Estrogen-induced upregulation and 3’-UTR shortening of CDC6

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2013
Akman, H. Begüm
Alternative polyadenylation (APA) may cause mRNA 3’-UTR (untranslated region) shortening in different physiological conditions and/or disease states. About half of mammalian genes use alternative cleavage and polyadenylation to generate multiple mRNA isoforms differing in their 3′-UTRs. Consequently, 3’-UTR shortening of mRNAs via APA has important consequences for gene expression. Studies showed that, by preferential use of proximal APA sites and switching to shorter 3’-UTRs, proliferating cells can avoid 3’-UTR dependent negative post-transcriptional regulations. Hence, such APA and 3’-UTR shortening events may explain the basis of some of the proto-oncogene activation cases observed in cancer cells. Based on the fact that certain cell types switch to more proximal poly(A) sites to rapidly increase translation rates by escaping from miRNAs, we hypothesized that upon estradiol (E2) treatment in estrogen receptor positive (ER+) breast cancer cells, such proximal poly(A) sites may be preferred to provide a rapid growth pattern. Initial probe based screen of independent expression arrays suggested upregulation and 3’-UTR shortening of an essential regulator of DNA replication, CDC6 (Cell Division Cycle 6), upon E2 treatment. Further investigations confirmed the E2 and ER dependent upregulation and 3’-UTR shortening of CDC6, which lead to increased CDC6 protein levels and higher BrdU incorporation. Consequently, miRNA binding predictions and dual luciferase assays suggested that 3’-UTR shortening of CDC6 was a likely mechanism to avoid 3’-UTR dependent negative regulations. In summary, we demonstrated CDC6 APA induction by the proliferative effect of E2 in ER+ cells and provided new insights into the complex regulation of APA. E2 induced APA is likely to be an important but previously overlooked mechanism of E2 responsive gene expression.