Abstract: Objective To investigate the mechanism of progesterone receptor membrane components 1(PGRMC1) promoting the proliferation of breast cancer cells during hormone therapy. Methods Estrogen receptor (ER) -positive breast cancer MCF7 cells were treated with estrogen and progesterone, and then infected with chronic disease venom overexpressing PGRMC1, knockdown ER prohibitin(shPHB1-1 and shPHB1-2) and their corresponding negative controls. The interaction between PGRMC1 and PHB complex (PHB1 and PHB2) was detected by co-immunoprecipitation combined with mass spectrometry and GST pull-down assay. The expressions of PHB1, PHB2 and PGRMC1 were detected by Western blot and RT-qPCR. The cell proliferation ability was detected by CCK-8 and EDU assay. Flow cytometry was used to detect the cell cycle, and RT-qPCR was used to detect the expression of downstream target genes of ER signaling pathway, including THBS1, CXCL12 and GREB1. Results Co-immunoprecipitation combined with mass spectrometry analysis showed that both PHB1 and PHB2 were present in the co-immunoprecipitation fraction of PGRMC1. GST pull-down identified a direct interaction between PGRMC1 and PHB complex in vitro. Compared with the control group, the proliferation rate of breast cancer cells overexpressing PGRMC1 and down-regulating PHB1 was significantly accelerated (all P<0.05), the proportions of positive cells in S and G2/M phases were significantly increased (all P<0.05), and the expressions of THBS1, CXCL12 and GREB1 in the downstream target genes of ER signaling pathway were significantly promoted (all P<0.01). The interaction between PHB1 and ER in MCF7 cells was attenuated after PGRMC1 overexpression. The proportion of positive cells in S and G2/M phases after down-regulating PHB1 and then overexpressing PGRMC1 had no significant change compared with that of down-regulating PHB1 alone (all P>0.05). Conclusions PGRMC1 may relieve the inhibitory effect of PHB complex on the ER signaling pathway by binding to PHB complex, thereby promoting the activation of the ER signaling pathway and the expressions of downstream target genes, and accelerating the malignant proliferation of breast cancer cells under hormone stimulation.

Key words: Breast cancer, Progesterone receptor membrane components 1, Estrogen receptor, Prohibitin 1, Prohibitin 2