The Allosteric Inhibitor Pentachloropseudilin Inhibits Myosin 1C ATPase Activity and Recapitulates Retinitis Pigmentosa Phenotypes in Mice

Unconventional myosins are molecular motors that move along actin filaments in an ATPase-dependent manner, thereby influencing intracellular cargo transport. Dysfunction of myosins due to loss-of-function mutations causes human disease phenotypes such as deafness, retinitis pigmentosa, renal failure, and hypertrophic cardiomyopathy. However, some genetic models lacking unconventional myosins do not recapitulate the retinal phenotypes observed in humans, necessitating alternative approaches. We previously showed that the myosin motor protein MYO1C is required for the trafficking of rhodopsin in mouse photoreceptors and for visual function. To investigate whether MYO1C could be nongenetically inhibited, we used the natural compound pentachloropseudilin (PCIP) to allosterically inhibit MYO1C-ATPase motor activity. PCIP treatment of COS1 cells coexpressing GFP-rhodopsin and mCherry-MYO1C resulted in an aggregation of GFP-rhodopsin protein in the cytoplasm and impaired the kinetics of rhodopsin foci movement. Conversely, GFP-rhodopsin trafficked efficiently to the plasma membrane in non-PCIP-treated COS1 cells. PCIP effects in vivo were then analyzed in wild-type mouse retinas based on evaluations of opsin trafficking, visual response measurements using ERGs, and quantification of rhodopsin recovery rates after photobleaching. Intravitreous injections of PCIP into WT mice caused significant rhodopsin mislocalization and shorter rod photoreceptor outer segments, resulting in reduced scotopic visual responses, thereby recapitulating retinitis pigmentosa phenotypes commonly observed in humans. Our study provides evidence from live-cell analysis and vertebrate retinas that using PCIP can recapitulate the retinal phenotypes observed in humans with myosin mutations. Furthermore, it confirms in a nongenetic model the requirement for MYO1C in photoreceptor opsin trafficking, maintenance of photoreceptor outer segments, and visual function.