title: Arf guanine nucleotide-exchange factors BIG1 and BIG2 regulate nonmuscle myosin IIA activity by anchoring myosin phosphatase complex.
abstract: Brefeldin A-inhibited guanine nucleotide-exchange factors BIG1 and BIG2 activate, through their Sec7 domains, ADP ribosylation factors (Arfs) by accelerating the replacement of Arf-bound GDP with GTP for initiation of vesicular transport or activation of specific enzymes that modify important phospholipids. They are also implicated in regulation of cell polarization and actin dynamics for directed migration. Reciprocal coimmunoprecipitation of endogenous HeLa cell BIG1 and BIG2 with myosin IIA was demonstrably independent of Arf guanine nucleotide-exchange factor activity, because effects of BIG1 and BIG2 depletion were reversed by overexpression of the cognate BIG molecule C-terminal sequence that follows the Arf activation site. Selective depletion of BIG1 or BIG2 enhanced specific phosphorylation of myosin regulatory light chain (T18/S19) and F-actin content, which impaired cell migration in Transwell assays. Our data are clear evidence of these newly recognized functions for BIG1 and BIG2 in transduction or integration of mechanical signals from integrin adhesions and myosin IIA-dependent actin dynamics. Thus, by anchoring or scaffolding the assembly, organization, and efficient operation of multimolecular myosin phosphatase complexes that include myosin IIA, protein phosphatase 1δ, and myosin phosphatase-targeting subunit 1, BIG1 and BIG2 serve to integrate diverse biophysical and biochemical events in cells.
authors.affiliation: Cardiovascular and Pulmonary Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Kang
authors.initials: K
authors.lastname: Le
authors.forename: Chun-Chun
authors.initials: CC
authors.lastname: Li
authors.forename: Guan
authors.initials: G
authors.lastname: Ye
authors.forename: Joel
authors.initials: J
authors.lastname: Moss
authors.forename: Martha
authors.initials: M
authors.lastname: Vaughan
mesh_terms: D000704:Analysis of Variance; D015153:Blotting, Western; D002465:Cell Movement / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D043263:Myosin-Light-Chain Phosphatase / Q000378:metabolism*; D024507:Nonmuscle Myosin Type IIA / Q000378:metabolism*; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000235:genetics
chemical_list: C119087:ARFGEF1 protein, human; C119088:ARFGEF2 protein, human; D020662:Guanine Nucleotide Exchange Factors; D034741:RNA, Small Interfering; D043263:Myosin-Light-Chain Phosphatase; D024507:Nonmuscle Myosin Type IIA
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