Association of cytoskeletal proteins with estrogen receptor in rat uterine cytosol: possible role in receptor movement into the nucleus.

Evidence is presented to demonstrate a close association between an estrogen receptor or an estrogen receptor activation factor and the cytoskeletal proteins, tubulin and actin in rat uterine cytosol. Exposure of uterine cytosol to protein kinase assay medium resulted in the phosphorylation of three proteins, of molecular mass 55, 50 and 45 kDa. These 55 and 50 kDa proteins apparently represent tubulin, while the 45 kDa protein, is presumed to be actin. Phosphorylation of these proteins is under the regulatory influence of estradiol and the cyclic nucleotides, cAMP and cGMP. It is proposed that the protein kinase involved in this process may be the non-activated estrogen receptor (naER).