METALLOELASTASE EXPRESSION IN A MOUSE MACROPHAGE CELL-LINE - REGULATION BY 4-BETA-PHORBOL 12-MYRISTATE 13-ACETATE, LIPOPOLYSACCHARIDE AND DEXAMETHASONE

The regulation of the expression of mouse macrophage elastase (MME) wa s investigated using the murine tumor cell line P388D1. The effects of three factors were studied: a phorbol ester (4 beta-phorbol 12-myrist ate 13-acetate, PMA), an endotoxin (lipopolysaccharide, LPS) and a cor ticosteroid (dexamethasone). Both in situ hybridization and northern b lot analysis showed that P388D1 cells constitutively express the MME g ene. Quantification of the MME mRNA by northern blot analysis showed t hat only PMA and dexamethasone significantly regulate MME gene express ion in a time-dependent and dose-dependent manner. After PMA treatment , the MME mRNA level was maximal between 4h and 9h !medium-term respon se), and the mean amplitude of the response to a concentration of 100 nM was 2.5-fold (P < 0.01). LPS did not induce any significant change in MME mRNA level even when 1 % serum was added to the cultures. Follo wing dexamethasone treatment, the MME mRNA level was minimal between 2 1 h and 33 h (long-term response), and the mean amplitude of the respo nse to a concentration of 100 nM was 0.49-fold (P < 0.05). Using actin omycin D, it appeared that the inhibition of RNA synthesis reduces the ulterior stimulating effect of PMA from 184 % to 121 %, and that MME mRNA has a half-life longer than 8 h, which is not diminished by dexam ethasone. These results strongly suggest that the two factors modify M ME mRNA level by stimulating (PMA) or inhibiting (dexamethasone) the t ranscription of the gene, rather than by modifying the transcript stab ility. Analysis of the cell-conditioned media by elastin zymography sh owed the MME as a lysis band in the 22-kDa region, the intensity of wh ich varied with the treatments. The MME secretion is stimulated by PMA , inhibited by dexamethasone and does not show any variation after LPS treatment.