Crosstalk between EGFR and extranuclear steroid receptors.

Epidermal growth factor (EGF) stimulates DNA synthesis and cytoskeletal rearrangement in human breast cancer (MCF-7) and human prostate cancer (LNCaP) cells. Both effects are inhibited by estrogen (ICI 182,780) and androgen (Casodex) antagonists. This supports the view that crosstalk exists between EGF and estradiol (ER) and androgen (AR) receptors and suggests that these receptors are directly involved in the EGF action. Our recent work shows that EGF stimulates ER phosphorylation on tyrosine and promotes the association of a complex between EGFR, AR/ER, and the kinase Src. The complex assembly triggers Src activity, epidermal growth factor receptor (EGFR) phosphorylation on tyrosine, and the EGF-dependent signaling pathway activation. In these cells, the AR/ER/Src complex is required for the EGF action, as the growth factor effects are abolished upon receptor silencing by specific SiRNAs and steroid antagonists or Src inhibition by the kinase inhibitor PP2.