Abstract
Both platelet-derived growth factor (PDGF) and interleukin-4 (IL-4) play major roles in cell proliferation, differentiation, chemotaxis, and other functional responses. Here, we demonstrate that Stat6, previously shown to be activated by only IL-4 and IL-3, becomes activated after PDGF stimulation of NIH 3T3 fibroblasts. PDGF BB, and to a lesser extent PDGF AA, rapidly induced DNA binding activity from NIH 3T3 cell lysates utilizing the immunoglobulin heavy chain germ line epsilon promoter (Iepsilon) that specifically binds to Stat6 in an electrophoretic mobility 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 Iepsilon binding activity was more pronounced in lysates of NIH 3T3 transfectants overexpressing human Stat6 (NIH 3T3-Stat6). The observed radiolabeled Iepsilon mobility shift was competed by unlabeled Iepsilon as well as by the beta-casein gene promoter but not by the interferon-alpha-stimulated response element or the interferon-gamma response region of the guanylate-binding protein gene. A Stat6-specific polyclonal antisera also supershifted the PDGF-induced Iepsilon mobility shift. After PDGF BB treatment, a 100-kDa tyrosine phosphorylated species was detected in anti-Stat6 immunoprecipitates. Cycloheximide had little effect on Stat6 tyrosine phosphorylation. In addition to Stat6, Stat5a, and Stat5b, PDGF BB also induced Jak1 tyrosine phosphorylation suggesting a potential pathway for Stat activation. Strikingly, the concurrent addition of IL-4 enhanced PDGF BB-induced Iepsilon binding activity, Jak1 tyrosine phosphorylation, and [3H]thymidine incorporation. These results provide evidence that Stat6 and Jak1 are common elements in PDGF and IL-4 signaling pathways and suggest that IL-4 could play a role in potentiating certain known PDGF-induced biological responses.
Highlights
Major mitogen and chemotactic factor for mesenchymal cells such as fibroblasts and smooth muscle cells [1, 2]
To determine whether platelet-derived growth factor (PDGF) BB induced I⑀ binding activity, we stimulated NIH 3T3 fibroblasts with this growth factor for varying times
IL-4 Enhances PDGF BB Induction of I⑀ Binding Activity and Jak1 Tyrosine Phosphorylation—While these results demonstrated that tyrosine-phosphorylated Stat6 and Jak1 were common elements in both IL-4 and PDGF BB signal transduction pathways, they did not address whether IL-4 and PDGF BB cooperated in the activation of either signaling molecule in NIH 3T3 fibroblasts
Summary
Vol 271, No 36, Issue of September 6, pp. 22175–22182, 1996 Printed in U.S.A. Stat and Jak Are Common Elements in Platelet-derived Growth Factor and Interleukin-4 Signal Transduction Pathways in NIH 3T3 Fibroblasts*. From the Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, Maryland 20892 Both platelet-derived growth factor (PDGF) and interleukin-4 (IL-4) play major roles in cell proliferation, differentiation, chemotaxis, and other functional responses. In addition to Stat, Stat5a, and Stat5b, PDGF BB induced Jak tyrosine phosphorylation suggesting a potential pathway for Stat activation. The concurrent addition of IL-4 enhanced PDGF BB-induced I⑀ binding activity, Jak tyrosine phosphorylation, and [3H]thymidine incorporation. These results provide evidence that Stat and Jak are common elements in PDGF and IL-4 signaling pathways and suggest that IL-4 could play a role in potentiating certain known PDGFinduced biological responses. Our results provide evidence that IL-4 can act to enhance PDGF-induced I⑀ binding activity, Jak activation, and fibroblast proliferation, suggesting that IL-4 might synergize with PDGF to enhance PDGF-mediated biological responses in vivo
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