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

HIPK2 in Colon Cancer: A Potential Biomarker for Tumor Progression and Response to Therapies

Colon cancer, one of the most common and fatal cancers worldwide, is characterized by stepwise accumulation of specific genetic alterations in tumor suppressor genes or oncogenes, leading to tumor growth and metastasis. HIPK2 (homeodomain-interacting protein kinase 2) is a serine/threonine protein kinase and a "bona fide" oncosuppressor protein. Its activation inhibits tumor growth mainly by promoting apoptosis, while its inactivation increases tumorigenicity and resistance to therapies of many different cancer types, including colon cancer. HIPK2 interacts with many molecular pathways by means of its kinase activity or transcriptional co-repressor function modulating cell growth and apoptosis, invasion, angiogenesis, inflammation and hypoxia. HIPK2 has been shown to participate in several molecular pathways involved in colon cancer including p53, Wnt/β-catenin and the newly identified nuclear factor erythroid 2 (NF-E2) p45-related factor 2 (NRF2). HIPK2 also plays a role in tumor-host interaction in the tumor microenvironment (TME) by inducing angiogenesis and cancer-associated fibroblast (CAF) differentiation. The aim of this review is to assess the role of HIPK2 in colon cancer and the underlying molecular pathways for a better understanding of its involvement in colon cancer carcinogenesis and response to therapies, which will likely pave the way for novel colon cancer therapies.

ZC3H13 Accelerates Keloid Formation by Mediating N6-methyladenosine Modification of HIPK2

Keloids are fibroproliferative skin disorders caused by the improper healing of wounded skin. A growing body of evidence suggests the involvement of N6-Methyladenosine (m6A) modification in various bioprocesses; however, its role in keloid formation has not yet been investigated. The aim of this study was to determine the effect of the m6A regulator zinc finger CCCH domain containing protein 13 (ZC3H13) on the pathogenesis of keloid formation. ZC3H13 and homeodomain-interacting protein kinase 2 (HIPK2) expression was evaluated in healthy skin and keloid tissues, as well as in human dermal fibroblasts and human keloid fibroblasts (HKF), using qRT-PCR and western blotting. The effects of ZC3H13 overexpression and knockdown on the cell function of HKFs were assessed using CCK8, transwell, and flow cytometry. Furthermore, the influence of ZC3H13 on HIPK2 m6A modification was assessed using MeRIP-qPCR and mRNA stability assays. Both ZC3H13 expression and m6A RNA methylation were upregulated in keloid tissues and HKFs. Silencing of ZC3H13 inhibited proliferation and migration, while enhancing apoptosis in HKFs, whereas overexpression had the opposite effect. Furthermore, HIPK2 levels were high in keloid tissues and HKFs, and a positive correlation was observed between ZC3H13 and HIPK2. In HKFs, ZC3H13 overexpression elevated the m6A levels of HIPK2 mRNA and reduced the rate of HIPK2 mRNA degradation. Mechanically, ZC3H13-induced m6A modifications significantly improved HIPK2 mRNA stability. Collectively, ZC3H13 accelerated keloid formation by mediating the m6A modification of HIPK2 mRNA and maintaining its stability.

Sparse estimation in semiparametric finite mixture of varying coefficient regression models

Finite mixture of regressions (FMR) are commonly used to model heterogeneous effects of covariates on a response variable in settings where there are unknown underlying subpopulations. FMRs, however, cannot accommodate situations where covariates' effects also vary according to an "index" variable-known as finite mixture of varying coefficient regression (FM-VCR). Although complex, this situation occurs in real data applications: the osteocalcin (OCN) data analyzed in this manuscript presents a heterogeneous relationship where the effect of a genetic variant on OCN in each hidden subpopulation varies over time. Oftentimes, the number of covariates with varying coefficients also presents a challenge: in the OCN study, genetic variants on the same chromosome are considered jointly. The relative proportions of hidden subpopulations may also change over time. Nevertheless, existing methods cannot provide suitable solutions for accommodating all these features in real data applications. To fill this gap, we develop statistical methodologies based on regularized local-kernel likelihood for simultaneous parameter estimation and variable selection in sparse FM-VCR models. We study large-sample properties of the proposed methods. We then carry out a simulation study to evaluate the performance of various penalties adopted for our regularized approach and ascertain the ability of a BIC-type criterion for estimating the number of subpopulations. Finally, we applied the FM-VCR model to analyze the OCN data and identified several covariates, including genetic variants, that have age-dependent effects on OCN.

The Sweet Side of HIPK2

HIPK2 is an evolutionary conserved protein kinase which modulates many molecular pathways involved in cellular functions such as apoptosis, DNA damage response, protein stability, and protein transcription. HIPK2 plays a key role in the cancer cell response to cytotoxic drugs as its deregulation impairs drug-induced cancer cell death. HIPK2 has also been involved in regulating fibrosis, angiogenesis, and neurological diseases. Recently, hyperglycemia was found to positively and/or negatively regulate HIPK2 activity, affecting not only cancer cell response to chemotherapy but also the progression of some diabetes complications. The present review will discuss how HIPK2 may be influenced by the high glucose (HG) metabolic condition and the consequences of such regulation in medical conditions.

Homeodomain-interacting protein kinase 2 regulates NLRP3 inflammasome activation through endoplasmic reticulum stress in septic liver injury

OBJECTIVE

Septic liver injury is a major burden for the clinical management of sepsis. Hepatocyte cell death plays a crucial pathophysiological role in sepsis. A recent study proposed that NLRP3 inflammasome-mediated pyroptosis participates in septic liver injury. Therefore, investigating the mechanism controlling this process may help manage sepsis.

METHODS

We investigated the role of homeodomain-interacting protein kinase 2 (HIPK2) in regulating the NLRP3 inflammasome in vivo using mouse models and in vitro in primary hepatocytes.

RESULTS

HIPK2 could improve liver injury and survival in a mouse model of sepsis. Overexpression of HIPK2 could suppress NLRP3 and caspase-1-p20 expression, while HIPK2 knockdown led to higher levels of these two molecules. Importantly, HIPK2 could suppress endoplasmic reticulum (ER) stress. Pharmacologically inhibiting ER stress could abolish activation of the NLRP3 inflammasome in hepatocytes with HIPK2 knockdown.

CONCLUSION

HIPK2 can regulate ER stress and NLRP3 inflammasome activation in the liver during sepsis, and HIPK2-mediated suppression of ER stress participates in regulating NLRP3 inflammasome activation. The present study highlights the role of HIPK2 in regulating the inflammasome in septic liver injury, which may serve as a target for managing sepsis.

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.

HIPK2 in cancer biology and therapy: Recent findings and future perspectives

Homeodomain-interacting protein kinase 2 (HIPK2) is a serine-threonine kinase that phosphorylates and regulates a plethora of transcriptional regulators and chromatin modifiers. The heterogeneity of its interactome allows HIPK2 to modulate several cellular processes and signaling pathways, ultimately regulating cell fate and proliferation. Because of its p53-dependent pro-apoptotic activity and its downregulation in many tumor types, HIPK2 is traditionally considered a bone fide tumor suppressor gene. However, recent findings revealed that the role of HIPK2 in the pathogenesis of cancer is much more complex, ranging from tumor suppressive to oncogenic, strongly depending on the cellular context. Here, we review the very recent data emerged in the last years about the involvement of HIPK2 in cancer biology and therapy, highlighting the various alterations of this kinase (downregulation, upregulation, mutations and/or delocalization) in dependence on the cancer types. In addition, we discuss the recent advancement in the understanding the tumor suppressive and oncogenic functions of HIPK2, its role in establishing the response to cancer therapies, and its regulation by cancer-associated microRNAs. All these data strengthen the idea that HIPK2 is a key player in many types of cancer; therefore, it could represent an important prognostic marker, a factor to predict therapy response, and even a therapeutic target itself.

NRF2 in Cancer: Cross-Talk with Oncogenic Pathways and Involvement in Gammaherpesvirus-Driven Carcinogenesis

Expanding knowledge of the molecular mechanisms at the basis of tumor development, especially the cross-talk between oncogenic pathways, will possibly lead to better tailoring of anticancer therapies. Nuclear factor erythroid 2-related factor 2 (NRF2) plays a central role in cancer progression, not only because of its antioxidant activity but also because it establishes cross-talk with several oncogenic pathways, including Heat Shock Factor1 (HSF1), mammalian target of rapamycin (mTOR), and mutant (mut) p53. Moreover, the involvement of NRF2 in gammaherpesvirus-driven carcinogenesis is particularly interesting. These viruses indeed hijack the NRF2 pathway to sustain the survival of tumor cells in which they establish a latent infection and to avoid a too-high increase of reactive oxygen species (ROS) when these cancer cells undergo treatments that induce viral replication. Interestingly, NRF2 activation may prevent gammaherpesvirus-driven oncogenic transformation, highlighting how manipulating the NRF2 pathway in the different phases of gammaherpesvirus-mediated carcinogenesis may lead to different outcomes. This review will highlight the mechanistic interplay between NRF2 and some oncogenic pathways and its involvement in gammaherpesviruses biology to recapitulate published evidence useful for potential application in cancer therapy.

Network-based approach for targeting human kinases commonly associated with amyotrophic lateral sclerosis and cancer

Background

Amyotrophic Lateral Sclerosis (ALS) is a rare progressive and chronic motor neuron degenerative disease for which at present no cure is available. In recent years, multiple genes encode kinases and other causative agents for ALS have been identified. Kinases are enzymes that show pleiotropic nature and regulate different signal transduction processes and pathways. The dysregulation of kinase activity results in dramatic changes in processes and causes many other human diseases including cancers.

Methods

In this study, we have adopted a network-based system biology approach to investigate the kinase-based molecular interplay between ALS and other human disorders. A list of 62 ALS-associated-kinases was first identified and then we identified the disease associated with them by scanning multiple disease-gene interaction databases to understand the link between the ALS-associated kinases and other disorders.

Results

An interaction network with 36 kinases and 381 different disorders associated with them was prepared, which represents the complexity and the comorbidity associated with the kinases. Further, we have identified 5 miRNAs targeting the majority of the kinases in the disease-causing network. The gene ontology and pathways enrichment analysis of those miRNAs were performed to understand their biological and molecular functions along with to identify the important pathways. We also identified 3 drug molecules that can perturb the disease-causing network by drug repurposing.

Conclusion

This network-based study presented hereby contributes to a better knowledge of the molecular underpinning of comorbidities associated with the kinases associated with the ALS disease and provides the potential therapeutic targets to disrupt the highly complex disease-causing network.

Molecular mechanisms underlying the action of carcinogens in gastric cancer with a glimpse into targeted therapy

BACKGROUND

Gastric cancer imposes a substantial global health burden despite its overall incidence decrease. A broad spectrum of inherited, environmental and infectious factors contributes to the development of gastric cancer. A profound understanding of the molecular underpinnings of gastric cancer has lagged compared to several other tumors with similar incidence and morbidity rates, owing to our limited knowledge of the role of carcinogens in this malignancy. The International Agency for Research on Cancer (IARC) has classified gastric carcinogenic agents into four groups based on scientific evidence from human and experimental animal studies. This review aims to explore the potential comprehensive molecular and biological impacts of carcinogens on gastric cancer development and their interactions and interferences with various cellular signaling pathways.

CONCLUSIONS

In this review, we highlight recent clinical trial data reported in the literature dealing with different ways to target various carcinogens in gastric cancer. Moreover, we touch upon other multidisciplinary therapeutic approaches such as surgery, adjuvant and neoadjuvant chemotherapy. Rational clinical trials focusing on identifying suitable patient populations are imperative to the success of single-agent therapeutics. Novel insights regarding signaling pathways that regulate gastric cancer can potentially improve treatment responses to targeted therapy alone or in combination with other/conventional treatments. Preventive strategies such as control of H. pylori infection through eradication or immunization as well as dietary habit and lifestyle changes may reduce the incidence of this multifactorial disease, especially in high prevalence areas. Further in-depth understanding of the molecular mechanisms involved in the role of carcinogenic agents in gastric cancer development may offer valuable information and update state-of-the-art resources for physicians and researchers to explore novel ways to combat this disease, from bench to bedside. A schematic outlining of the interaction between gastric carcinogenic agents and intracellular pathways in gastric cancer H. pylori stimulates multiple intracellular pathways, including PI3K/AKT, NF-κB, Wnt, Shh, Ras/Raf, c-MET, and JAK/STAT, leading to epithelial cell proliferation and differentiation, apoptosis, survival, motility, and inflammatory cytokine release. EBV can stimulate intracellular pathways such as the PI3K/Akt, RAS/RAF, JAK/STAT, Notch, TGF-β, and NF-κB, leading to cell survival and motility, proliferation, invasion, metastasis, and the transcription of anti-apoptotic genes and pro-inflammatory cytokines. Nicotine and alcohol can lead to angiogenesis, metastasis, survival, proliferation, pro-inflammatory, migration, and chemotactic by stimulating various intracellular signaling pathways such as PI3K/AKT, NF-κB, Ras/Raf, ROS, and JAK/STAT. Processed meat contains numerous carcinogenic compounds that affect multiple intracellular pathways such as sGC/cGMP, p38 MAPK, ERK, and PI3K/AKT, leading to anti-apoptosis, angiogenesis, metastasis, inflammatory responses, proliferation, and invasion. Lead compounds may interact with multiple signaling pathways such as PI3K/AKT, NF-κB, Ras/Raf, DNA methylation-dependent, and epigenetic-dependent, leading to tumorigenesis, carcinogenesis, malignancy, angiogenesis, DNA hypermethylation, cell survival, and cell proliferation. Stimulating signaling pathways such as PI3K/Akt, RAS/RAF, JAK/STAT, WNT, TGF-β, EGF, FGFR2, and E-cadherin through UV ionizing radiation leads to cell survival, proliferation, and immortalization in gastric cancer. The consequence of PI3K/AKT, NF-κB, Ras/Raf, ROS, JAK/STAT, and WNT signaling stimulation by the carcinogenic component of Pickled vegetables and salted fish is the Warburg effect, tumorigenesis, angiogenesis, proliferation, inflammatory response, and migration.

Transcriptome Changes in Glioma Cells Cultivated under Conditions of Neurosphere Formation

Glioma is the most common and heterogeneous primary brain tumor. The development of a new relevant preclinical models is necessary. As research moves from cultures of adherent gliomas to a more relevant model, neurospheres, it is necessary to understand the changes that cells undergo at the transcriptome level. In the present work, we used three patient-derived gliomas and two immortalized glioblastomas, while their cultivation was carried out under adherent culture and neurosphere (NS) conditions. When comparing the transcriptomes of monolayer (ML) and NS cell cultures, we used Enrichr genes sets enrichment analysis to describe transcription factors (TFs) and the pathways involved in the formation of glioma NS. It was observed that NS formation is accompanied by the activation of five common gliomas of TFs, SOX2, UBTF, NFE2L2, TCF3 and STAT3. The sets of transcripts controlled by TFs MYC and MAX were suppressed in NS. Upregulated genes are involved in the processes of the epithelial-mesenchymal transition, cancer stemness, invasion and migration of glioma cells. However, MYC/MAX-dependent downregulated genes are involved in translation, focal adhesion and apical junction. Furthermore, we found three EGFR and FGFR signaling feedback regulators common to all analyzed gliomas-SPRY4, ERRFI1, and RAB31-which can be used for creating new therapeutic strategies of suppressing the invasion and progression of gliomas.

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-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.

Siah1 in cancer and nervous system diseases (Review)

The dysregulation of the ubiquitin‑proteasome system will result in the abnormal accumulation and dysfunction of proteins, thus leading to severe diseases. Seven in absentia homolog 1 (Siah1), an E3 ubiquitin ligase, has attracted wide attention due to its varied functions in physiological and pathological conditions, and the numerous newly discovered Siah1 substrates. In cancer and nervous system diseases, the functions of Siah1 as a promoter or a suppressor of diseases are related to the change in cellular microenvironment and subcellular localization. At the same time, complex upstream regulations make Siah1 different from other E3 ubiquitin ligases. Understanding the molecular mechanism of Siah1 will help the study of various signaling pathways and benefit the therapeutic strategy of human diseases (e.g., cancer and nervous system diseases). In the present review, the functions and regulations of Siah1 are described. Moreover, novel substrates of Siah1 discovered in recent studies will be highlighted in cancer and nervous system diseases, providing ideas for future research and clinical targeted therapies using Siah1.

The cytotoxicity and apoptotic effects of verbascoside on breast cancer 4T1 cell line

BACKGROUND

Despite significant advancements in breast cancer therapy, novel drugs with lower side effects are still being demanded. In this regard, we investigated the anti-cancer features of verbascoside in 4 T1 mouse mammary tumor cell.

METHODS

First, MTT assay was performed with various concentrations (ranging between 5 to 200 μM) of verbascoside and IC50 was calculated. Then the expression of Bax, Bcl-2, and caspase-3 was evaluated in treated 4 T1 cells. In addition, we investigated the expression of TLR4, MyD88, and NF-κB to ascertain the underlying mechanism of the anti-proliferative feature of verbascoside. Also, flow cytometry followed by double PI and Annexin V was conducted to confirm the apoptosis-inducing effect of verbascoside.

RESULTS

Our results from MTT assay showed verbascoside inhibits proliferation of 4 T1 cancer cells (IC50 117 μM) while is safe for normal HEK293T cells. By qRT-PCR, we observed that verbascoside treatment (100, 117 and, 130 μM) increases the expression of caspase-3 and Bax while reduces the expression of Bcl-2. Also, verbascoside (100, 117 and, 130 μM) increased the expression of TLR4 only at 130 μM dose and the expression of MyD88 whereas reduced the expression of NF-κB at mRNA level. Flow cytometry analysis also confirmed verbascoside induces apoptosis in 4 T1 cells at 117 μM.

CONCLUSION

Taken together, our data showed verbascoside is a safe natural compound for normal cells while has apoptosis-inducing feature through TLR4 axis on 4 T1 cells.

Circ_0025908 regulates cell vitality and proliferation via miR-137/HIPK2 axis of rheumatic arthritis

BACKGROUND

Rheumatic arthritis (RA) is an autoimmune disease with bad effects. Recent researches have shown that circular RNAs (circRNAs) could affect the progress of RA, but the mechanism still indistinct. In this work, we explored the roles of circ_0025908 in RA.

METHODS

The levels of circ_0025908, microRNA-137 (miR-137), and mRNA of homeodomain-interacting protein kinase 2 (HIPK2) were detected by quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) in RA tissues. Meanwhile, the level of HIPK2 was quantified by Western blot analysis. Besides, the cell functions were examined by CCK8 assay, EdU assay, flow cytometry assay, ELISA, and Western blot. Furthermore, the interplay between miR-137 and circ_0025908 or HIPK2 was detected by dual-luciferase reporter assay.

RESULTS

The levels of circ_0025908 and HIPK2 were upregulated, and the miR-137 level was decreased in RA tissues in contrast to that in normal tissues. For functional analysis, circ_0025908 deficiency inhibited cell vitality, cell mitotic cycle, cell proliferation, and immunoreaction in RA cells, whereas promoted cell apoptosis. Moreover, miR-137 was confirmed to repress the progression of RA cells by suppressing HIPK2. In mechanism, circ_0025908 acted as a miR-137 sponge to regulate the level of HIPK2.

CONCLUSION

Circ_0025908 facilitates the development of RA through increasing HIPK2 expression by regulating miR-137, which also offered an underlying targeted therapy for RA treatment.

PTEN regulates adipose progenitor cell growth, differentiation, and replicative aging

The tumor suppressor phosphatase and tensin homolog (PTEN) negatively regulates the insulin signaling pathway. Germline PTEN pathogenic variants cause PTEN hamartoma tumor syndrome (PHTS), associated with lipoma development in children. Adipose progenitor cells (APCs) lose their capacity to differentiate into adipocytes during continuous culture, whereas APCs from lipomas of patients with PHTS retain their adipogenic potential over a prolonged period. It remains unclear which mechanisms trigger this aberrant adipose tissue growth. To investigate the role of PTEN in adipose tissue development, we performed functional assays and RNA-Seq of control and PTEN knockdown APCs. Reduction of PTEN levels using siRNA or CRISPR led to enhanced proliferation and differentiation of APCs. Forkhead box protein O1 (FOXO1) transcriptional activity is known to be regulated by insulin signaling, and FOXO1 was downregulated at the mRNA level while its inactivation through phosphorylation increased. FOXO1 phosphorylation initiates the expression of the lipogenesis-activating transcription factor sterol regulatory element-binding protein 1 (SREBP1). SREBP1 levels were higher after PTEN knockdown and may account for the observed enhanced adipogenesis. To validate this, we overexpressed constitutively active FOXO1 in PTEN CRISPR cells and found reduced adipogenesis, accompanied by SREBP1 downregulation. We observed that PTEN CRISPR cells showed less senescence compared with controls and the senescence marker CDKN1A (p21) was downregulated in PTEN knockdown cells. Cellular senescence was the most significantly enriched pathway found in RNA-Seq of PTEN knockdown versus control cells. These results provide evidence that PTEN is involved in the regulation of APC proliferation, differentiation, and senescence, thereby contributing to aberrant adipose tissue growth in patients with PHTS.

Impact of DNA repair and reactive oxygen species levels on radioresistance in pancreatic cancer

PURPOSE

Radioresistance in pancreatic cancer patients remains a critical obstacle to overcome. Understanding the molecular mechanisms underlying radioresistance may achieve better response to radiotherapy and thereby improving the poor treatment outcome. The aim of the present study was to elucidate the mechanisms leading to radioresistance by detailed characterization of isogenic radioresistant and radiosensitive cell lines.

METHODS

The human pancreatic cancer cell lines, Panc-1 and MIA PaCa-2 were repeatedly exposed to radiation to generate radioresistant (RR) isogenic cell lines. The surviving cells were expanded, and their radiosensitivity was measured using colony formation assay. Tumor growth delay after irradiation was determined in a mouse pancreatic cancer xenograft model. Gene and protein expression were analyzed using RNA sequencing and Western blot, respectively. Cell cycle distribution and apoptosis (Caspase 3/7) were measured by FACS analysis. Reactive oxygen species generation and DNA damage were analyzed by detection of CM-H₂DCFDA and γH2AX staining, respectively. Transwell chamber assays were used to investigate cell migration and invasion.

RESULTS

The acquired radioresistance of RR cell lines was demonstrated in vitro and validated in vivo. Ingenuity pathway analysis of RNA sequencing data predicted activation of cell viability in both RR cell lines. RR cancer cell lines demonstrated greater DNA repair efficiency and lower basal and radiation-induced reactive oxygen species levels. Migration and invasion were differentially affected in RR cell lines.

CONCLUSIONS

Our data indicate that repeated exposure to irradiation increases the expression of genes involved in cell viability and thereby leads to radioresistance. Mechanistically, increased DNA repair capacity and reduced oxidative stress might contribute to the radioresistant phenotype.

Regulation of the SIAH2-HIF-1 Axis by Protein Kinases and Its Implication in Cancer Therapy

The cellular response to hypoxia is a key biological process that facilitates adaptation of cells to oxygen deprivation (hypoxia). This process is critical for cancer cells to adapt to the hypoxic tumor microenvironment resulting from rapid tumor growth. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor and a master regulator of the cellular response to hypoxia. The activity of HIF-1 is dictated primarily by its alpha subunit (HIF-1α), whose level and/or activity are largely regulated by an oxygen-dependent and ubiquitin/proteasome-mediated process. Prolyl hydroxylases (PHDs) and the E3 ubiquitin ligase Von Hippel-Lindau factor (VHL) catalyze hydroxylation and subsequent ubiquitin-dependent degradation of HIF-1α by the proteasome. Seven in Absentia Homolog 2 (SIAH2), a RING finger-containing E3 ubiquitin ligase, stabilizes HIF-1α by targeting PHDs for ubiquitin-mediated degradation by the proteasome. This SIAH2-HIF-1 signaling axis is important for maintaining the level of HIF-1α under both normoxic and hypoxic conditions. A number of protein kinases have been shown to phosphorylate SIAH2, thereby regulating its stability, activity, or substrate binding. In this review, we will discuss the regulation of the SIAH2-HIF-1 axis via phosphorylation of SIAH2 by these kinases and the potential implication of this regulation in cancer biology and cancer therapy.

Overexpression of HIPK2 removes the transrepression of proapoptotic genes mediated by the CtBP1-p300-FOXO3a complex and increases the chemosensitivity in osteosarcoma cells

Decreased expression of proapoptotic genes can lead to the chemoresistenance in cancer therapy. Carboxyl-terminal binding protein 1 (CtBP1), a transcriptional corepressor with multiple oncogenic effects, has been previously identified to suppress the expression of two proapoptotic genes [BAX (BCL2 associated X) and BIM (Bcl-2 interacting mediator of cell death)] by assembling a complex with the Forkhead box O3 (FOXO3a) transcription factor and the p300 histone acetyltransferase. However, the upstream regulatory signaling of the CtBP1-p300-FOXO3a complex is obscure, and the effects of changing this signaling on chemosensitivity in osteosarcoma are unknown. Herein, we discovered that the downregulation of HIPK2 (Homeodomain-interacting protein kinase 2) was essential for the function of the CtBP1-p300-FOXO3a complex. Downregulation of HIPK2 prevented the phosphorylation and subsequent degradation of CtBP1, thereby allowing the assembly of the CtBP1-p300-FOXO3a complex and suppression of the expression of proapoptotic genes, such as BAX, BIM, BIK (Bcl-2 interacting killer) and NOXA/PMAIP1 (Phorbol-12-myristate-13-acetate-induced protein 1). Overexpression of HIPK2 promoted the phosphorylation of CtBP1 and the degradation of CtBP1 by proteasomes, thereby preventing the formation of the CtBP1-p300-FOXO3a complex. The abolition of CtBP1 transrepression increased the expression of proapoptotic genes to induce apoptosis and increase chemosensitivity in osteosarcoma cells. Taken together, our in vitro and in vivo results revealed that overexpression of HIPK2 could remove the CtBP1-mediated transrepression of proapoptotic genes, indicating a new therapeutic option for the treatment of osteosarcoma.

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.

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.

Protein kinase inhibitors for amyotrophic lateral sclerosis therapy

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that causes the progressive loss of motoneurons and, unfortunately, there is no effective treatment for this disease. Interconnecting multiple pathological mechanisms are involved in the neuropathology of this disease, including abnormal aggregation of proteins, neuroinflammation and dysregulation of the ubiquitin proteasome system. Such complex mechanisms, together with the lack of reliable animal models of the disease have hampered the development of drugs for this disease. Protein kinases, a key pharmacological target in several diseases, have been linked to ALS as they play a central role in the pathology of many diseases. Therefore several inhibitors are being currently trailed for clinical proof of concept in ALS patients. In this review, we examine the recent literature on protein kinase inhibitors currently in pharmaceutical development for this diseaseas future therapy for AS together with their involvement in the pathobiology of ALS. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

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.

HIPK2 suppresses tumor growth and progression of hepatocellular carcinoma through promoting the degradation of HIF-1α

Aberrant angiogenesis of hepatocellular carcinoma (HCC) leads to tumor growth and local or distant metastasis. Uncovering the underlying mechanisms for the neoangiogenesis of HCC can provide novel potential therapeutic targets in the clinic. Here, we reported that serine/threonine homeodomain-interacting protein kinase 2 (HIPK2) was frequently downregulated in HCC tissues compared with the adjacent normal tissues, and patients with lower HIPK2 protein expression were associated with worse overall survival. Both in vitro and in vivo, HIPK2 inhibited the migration of HCC cells, as well as tumor growth and metastasis in xenograft and orthotopic syngeneic HCC mouse models. Furthermore, HIPK2 inhibited the angiogenesis in HCC tumors. Under the hypoxic condition, HIPK2 knockdown enhanced the angiogenesis and the key regulator, HIF-1α signaling pathway; however, HIPK2 overexpression downregulated the tumoral angiogenesis and HIF-1α signaling. In HCC cells, HIPK2 could directly bind to HIF-1α and stimulate the ubiquitination of HIF-1α for proteasomal degradation. HIF-1α knockout partially rescued the promoting effect of HIPK2 depletion on angiogenesis and tumor growth. In conclusion, the downregulation of HIPK2 could enhance the angiogenesis in HCC through inducing the HIF-1α pathway, and further contribute to tumor growth and metastasis, which may provide a novel therapeutic strategy for HCC.

Involvement of homodomain interacting protein kinase 2-c-Jun N-terminal kinase/c-Jun cascade in the long-term synaptic toxicity and cognition impairment induced by neonatal Sevoflurane exposure

Sevoflurane is one of the most widely used anesthetics with recent concerns rising about its pediatric application. The synaptic toxicity and mechanisms underlying its long‐term cognition impairment remain unclear. In this study, we investigated the expression and roles of homeodomain interacting protein kinase 2 (HIPK2), a stress activating kinase involved in neuronal survival and synaptic plasticity, and its downstream c‐Jun N‐terminal kinase (JNK)/c‐Jun signaling in the long‐term toxicity of neonatal Sevoflurane exposure. Our data showed that neonatal Sevoflurane exposure results in impairment of memory, enhancement of anxiety, less number of excitatory synapses and lower levels of synaptic proteins in the hippocampus of adult rats without significant changes of hippocampal neuron numbers. Up‐regulation of HIPK2 and JNK/c‐Jun was observed in hippocampal granular neurons shortly after Sevoflurane exposure and persisted to adult. 5‐((6‐Oxo‐5‐(6‐(piperazin‐1‐yl)pyridin‐3‐yl)‐1,6‐dihydropyridin‐3‐yl)methylene)thiazolidine‐2,4‐dione trifluoroacetate, antagonist of HIPK2, could significantly rescue the cognition impairment, decrease in long‐term potentiation, reduction in spine density and activation of JNK/c‐Jun induced by Sevoflurane. JNK antagonist SP600125 partially restored synapse development and cognitive function without affecting the expression of HIPK2. These data, in together, revealed a novel role of HIPK2‐JNK/c‐Jun signaling in the long‐term synaptic toxicity and cognition impairment of neonatal Sevoflurane exposure, indicating HIPK2‐JNK/c‐Jun cascade as a potential target for reducing the synaptic toxicity of Sevoflurane.

Cover Image for this issue: doi: 10.1111/jnc.14757.

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.

Cardiomyocyte Homeodomain-Interacting Protein Kinase 2 Maintains Basal Cardiac Function via Extracellular Signal-Regulated Kinase Signaling

BACKGROUND

Cardiac kinases play a critical role in the development of heart failure, and represent potential tractable therapeutic targets. However, only a very small fraction of the cardiac kinome has been investigated. To identify novel cardiac kinases involved in heart failure, we used an integrated transcriptomics and bioinformatics analysis and identified Homeodomain-Interacting Protein Kinase 2 (HIPK2) as a novel candidate kinase. The role of HIPK2 in cardiac biology is unknown.

METHODS

We used the Expression2Kinase algorithm for the screening of kinase targets. To determine the role of HIPK2 in the heart, we generated cardiomyocyte (CM)-specific HIPK2 knockout and heterozygous mice. Heart function was examined by echocardiography, and related cellular and molecular mechanisms were examined. Adeno-associated virus serotype 9 carrying cardiac-specific constitutively active MEK1 (TnT-MEK1-CA) was administrated to rescue cardiac dysfunction in CM-HIPK2 knockout mice.

RESULTS

To our knowledge, this is the first study to define the role of HIPK2 in cardiac biology. Using multiple HIPK2 loss-of-function mouse models, we demonstrated that reduction of HIPK2 in CMs leads to cardiac dysfunction, suggesting a causal role in heart failure. It is important to note that cardiac dysfunction in HIPK2 knockout mice developed with advancing age, but not during development. In addition, CM-HIPK2 knockout mice and CM-HIPK2 heterozygous mice exhibited a gene dose-response relationship of CM-HIPK2 on heart function. HIPK2 expression in the heart was significantly reduced in human end-stage ischemic cardiomyopathy in comparison to nonfailing myocardium, suggesting a clinical relevance of HIPK2 in cardiac biology. In vitro studies with neonatal rat ventricular CMscorroborated the in vivo findings. Specifically, adenovirus-mediated overexpression of HIPK2 suppressed the expression of heart failure markers, NPPA and NPPB, at basal condition and abolished phenylephrine-induced pathological gene expression. An array of mechanistic studies revealed impaired extracellular signal-regulated kinase 1/2 signaling in HIPK2-deficient hearts. An in vivo rescue experiment with adeno-associated virus serotype 9 TnT-MEK1-CA nearly abolished the detrimental phenotype of knockout mice, suggesting that impaired extracellular signal-regulated kinase signaling mediated apoptosis as the key factor driving the detrimental phenotype in CM-HIPK2 knockout mice hearts.

CONCLUSIONS

Taken together, these findings suggest that CM-HIPK2 is required to maintain normal cardiac function via extracellular signal-regulated kinase signaling.

Exosomal miR-1229 derived from colorectal cancer cells promotes angiogenesis by targeting HIPK2

Circulating exosomal microRNAs (exomiR) have been demonstrated to be novel diagnostic biomarkers for various cancers. In this study, we found that circulating exomiR-1229 levels were significantly increased in the serum exosomes of patients with colorectal cancer (CRC) and significantly associated with tumor size, lymphatic metastasis, TNM stage and poor survival. Treatment with siRNA-Drosha, siRNA-ALIX and GW4869 repressed the expression of exomiR-1229 secreted from CRC cells. Both CRC-derived exosomes and exomiR-1229 mimic promoted the tubulogenesis of HUVECs, but transfection with exomiR-1229 inhibitor anta-miR-1229 significantly suppressed tube formation. Subsequently, HIPK2 was identified as a target of exomiR-1229 and responsible for the effect of exomiR-1229 on angiogenesis of HUVECs. ExomiR-1229 inhibited the protein expression of HIPK2, thereby activating VEGF pathway. Finally, anta-miR-1229 effectively inhibited tumor growth and angiogenesis in the nude mouse xenograft model. These results highlighted a novel mechanism of CRC angiogenesis and the biological roles of exomiR-1229.

HIPK2 is necessary for type I interferon-mediated antiviral immunity

Precise control of interferons (IFNs) is crucial to maintain immune homeostasis. Here, we demonstrated that homeodomain-interacting protein kinase 2 (HIPK2) was required for the production of type I IFNs in response to RNA virus infection. HIPK2 deficiency markedly impaired IFN production in macrophages after vesicular stomatitis virus (VSV) infection, and HIPK2-deficient mice were more susceptible to lethal VSV disease than were wild-type mice. After VSV infection, HIPK2 was cleaved by active caspases, which released a hyperactive, N-terminal fragment that translocated to the nucleus and further augmented antiviral responses. In part, HIPK2 interacted with ELF4 and promoted its phosphorylation at Ser³⁶⁹, which enabled Ifn-b transcription. In addition, HIPK2 production was stimulated by type I IFNs to further enhance antiviral immunity. These data suggest that the kinase activity and nuclear localization of HIPK2 are essential for the production of type I IFNs.

DNA methylation signature of smoking in lung cancer is enriched for exposure signatures in newborn and adult blood

Smoking impacts DNA methylation genome-wide in blood of newborns from maternal smoking during pregnancy and adults from personal smoking. We compared smoking-related DNA methylation in lung adenocarcinoma (61 never smokers, 91 current smokers, and 238 former smokers) quantified with the Illumina450k BeadArray in The Cancer Genome Atlas with published large consortium meta-analyses of newborn and adult blood. We assessed whether CpG sites related to smoking in blood from newborns and adults were enriched in the lung adenocarcinoma methylation signal. Testing CpGs differentially methylated by smoke exposure, we identified 296 in lung adenocarcinoma meeting a P < 10-4 cutoff, while previous meta-analyses identified 3,042 in newborn blood, and 8,898 in adult blood meeting the same P < 10-4 cutoff. Lung signals were highly enriched for those seen in newborn (24 overlapping CpGs, Penrichment = 1.2 × 10-18) and adult blood (66 overlapping CpGs, Penrichment = 1.2 × 10-48). The 105 genes annotated to CpGs differentially methylated in lung tumors, but not blood, were enriched for RNA processing ontologies. Some epigenetic alterations associated with cigarette smoke exposure are tissue specific, but others are common across tissues. These findings support the value of blood-based methylation biomarkers for assessing exposure effects in target tissues.

Tumor suppressive role for kinases phosphorylating p53 in DNA damage-induced apoptosis

Tumor suppressor p53 plays an important role in cancer prevention. Under normal conditions, p53 is maintained at a low level. However, in response to various cellular stresses, p53 is stabilized and activated, which, in turn, initiates DNA repair, cell-cycle arrest, senescence and apoptosis. Post-translational modifications of p53 including phosphorylation, ubiquitination, and acetylation at multiple sites are important to regulate its activation and subsequent transcriptional gene expression. Particularly, phosphorylation of p53 plays a critical role in modulating its activation to induce apoptosis in cancer cells. In this context, previous studies show that several serine/threonine kinases regulate p53 phosphorylation and downstream gene expression. The molecular basis by which p53 and its kinases induce apoptosis for cancer prevention has been extensively studied. However, the relationship between p53 phosphorylation and its kinases and how the activity of kinases is controlled are still largely unclear; hence, they need to be investigated. In this review, we discuss various roles for p53 phosphorylation and its responsible kinases to induce apoptosis and a new therapeutic approach in a broad range of cancers.

Overexpression of homeodomain-interacting protein kinase 2 (HIPK2) attenuates sepsis-mediated liver injury by restoring autophagy

Sepsis is the leading cause of death in intensive care units worldwide. Autophagy has recently been shown to protect against sepsis-induced liver injury. Here, we investigated the roles of homeodomain-interacting protein kinase 2 (HIPK2) in the molecular mechanism of sepsis-induced liver injury. HIPK2 expression was reduced in sepsis-induced liver injury, and HIPK2 overexpression increased the survival rate and improved caecal ligation and puncture (CLP)-induced liver injury by reducing serum and liver aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP) levels in mice with sepsis. HIPK2 overexpression significantly decreased CLP-induced release of inflammatory cytokines into the serum and attenuated oxidative stress-associated indicators in mice with CLP-induced liver injury, whereas HIPK2 knockdown produced the opposite results, suggesting that HIPK2 is a negative regulator of sepsis. Furthermore, HIPK2 overexpression inhibited lipopolysaccharide (LPS)-induced apoptosis of primary hepatocytes, increased the autophagic flux, and restored both autophagosome and autolysosome formation in the livers of CLP-induced mice by suppressing calpain signalling. Importantly, HIPK2 overexpression reduced the elevated cytosolic Ca²⁺ concentration in LPS-treated primary hepatocytes by interacting with calpain 1 and calmodulin. Finally, several anti-inflammatory drugs, including resveratrol, aspirin, vitamin E and ursolic acid, significantly increased the levels of the HIPK2 mRNA and protein by modulating promoter activity and the 3′-UTR stability of the HIPK2 gene. In conclusion, HIPK2 overexpression may improve sepsis-induced liver injury by restoring autophagy and thus might be a promising target for the clinical treatment of sepsis.

Overexpression of HIPK2 attenuates spinal cord injury in rats by modulating apoptosis, oxidative stress, and inflammation

HIPK2 is considered to be a tumor suppressor. It also has been implicated in several functions such as apoptosis and inflammation that are linked to spinal cord injury (SCI). However, whether HIPK2 ameliorates the neurological pain of SCI remains unclear. Here, we investigated the effects of HIPK2 on neurological function, oxidative stress, levels of inflammatory cytokines and expression of Bcl-2/Bax in an SCI model. Firstly, we evaluated the therapeutic effects of HIPK2 on neurological pain in the SCI rat using the Basso, Beattie and Bresnahan scores and H & E staining. Overexpression of HIPK2 significantly elevated the levels of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), and reduced the mRNA expression of Nogo-A and RhoA in SCI rats. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays showed that overexpression of HIPK2 significantly reduced the number of apoptotic cells. Overexpression of HIPK2 also decreased expression of Bax and Caspase-3 and elevated expression of Bcl-2 in the SCI model, indicating that HIPK2 exhibited its protective activity by inhibiting SCI-induced apoptosis. Then, we measured the serum concentrations of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-PX). We also determined the mRNA and protein levels of nuclear factor-κB p65 unit, tumor necrosis factor-α (TNF-α), and interleukin (IL)-1β. HIPK2 overexpression reduced oxidative stress and the levels of inflammatory cytokines compared with SCI control animals. Additionally, acetylation of HIPK2 was reduced in SCI rats. Overexpression of HIPK2 could enhance autophagy by elevating the expression of Beclin-1 and LC3-II while autophagy is regarded as a beneficial regulator to improve spinal cord injury. Together, overexpression of HIPK2 improved contusive SCI induced pain by modulating oxidative stress, Bcl‑2 and Bax signaling, and inflammation, and also regulating autophagy.

MicroRNA-222-3p associated with Helicobacter pylori targets HIPK2 to promote cell proliferation, invasion, and inhibits apoptosis in gastric cancer

Gastric cancer ranks as the second leading cause of malignancy-related death worldwide, and always diagnosed at advanced stage. MicroRNA-222-3p (miR-222-3p) is aberrantly upregulated in various malignant tumors including gastric cancer, but its role and underlying molecular mechanisms in gastric cancer remain largely unknown. Helicobacter pylori (H. pylori) infection acts as a trigger in the development of gastric cancer, and increasing evidence suggests that H. pylori affects microRNA expression. In this study, gastric cancer tissue samples were divided into H. pylori positive group (+) and negative group (-). QRT-PCR showed that miR-222-3p was significantly upregulated in H. pylori (+) group compared with H. pylori (-) group, and luciferase reporter assays identified homeodomain-interacting protein kinase 2 (HIPK2) as a novel target of miR-222-3p in gastric cancer. Immunohistochemistry revealed that HIPK2 levels were decreased in H. pylori (+) group compared with H. pylori (-). After that, functional experiments indicated that miR-222-3p overexpression promoted the proliferation and invasion, while inhibiting apoptosis of SGC7901 gastric cancer cells, but miR-222-3p knockdown exhibited the opposite effects. Also, HIPK2 knockdown induced similar effects as miR-222-3p overexpression in SGC7901 cells. Nude mouse experiments further suggested that HIPK2 overexpression signally attenuated the enhancing effect of miR-222-3p overexpression on cell proliferation, indicating that the effect of miR-222-3p on gastric cancer progression depends on HIPK2, at least in part. Overall, our results demonstrated that miR-222-3p/HIPK2 signal pathway regulated gastric cancer cell proliferation, apoptosis, and invasion, provided a novel therapeutic target for the treatment of gastric cancer infected by H. pylori.

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.

Effects of Y361-auto-phosphorylation on structural plasticity of the HIPK2 kinase domain

The dual-specificity activity of the homeodomain interacting protein kinase 2 (HIPK2) is regulated by cis-auto-phosphorylation of tyrosine 361 (Y361) on the activation loop. Inhibition of this process or substitution of Y361 with nonphosphorylatable amino acid residues result in aberrant HIPK2 forms that show altered functionalities, pathological-like cellular relocalization, and accumulation into cytoplasmic aggresomes. Here, we report an in vitro characterization of wild type HIPK2 kinase domain and of two mutants, one at the regulating Y361 (Y361F, mimicking a form of HIPK2 lacking Y361 phosphorylation) and another at the catalytic lysine 228 (K228A, inactivating the enzyme). Gel filtration and thermal denaturation analyzes along with equilibrium binding experiments and kinase assays performed in the presence or absence of ATP-competitors were performed. The effects induced by mutations on overall stability, oligomerization and activity support the existence of different conformations of the kinase domain linked to Y361 phosphorylation. In addition, our in vitro data are consistent with both the cross-talk between the catalytic site and the activation loop of HIPK2 and the aberrant activities and accumulation previously reported for the Y361 nonphosphorylated HIPK2 in mammalian cells.

circHIPK2-mediated σ-1R promotes endoplasmic reticulum stress in human pulmonary fibroblasts exposed to silica

Silicosis is characterized by fibroblast accumulation and excessive deposition of extracellular matrix. Although the roles of SiO2-induced chemokines and cytokines released from alveolar macrophages have received significant attention, the direct effects of SiO2 on protein production and functional changes in pulmonary fibroblasts have been less extensively studied. Sigma-1 receptor, which has been associated with cell proliferation and migration in the central nervous system, is expressed in the lung, but its role in silicosis remains unknown. To elucidate the role of sigma-1 receptor in fibrosis induced by silica, both the upstream molecular mechanisms and the functional effects on cell proliferation and migration were investigated. Both molecular biological assays and pharmacological techniques, combined with functional experiments, such as migration and proliferation, were applied in human pulmonary fibroblasts from adults to analyze the molecular and functional changes induced by SiO2. SiO2 induced endoplasmic reticulum stress in association with enhanced expression of sigma-1 receptor. Endoplasmic reticulum stress promoted migration and proliferation of human pulmonary fibroblasts-adult exposed to SiO2, inducing the development of silicosis. Inhibition of sigma-1 receptor ameliorated endoplasmic reticulum stress and fibroblast functional changes induced by SiO2. circHIPK2 is involved in the regulation of sigma-1 receptor in human pulmonary fibroblasts-adult exposed to SiO2. Our study elucidated a link between SiO2-induced fibrosis and sigma-1 receptor signaling, thereby providing novel insight into the potential use of sigma-1 receptor/endoplasmic reticulum stress in the development of novel therapeutic strategies for silicosis treatment.