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Arf guanine nucleotide-exchange factors BIG1 and BIG2 regulate non-muscle myosin IIA activity by anchoring myosin phosphatase complex

Thursday, November 07, 2013 — Poster Session II

12:00 p.m. – 2:00 p.m.

FAES Academic Center (Upper-Level Terrace)




  • K Le
  • C Li
  • G Ye
  • J Moss
  • M Vaughan


Brefeldin A-inhibited guanine nucleotide-exchange proteins BIG1 and BIG2, which activate human ADP-ribosylation factors (Arf) 1 and 3 by accelerating the replacement of Arf-bound GDP with GTP, are now implicated in regulation of cytoskeleton dynamics and cell migration, although details remain incomplete. Liquid chromatography MS/MS peptides analysis of proteins co-immunoprecipitated (IP) with BIG1 or BIG2 antibodies identified non-muscle myosin IIA (NM IIA), an actin-binding protein with both actin cross-linking and contractile functions. Reciprocal co-IP of endogenous proteins was consistent with interactions of NM IIA and BIG1 or BIG2. Phosphorylation of NM IIA regulatory light chain (RLC) and actin stress fiber abundance increased significantly after depletion of BIG1 or BIG2, perhaps because association of NMHC IIA with type 1 phosphoprotein phosphatase δ (PP1cδ), and myosin phosphatase target subunit 1 (MYPT1) complex was decreased. Experiments with in vitro-synthesized (wheat germ extract) proteins suggest direct interactions of BIG1 with NMHC IIA, BIG2, PP1cδ, and MYPT1. All observations are consistent with our new recognition of critical BIG1/2 roles as scaffolds for assembly and effective operation of multimolecular machines that receive and integrate mechanical signals to perform their demonstrated roles in establishing and maintaining cell polarization in directed migration. Funding: Intramural Research Program, NIH, NHLBI.

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