Identification of four novel phosphorylation sites in estrogen receptor alpha: impact on receptor-dependent gene expression and phosphorylation by protein kinase CK2.

Background: Estrogen receptor alpha (ERalpha) phosphorylation is important for estrogen-dependent transcription of ER-dependent genes, ligand-independent receptor activation and endocrine therapy response in breast cancer. However ERalpha phosphorylation at the previously identified sites does not fully account for these receptor functions. To determine if additional ERalpha phosphorylation sites exist, COS-1 cells expressing human ERalpha were labeled with [32P]H3PO4 in vivo and ERalpha tryptic phosphopeptides were isolated to identify phosphorylation sites.

Mechanistic differences in the activation of estrogen receptor-alpha (ER alpha)- and ER beta-dependent gene expression by cAMP signaling pathway(s).

Although increases in intracellular cAMP can stimulate estrogen receptor-alpha (ER alpha) activity in the absence of exogenous hormone, no studies have addressed whether ER beta can be similarly regulated. In transient transfections, forskolin plus 3-isobutyl-1-methylxanthine (IBMX), which increases intracellular cAMP, stimulated the transcriptional activities of both ER alpha and ER beta. This effect was blocked by the protein kinase A inhibitor H89 (N-(2-(p-bromocinnamylamino)-ethyl)-5-isoquinolinesulfonamide) and was dependent on an estrogen response element.