Expression and Alpha1-adrenoceptor Regulation of Caldesmon in Human Prostate Smooth Muscle

Abstract

To investigate expression and α1-adrenergic regulation of caldesmon in the human prostate. Caldesmon is an important mediator and regulator of contraction in different smooth muscle types. However, this has not been investigated in the prostate to date. The activity of caldesmon may be tightly regulated by serine-789 phosphorylation. Prostate tissue was obtained from patients undergoing radical prostatectomy. Caldesmon expression was studied by Western blot analysis and immunohistochemistry. The adrenergic regulation of caldesmon phosphorylation was investigated by Western blot analyses with a site- and phosphospecific antibody. Caldesmon expression was detectable by Western blot analysis in all investigated samples of human prostates (n = 8 patients). Immunoreactivity after staining with a caldesmon antibody was strong in smooth muscle cells, but not observed in glandular or epithelial cells (n = 5 patients). In double fluorescence staining, caldesmon co-localized with α1A-adrenoceptors and α-smooth muscle actin (n = 6 patients). Stimulation of prostate tissue with noradrenaline (30 μM, n = 6 patients) or the α1-adrenergic agonist phenylephrine (10 μM, n = 6 patients) resulted in progressive phosphorylation of caldesmon at serine-789. Noradrenaline-induced caldesmon phosphorylation was 1.5 ± 0.2-fold after 5 minutes (P<.04 vs basal phosphorylation), and 1.6 ± 0.2-fold after 10 minutes (P<.04). Phenylephrine-induced caldesmon phosphorylation was 1.7 ± 0.2-fold after 10 minutes (P<.02 vs basal phosphorylation), and 2.4 ± 0.6-fold after 20 minutes (P<.05). Caldesmon is an effector of α1-adrenoceptors in the human prostate. Caldesmon activation may be of importance for α1-adrenergic prostate contraction, and during therapy with α1-blockers.