Glucagon-like peptide 2 (GLP-2) is a 33-aa proglucagon-derived peptide produced by intestinal enteroendocrine cells. GLP-2 stimulates intestinal growth and upregulates villus height in the small intestine, concomitant with increased crypt cell proliferation and decreased enterocyte apoptosis. Moreover, GLP-2 prevents intestinal hypoplasia resulting from total parenteral nutrition. However, the mechanism underlying these actions has remained unclear. nM). GLP-2 analogs that activated GLP-2R signal transduction in vitro displayed intestinotrophic activity in vivo.These results strongly suggest that GLP-2, like glucagon and GLP-1, exerts its actions through a distinct and specific novel receptor expressed in its principal target tissue, the gastrointestinal tract.Glucagon-like peptides (GLPs) encoded by the proglucagon gene play key roles in glucose homeostasis, gastric emptying, insulin secretion, and appetite regulation (1). Glucagon and GLP-1 exert their effects through distinct G protein-coupled receptors (GPCRs). In contrast, unique receptors for GLP-2, glicentin, and oxyntomodulin have not yet been identified, despite considerable attempts at receptor isolation via classical molecular biology approaches (2). Recent studies have shown that GLP-2 is a potent intestinal growth factor that stimulates crypt cell proliferation and inhibits epithelial apoptosis (3). GLP-2 promotes epithelial proliferation in both small and large intestine; however, the mechanisms utilized by GLP-2 for promotion of intestinal growth remain unclear.To understand the mechanisms underlying GLP-2 action, we have carried out studies directed at the identification and cloning of the putative GLP-2 receptor. We now have isolated rat and human cDNAs encoding GLP-2-responsive GPCRs, which show highest similarity to receptors for glucagon and GLP-1. The GLP-2R is coupled to activation of adenylate cyclase, and the receptor is expressed selectively in rat hypothalamus and the gastrointestinal tract, known targets of GLP-2 action. These findings establish GLP-2 as a novel hormone that, like glucagon and GLP-1, exerts its actions through a distinct receptor expressed in a highly tissuerestricted manner. The GLP-2R should provide an important target for isolation of small molecules mimicking GLP-2 action and for future studies delineating specific mechanisms underlying GLP-2 action in the gut and central nervous system.

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A missing component in the experimental analysis of cell signaling by extracellular lysophospholipids such as lysophosphatidic acid (LPA) or sphingosine-1-phosphate (S1P) has been cloned receptors. Through studies on the developing brain, the first such receptor gene (referred to as vzg-1) was identified, representing a member of the G-protein coupled receptor (GPCR) super family (1). Here we review the neurobiological approach that led to both its cloning and identification as a receptor for LPA, along with related expression data. Summarized sequence and genomic structure analyses indicate that this first, functionally identified receptor is encoded by a member of a growing gene family that divides into at least two subgroups: genes most homologous to the high-affinity LPA receptor encoded by vzg-1, and those more homologous to an orphan receptor gene edg-1 that has recently been identified as a S1P receptor. A provisional nomenclature is proposed, based on published functional ligand actions, amino acid composition and genomic structure whereby the receptors encoded by these genes are referred to as lysophospholipid (LP) receptors, with subgroups distinguished by letter and number subscripts (e.g., LPA1 for Vzg-1, and LPB1 for Edg-1). Presented expression data support the recently published work indicating that members of the LPB1 subgroup are receptors for the structurally-related molecule, S1P. The availability of cloned LP receptors will enhance the analysis of the many documented LP effects, while their prominent expression in the nervous system indicates significant but as yet unknown roles in development, normal function, and neuropathology.

Glucagon-like peptide-2 (GLP-2The gastrointestinal mucosal epithelium contains a diverse number of specialized enteroendocrine cells that synthesize and secrete peptide hormones, frequently in a nutrient-dependent manner. Following secretion into circulation, gut-derived hormones may act in an endocrine manner by binding to receptors in tissues such as pancreas and liver, leading to the activation of signal transduction pathways and downstream physiological events. Consistent with their location in the intestinal mucosal epithelium, enteroendocrine peptides may function in part to regulate gastrointestinal motility and nutrient digestion and absorption. For example, gastrin promotes acid secretion, whereas secretin inhibits acid secretion and promotes pancreatic exocrine secretion. Peptide hormones structurally related to secretin, such as glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 (GLP-1), 1 stimulate glucose-dependent insulin secretion from the pancreatic beta cells, and GLP-1, unlike the glucose-dependent insulinotropic polypeptide, also inhibits gastric emptying, glucagon secretion, and food intake in vivo (1).The pleiotropic actions of the glucagon/secretin/glucose-dependent insulinotropic polypeptide peptide superfamily are mediated via binding to and activation of distinct G proteincoupled receptors (GPCRs). These GPCRs are encoded by unique genes, yet are structurally related, and often share common features with respect to utilization of signaling mechanisms following ligand activation. Glucagon-related peptides regulate metabolic events, hormone secretion, and intestinal growth. For example, glucagon regulates glycogenolysis and gluconeogenesis via activation of a hepatocyte glucagon receptor (2), whereas GLP-1 stimulates glucose-dependent insulin secretion following activation of an islet beta cell GLP-1 receptor (3). Studies of glucagon and GLP-1 receptor signaling in cells expressing the endogenous receptor or in heterologous cells expressing transfected receptors demonstrate that both these peptides activate downstream signaling mechanisms coupled to the cAMP-dependent pathway (1).In contrast to our understanding of the mechanisms underlying glucagon and GLP-1 action, much less is known about the biological activity of GLP-2, a 33-amino acid peptide located carboxyl-terminal to GLP-1 in the proglucagon precursor. GLP-2 administration to mice or rats promotes stimulation of crypt cell proliferation and inhibition of enterocyte apoptosis resulting in hyperplasia of the small bowel villous epithelium (4, 5). GLP-2 also exerts trophic effects in animal models of both small and large bowel injury such as experimental small bowel resection or chemically induced colitis (6, 7). In addition to stimulation of epithelial proliferation, GLP-2 also acutely regulates gastric emptying (8) and exerts rapid metabolic effects promoting stimulation of intestinal hexose transport

The p53 gene is rearranged in an erythroleukemic cell line (DP15-2) transformed by Friend retrovirus. Here, we characterize the mutation and identify a deletion of =3.0 kilobases that removes exon 2 coding sequences. The gene is expressed in DP15-2 cells and results in synthesis of a 44,000-dalton protein that is missing the N-terminal amino acid residues of p53. The truncated protein is unusually stable and accumulates to high levels intracellularly. Moreover, it appears to have undergone a change in conformation as revealed by epitope mapping studies. This study represents the first description of an altered p53 gene product arising by mutation during neoplastic progression and identifies a region in the p53 protein molecule that plays a role in determining p53 stability in vivo.There is now good evidence that the cellularly encoded nuclear phosphoprotein, p53, is involved in the transformation process (for reviews, see references 8, 20, and 35). p53 protein levels are elevated in a variety of transformed cells from different species, including cells transformed by viruses (22,23,26,32,43,45) and chemical agents (9). Recently, it was reported that expression of the murine p53 gene can immortalize early-passage rodent cells in culture (17) and that the p53 gene can replace myc in a myc-ras immortalization-transformation assay in rat embryo fibroblasts (12,17,37). Furthermore, overproduction of p53 protein in certain cells has been shown to confer an enhanced tumorigenic phenotype (11,19,32,53). Hence, the p53 gene appears to have oncogenic potential.Several studies indicate that p53 expression is correlated with cell cycling and may play a role in the proliferation of normnal cells (27)(28)(29)(30)40). p53 expression increases before DNA synthesis when resting cells are stimulated to divide by mitogen (30) or by serum (40). In addition, microinjection of p53-specific monoclonal antibodies into the nuclei of quiescent mouse cells blocks their proliferative response to serum stimulation (27,29). Finally, primary cultures of early mouse embryos synthesize p53 (31).Regulation of p53 expression in cells can occur at the level of mRNA abundancy or p53 protein stability (40, 41). Occurrence of the first mechanism was demonstrated in embryonal carcinoma cells (F9) which have nearly 20-foldhigher levels of p53 mRNA than their differentiated progeny (41) and in cells induced to proliferate (30,39,40). In general, however, p53 protein levels are not correlated with the amount of p53 mRNA, indicating that the amount of p53 protein is regulated at the posttranscriptional level, perhaps through changes in protein stability (25,36 the stability and steady-state levels of the p53 protein are considerably increased (36,41). Specific interaction between p53 and the major heat shock proteins HSP68 and HSP70 has also been reported (38).DNA rearrangements have been shown to alter the expression of the p53 gene, leading to complete gene inactivation (32, 54, 55) and expression of truncated proteins antigenically related to p53 (32)....

The Friend erythroleukemia virus complex contains no cell-derived oncogene. Transformation by this virus may therefore involve mutations affecting cellular gene expression. We provide evidence that inactivating mutations of the cellular p53 gene are a common feature in Friend virus-induced malignancy, consistent with an antioncogene role for p53 in this disease. We have shown that frequent rearrangements of the p53 gene cause loss of expression or synthesis of truncated proteins, whereas overexpression of p53 protein is seen in other Friend cell lines. We now demonstrate that p53 expression in the latter cells is also abnormal, as a result of missense mutations in regions encoding highly conserved amino acids. Three of these aberrant alleles obtained from cells from different mice were cloned and found to function as dominant oncogenes in gene transfer assays, supporting the view that certain naturally occurring missense mutations in p53 confer a dominant negative phenotype on the encoded protein.

MIA2G specificity and PPV were significantly improved compared with MIA, while sensitivity and NPV were unchanged. The second-generation test significantly improved the predicted efficiency of triage vs MIA without sacrificing high sensitivity and NPV, which are essential for effectiveness.

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