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Stat6 and Jak1 are common elements in platelet-derived growth factor and interleukin-4 signal transduction pathways
1Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, Maryland 20892, USA.
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.
Insights
Platelet-derived growth factor (PDGF) activates Stat6 in NIH 3T3 fibroblasts, a pathway previously linked only to interleukin-4 (IL-4). This discovery reveals common signaling elements between PDGF and IL-4 pathways, suggesting IL-4 can enhance PDGF responses.
Area of Science:
- Cellular signaling
- Molecular biology
- Immunology
Background:
- Platelet-derived growth factor (PDGF) and interleukin-4 (IL-4) are key regulators of cellular functions.
- Stat6 is a transcription factor known to be activated by IL-4 and IL-3.
Purpose of the Study:
- To investigate whether PDGF stimulation can activate Stat6.
- To explore the potential overlap between PDGF and IL-4 signaling pathways.
Main Methods:
- Electrophoretic mobility shift assays (EMSA) to detect DNA binding activity.
- Immunoprecipitation and Western blotting to assess protein phosphorylation.
- Use of NIH 3T3 fibroblasts and transfectants overexpressing Stat6.
Main Results:
- PDGF BB and PDGF AA induced Stat6 DNA binding activity to the immunoglobulin heavy chain germ line epsilon promoter (Iepsilon) in NIH 3T3 fibroblasts.
- Stat6 tyrosine phosphorylation was observed after PDGF BB stimulation.
- PDGF BB also induced Jak1 tyrosine phosphorylation, suggesting a role in Stat activation.
- Concurrent addition of IL-4 enhanced PDGF BB-induced Iepsilon binding activity, Jak1 phosphorylation, and [3H]thymidine incorporation.
Conclusions:
- Stat6 and Jak1 are common signaling elements in both PDGF and IL-4 pathways.
- IL-4 can potentiate certain PDGF-induced biological responses, such as cell proliferation.