| First Author | Saxena UH | Year | 2009 |
| Journal | Mol Cell Biol | Volume | 29 |
| Issue | 9 | Pages | 2335-45 |
| PubMed ID | 19237534 | Mgi Jnum | J:148421 |
| Mgi Id | MGI:3844774 | Doi | 10.1128/MCB.00687-08 |
| Citation | Saxena UH, et al. (2009) Phosphorylation by cyclin C/cyclin-dependent kinase 2 following mitogenic stimulation of murine fibroblasts inhibits transcriptional activity of LSF during G1 progression. Mol Cell Biol 29(9):2335-45 |
| abstractText | Transcription factor LSF is required for progression from quiescence through the cell cycle, regulating thymidylate synthase (Tyms) expression at the G(1)/S boundary. Given the constant level of LSF protein from G(0) through S, we investigated whether LSF is regulated by phosphorylation in G(1). In vitro, LSF is phosphorylated by cyclin E/cyclin-dependent kinase 2 (CDK2), cyclin C/CDK2, and cyclin C/CDK3, predominantly on S309. Phosphorylation of LSF on S309 is maximal 1 to 2 h after mitogenic stimulation of quiescent mouse fibroblasts. This phosphorylation is mediated by cyclin C-dependent kinases, as shown by coimmunoprecipitation of LSF and cyclin C in early G(1) and by abrogation of LSF S309 phosphorylation upon suppression of cyclin C with short interfering RNA. Although mouse fibroblasts lack functional CDK3 (the partner of cyclin C in early G(1) in human cells), CDK2 compensates for this absence. By transient transfection assays, phosphorylation at S309, mediated by cyclin C overexpression, inhibits LSF transactivation. Moreover, overexpression of cyclin C and CDK3 inhibits induction of endogenous Tyms expression at the G(1)/S transition. These results identify LSF as only the second known target (in addition to pRb) of cyclin C/CDK activity during progression from quiescence to early G(1). Unexpectedly, this phosphorylation prevents induction of LSF target genes until late G(1). |
