STAT3 AND STAT5B ARE TARGETS OF 2 DIFFERENT SIGNAL PATHWAYS ACTIVATEDBY HEMATOPOIETIN RECEPTORS AND CONTROL TRANSCRIPTION VIA SEPARATE CYTOKINE RESPONSE ELEMENTS

Transient transfection of expression vectors for various members of th e hematopoietin receptor family and STAT proteins into COS-1 cells ind icated that each receptor was capable of stimulating the DNA binding a ctivity of STAT1, STAT3, and STAT5B. However, gp130 preferentially act ivated STAT1 and STAT3. Activation of STAT5B differed from that of the other two in that the box 3 sequence motif in the cytoplasmic domain of gp130 was not required. Moreover, STAT5B and STAT3 enhanced gene tr anscription via separate regulatory elements. This study has identifie d two potential signal transduction pathways by which hematopoietin re ceptors, including the interleukin-6 receptor, control transcription o f acute phase plasma protein genes in hepatic cells.