Regulation of the Pur-alpha promoter by E2F-1.

Puralpha is a ubiquitously expressed multifunctional nucleic acid-binding protein that is involved in many cellular processes including transcriptional regulation, the cell cycle, oncogenic transformation, and post-natal brain development. Previously, Puralpha protein was found to bind to E2F-1, inhibit E2F-1 transcriptional activity, and reverse the effects of ectopic E2F-1 expression on cell growth. Also Puralpha binds to a GC/GA-rich sequence within its own promoter and inhibits gene expression, that is, Puralpha is autoregulated. We now report that the Puralpha promoter (pPuralpha) is induced by E2F-1 and that this activity maps to a consensus E2F-1 binding motif that is juxtaposed to the Puralpha binding site. Deletion mutants of the E2F-1 protein showed that the region between amino acid residues 88-241 is important for this activity. E2F-1-associated activation of the pPuralpha was inhibited by co-expression of Puralpha, pRb, and an RNA species with specific binding to E2F-1. Chromatin immunoprecipitation (ChIP) assay using primers that flanked the juxtaposed Puralpha and E2F-1 binding sites verified the presence of Puralpha and E2F-1 on the pPuralpha in vivo. In a Tet-inducible cell line, Puralpha delayed cell cycle progression. Thus, E2F-1 and Puralpha interplay appears to be involved in the regulation of Puralpha expression and the cell cycle.