Enhancement of the surface expression of tumor necrosis factor α (TNFα) but not the p55 TNFα receptor in the THP-1 monocytic cell line by matrix metalloprotease inhibitors

The monocytic cell line THP-1 can be induced to express and release tumor necrosis factor alpha (TNF alpha) and both TNF alpha receptors (p55 and p75) upon exposure to bacterial lipopolysaccharide (LPS). The broad-spectrum matrix metalloprotease (MMP) inhibitors [4-(N-hydroxyamino)-2R-isobutyl-3S-(phenylthiomethyl)succinyl]-L-phenylalanine-N-methylamide (GI-129471) and marimastat [2S-[N4(R*,3S*)]]-N4-[2,2-dimethyl-1-[(methylamino)carbonyl]propyl]-N1,2-dihydroxy-3-(2-methylpropyl)butanediamide (BB-2516) were effective inhibitors of LPS-induced TNF alpha (soluble) release with IC50 values of 0.2 and 4.0 mu M, respectively. Upon LPS stimulation, the expression pro-TNF-alpha (membrane associated) on the cell surface (FACS analysis) could not be observed. However, in the presence of GI-129471, a concentration-dependent increase in TNF alpha surface expression was observed. Peak expression (percentage of cells expressing pro-TNF alpha and mean fluorescence units) in the presence of GI-129471 was at 2 hr, and steadily declined to return to near control levels by 8 hr. This time course was similar to TNF alpha release, which also peaked at 2-4 hr after LPS exposure and then declined. Stimulation of THP-1 cells with LPS + phorbol myristate acetate increased the percentage of cells expressing pro-TNF alpha by 10-fold. In the presence of GI-129471, these increases were augmented further and peaked between 2 and 4 hr, but also returned to near control levels of expression by 24 hr. This was in contrast to te release of soluble TNF alpha, which continued to accumulate over a 24-hr time course. TNF alpha receptor I (p55, TNFRI) and 11 (p75, TNFR11) shedding was also inhibited by GI-129471 (IC50 = 1.5 and 3.1 mu M, respectively) and BB-2516 (IC50 = 14 and 15 mu M, respectively). Unlike pro-TNF alpha surface expression, TNFRI surface expression was not augmented by these MMP inhibitors. These results suggest that even in the continued presence of LPS stimulation and an inhibitor of TNF alpha processing, the augmented surface expression of TNF alpha is transient. The potential "deleterious" implications of high levels of surface pro-TNF alpha expression in the presence of these inhibitors may be lessened by its transient nature. (C) 1998 Elsevier Science Inc.