Calcitriol enhances transcriptional activity of lysozyme and cathepsin D genes in U937 promonocytes.

Calcitriol (1,25-dihydroxyvitamin D3) has been reported to enhance the rate of synthesis of lysozyme [Rouis, Thomopoulos, Louache, Testa, Heroy & Titeux, (1985) Exp. Cell Res. 157, 539-543] and of cathepsin D [Stein, Braulke, von Figura & Hasilik (1987) Biol. Chem. Hoppe-Seyler 368, 413-418] in human promonocytes U937. In this study we show hat the hormone enhances the steady-state levels of cathepsin D and lysozyme mRNAs. The enhancement of the latter but not of the former is strongly inhibited by cycloheximide. The degradation rates of cathepsin D and lysozyme mRNAs as revealed in the presence of actinomycin D are not significantly affected by the treatment of the cells with calcitriol. In nuclei prepared from calcitriol-treated cells, an enhanced rate of synthesis of cathepsin D and lysozyme mRNA precursors is observed. These results suggest that in human promonocytes the rate of the transcription of cathepsin D and lysozyme genes is enhanced in the presence of calcitriol and that the regulation by the hormone of the transcription of lysozyme gene involves a short-lived or an induced protein.