, and VEGF. H&E staining was utilized to examine retinal neovascularization. CCK-8 assay, transwell assay, and vascular tube formation assay were used to assess the cell viability, migration, and angiogenesis. Dual luciferase assay was performed to validate interactions between E2F1 and miR-423-5p, miR-423-5p and HIPK2.

RESULTS

HG treatment increased the cell viability, migration, and angiogenesis accompanied by upregulation of E2F1, miR-423-5p, HIF1α, and VEGF levels, but reduction in HIPK2 expression. Knockdown of E2F1 or miR-423-5p suppressed the HG-induced increases in cell viability, migration, and angiogenesis. E2F1 transcriptionally activated miR-423-5p expression and miR-423-5p mimics blocked the effects of E2F1 knockdown on angiogenesis. Moreover, miR-423-5p directly targeted HIPK2 to disinhibit HIF1α/VEGF signaling. Knockdown of HIPK2 reversed the effects of miR-423-5p inhibitor on cell viability, migration, and angiogenesis. Knockdown of E2F1 suppressed neovascularization during DR in vivo.

CONCLUSIONS

E2F1 activates miR-423-5p transcription during DR to promote angiogenesis via suppressing HIPK2 expression to disinhibit HIF1α/VEGF signaling. Strategies targeting E2F1/miR-423-5p/HIPK2 axis could be potentially used for DR treatment.

Abemaciclib is a potent inhibitor of DYRK1A and HIP kinases involved in transcriptional regulation

Homeodomain-interacting protein kinases (HIPKs) belong to the CMGC kinase family and are closely related to dual-specificity tyrosine phosphorylation-regulated kinases (DYRKs). HIPKs are regulators of various signaling pathways and involved in the pathology of cancer, chronic fibrosis, diabetes, and multiple neurodegenerative diseases. Here, we report the crystal structure of HIPK3 in its apo form at 2.5 Å resolution. Recombinant HIPKs and DYRK1A are auto-activated and phosphorylate the negative elongation factor SPT5, the transcription factor c-Myc, and the C-terminal domain of RNA polymerase II, suggesting a direct function in transcriptional regulation. Based on a database search, we identified abemaciclib, an FDA-approved Cdk4/Cdk6 inhibitor used for the treatment of metastatic breast cancer, as potent inhibitor of HIPK2, HIPK3, and DYRK1A. We determined the crystal structures of HIPK3 and DYRK1A bound to abemaciclib, showing a similar binding mode to the hinge region of the kinase as observed for Cdk6. Remarkably, DYRK1A is inhibited by abemaciclib to the same extent as Cdk4/Cdk6 in vitro, raising the question of whether targeting of DYRK1A contributes to the transcriptional inhibition and therapeutic activity of abemaciclib.

Phenotypic Effects of Homeodomain-Interacting Protein Kinase 2 Deletion in Mice

Homeodomain-interacting protein kinase 2 (HIPK2) is a serine-threonine kinase that phosphorylates various transcriptional and chromatin regulators, thus modulating numerous important cellular processes, such as proliferation, apoptosis, DNA damage response, and oxidative stress. The role of HIPK2 in the pathogenesis of cancer and fibrosis is well established, and evidence of its involvement in the homeostasis of multiple organs has been recently emerging. We have previously demonstrated that Hipk2-null (Hipk2-KO) mice present cerebellar alterations associated with psychomotor abnormalities and that the double ablation of HIPK2 and its interactor HMGA1 causes perinatal death due to respiratory failure. To identify other alterations caused by the loss of HIPK2, we performed a systematic morphological analysis of Hipk2-KO mice. Post-mortem examinations and histological analysis revealed that Hipk2 ablation causes neuronal loss, neuronal morphological alterations, and satellitosis throughout the whole central nervous system (CNS); a myopathic phenotype characterized by variable fiber size, mitochondrial proliferation, sarcoplasmic inclusions, morphological alterations at neuromuscular junctions; and a cardiac phenotype characterized by fibrosis and cardiomyocyte hypertrophy. These data demonstrate the importance of HIPK2 in the physiology of skeletal and cardiac muscles and of different parts of the CNS, thus suggesting its potential relevance for different new aspects of human pathology.

Exosomal miR-1260b derived from non-small cell lung cancer promotes tumor metastasis through the inhibition of HIPK2

Tumor-derived exosomes (TEXs) contain enriched miRNAs, and exosomal miRNAs can affect tumor growth, including cell proliferation, metastasis, and drug resistance through cell-to-cell communication. We investigated the role of exosomal miR-1260b derived from non-small cell lung cancer (NSCLC) in tumor progression. Exosomal miR-1260b induced angiogenesis by targeting homeodomain-interacting protein kinase-2 (HIPK2) in human umbilical vein endothelial cells (HUVECs). Furthermore, exosomal miR-1260b or suppression of HIPK2 led to enhanced cellular mobility and cisplatin resistance in NSCLC cells. In patients with NSCLC, the level of HIPK2 was significantly lower in tumor tissues than in normal lung tissues, while that of miR-1260b was higher in tumor tissues. HIPK2 and miR-1260b expression showed an inverse correlation, and this correlation was strong in distant metastasis. Finally, the expression level of exosomal miR-1260b in plasma was higher in patients with NSCLC than in healthy individuals, and higher levels of exosomal miR-1260b were associated with high-grade disease, metastasis, and poor survival. In conclusion, exosomal miR-1260b can promote angiogenesis in HUVECs and metastasis of NSCLC by regulating HIPK2 and may serve as a prognostic marker for lung cancers.

DAZAP2 acts as specifier of the p53 response to DNA damage

The DNA damage-responsive tumor suppressors p53 and HIPK2 are well established regulators of cell fate decision-making and regulate the cellular sensitivity to DNA-damaging drugs. Here, we identify Deleted in Azoospermia-associated protein 2 (DAZAP2), a small adaptor protein, as a novel regulator of HIPK2 and specifier of the DNA damage-induced p53 response. Knock-down or genetic deletion of DAZAP2 strongly potentiates cancer cell chemosensitivity both in cells and in vivo using a mouse tumour xenograft model. In unstressed cells, DAZAP2 stimulates HIPK2 polyubiquitination and degradation through interplay with the ubiquitin ligase SIAH1. Upon DNA damage, HIPK2 site-specifically phosphorylates DAZAP2, which terminates its HIPK2-degrading function and triggers its re-localization to the cell nucleus. Interestingly, nuclear DAZAP2 interacts with p53 and specifies target gene expression through modulating a defined subset of p53 target genes. Furthermore, our results suggest that DAZAP2 co-occupies p53 response elements to specify target gene expression. Collectively, our findings propose DAZAP2 as novel regulator of the DNA damage-induced p53 response that controls cancer cell chemosensitivity.

Identification of HIPK3 as a potential biomarker and an inhibitor of clear cell renal cell carcinoma

Invasion and metastasis are the main causes of poor prognosis in patients with clear cell renal cell carcinoma (ccRCC). The homeodomain interacting protein kinases (HIPKs) can regulate cell proliferation and apoptosis. Little is known about the prognostic role of HIPKs in ccRCC. Here we use Kaplan-Meier survival analysis and multivariate analysis to analyze the correlation of overall survival (OS) and disease–free survival (DFS). ROC curves analyzed the relationship between clinicopathological parameters and HIPK3 expression in ccRCC. Univariate analysis and multivariate analysis confirmed that the expression of HIPK3 was associated with OS (HR, 0.701; P=0.041) and DFS (HR, 0.630; P=0.012). Low HIPK3 expression was a poor prognostic factor and HIPK3 expression was significantly down-regulated in ccRCC cancer tissues when compared with normal renal tissues. In vitro cell results also confirmed that HIPK3 over-expression could inhibit tumor growth and malignant characteristics. The results indicate that low expression of HIPK3 in ccRCC tissues is significantly associated with poor survival rates in tumor patients, and HIPK3 may be used as a valuable biomarker and inhibitor of ccRCC.

Inactivation of homeodomain-interacting protein kinase 2 promotes oral squamous cell carcinoma metastasis through inhibition of P53-dependent E-cadherin expression

Homeodomain-interacting protein kinase 2 (HIPK2), a well-known tumor suppressor, shows contradictory expression patterns in different cancers. This study was undertaken to clarify HIPK2 expression in oral squamous cell carcinoma (OSCC) and to reveal the potential mechanism of HIPK2 involvement in OSCC metastasis. Two hundred and four OSCC tissues, together with paired adjacent normal epithelia, dysplastic epithelia, and lymph node metastasis specimens, were collected to profile HIPK2 expression by immunohistochemical staining. High throughput RNA-sequencing was used to detect the dysregulated signaling pathways in HIPK2-deficient OSCC cells. Transwell assay and lymphatic metastatic orthotopic mouse model assay were undertaken to identify the effect of HIPK2 on tumor invasion. Western blotting and luciferase reporter assay were used to examine the HIPK2/P53/E-cadherin axis in OSCC. Nuclear delocalization of HIPK2 was observed during oral epithelial cancerization progression and was associated with cervical lymph node metastasis and poor outcome. Depletion of HIPK2 promoted tumor cell invasion in vitro and facilitated cervical lymph node metastasis in vivo. According to mRNA-sequencing, pathways closely related to tumor invasion were notably activated. Homeodomain-interacting protein kinase 2 was found to trigger E-cadherin expression by mediating P53, which directly targets the CDH1 (coding E-cadherin) promoter. Restoring P53 expression rescued the E-cadherin suppression induced by HIPK2 deficiency, whereas rescued cytoplasmic HIPK2 expression had no influence on the expression of E-cadherin and cell mobility. Together, nuclear delocalization of HIPK2 might serve as a valuable negative biomarker for poor prognosis of OSCC and lymph node metastasis. The depletion of HIPK2 expression promoted OSCC metastasis by suppressing the P53/E-cadherin axis, which might be a promising target for anticancer therapies.

Spastin recovery in hereditary spastic paraplegia by preventing neddylation-dependent degradation

Hereditary Spastic Paraplegia (HSP) is a neurodegenerative disease most commonly caused by autosomal dominant mutations in the SPG4 gene encoding the microtubule-severing protein spastin. We hypothesise that SPG4-HSP is attributable to reduced spastin function because of haploinsufficiency; thus, therapeutic approaches which elevate levels of the wild-type spastin allele may be an effective therapy. However, until now, how spastin levels are regulated is largely unknown. Here, we show that the kinase HIPK2 regulates spastin protein levels in proliferating cells, in differentiated neurons and in vivo. Our work reveals that HIPK2-mediated phosphorylation of spastin at S268 inhibits spastin K48-poly-ubiquitination at K554 and prevents its neddylation-dependent proteasomal degradation. In a spastin RNAi neuronal cell model, overexpression of HIPK2, or inhibition of neddylation, restores spastin levels and rescues neurite defects. Notably, we demonstrate that spastin levels can be restored pharmacologically by inhibiting its neddylation-mediated degradation in neurons derived from a spastin mouse model of HSP and in patient-derived cells, thus revealing novel therapeutic targets for the treatment of SPG4-HSP.

Chromatin Targeting of HIPK2 Leads to Acetylation-Dependent Chromatin Decondensation

The protein kinase homeodomain-interacting protein kinase 2 (HIPK2) plays an important role in development and in the response to external cues. The kinase associates with an exceptionally large number of different transcription factors and chromatin regulatory proteins to direct distinct gene expression programs. In order to investigate the function of HIPK2 for chromatin compaction, HIPK2 was fused to the DNA-binding domains of Gal4 or LacI, thus allowing its specific targeting to binding sites for these transcription factors that were integrated in specific chromosome loci. Tethering of HIPK2 resulted in strong decompaction of euchromatic and heterochromatic areas. HIPK2-mediated heterochromatin decondensation started already 4 h after its chromatin association and required the functionality of its SUMO-interacting motif. This process was paralleled by disappearance of the repressive H3K27me3 chromatin mark, recruitment of the acetyltransferases CBP and p300 and increased histone acetylation at H3K18 and H4K5. HIPK2-mediated chromatin decompaction was strongly inhibited in the presence of a CBP/p300 inhibitor and completely blocked by the BET inhibitor JQ1, consistent with a causative role of acetylations for this process. Chromatin tethering of HIPK2 had only a minor effect on basal transcription, while it strongly boosted estrogen-triggered gene expression by acting as a transcriptional cofactor.

HIPK2 Is Required for Midbody Remnant Removal Through Autophagy-Mediated Degradation

At the end of abscission, the residual midbody forms the so-called midbody remnant (MBR), a platform affecting cell fate with emerging key role in differentiation, development, and tumorigenicity. Depending on cell type and pathophysiological context, MBRs undergo different outcomes: they can be retained, released, internalized by nearby cells, or removed through autophagy-mediated degradation. Although mechanisms underlying MBR formation, positioning, and processing have been recently identified, their regulation is still largely unknown. Here, we report that the multifunctional kinase HIPK2 regulates MBR processing contributing to MBR removal. In the process of studying the role of HIPK2 in abscission, we observed that, in addition to cytokinesis failure, HIPK2 depletion leads to significant accumulation of MBRs. In particular, we detected comparable accumulation of MBRs after HIPK2 depletion or treatment with the autophagic inhibitor chloroquine. In contrast, single depletion of the two independent HIPK2 abscission targets, extrachromosomal histone H2B and severing enzyme Spastin, only marginally increased MBR retention, suggesting that MBR accumulation is not just linked to cytokinesis failure. We found that HIPK2 depletion leads to (i) increased levels of CEP55, a key effector of both midbody formation and MBR degradation; (ii) decreased levels of the selective autophagy receptors NBR1 and p62/SQSTM1; and (iii) impaired autophagic flux. These data suggest that HIPK2 contributes to MBR processing by regulating its autophagy-mediated degradation.

Nuclear factor erythroid 2 (NF-E2) p45-related factor 2 interferes with homeodomain-interacting protein kinase 2/p53 activity to impair solid tumors chemosensitivity

Resistance to chemotherapy represents a major hurdle to successful cancer treatment. A key role for efficient response to anticancer therapies is played by TP53 oncosuppressor gene that indeed is mutated in 50% of human cancers or inactivated at protein level in the remaining 50%. Homeodomain-interacting protein kinase 2 (HIPK2) is the wild-type p53 (wtp53) apoptotic activator, and its inhibition by hypoxia or hyperglycemia may contribute to tumor chemoresistance mainly by impairing p53 apoptotic activity. Another important molecule able to induce chemoresistance is nuclear factor erythroid 2 (NF-E2) p45-related factor 2 (NRF2) transcription factor, whose activation by oxidative and/or electrophilic stress regulates a transcriptional antioxidant program allowing cancer cells to adapt and survive to stresses. NRF2 may shift from cytoprotective to tumor-promoting function, according to tumor phases. NRF2 may crosstalk with both wtp53 and mutant p53 (mutp53), inhibiting the wtp53 apoptotic function and strengthening the mutp53 oncogenic function. NRF2 has also been shown to induce HIPK2 mRNA expression cooperating in inducing cytoprotection. Although HIPK2, p53, and NRF2 have been individually extensively studied, their interplay has not been clearly addressed yet. On the basis of the background and our results, we aim at hypothesizing the unexpected pro-survival activity played by the NRF2/HIPK2/p53 interplay that can be hijacked by cancer cells to bypass drugs cytotoxicity.

An Alternative Splice Variant of HIPK2 with Intron Retention Contributes to Cytokinesis

HIPK2 is a DYRK-like kinase involved in cellular stress response pathways, development, and cell division. Two alternative splice variants of HIPK2, HIPK2-FL and HIPK2-Δe8, have been previously identified as having different protein stability but similar functional activity in the stress response. Here, we describe one additional HIPK2 splice variant with a distinct subcellular distribution and functional activity in cytokinesis. This novel splice variant lacks the last two exons and retains intron13 with a stop codon after 89 bp of the intron, generating a short isoform, HIPK2-S, that is detectable by 2D Western blots. RT-PCR analyses of tissue arrays and tumor samples show that HIPK2-FL and HIPK2-S are expressed in normal human tissues in a tissue-dependent manner and differentially expressed in human colorectal and pancreatic cancers. Gain- and loss-of-function experiments showed that in contrast to HIPK2-FL, HIPK2-S has a diffuse, non-speckled distribution and is not involved in the DNA damage response. Rather, we found that HIPK2-S, but not HIPK2-FL, localizes at the intercellular bridge, where it phosphorylates histone H2B and spastin, both required for faithful cell division. Altogether, these data show that distinct human HIPK2 splice variants are involved in distinct HIPK2-regulated functions like stress response and cytokinesis.

Novel Mutation Hotspots within Non-Coding Regulatory Regions of the Chronic Lymphocytic Leukemia Genome

Mutations in non-coding DNA regions are increasingly recognized as cancer drivers. These mutations can modify gene expression in cis or by inducing high-order chormatin structure modifications with long-range effects. Previous analysis reported the detection of recurrent and functional non-coding DNA mutations in the chronic lymphocytic leukemia (CLL) genome, such as those in the 3′ untranslated region of NOTCH1 and in the PAX5 super-enhancer. In this report, we used whole genome sequencing data produced by the International Cancer Genome Consortium in order to analyze regions with previously reported regulatory activity. This approach enabled the identification of numerous recurrently mutated regions that were frequently positioned in the proximity of genes involved in immune and oncogenic pathways. By correlating these mutations with expression of their nearest genes, we detected significant transcriptional changes in genes such as PHF2 and S1PR2. More research is needed to clarify the function of these mutations in CLL, particularly those found in intergenic regions.

HIPK2 role in the tumor-host interaction: Impact on fibroblasts transdifferentiation CAF-like

The dialogue between cancer cells and the surrounding fibroblasts, tumor-associated macrophages (TAM), and immune cells can create a tumor microenvironment (TME) able to promote tumor progression and metastasis and induce resistance to anticancer therapies. Cancer cells, by producing growth factors and cytokines, can recruit and activate fibroblasts in the TME inducing their transdifferention in cancer-associated fibroblasts (CAFs). Then, CAFs, in a reciprocal cross-talk with cancer cells, sustain cancer growth and survival and support malignancy and tumor resistance to therapies. Therefore, the identification of the molecular mechanisms regulating the interplay between cancer cells and fibroblasts can offer an intriguing opportunity for novel diagnostic and therapeutic anticancer purpose. HIPK2 is a multifunctional tumor suppressor protein that modulates cancer cell growth and apoptosis in response to anticancer drugs and negatively regulates pathways involved in tumor progression and chemoresistance. HIPK2 protein downregulation is induced by hypoxia and hyperglycemia and HIPK2 knockdown favors tumor progression and resistance to therapy other than a pseudohypoxic, inflammatory, and angiogenic cancer phenotype. Therefore, we hypothesized that HIPK2 modulation in cancer cells could contribute to modify the tumor-host interaction. In support of our hypothesis, here we provide evidence that culturing human fibroblasts (hFB) with conditioned media derived from cancer cells undergoing HIPK2 knockdown (CMsiHIPK2 ) triggered their transdifferentiation CAF-like, compared to hFB cultured with CM-derived from HIPK2-carrying control cancer cells. CAF transdifferentiation was identified by expression of several markers including α-smooth muscle actin (α-SMA) and collagen I and correlated with autophagy-mediated caveolin-1 degradation. Although the molecular mechanisms dictating CAF-transdifferentiation need to be elucidated, these results open the way to further study the role of HIPK2 in TME remodeling for prognostic and therapeutic purpose.

Double knock-out of Hmga1 and Hipk2 genes causes perinatal death associated to respiratory distress and thyroid abnormalities in mice

The serine–threonine kinase homeodomain-interacting protein kinase 2 (HIPK2) modulates important cellular functions during development, acting as a signal integrator of a wide variety of stress signals, and as a regulator of transcription factors and cofactors. We have previously demonstrated that HIPK2 binds and phosphorylates High-Mobility Group A1 (HMGA1), an architectural chromatinic protein ubiquitously expressed in embryonic tissues, decreasing its binding affinity to DNA. To better define the functional role of HIPK2 and HMGA1 interaction in vivo, we generated mice in which both genes are disrupted. About 50% of these Hmga1/Hipk2 double knock-out (DKO) mice die within 12 h of life (P1) for respiratory failure. The DKO mice present an altered lung morphology, likely owing to a drastic reduction in the expression of surfactant proteins, that are required for lung development. Consistently, we report that both HMGA1 and HIPK2 proteins positively regulate the transcriptional activity of the genes encoding the surfactant proteins. Moreover, these mice display an altered expression of thyroid differentiation markers, reasonably because of a drastic reduction in the expression of the thyroid-specific transcription factors PAX8 and FOXE1, which we demonstrate here to be positively regulated by HMGA1 and HIPK2. Therefore, these data indicate a critical role of HIPK2/HMGA1 cooperation in lung and thyroid development and function, suggesting the potential involvement of their impairment in the pathogenesis of human lung and thyroid diseases.

Effects of hyperglycemia on the progression of tumor diseases

Malignant tumors are often multifactorial. Epidemiological studies have shown that hyperglycemia raises the prevalence and mortality of certain malignancies, like breast, liver, bladder, pancreatic, colorectal, endometrial cancers. Hyperglycemia can promote the proliferation, invasion and migration, induce the apoptotic resistance and enhance the chemoresistance of tumor cells. This review focuses on the new findings in the relationship between hyperglycemia and tumor development.

HIPK2 Phosphorylates the Microtubule-Severing Enzyme Spastin at S268 for Abscission

Abscission is the final step of cell division, mediating the physical separation of the two daughter cells. A key player in this process is the microtubule-severing enzyme spastin that localizes at the midbody where its activity is crucial to cut microtubules and culminate the cytokinesis. Recently, we demonstrated that HIPK2, a multifunctional kinase involved in several cellular pathways, contributes to abscission and prevents tetraploidization. Here, we show that HIPK2 binds and phosphorylates spastin at serine 268. During cytokinesis, the midbody-localized spastin is phosphorylated at S268 in HIPK2-proficient cells. In contrast, no spastin is detectable at the midbody in HIPK2-depleted cells. The non-phosphorylatable spastin-S268A mutant does not localize at the midbody and cannot rescue HIPK2-depleted cells from abscission defects. In contrast, the phosphomimetic spastin-S268D mutant localizes at the midbody and restores successful abscission in the HIPK2-depleted cells. These results show that spastin is a novel target of HIPK2 and that HIPK2-mediated phosphorylation of spastin contributes to its midbody localization for successful abscission.

Differential intracellular localization and dynamic nucleocytoplasmic shuttling of homeodomain-interacting protein kinase family members

The three canonical members of the family of homeodomain-interacting protein (HIP) kinases fulfill overlapping and distinct roles in cellular stress response pathways. Here we systematically compared all three endogenous HIPKs for their intracellular distribution and mutual interactions. The endogenous HIPKs are contained in high molecular weight complexes of ~700 kDa but do not directly interact physically. Under basal conditions, HIPK1 was mostly cytoplasmic, while HIPK3 was found in the nucleus and HIPK2 occurred in both compartments. Inhibition of nuclear export by leptomycin B resulted in the nuclear accumulation of mainly HIPK1 and HIPK2, indicating constitutive dynamic nucleocytoplasmic shuttling. The carcinogenic chemical stressor sodium arsenite caused the induction of HIPK2-dependent cell death and also resulted in a rapid and complete nuclear translocation of HIPK2, showing that the intracellular distribution of this kinase can undergo dynamic regulation.

Drosophila Homeodomain-Interacting Protein Kinase (Hipk) Phosphorylates the Homeodomain Proteins Homeobrain, Empty Spiracles, and Muscle Segment Homeobox

The Drosophila homeodomain-interacting protein kinase (Hipk) is the fly representative of the well-conserved group of HIPKs in vertebrates. It was initially found through its characteristic interactions with homeodomain proteins. Hipk is involved in a variety of important developmental processes, such as the development of the eye or the nervous system. In the present study, we set Hipk and the Drosophila homeodomain proteins Homeobrain (Hbn), Empty spiracles (Ems), and Muscle segment homeobox (Msh) in an enzyme-substrate relationship. These homeoproteins are transcription factors that function during Drosophila neurogenesis and are, at least in part, conserved in vertebrates. We reveal a physical interaction between Hipk and the three homeodomain proteins in vivo using bimolecular fluorescence complementation (BiFC). In the course of in vitro phosphorylation analysis and subsequent mutational analysis we mapped several Hipk phosphorylation sites of Hbn, Ems, and Msh. The phosphorylation of Hbn, Ems, and Msh may provide further insight into the function of Hipk during development of the Drosophila nervous system.

HIPK2 and extrachromosomal histone H2B are separately recruited by Aurora-B for cytokinesis

Cytokinesis, the final phase of cell division, is necessary to form two distinct daughter cells with correct distribution of genomic and cytoplasmic materials. Its failure provokes genetically unstable states, such as tetraploidization and polyploidization, which can contribute to tumorigenesis. Aurora-B kinase controls multiple cytokinetic events, from chromosome condensation to abscission when the midbody is severed. We have previously shown that HIPK2, a kinase involved in DNA damage response and development, localizes at the midbody and contributes to abscission by phosphorylating extrachromosomal histone H2B at Ser14. Of relevance, HIPK2-defective cells do not phosphorylate H2B and do not successfully complete cytokinesis leading to accumulation of binucleated cells, chromosomal instability, and increased tumorigenicity. However, how HIPK2 and H2B are recruited to the midbody during cytokinesis is still unknown. Here, we show that regardless of their direct (H2B) and indirect (HIPK2) binding of chromosomal DNA, both H2B and HIPK2 localize at the midbody independently of nucleic acids. Instead, by using mitotic kinase-specific inhibitors in a spatio-temporal regulated manner, we found that Aurora-B kinase activity is required to recruit both HIPK2 and H2B to the midbody. Molecular characterization showed that Aurora-B directly binds and phosphorylates H2B at Ser32 while indirectly recruits HIPK2 through the central spindle components MgcRacGAP and PRC1. Thus, among different cytokinetic functions, Aurora-B separately recruits HIPK2 and H2B to the midbody and these activities contribute to faithful cytokinesis.

Hyperglycemia triggers HIPK2 protein degradation

Homeodomain interacting protein kinase-2 (HIPK2) is an evolutionary conserved kinase that modulates several key molecular pathways to restrain tumor growth and induce p53-depending apoptotic cell-death in response to anticancer therapies. HIPK2 silencing in cancer cells leads to chemoresistance and cancer progression, in part due to p53 inhibition. Recently, hyperglycemia has been shown to reduce p53 phosphorylation at serine 46 (Ser46), the target residue of HIPK2, thus impairing p53 apoptotic function. Here we asked whether hyperglycemia could, upstream of p53, target HIPK2. We focused on the effect of high glucose (HG) on HIPK2 protein stability and the underlying mechanisms. We found that HG reduced HIPK2 protein levels, therefore impairing HIPK2-induced p53 apoptotic activity. HG-triggered HIPK2 protein downregulation was rescued by both proteasome inhibitor MG132 and by protein phosphatase inhibitors Calyculin A (CL-A) and Okadaic Acid (OA). Looking for the phosphatase involved, we found that protein phosphatase 2A (PP2A) induced HIPK2 degradation, as evidenced by directly activating PP2A with FTY720 or by silencing PP2A with siRNA in HG condition. The effect of PP2A on HIPK2 protein degradation could be in part due to hypoxia-inducible factor-1 (HIF-1) activity which has been previously shown to induce HIPK2 proteasomal degradation through several ubiquitin ligases. Validation analysed performed with HIF-1α dominant negative or with silencing of Siah2 ubiquitin ligase clearly showed rescue of HG-induced HIPK2 degradation. These findings demonstrate how hyperglycemia, through a complex protein cascade, induced HIPK2 downregulation and consequently impaired p53 apoptotic activity, revealing a novel link between diabetes/obesity and tumor resistance to therapies.

Homeodomain-interacting protein kinase 2 (HIPK2): a promising target for anti-cancer therapies

The HIPK2 (serine/threonine homeodomain-interacting protein kinase 2) is a "caretaker" gene, its inactivation increases tumorigenicity while its activation inhibits tumor growth. This report reviews the anti-tumorigenic mechanisms of HIPK2, which include promotion of apoptosis, inhibition of angiogenesis in hypoxia, prevention of tumor invasion/metastasis and attenuation of multidrug resistance in cancer. Additionally, we summarize conditions or factors that may increase HIPK2 activity.

HIPK2-T566 autophosphorylation diversely contributes to UV- and doxorubicin-induced HIPK2 activation

HIPK2 is a Y-regulated S/T kinase involved in various cellular processes, including cell-fate decision during development and DNA damage response. Cis-autophosphorylation in the activation-loop and trans-autophosphorylation at several S/T sites along the protein are required for HIPK2 activation, subcellular localization, and subsequent posttranslational modifications. The specific function of a few of these autophosphorylations has been recently clarified; however, most of the sites found phosphorylated by mass spectrometry in human and/or mouse HIPK2 are still uncharacterized. In the process of studying HIPK2 in human colorectal cancers, we identified a mutation (T566P) in a site we previously found autophosphorylated in mouse Hipk2. Biochemical and functional characterization of this site showed that compared to wild type (wt) HIPK2, HIPK2-T566P maintains nuclear-speckle localization and has only a mild reduction in kinase and growth arresting activities upon overexpression. Next, we assessed cell response following UV-irradiation or treatment with doxorubicin, two well-known HIPK2 activators, by evaluating cell number and viability, p53-Ser46 phosphorylation, p21 induction, and caspase cleavage. Interestingly, cells expressing HIPK2-T566P mutant did not respond to UV-irradiation, while behaved similarly to wt HIPK2 upon doxorubicin-treatment. Evaluation of HIPK2-T566 phosphorylation status by a T566-phospho-specific antibody showed constitutive phosphorylation in unstressed cells, which was maintained after doxorubicin-treatment but inhibited by UV-irradiation. Taken together, these data show that HIPK2-T566 phosphorylation contributes to UV-induced HIPK2 activity but it is dispensable for doxorubicin response.

HIPK2 Overexpression and Its Prognostic Role in Human Papillomavirus-Positive Tonsillar Squamous Cell Carcinoma

Tonsillar squamous cell carcinomas (TSCCs) are the most common human papillomavirus- (HPV-) associated oropharyngeal cancers with poor prognosis. Homeodomain-interacting protein kinase 2 (HIPK2) is a central regulator of p53, which participates in apoptosis during the DNA damage response. HIPK2 is involved in HPV-associated uterine cervical and cutaneous carcinogenesis through its binding of HPV E6, thereby preventing apoptosis and contributing to tumor progression. However, its clinical and prognostic significance in TSCC remains unclear. HIPK2 mRNA levels were analyzed in 20 normal tonsils and 20 TSCC specimens using real-time reverse transcription polymerase chain reaction. Immunohistochemistry of HIPK2 was performed in 79 resected specimens. HIPK2 was expressed in 57% of the TSCCs, and HIPK2 protein expression and HIPK2 mRNA levels were higher in TSCCs than in normal tonsils. HIPK2 overexpression was associated with poorly differentiated carcinoma and low alcohol consumption and was an independent prognostic factor for overall survival and disease-free survival (DFS) in TSCC and a negative independent prognostic factor for DFS in patients receiving postoperative radiotherapy. HIPK2 overexpression had a significant association with poorer DFS in HPV-positive TSCCs, but not in HPV-negative tumors. HIPK2 overexpression may be a potential prognostic marker for predicting prognoses and a high risk of recurrence, particularly in patients with HPV-positive TSCC.

Homeodomain-Interacting Protein Kinases: Diverse and Complex Roles in Development and Disease

The Homeodomain-interacting protein kinase (Hipk) family of proteins plays diverse, and at times conflicting, biological roles in normal development and disease. In this review we will highlight developmental and cellular roles for Hipk proteins, with an emphasis on the pleiotropic and essential physiological roles revealed through genetic studies. We discuss the myriad ways of regulating Hipk protein function, and how these may contribute to the diverse cellular roles. Furthermore we will describe the context-specific activities of Hipk family members in diseases such as cancer and fibrosis, including seemingly contradictory tumor-suppressive and oncogenic activities. Given the diverse signaling pathways regulated by Hipk proteins, it is likely that Hipks act to fine-tune signaling and may mediate cross talk in certain contexts. Such regulation is emerging as vital for development and in disease.

Racial differences in genome-wide methylation profiling and gene expression in breast tissues from healthy women

Breast cancer is more common in European Americans (EAs) than in African Americans (AAs) but mortality from breast cancer is higher among AAs. While there are racial differences in DNA methylation and gene expression in breast tumors, little is known whether such racial differences exist in breast tissues of healthy women. Genome-wide DNA methylation and gene expression profiling was performed in histologically normal breast tissues of healthy women. Linear regression models were used to identify differentially-methylated CpG sites (CpGs) between EAs (n = 61) and AAs (n = 22). Correlations for methylation and expression were assessed. Biological functions of the differentially-methylated genes were assigned using the Ingenuity Pathway Analysis. Among 485 differentially-methylated CpGs by race, 203 were hypermethylated in EAs, and 282 were hypermethylated in AAs. Promoter-related differentially-methylated CpGs were more frequently hypermethylated in EAs (52%) than AAs (27%) while gene body and intergenic CpGs were more frequently hypermethylated in AAs. The differentially-methylated CpGs were enriched for cancer-associated genes with roles in cell death and survival, cellular development, and cell-to-cell signaling. In a separate analysis for correlation in EAs and AAs, different patterns of correlation were found between EAs and AAs. The correlated genes showed different biological networks between EAs and AAs; networks were connected by Ubiquitin C. To our knowledge, this is the first comprehensive genome-wide study to identify differences in methylation and gene expression between EAs and AAs in breast tissues from healthy women. These findings may provide further insights regarding the contribution of epigenetic differences to racial disparities in breast cancer.

PARP1 regulates the protein stability and proapoptotic function of HIPK2

Homeodomain-interacting protein kinase 2 (HIPK2) is a nuclear serine/threonine kinase that functions in DNA damage response and development. In the present study, we propose that the protein stability and proapoptotic function of HIPK2 are regulated by poly(ADP-ribose) polymerase 1 (PARP1). We present evidence indicating that PARP1 promotes the proteasomal degradation of HIPK2. The tryptophan-glycine-arginine (WGR) domain of PARP1 was necessary and sufficient for the promotion of HIPK2 degradation independently of the PARP1 enzymatic activity. The WGR domain mediated the interaction between HIPK2 and C-terminus of HSP70-interacting protein (CHIP) via HSP70. We found that CHIP can function as a ubiquitin ligase for HIPK2. The interaction between PAPR1 and HIPK2 was weakened following DNA damage. Importantly, PARP1 reduced the HIPK2-mediated p53 phosphorylation, proapoptotic transcriptional activity and cell death. These results suggest that PARP1 can modulate the tumor-suppressing function of HIPK2 by regulating the protein stability of HIPK2.

The DNA damage-induced cell death response: a roadmap to kill cancer cells

Upon massive DNA damage cells fail to undergo productive DNA repair and trigger the cell death response. Resistance to cell death is linked to cellular transformation and carcinogenesis as well as radio- and chemoresistance, making the underlying signaling pathways a promising target for therapeutic intervention. Diverse DNA damage-induced cell death pathways are operative in mammalian cells and finally culminate in the induction of programmed cell death via activation of apoptosis or necroptosis. These signaling routes affect nuclear, mitochondria- and plasma membrane-associated key molecules to activate the apoptotic or necroptotic response. In this review, we highlight the main signaling pathways, molecular players and mechanisms guiding the DNA damage-induced cell death response.

HIPK family kinases bind and regulate the function of the CCR4-NOT complex

Down-regulation of the HIPK interactor CNOT2 leads to reduced HIPK2 protein levels, identifying the CCR4-NOT complex as a new regulator of HIPK2 abundance. Functional assays reveal that HIPK2 and HIPK1 restrict CNOT2-dependent mRNA decay, thus extending the regulatory potential of these kinases to the level of posttranscriptional gene regulation.

The serine/threonine kinase HIPK2 functions as a regulator of developmental processes and as a signal integrator of a wide variety of stress signals, such as DNA damage, hypoxia, and reactive oxygen intermediates. Because the kinase is generated in a constitutively active form, its expression levels are restricted by a variety of different mechanisms. Here we identify the CCR4-NOT complex as a new regulator of HIPK2 abundance. Down-regulation or knockout of the CCR4-NOT complex member CNOT2 leads to reduced HIPK2 protein levels without affecting the expression level of HIPK1 or HIPK3. A fraction of all HIPK family members associates with the CCR4-NOT components CNOT2 and CNOT3. HIPKs also phosphorylate the CCR4-NOT complex, a feature that is shared with their yeast progenitor kinase, YAK1. Functional assays reveal that HIPK2 and HIPK1 restrict CNOT2-dependent mRNA decay. HIPKs are well known regulators of transcription, but the mutual regulation between CCR4-NOT and HIPKs extends the regulatory potential of these kinases by enabling posttranscriptional gene regulation.

Microarray Expression Data Identify DCC as a Candidate Gene for Early Meningioma Progression

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.

HIPK2 deficiency causes chromosomal instability by cytokinesis failure and increases tumorigenicity

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.

Heat shock modulates the subcellular localization, stability, and activity of HIPK2

The homeodomain-interacting protein kinase-2 (HIPK2) is a highly conserved serine/threonine kinase and is involved in transcriptional regulation. HIPK2 is a highly unstable protein, and is kept at a low level under normal physiological conditions. However, exposure of cells to physiological stress - such as hypoxia, oxidative stress, or UV damage - is known to stabilize HIPK2, leading to the HIPK2-dependent activation of p53 and the cell death pathway. Therefore HIPK2 is also known as a stress kinase and as a stress-activated pro-apoptotic factor. We demonstrate here that exposure of cells to heat shock results in the stabilization of HIPK2 and the stabilization is mediated via K63-linked ubiquitination. Intriguingly, a sub-lethal heat shock (42 °C, 1 h) results in the cytoplasmic localization of HIPK2, while a lethal heat shock (45 °C, 1 h) results in its nuclear localization. Cells exposed to the lethal heat shock showed significantly higher levels of the p53 activity than those exposed to the sub-lethal thermal stress, suggesting that both the level and the nuclear localization are essential for the pro-apoptotic activity of HIPK2 and that the lethal heat shock could retain the HIPK2 in the nucleus to promote the cell death. Taken together our study underscores the importance of HIPK2 in stress mediated cell death, and that the HIPK2 is a generic stress kinase that gets activated by diverse set of physiological stressors.

Apoptosis induced by a HIPK2 full-length-specific siRNA is due to off-target effects rather than prevalence of HIPK2-Δe8 isoform

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.

Genetic ablation of homeodomain-interacting protein kinase 2 selectively induces apoptosis of cerebellar Purkinje cells during adulthood and generates an ataxic-like phenotype

Homeodomain-interacting protein kinase 2 (HIPK2) is a multitalented coregulator of an increasing number of transcription factors and cofactors involved in cell death and proliferation in several organs and systems. As Hipk2^−/− mice show behavioral abnormalities consistent with cerebellar dysfunction, we investigated whether Hipk2 is involved in these neurological symptoms. To this aim, we characterized the postnatal developmental expression profile of Hipk2 in the brain cortex, hippocampus, striatum, and cerebellum of mice by real-time PCR, western blot analysis, and immunohistochemistry. Notably, we found that whereas in the brain cortex, hippocampus, and striatum, HIPK2 expression progressively decreased with age, that is, from postnatal day 1 to adulthood, it increased in the cerebellum. Interestingly, mice lacking Hipk2 displayed atrophic lobules and a visibly smaller cerebellum than did wild-type mice. More important, the cerebellum of Hipk2^−/− mice showed a strong reduction in cerebellar Purkinje neurons during adulthood. Such reduction is due to the activation of an apoptotic process associated with a compromised proteasomal function followed by an unpredicted accumulation of ubiquitinated proteins. In particular, Purkinje cell dysfunction was characterized by a strong accumulation of ubiquitinated β-catenin. Moreover, our behavioral tests showed that Hipk2^−/− mice displayed muscle and balance impairment, indicative of Hipk2 involvement in cerebellar function. Taken together, these results indicate that Hipk2 exerts a relevant role in the survival of cerebellar Purkinje cells and that Hipk2 genetic ablation generates cerebellar dysfunction compatible with an ataxic-like phenotype.