The Novel Effects And Mechanisms Of Estrogen Receptor α 36 In Resistance To Breast Cancer Drugs

● BackgroundBoth Estrogen receptor (ER) and EGFR//HER2 signaling pathways are involved in growth, proliferation and differentiation of breast cancer cells. For the treatment of breast cancer, therapeutic approaches have been developed based on particular molecular alterations. These include a monoclonal antibody termed trastuzumab/Herceptin to the receptor protein HER2 for patients whose tumors express the HER2 receptor, and endocrine therapy such as Tamoxifen for patients whose tumors express ER, progesterone receptor (PR), or both. However, Despite the presence of the ER and PR, only half of the patients will respond to endocrine therapy, and less than 35% of patients with HER2-overexpressing metastatic breast cancer will respond to trastuzumab as a single agent. Furthermore, the majority of patients who achieve an initial response generally acquire resistance within 1 year. ER-a36, a novel variant of human estrogen receptor-alpha, is predominantly localized to the plasma membrane and the cytoplasm, mediating a rapid membrane-initiated nongenomic signaling pathway. The crosstalk between ER-a36 and EGFR/HER2 signalings might be associated with Tamoxifen or Herceptin resistance in breat cancer cells.Tamoxifen is a selective estrogen receptor modulator (SERM),which has been used widely as an effective treatment of all stages of estrogen receptor (ER)-positive breast cancer.The major obstacle to Tamoxifen usage is Tamoxifen resistance, which mechanisms are poorly understood. It has been well demonstrated that estogen(E2) non-genomic activity mediated by ER-a66 induces Tamoxifen resistance through cross-talk with HER2 signalling in ER-a66 positive breast cancer cells. The membrane-initiated non-genomic signaling mediated by ER-a36 is also involving in Tamoxifen resistance. The clinical data showed that ER-a36 was high expressed in 40 percent of ER-a66 positive breast cancer and enhances the resistance of Tamoxifen. So, it is deduced that Tamoxifen resistance in ER-a66 and ER-a36 co-expressing breast cancer cells can be enhanced through ER-a66 or ER-a36-mediated non genomic activity, respectively.Trastuzumab/Herceptin is a humanized monoclonal antibody directed against Her2, as same as Tamoxifen resistance, Herceptin resistance is often occurred in clinic and the precise mechanism has not been fully characterized. Because effectively Herceptin dosage blocking HER2 signalling activated by ER-a36-mediated non-genomic activity might be forced to be increased, and our previous study demonstrated that sensitivity of Herceptin in ER positive breast cancer cells could be interferred by ER-α66-mediated non-genomic activity, it is indicated that ER-α36 may affect the sensitivity of Herceptin in breast cancer cells through its non-genomic activity, which may be involved in the generation of Herception resistance. Our current project will focus on the novel effects and mechanisms of ER-α36 in resistance to breast cancer drugs inculding Tamoxifen and Herceptin.● Contents(1)The effect and mechanism of the co-expression of ER-α66 and ER-α36 on Tamoxifen sensitivity in breast cancer cells was observed, using Western blot,CCK-8 and Confocal assay.(2)The effect and mechanism of ER-α36 on Herceptin sensitivity in breast cancer cells was explored, using Western blot,CCK-8 assay.● Results(一) The effect and mechanism of the co-expression of ER-α66 and ER-α36 on Tamoxifen sensitivity in breast cancer cells(1) the ER-α66 and ER-α36 can co-localized to the membrane or cytoplasm in ER-α66 and ER-α36 co-expressing breast cancer cells.(2) Co-expression of ER-α66 and ER-α36 in breast cancer cells can enhance E2 or Tamoxifen-mediated phosphorylation of MAPK and Akt, which are downstream molecules of HER2 signalling.(3) Tamoxifen-stimulated cell proliferation can be enhanced in ER-a66 and ER-a36 co-expressing breast cancer cells(二) The effect and mechanism of ER-a36 on Herceptin sensitivity in breast cancer cells(1) ER-a36 can significantly decrease the sensitivity of Herceptin in breast cancer cells.(2) E2 can significantly decrease the sensitivity of Herceptin in breast cancer cells through ER-a36-mediated non-genomic activity.(3) E2-stimulating ER-a36 non-genomic activity can interfer the inhibitory effect of Herceptin on the phosphorylation of MAPK and Akt.● Conclusions(1) Tamoxifen resistance can be enhanced in ER-a66 and ER-a36 co-expressing breast cancer cells through ER-a66 or ER-a36-mediated non-genomic activity, respectively.(2) ER-a36 can decrease the sensitivity of Herceptin in breast cancer cells through its non-genomic activity.● Purpose and significance(1) The study about the relation between the co-expression of ER-a66 and ER-a36 and Tamoxifen sensitivity in breast cancer cells will provide a new mechanism for study on Tamoxifen resistance. It will also determine the role of ER-a36 as an important marker for Tamoxifen therapy in ER-α66 positive breast cancer, and provide a new theoretical basis on the strategy of combined therapy based on Tamoxifen for breast cancer patients.(2) The study about the relation between ER-a36 and sensitivity of Herceptin in breast cancer cells may provide a new and important mechanism for Herceptin resistance and a new theoretical basis on the strategy of combined therapy based on Herceptin for breast cancer patients.