Homeodomain interacting protein kinase 2 promotes apoptosis by downregulating the transcriptional corepressor CtBP

Interpretable identification of cancer genes across biological networks via transformer-powered graph representation learning

Graph representation learning has been leveraged to identify cancer genes from biological networks. However, its applicability is limited by insufficient interpretability and generalizability under integrative network analysis. Here we report the development of an interpretable and generalizable transformer-based model that accurately predicts cancer genes by leveraging graph representation learning and the integration of multi-omics data with the topologies of homogeneous and heterogeneous networks of biological interactions. The model allows for the interpretation of the respective importance of multi-omic and higher-order structural features, achieved state-of-the-art performance in the prediction of cancer genes across biological networks (including networks of interactions between miRNA and proteins, transcription factors and proteins, and transcription factors and miRNA) in pan-cancer and cancer-specific scenarios, and predicted 57 cancer-gene candidates (including three genes that had not been identified by other models) among 4,729 unlabelled genes across 8 pan-cancer datasets. The model's interpretability and generalization may facilitate the understanding of gene-related regulatory mechanisms and the discovery of new cancer genes.

Endothelial nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome regulation in atherosclerosis

AIMS

The activation of nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome in endothelial cells (ECs) contributes to vascular inflammation in atherosclerosis. Considering the high glycolytic rate of ECs, we delineated whether and how glycolysis determines endothelial NLRP3 inflammasome activation in atherosclerosis.

METHODS AND RESULTS

Our results demonstrated a significant up-regulation of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), a key regulator of glycolysis, in human and mouse atherosclerotic endothelium, which positively correlated with NLRP3 levels. Atherosclerotic stimuli up-regulated endothelial PFKFB3 expression via sterol regulatory element-binding protein 2 (SREBP2) transactivation. EC-selective haplodeficiency of Pfkfb3 in Apoe-/- mice resulted in reduced endothelial NLRP3 inflammasome activation and attenuation of atherogenesis. Mechanistic investigations revealed that PFKFB3-driven glycolysis increased the NADH content and induced oligomerization of C-terminal binding protein 1 (CtBP1), an NADH-sensitive transcriptional co-repressor. The monomer form, but not the oligomer form, of CtBP1 was found to associate with the transcriptional repressor Forkhead box P1 (FOXP1) and acted as a transrepressor of inflammasome components, including NLRP3, caspase-1, and interleukin-1β (IL-1β). Interfering with NADH-induced CtBP1 oligomerization restored its binding to FOXP1 and inhibited the glycolysis-dependent up-regulation of NLRP3, Caspase-1, and IL-1β. Additionally, EC-specific overexpression of NADH-insensitive CtBP1 alleviates atherosclerosis.

CONCLUSION

Our findings highlight the existence of a glycolysis-dependent NADH/CtBP/FOXP1-transrepression pathway that regulates endothelial NLRP3 inflammasome activation in atherogenesis. This pathway represents a potential target for selective PFKFB3 inhibitors or strategies aimed at disrupting CtBP1 oligomerization to modulate atherosclerosis.

Fibroblasts in Pulmonary Hypertension: Roles and Molecular Mechanisms

Fibroblasts, among the most prevalent and widely distributed cell types in the human body, play a crucial role in defining tissue structure. They do this by depositing and remodeling extracellular matrixes and organizing functional tissue networks, which are essential for tissue homeostasis and various human diseases. Pulmonary hypertension (PH) is a devastating syndrome with high mortality, characterized by remodeling of the pulmonary vasculature and significant cellular and structural changes within the intima, media, and adventitia layers. Most research on PH has focused on alterations in the intima (endothelial cells) and media (smooth muscle cells). However, research over the past decade has provided strong evidence of the critical role played by pulmonary artery adventitial fibroblasts in PH. These fibroblasts exhibit the earliest, most dramatic, and most sustained proliferative, apoptosis-resistant, and inflammatory responses to vascular stress. This review examines the aberrant phenotypes of PH fibroblasts and their role in the pathogenesis of PH, discusses potential molecular signaling pathways underlying these activated phenotypes, and highlights areas of research that merit further study to identify promising targets for the prevention and treatment of PH.

Transcriptional corepressor activity of CtBP1 is regulated by ISG15 modification

C-terminal binding protein 1 (CtBP1) is a critical transcriptional corepressor of many tumor suppressor genes and plays diverse roles in the progression of cancers. The transcriptional repression function of CtBP1 is mediated by recruiting histone-modifying enzymes, such as histone deacetylases and histone methyltransferases, to target genes by binding with DNA-interacting factors. Several post-translational modifications of CtBP1 have been identified, including ubiquitination, phosphorylation, and SUMOylation. This paper reports that CtBP1 is conjugated by ISG15. Endogenous CtBP1 was modified by ISG15 after interferon-α treatment in HeLa cells. The ISGylation process of CtBP1 was regulated by deISGylation enzyme USP18 and ISG15 E3 ligase EFP. Interestingly, CtBP1 ISGylation affected the binding affinity between CtBP1 and some components of CtBP1-associated transcriptional complexes. HDAC1 and LSD1 bound more efficiently to ISG15-conjugated CtBP1 than non-conjugated CtBP1. On the other hand, binding between CtBP1 and HDAC4 was unaffected by ISG15 modification. Furthermore, ISG15 modification enhanced the transcriptional repression activity of CtBP1 on several target genes related to EMT and apoptosis. These findings suggest that the ISG15 modification of CtBP1 modulates the function and activity of CtBP1 and that CtBP1 ISGylation may provide a new insight for CtBP1-mediated cancers.

A Novel Cre Recombinase Mouse Strain for Cell-Specific Deletion of Floxed Genes in Ribbon Synapse-Forming Retinal Neurons

We generated a novel Cre mouse strain for cell-specific deletion of floxed genes in ribbon synapse-forming retinal neurons. Previous studies have shown that the RIBEYE promotor targets the expression of recombinant proteins such as fluorescently tagged RIBEYE to photoreceptors and retinal bipolar cells and generates fluorescent synaptic ribbons in situ in these neurons. Here, we used the same promotor to generate a novel transgenic mouse strain in which the RIBEYE promotor controls the expression of a Cre-ER(T2) recombinase (RIBEYE-Cre). To visualize Cre expression, the RIBEYE-Cre animals were crossed with ROSA26 tau-GFP (R26-τGFP) reporter mice. In the resulting RIBEYE-Cre/R26 τGFP animals, Cre-mediated removal of a transcriptional STOP cassette results in the expression of green fluorescent tau protein (tau-GFP) that binds to cellular microtubules. We detected robust tau-GFP expression in retinal bipolar cells. Surprisingly, we did not find fluorescent tau-GFP expression in mouse photoreceptors. The lack of tau-GFP reporter protein in these cells could be based on the previously reported absence of tau protein in mouse photoreceptors which could lead to the degradation of the recombinant tau protein. Consistent with this, we detected Cre and tau-GFP mRNA in mouse photoreceptor slices by RT-PCR. The transgenic RIBEYE-Cre mouse strain provides a new tool to study the deletion of floxed genes in ribbon synapse-forming neurons of the retina and will also allow for analyzing gene deletions that are lethal if globally deleted in neurons.

The emerging role of miRNAs in myocardial infarction: From molecular signatures to therapeutic targets

Globally, myocardial infarction (MI) and other cardiovascular illnesses have long been considered the top killers. Heart failure and mortality are the results of myocardial apoptosis, cardiomyocyte fibrosis, and cardiomyocyte hypertrophy, all of which are caused by MI. MicroRNAs (miRNAs) play a crucial regulatory function in the progression and advancement of heart disease following an MI. By consolidating the existing data on miRNAs, our aim is to gain a more comprehensive understanding of their role in the pathological progression of myocardial injury after MI and to identify potential crucial target pathways. Also included are the primary treatment modalities and their most recent developments. miRNAs have the ability to regulate both normal and pathological activity, including the key signaling pathways. As a result, they may exert medicinal benefits. This review presents a comprehensive analysis of the role of miRNAs in MI with a specific emphasis on their impact on the regeneration of cardiomyocytes and other forms of cell death, such as apoptosis, necrosis, and autophagy. Furthermore, the targets of pro- and anti-MI miRNAs are comparatively elucidated.

Functions of SRPK, CLK and DYRK kinases in stem cells, development, and human developmental disorders

Human developmental disorders encompass a wide range of debilitating physical conditions and intellectual disabilities. Perturbation of protein kinase signalling underlies the development of some of these disorders. For example, disrupted SRPK signalling is associated with intellectual disabilities, and the gene dosage of DYRKs can dictate the pathology of disorders including Down's syndrome. Here, we review the emerging roles of the CMGC kinase families SRPK, CLK, DYRK, and sub-family HIPK during embryonic development and in developmental disorders. In particular, SRPK, CLK, and DYRK kinase families have key roles in developmental signalling and stem cell regulation, and can co-ordinate neuronal development and function. Genetic studies in model organisms reveal critical phenotypes including embryonic lethality, sterility, musculoskeletal errors, and most notably, altered neurological behaviours arising from defects of the neuroectoderm and altered neuronal signalling. Further unpicking the mechanisms of specific kinases using human stem cell models of neuronal differentiation and function will improve our understanding of human developmental disorders and may provide avenues for therapeutic strategies.

miRNAs orchestration of cardiovascular diseases - Particular emphasis on diagnosis, and progression

MicroRNAs (miRNAs; miRs) are small non-coding ribonucleic acids sequences vital in regulating gene expression. They are significant in many biological and pathological processes and are even detectable in various body fluids such as serum, plasma, and urine. Research has demonstrated that the irregularity of miRNA in multiplying cardiac cells is linked to developmental deformities in the heart's structure. It has also shown that miRNAs are crucial in diagnosing and progressing several cardiovascular diseases (CVDs). The review covers the function of miRNAs in the pathophysiology of CVD. Additionally, the review provides an overview of the potential role of miRNAs as disease-specific diagnostic and prognostic biomarkers for human CVD, as well as their biological implications in CVD.

CtBP Neuroprotective Role in Toxin-Based Parkinson's Disease Models: From Expression Pattern to Dopaminergic Survival

C-terminal binding proteins (CtBP) are transcriptional co-repressors regulating gene expression. CtBP promote neuronal survival through repression of pro-apoptotic genes, and may represent relevant targets for neurodegenerative disorders, such as Parkinson's disease (PD). Nevertheless, evidence of the role of CtBP1 and CtBP2 in neurodegeneration are scarce. Herein, we showed that CtBP1 and CtBP2 are expressed in neurons, dopaminergic neurons, astrocytes, and microglia in the substantia nigra (SN) and striatum of adult mice. Old mice showed a lower expression of CtBP1 in the SN and higher expression of CtPB2 in the SN and striatum compared with adult mice. In vivo models for PD (paraquat, MPTP, 6-OHDA) showed increased expression of CtBP1 in the SN and striatum while CtBP2 expression was increased in the striatum of paraquat-treated rats only. Moreover, an increased expression of both CtBP was found in a dopaminergic cell line (N27) exposed to 6-OHDA. In the 6-OHDA PD model, we found a dual effect using an unspecific ligand of CtBP, the 4-methylthio 2-oxobutyric acid (MTOB): higher concentrations (e.g. 2500 µM, 1000 µM) inhibited dopaminergic survival, while at 250 μM it counteracted cell death. In vitro, this latter protective role was absent after the siRNA silencing of CtBP1 or CtBP2. Altogether, this is the first report exploring the cellular and regional expression pattern of CtBP in the nigrostriatal pathway and the neuroprotective role in PD toxin-based models. CtBP could counteract dopaminergic cell death in the 6-OHDA PD model and, therefore, CtBP function and therapeutic potential in PD should be further explored.

HIPK1 Inhibition Protects against Pathological Cardiac Hypertrophy by Inhibiting the CREB-C/EBPβ Axis

Inhibition of pathological cardiac hypertrophy is recognized as an important therapeutic strategy for heart failure, although effective targets are still lacking in clinical practice. Homeodomain interacting protein kinase 1 (HIPK1) is a conserved serine/threonine kinase that can respond to different stress signals, however, whether and how HIPK1 regulates myocardial function is not reported. Here, it is observed that HIPK1 is increased during pathological cardiac hypertrophy. Both genetic ablation and gene therapy targeting HIPK1 are protective against pathological hypertrophy and heart failure in vivo. Hypertrophic stress-induced HIPK1 is present in the nucleus of cardiomyocytes, while HIPK1 inhibition prevents phenylephrine-induced cardiomyocyte hypertrophy through inhibiting cAMP-response element binding protein (CREB) phosphorylation at Ser271 and inactivating CCAAT/enhancer-binding protein β (C/EBPβ)-mediated transcription of pathological response genes. Inhibition of HIPK1 and CREB forms a synergistic pathway in preventing pathological cardiac hypertrophy. In conclusion, HIPK1 inhibition may serve as a promising novel therapeutic strategy to attenuate pathological cardiac hypertrophy and heart failure.

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.

The Cynosure of CtBP: Evolution of a Bilaterian Transcriptional Corepressor

Evolution of sequence-specific transcription factors clearly drives lineage-specific innovations, but less is known about how changes in the central transcriptional machinery may contribute to evolutionary transformations. In particular, transcriptional regulators are rich in intrinsically disordered regions that appear to be magnets for evolutionary innovation. The C-terminal Binding Protein (CtBP) is a transcriptional corepressor derived from an ancestral lineage of alpha hydroxyacid dehydrogenases; it is found in mammals and invertebrates, and features a core NAD-binding domain as well as an unstructured C-terminus (CTD) of unknown function. CtBP can act on promoters and enhancers to repress transcription through chromatin-linked mechanisms. Our comparative phylogenetic study shows that CtBP is a bilaterian innovation whose CTD of about 100 residues is present in almost all orthologs. CtBP CTDs contain conserved blocks of residues and retain a predicted disordered property, despite having variations in the primary sequence. Interestingly, the structure of the C-terminus has undergone radical transformation independently in certain lineages including flatworms and nematodes. Also contributing to CTD diversity is the production of myriad alternative RNA splicing products, including the production of "short" tailless forms of CtBP in Drosophila. Additional diversity stems from multiple gene duplications in vertebrates, where up to five CtBP orthologs have been observed. Vertebrate lineages show fewer major modifications in the unstructured CTD, possibly because gene regulatory constraints of the vertebrate body plan place specific constraints on this domain. Our study highlights the rich regulatory potential of this previously unstudied domain of a central transcriptional regulator.

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.

Inhibition of CtBP-Regulated Proinflammatory Gene Transcription Attenuates Psoriatic Skin Inflammation

Psoriasis is a chronic immune-mediated disease characterized by excessive proliferation of epidermal keratinocytes and increased immune cell infiltration to the skin. Although it is well-known that psoriasis pathogenesis is driven by aberrant production of proinflammatory cytokines, the mechanisms underlying the imbalance between proinflammatory and anti-inflammatory cytokine expression are incompletely understood. In this study, we report that the transcriptional coregulators CtBP1 and 2 can transactivate a common set of proinflammatory genes both in the skin of imiquimod-induced mouse psoriasis model and in human keratinocytes and macrophages stimulated by imiquimod. We find that mice overexpressing CtBP1 in epidermal keratinocytes display severe skin inflammation phenotypes with increased expression of T helper type 1 and T helper type 17 cytokines. We also find that the expression of CtBPs and CtBP-target genes is elevated both in human psoriatic lesions and in the mouse imiquimod psoriasis model. Moreover, we were able to show that topical treatment with a peptidic inhibitor of CtBP effectively suppresses the CtBP-regulated proinflammatory gene expression and thus attenuates psoriatic inflammation in the imiquimod mouse model. Together, our findings suggest to our knowledge previously unreported strategies for therapeutic modulation of the immune response in inflammatory skin diseases.

CtBP1/2 differentially regulate genomic stability and DNA repair pathway in high-grade serous ovarian cancer cell

The C-terminal binding proteins (CtBPs), CtBP1 and CtBP2, are transcriptional co-repressor that interacts with multiple transcriptional factors to modulate the stability of chromatin. CtBP proteins were identified with overexpression in the high-grade serous ovarian carcinoma (HGSOC). However, little is known about CtBP proteins’ regulatory roles in genomic stability and DNA repair in HGSOC. In this study, we combined whole-transcriptome analysis with multiple research methods to investigate the role of CtBP1/2 in genomic stability. Several key functional pathways were significantly enriched through whole transcription profile analysis of CtBP1/2 knockdown SKOV3 cells, including DNA damage repair, apoptosis, and cell cycle. CtBP1/2 knockdown induced cancer cell apoptosis, increased genetic instability, and enhanced the sensitivity to DNA damage agents, such as γ-irradiation and chemotherapy drug (Carboplatin and etoposide). The results of DNA fiber assay revealed that CtBP1/2 contribute differentially to the integrity of DNA replication track and stability of DNA replication recovery. CtBP1 protects the integrity of stalled forks under metabolic stress condition during prolonged periods of replication, whereas CtBP2 acts a dominant role in stability of DNA replication recovery. Furthermore, CtBP1/2 knockdown shifted the DSBs repair pathway from homologous recombination (HR) to non-homologous end joining (NHEJ) and activated DNA-PK in SKOV3 cells. Interesting, blast through TCGA tumor cases, patients with CtBP2 genetic alternation had a significantly longer overall survival time than unaltered patients. Together, these results revealed that CtBP1/2 play a different regulatory role in genomic stability and DSBs repair pathway bias in serous ovarian cancer cells. It is possible to generate novel potential targeted therapy strategy and translational application for serous ovarian carcinoma patients with a predictable better clinical outcome.

The Role of p53 Signaling in Colorectal Cancer

The transcription factor p53 functions as a critical tumor suppressor by orchestrating a plethora of cellular responses such as DNA repair, cell cycle arrest, cellular senescence, cell death, cell differentiation, and metabolism. In unstressed cells, p53 levels are kept low due to its polyubiquitination by the E3 ubiquitin ligase MDM2. In response to various stress signals, including DNA damage and aberrant growth signals, the interaction between p53 and MDM2 is blocked and p53 becomes stabilized, allowing p53 to regulate a diverse set of cellular responses mainly through the transactivation of its target genes. The outcome of p53 activation is controlled by its dynamics, its interactions with other proteins, and post-translational modifications. Due to its involvement in several tumor-suppressing pathways, p53 function is frequently impaired in human cancers. In colorectal cancer (CRC), the TP53 gene is mutated in 43% of tumors, and the remaining tumors often have compromised p53 functioning because of alterations in the genes encoding proteins involved in p53 regulation, such as ATM (13%) or DNA-PKcs (11%). TP53 mutations in CRC are usually missense mutations that impair wild-type p53 function (loss-of-function) and that even might provide neo-morphic (gain-of-function) activities such as promoting cancer cell stemness, cell proliferation, invasion, and metastasis, thereby promoting cancer progression. Although the first compounds targeting p53 are in clinical trials, a better understanding of wild-type and mutant p53 functions will likely pave the way for novel CRC therapies.

Transcriptional Analyses of Acute Exposure to Methylmercury on Erythrocytes of Loggerhead Sea Turtle

To understand changes in enzyme activity and gene expression as biomarkers of exposure to methylmercury, we exposed loggerhead turtle erythrocytes (RBCs) to concentrations of 0, 1, and 5 mg L-1 of MeHg and de novo transcriptome were assembled using RNA-seq. The analysis of differentially expressed genes (DEGs) indicated that 79 unique genes were dysregulated (39 upregulated and 44 downregulated genes). The results showed that MeHg altered gene expression patterns as a response to the cellular stress produced, reflected in cell cycle regulation, lysosomal activity, autophagy, calcium regulation, mitochondrial regulation, apoptosis, and regulation of transcription and translation. The analysis of DEGs showed a low response of the antioxidant machinery to MeHg, evidenced by the fact that genes of early response to oxidative stress were not dysregulated. The RBCs maintained a constitutive expression of proteins that represented a good part of the defense against reactive oxygen species (ROS) induced by MeHg.

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.

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.

Harmonization of L1CAM expression facilitates axon outgrowth and guidance of a motor neuron

Brain development requires precise regulation of axon outgrowth, guidance and termination by multiple signaling and adhesion molecules. How the expression of these neurodevelopmental regulators is transcriptionally controlled is poorly understood. The Caenorhabditis elegans SMD motor neurons terminate axon outgrowth upon sexual maturity and partially retract their axons during early adulthood. Here we show that C-terminal binding protein 1 (CTBP-1), a transcriptional corepressor, is required for correct SMD axonal development. Loss of CTBP-1 causes multiple defects in SMD axon development: premature outgrowth, defective guidance, delayed termination and absence of retraction. CTBP-1 controls SMD axon guidance by repressing the expression of SAX-7, an L1 cell adhesion molecule (L1CAM). CTBP-1-regulated repression is crucial because deregulated SAX-7/L1CAM causes severely aberrant SMD axons. We found that axonal defects caused by deregulated SAX-7/L1CAM are dependent on a distinct L1CAM, called LAD-2, which itself plays a parallel role in SMD axon guidance. Our results reveal that harmonization of L1CAM expression controls the development and maturation of a single neuron.

Stabilization of C-terminal binding protein 2 by cellular inhibitor of apoptosis protein 1 via BIR domains without E3 ligase activity

C-terminal binding protein 2 (CtBP2) is a transcriptional co-repressor that regulates many genes involved in normal cellular events. Because CtBP2 overexpression has been implicated in various human cancers, its protein levels must be precisely regulated. Previously, we reported that CtBP1 and CtBP1-mediated transcriptional repression are regulated by X-linked inhibitor of apoptosis protein (XIAP). In the present study, we sought to investigate whether CtBP2 is also regulated by XIAP or any other human IAP. We found that cIAP1 interacts with CtBP2 via through BIR domains to regulates the steady-state levels of CtBP2 protein in the nucleus. The levels of CtBP2 were gradually increased upon cIAP1 overexpression and downregulated upon cIAP1 depletion. Interestingly, the RING domain of cIAP1 responsible for E3 ligase activity was not required for this regulation. Finally, the levels of CtBP2 modulated by cIAP1 affected the transcription of CtBP2 target genes and subsequent cell migration. Taken together, our data demonstrate a novel function of cIAP1 which involves protecting CtBP2 from degradation to stabilize its steady-state level. These results suggest that cIAP1 might be a useful target in strategies aiming to downregulate the steady-state level of CtBP2 protein in treating human cancers.

Tubular HIPK2 is a key contributor to renal fibrosis

We previously used global Hipk2-null mice in various models of kidney disease to demonstrate the central role of homeodomain-interacting protein kinase 2 (HIPK2) in renal fibrosis development. However, renal tubular epithelial cell–specific (RTEC-specific) HIPK2 function in renal fibrogenesis has yet to be determined. Here, we show that modulation of tubular HIPK2 expression and activity affects renal fibrosis development in vivo. The loss of HIPK2 expression in RTECs resulted in a marked diminution of renal fibrosis in unilateral ureteral obstruction (UUO) mouse models and HIV-associated nephropathy (HIVAN) mouse models, which was associated with the reduction of Smad3 activation and downstream expression of profibrotic markers. Conversely, WT HIPK2 overexpression in RTECs accentuated the extent of renal fibrosis in the setting of UUO, HIVAN, and folic acid–induced nephropathy in mice. Notably, kinase-dead HIPK2 mutant overexpression or administration of BT173, an allosteric inhibitor of HIPK2-Smad3 interaction, markedly attenuated the renal fibrosis in these mouse models of kidney disease, indicating that HIPK2 requires both the kinase activity and its interaction with Smad3 to promote TGF-β–mediated renal fibrosis. Together, these results establish an important RTEC-specific role of HIPK2 in kidney fibrosis and further substantiate the inhibition of HIPK2 as a therapeutic approach against renal fibrosis.

Modulation of HIPK2 expression in murine renal tubular epithelial cells reveals an important role in renal fibrosis development.

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.

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.

miR-770-5p modulates resistance to methotrexate in human colorectal adenocarcinoma cells by downregulating HIPK1

Colon cancer is one of the most common types of cancer worldwide. Methotrexate (MTX) is a chemotherapy drug used for the treatment of multiple types of cancer, such as colon and breast cancer. To determine the effects of MTX treatment on colorectal adenocarcinoma cell lines, a microRNA (miRNA) microarray was used to detect miRNA expression profiles of HT-29 colorectal adenocarcinoma MTX-resistant cells and their parental cells. The results demonstrated that 641 genes and 43 miRNAs were differentially expressed between HT-29 MTX-sensitive cells and MTX-resistant cells. In addition, 12 miRNAs and their co-expressed genes were highly correlated in MTX treatment, and one of the identified miRNAs, miR-770-5p, was studied in subsequent experiments. Upregulation of miR-770-5p significantly decreased the sensitivity of HT-29 cells to MTX. Using bioinformatics software, homeodomain-interacting protein kinase 1 (HIPK1) was identified to be a putative target gene of miR-770-5p, which was confirmed by a luciferase reporter assay. Downregulation of miR-770-5p target gene HIPK1 significantly decreased the sensitivity of HT-29 cells to MTX. These results suggest that miR-770-5p may be involved in the regulation of colon cancer resistance to MTX by regulating the expression of the target gene HIPK1.

The crystal structure of the protein kinase HIPK2 reveals a unique architecture of its CMGC-insert region

The homeodomain-interacting protein kinase (HIPK) family is comprised of four nuclear protein kinases, HIPK1-4. HIPK proteins phosphorylate a diverse range of transcription factors involved in cell proliferation, differentiation, and apoptosis. HIPK2, thus far the best-characterized member of this largely understudied family of protein kinases, plays a role in the activation of p53 in response to DNA damage. Despite this tumor-suppressor function, HIPK2 is also found overexpressed in several cancers, and its hyperactivation causes chronic fibrosis. There are currently no structures of HIPK2 or of any other HIPK kinase. Here, we report the crystal structure of HIPK2's kinase domain bound to CX-4945, a casein kinase 2α (CK2α) inhibitor currently in clinical trials against several cancers. The structure, determined at 2.2 Å resolution, revealed that CX-4945 engages the HIPK2 active site in a hybrid binding mode between that seen in structures of CK2α and Pim1 kinases. The HIPK2 kinase domain crystallized in the active conformation, which was stabilized by phosphorylation of the activation loop. We noted that the overall kinase domain fold of HIPK2 closely resembles that of evolutionarily related dual-specificity tyrosine-regulated kinases (DYRKs). Most significant structural differences between HIPK2 and DYRKs included an absence of the regulatory N-terminal domain and a unique conformation of the CMGC-insert region and of a newly defined insert segment in the αC-β4 loop. This first crystal structure of HIPK2 paves the way for characterizing the understudied members of the HIPK family and for developing HIPK2-directed therapies for managing cancer and fibrosis.

Homeodomain-interacting protein kinase 2 suppresses proliferation and aerobic glycolysis via ERK/cMyc axis in pancreatic cancer

OBJECTIVES

To investigate the roles of the homeodomain-interacting protein kinase (HIPK) family of proteins in pancreatic cancer prognosis and the possible molecular mechanism.

MATERIALS AND METHODS

The expression of HIPK family genes and their roles in pancreatic cancer prognosis were analysed by using The Cancer Genome Atlas (TCGA). The roles of HIPK2 in pancreatic cancer proliferation and glycolysis were tested by overexpression of HIPK2 in pancreatic cancer cells, followed by cell proliferation assay, glucose uptake analysis and Seahorse extracellular flux analysis. The mechanism of action of HIPK2 in pancreatic cancer proliferation and glycolysis was explored by examining its effect on the ERK/cMyc axis.

RESULTS

Decreased HIPK2 expression indicated worse prognosis of pancreatic cancer. Overexpression of HIPK2 in pancreatic cancer cells decreased cell proliferation and attenuated aerobic glycolysis, which sustained proliferation of cancer cells. HIPK2 decreased cMyc protein levels and expression of cMyc-targeted glycolytic genes. cMyc was a mediator that regulated HIPK2-induced decrease in aerobic glycolysis. HIPK2 regulated cMyc protein stability via ERK activation, which phosphorylated and controlled cMyc protein stability.

CONCLUSIONS

HIPK2 suppressed proliferation of pancreatic cancer in part through inhibiting the ERK/cMyc axis and related aerobic glycolysis.

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.

C-Terminal Binding Protein 1 Modulates Cellular Redox via Feedback Regulation of MPC1 and MPC2 in Melanoma Cells

BACKGROUND Recent studies have illustrated that the transcription co-repressor, C-terminal binding protein 1 (CtBP1), links the metabolic alterations to transcription controls in proliferation, EMT, genome stability, metabolism, and lifespan, but whether CtBP1 affects the cellular redox homeostasis is unexplored. This study was designed to investigate the mechanism of CtBP1-mediated transcription repression that contributes to the metabolic reprogramming. MATERIAL AND METHODS Knockdown of CtBP1 in both mouse MEF cells and human melanoma cells changed cell redox homeostasis. Further, chromatin immunoprecipitation (ChIP) and luciferase reporter assay were performed for identification of CtBP1 downstream targets, pyruvate carrier 1 and 2 genes (MPC1 and MPC2), which contribute to redox homeostasis and are transcriptionally regulated by CtBP1. Moreover, blockage of the cellular NADH level with the glycolysis inhibitor 2-Deoxy-D-Glucose (2-DG) rescued MPC1 and MPC2 expression. MTT assay and scratch assay were performed to investigate the effect of MPC1 and MPC2 expression on malignant properties of melanoma cells. RESULTS The data demonstrated that CtBP1 directly bound to the promoters of MPC1 and MPC2 and transcriptionally repressed them, leading to increased levels of free NADH in the cytosol and nucleus, thus positively feeding back CtBP1's functions. Consequently, restoring MPC1 and MPC2 in human tumor cells decreases free NADH and inhibits melanoma cell proliferation and migration. CONCLUSIONS Our data indicate that MPC1 and MPC2 are principal mediators that link CtBP1-mediated transcription regulation to NADH production. The discovery of CtBP1 as an NADH regulator in addition to being an NADH sensor shows that CtBP1 is at the center of tumor metabolism and transcription control.

The expression level and prognostic value of HIPK3 among non-small-cell lung cancer patients in China

Background

Lung cancer is one of the most common malignancies in the world and is at the forefront of causes of all cancer deaths. Identification of new prognostic predictors or therapeutic targets might improve a patient's survival rate.

Purpose

The Homeodomain interacting protein kinases (HIPKs) function as modulators of cellular stress responses and regulate cell differentiation, proliferation and apoptosis, but the function of HIPK3 is remain unknown.

Patients and methods

We used quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting methods to detective the expression of HIPK3. A total of 206 samples were obtained from patients and Immunochemical evaluation to determine HIPK3 protein expression. HIPK3 protein levels in in non-small cell lung cancer (NSCLC) were correlated with the clinical characteristics of patients and their 5-year survival rate. In addition, HIPK3 knockdown by specific RNAi promoted cell proliferation, migration, and invasion in A549 and HCC827 cancer cell lines.

Results

The quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting methods to demonstrate that HIPK3 expression was significantly down-regulated in non-small cell lung cancer (NSCLC) tissues compared with that in normal lung tissues. At the same time, the results of immunohistochemistry assays showed that low expression of HIPK3 was significantly associated with pathology grade; tumor, node, and metastases (TNM) stage; lymph node metastasis; Ki-67 expression; and the 5-year survival rate in NSCLC patients. Univariate analysis revealed that HIPK3 expression, Ki-67 expression, tumor diameter, TNM stage, and age were significantly associated with a poor prognosis. The multivariable analysis illustrated that HIPK3, tumor diameter, TNM, Ki-67 expression, and age had effects on the overall survival of NSCLC patients independently. Kaplan-Meier survival curves revealed that NSCLC patients with a lower HIPK3 expression had a poorer prognosis. In addition, in vivo results also confirmed that HIPK3 over-expression could inhibit tumor growth.

Conclusion

Our findings confirmed that low expression of HIPK3 in NSCLC tissues was significantly correlated with poor survival rates after curative resection. HIPK3 could potentially be used as a valuable biomarker in the prognosis of the survival of NSCLC patients.

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.

p300-mediated acetylation increased the protein stability of HIPK2 and enhanced its tumor suppressor function

Homeodomain-interacting protein kinase 2 (HIPK2) is a nuclear serine/threonine kinase that functions in development and tumor suppression. One of the prominent features of this kinase is that it is tightly regulated by proteasomal degradation. In the present study, we present evidence suggesting that the protein stability of HIPK2 can be regulated by p300-mediated acetylation. p300 increased the protein level of HIPK2 via its acetyltransferase activity. p300 increased the acetylation of HIPK2 while decreased polyubiquitination and its proteasomal degradation. We also observed that DNA damage induced acetylation of HIPK2 along with an increase in the protein amount, which was inhibited by p300 RNAi. Importantly, p300 promoted p53 activation and the HIPK2-mediated suppression of cell proliferation, suggesting acetylation-induced HIPK2 stabilization contributed to the enhanced activation of HIPK2. Overexpression of p300 promoted the HIPK2-mediated suppression of tumor growth in mouse xenograft model as well. Taken together, our data suggest that p300-mediated acetylation of HIPK2 increases the protein stability of HIPK2 and enhances its tumor suppressor function.

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.

CtBP- an emerging oncogene and novel small molecule drug target: Advances in the understanding of its oncogenic action and identification of therapeutic inhibitors

C-terminal Binding Proteins (CtBP) 1 and 2 are oncogenic transcriptional co-regulators overexpressed in many cancer types, with their expression level correlating to worse prognostic outcomes and aggressive tumor features. CtBP negatively regulates the expression of many tumor suppressor genes, while coactivating genes that promote proliferation, epithelial-mesenchymal transition, and cancer stem cell self-renewal activity. In light of this evidence, the development of novel inhibitors that mitigate CtBP function may provide clinically actionable therapeutic tools. This review article focuses on the progress made in understanding CtBP structure, role in tumor progression, and discovery and development of CtBP inhibitors that target CtBP's dehydrogenase activity and other functions, with a focus on the theory and rationale behind the designs of current inhibitors. We provide insight into the future development and use of rational combination therapy that may further augment the efficacy of CtBP inhibitors, specifically addressing metastasis and cancer stem cell populations within tumors.

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.

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.

Arsenic-Induced Activation of the Homeodomain-Interacting Protein Kinase 2 (HIPK2) to cAMP-Response Element Binding Protein (CREB) Axis

Cyclic AMP-response element-binding protein (CREB) plays key transcriptional roles in cell metabolism, proliferation, and survival. Ser133 phosphorylation by protein kinase A (PKA) is a well-characterized CREB activation mechanism. Homeodomain-interacting protein kinase (HIPK) 2, a nuclear serine/threonine kinase, activates CREB through Ser271 phosphorylation; however, the regulatory mechanism remains uncharacterized. Transfection of CREB in HEK293 cells together with the kinase demonstrated that HIPK2 phosphorylated CREB at Ser271 but not Ser133; likewise, PKA phosphorylated CREB at Ser133 but not Ser271, suggesting two distinct CREB regulatory mechanisms by HIPK2 and PKA. In vitro kinase assay revealed that HIPK2, and HIPK1 and HIPK3, directly phosphorylated CREB. Cells exposed to 10μM sodium arsenite increased the stability of HIPK1 and HIPK2 proteins, leading to CREB activation via Ser271 phosphorylation. Phospho-Ser271 CREB showed facilitated interaction with the TFIID subunit coactivator TAF4 assessed by immunoprecipitation. Furthermore, a focused gene array between cells transfected with CREB alone and CREB plus HIPK2 over empty vector-transfected control displayed 14- and 32-fold upregulation of cyclin A1, respectively, while no upregulation was displayed by HIPK2 alone. These results suggest that the HIPK2-phospho-Ser271 CREB axis is a new arsenic-responsive CREB activation mechanism in parallel with the PKA-phospho-Ser133 CREB axis.

Metabolic Reprogramming Regulates the Proliferative and Inflammatory Phenotype of Adventitial Fibroblasts in Pulmonary Hypertension Through the Transcriptional Corepressor C-Terminal Binding Protein-1

BACKGROUND

Changes in metabolism have been suggested to contribute to the aberrant phenotype of vascular wall cells, including fibroblasts, in pulmonary hypertension (PH). Here, we test the hypothesis that metabolic reprogramming to aerobic glycolysis is a critical adaptation of fibroblasts in the hypertensive vessel wall that drives proliferative and proinflammatory activation through a mechanism involving increased activity of the NADH-sensitive transcriptional corepressor C-terminal binding protein 1 (CtBP1).

METHODS

RNA sequencing, quantitative polymerase chain reaction,13C-nuclear magnetic resonance, fluorescence-lifetime imaging, mass spectrometry-based metabolomics, and tracing experiments with U-13C-glucose were used to assess glycolytic reprogramming and to measure the NADH/NAD+ ratio in bovine and human adventitial fibroblasts and mouse lung tissues. Immunohistochemistry was used to assess CtBP1 expression in the whole-lung tissues. CtBP1 siRNA and the pharmacological inhibitor 4-methylthio-2-oxobutyric acid (MTOB) were used to abrogate CtBP1 activity in cells and hypoxic mice.

RESULTS

We found that adventitial fibroblasts from calves with severe hypoxia-induced PH and humans with idiopathic pulmonary arterial hypertension (PH-Fibs) displayed aerobic glycolysis when cultured under normoxia, accompanied by increased free NADH and NADH/NAD+ ratios. Expression of the NADH sensor CtBP1 was increased in vivo and in vitro in fibroblasts within the pulmonary adventitia of humans with idiopathic pulmonary arterial hypertension and animals with PH and cultured PH-Fibs, respectively. Decreasing NADH pharmacologically with MTOB or genetically blocking CtBP1 with siRNA upregulated the cyclin-dependent genes (p15 and p21) and proapoptotic regulators (NOXA and PERP), attenuated proliferation, corrected the glycolytic reprogramming phenotype of PH-Fibs, and augmented transcription of the anti-inflammatory gene HMOX1. Chromatin immunoprecipitation analysis demonstrated that CtBP1 directly binds the HMOX1 promoter. Treatment of hypoxic mice with MTOB decreased glycolysis and expression of inflammatory genes, attenuated proliferation, and suppressed macrophage numbers and remodeling in the distal pulmonary vasculature.

CONCLUSIONS

CtBP1 is a critical factor linking changes in cell metabolism to cell phenotype in hypoxic and other forms of PH and a therapeutic target.

Homeodomain-Interacting Protein Kinase-2: A Critical Regulator of the DNA Damage Response and the Epigenome

Homeodomain-interacting protein kinase 2 (HIPK2) is a serine/threonine kinase that phosphorylates and activates the apoptotic program through interaction with diverse downstream targets including tumor suppressor p53. HIPK2 is activated by genotoxic stimuli and modulates cell fate following DNA damage. The DNA damage response (DDR) is triggered by DNA lesions or chromatin alterations. The DDR regulates DNA repair, cell cycle checkpoint activation, and apoptosis to restore genome integrity and cellular homeostasis. Maintenance of the DDR is essential to prevent development of diseases caused by genomic instability, including cancer, defects of development, and neurodegenerative disorders. Recent studies reveal a novel HIPK2-mediated pathway for DDR through interaction with chromatin remodeling factor homeodomain protein 1γ. In this review, we will highlight the molecular mechanisms of HIPK2 and show its functions as a crucial DDR regulator.

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.

The adaptor protein DCAF7 mediates the interaction of the adenovirus E1A oncoprotein with the protein kinases DYRK1A and HIPK2

DYRK1A is a constitutively active protein kinase that has a critical role in growth and development which functions by regulating cell proliferation, differentiation and survival. DCAF7 (also termed WDR68 or HAN11) is a cellular binding partner of DYRK1A and also regulates signalling by the protein kinase HIPK2. DCAF7 is an evolutionarily conserved protein with a single WD40 repeat domain and has no catalytic activity. We have defined a DCAF7 binding motif of 12 amino acids in the N-terminal domain of class 1 DYRKs that is functionally conserved in DYRK1 orthologs from Xenopus, Danio rerio and the slime mold Dictyostelium discoideum. A similar sequence was essential for DCAF7 binding to HIPK2, whereas the closely related HIPK1 family member did not bind DCAF7. Immunoprecipitation and pulldown experiments identified DCAF7 as an adaptor for the association of the adenovirus E1A protein with DYRK1A and HIPK2. Furthermore, DCAF7 was required for the hyperphosphorylation of E1A in DYRK1A or HIPK2 overexpressing cells. Our results characterize DCAF7 as a substrate recruiting subunit of DYRK1A and HIPK2 and suggest that it is required for the negative effect of DYRK1A on E1A-induced oncogenic transformation.

Silencing of CtBP1 suppresses the migration in human glioma cells

Carboxyl-terminal binding protein 1 (CtBP1), up-regulated in various types of human cancers, has been functionally associated with proliferation, anti-apoptosis, and EMT in vitro studies. However, the functional significance of CtBP1 in the pathophysiology of glioma remains unknown. In the present study, we showed the expression of CtBP1 was markedly higher in glioma tissues compared with normal brain tissues by Western blot analysis. Immunohistochemical analysis revealed that CtBP1 mainly localized in the nucleus of glioma cells. Statistical analysis suggested the upregulation of CtBP1 was considerably correlated with the WHO grade (P < 0.05) and those patients with high CtBP1 levels exhibited shorter survival time (P < 0.01). Silencing CtBP1 by short hairpin RNAi caused an inhibition of cell migration. Moreover, knockdown of CtBP1 increases E-cadherin expression and decreases vimentin expression. These data uncovered that CtBP1 protein is a valuable marker of glioma pathogenic process and that CtBP1 can serve as a novel prognostic marker for glioma therapy.

MicroRNA networks regulated by all-trans retinoic acid and Lapatinib control the growth, survival and motility of breast cancer cells

SKBR3-cells, characterized by ERBB2/RARA co-amplification, represent a subgroup of HER2⁺ breast-cancers sensitive to all-trans retinoic acid (ATRA) and Lapatinib. In this model, the two agents alone or in combination modulate the expression of 174 microRNAs (miRs). These miRs and predicted target-transcripts are organized in four interconnected modules (Module-1 to -4). Module-1 and Module-3 consist of ATRA/Lapatinib up-regulated and potentially anti-oncogenic miRs, while Module-2 contains ATRA/Lapatinib down-regulated and potentially pro-oncogenic miRs. Consistent with this, the expression levels of Module-1/-3 and Module-2 miRs are higher and lower, respectively, in normal mammary tissues relative to ductal-carcinoma-in-situ, invasive-ductal-carcinoma and metastases. This indicates associations between tumor-progression and the expression profiles of Module-1 to -3 miRs. Similar associations are observed with tumor proliferation-scores, staging, size and overall-survival using TCGA (The Cancer Genome Atlas) data. Forced expression of Module-1 miRs, (miR-29a-3p; miR-874-3p) inhibit SKBR3-cell growth and Module-3 miRs (miR-575; miR-1225-5p) reduce growth and motility. Module-2 miRs (miR-125a; miR-193; miR-210) increase SKBR3 cell growth, survival and motility. Some of these effects are of general significance, being replicated in other breast cancer cell lines representing the heterogeneity of this disease. Finally, our study demonstrates that HIPK2-kinase and the PLCXD1-phospholipase-C are novel targets of miR-193a-5p/miR-210-3p and miR-575/miR-1225-5p, respectively.

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.

The role of cullin 5-containing ubiquitin ligases

The suppressor of cytokine signaling (SOCS) box consists of the BC box and the cullin 5 (Cul5) box, which interact with Elongin BC and Cul5, respectively. SOCS box-containing proteins have ubiquitin ligase activity mediated by the formation of a complex with the scaffold protein Cul5 and the RING domain protein Rbx2, and are thereby members of the cullin RING ligase superfamily. Cul5-type ubiquitin ligases have a variety of substrates that are targeted for polyubiquitination and proteasomal degradation. Here, we review the current knowledge on the identification of Cul5 and the regulation of its expression, as well as the signaling pathways regulated by Cul5 and how viruses highjack the Cul5 system to overcome antiviral responses.

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.

ZEB1 and TCF4 reciprocally modulate their transcriptional activities to regulate Wnt target gene expression

The canonical Wnt pathway (TCF4/β-catenin) has important roles during normal differentiation and in disease. Some Wnt functions depend on signaling gradients requiring the pathway to be tightly regulated. A key Wnt target is the transcription factor ZEB1 whose expression by cancer cells promotes tumor invasiveness by repressing the expression of epithelial specification markers and activating mesenchymal genes, including a number of Wnt targets such as LAMC2 and uPA. The ability of ZEB1 to activate/repress its target genes depends on its recruitment of corepressors (CtBP, BRG1) or coactivators (p300) although conditions under which ZEB1 binds these cofactors are not elucidated. Here, we show that TCF4 and ZEB1 reciprocally modulate each other's transcriptional activity: ZEB1 enhances TCF4/β-catenin-mediated transcription and, in turn, Wnt signaling switches ZEB1 from a repressor into an activator. In colorectal cancer (CRC) cells with active Wnt signaling, ZEB1 enhances transcriptional activation of LAMC2 and uPA by TCF4/β-catenin. However, in CRC cells with inactive Wnt, ZEB1 represses both genes. Reciprocal modulation of ZEB1 and TCF4 activities involves their binding to DNA and mutual interaction. Wnt signaling turns ZEB1 into an activator by replacing binding of CtBP/BRG1 in favor of p300. Using a mouse model of Wnt-induced intestinal tumorigenesis, we found that downregulation of ZEB1 reduces the expression of LAMC2 in vivo. These results identify a mechanism through which Wnt and ZEB1 transcriptional activities are modulated, offering new approaches in cancer therapy.