INTERLEUKIN-3, ERYTHROPOIETIN, AND PROLACTIN ACTIVATE A STAT5-LIKE FACTOR IN LYMPHOID-CELLS

Interleukin-3 (IL-3)-, erythropoietin (EPO)-, and prolactin (PRL)-indu ced signal transduction via the JAK/STAT pathway was studied in the IL -3-dependent BAF-3 lymphoid cell Line. Transfected cells expressing ei ther the long form of the PRL receptor or the EPO receptor were used. We demonstrated that IL-3, EPO, and PRL activated a transcription fact or related to the mammary transcription factor STATS but not to STAT1, -2, -3, or -4 as opposed to interferon gamma (IFN gamma) which activa ted STAT1 in the same cells. Similarly, PRL and EPO activated a STAT5- like factor (STAT5-L) in the rat Nb2 and the human UT7 cells expressin g endogenous PRL and EPO receptors, respectively. The hematopoietic ST AT5-L activated by IL-3, EPO, or PRL was identified as a 97-kDa tyrosi ne-phosphorylated protein. These results confer to STAT5 a much broade r role than previously suggested.