Myosin IIA Heavy Chain Phosphorylation Mediates Adhesion Maturation and Protrusion in 3D [Cell Biology]

Nonmuscle myosin II (NMII) is a conserved force-producing cytoskeletal enzyme with important but poorly understood roles in cell migration. To investigate myosin heavy chain (MHC) phosphorylation roles in 3D migration, we expressed GFP-tagged NMIIA wild type or mutant constructs in cells depleted of endogenous NMIIA protein. We find that individual mutation or double mutation of S1916 or S1943 to alanine potently blocks recruitment of GFP-NM-IIA filaments to leading edge protrusions in 2D, and this in turn blocks maturation of anterior focal adhesions. When placed in 3D collagen gels, cells expressing wild-type GFP MHC-IIA behave like parental cells, displaying robust and active formation and retraction of protrusions. However, cells depleted of NMIIA, or cells expressing the mutant GFP MHC-IIA display severe defects in invasion and in stabilizing protrusions in 3D. These studies reveal an NMIIA-specific role in 3D invasion that requires competence for NMIIA phosphorylation at S1916 and S1943. In sum, these results demonstrate a critical and previously unrecognized role for NMIIA phosphorylation in 3D invasion.

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