| Estrogen receptor(ER) consisting of ERαand ERβcan modulate the target gene expression when bind to ligand mainly through binding the estrogen response element (ERE). The complex biological effects mediated by ER involve communication between many proteins and signaling pathways. The activity of these transcription factors is regulated by a variety of factors, including ligand binding, phosphorylation, coregulators and the effector pathways. The end result of target gene transcription is to modulate physiological processes, such as reproductive organ development and function, bone density, and unfortunate contribution to the growth and development of breast cancer. ERβwas first cloned from rat prostate using degenerate PCR. The role of ERβin breast cancer growth and development is not as clear as the role of ERα. ERβmight have a modulating effect in breast cancer. Overall, the majority of studies suggest that the presence of ERβis a good prognostic marker for breast cancer.The quaking gene (qki) encodes a highly conserved RNA binding protein (QKI), which is a member of the"STAR"(signal transduction and activation of RNA) family of RNA binding proteins. Quaking has a critical role in myelination. Some homozygous mutant quaking mice died prior to birth becanse of the defect of cardiovascular and muscle development. Others have severe central nervous system dysmyelination, causing quaking movements during normal motor activities from10 days postnatal and tonic convulsion when growing up.In addition to its fundamental role in myelination, QKI also participated in vascular development, apoptosis, cell adhesion, cell growth, morphogenesis and organogenesis. In light of the validated target motif and RNA binding specificity of QKI targets, there are about 1430 putative QKI targets and about 24% putative mRNA targets having function in proliferation and migration. Further, the promotor region of QKI contains a conserved ERE, suggesting a role of QKI in breast cancer. In this study, we analyzed the expression of QKI with or without the treatment of estrogen or tamoxifen in multiple breast cancer cell lines both at mRNA and protein level. In addition, we validate the response of QKI promoter to estrogen through reporter assay. Furthermore, through construction of adenovirus of QKI, we compared the expression of CDC42 and Par1 both under forced QKI expression and control. The main findings of our study are as follows:1.The recombinant adenovirus of Qki-5 has been successfully constructed and expressed in the MDA-MB-231 cells of breast cancer.2.RT-PCR and Western-blot results showed that the mRNA and protein level of qki increased under the stimulation of 17β-estradiol. The activity of qki promoter was upregulated under the stimulation of17β-estradiol.RT-PCR results showed the transcriptional level of qki and activity of qki promoter was downregulated under the stimulation of tamoxifen. In other words, ERE in the QKI promoter region might mediate the QKI response to estrogen. We also observed that transcriptional level of cyclinD1 was downregulated under the stimulation of 17β-estradiol in MDA-MB-231(ERα-/ERβ+).3.Upon overexpression and specifically silencing the expression of QKI, endogenous expression of cdc42 and par1 were significantly changed. Consistently, wounding assay shows that forced expression of QKI nearly abrogate the migration of breast cancer cells.In conclusion, our results primarily set a model that during the breast cancer development, ER signal aberration leads to downregulation of QKI, which in turn enhances the expression of CDC42 and Par1, and thus facilitate the process of tumor metastasis.
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