Lipocortin-1 inhibits proliferation of cultured human mesangial cells

Lipocortin-1, a 37-kDa member of the annexin family of proteins, originally evoked interest as one of the second messengers for the anti-inflammatory actions of glucocorticoids. Studies showed that glucocorticoids inhibited the proliferation of various cell types and lipocortin-1 mediated growth inhibition of glucocorticoids in a human lung adenocarcinoma cell line. The presence of specific lipocortin-1-binding sites (receptor-like molecules) on monocytic cells has been demonstrated. This study was performed to evaluate the effects of hydrocortisone and recombinant human lipocortin-1 on cultured human mesangial cells (CHMC), and the effects of anti-lipocortin-1 antibody on the hydrocortisone-induced inhibition of CHMC proliferation. The existence of specific binding sites for lipocortin-1 was also investigated. Lipocortin-1 inhibited CHMC proliferation in a dose-dependent manner as determined by [3H]thymidine uptake and cell count. Growth of CHMC was inhibited to 18% of the control in the presence of 5 micrograms/ml of lipocortin-1. Similar growth-inhibitory activity by lipocortin-1 was observed in CHMC activated by platelet-derived growth factor. Hydrocortisone also inhibited cell proliferation in a dose-dependent manner. One to 5,000 dilution of anti-lipocortin-1 antibody reversed hydrocortisone-induced inhibition of CHMC proliferation partially, whereas concentrations over 1:1,000 reversed the inhibition completely. Flow cytometry analysis as well as indirect immunofluorescent microscopy revealed specific binding sites on the surface of CHMC. These results support the hypothesis that corticosteroids act by inducing CHMC to synthesize or secrete lipocortin-1, and that lipocortin-1 generates proliferation-suppressive signal(s) through specific binding sites on CHMC.