Inhibition of connexin43 gap junctional intercellular communication by TPArequires ERK activation

The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), is a potent inhibitor of gap junctional intercellular communication (GJIC). This inhibi tion requires activation of protein kinase C (PKC), but the events downstre am of this kinase are not known. Since PKC can activate extracellular signa l regulated kinases (ERKs) and these also downregulate GJIC, we hypothesize d that the inhibition of GJIC by TPA involved ERKs. TPA treatment (10 ng/ml for 30 min) of WB-F344 rat liver epithelial cells strongly activated p42 a nd p44 ERK-1 and -2, blocked gap junction-mediated fluorescent dye-coupling , and induced connexin43 hyperphosphorylation and gap junction internalizat ion. These effects were completely prevented by inhibitors of PKC (bis-indo lylmaleimide I; 2 muM) and ERK activation (U-0126; 10 muM). These data sugg est that ERKs are activated by PKC in response to TPA treatment and are dow nstream mediators of the gap junction effects of the phorbol ester. J. Cell . Biochem. 83: 163-169, 2001. (C) 2001 Wiley-Liss, Inc.