Phosphorylation of PEA-15 switches its binding specificity from ERK/MAPK to FADD

Cell signalling pathways that regulate proliferation and those that regulate programmed cell death (apoptosis) are co-ordinated. The proteins and mechanisms that mediate the integration of these pathways are not yet fully described. The phosphoprotein PEA-15 (phosphoprotein enriched in astrocytes) can regulate both the ERK (extracellular-signal-regulated kinase)/MAPK (mitogen-activated protein kinase) pathway and the death receptor-initiated apoptosis pathway. This is the result of PEA-15 binding to the ERK/MAPK or the proapoptotic protein FADD (Fas-activated death domain protein) respectively. The mechanism by which binding of PEA-15 to these proteins is controlled has not been elucidated. PEA-15 is a phosphoprotein containing a Ser-104 phosphorylated by protein kinase C and a Ser-116 phosphorylated by CamKII (calcium/calmodulin-dependent protein kinase II) or AKT. Phosphorylation of Ser-104 is implicated in the regulation of glucose metabolism, while phosphorylation at Ser-116 is required for PEA-15 recruitment to the DISC (death-initiation signalling complex). Moreover, PEA-15 must be phosphorylated at Ser-116 to inhibit apoptosis. In the present study, we report that phosphorylation at Ser-104 blocks ERK binding to PEA-15 in vitro and in vivo, whereas phosphorylation at Ser-116 promotes its binding to FADD. We further characterize phospho-epitope-binding antibodies to these sites. We report that phosphorylation does not influence the distribution of PEA-15 between the cytoplasm and nucleus of the cell since all phosphorylated states are found predominantly in the cytoplasm. We propose that phosphorylation of PEA-15 acts as the switch that controls whether PEA-15 influences proliferation or apoptosis

The death effector domain protein PEA-15 negatively regulates T-cell receptor signaling

PEA-15 is a death effector domain-containing phosphoprotein that binds ERK and restricts it to the cytoplasm. PEA-15 also binds to FADD and thereby blocks apoptosis induced by death receptors. Abnormal expression of PEA-15 is associated with type II diabetes and some cancers; however, its physiological function remains unclear. To determine the function of PEA-15 in vivo, we used C57BL/6 mice in which the PEA-15 coding region was deleted. We thereby found that PEA-15 regulates T-cell proliferation. PEA-15-null mice did not have altered thymic or splenic lymphocyte cellularity or differentiation. However, PEA-15 deficient T cells had increased CD3/CD28-induced nuclear translocation of ERK and increased activation of IL-2 transcription and secretion in comparison to control wild-type littermates. Indeed, activation of the T-cell receptor in wild-type mice caused PEA-15 release of ERK. In contrast, overexpression of PEA-15 in Jurkat T cells blocked nuclear translocation of ERK and IL-2 transcription. Finally, PEA-15-null T cells showed increased IL-2 dependent proliferation on stimulation. No differences in T cell susceptibility to apoptosis were found. Thus, PEA-15 is a novel player in T-cell homeostasis. As such this work may have far reaching implications in understanding how the immune response is controlled.—Pastorino, S., Renganathan, H., Caliva, M. J., Filbert, E. L., Opoku-Ansah, J., Sulzmaier, F. J., Gawecka, J. E., Werlen, G., Shaw, A. S., Ramos, J. W. The death effector domain protein PEA-15 negatively regulates T-cell receptor signaling