The Cellular Life of Pannexins
WIREs Membrane Transport and Signaling
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The mammalian pannexin family of channel-forming proteins consisting of Panx1, Panx2, and Panx3 has received considerable attention in the last 10 years given their newly discovered physiological roles in development and disease. Pannexins exhibit diverse subcellular profiles indicating that they may serve distinct roles in cells and tissues of different origin. This complexity in cellular residencies may be rooted in the fact that pannexin genes consist of multiple exons that have led to the identification of several splice variants. Additionally, post-translational modifications, especially N-glycosylation, appear to be important in regulating trafficking and intermixing of pannexin family members increasing the diversity of assembled channels. These long-lived membrane proteins are typically trafficked through the classical secretory pathway before reaching the plasma membrane although Panx2 tends to often be retained in intracellular compartments. Trafficking, stability, and function of pannexins likely enlist the services of an interactome that continues to expand. The research field has been amazed by the fact that Panx1 null mice are generally healthy with distinct phenotypes only being revealed when mutant mice encounter additional stress or have comorbidities. The emerging field of pannexin biology has also begun to explore the relationships and potential cross-talk between pannexin channels and connexin hemichannels. It is imperative to dissect the different constituents of the channels and the molecules that pass through these distinct channel types. Finally, as witnessed in connexin biology throughout the 90s, the field awaits to see if germline mutations in the genes that encode pannexins also cause disease.