Protein-tyrosine phosphatase 1B (PTP-1B) is a major protein-tyrosine phosphatase that has been implicated in the regulation of insulin action, as well as in other signal transduction pathways. To investigate the role of PTP-1B in vivo, we generated homozygotic PTP-1B-null mice by targeted gene disruption. PTP-1B-deficient mice have remarkably low adiposity and are protected from diet-induced obesity. Decreased adiposity is due to a marked reduction in fat cell mass without a decrease in adipocyte number. Leanness in PTP-1B-deficient mice is accompanied by increased basal metabolic rate and total energy expenditure, without marked alteration of uncoupling protein mRNA expression. In addition, insulin-stimulated whole-body glucose disposal is enhanced significantly in PTP-1B-deficient animals, as shown by hyperinsulinemic-euglycemic clamp studies. Remarkably, increased insulin sensitivity in PTP-1B-deficient mice is tissue specific, as insulin-stimulated glucose uptake is elevated in skeletal muscle, whereas adipose tissue is unaffected. Our results identify PTP-1B as a major regulator of energy balance, insulin sensitivity, and body fat stores in vivo.Obesity and diabetes mellitus represent major public health problems. Type 2 diabetes is a polygenic disease affecting over 100 million people worldwide. The risk of developing type 2 diabetes is increased in populations that lead a sedentary lifestyle and consume a typical western diet, in which more than 50% of the calories are derived from fat (34, 37). A high-fat diet and low energy expenditure predispose to obesity, a condition characterized by increased insulin resistance in insulinresponsive tissues, such as skeletal muscle, liver, and white adipose tissue (9, 42). Body weight also is subject to polygenic regulation (18). Many of the key genes that regulate body mass and glucose homeostasis remain to be identified (27).Insulin plays a critical role in regulating glucose homeostasis, lipid metabolism, and energy balance. Insulin signaling is initiated by binding of insulin to the insulin receptor (IR), a receptor tyrosine kinase. Insulin binding evokes a cascade of phosphorylation events, beginning with the autophosphorylation of the IR on multiple tyrosyl residues. Autophosphorylation enhances IR kinase activity and triggers downstream signaling events. These include tyrosyl phosphorylation of IR substrate (IRS) proteins (IRS-1 to -4) and other adapter molecules (e.g., Grb2 and Shc), whose combined actions mediate the biological effects of insulin (reviewed in references 24, 43, 54, and 69).

Dos/Gab family scaffolding adapters (Dos, Gab1, Gab2) bind several signal relay molecules, including the protein-tyrosine phosphatase Shp-2 and phosphatidylinositol-3-OH kinase (PI(3)K); they are also implicated in growth factor, cytokine and antigen receptor signal transduction. Mice lacking Gab1 die during embryogenesis and show defective responses to several stimuli. Here we report that Gab2-/- mice are viable and generally healthy; however, the response (for example, degranulation and cytokine gene expression) of Gab2-/- mast cells to stimulation of the high affinity immunoglobulin-epsilon (IgE) receptor Fc(epsilon)RI is defective. Accordingly, allergic reactions such as passive cutaneous and systemic anaphylaxis are markedly impaired in Gab2-/- mice. Biochemical analyses reveal that signalling pathways dependent on PI(3)K, a critical component of Fc(epsilon)RI signalling, are defective in Gab2-/- mast cells. Our data identify Gab2 as the principal activator of PI(3)K in response to Fc(epsilon)RI activation, thereby providing genetic evidence that Dos/Gab family scaffolds regulate the PI(3)K pathway in vivo. Gab2 and/or its associated signalling molecules may be new targets for developing drugs to treat allergy.

Little is known about how growth factors control tissue stem cell survival and proliferation. We analyzed mice with a null mutation of Shp2 (Ptpn11), a key component of receptor tyrosine kinase signaling. Null embryos die peri-implantation, much earlier than mice that express an Shp2 truncation. Shp2 null blastocysts initially develop normally, but they subsequently exhibit inner cell mass death, diminished numbers of trophoblast giant cells, and failure to yield trophoblast stem (TS) cell lines. Molecular markers reveal that the trophoblast lineage, which requires fibroblast growth factor-4 (FGF4), is specified but fails to expand normally. Moreover, deletion of Shp2 in TS cells causes rapid apoptosis. We show that Shp2 is required for FGF4-evoked activation of the Src/Ras/Erk pathway that culminates in phosphorylation and destabilization of the proapoptotic protein Bim. Bim depletion substantially blocks apoptosis and significantly restores Shp2 null TS cell proliferation, thereby establishing a key mechanism by which FGF4 controls stem cell survival.

Receptor tyrosine kinases (RTKs) are key regulators of cellular homeostasis. Based on in vitro and ex vivo studies, protein tyrosine phosphatase-1B (PTP1B) was implicated in the regulation of several RTKs, yet mice lacking PTP1B show defects mainly in insulin and leptin receptor signaling. To address this apparent paradox, we studied RTK signaling in primary and immortalized fibroblasts from PTP1B ؊/؊ mice. After growth factor treatment, cells lacking PTP1B exhibit increased and sustained phosphorylation of the epidermal growth factor receptor (EGFR) and the platelet-derived growth factor receptor (PDGFR). However, Erk activation is enhanced only slightly, and there is no increase in Akt activation in PTP1B-deficient cells. Our results show that PTP1B does play a role in regulating EGFR and PDGFR phosphorylation but that other signaling mechanisms can largely compensate for PTP1B deficiency. In-gel phosphatase experiments suggest that other PTPs may help to regulate the EGFR and PDGFR in PTP1Bfibroblasts. This and other compensatory mechanisms prevent widespread, uncontrolled activation of RTKs in the absence of PTP1B and probably explain the relatively mild effects of PTP1B deletion in mice.Regulation of cellular proliferation, adhesion, and migration is pivotal for maintaining homeostasis. Multiple peptide growth factors direct these processes to differing extents in primary fibroblasts and fibroblast cell lines. These growth factors signal via receptors with intrinsic protein-tyrosine kinase activity, termed receptor tyrosine kinases (RTKs).1 Ligand binding activates the intrinsic kinase activity of these receptors, resulting in the phosphorylation of multiple receptor tyrosyl residues. These serve as docking sites to recruit signal relay molecules containing src homology-2 and/or phosphotyrosine binding domains, most of which also are RTK substrates. Based largely on experiments in which wild-type PTPs or their catalytically impaired (dominant-negative) mutants were overexpressed, multiple PTPs, including LAR (7), DEP-1 (8), TC-PTP (9, 10), Shp-1 (11, 12), Shp-2 (13), and PTP1B (14 -17) have been implicated in the dephosphorylation of various RTKs. Which, if any, of these PTPs regulate RTK signaling under physiologically relevant conditions of expression has remained largely unclear. Also unknown is the extent to which RTK dephosphorylation, as opposed to other down-regulatory mechanisms such as RTK degradation and/or inhibitory seryl phosphorylation, plays the (a) key role in receptor inactivation.PTP1B is a widely expressed non-receptor PTP that is localized on intracellular membranes via a hydrophobic C-terminal targeting sequence (18,19). A role for PTP1B in the regulation of many cellular functions has been suggested, including integrin (20 -23), cadherin (24, 25), and cytokine receptor signaling (26 -28), cell cycle regulation (29 -31), and the response to cellular stress (32). Multiple studies indicated that PTP1B dephosphorylates the EGFR (16, 17) and the insulin receptor (IR) (14,(33)(34)(35). Analy...