Publications

Characteristically, an individual member of the superfamily of G protein-coupled receptors can interact only with a limited number of the many structurally closely related G protein heterotrimers that are expressed within a cell. Interestingly, the N termini of two G protein alpha subunits, Galphaq and Galpha11, differ from those of other alpha subunits in that they display a unique, highly conserved six-amino acid extension. To test the hypothesis that this sequence element is critical for proper receptor recognition, we prepared a Galphaq deletion mutant (-6q) lacking these first six amino acids. The -6q construct (or wild type Galphaq as a control) was coexpressed (in COS-7 cells) with several different Gi/o- or Gs-coupled receptors, and ligand-induced increases in inositol phosphate production were determined as a measure of G protein activation. Whereas these receptors did not efficiently interact with wild type Galphaq, most of them gained the ability to productively couple to -6q. Additional experiments indicated that the observed functional promiscuity of -6q is not due to overexpression (as compared with wild type Galphaq) or to a lack of palmitoylation. We conclude that the N-terminal extension characteristic for Galphaq/11 proteins is critical for constraining the receptor coupling selectivity of these subunits, indicative of a novel mechanism by which the fidelity of receptor-G protein interactions can be regulated.

The genes encoding the functionally related hepatocyte nuclear factors HNF-1alpha and HNF-4alpha play a critical role in normal pancreatic beta-cell function. Mutations in these liver-enriched transcription factors result in two forms of early-onset type 2 diabetes (maturity-onset diabetes of the young [MODY]), MODY3 and MODY1, which are characterized by impaired glucose-stimulated insulin secretion, early disease onset, and autosomal dominant inheritance. The transcriptional hierarchy of HNFs suggests that other proteins of the regulatory cascade might be responsible for other forms of MODY and/or late-onset type 2 diabetes. In this study, we show that HNF-3alpha, -3beta, -3gamma, -4gamma, and -6 are expressed in pancreatic beta-cells. We report the identification and characterization of simple tandem repeat DNA polymorphisms in the genes encoding HNF-3alpha, -3beta, -3gamma, -4gamma, and -6 and the mapping of HNF-6 to chromosome bands 15q21.1-21.2 by fluorescence in situ hybridization. These markers will be useful to study the role of genetic variation in these genes in the pathogenesis of type 2 diabetes.

The activation of naive CD4+ T cells requires two discrete signals: a signal delivered by the T cell receptor following recognition of antigen and an accessory signal transduced when costimulatory receptors interact with their ligands. Particularly important in the development of an immune response to foreign antigens is the T cell molecule CD28, which delivers a potent costimulus when engaged by ligands, B7-1 and B7-2, on antigen-presenting cells. It is interesting that blockade of B7 molecules, which disrupts interactions with CD28 and prevents delivery of the CD28 costimulus, also alters the immune responses to self antigens and prevents the development of clinical disease in murine models of systemic and organ-specific autoimmunity. Herein we review the roles of CD28 and its B7 ligands in the pathogenesis of autoimmunity, discuss efforts to treat animal models of autoimmunity by modifying the CD28 signal, and consider the mechanisms by which manipulation of the CD28 signal alters the course of experimental autoimmune disease.

Systematic exercise training results in changes in skeletal muscle that increase oxidative capacity and vascular conductance, which lead to an increase in maximal A-VO2. Also, maximal cardiac output is increased, largely because of an increase in maximal stroke volume. Heart rate is decreased at rest and during submaximal exercise because of increased parasympathetic tone and the effect of increased stroke volume on reflex sympathetic tone. The increases in maximal A-VO2 and cardiac output result in increased maximal VO2, the hallmark of the dynamically trained individual. Predominant static exercise training results in fewer increases in maximal VO2 and more local muscle strength enhancements. The systematic application of cross-training can increase both cardiovascular and strength parameters, leading to enhanced athletic performance.

In this study we identified tenascin-C (TN-C) and one of its integrin receptors, alpha(v)beta6, in oral squamous-cell carcinoma (SCC) specimens. Neither TN-C nor alpha(v)beta6 are expressed in normal oral mucosa. We also studied 2 human oral squamous-cell carcinoma cell lines: the highly invasive HSC-3 cells, and the poorly invasive SCC-25 cells. We determined that adhesion of these cells to TN-C involves both alpha2 and alpha(v) integrins. Migration on TN-C by oral SCC cells required fibroblast-conditioned medium and did not occur in its absence. This migration was blocked by anti-alpha2 and anti-alpha(v) antibodies and was partially inhibited by antibodies to hepatocyte growth factor, epidermal growth factor and transforming growth factor-beta1. When seeded on TN-C, the poorly invasive SCC-25 cells formed alpha(v)beta6-positive focal contacts; the HSC-3 cells did not. HSC-3, SCC-25 and PTF cells secrete TN-C into the culture medium, as determined by Western blot. However, when HSC-3 cells were inoculated into the floor of the mouth of nude mice, only murine TN-C could be identified in the reactive stroma adjacent to the resulting tumor nests, demonstrating that in vivo, HSC-3 cells do not secrete TN-C. Our results demonstrate that alpha(v)beta6 and tenascin-C are neo-expressed in oral squamous-cell carcinoma, and that the tumor stromal environment is influential in oral SCC behavior.