FOXC1 Inhibits Pulmonary Metastasis Of Breast Cancer Cells In Vivo And CARM1 Inhibits Senescence And Sahf Of Cancer Cells Through The Site-specific Methylation Of HP1γ

This thesis is composed of two parts of research work.Part I. FOXC1 inhibits migration and invasion of MDA-MB-231 HM breast cancer cells in vitro, and inhibits the pulmonary metastasis in vivo.Ore previous work showed that FOXC1 was a target gene of the polycomb group protein family, FOXC1 expression was related to breast cancer progression, and overexpression of FOXC1 inhibited metastasis in the MDA-MB-231 cells. However, whether FOXC1 can inhibit malignant metastasis in vivo is still unclear to date. A highly metastatic variant of the parental MDA-MB-231 cell line designated MDA-MB-231 HM, was a valuable model system for the study of the molecular events underlying breast cancer metastasis. We found that both the FOXC1 mRNA and protein levels were lower in MDA-MB-231 HM cells than in MDA-MB-231 cells. When FOXC1 was stably transfected into MDA-MB-231 and MDA-MB-231 HM cells, it prevented cell migration and invasion. Moreover, ectopic expression of FOXC1 in MDA-MB-231 HM cells inhibited the pulmonary metastasis in both tail vein injection and in mammary fat pad implant athymic mice. Our study demonstrated the function of FOXC1 in breast cancer, which contributes to the clinical decision making at the level of individualization for breast cancer patients.Part II. CARM1 inhibits senescence and SAHF formation through the site-specific methylation of HP1γPrevious work in our lab using epigenetic siRNA library screening revealed that CARM1(or PRMT4) might play a role in tumor cell senescence. In this study, we found that CARM1 was dramatically downregulated in senescent MDA-MB-231 and WI-38 cells. Overexpression of CARM1 impaired the Adriamycin(DOX)-induced senescence and SAHF in MDA-MB-231 cells. Moreover, knockdown of CARM1 through lentivirus induced the senescence and SAHF of MDA-MB-231. The Co-immunoprecipitation assay showed that CARM1 and HP1γ formed a complex in MDA-MB-231 cells; and the mass spectrometry study demonstrated that HP1γ was mono-methylated at arginine 91(R91) by CARM1. Through point mutation study, we found that suppression of the methylation of R91 induced senescence and SAHF of MDA-MB-231 cells. Phosphatase treatment and Western blotted assay showed that knockdown of CARM1 and suppression of the methylation of R91 induced the phosphorylation in HP1γ. Overall, our study elucidates a novel function of CARM1 in senescence and SAHF, i.e., the prosttranslational modification of HP1γ. This study provides the theoretical basis for the clinical decision.