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Engagement of Gab1 and Gab2 in erythropoietin signaling
A Wickrema1, S Uddin, A Sharma
1Section of Hematology-Oncology, University of Illinois at Chicago and West Side Veterans Affairs Medical Center, Chicago, Illinois 60607, USA. Awickrem@uic.edu
Abstract:
Several signaling cascades are activated during engagement of the erythropoietin receptor to mediate the biological effects of erythropoietin. The members of the insulin receptor substrate (IRS) family of proteins play a central role in signaling for various growth factor receptors and cytokines by acting as docking proteins for the SH2 domains of signaling elements, linking cytokine receptors to diverse downstream pathways. In the present study we provide evidence that the recently cloned IRS-related proteins, Gab1 and Gab2, of the Gab family of proteins, are rapidly phosphorylated on tyrosine during erythropoietin treatment of erythropoietin-responsive cells and provide docking sites for the engagement of the SHP2 phosphatase and the p85 subunit of the phosphatidylinositol 3'-kinase. Furthermore, our data show that Gab1 is the primary IRS-related protein activated by erythropoietin in primary erythroid progenitor cells. In studies to identify the erythropoietin receptor domains required for activation of Gab proteins, we found that tyrosines 425 and 367 in the cytoplasmic domain of the erythropoietin receptor are required for the phosphorylation of Gab2. Taken together, our data demonstrate that Gab proteins are engaged in erythropoietin signaling to mediate downstream activation of the SHP2 and phosphatidylinositol 3'-kinase pathways and possibly participate in the generation of the erythropoietin-induced mitogenic responses.
Insights
Erythropoietin receptor signaling activates Gab proteins, which act as docking sites for SHP2 phosphatase and phosphatidylinositol 3'-kinase. This study identifies key receptor tyrosines essential for Gab protein activation in erythropoietin-responsive cells.
Area of Science:
- Cellular signaling
- Molecular biology
- Hematopoiesis
Background:
- Erythropoietin receptor (EPO-R) activation initiates signaling cascades crucial for erythropoiesis.
- Insulin receptor substrate (IRS) proteins act as adaptors, linking cytokine receptors to downstream pathways.
- Gab proteins (Gab1, Gab2) are IRS-related adaptors involved in growth factor signaling.
Purpose of the Study:
- To investigate the role of Gab1 and Gab2 in erythropoietin receptor signaling.
- To identify the specific domains of EPO-R required for Gab protein activation.
- To elucidate the downstream pathways activated by EPO-R through Gab proteins.
Main Methods:
- Erythroid cell culture and treatment with erythropoietin.
- Western blotting to detect tyrosine phosphorylation of Gab1 and Gab2.
- Co-immunoprecipitation assays to assess protein interactions.
- Site-directed mutagenesis of EPO-R cytoplasmic domain.
Main Results:
- Gab1 and Gab2 are rapidly tyrosine phosphorylated upon erythropoietin stimulation.
- Phosphorylated Gab1 and Gab2 serve as docking sites for SHP2 phosphatase and phosphatidylinositol 3'-kinase (PI3K) p85 subunit.
- Gab1 is the predominant Gab protein activated in primary erythroid progenitor cells.
- Tyrosines 425 and 367 in the EPO-R cytoplasmic domain are critical for Gab2 phosphorylation.
Conclusions:
- Gab proteins are key mediators of erythropoietin signaling, linking EPO-R to SHP2 and PI3K pathways.
- Gab proteins likely contribute to erythropoietin-induced mitogenic responses.
- Specific EPO-R tyrosines are essential for the recruitment and activation of Gab proteins.