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Shc and CEACAM1 interact to regulate the mitogenic action of insulin
Matthew N Poy1, Randall J Ruch, Mats A Fernstrom
1Department of Pharmacology, Medical College of Ohio, Toledo, Ohio 43614, USA.
Abstract:
CEACAM1, a tumor suppressor (previously known as pp120), is a plasma membrane protein that undergoes phosphorylation on Tyr(488) in its cytoplasmic tail by the insulin receptor tyrosine kinase. Co-expression of CEACAM1 with insulin receptors decreased cell growth in response to insulin. Co-immunoprecipitation experiments in intact NIH 3T3 cells and glutathione S-transferase pull-down assays revealed that phosphorylated Tyr(488) in CEACAM1 binds to the SH2 domain of Shc, another substrate of the insulin receptor. Overexpressing Shc SH2 domain relieved endogenous Shc from binding to CEACAM1 and restored MAP kinase activity, growth of cells in response to insulin, and their colonization in soft agar. Thus, by binding to Shc, CEACAM1 sequesters this major coupler of Grb2 to the insulin receptor and down-regulates the Ras/MAP kinase mitogenesis pathway. Additionally, CEACAM1 binding to Shc enhances its ability to compete with IRS-1 for phosphorylation by the insulin receptor. This leads to a decrease in IRS-1 binding to phosphoinositide 3'-kinase and to the down-regulation of the phosphoinositide 3'-kinase/Akt pathway that mediates cell proliferation and survival. Thus, binding to Shc appears to constitute a major mechanism for the down-regulatory effect of CEACAM1 on cell proliferation.
Insights
Carcinoma cell adhesion molecule 1 (CEACAM1) suppresses tumor growth by inhibiting insulin-stimulated cell proliferation. CEACAM1 binds to Shc, blocking key signaling pathways like Ras/MAP kinase and PI3K/Akt.
Area of Science:
- Molecular Biology
- Cell Signaling
- Oncology
Background:
- Carcinoma cell adhesion molecule 1 (CEACAM1), a known tumor suppressor, is a plasma membrane protein.
- CEACAM1 is phosphorylated by the insulin receptor tyrosine kinase on Tyr(488) in its cytoplasmic tail.
Purpose of the Study:
- To elucidate the molecular mechanism by which CEACAM1 inhibits insulin-induced cell proliferation.
- To investigate the interaction between CEACAM1, Shc, and downstream signaling pathways.
Main Methods:
- Co-immunoprecipitation experiments in NIH 3T3 cells.
- Glutathione S-transferase (GST) pull-down assays.
- Overexpression of Shc SH2 domain.
Main Results:
- Phosphorylated Tyr(488) of CEACAM1 binds to the SH2 domain of Shc.
- Overexpression of the Shc SH2 domain disrupted CEACAM1-Shc binding, restoring insulin-induced MAP kinase activity and cell growth.
- CEACAM1 binding to Shc down-regulates the Ras/MAP kinase pathway and the phosphoinositide 3'-kinase/Akt pathway.
Conclusions:
- CEACAM1 acts as a tumor suppressor by inhibiting insulin-stimulated cell proliferation.
- CEACAM1 binding to Shc sequesters it from the insulin receptor, down-regulating mitogenesis and promoting apoptosis.
- CEACAM1 also enhances Shc's competition with IRS-1, further inhibiting the PI3K/Akt survival pathway.