Donald C. Robertson
BS 1962, U. of Dubuque
PhD 1967, Iowa St. U.
Postdoctoral Fellow 1967-70, Michigan St. U.
Current projects in my laboratory are focused on understanding the role(s) of extracellular proteins called enterotoxins in the pathogenesis of two kinds of diarrheagenic Escherichia coli and Yersinia enterocolitica. We have studied the mechanism of action of the E. coli low-molecular weight heat-stable enterotoxin known as STa and produced by enterotoxigenic strains of E. coli. The mechanism of action of two natural endogenous peptides called guanylin and uroguanylin is identical to E. coli STa. These peptides are produced in tissues as inactive pro-hormones and activated by proteases where needed for activation of guanylate cyclase C (GCC). In addition to intestinal secretory responses, guanylin and uroguanylin regulate fluid and ion fluxes associated with hypertension, congestive heart failure and renal failure. We cloned the guanylin gene from a bovine cDNA library in order to express the peptide and develop a specific immunological assay. Amounts of guanylin in bovine tissues will be quantified and changes correlated with different pathophysiological conditions.
We are also working on the low molecular weight enterotoxin (EAST1) produced by enteroaggregative E. coli that cause chronic watery diarrhea in children in underdeveloped countries and AIDS patients. The EAST1 gene has been cloned into a high yield expression vector for purification and characterization. Future projects involve development of a specific immunological assay and studies on its mechanism of action, which does not appear to involve activation of GCC.
Yersinia enterocolitica produces several enterotoxins including a classical low-molecular-weight heat-stable enterotoxin called YST. We have identified two additional enterotoxins in culture supernatants of atypical clinical isolates that do not produce YST; but cause watery diarrhea. One enterotoxin with a molecular weight of about 10,000 called YST-II cross-reacts with antibodies raised against YST but does not activate intestinal GCC. Experiments are in progress to clone and express YST-II in amounts sufficient for chemical characterization and studies on its mechanism of action.
Hoge, C.W., O. Sethabutr, P. Echeverria, D.C. Robertson, and J.G. Morris. 1990. Use of a synthetic oligonucleotide probe to detect strains of non-01 Vibrio cholerae carrying the gene for heat-stable enterotoxin (NAG-ST). J. Clin. Microbiol. 28:1473-1476.
Savarino, S.J., A. Fasano,D.C. Robertson, and M.M. Levine. 1991. Enteroaggregative Escherichia coli elaborate a heat-stable enterotoxin demonstrable in an in vitro rabbit intestinal model. J. Clin. Invest. 87:1450-1455.
Hugues, M., M.R. Crane, B.R. Thomas,D.C. Robertson, H. Gazzano, P. O'Hanley, and S.A. Waldman. 1991. Affinity purification of functional receptors for Escherichia coli heat-stable enterotoxin from rat intestine. Biochemistry 31:12-16.
Jaso-Friedmann, L., L.A. Dreyfus, S.C. Whipp, and D.C. Robertson. 1992. Effect of age on activation of porcine intestinal guanylate cyclase and binding of E. coli heat-stable enterotoxin (STa) to pig intestinal cells and brush border membranes. Am. J. Vet. Res. 53:2251-2258.
Amiromozafari, N., and D.C. Robertson. 1993. Nutritional requirements for synthesis of heat-stable enterotoxin by Yersinia enterocolitica. Appl. Environ. Microbiol. 59:3314-3320.
Carrithers, S.L., S.J. Parkinson, S. Goldstein, P. Park, D.C. Robertson, and S.A. Waldman. 1995. E. coli heat-stable toxin receptors in human tumors. Gastroenterology 107:1653-1661.
Deshmane, S.P., S.L. Carrithers, S.J. Parkinson, S.S. Crupper, D.C. Robertson, and S.A. Waldman. 1995. Rat guanylyl cyclase C expressed in COS-7 cells exhibits multiple affinities for Escherichia coli heat-stable enterotoxin. Biochemistry 34:9095-9102.
Deshmane, S.P., S.J. Parkinson, S.S. Crupper, D.C. Robertson, S. Schulz, and S.A. Waldman. 1997. Cytoplasmic domains mediate the ligand-induced affinity shift of guanylyl cyclase C. Biochemistry 36:12921-12929.
McVeigh, A., A. Fasano, A. D.A. Scott, S. Jelacic, S.L. Moseley, D.C. Robertson, and S.J. Savarino. 2000. IS1414, an Escherchia coli Insertion Sequence with a Heat-Stable Enterotoxin Gene Embedded in a Transposase-Like Gene. Infect. Immun. 68:5710-5715.