schulich school of medicine and denstistry The Laird Laboratory Western University

Pannexins in Health and Disease

In the last decade, a new family of proteins called pannexins was discovered based on their sequence similarity to invertebrate gap junction proteins. This family consists of three members: Panx1, Panx2 and Panx3. In 2005, our laboratory started a grass-roots project by generating and characterizing the molecular tools needed to rigorously study pannexins. Through these seminal efforts we have contributed extensively to the biochemical characterization, post-translational modifications, and trafficking of pannexins. Further studies have led to an understanding of pannexins as channel forming proteins involved in many functions including keratinocyte differentiation and cancer.

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The Pannexin Family

Pannexins are glycoproteins and the level of glycosylation regulates their localization at the cell surface and intermixing with other pannexins. We are interested in the life cycle of pannexins from their synthesis, delivery and cell surface dynamics to degradation and internalization. We use live imaging technology and fluorescence recovery after photobleaching to examine the mobility of GFP-tagged pannexins at the cell surface. Functionally, Panx1 has been described as a mechano-sensitive ATP release channel involved in cell death after ischemia, tumor suppression in glioma cells and the channel responsible for releasing ATP and UTP 'find-me' signals from apoptotic cells to phagocytes. In our lab we routinely examine channel function of single or mixed pannexin channels using fluorescent dye uptake assays and ATP release.

Panx1 and Panx3 are present in human and rodent skin. Our lab is interested in the role these pannexins play in skin differentiation, proliferation and apoptosis. For these studies we typically use an organotypic epidermis model grown from rat epidermal keratinocytes. This model has allowed us to see that the regulation of Panx1 plays a key role in keratinocyte differentiation. We also have at our disposal Panx1 and Panx3 knockout mice that are being fully characterized. Since pannexins have been paradoxically reported to be tumor suppressors in gliomas and proto-oncogenes in melanomas, we are exploring their role in malignant transformation in the skin and mammary glands.

Selected Publications

S. Penuela, R. Gehi and D.W. Laird (2013) “The biochemistry and function of pannexin channels” BBA-Biomembranes 1828:15-22.

S. Penuela, L. Gyenis, A. Ablack, J. Churko, A. Berger, D.W. Litchfield, J.D. Lewis and D.W. Laird (2012) “Loss of pannexin1 attenuates melanoma progression by reversion to a melanocytic phenotype” Journal of Biological Chemistry 287: 29184-29193. Highlight in press releases by CTV News, Western Research and the London Free Press.

A.W. Lohman, M. Billaud, A.C. Staub, S.R. Johnstone, A. Best, M. Lee, K. Barr, S. Penuela, D.W. Laird and B.E. Isakson (2012) “Expression of pannexin isoforms in systemic murine arterial network” Journal of Vascular Research 49:405-416.

S. Penuela and D.W. Laird (2012) “The cellular life of Pannexins” WIREs Membrane Transport and Signaling 1:621-632, doi:10.1002/wmts.63

A.W. Lohman, J.L. Weaver, M. Billaud, J.K. Sandilos, R. Griffiths, A.C. Straub, S. Penuela, N. Leitinger,  D.W. Laird, D.A. Bayliss and B.E. Isakson (2012) “S-nitrosylation inhibits pannexin 1 function” Journal of  Biological Chemistry 287 (47): 39602-12.

S.R. Bond, A. Lau, S. Penuela, A.V. Sampaio, T.M. Underhill, D.W. Laird and C.C. Naus (2011) “Pannexin3 is a novel target for Runx2 expressed by mature osteoblasts and hypertrophic chondrocytes” Journal of Bone and Mineral Research 26: 2911-2922.

M. Billaud, A.W. Lohman, A.C. Straub, R. Looft-Wilson,  C.A. Araj, A.K. Best, F. Chekeni, K. Ravichandran, S. Penuela, D.W. Laird and B.E. Isakson (2011) “Pannexin1 regulates a1-adrenoreceptor-mediated vasoconstriction” Circulation Research 109: 80-85.

L. Seminario-Vidal, S.F. Okada, J.I. Sesma, S.M. Kreda, C.A. van Heusden, Y. Zhu, L.C. Jones, W.K. O’Neal, S. Penuela, D.W. Laird, R.C. Boucher, E.R. Lazarowski (2011) “Rho signaling regulates pannexin1-mediated ATP release from airway epithelia. Journal of Biological Chemistry 286: 26277-26286.

R. Gehi, Q. Shao, D.W. Laird (2011) “Pathways regulating the trafficking and turnover of Pannexin1 and the role of the carboxyl terminal domains”Journal of Biological Chemistry 286:27639-27653.

R. Bhalla-Gehi, S. Penuela, J.M. Churko, Q. Shao and D.W. Laird (2010) “Pannexin1 and Pannexin3 delivery, cell surface dynamics and cytoskeletal interactions” Journal of Biological Chemistry 285: 9147-9160.

S.J. Celetti, K.N. Cowan, S. Penuela, Q. Shao and D.W. Laird (2010) “Implications of pannexin 1 and Pannexin 3 for keratinocyte differentiation”Journal of Cell Science 123: 1363-1372.

F.B. Chekeni, M.R. Elliot, J.K. Sandilo, S.F. Walk, J.M. Kinchen, E.R. Lararowski, A.J. Armstrong, S. Penuela, D.W. Laird, G.S. Salvesen, B.E. Isakson, D.A. Bayliss and K.S. Ravichandran (2010) “Pannexin 1 channels regulate “find-me” signal release and membrane permeability during apoptosis” Nature 467:863-867.

S. Penuela, R. Bhalla, K. Nag and D.W. Laird (2009) “Glycosylation regulates pannexin intermixing and cellular localization” Molecular Biology of the Cell 20:4313-4323.

S. Penuela, R. Bhalla, Q. Shao and D.W. Laird (2007) “Pannexin1 and pannexin3 are glycoproteins that exhibit many distinct characteristics from the connexin family of gap junction proteins” Journal of Cell Science 120: 3772-3783