Publications

The potential effects of insulin and insulin-like growth factor I (IGF-I) on mesangial cell (MC) metabolism and growth were examined. Radiolabeled insulin or IGF-I were incubated with cell membranes from rapidly proliferating (subconfluent) or nonproliferating (confluent) MC in the presence of increasing concentrations of unlabeled heterologous and homologous ligands (0-10(-6) M). Insulin binding to MC was specific and saturable, with Scatchard analysis of binding data showing the characteristic curvilinear plot. The predicted insulin binding maximum of 4.2 X 10(-12) M/100 micrograms protein for a theoretical high affinity site was consistent with a relatively low density of receptors, which were the same in proliferating and nonproliferating cell preparations. Specific binding of IGF-I to MC was also demonstrated. Binding data for membranes from proliferating cultures generated a linear Scatchard plot, which predicted a binding maximum of 3.5-9.7 X 10(-11) M/100 micrograms protein and a Kd of 2.0-3.2 X 10(-9) M. In contrast, membranes from nonproliferating cultures had no demonstrable specific binding of IGF-I. Covalent cross-linking of radiolabeled IGF-I to membranes from subconfluent cells demonstrated specific binding to a 145K membrane protein. A 95K membrane protein from a partially purified receptor preparation demonstrated autophosphorylation when incubated with 5 X 10(-9) M IGF-I. Incubation of MC with 10(-9) M IGF-I doubled cellular growth rates, an effect that could be duplicated only with high concentrations (10(-6) M) of insulin. These observations indicate that MC express predominantly receptors for IGF-I, and that growth stimulatory effects of physiological concentrations of IGF-I and pharmacological concentrations of insulin are probably mediated through the IGF-I receptor.

Acylation of cellular proteins with the fatty acids myristate or palmitate represents an important mechanism for the co- or posttranslational modification of proteins. Lipid A, the biologically active component of bacterial endotoxin, exerts a number of biochemical effects on responsive cell types. Evidence is presented that lipid A stimulates the synthesis and subsequent myristyl acylation of intracellular monocyte and glomerular mesangial cell proteins. Two of the myristylated monocyte proteins were identified by specific immunoprecipitation as the 33-kD IL 1 alpha and beta precursors; a similar myristylated protein was found in mesangial cells. The 17-kD secretory form of monocyte IL 1 beta did not contain covalently linked myristate. Myristyl acylation of the IL 1 precursor proteins may facilitate the processing or membrane localization of these proteins, which lack characteristic hydrophobic signal sequences. The acylated 33-kD IL 1 alpha may remain preferentially associated with the membrane in an active form, whereas limited proteolysis may convert the biologically inactive IL 1 beta precursor into the extracellular, nonacylated, active 17-kD protein.

Modification of risk factors in patients who have had myocardial infarctions has received little attention in the literature. Yet, major modifiable risk factors for recurrent coronary heart disease, including hypertension, smoking, increased serum cholesterol levels, sedentary lifestyle, and obesity are the same risk factors for its development. Although coronary atherosclerosis is already established in patients who have had a myocardial infarction, evidence suggests that important reductions in recurrent coronary heart disease and death can be achieved through secondary prevention programs that modify risk factors. The high risk for recurrence and mortality in patients who survive a heart attack means that substantial reductions in the rates of these events can be achieved with relatively small reductions in risk factors. Patients who have had a myocardial infarction are also active participants in health care and are likely to be highly motivated to modify their risks for cardiac disease.