Gp120-induced Bob/GPR15 activation: a possible cause of human immunodeficiency virus enteropathy.

Human immunodeficiency virus (HIV)-infected patients often develop malabsorption and increased intestinal permeability with diarrhea, called HIV enteropathy, even without enteric opportunistic infections. HIV gp120-induced calcium signaling, microtubule loss, and physiological changes resembling HIV enteropathy were previously found in the HT-29 intestinal cell line. How gp120 caused these changes was unclear. We show that the HIV co-receptor Bob/GPR15, unlike CCR5 and CXCR4, is abundant at the basal surface of small intestinal epithelium. The gp120-induced effects on HT-29 cells were inhibited by anti-Bob neutralizing antibodies, the selective G protein inhibitor pertussis toxin, and the phospholipase inhibitor U73122, but not neutralizing antibodies to CXCR4. Gp120 strains that induced signaling in HT-29 cells also induced calcium fluxes in Bob-transfected Ghost (3) cells, whereas gp120 strains not activating HT-29 cells also did not activate Bob-transfected cells. Bob is the first HIV co-receptor shown to be abundantly expressed on the basolateral surface of intestinal epithelium. Although Bob is an inefficient infection-inducing co-receptor, it mediates viral strain-specific gp120-induced calcium signaling at low, physiologically reasonable gp120 concentrations, up to 10,000-fold lower gp120 concentrations than the principal co-receptors. Gp120-induced Bob activation is a plausible cause of HIV enteropathy.

Carcinoid tumors.

Carcinoid tumors most commonly occur in the gastrointestinal tract and are known best for the bizarre manifestations of the carcinoid syndrome caused by the release of tumor products. However, many carcinoid tumors do not present with or cause the carcinoid syndrome, and this has led to the development of new diagnostic markers for these tumors. New treatments have emerged recently and are being developed, because although these tumors are relatively indolent, they can metastasize. The biology of carcinoid tumors of the gastrointestinal tract can be classified in large part by the embryologic regions of the gut in which they occur. More carcinoid tumors will be discovered as the indications and use of gastrointestinal endoscopies increase, so the diagnosis and initial management of carcinoid tumors will fall largely on the gastroenterologist.

Integrin alpha5/beta1 mediates fibronectin-dependent epithelial cell proliferation through epidermal growth factor receptor activation.

Human integrin alpha5 was transfected into the integrin alpha5/beta1-negative intestinal epithelial cell line Caco-2 to study EGF receptor (EGFR) and integrin alpha5/beta1 signaling interactions involved in epithelial cell proliferation. On uncoated or fibronectin-coated plastic, the integrin alpha5 and control (vector only) transfectants grew at similar rates. In the presence of the EGFR antagonistic mAb 225, the integrin alpha5 transfectants and controls were significantly growth inhibited on plastic. However, when cultured on fibronectin, the integrin alpha5 transfectants were not growth inhibited by mAb 225. The reversal of mAb 225-mediated growth inhibition on fibronectin for the integrin alpha5 transfectants correlated with activation of the EGFR, activation of MAPK, and expression of proliferating cell nuclear antigen. EGFR kinase activity was necessary for both MAPK activation and integrin alpha5/beta1-mediated cell proliferation. Although EGFR activation occurred when either the integrin alpha5-transfected or control cells were cultured on fibronectin, coprecipitation of the EGFR with SHC could be demonstrated only in the integrin alpha5-transfected cells. These results suggest that integrin alpha5/beta1 mediates fibronectin-induced epithelial cell proliferation through activation of the EGFR.

Colorectal cancer 2000. Education and screening are essential if outcomes are to improve.

Mortality from colorectal cancer is less threatening than it was 10 years ago, but this cancer is still a leading cause of death in the United States and the world. Careful history taking, education about the importance of a high-fiber, low-fat diet and exercise, and regular screening are important steps in improving outcomes. For the busy primary care physician and the equally busy patient, prevention can become a low priority. However, the benefits of early preventive intervention are clearly worth the effort.

Today's approach to esophageal cancer. What is the role of the primary care physician?

Esophageal cancer is a devastating disease. Patients are most likely to first present to a primary care physician, who should immediately undertake an initial diagnostic and staging evaluation. The approach then should become multidisciplinary, involving surgical and medical oncologists, radiation oncologists, and gastroenterologists. Optimal therapy of esophageal cancer continues to evolve. While multimodality therapy remains controversial, studies are ongoing to determine the best approaches to improve survival. Further studies to define the role of surveillance endoscopy in certain high-risk patients are warranted.

The dynamic expression of the epidermal growth factor receptor and epidermal growth factor ligand family in a differentiating intestinal epithelial cell line.

The Caco-2 intestinal epithelial cell line differentiates when cultured on plastic or permeable filters, and offers a valuable system to study events associated with enterocytic differentiation in vitro. Little is known as to whether the expression of the epidermal growth factor receptor (EGFR) and its ligands changes as intestinal epithelial cells differentiate. We found that total cellular EGFR protein and mRNA transcript levels were relatively unchanged during Caco-2 cell differentiation, but the expression of surface EGFR and patterns of steady state epidermal growth factor (EGF)-family ligand expression changed significantly. EGFR affinity, surface EGFR expression levels, and the repertoire of expressed EGF-family ligands, were different between Caco-2 cells cultured on plastic and filters. Functionally, EGFR-mediated cell proliferation and tyrosine phosphorylation of the signal transduction protein SHC could be inhibited in Caco-2 cells cultured on filters, but not on plastic. Thus, the substrate on which the cells were grown and the degree of cell differentiation strongly modulate EGFR affinity, EGFR surface expression, the steady state expression of EGF-family ligands, as well as, EGFR-mediated cellular responses. Our results suggest that the EGFR system is regulated during intestinal epithelial cell differentiation primarily at the level of ligand expression.

Amphiregulin acts as an autocrine growth factor in two human polarizing colon cancer lines that exhibit domain selective EGF receptor mitogenesis.

Colonic enterocytes, like many epithelial cells in vivo, are polarized with functionally distinct apical and basolateral membrane domains. The aims of this study were to characterize the endogenous epidermal growth factor (EGF)-like ligands expressed in two polarizing colon cancer cell lines, HCA-7 Colony 29 (HCA-7) and Caco-2, and to examine the effects of cell polarity on EGF receptor-mediated mitogenesis. HCA-7 and Caco-2 cells were grown on plastic, or as a polarized monolayer on Transwell filters. Cell proliferation was measured by 3H-thymidine incorporation and EGF receptor (EGFR) binding was assessed by Scatchard analysis. EGFR ligand expression was determined by Northern blot analysis, reverse transcription polymerase chain reaction, metabolic labelling and confocal microscopy. We found that amphiregulin (AR) was the most abundant EGFR ligand expressed in HCA-7 and Caco-2 cells. AR was localized to the basolateral surface and detected in basolateral-conditioned medium. Basolateral administration of neutralizing AR antibodies significantly reduced basal DNA replication. A single class of high-affinity EGFRs was detected in the basolateral compartment, whereas the apical compartment of polarized cells, and cells cultured on plastic, displayed two classes of receptor affinity. Basolateral administration of transforming growth factor alpha (TGF-alpha) or an EGFR neutralizing antibody also resulted in a dose-dependent stimulation or attenuation, respectively, of DNA replication. However, no mitogenic response was observed when these agents were added to the apical compartment or to confluent cells cultured on plastic. We conclude that amphiregulin acts as an autocrine growth factor in HCA-7 and Caco-2 cells, and EGFR ligand-induced proliferation is influenced by cellular polarity.

Membrane receptor location defines receptor interaction with signaling proteins in a polarized epithelium.

Signal transduction from receptors is mediated by the interaction of activated receptors with proximate downstream signaling proteins. In polarized epithelial cells, the membrane is divided into subdomains: the apical and basolateral membranes. Membrane receptors may be present in one or both subdomains. Using a combination of immunoprecipitation and Western blot analyses, we tested the hypothesis that a tyrosine kinase growth factor receptor, epidermal growth factor receptor (EGFR), interacts with distinct signaling proteins when present at the apical vs. basolateral membrane of a polarized renal epithelial cell. We report here that tyrosine phosphorylation of phospholipase C-gamma (PLC-gamma) was induced only when basolateral EGFR was activated. In contrast, tyrosine phosphorylation of several other signaling proteins was increased by activation of receptor at either surface. All signaling proteins were distributed diffusely throughout the cytoplasm; however, PLC-gamma protein also displayed a concentration at lateral cell borders. These results demonstrate that in polarized epithelial cells the array of signaling pathways initiated by activation of a membrane receptor is defined, at least in part, by the membrane location of the receptor.

Differential signaling and regulation of apical vs. basolateral EGFR in polarized epithelial cells.

Overexpression of the epidermal growth factor receptors (EGFR) in polarized kidney epithelial cells caused them to appear in high numbers at both the basolateral and apical cell surfaces. We utilized these cells to look for differences in the regulation and signaling of apical vs. basolateral EGFR. Apical and basolateral EGFR were biologically active and mediated EGF-induced cell proliferation to similar degrees. Receptor downregulation and endocytosis were less efficient at the apical surface, resulting in prolonged EGF-induced tyrosine kinase activity at the apical cell membrane. Tyrosine phosphorylation of EGFR substrates known to mediate cell proliferation, Src-homologous and collagen protein (SHC), extracellularly regulated kinase 1 (ERK1), and ERK2 could be induced similarly by activation of apical or basolateral EGFR. Focal adhesion kinase was tyrosine phosphorylated more by basolateral than by apical EGFR; however, beta-catenin was tyrosine phosphorylated to a much greater degree following the activation of mislocalized apical EGFR. Thus EGFR regulation and EGFR-mediated phosphorylation of certain substrates differ at the apical and basolateral cell membrane domains. This suggests that EGFR mislocalization could result in abnormal signal transduction and aberrant cell behavior.

The clinical features of the hereditary and nonhereditary polyposis syndromes.

The polyposis syndromes are rare familial and noninherited syndromes associated with intestinal as well as extraintestinal malignancies in many cases. Their recognition and classification are critical in determining the appropriate management strategies.

The risk of withdrawing chronic anticoagulation because of acute GI bleeding.

OBJECTIVE: We sought evidence for thromboembolic sequelae after the transient withdrawal of chronic anti-coagulation because of acute GI bleeding. METHODS: Our Gastrointestinal Bleeding Team endoscopic database was reviewed over a 5-yr period to identify patients who underwent a transient withdrawal from chronic anticoagulation as a result of acute GI bleeding. Long term follow-up records were available for all study patients and were carefully scrutinized for any symptomatic thromboembolic events. RESULTS: Twenty-seven patients were included in the study, of which 17 (63%) were on chronic anticoagulation for prosthetic heart valves. Chronic anticoagulation was withheld for a median period of 3 days (range = 2-7 days) for patients with prosthetic heart valves and 7 days (range = 2-15 days) for patients on chronic anticoagulation for other indications. Over a median follow-up period of 8 months (range = 1-54 months), one patient developed documented lower extremity thromboembolism. CONCLUSIONS: We conclude that symptomatic thromboembolism can occur after the transient withdrawal of chronic anticoagulation for acute GI bleeding but that it does not occur frequently.

Long-term outcome of endoscopic dilation of nonmalignant pyloric stenosis.

Although the immediate success of endoscopic balloon dilation of nonmalignant and noncongenital pyloric stenosis is known, little information is available on the long-term results of such therapy. Of 19 patients who underwent this treatment at our institution for gastric outlet obstruction, 3 (16%) experienced sustained relief and 16 (84%) had a recurrence of symptoms during a median follow-up period of 45 months. Twelve of the patients who had a recurrence of gastric outlet obstructive symptoms required further therapy. Our results suggest that if followed for a prolonged period of time, patients who have undergone endoscopic balloon dilation of nonmalignant pyloric stenosis have a high recurrence rate of symptomatic gastric outlet obstruction.

Non-A, non-B fulminant hepatitis is also non-E and non-C.

OBJECTIVES: to define the roles of the hepatitis C and E viruses (HCV and HEV) in non-A, non-B (NANB) fulminant hepatitis. METHODS: we utilized the polymerase chain reaction to amplify HCV and HEV RNA sequences and assays to detect antibodies to HCV and HEV in the acute phase sera of eight presumed viral NANB and seven nonviral NANB fulminant hepatic failure (FHF) patients. RESULTS: none of the 15 patients had detectable HCV or HEV RNA or elevated HCV and IgM-HEV antibody titers in their acute phase sera. Three patients, all with features of autoimmune hepatitis, had raised IgG-HEV antibody titers. Due to the possibility of serologically undetectable hepatitis B virus (HBV) infection in fulminant hepatitis patients, we performed polymerase chain reaction amplification of HBV genomic DNA in acute phase sera of the presumed viral NANB FHF patients and subsequently found no evidence of HBV DNA. CONCLUSIONS: we did not find evidence implicating HCV or HEV in presumed viral NANB FHF or as agents contributing to or causing the liver failure in nonviral NANB FHF patients with autoimmune hepatitis, drug-induced hepatotoxicity, or halothane hepatotoxicity.