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Interplay between PKC and the MAP kinase pathway in Connexin43 phosphorylation and inhibition of gap junction

Solveig Sirnes1, Ane Kjenseth, Edward Leithe

  • 1Department of Cancer Prevention, Institute for Cancer Research, Norwegian Radium Hospital, Montebello, Oslo, Norway.

Biochemical and Biophysical Research Communications
|March 5, 2009
PubMed

Insights

Tumor promoter TPA inhibits gap junction intercellular communication (GJIC) by affecting Connexin43 (Cx43) phosphorylation. Both PKC and MAP kinase pathways mediate this inhibition, revealing complex signaling interactions.

Area of Science:

  • Cellular biology
  • Molecular signaling
  • Cancer research

Background:

  • Gap junction channels, formed by connexins, facilitate direct cell-to-cell communication.
  • Connexin43 (Cx43) is a key connexin protein, with its C-terminus being a site for regulatory phosphorylation.
  • The tumor-promoting phorbol ester TPA is known to inhibit Cx43 gap junction channels.

Purpose of the Study:

  • To investigate the molecular mechanisms underlying TPA-induced phosphorylation of Cx43.
  • To elucidate how TPA inhibits gap junction intercellular communication (GJIC).
  • To understand the interplay between protein kinase C (PKC), MAP kinase, and epidermal growth factor receptor (EGFR) signaling in Cx43 regulation.

Main Methods:

  • Utilized biochemical assays to study TPA-induced phosphorylation of Cx43.
  • Investigated the roles of PKC and MAP kinase pathways in TPA's effects on GJIC.
  • Examined the involvement of Src and EGF receptor trans-activation in the signaling cascade.
  • Analyzed Cx43 phosphorylation sites and their impact on SDS-PAGE mobility.

Main Results:

  • TPA-induced inhibition of GJIC is dependent on both PKC and the MAP kinase pathway.
  • PKC-induced activation of MAP kinase involves Src-independent trans-activation of the EGF receptor.
  • TPA induces Cx43 phosphorylation at S255 and S262 in a MAP kinase-dependent manner.
  • Phosphorylation of Cx43 at S368 by PKC does not alter its gel migration, while MAP kinase phosphorylation causes a shift in SDS-PAGE mobility.

Conclusions:

  • TPA modulates Cx43 function through complex signaling pathways involving PKC, MAP kinase, and EGFR.
  • MAP kinase-dependent phosphorylation of Cx43 at specific sites (S255, S262) contributes to TPA-induced inhibition of GJIC.
  • These findings enhance the understanding of how signaling pathway crosstalk regulates gap junction communication, with implications for cancer research.

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