Collagen remodeling by phagocytosis is determined by collagen substrate topology and calcium-dependent interactions of gelsolin with nonmuscle myosin IIA in cell adhesions

Abstract

Cell adhesion to collagen presented on beads activates Ca ²⁺ entry and promotes the formation of phagosomes enriched with NMMIIA and gelsolin. The Ca ²⁺-dependent interaction of gelsolin and NMMIIA in turn enables actin remodeling and enhances collagen degradation by phagocytosis.

Abstract

We examine how collagen substrate topography, free intracellular calcium ion concentration ([Ca ²⁺] _i, and the association of gelsolin with nonmuscle myosin IIA (NMMIIA) at collagen adhesions are regulated to enable collagen phagocytosis. Fibroblasts plated on planar, collagen-coated substrates show minimal increase of [Ca ²⁺] _i, minimal colocalization of gelsolin and NMMIIA in focal adhesions, and minimal intracellular collagen degradation. In fibroblasts plated on collagen-coated latex beads there are large increases of [Ca ²⁺] _i, time- and Ca ²⁺-dependent enrichment of NMMIIA and gelsolin at collagen adhesions, and abundant intracellular collagen degradation. NMMIIA knockdown retards gelsolin recruitment to adhesions and blocks collagen phagocytosis. Gelsolin exhibits tight, Ca ²⁺-dependent binding to full-length NMMIIA. Gelsolin domains G4–G6 selectively require Ca ²⁺ to interact with NMMIIA, which is restricted to residues 1339–1899 of NMMIIA. We conclude that cell adhesion to collagen presented on beads activates Ca ²⁺ entry and promotes the formation of phagosomes enriched with NMMIIA and gelsolin. The Ca ²⁺ -dependent interaction of gelsolin and NMMIIA in turn enables actin remodeling and enhances collagen degradation by phagocytosis.