Identification Of A New Human Estrogen Recepter α In Breast Cancer,ERα30,and Its Function And Mechanism

Alternative splicing produ ces many different mRNAs(splice variants)from the same gene,so that a limited number of genes can encode a variety of different proteins.There is increasing evidence that splice variants have significant roles in the development,clinical diagnosis,and treatment of cancer.From the early 1990 s to now,many human estrogen receptor-α(hER-α)splice variants have been discovered,most with one or more exons deleted and that are expressed as proteins.Some of these variants exhibit modified the function of the full-length hER-α(ER-α66).They may become abnormal during the formation and progression of breast cancer,resulting in increased influence on the behaviors of breast cancer cells via as yet undescribed mechanisms and may promote the progression of breast cancer to phenotypes that are more aggressive,such as loss of the responsiveness to anti-estrogen treatment.Here,we identified and cloned a new human estrogen receptor-α(hER-α)splice variant,ERα30,from a triple negative breast cancer tissue.The splice is distinct with the first 24 bp of exon 4 directly spliced to the last 44 bp of exon 6 of the hER-α genomic sequence.Because exon 5 and exon 7 are completely deleted,the open-reading frame of ER-α30 predicts a truncated protein with a 30 kDa molecular weight that differs from the traditional full-length h ER-α(ER-α66)by lacking part of the hinge domain,the ligand-binding domain,and ligand-dependent transcriptional activation domain(LBD/AF2),but possessing a unique C-terminal 10 amino acid domain.The predicted truncated 30 kDa protein was subsequently expressed in stably transfected breast cancer cells MDA-MB-231.We examined the expression of ER-α30 mRNA in specimens from 33 breast cancer patients and found that 11 specimens(33.3%)expressed ER-α30 on mRNA level.The expression of ERα30 was associated with ERα66 and progesterone receptor negative(PR negative)breast cancers and the over-expression of ERα30 in MDA-MB-231 cells enhanced in vitro malignant biological behaviors of cell proliferation,migration,and invasion.The ERα30-EGFP fusion protein was expressed in the nuclear of MDA-MB-231,and the result of real time RT-PCR assay showed that ERα30 upregulated the expresstion of EGFR and c-jun,suggesting ERα30 may mediated the “nonclassical” pathways,such as the ligand-independent ERα signaling,in which gene activation occurs through second messengers downstream of growth factor signaling pathway and ERE-independent signaling,in which ERα regulates genes via protein-protein interactions with other transcription factors.In summary,we identified a new human estrogen receptor-α(hER-α)splice variant,ER-α30,and preliminarily investigated its function and mechamism.However,many scientific questions remain unclear,and further studies are needed to determine the significance of ER-α30 in human breast cance.These studies will provide new insight into complex biological aspects of breast cancer.