Activation of the Ras/MAPK signaling cascade is essential for growth factor-induced cell proliferation and differentiation. In this report, we describe the purification, cloning, and characterization of a novel protein, designated FRS2, that is tyrosine phosphorylated and binds to Grb2/Sos in response to FGF or NGF stimulation. We find that FRS2 is myristylated and that this modification is essential for membrane localization, tyrosine phosphorylation, Grb2/Sos recruitment, and MAPK activation. FRS2 functions as a lipid-anchored docking protein that targets signaling molecules to the plasma membrane in response to FGF stimulation to link receptor activation with the MAPK and other signaling pathways essential for cell growth and differentiation. Finally, we demonstrate that FRS2 is closely related and probably indentical to SNT, the long-sought target of FGF and NGF receptors.

Phosphotyrosine phosphatases are critical negative or positive regulators in the intracellular signalling pathways that result in growth-factor-specific cell responses such as mitosis, differentiation, migration, survival, transformation or death. The SH2-domain-containing phosphotyrosine phosphatase SHP-2 is a positive signal transducer for several receptor tyrosine kinases (RTKs) and cytokine receptors. To investigate its mechanism of action we purified a tyrosine-phosphorylated glycoprotein which in different cell types associates tightly with SHP-2 and appears to serve as its substrate. Peptide sequencing in conjunction with complementary DNA cloning revealed a new gene family of at least fifteen members designated signal-regulatory proteins (SIRPs). They consist of two subtypes distinguished by the presence or absence of a cytoplasmic SHP-2-binding domain. The transmembrane polypeptide SIRP alpha1 is a substrate of activated RTKs and in its tyrosine-phosphorylated form binds SHP-2 through SH2 interactions and acts as its substrate. It also binds SHP-1 and Grb2 in vitro and has negative regulatory effects on cellular responses induced by growth factors, oncogenes or insulin. Our findings indicate that proteins belonging to the SIRP family generally regulate signals defining different physiological and pathological processes.

Barnea et al., 1994;Maurel et al., 1994). It has been expressed on the surface of glial cells binds to the shown that the expression of RPTPβ is restricted to the glycosylphosphatidylinositol (GPI)-anchored recogninervous system. RPTPβ is expressed in cells that have been tion molecule contactin on neuronal cells leading to implicated in neuronal migration and axonal guidance, neurite outgrowth. We describe the cloning of a novel including glial precursors, radial glia and astrocytes (Rauch contactin-associated transmembrane receptor (p190 Canoll et al., 1993). RPTPβ also bears the Caspr) containing a mosaic of domains implicated in HNK-1 carbohydrate epitope that is found in several protein-protein interactions. The extracellular domain neuronal adhesion molecules and was implicated in cell of Caspr contains a neurophilin/coagulation factor recognition and axonal guidance (Rauch et al., 1991). In homology domain, a region related to fibrinogen β/γ, Drosophila, the analogous HRP carbohydrate epitope was epidermal growth factor-like repeats, neurexin motifs found in neural recognition molecules as well as in as well as unique PGY repeats found in a molluscan receptor protein tyrosine phosphatases that are expressed adhesive protein. The cytoplasmic domain of Caspr in the developing nervous system (Desai et al., 1994). It contains a proline-rich sequence capable of binding to was demonstrated recently that loss-of-function mutations a subclass of SH3 domains of signaling molecules.in Drosophila RPTPs result in erroneous pathfinding Caspr and contactin exist as a complex in rat brain of certain motor axons (Desai et al., 1996; Krueger and are bound to each other by means of lateral (cis) et al., 1996). interactions in the plasma membrane. We proposeIn our attempts to identify specific ligands of RPTPβ, that Caspr may function as a signaling component we used soluble, recombinant CAH or FNIII domains of of contactin, enabling recruitment and activation of this receptor phosphatase as specific reagents for the intracellular signaling pathways in neurons. The bindidentification of cellular proteins that bind to RPTPβ. We ing of RPTPβ to the contactin-Caspr complex could have demonstrated that the FNIII repeat binds specifically provide a mechanism for cell-cell communication to glial cells while the CAH domain of RPTPβ binds to between glial cells and neurons during development.neurons or cells of neuronal origin .

The primary structures of three human neutrophil antimicrobial peptides (HNP) were determined. The peptides, HNP-1, HNP-2, and HNP-3, which we have termed defensins, were rich in cystine, arginine, and aromatic residues, but were devoid of free sulfhydryl groups and carbohydrate moieties. They were 29-30 residues in length and identical in sequence in all but their amino terminal residues. The defensins were homologous in sequence to peptides of similar size and biological activity previously purified from rabbit polymorphonuclear leukocytes, but unrelated to other neutrophil proteins of known sequence. 11 amino acid residues of the human defensins, including all six cysteinyl residues, were invariantly conserved in the six rabbit members of this multigene peptide family. That similarly structured antimicrobial peptides are present in both rabbit and human leukocytes supports their purported role as cidal agents in phagocyte-mediated host defense.

The amyloid proteins isolated from neuritic plaques and the cerebrovasculature of Alzheimer's disease are self-aggregating moieties termed A4 protein and beta-protein, respectively. A putative A4 amyloid precursor (herein termed A4(695] has been characterized by analysis of a human brain complementary DNA. We report here the sequence of a closely related amyloid cDNA, A4(751), distinguished from A4(695) by the presence of a 168 base-pair (bp) sequence which adds 57 amino acids to, and removes one residue from, the predicted A4(695) protein. The peptide predicted from this insert is very similar to the Kunitz family of serine proteinase inhibitors. The two A4-specific messenger RNAs are differentially expressed: in a limited survey, A4(751) mRNA appears to be ubiquitous, whereas A4(695) mRNA has a restricted pattern of expression which includes cells from neuronal tissue. These data may have significant implications for understanding amyloid deposition in Alzheimer's disease.

Receptor-type protein tyrosine phosphatase beta (RPTP beta) is expressed in the developing nervous system and contains a carbonic anhydrase (CAH) domain as well as a fibronectin type III repeat in its extracellular domain. Fusion proteins containing these domains were used to search for ligands of RPTP beta. The CAH domain bound specifically to a 140 kDa protein expressed on the surface of neuronal cells. Expression cloning in COS7 cells revealed that this protein is contactin, a GPI membrane-anchored neuronal cell recognition molecule. The CAH domain of RPTP beta induced cell adhesion and neurite growth of primary tectal neurons, and differentiation of neuroblastoma cells. These responses were blocked by antibodies against contactin, demonstrating that contactin is a neuronal receptor for RPTP beta. These experiments show that an individual domain of RPTP beta acts as a functional ligand for the neuronal receptor contactin. The interaction between contactin and RPTP beta may generate unidirectional or bidirectional signals during neural development.

Pulmonary surfactant is a lipid-rich material that promotes alveolar stability by lowering the surface tension at the air-fluid interface in the peripheral air spaces. The turnover of surfactant phospholipids in the alveolar space is fast, and several lines of evidence suggest there is rapid formation and replenishment of the phospholipid surface film during normal respiration. Specific proteins may regulate these dynamic surface properties. The predominant surfactant protein is a well-characterized, lipid-associated glycoprotein, SP [28][29][30][31][32][33][34][35][36] Pulmonary surfactant is a lipid-rich material secreted as tightly packed lamellae into the extracellular alveolar fluid layer (1). Within the alveolar space, surfactant lipids are found in a number of different structural forms, including lamellar bodies, tubular myelin, and various vesicular structures (2). Although the lipid compositions of the surfactant structures are similar, the physical properties, particularly the ability ofthe lipoprotein complexes to form a surface film, are quite different (3). Specific proteins appear to influence the structure and surface activity of surfactant-lipid complexes (4-10).The predominant surfactant-associated protein is the glycoprotein SP 28-36 (28-36 kDa) characterized by a collagenlike NH2-terminal domain and variable N-linked glycosylation of the COOH-terminal region (11-13). SP 28-36 is water soluble but readily associates with phospholipids (PLs) (14). In the presence of calcium, SP 28-36 causes PL aggregation and increases the rate of adsorption of surfactant lipids to an air-fluid interface (6,8,14). A second group of very hydrophobic proteins has been identified in lamellar bodies isolated from lung homogenate and in surfactant isolated from the bronchoalveolar wash (4, 9, 10, 15-17). Very little is known about the homogeneity, structure, or function ofthis group of hydrophobic proteins, but it has been reported that at least one of these proteins enhances PL surface film formation (9,10,18 (20). The surfactant in water (-16 mg of PL per ml, 2 mg of protein per ml) was extracted in 1-butanol (1:50, vol/vol) at room temperature (21). The surfactant/butanol mixture was spun twice at 10,000 X gav for 20 min to sediment the butanolinsoluble protein (94% of the total). The butanol supernatant was dried by rotary evaporation and the residue was resuspended in chloroform/methanol/0.1 M HCl, 1:1:0.5, vol/vol). A small amount of insoluble material was removed by centrifugation and the supernatant, containing 30 mg ofPL in 1 ml, was applied to a 1 cm x 45 cm column of Sephadex and eluted at 4 ml/hr with the same solvent at 40C. The eluted fractions, 0.5 ml, were assayed for protein (22) in the presence of 1% NaDodSO4, phosphorus (23) for the calculation of the PL content, and cholesterol (24). An aliquot of each fraction containing protein was analyzed by NaDodSO4/PAGE (25) and silver staining (26). 66The publication costs of this article were defrayed in part by page charge payment. This article...

A growth factor with specificity for vascular endothelial cells has been identified in conditioned medium of pituitary-derived folliculo stellate cells. This factor, named folliculo stellate-derived growth factor (FSdGF), was purified to homogeneity by a combination of heparin-Sepharose affinity chromatography, Bio-Gel P-60 exclusion chromatography, Mono S ion-exchange chromatography, and hydrophobic chromatography on a C4 reverse-phase HPLC column. FSdGF was characterized as a homodimer composed of two subunits with a molecular mass of 23 kDa. FSdGF was a potent mitogen for vascular endothelial cells with activity detectable at 25 pg/ml and saturation at 500 pg/ml. It did not stimulate the proliferation of other cell types such as bovine vascular smooth muscle cells, corneal endothelial cells, adrenal cortex cells,