Involvement of proteasomes in migration and matrix metalloproteinase-9 production of oral squamous cell carcinoma

We investigated whether proteasomes were involved in the invasiveness of oral squamous cell carcinoma (SCC) cells. The migration of SCC cells through a gelatin-coated membrane was enhanced with tumor necrosis factor α (TNFα), which was strongly inhibited by a peptide aldehyde, N-acetyl-Leu-Leu- norleucinal (ALLN), but not; by its structurally related compound, N-acetyl- Leu-Leu-methioninal (ALLM). Since ALLN is a more potent inhibitor against proteasomal proteolysis than ALLM, cell migration inhibited by ALLN may thus likely depend on proteasomes. The TNFα-induced migration through gelatin appeared to be associated with the gelatinolytic activity from the cells, since TNFα strongly enhanced the production of matrix metalloproteinase (MMP)-9/gelatinase B in the SCC cells, as detected by gelatin zymography. The production of MMP-9 was also inhibited by pretreatment with ALLN, but not ALLM, in a dose-dependent manner. Moreover, ALLN could block the activation and nuclear translocation of a transcription-activating factor, NF-κB, which is known to regulate MMP-9 expression in TNFα-stimulated SCC cells. The TNFα-induced degradation of IκBα was also suppressed by ALLN treatment, thus implying that the molecule linking proteasome to MMP-9 production should be IκBα. We finally reconfirmed the involvement of proteasomes in the invasive behavior of oral SCC using lactacystin, a specific proteasome inhibitor, which could prevent TNFα from enhancing PIMP-9 production, NF- κB activation, induction of MMP-9 mRNA and cell migration.