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Overexpression of B7-H3 augments anti-apoptosis of colorectal cancer cells by Jak2-STAT3

Overexpression of B7-H3 augments anti-apoptosis colorectal cancer cells by Jak2-STAT3

Journal Reference

Zhang T, Jiang B, Zou ST, Liu F, Hua D. World J Gastroenterol. 2015 ;21(6):1804-13.

Institute of Cancer, Affiliated hospital of Jiangnan University, Wuxi 214062, Jiangsu Province, China.

Abstract

The novel expression of B7-H3 has been positively correlated with poor prognosis in many types of cancer. Previous studies have illuminated the relationship between B7-H3 and tumor invasion and metastasis. In present study, the role of B7-H3 in apoptosis in colorectal cancer have been investigated. To investigate the role of the overexpression of B7-H3 in apoptosis in colorectal cancer cell lines and the underlying molecular mechanisms, we constructed SW620 cells that highly overexpressed B7-H3 (SW620-B7-H3-EGFP) and HCT8 cells stably transfected with B7-H3 shRNA (HCT8-shB7-H3). Cells transfected with pIRES2-EGFP were used as negative controls (SW620-NC and HCT8-NC). Real-time PCR and western blotting analysis were used to detect the mRNA and protein expressions of the apoptosis regulator proteins Bcl-2, Bcl-xl and Bax. A cell proliferation assay was used to evaluate the survival rate and drug sensitivity of the cells. The effect of drug resistance was detected by sub-G1 peaks measured with CFM. Active caspase-3 was used to reflect the anti-apoptotic ability of cells. Western blotting was also performed to determine the expression of proteins associated with the Jak2-STAT3 signaling pathway and the apoptosis regulator proteins after the treatment with AG490, a Jak2 specific inhibitor, in B7-H3 overexpressing cells. The data were analyzed by GraphPad Prism 6 using a non-paired t-test. The study results showed that whether overexpression in SW620 cells or downregulation in HCT8, B7-H3 significantly affected the expression of anti- and pro-apoptotic proteins, at both the transcriptional and translational levels, compared with the negative control. B7-H3 overexpression increased the drug resistance of cells and resulted in a higher survival rate, also inhibited apoptosis in colorectal cancer cell lines. Furthermore, B7-H3 overexpression improved Jak2 and STAT3 phosphorylation and, in turn, increased the expression of the downstream anti-apoptotic proteins Bcl-2 and Bcl-xl. After treating B7-H3 overexpressing cells with the Jak2-specific inhibitor AG490, the phosphorylation of Jak2 and STAT3, and the expression of Bcl-2 and Bcl-xl, decreased accordingly. This finding suggested that the Jak2-STAT3 pathway is involved in anti-apoptotic ability of B7-H3. Taken together, our results showed that overexpression of B7-H3 induced resistance to apoptosis in colorectal cancer cell lines by upregulating the Jak2-STAT3 signaling pathway. These results provide a new vision for designing therapeutics targeting B7-H3 and its associated signaling pathways in the treatment of colorectal cancer.

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