Phosphorylation and steroid hormone action

This chapter describes the different aspects of phosphorylation and steroid hormone action. Group A receptors form complexes with heat-shock proteins in the absence of hormone. After hormone binding, the receptors dissociate from some of the heat-shock proteins and are transformed into complexes in which the receptors dimerize, bind DNA, and activate or repress the transcription of target genes. In the absence of hormone, group B receptors usually bind to DNA. Most steroid receptors are phosphorylated in vivo at multiple sites, suggesting that phosphorylation may play multiple roles in receptor function. Several features of chicken progesterone receptor (cPR) phosphorylation are common to the members of the steroid hormone receptor superfamily, especially the group A receptors. First, the phosphorylation sites can be basal, ligand-dependent, or DNA-dependent. Both cPR and human progesterone receptor (hPR) are phosphorylated in a DNA-dependent manner during cell-free transcription in HeLa cell nuclear extracts. The phosphorylation is increased in vivo after the activation of either protein kinase A (PKA) or protein kinase C (PKC) pathways, and treatment with H7, which can inhibit several kinases, including PKA and PKC, resulted in both a dose-dependent inhibition of the phosphorylation and the induction of terminal differentiation of the erythroblasts. © 1995 Academic Press Inc.