Cyclin-Dependent Kinase Activity Is Required for Progesterone Receptor Function: Novel Role for Cyclin A/Cdk2 as a Progesterone Receptor Coactivator

Abstract

Our studies examining the role of the cell cycle-regulated kinase cyclin A/Cdk2 in progesterone receptor (PR) action have demonstrated that cyclin-dependent kinase activity is required for PR function and that cyclin A/Cdk2 functions as a PR coactivator. Although Cdk2 can phosphorylate PR, elimination of these phosphorylation sites has little effect on the ability of cyclin A/Cdk2 to stimulate PR activity. PR interacts with cyclin A and recruits cyclin A/Cdk2 to progestin-responsive promoters, stimulating transcription. Inhibition of Cdk2 activity abolishes progesterone-dependent activation of PR target genes in part through inhibition of PR-dependent recruitment of steroid receptor coactivator 1 (SRC-1) and subsequent histone H4 acetylation at the target promoter. In vitro studies revealed that the interaction between SRC-1 and PR is dependent upon phosphorylation of SRC-1. This heretofore-unknown mechanism provides a potential means for integrating the regulation of PR activity with cell cycle progression. Moreover, the ability of PR to recruit cyclin A/Cdk2 to target promoters provides locally elevated levels of kinase, which can preferentially facilitate phosphorylation-dependent interactions and enzymatic activities of coactivators at the target promoter.

ACKNOWLEDGMENTS

We thank Kurt Christensen and the UC Cancer Center Tissue Culture Core facility for assistance with baculovirus production of recombinant PR, SRC-1, and cyclin A/Cdk2 and Lori Sherman (UCHSC) for the production and purification of 1294 monoclonal antibody. We thank William Edward Bingman III, Jared Gilliam, Judy Roscoe, and Cheryl Parker for assistance with tissue culture and transfection studies.

This work was supported by Public Health Service grant R01 CA-57539 (to N.L.W. and D.P.E.) from the National Cancer Institute and Public Health Service training grant T32 HDO7165 (to R.N.).