Shc and CEACAM1 Interact to Regulate the Mitogenic Action of Insulin

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.Insulin binding to its receptor activates its tyrosine kinase to cause phosphorylation of the receptor and of endogenous substrates, including CEACAM1 (previously known as pp120) (1), insulin receptor substrate proteins (IRS-1-4), 1 Shc (2, 3), and others. Phosphorylation of different substrates is required to mediate the diverse effects of hormones on metabolism and growth (4 -6). Shc is a Src homology 2 (SH2)-containing cytoplasmic adaptor protein that undergoes phosphorylation by receptors of the tyrosine kinase family (7). Activation of receptors causes redistribution of Shc from the perinuclear region to the cytosolic site of the plasma membrane (8). The tyrosine kinase receptors that phosphorylate Shc include insulin and insulin-like growth factor 1 (IGF-1) receptors (2, 9). The Shc family of proteins consists of three isoforms. p46/p52 that are ubiquitously expressed are the products of the same transcript and result from alternative usage of two in-frame ATGs. In contrast, p66 that is mostly expressed in epithelial cells is translated from a different transcript (10, 11). The three isoforms have overlapping domains as follows: an SH2 domain at the C terminus, an adjacent glycine/proline-rich collagen homology (CH1) domain, and a phosphotyrosine binding (PTB) domain in the N terminus of p46/p52. p66Shc contains an additional collagen homology (CH2) domain at its N terminus end.By binding to other signaling proteins, Shc exerts many effects on the cell. Upon its phosphorylation on Tyr 317 in the CH1 domain by the insulin receptor, Shc binds to the SH2 domain of Grb2 and couples it to the receptor (12, 13). This leads to the association of Grb2 with the Son of Sevenless Ras GDP/GTP exchanger, causing translocation of Son of Sevenless...

Intestinal tumor progression is promoted by decreased apoptosis and dysregulated Wnt signaling in Ceacam1−/− mice

“…The Ceacam1 À/À intestinal proliferation index was similar to that of the WT mice ( Figure 1C). CEACAM1-L regulates hepatocyte proliferation through its insulin receptor- (Poy et al, 2002a) and EGFR-mediated-Tyr phosphorylation (Abou-Rjaily et al, 2004) with consequent downregulation of the Ras-mitogen-activated protein kinase (MAPK) signaling. Hence, we monitored Erk activity by determining phospho-ERK expression in the Ceacam1 À/À normal jejunum and ileum ( Figure 1D) and found no significant differences between the WT and CEACAM1-null mice.…”

PI3-Kinase Upregulation and Involvement in Spontaneous Tone in Arteries From DOCA-Salt Rats

“…The PI3-kinase assay was performed as previously described. 7,14,15 Briefly, the immunoprecipitated p110␦ from aortic homogenates from DOCA-salt and sham rats were incubated with phosphatidylinositol (PI) in the presence of …”

“…7,14,15 p110␦ Antibody (5 L) and protein A agarose beads (70 L) were added to equal amounts of total protein and the samples rocked (4°C) for 2 hours. The PI3-kinase assay was performed as previously described.…”

Vitamin D inhibits CEACAM1 to promote insulin/IGF-I receptor signaling without compromising anti-proliferative action

“…Several mechanisms have been suggested, including sequestration of the Shc adaptor protein. 15 Binding to Shc, CEACAM1 competes with the insulin and its related IGF-I receptor for IRS-1 recruitment. Thus, the presence of CEA-CAM1 would be expected to impair Akt activation a point of common downstream signaling for the insulin and IGF-I receptors.…”

“…Importantly, CEACAM1 is also a substrate of the insulin receptor (IR). IR-mediated phosphorylation of CEACAM1 14 results in binding and sequestration of the Shc adaptor protein, 15,16 thus potentially limiting insulin signaling. Additionally, CEACAM1 modulates hepatic insulin clearance.…”