Membrane type I-matrix metalloproteinase-mediated degradation of type I collagen by oral squamous cell carcinoma cells

Oral squamous cell carcinomas are highly invasive lesions that: destroy adj acent tissues and invade bone and muscle, which is most likely the result o f matrix metalloproteinase (MMP) activity. We examined three cell lines der ived from squamous cell carcinoma of the tongue for their intrinsic capacit ies to degrade interstitial collagen with the goal of identifying the matri x-degrading enzymes. SCC-25 and SCC-15 cells degrade reconstituted fibrilla r type I collagen in the absence of exogenous growth factors or cytokines w hen seeded as a colony on dried films. Degradation is confined to the subja cent matrix, is enhanced 2-3-fold by phorbol ester, and is strictly MMP-dep endent, as it is blocked by BB-94 and tissue inhibitor of metalloproteinase s-2 but not by inhibitors of serine and cysteine proteinases. Both cell lin es express active (M-r 57,000) membrane type I-MMP (MT1-MMP) on their surfa ces, as detected by surface biotinylation and immunoprecipitation. Concomit antly, both cell lines activate endogenous MMP-2 when cultured on type I co llagen films, as assessed by zymography. Phorbol ester treatment enhances c ollagen-induced MMP-2 activation, which is accompanied by the appearance of a surface-labeled M-r 43,000 form of MT1-MMP. Treatment of cells with a sy nthetic furin inhibitor, which inhibits processing of the MT1-MMP zymogen, blocks collagen degradation. In contrast, CAL 27 cells do not degrade colla gen under either basal or phorbol 12-myristate 13-acetate-stimulated condit ions. Although proMT1-MMP (M-r 63,000/65,000) is detectable in these cells by immunoblot analysis, they express greatly reduced levels of active MT1-M MP on their surfaces relative to SCC-25 and SCC-15 cells. Correspondingly, CAL 27 cells cultured on collagen express neither latent nor active gelatin ases. Immunoblots of lysates and conditioned media revealed the constitutiv e expression of proMMP-1 and proMMP-13 in all three cell lines. We conclude that in the absence of exogenous growth factors or accessory stromal cells , degradation of interstitial collagen by oral squamous cell carcinoma cell s requires a threshold level of active MT1-MMP on cell surfaces.