Metalloelastase Expression in a Mouse Macrophage Cell Line Regulation by 4β‐Phorbol 12‐Myristate 13‐Acetate, Lipopolysaccharide and Dexamethasone

Abstract

The regulation of the expression of mouse macrophage elastase (MME) was investigated using the murine tumor cell line P388D1. The effects of three factors were studied: a phorbol ester (4P-phorbol 12-myristate 13-acetate, PMA), an endotoxin (lipopolysaccharide, LPS) and a corticosteroid (dexamethasone). Both in situ hybridization and northern blot analysis showed that P388D1 cells constitutively express the MME gene. Quantification of the MME mRNA by northern blot analysis showed that only PMA and dexamethasone significantly regulate MME gene expression in a time-dependent and dosedependent manner. After PMA treatment, the MME mRNA level was maximal between 4 h and 9 h (medium-term response), and the mean amplitude of the response to a concentration of 100 nM was 2.5-fold (P<O.Ol). LPS did not induce any significant change in MME mRNA level even when 1 % serum was added to the cultures. Following dexamethasone treatment, the MME mRNA level was minimal between 21 h and 33 h (long-term response), and the mean amplitude of the response to a concentration of 100 nM was 0.49-fold ( P < 0.05). Using actinomycin 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 dexamethasone. These results strongly suggest that the two factors modify MME mRNA level by stimulating (PMA) or inhibiting (dexamethasone) the transcription of the gene, rather than by modifying the transcript stability. Analysis of the cell-conditioned media by elastin zymography showed the MME as a lysis band in the 22-kDa region, the intensity of which varied with the treatments. The MME secretion is stimulated by PMA, inhibited by dexamethasone and does not show any variation after LPS treatment.

Role of monocytes and macrophages in angiogenesis

“…This progressively induced an inflammatory infiltrate, of which the MC/Mph population represented a main component [99]. We observed a system of tissular "tunnels" with a cross-sectional size comparable to the diameter of the infiltrating cells [97], similar to those produced by the penetration of phorbol ester-activated Mph in a fibrin matrix in vitro [100] (phorbol ester also induces the expression of MME [101]). …”

Retention of Oxidized LDL by Extracellular Matrix Proteoglycans Leads to Its Uptake by Macrophages

“…61 PMA increased mouse macrophage elastase mRNA by 2.5-fold, whereas LPS did not induce any changes. 62 These differences could result from differences in signal transduction. Although both PMA and LPS have been shown to induce PKC in MPMs, PMA was shown to induce translocation of several PKC subtypes (PKC␤, ␦, and ⑀), whereas LPS induced only PKC␤ translocation but failed to induce translocation of PKC␦ and ⑀.…”

Elastin accumulation is regulated at the level of degradation by macrophage metalloelastase (MMP-12) during experimental liver fibrosis

“…Two main cell types are responsible for elastin degradation, neutrophils, secreting neutrophil elastase (NE), and macrophages through macrophage metalloelastase (MMP‐12) 20. Like other MMPs, MMP‐12 is transcriptionally regulated,21 secreted as a proenzyme, and subsequently activated by (self)‐cleavage in the extracellular space.…”