STAT6 AND JAK1 ARE COMMON ELEMENTS IN PLATELET-DERIVED GROWTH-FACTOR AND INTERLEUKIN-4 SIGNAL-TRANSDUCTION PATHWAYS IN NIH 3T3 FIBROBLASTS

Both platelet-derived growth factor (PDGF) and interleukin-4 (IL-4) pl ay major roles in cell proliferation, differentiation, chemotaxis, and other functional responses, Here, we demonstrate that Stat6, previous ly shown to be activated by only IL-4 and IL-3, becomes activated afte r PDGF stimulation of NIH 3T3 fibroblasts, PDGF BB, and to a lesser ex tent PDGF AA, rapidly induced DNA binding activity from NIH 3T3 cell l ysates utilizing the immunoglobulin heavy chain germ line a promoter ( I epsilon) that specifically binds to StatG in an electrophoretic mobi lity shift assay. DNA binding activity could be detected within 5 min and reached maximum levels at approximately 20 min in parental NIH 3T3 cells, An identical mobility shift and time course of PDGF-mediated I epsilon binding activity was more pronounced in lysates of NIH 3T3 tr ansfectants overexpressing human Stat6 (NIH 3T3-Stat6), The observed r adiolabeled I epsilon mobility shift was competed by unlabeled I epsil on as well as by the beta-casein gene promoter but not by the interfer on-alpha-stimulated response element or the interferon-gamma response region of the guanylate-binding protein gene, A StatG specific polyclo nal antisera also supershifted the PDGF-induced I epsilon mobility shi ft, After PDGF BB treatment, a 100-kDa tyrosine phosphorylated species was detected in anti-Stat6 immunoprecipitates. Cycloheximide had litt le effect on Stat6 tyrosine phosphorylation, In addition to State, Sta t5a, and Stat5b, PDGF BE also induced Jak1 tyrosine phosphorylation su ggesting a potential pathway for Stat activation, Strikingly, the conc urrent addition of IL-4 enhanced PDGF BE-induced I epsilon binding act ivity, Jak1 tyrosine phosphorylation, and [H-3]thymidine incorporation . These results provide evidence that State and Jak1 are common elemen ts in PDGF and IL-4 signaling pathways and suggest that IL-4 could pla y a role in potentiating certain known PDGF-induced biological respons es.