The long noncoding RNA OTUD6B-AS1 enhances cell proliferation and the invasion of hepatocellular carcinoma cells through modulating GSKIP/Wnt/ß-catenin signalling via the sequestration of miR-664b-3p.

Ovarian tumour domain containing 6B antisense RNA1 (OTUD6B-AS1), a newly identified long noncoding RNA (lncRNA), has been reported as a key cancer-related lncRNA. However, the detailed relevance of OTUD6B-AS1 in hepatocellular carcinoma (HCC) remains undetermined. This study was designed to determine the functional significance and regulatory mechanism of OTUD6B-AS1 in HCC. We found that the expression of OTUD6B-AS1 was up-regulated in HCC tissues, and patients with high levels of OTUD6B-AS1 expression had shorter survival rates than those with low OTUD6B-AS1 expression. Elevated expression of the lncRNA was also found in multiple HCC cell lines and the silencing of OTUD6B-AS1 significantly decreased proliferation, colony formation and invasion. Correspondingly, OTUD6B-AS1 overexpression had the opposite effect on HCC cell invasion, colony formation and proliferation. Notably, OTUD6B-AS1 was identified as a molecular sponge of microRNA-664b-3p (miR-664b-3p). The down-regulation of miR-664b-3p was detected in HCC tissues and cell lines, and the up-regulation of miR-664b-3p repressed proliferation and invasion in HCC cells by targeting the glycogen synthase kinase-3ß interaction protein (GSKIP). Moreover, OTUD6B-AS1 knockdown or miR-664b-3p up-regulation exerted a suppressive effect on Wnt/ß-catenin signalling via the down-regulation of GSKIP. In addition, GSKIP overexpression markedly reversed OTUD6B-AS1 knockdown- or miR-664b-3p overexpression-induced antitumour effects in HCC. Further data confirmed that OTUD6B-AS1 knockdown exerted a tumour-inhibition role in HCC in vivo. Overall, these findings indicate that the lncRNA OTUD6B-AS1 accelerates the proliferation and invasion of HCC cells by enhancing GSKIP/Wnt/ß-catenin signalling via the sequestration of miR-664b-3p. Our study reveals a novel molecular mechanism, mediated by lncRNA OTUD6B-AS1, which may play a key role in regulating the progression of HCC.

GSKIP protects cardiomyocytes from hypoxia/reoxygenation-induced injury by enhancing Nrf2 activation via GSK-3ß inhibition.

Glycogen synthase kinase (GSK)-3ß interaction protein (GSKIP), a key regulator of signaling transduction, is implicated in multiple pathological processes. However, whether GSKIP is involved in myocardial infarction is unknown. The present study was designed to determine the potential involvement of GSKIP in myocardial hypoxia/reoxygenation (H/R) injury, as an in vitro model for the study of myocardial infarction. Our data showed that H/R treatment triggered a marked decrease in GSKIP expression in cardiomyocytes. The upregulation of GSKIP significantly rescued the decreased viability of H/R-exposed cardiomyocytes and attenuated H/R-induced apoptosis and reactive oxygen species (ROS) generation. On the contrary, the depletion of GSKIP enhanced the sensitivity of cardiomyocytes to H/R-induced injury. Further data exhibited that GSKIP overexpression upregulated the nuclear expression of nuclear factor-erythroid-derived 2-related factor 2 (Nrf2) and increased Nrf2/antioxidant response element (ARE)-mediated transcription activity associated with upregulation of GSK-3ß phosphorylation. Interestingly, inhibition of GSK-3ß by a chemical inhibitor markedly enhanced Nrf2/ARE activation and abrogated GSKIP depletion-exacerbated sensitivity to H/R-induced injury. In addition, Nrf2 inhibition markedly reversed GSKIP overexpression-induced cardioprotective effect against H/R injury. Overall, these results demonstrate that overexpression of GSKIP alleviates H/R-induced apoptosis and oxidative stress in cardiomyocytes by enhancing Nrf2/ARE antioxidant signaling via GSK-3ß inhibition. Our study indicates a potential role of GSKIP in myocardial infarction and GSKIP may serve as a promising molecular target for cardioprotection.

The origin of GSKIP, a multifaceted regulatory factor in the mammalian Wnt pathway.

GSK3ß interacting protein (GSKIP) is a naturally occurring negative regulator of GSK3ß and retains both the Protein Kinase A Regulatory subunit binding (PKA-RII) domain and GSK3ß interacting domain. Of these two domains, we found that PKA-RII is required for forming a working complex comprising PKA/GSKIP/GSK3ß/Drp1 to influence phosphorylation of Drp1 Ser637. In this study, bioinformatics and experimental explorations re-analyzing GSKIP's biofunctions suggest that the evolutionarily conserved Domain of Unknown Function (DUF727) is an ancestral prototype of GSKIP in prokaryotes, and acquired the C-terminal GSK3ß binding site (tail) in invertebrates except for Saccharomyces spp., after which the N-terminal PKA-RII binding region (head) evolved in vertebrates. These two regions mutually influence each other and modulate GSKIP binding to GSK3ß in yeast two-hybrid assays and co-immunoprecipitation. Molecular modeling showed that mammalian GSKIP could form a dimer through the L130 residue (GSK3ß binding site) rather than V41/L45 residues. In contrast, V41/L45P mutant facilitated a gain-of-function effect on GSKIP dimerization, further influencing binding behavior to GSK3ß compared to GSKIP wild-type (wt). The V41/L45 residues are not only responsible for PKA RII binding that controls GSK3ß activity, but also affect dimerization of GSKIP monomer, with net results of gain-of-function in GSKIP-GSK3ß interaction. In addition to its reported role in modulating Drp1, Ser637 phosphorylation caused mitochondrial elongation; we postulated that GSKIP might be involved in the Wnt signaling pathway as a scavenger to recruit GSK3ß away from the ß-catenin destruction complex and as a competitor to compete for GSK3ß binding, resulting in accumulation of S675 phosphorylated ß-catenin.

Loss of PPARγ in endothelial cells leads to impaired angiogenesis.

Tie2-promoter-mediated loss of peroxisome proliferator-activated receptor gamma (PPARγ, also known as PPARG) in mice leads to osteopetrosis and pulmonary arterial hypertension. Vascular disease is associated with loss of PPARγ in pulmonary microvascular endothelial cells (PMVEC); we evaluated the role of PPARγ in PMVEC functions, such as angiogenesis and migration. The role of PPARγ in angiogenesis was evaluated in Tie2CrePPARγ(flox/flox) and wild-type mice, and in mouse and human PMVECs. RNA sequencing and bioinformatic approaches were utilized to reveal angiogenesis-associated targets for PPARγ. Tie2CrePPARγ(flox/flox) mice showed an impaired angiogenic capacity. Analysis of endothelial progenitor-like cells using bone marrow transplantation combined with evaluation of isolated PMVECs revealed that loss of PPARγ attenuates the migration and angiogenic capacity of mature PMVECs. PPARγ-deficient human PMVECs showed a similar migration defect in culture. Bioinformatic and experimental analyses newly revealed E2F1 as a target of PPARγ in the regulation of PMVEC migration. Disruption of the PPARγ-E2F1 axis was associated with a dysregulated Wnt pathway related to the GSK3B interacting protein (GSKIP). In conclusion, PPARγ plays an important role in sustaining angiogenic potential in mature PMVECs through E2F1-mediated gene regulation.

The A-Kinase Anchoring Protein (AKAP) Glycogen Synthase Kinase 3ß Interaction Protein (GSKIP) Regulates ß-Catenin through Its Interactions with Both Protein Kinase A (PKA) and GSK3ß.

The A-kinase anchoring protein (AKAP) GSK3ß interaction protein (GSKIP) is a cytosolic scaffolding protein binding protein kinase A (PKA) and glycogen synthase kinase 3ß (GSK3ß). Here we show that both the AKAP function of GSKIP, i.e. its direct interaction with PKA, and its direct interaction with GSK3ß are required for the regulation of ß-catenin and thus Wnt signaling. A cytoplasmic destruction complex targets ß-catenin for degradation and thus prevents Wnt signaling. Wnt signals cause ß-catenin accumulation and translocation into the nucleus, where it induces Wnt target gene expression. GSKIP facilitates control of the ß-catenin stabilizing phosphorylation at Ser-675 by PKA. Its interaction with GSK3ß facilitates control of the destabilizing phosphorylation of ß-catenin at Ser-33/Ser-37/Thr-41. The influence of GSKIP on ß-catenin is explained by its scavenger function; it recruits the kinases away from the destruction complex without forming a complex with ß-catenin. The regulation of ß-catenin by GSKIP is specific for this AKAP as AKAP220, which also binds PKA and GSK3ß, did not affect Wnt signaling. We find that the binding domain of AKAP220 for GSK3ß is a conserved GSK3ß interaction domain (GID), which is also present in GSKIP. Our findings highlight an essential compartmentalization of both PKA and GSK3ß by GSKIP, and ascribe a function to a cytosolic AKAP-PKA interaction as a regulatory factor in the control of canonical Wnt signaling. Wnt signaling controls different biological processes, including embryonic development, cell cycle progression, glycogen metabolism, and immune regulation; deregulation is associated with diseases such as cancer, type 2 diabetes, inflammatory, and Alzheimer's and Parkinson's diseases.

LncRNA HANR Promotes Tumorigenesis and Increase of Chemoresistance in Hepatocellular Carcinoma.

BACKGROUND/AIMS: Hepatocellular carcinoma (HCC) is the fifth most common cancer in the world and the third leading cause of cancer-related death. Critical roles for long non-coding RNAs (lncRNAs) have recently been demonstrated for a variety of cancers, including hepatocellular carcinoma. However, the effect and mechanism of lncRNAs in HCC tumorigenesis and chemoresistance have not been extensively characterized. METHODS: In the current study, we have identified a HCC-expressed lncRNA termed as HANR (HCC associated long non-coding RNA). We identified HANR by microarray analysis and validated its up-regulated expression by quantitative PCR. RNA pull-down and pathway analyses were conducted to evaluate physical and functional interactions with HANR. In vivo experiments were performed to assess tumorigenesis and increase of chemoresistance. In addition, the HANR expression in HCC specimens was detected by FISH. Xenograft and orthotopic mice model was constructed to observe the effect of HANR on tumorigenesis and chemoresistance in vivo. RESULTS: HANR was demonstrated to be up-regulated in HCC patients and HCC cell lines. Increased HANR expression in HCC predicted short survival of patients. Knock-down of HANR markedly retarded cell proliferation, suppressed HCC xenograft/orthotopic tumor growth, induced apoptosis and enhanced chemosensitivity to doxorubicin, while over-expression of HANR showed the opposite effects. It was found that HANR bind to GSKIP for regulating the phosphorylation of GSK3ß in HCC. CONCLUSION: Our results demonstrate that HANR contributes to the development of HCC and is a promising therapeutic target for chemosensitization of HCC cells to doxorubicin, which may represent a promising therapeutic target in the future.

GSKIP- and GSK3-mediated anchoring strengthens cAMP/PKA/Drp1 axis signaling in the regulation of mitochondrial elongation.

GSK3ß binding of GSKIP affects neurite outgrowth, but the physiological significance of PKA binding to GSKIP remains to be determined. We hypothesized that GSKIP and GSK3ß mediate cAMP/PKA/Drp1 axis signaling and modulate mitochondrial morphology by forming a working complex comprising PKA/GSKIP/GSK3ß/Drp1. We demonstrated that GSKIP wild-type overexpression increased phosphorylation of Drp1 S637 by 7-8-fold compared to PKA kinase-inactive mutants (V41/L45) and a GSK3ß binding-defective mutant (L130) under H2O2 and forskolin challenge in HEK293 cells, indicating that not only V41/L45, but also L130 may be involved in Drp1-associated protection of GSKIP. Interestingly, silencing either GSKIP or GSK3ß but not GSK3α resulted in a dramatic decrease in Drp1 S637 phosphorylation, revealing that both GSKIP and GSK3ß are required in this novel PKA/GSKIP/GSK3ß/Drp1 complex. Moreover, overexpressed kinase-dead GSK3ß-K85R, which retains the capacity to bind GSKIP, but not K85M which shows total loss of GSKIP-binding, has a higher Drp1 S637 phosphorylation similar to the GSKIP wt overexpression group, indicating that GSK3ß recruits Drp1 by anchoring rather than in a kinase role. With further overexpression of either V41/L45P or the L130P GSKIP mutant, the elongated mitochondrial phenotype was lost; however, ectopically expressed Drp1 S637D, a phosphomimetic mutant, but not S637A, a non-phosphorylated mutant, restored the elongated mitochondrial morphology, indicating that Drp1 is a downstream effector of direct PKA signaling and possibly has an indirect GSKIP function involved in the cAMP/PKA/Drp1 signaling axis. Collectively, our data revealed that both GSKIP and GSK3ß function as anchoring proteins in the cAMP/PKA/Drp1 signaling axis modulating Drp1 phosphorylation.

GSKIP modulates cell aggregation through EMT/MET signaling rather than differentiation in SH-SY5Y human neuroblastoma cells.

GSK3ß interacting protein (GSKIP) is a small A-kinase anchor protein previously reported to mediate the N-cadherin/ß-catenin pool for differentiation in SH-SY5Y cells through overexpression of GSKIP to present the neuron outgrowth phenotype. To further investigate how GSKIP functions in neurons, CRISPR/Cas9 technology was utilized to knock out GSKIP (GSKIP-KO) in SH-SY5Y. Several GSKIP-KO clones resulted in an aggregation phenotype and reduced cell growth without retinoic acid (RA) treatment. However, neuron outgrowth was still observed in GSKIP-KO clones treated with RA. The GSKIP-KO clones exhibited an aggregation phenotype through suppression of GSK3ß/ß-catenin pathways and cell cycle progression rather than cell differentiation. Gene set enrichment analysis indicated that GSKIP-KO was related to epithelial mesenchymal transition/mesenchymal epithelial transition (EMT/MET) and Wnt/ß-catenin/cadherin signaling pathways, suppressing cell migration and tumorigenesis through the inhibition of Wnt/ß-catenin mediated EMT/MET. Conversely, reintroduction of GSKIP into GSKIP-KO clones restored cell migration and tumorigenesis. Notably, phosphor-ß-catenin (S675) and ß-catenin (S552) but not phosphor-ß-catenin (S33/S37/T41) translocated into the nucleus for further gene activation. Collectively, these results suggested that GSKIP may function as an oncogene to form an aggregation phenotype for cell survival in harsh environments through EMT/MET rather than differentiation in the GSKIP-KO of SH-SY5Y cells. GSKIP Implication in Signaling Pathways with Potential Impact on SHSY-5Y Cell Aggregation.

Many faces and functions of GSKIP: a temporospatial regulation view.

Glycogen synthase kinase 3 (GSK3)-ß (GSK3ß) interaction protein (GSKIP) is one of the smallest A-kinase anchoring proteins that possesses a binding site for GSK3ß. Recently, our group identified the protein kinase A (PKA)-GSKIP-GSK3ß-X axis; knowledge of this axis may help us decipher the many roles of GSKIP and perhaps help explain the evolutionary reason behind the interaction between GSK3ß and PKA. In this review, we highlight the critical and multifaceted role of GSKIP in facilitating PKA kinase activity and its function as a scaffolding protein in signaling pathways. We also highlight how these pivotal PKA and GSK3 kinases can control context-specific functions and interact with multiple target proteins, such as ß-catenin, Drp1, Tau, and other proteins. GSKIP is a key regulator of multiple mechanisms because of not only its location at certain subcellular compartments but also its serial changes during the developmental process. Moreover, the involvement of critical upstream regulatory signaling pathways in GSKIP signaling in various cancers, such as miRNA (microRNA) and lncRNA (long noncoding RNA), may help in the identification of therapeutic targets in the era of precision medicine and personalized therapy. Finally, we emphasize on the model of the early stage of pathogenesis of Alzheimer Disease (AD). Although the model requires validation, it can serve as a basis for diagnostic biomarkers development and drug discovery for early-stage AD.

Loss of Atg2b and Gskip Impairs the Maintenance of the Hematopoietic Stem Cell Pool Size.

A germ line copy number duplication of chromosome 14q32, which contains ATG2B and GSKIP, was identified in families with myeloproliferative neoplasm (MPN). Here, we show that mice lacking both Atg2b and Gskip, but not either alone, exhibited decreased hematopoiesis, resulting in death in utero accompanied by anemia. In marked contrast to MPN patients with duplication of ATG2B and GSKIP, the number of hematopoietic stem cells (HSCs), in particular long-term HSCs, in double-knockout fetal livers was significantly decreased due to increased cell death. Although the remaining HSCs still had the ability to differentiate into hematopoietic progenitor cells, the differentiation efficiency was quite low. Remarkably, mice with knockout of Atg2b or Gskip alone did not show any hematopoietic abnormality. Mechanistically, while loss of both genes had no effect on autophagy, it increased the expression of genes encoding enzymes involved in oxidative phosphorylation. Taken together, our results indicate that Atg2b and Gskip play a synergistic effect in maintaining the pool size of HSCs.

Variation in the Ovine Glycogen Synthase Kinase 3 Beta-Interaction Protein Gene (GSKIP) Affects Carcass and Growth Traits in Romney Sheep.

The glycogen synthase kinase 3 beta (GSK3ß)-interacting protein (encoded by the gene GSKIP) is a small A-kinase anchoring protein, which complexes with GSK3ßand protein kinase A (PKA) and acts synergistically with cAMP/PKA signaling to inhibit GSK3ß activity. The protein plays a role in regulating glycogen metabolism, protein synthesis, the cell cycle, and in regulating gene expression. In this study, PCR-single strand conformation polymorphism (PCR-SSCP) analyses were used to screen for variation in exon 1 and exon 2 of GSKIP in 840 New Zealand (NZ) Romney sheep. Two SSCP banding patterns representing two different nucleotide variants (A and B) were detected in an exon 1 region, whereas in an exon 2 region only one pattern was detected. Variants A and B of exon 1 had one non-synonymous nucleotide difference c.37A/G (p.Met13Val). The birthweight of sheep of genotype AA (5.9 ± 0.06 kg) was different (p = 0.023) to sheep of genotype AB (5.7 ± 0.06 kg) and BB (5.7 ± 0.06 kg). The hot carcass weight (HCW) of sheep of genotype AA (17.2 ± 0.22 kg) was different (p = 0.012) to sheep of genotype AB (17.6 ± 0.22 kg) and BB (18.0 ± 0.29 kg), and the fat depth at the 12th rib (V-GR) of sheep of genotype AA (7.7 ± 0.31 mm) was different (p = 0.016) to sheep of genotype AB (8.3 ± 0.30 mm) and BB (8.5 ± 0.39 mm). The results suggest that the c.37A/G substitution in ovine GSKIP may affect sheep growth and carcass traits.

GSKIP-Mediated Anchoring Increases Phosphorylation of Tau by PKA but Not by GSK3beta via cAMP/PKA/GSKIP/GSK3/Tau Axis Signaling in Cerebrospinal Fluid and iPS Cells in Alzheimer Disease.

Based on the protein kinase A (PKA)/GSK3ß interaction protein (GSKIP)/glycogen synthase kinase 3ß (GSK3ß) axis, we hypothesized that these might play a role in Tau phosphorylation. Here, we report that the phosphorylation of Tau Ser409 in SHSY5Y cells was increased by overexpression of GSKIP WT more than by PKA- and GSK3ß-binding defective mutants (V41/L45 and L130, respectively). We conducted in vitro assays of various kinase combinations to show that a combination of GSK3ß with PKA but not Ca2+/calmodulin-dependent protein kinase II (CaMK II) might provide a conformational shelter to harbor Tau Ser409. Cerebrospinal fluid (CSF) was evaluated to extend the clinical significance of Tau phosphorylation status in Alzheimer's disease (AD), neurological disorders (NAD), and mild cognitive impairment (MCI). We found higher levels of different PKA-Tau phosphorylation sites (Ser214, Ser262, and Ser409) in AD than in NAD, MCI, and normal groups. Moreover, we used the CRISPR/Cas9 system to produce amyloid precursor protein (APPWT/D678H) isogenic mutants. These results demonstrated an enhanced level of phosphorylation by PKA but not by the control. This study is the first to demonstrate a transient increase in phosphor-Tau caused by PKA, but not GSK3ß, in the CSF and induced pluripotent stem cells (iPSCs) of AD, implying that both GSKIP and GSK3ß function as anchoring proteins to strengthen the cAMP/PKA/Tau axis signaling during AD pathogenesis.

ATG2B and GSKIP: 2 new genes predisposing to myeloid malignancies.

We have recently identified a 700-kb tandem duplication at locus 14q32.13-q32.2 involving 2 genes, autophagy-related protein 2 homolog B (ATG2B) and GSK3B interacting protein (GSKIP), that increases the predisposition to myeloid malignancies. Here, we discuss the clinical relevance of these findings.

Myelodysplastic syndromes and acute leukemia with genetic predispositions: a new challenge for hematologists.

INTRODUCTION: The determination of an underlying genetic predisposition is not automatically part of the diagnosis of hematological malignancies (HM) in routine practice. However, it is assumed that genetic predispositions to HM are currently underestimated due to great variations in disease phenotype, variable latency and incomplete penetrance. Most of patients do not display any biological or clinical signs besides the overt hematological disease and many of them have a lack of personal or family history of malignancies. Areas covered: Collaborative studies and important advances in molecular testing have led to the discovery of several genes recurrently deregulated in familial HM including RUNX1, CEBPA, GATA2, ANKRD26, SRP72, PAX5, DDX41, ETV6, ATG2B/GSKIP and TERT/TERC. This review summarizes biological and clinical findings encountered within these disorders. Expert commentary: Identify and manage individuals with genetic predisposition is a current challenge for hematologists. Their identification has immediate implications for hematopoietic stem cell transplantation including donor selection and conditioning regimen. Importantly, several features, including familial and personal history as well as molecular and cytogenetic findings, may help clinicians to suspect an underlying genetic predisposition.