Pannexin 1 (PANX1) is a channel-forming glycoprotein expressed in many tissues including the skin. PANX1 channels allow the passage of ions and molecules up to 1 kDa, including ATP and other metabolites. In this study, we show that PANX1 is highly expressed in human melanoma tumors at all stages of disease progression, as well as in patient-derived cells and established melanoma cell lines. Reducing PANX1 protein levels using shRNA or inhibiting channel function with the channel blockers, carbenoxolone (CBX) and probenecid (PBN), significantly decreased cell growth and migration, and increased melanin production in A375-P and A375-MA2 cell lines. Further, treatment of A375-MA2 tumors in chicken embryo xenografts with CBX or PBN significantly reduced melanoma tumor weight and invasiveness. Blocking PANX1 channels with PBN reduced ATP release in A375-P cells, suggesting a potential role for PANX1 in purinergic signaling of melanoma cells. In addition, cell-surface biotinylation assays indicate that there is an intracellular pool of PANX1 in melanoma cells. PANX1 likely modulates signaling through the Wnt/β-catenin pathway, because β-catenin levels were significantly decreased upon PANX1 silencing. Collectively, our findings identify a role for PANX1 in controlling growth and tumorigenic properties of melanoma cells contributing to signaling pathways that modulate melanoma progression.

Melanoma is the deadliest skin cancer and its incidence is still on the rise. Despite new advances with immunotherapy drugs, nearly 70% of patients still do not respond to treatments, underscoring the importance of finding new treatment targets and combination therapies. Pannexin 1 (PANX1 human; Panx1 mouse) is a channel‐forming glycoprotein expressed in many mammalian organs and tissues including the skin at early stages of development. Pannexin 1 channels allow the passage of ions and important signaling molecules up to 1 kDa, including ATP and other metabolites. We previously found that a knockdown of Panx1 resulted in reduced tumorigenic properties of mouse melanoma cell lines in vitro. In this study, we found that PANX1 is highly expressed in human melanoma tumors compared to normal skin. Using Western blot and immunohistochemistry, we showed that high PANX1 levels are present in melanoma tumors at all disease stages, as well as in patient‐derived cells and established melanoma cell lines. We demonstrated that inhibiting PANX1 function using shRNA or channel blockers, such as Carbenoxolone (CBX) and Probenecid (PBN), significantly reduced cell growth and cell migration, and substantially increased the production of melanin (used as a differentiation marker) in A375‐P and A375‐MA2 human melanoma cells. In addition, treatment with CBX or PBN in A375‐MA2 cells xenografted onto the chorioallantoic membrane of a chicken embryo model, significantly reduced primary melanoma tumor weight as well as tumor invasion. Blocking PANX1 channels using PBN reduced ATP release in A375‐P melanoma cells, suggesting a role for PANX1 in regulating the tumor microenvironment through purinergic signaling at the cell surface. In addition, our findings from cell‐surface biotinylation assays indicate that there is also a significant intracellular pool of PANX1 in melanoma cells that likely modulates signaling pathways such as Wnt/β‐catenin, since β‐catenin levels are significantly decreased upon shRNA knockdown of PANX1 in melanoma cells. Collectively, our findings suggest that PANX1 is a novel modulator of tumorigenic properties in human melanoma cells, contributing to signaling pathways that regulate melanoma progression and highlights PANX1 as a potential target for therapeutic intervention.Support or Funding InformationFunded by a Canadian Institutes of Health Research (CIHR) Project Grant to Silvia PenuelaThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.