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

Abstract

The monocytic cell line THP-1 can be induced to express and release tumor necrosis factor α (TNFα) and both TNFα receptors (p55 and p75) upon exposure to bacterial lipopolysaccharide (LPS). The broad-spectrum matrix metalloprotease (MMP) inhibitors [4-( N-hydroxyamino)-2 R-isobutyl-3 S-(phenylthiomethyl)succinyl]- l-phenylalanine- N-methylamide (GI-129471) and marimastat [2 S-[ N4( R∗),2 R∗,3 S∗]]- N4-[2,2-dimethyl-1-[(methylamino)carbonyl]propyl]- N1,2-dihydroxy-3-(2-methylpropyl)butanediamide (BB-2516) were effective inhibitors of LPS-induced TNFα (soluble) release with ic 50 values of 0.2 and 4.0 μM, respectively. Upon LPS stimulation, the expression of pro-TNFα (membrane associated) on the cell surface (FACS analysis) could not be observed. However, in the presence of GI-129471, a concentration-dependent increase in TNFα surface expression was observed. Peak expression (percentage of cells expressing pro-TNFα 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 TNFα 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-TNFα 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 the release of soluble TNFα, which continued to accumulate over a 24-hr time course. TNFα receptor I (p55, TNFRI) and II (p75, TNFRII) shedding was also inhibited by GI-129471 ( ic 50 = 1.5 and 3.1 μM, respectively) and BB-2516 ( ic 50 = 14 and 15 μM, respectively). Unlike pro-TNFα surface expression, surface expression of both TNFα receptors steadily increased over 72 hr. In contrast to pro-TNFα surface expression, TNFRI surface expression was not augmented by these MMP inhibitors in THP-1 cells after LPS stimulation. Surface expression of TNFRII was augmented by these MMP inhibitors. These results suggest that even in the continued presence of LPS stimulation and an inhibitor of TNFα processing, the augmented surface expression of TNFα is transient. The potential “deleterious” implications of high levels of surface pro-TNFα expression in the presence of these inhibitors may be lessened by its transient nature.