Non-muscle Myosin IInew mechanisms of regulation and functional characterization of MYH9 pathological variants

Resumo

Generation of mechanical forces is essential for multiple biological processes, e.g tissue formation and homeostasis, cell migration and division, etc. Class II myosins generate most of these forces. Myosin II is expressed in muscle and non-muscle cells as different paralogs. These proteins are endowed with actin-binding and ATPase-mediated contraction activities. Additionally, they organize into polymers (myosin filaments) that exert forces through the concerted movement of actin filaments. There are three paralogs of non-muscle myosin II (NMII), NMII-A, NMII-B and NMII-C. Together with actin filaments, NMII participates in the generation of multiple cellular structures that support mechanical stresses and exert traction forces. These actomyosin structures are involved in the maintenance of cellular integrity during cell migration and division, etc. Since NMII function relies on its assembly into filaments and its binding to actin, these steps are tightly regulated. This work is divided in two parts. First, we characterize a new mode of regulation through Tyr phosphorylation on the regulatory light chain of NMII. This phosphorylation prevents the formation of a functional NMII units, repressing its assembly into filaments. In the second part, we delineate new aspects of NMII functionality by characterizing several mutations that affect diverse functional domains of the NMII-A paralog. Appearance of these mutations causes a group of disorders collectively named MYH9-related diseases (MYH9-RD). We showed that the mutations translate into specific alterations of NMII-A stability in filaments and cellular functions that depend on actin, e.g. adhesion dynamics. Additionally, we characterize the morphological and functional alterations of primary leukocytes from a patient with the MYH9 variant c.3486G>T (R1162S). We found morphological alterations in activated T cells, monocyte-derived dendritic cells and neutrophils.