title: Connexin43 synthesis, phosphorylation, and degradation in regulation of transient inhibition of gap junction intercellular communication by the phorbol ester TPA in rat liver epithelial cells.
abstract: The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induces transient inhibition of gap junction intercellular communication (GJIC) in several cell types. The initial block in GJIC has been attributed to protein kinase C (PKC) mediated phosphorylation of connexin gap junction proteins, including connexin43 (Cx43). Restoration of GJIC, associated with normalization of the Cx43 phosphorylation status, has been ascribed to different events, including dephosphorylation of Cx43 and de novo synthesis of Cx43 or other, non-gap junctional, proteins. The data presented suggest that restoration of GJIC during continuous TPA exposure in normal and transformed rat liver epithelial cells is dependent on synthesis of Cx43 protein, as well as the transport of already synthesized Cx43 from intracellular pools to the plasma membrane. Reactivation of inactivated Cx43 by dephosphorylation does not appear to be involved in the recovery of GJIC. Both PKC and MAP kinase is involved in TPA-induced degradation of Cx43 and inhibition of GJIC. We show that coincubation of TPA with the protein synthesis inhibitor cycloheximide or the transcription inhibitor actinomycin D results in synergistic enhancement of the level of activated ERK1/2. Together, the present data highlight Cx43 degradation and synthesis as critical determinants in TPA-induced modifications of cell-cell communication via gap junctions.
authors.affiliation: Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, N-0310 Oslo, Norway.
authors.forename: Edgar
authors.initials: E
authors.lastname: Rivedal
authors.forename: Edward
authors.initials: E
authors.lastname: Leithe
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002273:Carcinogens / Q000494:pharmacology*; D002450:Cell Communication / Q000187:drug effects* / Q000502:physiology; D002460:Cell Line; D045744:Cell Line, Tumor; D018031:Connexin 43 / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D005456:Fluorescent Dyes; D017629:Gap Junctions / Q000187:drug effects* / Q000201:enzymology; D007091:Image Processing, Computer-Assisted; D007211:Indoles / Q000494:pharmacology; D007546:Isoquinolines; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008301:Maleimides / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D002273:Carcinogens; D018031:Connexin 43; D004791:Enzyme Inhibitors; D005419:Flavonoids; D005456:Fluorescent Dyes; D007211:Indoles; D007546:Isoquinolines; D008301:Maleimides; D011500:Protein Synthesis Inhibitors; D003609:Dactinomycin; C017475:lucifer yellow; D003513:Cycloheximide; D011493:Protein Kinase C; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one