A NAV2729-sensitive mechanism promotes adrenergic smooth muscle contraction and growth of stromal cells in the human prostate.

Voiding symptoms in benign prostatic hyperplasia (BPH) are driven by prostate smooth muscle contraction and prostate growth. Smooth muscle contraction in the prostate and other organs critically depends on activation of the small monomeric GTPase RhoA and probably Rac1. A role of another GTPase, ADP-ribosylation factor 6 (ARF6), for smooth muscle contraction has been recently suggested by indirect evidence but remains to be proven for any organ. Here, we report effects of NAV2729, an inhibitor with assumed specificity for ARF6, in human prostate tissues and cultured prostate stromal cells (WPMY-1). NAV2729 (5 μm) inhibited neurogenic and α1-adrenergic contractions of human prostate tissues. Contractions induced by endothelin-1, by the thromboxane A2 agonist U46619, or by high molar KCl were not inhibited. Correlation analyses suggested up-regulation of prostatic ARF6 expression with increasing degree of BPH, as ARF6 expression increased with the content of prostate-specific antigen (PSA) of prostate tissues. NAV2729 inhibited ARF6 activity but not other GTPases (ARF1, RhoA, Rac1) in prostate tissues and in WPMY-1 cells. Proliferation of WPMY-1 cells was inhibited concentration-dependently by NAV2726, as reflected by decreased viability, 5-ethynyl-2'-deoxyuridine (EdU) assay, colony formation assay, and expression of Ki-67. Silencing of ARF6 expression mimicked effects of NAV2729 on viability and in the EdU assay. Effects of NAV2729 on viability and proliferation were attenuated in cells with silenced ARF6 expression. Our findings suggest that a NAV2729-sensitive mechanism promotes adrenergic contraction and stromal cell growth in the human prostate, which is probably ARF6-mediated. Similar actions in other organs and urodynamic effects of NAV2729 appear possible.