An AU-rich element in the 3' untranslated region of the C/EBP delta mRNA is important for protein binding during G0 growth arrest.

Posttranscriptional regulation at the level of mRNA stability is becoming increasingly recognized as an important mechanism to control the levels of mRNAs that encode key cell fate determining proteins. Previous work from our laboratory demonstrated that C/EBPdelta is a highly unstable mRNA in G(0) growth arrested mammary epithelial cells. In this report we investigated trans-acting factor binding to the C/EBPdelta 3'-UTR and identified a cis-acting element important for this interaction. RNA electromobility shift assays (REMSAs) demonstrate that the C/EBPdelta mRNA 3'-UTR binds trans-acting factor(s) present in G(0) growth arrested mammary epithelial cell lysates. This binding was not detected in the presence of lysates from growing cells. UV-binding analysis detected a RNA/protein complex of approximately 35kDa following incubation of the full-length C/EBPdelta 3'UTR with lysates from G(0) growth arrested mammary epithelial cells. Competition assays indicate that a specific AU-rich region (U1) is necessary for trans-acting factor binding to the C/EBPdelta 3'-UTR. These studies have identified an AU-rich element located within the C/EBPdelta 3'-UTR that interacts with a putative G(0) growth arrest-specific trans-acting factor(s), which may regulate C/EBPdelta mRNA decay.