Transactivation of ErbB1 and ErbB2 receptors by angiotensin II in normal human prostate stromal cells

BACKGROUND: Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is synthesized primarily in the stromal compartment of the human prostate and may regulate stromal as well as epithelial cell growth and survival. The primary cognate HB-EGF receptor, ErbB1, has been shown recently to be transactivated by G-protein coupled receptors (GPCRs) through regulated proteolytic cleavage of the membrane-bound, precursor form of HB-EGF. Previous studies have demonstrated that human prostate tissue, especially tissue from benign prostatic hyperplasia (BPH), has high angiotensin converting enzyme activity, and a high density of angiotensin (Ang) receptors in periurethral stromal cells. Because the pressor peptide Ang II signals through GPCRs, we tested the possibility that Ang II could transactivate ErbB1/ErbB2 in human prostate stromal (hPS) cells. METHODS: Primary and early passage hPS cells were used as an in vitro model. Cells were stimulated by recombinant HB-EGF or Ang II and total cell lysates were harvested for immunoprecipitation and Western blot. Cell growth was measured by [(3)H]thymidine incorporation assay and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazoliumbromide (MTT) assay. RESULTS: Ang II receptors AT1 and AT2 were expressed in hPS cells. ErbB1 and ErbB2 receptors were activated by HB-EGF. Furthermore, Ang II was able to transactivate both ErbB1 and ErbB2, and this transactivation activity could be abolished by pretreatment with [Glu-52]-diphtheria toxin/CRM197, a specific inhibitor of HB-EGF bioactivity. Consistent with its transactivation activity, Ang II modestly promoted hPS cell growth and this effect was abolished by pretreatment with the ErbB1 antagonist AG1478. CONCLUSION: These experiments suggest a regulatory role for Ang II in the prostate stroma and implicate the endogenous stromal growth factor HB-EGF as a mediator of Ang II signaling in the prostate.