MGC5306 Regulate On Proliferation Of Breast Cancer Cell MCF-7 By P53-dependent Pathway

Although the complete sequence of human MGC5306 gene has been discovered, its function remains to be discovered. In this study, we focused on roles of MGC5306 in regulating cell growth and proliferation of human breast cancer MCF-7 cells.Structure and sequence analysis of MGC5306 protein were performed by computer software. We found that there are several potential phosphorylation sites as well as a sumolyation site and a nuclear localization signal in this protein sequence. So, we guess that MGC5306 might be an undiscovered nuclear protein.MGC5306 mRNA levels were detected in various cell lines by RT-PCR. We found that the mRNA expression levels of MGC5306 in five solid tumor cells are higher than that in HL-60 and A172 cells. However, the levels of MGC5306 mRNA in normal tissues/cells were unable to be detected. These results suggested that MGC5306 may play a key role in tumorigenesis.In addition, we transiently overexpressed MGC5306 and pSUPER-MGC5306 siRNA in hTERT-BJ and MCF-7 cells. Then cell growth rate was analysesed subsequently. The results indicated that MGC5306 could accelerate growth rate of normal cell; and MGC5306 siRNA could inhibit the growth rate of MCF-7 tumor cells. These results suggested that MGC5306 increases cell malignant.Flow cytometry assays showed that cells were arrested in S phase, abolished G2/M phase and induced apoptosis in MGC5306 siRNA transfected MCF-7 cells. The above results implicated that MGC5306 may be involved in cell growth control and regulation.Meanwhile, we have analysesed the protein levels of p53, MDM2 and p21 in MCF-7 and hTERT-BJ cells by Western blot. Results indicated that MDM2 expression was decreased whereas p53 and p21 levels were increased in MCF-7 cells transfected with pSUPER-MGC5306 siRNA, but the p21 expression was decreased in hTERT-BJ cell, a normal human fibroblast cell line transfected with pEGFP-MGC5306. These results indicated that MGC5306 could facilitate cell proliferation by MDM2 activation and repression by p53 and p21. We concluded that the regulation of cell proliferation by MGC5306 is p53-dependent.Finally, we found that the expression level of Bcl-2 was not changed in MCF-7 tranfected with pSUPER-MGC5306 siRNA. So, we suggested that the role of MGC5306 in regulating cell apoptosis were dependent on death receptor pathway and independent on mitochondrial pathway.In summary, we discussed the possible roles of MGC5306 in regulating cell growth and proliferation of human breast cancer MCF-7 cells. Our findings provided fundamental basis for better understanding of MGC5306 in cell growth and tumorigenesis..