Abstract

The presumed ADP ribosylation factor (ARF) 6 inhibitor NAV2729 inhibits human prostate smooth muscle contraction and proliferation of stromal cells, which are driving factors of voiding symptoms in benign prostatic hyperplasia (BPH). However, its specificity and a confirmed role of ARF6 for smooth muscle contraction are still pending. Here, we generated monoclonal ARF6 knockouts in human prostate stromal cells (WPMY-1), and characterized phenotypes of contractility, growth-related functions, and susceptibility to NAV2729 in knockout and control clones. ARF6 knockout was verified by Western blot. Knockout clones showed impaired contraction and actin organization, reduced proliferation and viability, and increased apoptosis and cell death. In ARF6-expressing control clones, NAV2729 (5 µM) strongly inhibited contraction (67% inhibition across all three control clones), actin organization (72%), proliferation (97%), and viability (up to 82%), and increased apoptosis (5-fold) and cell death (6-fold). In ARF6 knockouts, effects of NAV2729 (5 µM) were widely reduced, including lacking or minor effects on contractions (0% inhibition across all three knockout clones), actin (18%) and proliferation (13%), and lacking increases of apoptosis and cell death. Viability was reduced by NAV2729 with an IC₅₀ of 3.3 µM across all three ARF6 control clones, but of 4.5–8.2 µM in ARF6 knockouts. In conclusion, ARF6 promotes prostate smooth muscle contraction and proliferation of stromal cells. Both are inhibited by NAV2729, which showed high specificity for ARF6 up to 5 µM and represents an attractive compound in the context of BPH. Considering the relevance of smooth muscle-based diseases, shared roles of ARF6 in other smooth muscle types merit further investigation.