Prevention of apoptosis in J2E erythroid cells by erythropoietin: involvement of JAK2 but not MAP kinases

The J2E erythroid cell line, transformed by retroviral v-raf/v-myc oncogenes, proliferates and differentiates in response to erythropoietin. Here we show that J2E cells undergo apoptosis rapidly after serum withdrawal and that only erythropoietin of seven growth factors tested, could protect the cells from death. The role of JAK2 and MAP kinases in transmitting viability signals initiated by erythropoietin was examined in these cells. Despite constitutive raf kinase activity, phosphorylation of MAP kinases fell after serum withdrawal. However, an antisense oligonucleotide strategy revealed that JAK2, but not the MAP kinases, was involved in transmitting signals to maintain the viability of J2E cells. Several cell cycle proteins and transcription factors were also studied; although c-jun rose sharply during apoptosis, erythropoietin could not suppress this increase. It was concluded that erythropoietin-induced protection from apoptosis involved JAK2, but not MAP kinases or c-jun.