Modulation of junctional communication by phosphorylation: protein phosphatases, the missing link in the chain.

Protein phosphorylation has been proposed to control the degree of intercellular gap junctional communication at several steps, from gene expression to protein degradation. In vertebrates, gap junctions are composed of proteins from the "connexin" (Cx) gene family, and the majority of connexins are post-translationally modified by phosphorylation. Alterations in the phosphorylation status of proteins, resulting from the dynamic interplay of protein kinases and protein phosphatases, are thought to be involved in a broad variety of connexin processes (such as the trafficking, assembly/disassembly and degradation, as well as the gating of gap junction channels), but the underlying mechanisms remain poorly understood. Although protein kinases have an established role in this process (see Cruciani and Mikalsen, this issue), less is known about the involvement of protein phosphatases. The present review examines the role played by protein dephosphorylation catalysers in the regulation of gap junctional communication.