DISRUPTED SIGNALING IN A MUTANT J2E CELL-LINE THAT SHOWS ENHANCED VIABILITY, BUT DOES NOT PROLIFERATE OR DIFFERENTIATE, WITH ERYTHROPOIETIN

The immature erythroid J2E cell line proliferates and terminally diffe rentiates following erythropoietin stimulation, In contrast, the mutan t J2E-NR clone does not respond to erythropoietin by either proliferat ing or differentiating. Here we show that erythropoietin can act as a viability factor for both the J2E and J2E-NR lines, indicating that er ythropoietin-initiated maturation is separable from the prevention of cell death. The inability of J2E-NR cells to mature in response to ery thropoietin was not due to a defect in the erythropoietin receptor seq uence, although surface receptor numbers were reduced, Both the recept or and Janus kinase 2 were phosphorylated after erythropoietin stimula tion of J2E-NR cells, However, protein interactions with the erythropo ietin receptor and Grb2 were restricted in the mutant cells. Subsequen t investigation of several other signaling molecules exposed numerous alterations in J2E-NR cells; phosphorylation changes to phosphatidylin ositol 3-kinase, phospholipase C gamma, p120 GAP, and mitogen-activate d protein kinases (p42 and p44) observed in erythropoietin-stimulated J2E cells were not seen in the J2E-NR line. These data indicate that s ome pathways activated during erythropoietin-induced differentiation m ay not be essential for the prevention of apoptosis.