CacyBP/SIP nuclear translocation regulates p27Kip1 stability in gastric cancer cells

Construction of a immune-associated genes based prognostic signature in bladder cancer

Current studies indicated that immune-associated genes (IAGs) have important roles in the occurrence and development of bladder cancer (BC). The current work aims to identify the prognostic values of IAGs in BC and establish a prognostic signature based on IAGs. RNA sequencing data and protein expression data were used to identify differentially expressed IAGs in BC. An IAGs based signature was further constructed and the prognostic and predictive values of the signature were evaluated by survival analysis and nomogram. RNA isolation and reverse transcription-quantitative PCR (RT-qPCR) were further performed to investigate the expression levels of IAGs in BC cells and were used to explore the relationship between IAGs and M2 tumour-associated macrophages (TAMs) secreted transforming growth factor-β1 (TGF-β1) in BC cells. We selected five IAGs to develop an IAGs signature model, which were significantly related to survival outcomes of BC patients. RT-qPCR showed that five IAGs were significantly differentially expressed and three IAGs were positively correlated with M2 TAMs secreted TGF-β1 in T24 cells. We identified and validated an IAGs based signature to predict the prognosis of BC patients. Furthermore, M2 TAMs may promote the expression of IAGs in BC via the TGF-β1 signalling pathway.

Bioinformatic analysis of Cacybp-associated proteins using human glioma databases

The ubiquitin-proteasome system is the primary cellular pathway for protein degradation, mediating 80% of intracellular protein degradation. Because of the widespread presence of ubiquitin-modified protein substrates, ubiquitination can regulate a variety of cellular activities including cell proliferation, apoptosis, autophagy, endocytosis, DNA damage repair, and immune responses. With the continuous generation of genomics data in recent years it has become particularly important to analyze these data effectively and reasonably. Cacybp forms a complex with the E3 ubiquitinated ligase Siah1 to participate in ubiquitination. We analyzed Cacybp-associated genes using the Gene Expression Omnibus (GEO) and CGGA (Chinese Glioma Genome Atlas) databases and identified 121 differentially expressed genes (DEGs), of which 46 were downregulated and 75 were upregulated. The biological processes, molecular functions, and protein-protein interaction (PPI) network of differential genes were analyzed by Cytoscape software and STRING software. We found no difference in Cacybp expression among different grades of gliomas and there was no significant association between the expression level of Cacybp and the prognosis of patients with glioma in LGG and GBM. © 2019 IUBMB Life, 1-8, 2019.

Interaction of CacyBP/SIP with NPM1 and its influence on NPM1 localization and function in oxidative stress

Calcyclin (S100A6) binding protein/Siah-1 interacting protein (CacyBP/SIP) is mainly a cytoplasmic protein; however, some literature data suggested its presence in the nucleus. In this work we examined more precisely the nuclear localization and function of CacyBP/SIP. By applying mass spectrometry, we have identified several nuclear proteins, among them is nucleophosmin (NPM1), that may interact with CacyBP/SIP. Subsequent assays revealed that CacyBP/SIP forms complexes with NPM1 in the cell and that the interaction between these two proteins is direct. Interestingly, although CacyBP/SIP exhibits phosphatase activity, we have found that its overexpression favors phosphorylation of NPM1 on S125. In turn, the RNA immunoprecipitation assay indicated that the altered CacyBP/SIP level has an impact on the amount of 28S and 18S rRNA bound to NPM1. The overexpression of CacyBP/SIP resulted in a significant increase in the binding of 28S and 18S rRNA to NPM1, whereas silencing of CacyBP/SIP expression decreased 28S rRNA binding and had no effect on the binding of 18S rRNA. Further studies have shown that under oxidative stress, CacyBP/SIP overexpression alters NPM1 distribution in cell nuclei. In addition, staining for a nucleolar marker, fibrillarin, revealed that CacyBP/SIP is indispensable for maintaining the nucleolar structure. These results are in agreement with data obtained by western blot analysis, which show that upon oxidative stress the NPM1 level decreases but that CacyBP/SIP overexpression counteracts the effect of stress. Altogether, our results show for the first time that CacyBP/SIP binds to and affects the properties of a nuclear protein, NPM1, and that it is indispensable for preserving the structure of nucleoli under oxidative stress.

The effect of S100A6 on nuclear translocation of CacyBP/SIP in colon cancer cells

BACKGROUND

Calcyclin Binding Protein/(Siah-1 interacting protein) (CacyBP/SIP) acts as an oncogene in colorectal cancer. The nuclear accumulation of CacyBP/SIP has been linked to the proliferation of cancer cells. It has been reported that intracellular Ca2+ induces the nuclear translocation of CacyBP/SIP. However, the molecular mechanism of CacyBP/SIP nuclear translocation has yet to be elucidated. The purpose of this study was to test whether the Ca2+-dependent binding partner S100 protein is involved in CacyBP/SIP nuclear translocation in colon cancer SW480 cells.

METHODS

The subcellular localization of endogenous CacyBP/SIP was observed following the stimulation of ionomycin or BAPTA/AM by immunofluorescence staining in SW480 cells. S100A6 small interfering RNAs (siRNA) were transfected into SW480 cells. Immunoprecipitation assays detected whether S100 protein is relevant to the nuclear translocation of CacyBP/SIP in response to changes in [Ca2+]i.

RESULTS

We observed that endogenous CacyBP/SIP is translocated from the cytosol to the nucleus following the elevation of [Ca2+]i by ionomycin in SW480 cells. Co-immunoprecipitation experiments showed that the interaction between S100A6 and CacyBP/SIP was increased simultaneously with elevated Ca2+. Knockdown of S100A6 abolished the Ca2+ effect on the subcellular translocation of CacyBP/SIP.

CONCLUSION

Thus, we demonstrated that S100A6 is required for the Ca2+-dependent nuclear translocation of CacyBP/SIP in colon cancer SW480 cells.

Cell cycle-dependent translocation and regulatory mechanism of CacyBP/SIP in gastric cancer cells

Our previous results showed that calcyclin-binding protein/Siah-1-interacting protein (CacyBP/SIP) inhibits the proliferation and tumorigenicity of gastric cancer; however, the exact mechanism remains unclear, especially from the aspect of cell cycle. The subcellular localization of CacyBP/SIP, Siah-1, and Skp1 in SGC7901 gastric cancer cells was assessed by immunofluorescence after cell cycle synchronization. Levels of CacyBP/SIP, Siah-1, Skp1, β-catenin, and p-ERK1/2 were analyzed by western blotting. CacyBP/SIP phosphorylation (p-CacyBP/SIP) and the combining capacity of Siah-1 and Skp1 with CacyBP/SIP in nucleoprotein were determined by immunoprecipitation. CacyBP/SIP, Siah-1, and Skp1 were mainly in the cytoplasm in the G1 phase, but translocated to the nucleus during G2. Their expression in total protein was not altered, but elevated in the G2 phase in nucleoprotein. The CacyBP/SIP nucleus translocation of cells transfected with mutant CacyBP/SIP that does not bind S100 (CacyBP-ΔS100) was significantly increased compared with wild-type CacyBP/SIP. In the G2 phase, p-CacyBP/SIP expression and the combining capacity of Siah-1 and Skp1 with CacyBP/SIP were all increased, whereas levels of β-catenin and p-ERK1/2 reduced, compared with the G1 phase. CacyBP/SIP or CacyBP-ΔS100 overexpression was correlated with constitutively low β-catenin expression and affected its level through cell cycle. CacyBP/SIP overexpression led to retarded proliferation, G1 arrest, and β-catenin reduction, which could be abolished by lithium chloride, β-catenin activator, and further enhanced by the Wnt inhibitor XAV-939. In addition, CacyBP-ΔS100 further suppressed cell proliferation and induced G1 arrest compared with CacyBP/SIP. In conclusion, CacyBP/SIP nuclear localization, dependent on S100 protein, suppresses gastric cancer tumorigenesis through β-catenin degradation and the dephosphorylation of ERK1/2 during the G2 phase.

Gastrin induces multidrug resistance via the degradation of p27Kip1 in the gastric carcinoma cell line SGC7901

Multidrug resistance (MDR) is one of the major reasons for the failure of chemotherapy-based gastric carcinoma (GC) treatments, hence, biologically based therapies are urgently needed. Gastrin (GAS), a key gastrointestinal (GI) hormone, was found to be involved in tumor formation, progression, and metastasis. In this study, quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemical staining analysis revealed a high level of expression of GAS in drug-insensitive GC tissues (P<0.01) and similar results were revealed in GC cell lines SGC7901 and its multidrug-resistant variants SGC7901/VCR and SGC7901/ADR. We constructed a eukaryotic expression vector pCDNA3.1(+)/GAS for GAS overexpression and recombinant lentiviral vectors for specific siRNA (siGAS). Transfection of pCDNA3.1(+)/GAS increased (P<0.05) while transfection of siGAS (P<0.05) and co-treated with paclitaxel (TAX) and vincristine (VCR) combination (TAX-VCR) decreased (P<0.01) the cell viability of SGC7901, SGC7901/VCR and SGC7901/ADR. Apoptosis rates of SGC7901/VCR and SGC7901/ADR were reduced by pCDNA3.1(+)/GAS and increased by siGAS (P<0.05). The apoptosis rates of SGC7901/VCR, SGC7901/ADR and SGC7901 were all upregulated (P<0.01) when cells were co-treated with a combination of siGAS and TAX-VCR. Additionally, siGAS significantly downregulated the expression of Bcl-2 and multidrug-resistant associate protein (MRP1) and P-glycoprotein (Pgp) (P<0.05) in SGC7901/VCR and SGC7901/ADR cells. Moreover, GAS overexpression in SGC7901 cells significantly inhibited p27Kip1 expression but increased phosphorylation levels of p27Kip1 on Thr (187) and Ser (10) sites (P<0.05), as well as increasing nuclear accumulation of S-phase kinase-associated protein 2 (Skp2) and cytoplasmic accumulation of the Kip1 ubiquitination-promoting complex (KPC) (P<0.05). Silencing of Skp2 blocked the promoting effects of pCDNA3.1(+)/GAS on viability, the expression of MRP1 and Pgp and the inhibitory effects of pCDNA3.1(+)/GAS on apoptosis. In conclusion, we suggest that GAS contributes to the emergence of MDR of SGC7901 cells via the degradation of p27Kip1.