The production, survival, and function of monocytes and macrophages is regulated by the macrophage colony-stimulating factor (M-CSF or CSF-1) through its tyrosine kinase receptor Fms. Binding of M-CSF to Fms induces the tyrosine phosphorylation and association of a 150-kD protein with the phosphotyrosine-binding (PTB) domain of Shc. We have cloned p150 using a modified yeast two-hybrid screen.

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The fibronectin (FN) receptor in avian cells has been characterized previously as a complex of three membrane glycoproteins of about Mr 160,000, Mr 140,000, and Mr 120,000 (simply termed protein band 1, band 2, and band 3, respectively). Monoclonal antibodies to the band 3 protein of the complex prevent FN and laminin binding both in vivo and in vitro and enable the detection of the receptor proteins in the plasma membrane and in adhesion plaques. Association of the FN receptor proteins with the adhesion-plaque protein talin also has been reported. We now find that the band 2 and band 3 proteins in the complex are phosphorylated in Rous sarcoma virus-transformed chicken cells but not in normal chicken cells. Phosphorylation occurs predominantly on tyrosine and is accompanied by a reorganization ofthe receptor complex in the membrane of the transformed cells. Whereas normal cells contain the FN receptor in focal contacts and cellular processes between cells, v-src-transformed cells exhibit a more diffuse distribution of this receptor. In addition to the viral v-src oncogene, cells transformed by other avian oncogenes that also encode tyrosine kinases (v-.fs, v-erbB, and v-yes) also express the receptor complex proteins in the phosphorylated state regardless of whether the transforming protein is detectable in adhesion plaques. These results suggest that the altered FN and laminin receptor proteins may contribute to the transformed phenotype, but their significance and role in the transformed state remain to be established.Transformation by Rous sarcoma virus (RSV) is initiated and maintained by the protein product of the viral v-src gene (1, 2). This protein, designated pp60src, possesses an inherent tyrosine kinase activity essential for transformation and is situated along the cytoplasmic face of the plasma membrane and concentrated within cell-substratum adhesion sites (3). These latter sites are termed focal contacts or adhesion plaques and are associated either directly or indirectly with several functions that are altered in RSV-transformed cells. Focal contacts mediate not only the physical associations of cells to each other and to substrata (via extracellular molecules) but also serve as organizing centers for attachment of extracellular matrix protein and intracellular focal points for stress-fiber termination (4-10). These sites are very specialized regions of the plasma membrane, and proteins within these structures are logical targets for such RSV-induced alterations as decreased cellular adhesiveness, loss of cell surface fibronectin (FN), abnormal cell migration, dissolution of stress-fiber bundles, and ultimately the rounded transformed cell morphology.Little is known of the molecular composition and complexity of adhesion plaques; however, several proteins have been identified as constituents of these structures (7,(11)(12)(13)(14)(15)(16).Of these proteins, vinculin has received considerable attention because it was shown to contain increased levels of phosphotyrosine in RSV-transformed...

Gab proteins, including mammalian Gab1, Gab2, Gab3, Drosophila DOS and Caenorhabditis elegans Soc1, comprise a growing family of scaffolding/docking molecules involved in multiple signaling pathways mediated by receptor tyrosine kinases (RTKs) and non-RTK receptors. This paper reviews the structure/function relationships of Gab proteins and their biological roles during normal growth, differentiation and development programs. ß

The protein tyrosine phosphatase SHP-1 is a critical regulator of macrophage biology, but its detailed mechanism of action remains largely undefined. SHP-1 associates with a 130-kDa tyrosyl-phosphorylated species (P130) in macrophages, suggesting that P130 might be an SHP-1 regulator and/or substrate. Here we show that P130 consists of two transmembrane glycoproteins, which we identify as PIR-B/p91A and the signal-regulatory protein (SIRP) family member BIT. These proteins also form separate complexes with SHP-2. BIT, but not PIR-B, is in a complex with the colony-stimulating factor 1 receptor (CSF-1R), suggesting that BIT may direct SHP-1 to the CSF-1R. BIT and PIR-B bind preferentially to substrate-trapping mutants of SHP-1 and are hyperphosphorylated in macrophages from motheaten viable mice, which express catalytically impaired forms of SHP-1, indicating that these proteins are SHP-1 substrates. However, BIT and PIR-B are hypophosphorylated in motheaten macrophages, which completely lack SHP-1 expression. These data suggest a model in which SHP-1 dephosphorylates specific sites on BIT and PIR-B while protecting other sites from dephosphorylation via its SH2 domains. Finally, BIT and PIR-B associate with two tyrosyl phosphoproteins and a tyrosine kinase activity. Tyrosyl phosphorylation of these proteins and the level of the associated kinase activity are increased in the absence of SHP-1. Our data suggest that BIT and PIR-B recruit multiple signaling molecules to receptor complexes, where they are regulated by SHP-1 and/or SHP-2.Protein tyrosine phosphatases (PTPs) and protein tyrosine kinases (PTKs) control the level of tyrosyl phosphorylation on cellular proteins (reviewed in references 38, 52, and 56). Although many substrates for PTKs have been identified, the specific targets of individual PTP family members, along with the consequences of protein dephosphorylation for cellular physiology, remain largely unknown. The finding that some PTPs possess SH2 domains suggested that these molecules might be recruited to specific phosphotyrosyl (pY) sites (via their SH2 domains), where their PTP domains could catalytically amplify or terminate phosphotyrosine-mediated signals (14, 37). Two vertebrate SH2-containing PTPs (SHPs), SHP-1 and SHP-2 (1), have been cloned and characterized (reviewed in reference 37). Despite their structural similarity, SHP-1 and SHP-2 appear to possess distinct biological functions (reviewed in references 3, 36 to 38, 52, and 56). SHP-2 is expressed ubiquitously and typically transmits positive (i.e., signal-enhancing) signals downstream of receptor tyrosine kinases, cytokine receptors, and multichain immune recognition receptors, although recent work suggests that it may have negative (i.e., signal-attenuating) effects in some pathways (33, 54). In contrast, SHP-1 is expressed predominantly in hematopoietic cells, where it negatively regulates multiple growth factor and cytokine signaling pathways (reviewed in references 36, 38 and 56).Our current understanding of the role played by S...