Tyrosine phosphorylation of the gap junction protein connexin43 is required for the pp60v-src-induced inhibition of communication.

TLDR

pp60v-src, a viral tyrosine kinase, inhibits gap junction communication and induces serine and tyrosine phosphorylation of connexin43 (Cx43) in cells expressing the oncogene. The study aimed to determine whether v‑src’s inhibition of communication is directly mediated by tyrosine phosphorylation of Cx43 or by other pathways, and to assess its effect on other connexins. Using paired Xenopus oocytes expressing different connexins, the authors examined how v‑src expression alters intercellular communication. pp60v-src completely blocked Cx43‑mediated communication, induced its tyrosine phosphorylation, and this inhibition was lost when tyrosine 265 was mutated, whereas Cx32 communication was only modestly affected, indicating a connexin‑specific, tyrosine‑phosphorylation‑dependent mechanism.

Abstract

Gap junction communication in some cells has been shown to be inhibited by pp60v-src, a protein tyrosine kinase encoded by the viral oncogene v-src. The gap junction protein connexin43 (Cx43) has been shown to be phosphorylated on serine in the absence of pp60v-src and on both serine and tyrosine in cells expressing pp60v-src. However, it is not known if the effect of v-src expression on communication results directly from tyrosine phosphorylation of the Cx43 or indirectly, for example, by activation of other second-messenger systems. In addition, the effect of v-src expression on communication based on other connexins has not been examined. We have used a functional expression system consisting of paired Xenopus oocytes to examine the effect of v-src expression on the regulation of communication by gap junctions comprised of different connexins. Expression of pp60v-src completely blocked the communication induced by Cx43 but had only a modest effect on communication induced by connexin32 (Cx32). Phosphoamino acid analysis showed that pp60v-src induced tyrosine phosphorylation of Cx43, but not Cx32. A mutation replacing tyrosine 265 of Cx43 with phenylalanine abolished both the inhibition of communication and the tyrosine phosphorylation induced by pp60v-src without affecting the ability of this protein to form gap junctions. These data show that the effect of pp60v-src on gap junctional communication is connexin specific and that the inhibition of Cx43-mediated junctional communication by pp60v-src requires tyrosine phosphorylation of Cx43.