REGULATION OF CONNEXIN-43 GAP JUNCTIONAL INTERCELLULAR COMMUNICATION BY MITOGEN-ACTIVATED PROTEIN-KINASE

Activation of the Ras/Raf/mitogen-activated protein kinase kinase/mito gen-activated protein (MAP) kinase signaling cascade is initiated by a ctivation of growth factor receptors and regulates many cellular event s, including cell cycle control, Our previous studies suggested that t he connexin-43 gap junction protein may be a target of activated MAP k inase and that MAP kinase may regulate connexin 43 function, We identi fied the sites of MAP kinase phosphorylation in in vitro studies as th e consensus MAP kinase recognition sites in the cytoplasmic carboxyl t ail of connexin-43, Ser(255), Ser(279), and Ser(282). In this study, w e demonstrate that activation of MAP kinase by ligand-induced activati on of the epidermal growth factor (EGF) or lysophosphatidic acid recep tors or by pervanadate-induced inhibition of tyrosine phosphatases res ults in increased phosphorylation on connexin-43, EGF and lysophosphat idic acid-induced phosphorylation on connexin-43 and the down-regulati on of gap junctional communication in EGF-treated cells were blocked b y a specific mitogen-activated protein kinase kinase inhibitor (PD9805 9) that prevented activation of MAP kinase, These studies confirm that connexin-43 is a MAP kinase substrate in vivo and that phosphorylatio n on Ser(255), Ser(279), and/or Ser(282) initiates the down-regulation of gap junctional communication, Studies with connexin-43 mutants sug gest that MAP kinase phosphorylation at one or more of the tandem Ser( 279)/Ser(282) sites is sufficient to disrupt gap junctional intercellu lar communication.