The P2X7 receptor-pannexin connection to dye uptake and IL-1β release

The P2X(7) receptor (P2X(7)R) is uniquely associated with two distinct cellular responses: activation of a dye-permeable pathway allowing passage of molecules up to 900 Da and rapid release of the pro-inflammatory cytokine, interleukin-1 beta (IL-1 beta), from activated macrophage. How this dye uptake path forms and whether it is involved in IL-1 beta release has not been known. Pannexin-1 is a recently identified protein found to physically associate with the P2X(7)R. Inhibition of pannexin-1 does not alter P2X(7)R ion channel activation or associated calcium flux but blocks one component of P2X(7)R-induced dye uptake and unmasks a slower, previously undetected, dye uptake pathway. Inhibition of pannexin-1 blocks P2X(7)R-mediated IL-1 beta release from macrophage as well as release mediated by other stimuli which couple to activation of capase-1 and additionally inhibits the release of interleukin-1 alpha, a member of the IL-1 family whose processing does not require caspase-1 activation. Thus, pannexin-1 is linked to both dye uptake and IL-1 beta release but via distinct mechanisms.