Down-regulation of MT1-MMP expression by the α3 chain of type IV collagen inhibits bronchial tumor cell line invasion

Abstract

The basement membrane (BM) is the first barrier encountered by tumor cells when they become invasive. Moreover, some invasive tumor clusters are surrounded by a remnant or neosynthetized BM material. We have previously reported the presence of a particular α chain of type IV collagen, the α3(IV) chain, in bronchopulmonary carcinomas. This chain was not detected in the normal bronchial epithelium, but was found around some invasive tumor cluster BM. In the present study, we examined the effects of the α3(IV) chain on the invasive properties of bronchial tumor cell lines, with special emphasis on their expression of matrix metalloproteinase-2 (MMP-2) and its activator, membrane type 1-matrix metalloproteinase (MT1-MMP), which is largely involved in tumor progression. Two epithelial bronchial cell lines (16HBE14ο- and BZR), showing different invasive abilities, were evaluated. Using the Boyden chamber invasion assay, we demonstrated that the α3(IV) chain inhibits the invasive properties of BZR cells and modifies their morphology by inducing an epithelial cell shape. In the presence of the recombinant NC1 domain of the α3(IV) chain, the expression of MMP-2 and tissue inhibitor of metalloproteinase-2 (TIMP-2) was not modified in either cell line. The NC1 α3(IV) domain did not modulate the MT1-MMP expression of noninvasive 16HBE14ο- cells, whereas a 50% decrease of MT1-MMP mRNA was observed in invasive BZR cells. Accordingly, Western blot analyses showed a disappearance of the 45-kd MT1-MMP form when BZR cells were treated with the recombinant NC1 α3(IV) domain. These findings suggest that the α3 chain of type IV collagen may play a role in tumor invasion, at least by decreasing the expression and synthesis of MT1-MMP.