Sterol metabolism and lymphocyte responsiveness: Inhibition of endogenous sterol synthesis prevents mitogen-induced human T cell proliferation

The role of endogenous sterol synthesis in mitogen-induced proliferation of human T lymphocytes was examined. The rate-limiting enzyme in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, was blocked with the oxygenated sterol 7-ketocholesterol (7-KC) or with ML-236B. Mitogen-induced T lymphocyte blast transformation was assessed by measuring the change in the volume of the stimulated cells. Inhibition of sterol synthesis had little effect on the absolute number of cells initially stimulated by mitogen to undergo blast transformation or on the average volume of the stimulated cells measured after a 24-hr incubation. However, the additional enlargement of the stimulated cells observed in control cultures beyond a 24-hr incubation was suppressed by inhibition of HMG-CoA reductase activity. This inhibition of the enlargement of mitogen-stimulated lymphoblast was prevented by mevalonate, the product of the inhibited enzyme. Mitogen-induced lympocyte DNA synthesis, measured by flow cytofluorometry after staining of cellular DNA with mithramycin, was unaltered by either 7-KC or ML-236B (0.5 μM). However, higher concentrations of ML-236B resulted in inhibition of DNA synthesis that could be prevented by mevalonate. Lymphocyte proliferation, assessed by measuring the increase in the number of cells in mitogen-stimulated cultures, was totally abolished by 7-KC and by concentrations of ML-236B that had no direct effect on DNA synthesis. This inhibition of lymphocyte proliferation was reversed by mevalonate. These data indicate that inhibition of endogenous sterol biosynthesis does not alter initial lymphocyte activation and blast transformation but rather prevents subsequent enlargement and cell division.