Role for the pleckstrin homology domain-containing protein CKIP-1 in AP-1 regulation and apoptosis

The Transcription Factor ATF2 Accelerates Clear Cell Renal Cell Carcinoma Progression Through Activating the PLEKHO1/NUS1 Pathway

Clear cell renal cell carcinoma (ccRCC) is a common malignant cancer with high mortality rate. Activating transcription factor 2 (ATF2) and pleckstrin homology domain containing O1 (PLEKHO1) were reported to participate in numerous cancers. However, their roles and the detailed mechanisms in ccRCC development remain largely unknown. RT-qPCR and western blot were used to measure the levels of PLEKHO1, ATF2, and nuclear undecaprenyl pyrophosphate synthase 1 (NUS1). Cell proliferation, apoptosis, invasion, migration and stemness were evaluated using CCK-8 assay, flow cytometry, transwell invasion assay, wound-healing assay and sphere formation assay, respectively. Dual-luciferase reporter assay was conducted to verify the relationship between ATF2 and PLEKHO1. The interaction between PLEKHO1 and NUS1 was proved by Co-IP assay. Xenograft models were utilized to evaluate the tumorigenic capability of ccRCC cells upon PLEKHO1 knockdown. PLEKHO1, ATF2 and NUS1 expression were significantly elevated in ccRCC, and PLEKHO1 might be a prognosis biomarker for ccRCC. PLEKHO1 depletion significantly inhibited cell proliferation, invasion, migration, stemness, and induced cell apoptosis in ccRCC cells. ATF2 activated PLEKHO1 expression via transcription regulation, and PLEKHO1 overexpression could reverse the suppressive effects of ATF2 knockdown on the malignant behaviors of ccRCC cells. Moreover, PLEKHO1 directly bound to NUS1, and PLEKHO1 depletion markedly restrained ccRCC progression through targeting NUS1 in vitro and in vivo. Our findings suggested that ATF2 transcriptionally activated PLEKHO1 to promote the development of ccRCC via regulating NUS1 expression.

Modulating PAK1: Accessory Proteins as Promising Therapeutic Targets

The p21-activated kinase (PAK1), a serine/threonine protein kinase, is critical in regulating various cellular processes, including muscle contraction, neutrophil chemotaxis, neuronal polarization, and endothelial barrier function. Aberrant PAK1 activity has been implicated in the progression of several human diseases, including cancer, heart disease, and neurological disorders. Increased PAK1 expression is often associated with poor clinical prognosis, invasive tumor characteristics, and therapeutic resistance. Despite its importance, the cellular mechanisms that modulate PAK1 function remain poorly understood. Accessory proteins, essential for the precise assembly and temporal regulation of signaling pathways, offer unique advantages as therapeutic targets. Unlike core signaling components, these modulators can attenuate aberrant signaling without completely abolishing it, potentially restoring signaling to physiological levels. This review highlights PAK1 accessory proteins as promising and novel therapeutic targets, opening new horizons for disease treatment.

The Discovery of a Specific CKIP-1 Ligand for the Potential Treatment of Disuse Osteoporosis

Bone homeostasis relies on the delicate balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. The casein kinase 2 interacting protein-1 (CKIP-1), a specific CK2α subunit-interacting protein, has been documented as one of the crucial negative regulators of bone formation. CKIP-1 siRNA therapy has constraints that limit its use in clinical applications. Therefore, it is necessary to explore effective targeting strategies for CKIP-1. In this study, we observed an upregulation of CKIP-1 protein expression in the microgravity environment, while its ubiquitination levels decreased. We further investigated the interaction between CKIP-1 and VHL and found that VHL enhanced CKIP-1 degradation through the ubiquitylation-proteasome system (UPS). Additionally, we discovered a small molecule ligand, named C77, through DNA-encoded library (DEL) screening, which binds to CKIP-1 both in vivo and in vitro, as confirmed by Surface Plasmon Resonance (SPR) and the Cellular Thermal shift assay (CETSA), respectively. Our findings demonstrated the potential of VHL and C77 as guiding factors in the development of CKIP-1-based Proteolysis-Targeting Chimeras (PROTACs), which could be future therapeutic interventions in disuse osteoporosis.

Genome-wide expression analysis in a Fabry disease human podocyte cell line

Fabry disease (FD) is an X-linked lysosomal disease caused by an enzyme deficiency of alpha-galactosidase A (α-gal A). This deficiency leads to the accumulation of glycosphingolipids in lysosomes, resulting in a range of clinical symptoms. The complex pathogenesis of FD involves lysosomal dysfunction, altered autophagy, and mitochondrial abnormalities. Omics sciences, particularly transcriptomic analysis, comprehensively understand molecular mechanisms underlying diseases. This study focuses on genome-wide expression analysis in an FD human podocyte model to gain insights into the underlying mechanisms of podocyte dysfunction. Human control and GLA-edited podocytes were used. Gene expression data was generated using RNA-seq analysis, and differentially expressed genes were identified using DESeq2. Principal component analysis and Spearman correlation have explored gene expression trends. Functional enrichment and Reporter metabolite analyses were conducted to identify significantly affected metabolites and metabolic pathways. Differential expression analysis revealed 247 genes with altered expression levels in GLA-edited podocytes compared to control podocytes. Among these genes, 136 were underexpressed, and 111 were overexpressed in GLA-edited cells. Functional analysis of differentially expressed genes showed their involvement in various pathways related to oxidative stress, inflammation, fatty acid metabolism, collagen and extracellular matrix homeostasis, kidney injury, apoptosis, autophagy, and cellular stress response. The study provides insights into molecular mechanisms underlying Fabry podocyte dysfunction. Integrating transcriptomics data with genome-scale metabolic modeling further unveiled metabolic alterations in GLA-edited podocytes. This comprehensive approach contributes to a better understanding of Fabry disease and may lead to identifying new biomarkers and therapeutic targets for this rare lysosomal disorder.

Ckip-1 3'UTR alleviates prolonged sleep deprivation induced cardiac dysfunction by activating CaMKK2/AMPK/cTNI pathway

Sleep deprivation (SD) has emerged as a critical concern impacting human health, leading to significant damage to the cardiovascular system. However, the underlying mechanisms are still unclear, and the development of targeted drugs is lagging. Here, we used mice to explore the effects of prolonged SD on cardiac structure and function. Echocardiography analysis revealed that cardiac function was significantly decreased in mice after five weeks of SD. Real-time quantitative PCR (RT-q-PCR) and Masson staining analysis showed that cardiac remodeling marker gene Anp (atrial natriuretic peptide) and fibrosis were increased, Elisa assay of serum showed that the levels of creatine kinase (CK), creatine kinase-MB (CK-MB), ANP, brain natriuretic peptide (BNP) and cardiac troponin T (cTn-T) were increased after SD, suggesting that cardiac remodeling and injury occurred. Transcript sequencing analysis indicated that genes involved in the regulation of calcium signaling pathway, dilated cardiomyopathy, and cardiac muscle contraction were changed after SD. Accordingly, Western blotting analysis demonstrated that the cardiac-contraction associated CaMKK2/AMPK/cTNI pathway was inhibited. Since our preliminary research has confirmed the vital role of Casein Kinase-2 -Interacting Protein-1 (CKIP-1, also known as PLEKHO1) in cardiac remodeling regulation. Here, we found the levels of the 3' untranslated region of Ckip-1 (Ckip-1 3'UTR) decreased, while the coding sequence of Ckip-1 (Ckip-1 CDS) remained unchanged after SD. Significantly, adenovirus-mediated overexpression of Ckip-1 3'UTR alleviated SD-induced cardiac dysfunction and remodeling by activating CaMKK2/AMPK/cTNI pathway, which proposed the therapeutic potential of Ckip-1 3'UTR in treating SD-induced heart disease.

Paeonol can improve hypoxic-induced H9c2 cells injury and ion channel activity by up-regulating the expression of CKIP-1

BACKGROUND

Paeonol is a representative active ingredient of the traditional Chinese medicinal herbs Cortex Moutan, which has a well-established cardioprotective effect on ischemic heart disease. However, there is little evidence of the protective effect of paeonol, and its pharmacological mechanism is also unclear. This study aims to explore the protective effect and mechanism of Paeonol on myocardial infarction rat and hypoxic H9c2 cells.

METHODS

Myocardial ischemia/reperfusion (I/R) was induced by occlusion of the left anterior descending coronary artery for 1 h followed by 3 h of reperfusion, and then gavage with Paeonol for 7 days. H9c2 cells were applied for the in vitro experiments and hypoxia/reoxygenation (H/R) model was established. CKIP-1 expression was evaluated by qPCR and western blot. The expression of genes involved in apoptosis, inflammation and ion channel was measured by western blot. The currents levels of Nav1.5 and Kir2.1 were measured by whole-cell patch-clamp recording.

RESULTS

CKIP-1 expression was decreased in H/R-induced H9c2 cells, which was inversely increased after Paeonol treatment. Paeonol treatment could increase the viability of H/R-induced H9c2 cells and diminish the apoptosis and inflammation of H/R-induced H9c2 cells, while si-CKIP-1 treatment inhibited the phenomena. Moreover, the currents levels of Nav1.5 and Kir2.1 were reduced in H/R-induced H9c2 cells, which were inhibited after Paeonol treatment. Intragastric Paeonol can reduce the ventricular arrhythmias in rats with myocardial infarction.

CONCLUSIONS

The protective effects of Paeonol on myocardial infarction rats and hypoxic H9c2 cells were achieved by up-regulating CKIP-1.

CKIP-1 mediates P. gingivalis-suppressed osteogenic/cementogenic differentiation of periodontal ligament cells partially via p38 signaling pathway

OBJECTIVES

Casein kinase 2 interacting protein-1 (CKIP-1) is a versatile player involved in various biological processes. However, whether CKIP-1 mediates the osteogenic/cementogenic differentiation of periodontal ligament cells (PDLCs) under Porphyromonas gingivalis (Pg) stimulation remains unknown.

MATERIAL AND METHODS

The effect of Pg on PDLC differentiation was first verified. CKIP-1 expression in Pg-infected PDLCs or in PDL of apical periodontitis (AP) mice was detected. The changes of CKIP-1 during PDLC differentiation was also determined. PDLC differentiation capacity in CKIP-1 knockout (KO) mice and CKIP-1-silenced PDLCs with or without Pg stimulation were further studied. Inhibitor was finally applied to verify the involvement of p38 signaling pathway in PDLC differentiation.

RESULTS

The suppression effect of Pg on PDLC differentiation was demonstrated. CKIP-1 increased in the PDL of AP mice and Pg-induced PDLCs, and decreased gradually during PDLC differentiation. Increased OSX and RUNX2 expression in PDL were observed in CKIP-1 KO mice. Also, CKIP-1 silencing facilitated and rescued Pg-inhibited PDLC differentiation. Inhibitor for p38 signaling pathway blocked CKIP-1 silencing-facilitated PDLC differentiation.

CONCLUSIONS

CKIP-1 mediated the osteogenic/cementogenic differentiation of PDLCs partially through p38 signaling pathway, which may provide evidence for the regeneration of periodontal hard tissues damaged by Pg.

Dysregulation of microRNA and Intracerebral Hemorrhage: Roles in Neuroinflammation

Intracerebral hemorrhage (ICH) is a major public health problem and devastating subtype of stroke with high morbidity and mortality. Notably, there is no effective treatment for ICH. Neuroinflammation, a pathological hallmark of ICH, contributes to both brain injury and repair and hence, it is regarded as a potential target for therapeutic intervention. Recent studies document that microRNAs, small non-coding RNA molecules, can regulate inflammatory brain response after ICH and are viable molecular targets to alter brain function. Therefore, there is an escalating interest in studying the role of microRNAs in the pathophysiology of ICH. Herein, we provide, for the first time, an overview of the microRNAs that play roles in ICH-induced neuroinflammation and identify the critical knowledge gap in the field, as it would help design future studies.

PLEKHO2 inhibits TNFα-induced cell death by suppressing RIPK1 activation

Receptor interaction protein kinase 1 (RIPK1) plays a diverse role in tumor necrosis factor α (TNFα) signalings. The ubiquitination of RIPK1 is essential for NF-κB activation, whereas its kinase activity promotes apoptosis and necroptosis. However, the mechanisms underlying have not been fully illuminated. Here we report that PH domain-containing family O member 2 (PLEKHO2) inhibits RIPK1-dependent cell death and is necessary for NF-κB activation in response to TNFα. Cells of PLKEHO2 deficiency are more susceptible to TNF-α induced apoptosis and necroptosis with increased RIPK1 activation, which is consistent with the observation that the susceptibility of PLEKHO2-/- cells is effectively prevented by treatment of RIPK1 kinase inhibitor. Moreover, PLEKHO2 deficient cells exhibit compromised RIPK1 ubiquitination and NF-κB activation in response to TNFα. Ultimately, PLEKHO2-deficient mice display greatly increased hepatotoxicity and lethality after TNFα-induced hepatitis. In summary, our study revealed that PLEKHO2 is a novel inhibitor of apoptosis and necroptosis, which plays a key role in regulating RIPK1 ubiquitination and activation.

Ckip-1 regulates C3H10T1/2 mesenchymal cell proliferation and osteogenic differentiation via Lrp5

Casein kinase-2 interaction protein-1 (Ckip-1) is a negative regulator of bone formation. The identification of novel Ckip-1-related targets and their associated signaling pathways that regulate mesenchymal stem cell (MSC) osteogenic differentiation is required. The present study aimed to evaluate the effects of Ckip-1 knockdown on C3H10T1/2 MSC proliferation and osteogenic differentiation, and to explore the role of the canonical Wnt-signaling receptor Lrp5. Ckip-1-knockdown (shCkip-1), Ckip-1-overexpression (Ckip-1) and their corresponding control [shCtrl and empty vector (EV), respectively] cell groups were used in the present study. Immunofluorescence localization of Ckip-1 was observed. The expression of the key molecules of the canonical Wnt signaling pathway was examined in C3H10T1/2 cells following osteogenic induction. Moreover, the effects of Lrp5 knockdown in the presence or absence of Ckip-1 knockdown were examined on C3H10T1/2 cell proliferation and osteogenic differentiation. The results indicated an increase in cell proliferation and osteogenic differentiation in the shCkip-1 group compared with the shCtrl group. The expression levels of LDL receptor related protein 5 (Lrp5), lymphoid enhancer binding factor 1 (Lef1) and transcription factor 1 in C3H10T1/2 cells were significantly increased in shCkip-1 cells following 7-day osteoinduction compared with shCtrl cells. Moreover, the involvement of Lrp5 in shCkip-1-induced osteogenic differentiation of C3H10T1/2 cells was further verified. The results indicated that Ckip-1 reduced C3H10T1/2 MSC proliferation and osteogenic differentiation via the canonical Wnt-signaling receptor Lrp5, which is essential for the improvement of bone tissue engineering.

High expression of the CKIP-1 gene might promote apoptosis through downregulation of the Ras/ERK signalling pathway in the intestinal type of gastric cancer

Objective

To investigate the effect of the casein kinase 2 interacting protein 1 (CKIP-1) on the apoptosis of the intestinal type of gastric cancer (GC).

Methods

The levels of CKIP-1 protein and the rates of apoptosis were measured in tissue samples of the intestinal type of GC and human GC cell lines. The rate of apoptosis and the protein levels of B cell lymphoma-2 (Bcl-2), Bcl-2 associated X protein (Bax), cleaved cysteinyl aspartate specific protease 3 (cleaved caspase-3), cleaved caspase-9, rat sarcoma (Ras), extracellular signal-regulated kinase 1 and 2 (ERK1/2) and phosphorylated extracellular signal-regulated kinase 1 and 2 (p-ERK1/2) were analysed in SGC7901 cells expressing CKIP-1 short hairpin RNA (shRNA; knockdown) and SGC7901 cells overexpressing CKIP-1.

Results

The levels of CKIP-1 protein were significantly lower in the intestinal type of GC tissues compared with the samples of intestinal metaplasia. Both the levels of CKIP-1 protein and the levels of apoptosis decreased gradually with decreasing cell differentiation in the intestinal type of GC tissue and cell lines; and they were positively correlated. In the CKIP-1 shRNA group, the rate of apoptosis and the levels of Bax, cleaved caspase-3 and cleaved caspase-9 were decreased; and the levels of Bcl-2, Ras and the ratio of p-ERK/ERK were increased, compared with the control group. Opposite results were observed in the CKIP-1 overexpression group.

Conclusion

High levels of CKIP-1 protein may promote apoptosis in the intestinal type of GC, possibly via the downregulation of the Ras/ERK signalling pathway.

CKIP-1 acts downstream to Cx43 on the activation of Nrf2 signaling pathway to protect from renal fibrosis in diabetes

We previously reported that both Cx43 and CKIP-1 attenuated diabetic renal fibrosis via the activation of Nrf2 signaling pathway. However, whether CKIP-1, a scaffold protein, participates in regulating the activation of Nrf2 signaling pathway by Cx43 remains to be elucidated. In this study, the effect of adenovirus-mediated Cx43 overexpression on renal fibrosis in CKIP-1-/- diabetic mice was investigated. We found that overexpression of Cx43 could significantly alleviate renal fibrosis by activating the Nrf2 pathway in diabetic mice, but have no obvious effect in CKIP-1-/- diabetic mice. Cx43 overexpressed plasmid and CKIP-1 small interfering RNA were simultaneously transfected into glomerular mesangial cells and the result demonstrated that the effect of activation of Nrf2 signaling pathway by Cx43 was blocked by CKIP-1 depletion. The interaction between Cx43 and CKIP-1 was analyzed by immunofluorescence and immunoprecipitation assays. We found that Cx43 interacted with CKIP-1, and the interaction was weakened by high glucose treatment. Moreover, Cx43 regulated the expression of CKIP-1 and the interaction of CKIP-1 with Nrf2 via Cx43 carboxyl terminus (CT) domain, thereby activating Nrf2 signaling pathway. According to the results, we preliminary infer that CKIP-1 acts downstream to CX43 on the activation of Nrf2 signaling pathway to protect from renal fibrosis in diabetes, the mechanism of which might be related to the interaction of CKIP-1 with Nrf2 through Cx43 CT. Our study provides further experimental basis for targeting the Cx43-CKIP-1-Nrf2 axis to resist diabetic renal fibrosis.

CKIP-1 augments autophagy in steatotic hepatocytes by inhibiting Akt/mTOR signal pathway

Nonalcoholic fatty liver disease (NAFLD), which is characterized by aberrant accumulation of intrahepatic triglycerides and lipid droplets (LDs) in the liver cells, is becoming increasingly prevalent at an alarming rate worldwide. LDs can be consumed by either hydrolysis or autophagy, which is shown to be of importance in the regulation of hepatic lipid metabolism. We have shown that deficiency of pleckstrin homology domain-containing casein kinase 2 interacting protein-1 (CKIP-1), a scaffold protein that interacts with various proteins in multiple signal pathways, in mice aggravates high-fat diet induced fatty liver. However, its underlying mechanisms remain largely unknown. In this study, we found that the mRNA and protein levels of CKIP-1 decreased dramatically in steatotic HepG2 cells induced by oleic acid (OA) treatment. Coincidently, hepatic autophagy was also dynamically regulated in steatotic HepG2 cells. In addition, overexpression of CKIP-1 activated autophagy by suppression of Akt/mTOR signaling, which in turn reduced lipid accumulation. Moreover, these phenomena were reversed in CKIP-1-shRNA transfected steatotic hepatocytes. To further evaluate the potential role of CKIP-1 in autophagy, we determined the level of autophagy related proteins in CKIP-1 knockout mice. These results supported our findings in vitro. In summary, we found CKIP-1 to be a positive regulator of hepatic autophagy and a promising therapeutic target for treatment of NAFLD.

Modulation of microglial phenotypes improves sepsis-induced hippocampus-dependent cognitive impairments and decreases brain inflammation in an animal model of sepsis

BACKGROUND

In order to modulate microglial phenotypes in vivo, M1 microglia were depleted by administration of gadolinium chloride and the expression of M2 microglia was induced by IL-4 administration in an animal model of sepsis to better characterize the role of microglial phenotypes in sepsis-induced brain dysfunction.

METHODS

Wistar rats were submitted to sham or cecal ligation and perforation (CLP) and treated with IL-4 or GdCl3. Animals were submitted to behavioral tests 10 days after surgery. In a separated cohort of animals at 24 h, 3 and 10 days after surgery, hippocampus was removed and cytokine levels, M1/M2 markers and CKIP-1 levels were determined.

RESULTS

Modulation of microglia by IL-4 and GdCl3 was associated with an improvement in long-term cognitive impairment. When treated with IL-4 and GdCl3, the reduction of pro-inflammatory cytokines was apparent in almost all analyzed time points. Additionally, CD11b and iNOS were increased after CLP at all time points, and both IL-4 and GdCl3 treatments were able to reverse this. There was a significant decrease in CD11b gene expression in the CLP+GdCl3 group. IL-4 treatment was able to decrease iNOS expression after sepsis. Furthermore, there was an increase of CKIP-1 in the hippocampus of GdCl3 and IL-4 treated animals 10 days after CLP induction.

CONCLUSIONS

GdCl3 and IL-4 are able to manipulate microglial phenotype in an animal models of sepsis, by increasing the polarization toward an M2 phenotype IL-4 and GdCl3 treatment was associated with decreased brain inflammation and functional recovery.

Superior CKIP-1 sensitivity of orofacial bone-derived mesenchymal stem cells in proliferation and osteogenic differentiation compared to long bone-derived mesenchymal stem cells

Maxillofacial bone defects caused by multiple factors, including congenital deformations and tumors, have become a research focus in the field of oral medicine. Bone tissue engineering is increasingly regarded as a potential approach for maxillofacial bone repair. Mesenchymal stem cells (MSCs) with different origins display various biological characteristics. The aim of the present study was to investigate the effects of casein kinase‑2 interaction protein‑1 (CKIP‑1) on MSCs, including femoral bone marrow‑derived MSCs (BMMSCs) and orofacial bone‑derived MSCs (OMSCs), isolated from the femoral and orofacial bones of wild‑type (WT) and CKIP‑1 knockout (KO) mice. MSCs were isolated using collagenase II and the main biological characteristics, including proliferation, apoptosis and osteogenic differentiation, were investigated. Subcutaneous transplantation of MSCs in mice was also performed to assess ectopic bone formation. MTT and clone formation assay results indicated that cell proliferation in the KO group was increased compared with the WT group, and OMSCs exhibited significantly increased levels of proliferation compared with BMMSCs. However, the proportion of apoptotic cells was not significantly different between CKIP‑1 KO OMSCs and BMMSCs. Furthermore, it was revealed that osteogenic differentiation was increased in CKIP‑1 KO MSCs compared with WT MSCs, particularly in OMSCs. Consistent with the in vitro results, enhanced ectopic bone formation was observed in CKIP‑1 KO mice compared with WT mice, particularly in OMSCs compared with BMMSCs. In conclusion, the present results indicated that OMSCs may have a superior sensitivity to CKIP‑1 in promoting osteogenesis compared with BMMSCs; therefore, CKIP‑1 KO in OMSCs may serve as an efficient strategy for maxillofacial bone repair.

Physiological functions of CKIP-1: From molecular mechanisms to therapy implications

The casein kinase 2 interacting protein-1 (CKIP-1, also known as PLEKHO1) is initially identified as a specific CK2α subunit-interacting protein. Subsequently, various proteins, including CPα, PAK1, Arp2/3, HDAC1, c-Jun, ATM, Smurf1, Rpt6, Akt, IFP35, TRAF6, REGγ and CARMA1, were reported to interact with CKIP-1. Owing to the great diversity of interacted proteins, CKIP-1 exhibits multiple biologic functions in cell morphology, cell differentiation and cell apoptosis. Besides, these functions are subcellular localization, cell type, and regulatory signaling dependent. CKIP-1 is involved in biological processes consisting of bone formation, tumorigenesis and immune regulation. Importantly, deregulation of CKIP-1 results in osteoporosis, tumor, and atherosclerosis. In this review, we introduce the molecular functions, biological processes and promising of therapeutic strategies. Through summarizing the intrinsic mechanisms, we expect to open new therapeutic avenues for CKIP-1.

Casein Kinase 2 Interacting Protein-1 Suppresses Glioma Cell Proliferation via Regulating the AKT/GSK3β/β-Catenin Pathway

Objective

Casein kinase 2 interacting protein-1 (CKIP-1) has exhibited multiple functions in regulating cell proliferation, apoptosis, differentiation, and cytoskeleton. CKIP-1 also plays an important role as a critical regulator in tumorigenesis. The aim of this study is to further examine the function of CKIP-1 in glioma cells.

Methods

The expression level of CKIP-1 protein was determined in gliomas tissues and cell lines by immunohistochemistry stain and western blotting while the association of CKIP-1 expression with prognosis was analyzed by Kaplan-Meier method and compared by log-rank test. CKIP-1 was overexpressed or silenced in gliomas cell lines. CCK-8, colony formation assay, and BrdU incorporation assay were used to determine cell proliferation and DNA synthesis. Cell cycle and apoptosis rate were determined with fluorescence-activated cell sorting (FACS) method. Then, expression of key members in AKT/GSK3β/β-catenin pathway was detected by western blot analysis.

Results

In the present study, we reported new evidence that CKIP-1 was reversely associated with the proliferation of glioma cells and survival in glioma patients. Additionally, the overexpressed CKIP-1 significantly inhibited glioma cell proliferation. Further experiments revealed that CKIP-1 functioned through its antiproliferative and proapoptotic activity in glioma cells. Importantly, mechanistic investigations suggested that CKIP-1 sharply suppressed the activity of AKT by inhibiting the phosphorylation, markedly downregulated the phosphorylated GSK3β at Ser9, and promoted β-catenin degradation.

Conclusions

Overall, our results provided new insights into the clinical significance and molecular mechanism of CKIP-1 in glioma, which indicated CKIP1 might function as a therapeutic target for clinical treatment of glioma.

PLEKHO1 knockdown inhibits RCC cell viability in vitro and in vivo, potentially by the Hippo and MAPK/JNK pathways

Renal cell carcinoma (RCC) is the most common type of kidney cancer. By analysing The Cancer Genome Atlas (TCGA) database, 16 genes were identified to be consistently highly expressed in RCC tissues compared with the matched para‑tumour tissues. Using a high‑throughput cell viability screening method, it was found that downregulation of only two genes significantly inhibited the viability of 786‑O cells. Among the two genes, pleckstrin homology domain containing O1 (PLEKHO1) has never been studied in RCC, to the best of our knowledge, and its expression level was shown to be associated with the prognosis of patients with RCC in TCGA dataset. The upregulation of PLEKHO1 in RCC was first confirmed in 30 paired tumour and para‑tumour tissues. Then, the effect of PLEKHO1 on cell proliferation and apoptosis was assessed in vitro. Additionally, xenograft tumour models were established to investigate the function of PLEKHO1 in vivo. The results showed that PLEKHO1 knockdown significantly inhibited cell viability and facilitated apoptosis in vitro and impaired tumour formation in vivo. Thus, PLEKHO1 is likely to be associated with the viability of RCC cells in vitro and in vivo. Further gene expression microarray and co‑expression analyses showed that PLEKHO1 may be involved in the serine/threonine‑protein kinase hippo and JNK signalling pathways. Together, the results of the present study suggest that PLEKHO1 may contribute to the development of RCC, and therefore, further study is needed to explore its potential as a therapeutic target.

CKIP-1 suppresses odontoblastic differentiation of dental pulp stem cells via BMP2 pathway and can interact with NRP1

AIM

Casein kinase 2 interacting protein-1 (CKIP-1) is a recently discovered intracellular regulator of bone formation, muscle cell differentiation, and tumor cell proliferation. Our study aims to identify the inhibition of BMP2-Smad1/5 signaling by CKIP-1 in odontoblastic differentiation of human dental pulp stem cells (DPSCs).

MATERIALS AND METHODS

DPSCs infected CKIP-1 siRNA or transfected CKIP-1 full-length plasmid were cultured in odontoblastic differentiation medium or added noggin (200 ng/mL) for 21 days. We examined the effects of CKIP-1 on odontoblastic differentiation, mineralized nodules formation, and interaction by western blot, real-time polymerase chain reaction (RT-PCR), alkaline phosphatase (ALP) staining, alizarin red S staining, and immunoprecipitation.

RESULTS

Firstly, we have demonstrated that CKIP-1 expression markedly decreased time-dependently along with cell odontoblastic differentiation. Indeed, the silence of CKIP-1 upregulated odontoblastic differentiation via BMP2-Smad1/5 signaling, while CKIP-1 over-expression had a negative effect on odontoblastic differentiation of DPSCs. Furthermore, CKIP-1 could interact with Neuropilin-1 (NRP1).

CONCLUSIONS

This work provides data that advocates a novel perception on odontoblastic differentiation of DPSCs. Therefore, inhibiting the expression of CKIP-1 may be of great significance to the development of dental caries.

CKIP-1 limits foam cell formation and inhibits atherosclerosis by promoting degradation of Oct-1 by REGγ

Atherosclerosis-related cardiovascular diseases are the leading cause of mortality worldwide. Macrophages uptake modified lipoproteins and transform into foam cells, triggering an inflammatory response and thereby promoting plaque formation. Here we show that casein kinase 2-interacting protein-1 (CKIP-1) is a suppressor of foam cell formation and atherosclerosis. Ckip-1 deficiency in mice leads to increased lipoprotein uptake and foam cell formation, indicating a protective role of CKIP-1 in this process. Ablation of Ckip-1 specifically upregulates the transcription of scavenger receptor LOX-1, but not that of CD36 and SR-A. Mechanistically, CKIP-1 interacts with the proteasome activator REGγ and targets the transcriptional factor Oct-1 for degradation, thereby suppressing the transcription of LOX-1 by Oct-1. Moreover, Ckip-1-deficient mice undergo accelerated atherosclerosis, and bone marrow transplantation reveals that Ckip-1 deficiency in hematopoietic cells is sufficient to increase atherosclerotic plaque formation. Therefore, CKIP-1 plays an essential anti-atherosclerotic role through regulation of foam cell formation and cholesterol metabolism.

In atherosclerotic plaques, transformation of macrophages into foam cells is a key step in initiating the inflammatory response. Here Fan et al. show that casein kinase 2-interacting protein-1 (CKIP-1) limits foam cell formation and atherosclerosis by preventing expression of the scavenger receptor LOX-1 through REGγ-mediated degradation of Oct-1.

ABCA1 haplodeficiency affects the brain transcriptome following traumatic brain injury in mice expressing human APOE isoforms

Expression of human Apolipoprotein E (APOE) modulates the inflammatory response in an isoform specific manner, with APOE4 isoform eliciting a stronger pro-inflammatory response, suggesting a possible mechanism for worse outcome following traumatic brain injury (TBI). APOE lipidation and stability is modulated by ATP-binding cassette transporter A1 (ABCA1), a transmembrane protein that transports lipids and cholesterol onto APOE. We examined the impact of Abca1 deficiency and APOE isoform expression on the response to TBI using 3-months-old, human APOE3+/+ (E3/Abca1+/+) and APOE4+/+ (E4/Abca1+/+) targeted replacement mice, and APOE3+/+ and APOE4+/+ mice with only one functional copy of the Abca1 gene (E3/Abca1+/-; E4/Abca1+/-). TBI-treated mice received a craniotomy followed by a controlled cortical impact (CCI) brain injury in the left hemisphere; sham-treated mice received the same surgical procedure without the impact. We performed RNA-seq using samples from cortices and hippocampi followed by genome-wide differential gene expression analysis. We found that TBI significantly impacted unique transcripts within each group, however, the proportion of unique transcripts was highest in E4/Abca1+/- mice. Additionally, we found that Abca1 haplodeficiency increased the expression of microglia sensome genes among only APOE4 injured mice, a response not seen in injured APOE3 mice, nor in either group of sham-treated mice. To identify gene networks, or modules, correlated to TBI, APOE isoform and Abca1 haplodeficiency, we used weighted gene co-expression network analysis (WGCNA). The module that positively correlated to TBI groups was associated with immune response and featured hub genes that were microglia-specific, including Trem2, Tyrobp, Cd68 and Hexb. The modules positively correlated with APOE4 isoform and negatively to Abca1 haplodeficient mice represented "protein translation" and "oxidation-reduction process", respectively. Our results reveal E4/Abca1+/- TBI mice have a distinct response to injury, and unique gene networks are associated with APOE isoform, Abca1 insufficiency and injury.

Let-7a promotes microglia M2 polarization by targeting CKIP-1 following ICH

Microglia polarization plays a crucial role in initiating brain inflammatory injury after intracerebral hemorrhage (ICH). Casein Kinase 2 Interacting Protein 1(CKIP-1) has been identified as a transcriptional molecular to manipulate microglia polarization. MiRNAs regulate gene expression and microglia polarization. In the experiment, CKIP-1 has been predicted as a target gene of let-7a. Let-7a, CKIP-1 and downstream proinflammatory mediator production of ICH mice were analyzed. In addition, inflammation, brain edema, and neurological functions in ICH mice were also assessed. Furthermore, let-7a mimic or inhibitors was administrated to study the potential role to manipulate microglia polarization after ICH. We reported that let-7a levels decreased but CKIP-1 levels increased after ICH. Using a dual-luciferase reporter assay, it was demonstrated that CKIP-1 was the target gene of let-7a. Let-7a overexpression decreased the protein levels of CKIP-1 and inhibition of let-7a increased the protein levels of CKIP-1. In addition, our results indicate that let-7a could inhibit expression of proinflammatory cytokines, reduce brain edema, and improve neurological functions in ICH mice. The study indicated that CKIP-1 was a target gene of let-7a and that let-7a regulated microglia M2 polarization by targeting CKIP-1 following ICH.

The role of CKIP-1 in osteoporosis development and treatment

Osteoporosis is a systemic skeletal disorder characterized by reduced bone mass and deterioration of bone microarchitecture, which results in increased bone fragility and fracture risk. Casein kinase 2-interacting protein-1 (CKIP-1) is a protein that plays an important role in regulation of bone formation. The effect of CKIP-1 on bone formation is mainly mediated through negative regulation of the bone morphogenetic protein pathway. In addition, CKIP-1 has an important role in the progression of osteoporosis. This review provides a summary of the recent studies on the role of CKIP-1 in osteoporosis development and treatment.

Cite this article: X. Peng, X. Wu, J. Zhang, G. Zhang, G. Li, X. Pan. The role of CKIP-1 in osteoporosis development and treatment. Bone Joint Res 2018;7:173–178. DOI: 10.1302/2046-3758.72.BJR-2017-0172.R1.

Association of CKIP-1 P21A polymorphism with risk of chronic heart failure in a Chinese population

Pathological cardiac hypertrophy is an independent risk factor for chronic heart failure. Casein kinase-2 interacting protein-1 (CKIP-1) can inhibit pathological cardiac hypertrophy. Therefore, we investigated whether CKIP-1 nonsynonymous polymorphism rs2306235 (Pro21Ala) contributes to risk and prognosis of chronic heart failure in a Chinese population.A total of 923 adult patients with chronic heart failure and 1020 age- and gender-matched healthy controls were recruited. CKIP-1 rs2306235 polymorphism was genotyped using PCR-restriction fragment length polymorphism. Additional follow-up data for 140 chronic heart failure patients was evaluated. The rs2306235 G allele was associated with an increased risk of chronic heart failure (OR = 1.38, 95% CI = 1.09-1.75, p = 0.007), especially in patients with hypertension (OR = 1.45, 95% CI = 1.09-1.75, p = 0.006) and coronary heart disease (OR = 1.41, 95% CI = 1.09-1.83, p = 0.010) after adjustment for multiple cardiovascular risk factors. However, rs2306235 polymorphism was not associated with cardiovascular mortality in chronic heart failure (p = 0.875). CKIP-1 rs2306235 polymorphism may be a risk factor for chronic heart failure in a Chinese Han population.

A novel role of CKIP-1 in promoting megakaryocytic differentiation

Casein kinase 2-interacting protein-1 (CKIP-1) is a known regulator of cardiomyocytes and macrophage proliferation. In this study, we showed that CKIP-1 was involved in the process of megakaryocytic differentiation. During megakaryocytic differentiation of K562 cells, CKIP-1 was dramatically upregulated and this upregulation induced by PMA was mediated through downregulation of transcription factor GATA-1. By transient transfection, oligonucleotide-directed mutagenesis and chromatin immunoprecipitation assays, we identified the transcriptional regulation of CKIP-1 by GATA-1. Overexpression of CKIP-1 initiated events of spontaneous megakaryocytic differentiation in K562 cells. Conversely, knockdown of CKIP-1 in cell lines suppressed megakaryocytic differentiation. Mechanistically, overexpression of CKIP-1 changed the expression levels of transcription factors that have been shown to be critical in erythro-megakaryocytic differentiation such as Fli-1, c-Myb and c-Myc. In vivo analysis confirmed that CKIP-1^−/− mice had decreased number of CD41⁺ cells harvested from bone marrow, and lower platelet levels when compared to wild-type littermates. This is the first direct evidence suggesting that CKIP-1 is a novel regulator of megakaryocytic differentiation.

CKIP-1 affects the polyubiquitination of Nrf2 and Keap1 via mediating Smurf1 to resist HG-induced renal fibrosis in GMCs and diabetic mice kidneys

Our previous study indicated that Casein kinase 2 interacting protein-1 (CKIP-1) could promote the activation of the nuclear factor E2-related factor 2 (Nrf2)/ antioxidant response element (ARE) pathway, playing a significant role in inhibiting the fibrosis of diabetic nephropathy (DN). However, the underlying mechanism is still unknown. Here, we investigated whether CKIP-1 affects the polyubiquitination of Nrf2 and its cytosolic inhibitor kelch like ECH-associated protein 1 (Keap1) via mediating Smad ubiquitylation regulatory factor-1 (Smurf1) to promote the activation of the Nrf2/ARE signaling and resist high glucose (HG)-induced renal fibrosis in glomerular mesangial cells (GMCs) and diabetic mice kidneys. Results showed that the expression of Smurf1 increased in HG-induced GMCs, with a paramount upregulation at 1h. Overexpression of wild-type Smurf1 plasmid further promoted the HG-induced the over-production of fibronectin (FN) and intercellular adhesionmolecule-1 (ICAM-1), and depletion of Smurf1 dramatically reduced the expression of FN and ICAM-1. Overexpression of CKIP-1 decreased the K48-linked polyubiquitination and increased the K63-linked polyubiquitination of Nrf2 as well as enhanced the K48-linked polyubiquitination and reduced K63-linked polyubiquitination of Keap1, promoting the activation of the Nrf2/ARE pathway. Overexpression of Smurf1 increased the K48-linked polyubiquitination and decreased the K63-linked polyubiquitination of Nrf2, and down-regulated the K48-linked polyubiquitination and up-regulated the K63-linked polyubiquitination of Keap1, inhibiting the activation of the Nrf2/ARE pathway. CKIP-1 promoted the degradation of Smurf1 by increasing the ubiquitination of Smurf1. Treatment of CKIP-1 adenovirus infection reduced the Smurf1 levels, promoted the activation of the Nrf2/ARE pathway as well as suppressed the production of reactive oxygen species (ROS), and then improved the failure of renal function of diabetic mice. Experiments above suggested that CKIP-1 affects the polyubiquitination of Nrf2 and Keap1 and promotes the Nrf2-ARE pathway through down-regulating Smurf1 to resist HG-induced up-regulation of FN and ICAM-1 in GMCs and diabetic mice kidneys.

Myocardial CKIP-1 Overexpression Protects from Simulated Microgravity-Induced Cardiac Remodeling

Human cardiovascular system has adapted to Earth's gravity of 1G. The microgravity during space flight can induce cardiac remodeling and decline of cardiac function. At present, the mechanism of cardiac remodeling induced by microgravity remains to be disclosed. Casein kinase-2 interacting protein-1 (CKIP-1) is an important inhibitor of pressure-overload induced cardiac remodeling by decreasing the phosphorylation level of HDAC4. However, the role of CKIP-1 in the cardiac remodeling induced by microgravity is unknown. The purpose of this study was to determine whether CKIP-1 was also involved in the regulation of cardiac remodeling induced by microgravity. We first detected the expression of CKIP-1 in the heart from mice and monkey after simulated microgravity using Q-PCR and western blotting. Then, myocardial specific CKIP-1 transgenic (TG) and wild type mice were hindlimb-suspended (HU) to simulate microgravity effect. We estimated the cardiac remodeling in morphology and function by histological analysis and echocardiography. Finally, we detected the phosphorylation of AMPK, ERK1/2, and HDAC4 in the heart from wild type and CKIP-1 transgenic mice after HU. The results revealed the reduced expression of CKIP-1 in the heart both from mice and monkey after simulated microgravity. Myocardial CKIP-1 overexpression protected from simulated microgravity-induced decline of cardiac function and loss of left ventricular mass. Histological analysis demonstrated CKIP-1 TG inhibited the decreases in the size of individual cardiomyocytes of mice after hindlimb unloading. CKIP-1 TG can inhibit the activation of HDAC4 and ERK1/2 and the inactivation of AMPK in heart of mice induced by simulated microgravity. These results demonstrated CKIP-1 was a suppressor of cardiac remodeling induced by simulated microgravity.

Casein Kinase 2 Interacting Protein-1 regulates M1 and M2 inflammatory macrophage polarization

The importance of macrophage plasticity, albeit being discovered recently, has been highlighted in a broad spectrum of biological processes operative in physiological and pathological environments. Macrophage polarized activation and inactivation has profound effects on immune and inflammatory responses with several major pathways being elucidated in the past few years. However, transcriptional regulation mechanisms governing macrophage polarization is still preliminary. In this study, we identify the Casein Kinase 2 Interacting Protein 1 (CKIP-1) as a molecular toggle manipulating macrophage speciation. CKIP-1 expression was strongly induced by pro-inflammatory M1 stimuli (LPS and IFN-γ) and robustly suppressed by M2 stimuli (IL-4 and IL-13) in human and murine macrophage. Gain and loss of function studies suggest that CKIP-1 is a prerequisite for optimal LPS-induced pro-inflammatory gene activation, which exhibits its roles in a NF-κB dependent manner. Furthermore, CKIP-1 inhibits anti-inflammatory gene expression by negatively regulating JAK1-STAT6 activation in macrophages. Taken together, these data integrated CKIP-1 expression and function as a novel transcriptional regulator of macrophage polarization and identified a double feedback loop consisting of CKIP-1 and the key regulators of the M1 and M2 macrophage effectors in polarization pathway. Moreover, the inhibitory roles of CKIP-1 in LPS-mediated sepsis and TPA-mediated cutaneous provide a new target for treatments of acute inflammation.

Itch promotes the neddylation of JunB and regulates JunB-dependent transcription

Protein neddylation is essential for the viability of most organisms and is widely involved in the regulation of immunity, DNA damage and repair, cell signaling and cell cycle. Unlike RING-type neddylation ligases, HECT-type neddylation ligase remains less defined. Here, we show that Itch is a novel HECT-type neddylation E3 ligase and we identify JunB as a substrate of Nedd8 modification by Itch. JunB neddylation attenuates its transcriptional activity. In addition, JunB neddylation mediated by Itch promotes its ubiquitination-dependent degradation. Therefore, these findings define a new HECT-type neddylation ligase and its neddylation substrate.

CKIP-1 suppresses the adipogenesis of mesenchymal stem cells by enhancing HDAC1-associated repression of C/EBPα

Mesenchymal stem cells (MSCs) are considered as the developmental origin of multiple lineage cells including osteocytes, adipocytes, and muscle cells. Previous studies demonstrated that the PH domain-containing protein CKIP-1 plays an important role in the development of osteoblasts and cardiomyocytes. However, whether CKIP-1 is involved in the generation of adipocytes as well as the MSC differentiation remains unknown. Here we show that CKIP-1 is a novel regulator of MSCs differentiating into adipocytes. MSCs derived from CKIP-1-deficient mice display enhanced adipogenesis upon induction. Further analysis showed that CKIP-1 interacts with the histone deacetylase HDAC1 in the nucleus and inhibits the transcription of CCAAT/enhancer-binding protein α (C/EBPα), which is a crucial adipogenic transcription factor. Ectopic expression of CKIP-1 in a MSC-like cell line C3H/10T1/2 reduced the generation of adipocytes due to suppression of adipogenic factors, including C/EBPα. Moreover, CKIP-1-deficient mice showed an increase in body weight and white adipose tissue gains when fed on a high-fat diet. Collectively, these results suggest that CKIP-1 is a novel inhibitor of MSC-originated adipogenesis by enhancing HDAC1-associated repression of C/EBPα.

Capping protein regulators fine-tune actin assembly dynamics

Capping protein (CP) binds the fast growing barbed end of the actin filament and regulates actin assembly by blocking the addition and loss of actin subunits. Recent studies provide new insights into how CP and barbed-end capping are regulated. Filament elongation factors, such as formins and ENA/VASP (enabled/vasodilator-stimulated phosphoprotein), indirectly regulate CP by competing with CP for binding to the barbed end, whereas other molecules, including V-1 and phospholipids, directly bind to CP and sterically block its interaction with the filament. In addition, a diverse and unrelated group of proteins interact with CP through a conserved 'capping protein interaction' (CPI) motif. These proteins, including CARMIL (capping protein, ARP2/3 and myosin I linker), CD2AP (CD2-associated protein) and the WASH (WASP and SCAR homologue) complex subunit FAM21, recruit CP to specific subcellular locations and modulate its actin-capping activity via allosteric effects.

Differentiation-associated genes regulated by c-Jun and decreased in the progression of esophageal squamous cell carcinoma

Transcription factor c-Jun plays a key role in controlling epithelium cell proliferation, apoptosis and differentiation. However, molecular mechanism and biological functions of c-Jun in squamous differentiation and the progression of esophageal squamous cell carcinoma (ESCC) remain elusive. In this study, we found that c-Jun bound directly to the promoter region, and activated the transcription of differentiation-associated genes including cystatin A, involucrin and SPRR3 in vivo. Ectopic expression of c-Jun enhanced SPRR3 transactivation in KYSE450 cells. Conversely, TAM67, a dominant negative mutant of c-Jun, inhibited SPRR3 transactivation. c-Jun increased expression of SPPR3 mainly via a PKC/JNK pathway in response to TPA in KYSE450 cells. Furthermore, c-Jun was remarkably reduced in esophageal cancer. Interestingly, cystatin A, involucrin and SPRR3 were significantly downregulated as well, and associated with differentiation grade. Expression of c-Jun was correlated with the expression of these genes in normal epithelium and ESCC. Importantly, the expression of these genes was remarkably decreased during the malignant transformation from normal epithelium to low-grade intraepithelial neoplasia (LGIN) or high-grade intraepithelial neoplasia (HGIN). The expression of cystatin A and involucrin was significantly reduced from LGIN to HGIN. These results suggest c-Jun was involved in the regulation of differentiation-associated genes in ESCC. These genes might serve as the potential markers in distinguishing normal epithelium from esophageal squamous intraepithelial neoplasia.

CKIP-1 regulates macrophage proliferation by inhibiting TRAF6-mediated Akt activation

Macrophages play pivotal roles in development, homeostasis, tissue repair and immunity. Macrophage proliferation is promoted by macrophage colony-stimulating factor (M-CSF)-induced Akt signaling; yet, how this process is terminated remains unclear. Here, we identify casein kinase 2-interacting protein-1 (CKIP-1) as a novel inhibitor of macrophage proliferation. In resting macrophages, CKIP-1 was phosphorylated at Serine 342 by constitutively active GSK3β, the downstream target of Akt. This phosphorylation triggers the polyubiquitination and proteasomal degradation of CKIP-1. Upon M-CSF stimulation, Akt is activated by CSF-1R-PI3K and then inactivates GSK3β, leading to the stabilization of CKIP-1 and β-catenin proteins. β-catenin promotes the expression of proliferation genes including cyclin D and c-Myc. CKIP-1 interacts with TRAF6, a ubiquitin ligase required for K63-linked ubiquitination and plasma membrane recruitment of Akt, and terminates TRAF6-mediated Akt activation. By this means, CKIP-1 inhibits macrophage proliferation specifically at the late stage after M-CSF stimulation. Furthermore, CKIP-1 deficiency results in increased proliferation and decreased apoptosis of macrophages in vitro and CKIP-1(-/-) mice spontaneously develop a macrophage-dominated splenomegaly and myeloproliferation. Together, these data demonstrate that CKIP-1 plays a critical role in the regulation of macrophage homeostasis by inhibiting TRAF6-mediated Akt activation.

CKIP-1 is an intrinsic negative regulator of T-cell activation through an interaction with CARMA1

The transcription factor NF-κB plays a key regulatory role in lymphocyte activation and generation of immune response. Stimulation of T cell receptor (TCR) induces phosphorylation of CARMA1 by PKCθ, resulting in formation of CARMA1-Bcl10-MALT1 (CBM) complex at lipid rafts and subsequently leading to NF-κB activation. While many molecular events leading to NF-κB activation have been reported, it is less understood how this activation is negatively regulated. We performed a cell-based screening for negative regulators of TCR-mediated NF-κB activation, using mutagenesis and complementation cloning strategies. Here we show that casein kinase-2 interacting protein-1 (CKIP-1) suppresses PKCθ-CBM-NF-κB signaling. We found that CKIP-1 interacts with CARMA1 and competes with PKCθ for association. We further confirmed that a PH domain of CKIP-1 is required for association with CARMA1 and its inhibitory effect. CKIP-1 represses NF-κB activity in unstimulated cells, and inhibits NF-κB activation induced by stimulation with PMA or constitutively active PKCθ, but not by stimulation with TNFα. Interestingly, CKIP-1 does not inhibit NF-κB activation induced by CD3/CD28 costimulation, which caused dissociation of CKIP-1 from lipid rafts. These data suggest that CKIP-1 contributes maintenance of a resting state on NF-κB activity or prevents T cells from being activated by inadequate signaling. In conclusion, we demonstrate that CKIP-1 interacts with CARMA1 and has an inhibitory effect on PKCθ-CBM-NF-κB signaling.

Crystallization and preliminary X-ray crystallographic analysis of the human CKIP-1 pleckstrin homology domain

The casein kinase 2 interacting protein-1 (CKIP-1) is involved in many cellular functions, including apoptosis, signalling pathways, cell growth, cytoskeleton and bone formation. Its N-terminal pleckstrin homology (PH) domain is thought to play an important role in membrane localization and controls shuttling of CKIP-1 between the plasma membrane and nucleus. In this study, the human CKIP-1 PH domain was purified but problems were encountered with nucleic acid contamination. An S84D/S86D/S88D triple mutant designed to abolish nucleic acid binding was purified and successfully crystallized. Single crystals diffracted to 1.7 Å resolution and belonged to space group P4₃2₁2 with unit-cell parameters a=53.0, b=53.0, c=113.8 Å, α=β=γ=90.0°.

CKIP-1: a scaffold protein and potential therapeutic target integrating multiple signaling pathways and physiological functions

The PH domain-containing casein kinase 2 interacting protein-1 (CKIP-1, also known as PLEKHO1) acts as a scaffold protein mediating interactions with multiple proteins, including CK2α, CPα, AP-1/c-Jun, Akt, ATM, IFP35/Nmi and Smurf1. CKIP-1 functions through different ways, such as plasma membrane recruitment, transcriptional activity modulation and posttranscriptional modification regulation. Moreover, the subcellular localization of CKIP-1 is determined by several key amino acids in a cell type dependent style, and the nucleus/plasma membrane shuttle of CKIP-1 is regulated by different cell stresses. As an adaptor protein, CKIP-1 is involved in various important signaling pathways, controlling cell growth, apoptosis, differentiation, cytoskeleton and bone formation. Strikingly, CKIP-1 has been recently demonstrated to be a promising target for treatment of osteoporosis in rat models. In addition, more evidences suggest that CKIP-1 might also function as a potential tumor suppressor.

CKIP-1 inhibits cardiac hypertrophy by regulating class II histone deacetylase phosphorylation through recruiting PP2A

BACKGROUND

Sustained cardiac pressure overload-induced hypertrophy and pathological remodeling frequently leads to heart failure. Casein kinase-2 interacting protein-1 (CKIP-1) has been identified to be an important regulator of cell proliferation, differentiation, and apoptosis. However, the physiological role of CKIP-1 in the heart is unknown.

METHODS AND RESULTS

The results of echocardiography and histology demonstrate that CKIP-1-deficient mice exhibit spontaneous cardiac hypertrophy with aging and hypersensitivity to pressure overload-induced pathological cardiac hypertrophy, as well. Transgenic mice with cardiac-specific overexpression of CKIP-1 showed resistance to cardiac hypertrophy in response to pressure overload. The results of GST pull-down and coimmunoprecipitation assays showed the interaction between CKIP-1 and histone deacetylase 4 (HDAC4), through which they synergistically inhibited transcriptional activity of myocyte-specific enhancer factor 2C. By directly interacting with the catalytic subunit of phosphatase 2A, CKIP-1 overexpression enhanced the binding of catalytic subunit of phosphatase-2A to HDAC4 and promoted HDAC4 dephosphorylation.

CONCLUSIONS

CKIP-1 was found to be an inhibitor of cardiac hypertrophy by upregulating the dephosphorylation of HDAC4 through the recruitment of protein phosphatase 2A. These results demonstrated a unique function of CKIP-1, by which it suppresses cardiac hypertrophy through its capacity to regulate HDAC4 dephosphorylation and fetal cardiac genes expression.

CKIP-1 regulates mammalian and zebrafish myoblast fusion

Multinucleated muscle fibres arise by fusion of precursor cells called myoblasts. We previously showed that CKIP-1 ectopic expression in C2C12 myoblasts increased cell fusion. In this work, we report that CKIP-1 depletion drastically impairs C2C12 myoblast fusion in vitro and in vivo during zebrafish muscle development. Within developing fast-twich myotome, Ckip-1 localises at the periphery of fast precursor cells, closed to the plasma membrane. Unlike wild-type myoblasts that form spatially arrayed multinucleated fast myofibres, Ckip-1-deficient myoblasts show a drastic reduction in fusion capacity. A search for CKIP-1 binding partners identified the ARPC1 subunit of Arp2/3 actin nucleation complex essential for myoblast fusion. We demonstrate that CKIP-1, through binding to plasma membrane phosphoinositides via its PH domain, regulates cell morphology and lamellipodia formation by recruiting the Arp2/3 complex at the plasma membrane. These results establish CKIP-1 as a regulator of cortical actin that recruits the Arp2/3 complex at the plasma membrane essential for muscle precursor elongation and fusion.

Literature and patent analysis of the cloning and identification of human functional genes in China

The Human Genome Project was launched at the end of the 1980s. Since then, the cloning and identification of functional genes has been a major focus of research across the world. In China too, the potentially profound impact of such studies on the life sciences and on human health was realized, and relevant studies were initiated in the 1990s. To advance China's involvement in the Human Genome Project, in the mid-1990s, Committee of Experts in Biology from National High Technology Research and Development Program of China (863 Program) proposed the "two 1%" goal. This goal envisaged China contributing 1% of the total sequencing work, and cloning and identifying 1% of the total human functional genes. Over the past 20 years, tremendous achievement has been accomplished by Chinese scientists. It is well known that scientists in China finished the 1% of sequencing work of the Human Genome Project, whereas, there is no comprehensive report about "whether China had finished cloning and identifying 1% of human functional genes". In the present study, the GenBank database at the National Center of Biotechnology Information, the PubMed search tool, and the patent database of the State Intellectual Property Office, China, were used to retrieve entries based on two screening standards: (i) Were the newly cloned and identified genes first reported by Chinese scientists? (ii) Were the Chinese scientists awarded the gene sequence patent? Entries were retrieved from the databases up to the cut-off date of 30 June 2011 and the obtained data were analyzed further. The results showed that 589 new human functional genes were first reported by Chinese scientists and 159 gene sequences were patented (http://gene.fudan.sh.cn/introduction/database/chinagene/chinagene.html). This study systematically summarizes China's contributions to human functional genomics research and answers the question "has China finished cloning and identifying 1% of human functional genes?" in the affirmative.

Expression of GSDML Associates with Tumor Progression in Uterine Cervix Cancer

Gasdermin-like (GSDML) belongs to the gasdermin-domain-containing protein family (GSDMDC family) that is involved in carcinogenesis and hearing impairment. However, the role of GSDML in carcinogenesis remains unclear. In this study, we identified four isoforms of GSDML gene. The primary and longest isoform GSDML1 is widely expressed in human cancer cell lines. GFP-GSDML1 fusion protein was localized predominantly in the nucleus of human breast cancer MCF7 and cervical cancer HeLa cells but exclusively in the cytoplasm of hepatocellular carcinoma HepG2 cells. Importantly, immunohistochemistry analysis showed that the GSDML protein in the nuclei is expressed at a higher level in uterine cervix cancer tissues than in the adjacent cancer tissues and corresponding nonneoplastic tissues. Such significance was not observed in hepatocellular carcinoma tissues. Ectopic expression of GSDML1 enhanced the growth of cultured cells, whereas inhibition of its endogenous expression decreased proliferation. Furthermore, GSDML1 had significant effects on promoting bromodeoxyuridine incorporation in cells. However, GSDML1 could neither promote malignant transformation nor gain the ability of colony formation or carcinogenicity on nude mice. Collectively, these results suggest that GSDML can promote cell proliferation, and it might be correlated with carcinogenesis and progression of uterine cervix cancer.

A miniaturized sandwich immunoassay platform for the detection of protein-protein interactions

Background

Analysis of protein-protein interactions (PPIs) is a valuable approach for the characterization of huge networks of protein complexes or proteins of unknown function. Co-immunoprecipitation (coIP) using affinity resins coupled to protein A/G is the most widely used method for PPI detection. However, this traditional large scale resin-based coIP is too laborious and time consuming. To overcome this problem, we developed a miniaturized sandwich immunoassay platform (MSIP) by combining antibody array technology and coIP methods.

Results

Based on anti-FLAG antibody spotted aldehyde slides, MSIP enables simple, rapid and large scale detection of PPIs by fluorescent labeling anti-myc antibody. By analyzing well-known interacting and non-interacting protein pairs, MSIP was demonstrated to be highly accurate and reproducible. Compared to traditional resin-based coIP, MSIP results in higher sensitivity and enhanced throughput, with the additional benefit of digital read-outs. In addition, MSIP was shown to be a highly useful validation platform to confirm PPI candidates that have been identified from yeast two hybrid systems.

Conclusions

In conclusion, MSIP is proved to be a simple, cost-saving and highly efficient technique for the comprehensive study of PPIs.

Negative regulation of HDM2 to attenuate p53 degradation by ribosomal protein L26

HDM2 is a p53-specific E3 ubiquitin ligase. Its overexpression leads to excessive inactivation of tumor protein p53, diminishing its tumor suppressor function. HDM2 also affects the cell cycle, apoptosis and tumorigenesis through interacting with other molecules, including several ribosomal proteins. To identify novel HDM2 regulators, we performed a yeast two-hybrid screening using HDM2 as bait. Among the candidates, ribosomal protein L26 (RPL26) was characterized as a novel HDM2-interactor. The interaction between HDM2 and RPL26 was further validated by in vivo and in vitro assays. RPL26 modulates the HDM2–p53 interaction by forming a ternary complex among RPL26, HDM2 and p53, which stabilize p53 through inhibiting the ubiquitin ligase activity of HDM2. The ribosomal stress caused by a low dose of Act D enhances RPL26–HDM2 interaction and activates p53. Overexpression of RPL26 results in activating of p53, inhibits cell proliferation and induces a p53-dependent cell cycle arrest. These results provide a novel regulatory mechanism of RPL26 to activate p53 by inhibiting HDM2.