Proteomic\nAnalysis Reveals Major Proteins and Pathways\nThat Mediate the Effect of 17-β-Estradiol in Cell Division and\nApoptosis in Breast Cancer MCF7 Cells

Despite extensive research, the genes/proteins and pathways\nresponsible\nfor the physiological effects of estrogen remain elusive. In this\nstudy, we determined the effect of estrogen on global protein expression\nin breast cancer MCF7 cells using a proteomic method. The expression\nof 77 cytosolic, 74 nuclear, and 81 membrane/organelle proteins was\nsignificantly altered by 17-β-estradiol (E2). Protein enrichment\nanalyses suggest that E2 may stimulate cell division primarily by\npromoting the G1 to S phase transition and advancing the G2/M checkpoint.\nThe effect of E2 on cell survival was complex, as it could simultaneously\nenhance and inhibit apoptosis. Bioinformatics analysis suggests that\nE2 may enhance apoptosis by promoting the accumulation of the pore-forming\nprotein Bax in the mitochondria and inhibit apoptosis by activating\nthe PI3K/AKT/mTOR signaling pathway. We verified the activation of\nthe PI3K signaling and the accumulation of Bax in the membrane/organelle\nfraction in E2-treated cells using immunoblotting. Treatment of MCF7\ncells with E2 and the PI3K inhibitor Ly294002 significantly enhanced\napoptosis compared to those treated with E2 alone, suggesting that\ncombining estrogen with a PI3K inhibitor could be a promising strategy\nfor treating ERα-positive breast cancer. Interestingly, many\nof the E2-upregulated proteins contained the HEAT, KH, and RRM domains.