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© The Rockefeller University Press, 0021-9525/2000//1503 $5.00
The Journal of Cell Biology, Volume 149, Number 7, , 2000 1503-1512

Original Article

Phosphorylation of Connexin43 on Serine368 by Protein Kinase C Regulates Gap Junctional Communication



Paul D. Lampea, Erica M. TenBroekb, Janis M. Burtc, Wendy E. Kuratad, Ross G. Johnsonb, and Alan F. Laud

a Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
b Department of Genetics, Cell Biology and Development, University of Minnesota, St. Paul, Minnesota 55108
c Department of Physiology, University of Arizona, Tucson, Arizona 85724
d Molecular Carcinogenesis Section, Cancer Research Center, University of Hawaii, Honolulu, Hawaii 96813
Fred Hutchinson Cancer Research Center, Mailstop DE-320, 1100 Fairview Avenue, N., Seattle, WA 98109.(206) 667-2537(206) 667-4123

plampe{at}fhcrc.org

Phorbol esters (e.g., TPA) activate protein kinase C (PKC), increase connexin43 (Cx43) phosphorylation, and decrease cell–cell communication via gap junctions in many cell types. We asked whether PKC directly phosphorylates and regulates Cx43. Rat epithelial T51B cells metabolically labeled with 32Pi yielded two-dimensional phosphotryptic maps of Cx43 with several phosphopeptides that increased in intensity upon TPA treatment. One of these peptides comigrated with the major phosphopeptide observed after PKC phosphorylation of immunoaffinity-purified Cx43. Purification of this comigrating peptide and subsequent sequencing indicated that the phosphorylated serine was residue 368. To pursue the functional importance of phosphorylation at this site, fibroblasts from Cx43–/– mice were transfected with either wild-type (Cx43wt) or mutant Cx43 (Cx43-S368A). Intercellular dye transfer studies revealed different responses to TPA and were followed by single channel analyses. TPA stimulation of T51B cells or Cx43wt-transfected fibroblasts caused a large increase in the relative frequency of ~50-pS channel events and a concomitant loss of ~100-pS channel events. This change to ~50-pS events was absent when cells transfected with Cx43-S368A were treated with TPA. These data strongly suggest that PKC directly phosphorylates Cx43 on S368 in vivo, which results in a change in single channel behavior that contributes to a decrease in intercellular communication.

Key Words: gap junctions • connexins • tumor promoter • phosphorylation • carcinogenesis

© 2000 The Rockefeller University Press

Abbreviations used in this paper: Cx43, connexin43; Cx43wt, wild-type connexin43; Cx43-S368A, S368A mutant Cx43; PKC, protein kinase C; TFA, trifluoroacetic acid; TPA, 12-O-tetradecanoylphorbol-13-acetate.


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