Recruitment of a myosin heavy chain kinase to actin-rich protrusions in Dictyostelium

Nonmuscle myosin II plays fundamental roles in cell body translocation during migration and is typically depleted or absent from actin-based cell protrusions such as lamellipodia, but the mechanisms preventing myosin II assembly in such structures have not been identified [1-3]. In Dictyostelium discoideum, myosin II filament assembly is controlled primarily through myosin heavy chain (MHC) phosphorylation. The phosphorylation of sites in the myosin tail domain by myosin heavy chain kinase A (MHCK A) drives the disassembly of myosin II filaments in vitro and in vivo [4]. To better understand the cellular regulation of MHCK A activity, and thus the regulation of myosin II filament assembly, we studied the in vivo localization of native and green fluorescent protein (GFP)-tagged MHCK A. MHCK A redistributes from the cytosol to the cell cortex in response to stimulation of Dictyostelium cells with chemoattractant in an F-actin-dependent manner. During chemotaxis, random migration, and phagocytic/endocytic events, MHCK A is recruited preferentially to actin-rich leading-edge extensions. Given the ability of MHCK A to disassemble myosin II filaments, this localization may represent a fundamental mechanism for disassembling myosin II filaments and preventing localized filament assembly at sites of actin-based protrusion.