Epithelial membrane proteins induce membrane blebbing and interact with the P2X7 receptor C terminus

The binding of extracellular ATP to the P2X(7) receptor opens an integral cation-permeable channel; it also leads to membrane blebbing and, in certain immune cells, interleukin-1beta secretion and eventual death. The latter three effects are unique to the P2X(7) receptor; also unique among P2X receptors is the long intracellular C terminus of the protein. We have shown that the C-terminal domain of the P2X(7) receptor is responsible for the cell blebbing phenotype. A screen for proteins that associate with the C-terminal domain of the P2X(7) receptor and might mediate the blebbing phenotype, identified epithelial membrane protein 2 (EMP-2). The interaction between EMP-2 and P2X(7) was confirmed biochemically by co-immunoprecipitation, co-purification, and glutathione S-transferase pull-down assays, and this interaction was entirely dependent on the C-terminal domain of P2X(7). The P2X(7) receptor also interacted with the other members of the epithelial membrane protein family (EMP-1, EMP-3, and PMP-22). All four EMPs were found to be expressed in HEK-293 cells and in THP-1 monocytes, which express P2X(7) receptors. Interestingly, the constitutive overexpression of any of the EMPs in HEK-293 cells led to cell blebbing, annexin V binding, and cell death, by a caspase-dependent pathway. These findings suggest that the P2X(7) C-terminal domain associates with EMPs, and this interaction may mediate some aspects of the downstream signaling following P2X(7) receptor activation.