TRPV4 mediates the Ca 2+ influx required for the interaction between flightless-1 and non-muscle myosin, and collagen remodeling.

Fibroblasts remodel extracellular matrix collagen, in part, through phagocytosis. This process requires formation of cell extensions, which in turn involves interaction of the actin-binding protein flightless-1 (FliI) with non-muscle myosin IIA (NMMIIA; heavy chain encoded by MYH9 ) at cell-matrix adhesion sites. As Ca ²⁺ plays a central role in controlling actomyosin-dependent functions, we examined how Ca ²⁺ controls the generation of cell extensions and collagen remodeling. Ratio fluorimetry demonstrated localized Ca ²⁺ influx at the extensions of fibroblasts. Western blotting and quantitative (q)PCR showed high expression levels of the Ca ²⁺ -permeable transient receptor potential vanilloid-4 (TRPV4) channel, which co-immunoprecipitated with β1 integrin and localized to adhesions. Treatment with α2β1-integrin-blocking antibody or the TRPV4-specific antagonist AB159908, as well as reduction of TRPV4 expression through means of siRNA, blocked Ca ²⁺ influx. These treatments also inhibited the interaction of FliI with NMMIIA, reduced the number and length of cell extensions, and blocked collagen remodeling. Pulldown assays showed that Ca ²⁺ depletion inhibited the interaction of purified FliI with NMMIIA filaments. Fluorescence resonance energy transfer experiments showed that FliI-NMMIIA interactions require Ca ²⁺ influx. We conclude that Ca ²⁺ influx through the TRPV4 channel regulates FliI-NMMIIA interaction, which in turn enables generation of the cell extensions essential for collagen remodeling.
Competing Interests: Competing interestsThe authors declare no competing or financial interests.
(© 2017. Published by The Company of Biologists Ltd.)