Role of Era Splicing Variants in Regulation of Ap-1 Directed Gene Transcription in Breast Cancer Cells

摘要

This report presents results from functional analysis of estrogen receptor-alpha (ERa) mRNA splicing variants and offers insight into the nature of their transcriptional activity. Efforts to establish a cellular transactivating role for ERa mRNA splicing variants have identified three genes, which do not contain consensus EREs in their promoters, that are regulated by one or both of the isoforms, ERAE3 and ERAE5. Expression of a reporter gene driven by the chicken ovalbumin promoter is induced by ERAE5 in cells treated with PMA, and by ERAE3 and wt ERa with E2 and PMA cotreatment. A short region of the collagenase promoter (-73 to +63 relative to the transcription start site) containing an AP-1 motif is activated by ERAE5 and E2-liganded ERAE3 in the presence of PMA. The human IGF-1 promoter is constitutively induced by ERAE5 but is not regulated by wt ERa or ERAE3. Overexpression of c-jun enhanced receptor activities on both the ovalbumin and collagenase prbmoters. It is likely that the regulation of these noncanonical promoters by wt ERa and ERa splicing variants involves protein-protein interactions with co-regulatory proteins and upstream factors that in turn act through their cognate DNA-response elements (e.g., c-jun and c-fos). in vitro binding studies show that wt ERa directly binds c-jun and c-fos; also, ERAE3, ERAE5 and wt ERa bind the steroid receptor corepressor SMRT.