Kim, HughHong, FelixMollica, Molly Y.Golla, KalyanDe Silva, EnoliSniadecki, Nathan J.López, José A.2024-09-242024-09-242024-08-27Kim, Hugh, Felix Hong, Molly Y Mollica, Kalyan Golla, Enoli De Silva, Nathan J Sniadecki, and José A López. “Filamin A Regulates Platelet Shape Change and Contractile Force Generation via Phosphorylation of the Myosin Light Chain.” Biochemical Journal, August 27, 2024, BCJ20240114. https://doi.org/10.1042/BCJ20240114.https://doi.org/10.1042/BCJ20240114http://hdl.handle.net/11603/36323Platelets are critical mediators of hemostasis and thrombosis. Platelets circulate as discs in their resting form but change shape rapidly upon activation by vascular damage and/or soluble agonists such as thrombin. Platelet shape change is driven by a dynamic remodeling of the actin cytoskeleton. Actin filaments interact with the protein myosin, which is phosphorylated on the myosin light chain (MLC) upon platelet activation. Actin-myosin interactions trigger contraction of the actin cytoskeleton, which drives platelet spreading and contractile force generation. Filamin A (FLNA) is an actin-crosslinking protein that stabilizes the attachment between subcortical actin filaments and the cell membrane. In addition, FLNA binds multiple proteins and serves as a critical intracellular signaling scaffold. Here, we used platelets from mice with a megakaryocyte/platelet-specific deletion of FLNA to investigate the role of FLNA in regulating platelet shape change. Relative to controls, FLNA-null platelets exhibited defects in stress fiber formation, contractile force generation, and MLC phosphorylation in response to thrombin stimulation. Blockade of Rho kinase (ROCK) and protein kinase C (PKC) with the inhibitors Y27632 and bisindolylmaleimide (BIM), respectively, also attenuated MLC phosphorylation; our data further indicate that ROCK and PKC promote MLC phosphorylation through independent pathways. Notably, the activity of both ROCK and PKC was diminished in the FLNA-deficient platelets. We conclude that FLNA regulates thrombin-induced MLC phosphorylation and platelet contraction, in a ROCK- and PKC-dependent manner.28 pagesen-USThis is an Accepted Manuscript; not the final Version of Record.Text