α1-adrenoceptor activation induces phosphorylation of β2-adrenoceptors in human prostate tissue

OBJECTIVE To test whether β1-adrenoceptor activation leads to phosphorylation of the β2-adrenoceptor in human prostate tissue. PATIENTS AND METHODS Prostate tissue from patients undergoing radical prostatectomy was stimulated in vitro with the α1-adrenergic agonist phenylephrine (10 μM). α2-adrenoceptor phosphorylation at serines 345/346 was studied using Western blot analysis with a phospho-specific antibody. The role of second messenger kinases was assessed by studying the effects of the protein kinase C (PKC) inhibitor Ro 31-8425 and the protein kinase A (PKA) inhibitor H89 on phenylephrine-induced phosphorylation. The expression of G protein-coupled receptor kinases (GRKs) 2/3 was analysed using quantitative reverse- transcriptase-polymerase chain reaction (RT-PCR), Western blot analysis and immunohistochemistry. RESULTS Stimulation of prostate tissue with phenylephrine resulted in phosphorylation of the β2-adrenoceptor (5, 10 and 20 min after stimulation). This α1-adrenoceptor-induced phosphorylation of β2-adrenoceptors was resistant to inhibition of PKC and PKA. Changes in phosphorylation levels were not attributable to changes in receptor levels, as these remained constant during stimulation. RT-PCR and Western blot analysis showed expression of GRK2/3 in human prostate tissues. Immunohistochemical staining showed that GRK2/3 expression in human prostate tissue is located to stromal and smooth muscle cells. CONCLUSIONS Activation of α1- adrenoceptors causes phosphorylation of β2-adrenoceptors in the human prostate. This may enhance α1-adrenergic contraction and is possibly mediated by GRK2, which is expressed in prostate smooth muscle. Mutual regulation between different adrenergic receptors might be involved in the therapeutic effects of α1-blockers in patients with benign prostate hyperplasia.