LIPOCORTIN-1 INHIBITS PROLIFERATION OF CULTURED HUMAN MESANGIAL CELLS

Lipocortin-l, a 37-kDa member of the annexin family of proteins, origi nally evoked interest as one of the second messengers for the anti-inf lammatory actions of glucocorticoids. Studies showed that glucocortico ids inhibited the proliferation of various cell types and lipocortin-l mediated growth inhibition of glucocorticoids in a human lung adenoca rcinoma cell line. The presence of specific lipocortin-1-binding sites (receptor-like molecules) on monocytic cells has been demonstrated. T his study was performed to evaluate the effects of hydrocortisone and recombinant human lipocortin-l on cultured human mesangial cells (CHMC ), and the effects of anti-lipocortin-l antibody on the hydrocortisone -induced inhibition of CHMC proliferation. The existence of specific b inding sites for lipocortin-l was also investigated. Lipocortin-l inhi bited CHMC proliferation in a dose-dependent manner as determined by [ H-3]thymidine uptake and cell count. Growth of CHMC was inhibited to 1 8% of the control in the presence of 5 mu g/ml of lipocortin-l. Simila r growth-inhibitory activity by lipocortin-l was observed in CHMC acti vated by platelet-derived growth factor. Hydrocortisone also inhibited cell proliferation in a dose-dependent manner. One to 5,000 dilution of anti-lipocortin-l antibody reversed hydrocortisone-induced inhibiti on of CHMC proliferation partially, whereas concentrations over 1:1,00 0 reversed the inhibition completely. Flow cytometry analysis as well as indirect immunofluorescent microscopy revealed specific binding sit es on the surface of CHMC. These results support the hypothesis that c orticosteroids act by inducing CHMC to synthesize or secrete lipocorti n-l, and that lipocortin-l generates proliferation-suppressive signal( s) through specific binding sites on CHMC.