Enhanced proteolytic activity is responsible for the aberrant morphogenetic development of SV40-immortalized normal...

A reconstituted basement membrane extract, Matrigel, is a potent inducer of cell growth and differentiation in vitro in a number of cell types. In this study, we examined the effect of Matrigel on the morphogenesis of cultured normal human salivary gland cells.

SV40-immortalized normal human salivary gland-cell clones with duct- (NS-SV-DC) or myoepithelial phenotype (NS-SV-MC), which had been established in our laboratory (Azuma M, et al., Lab Invest, 1993;69:24-42), were cultured on Matrigel in serum-free culture conditions, and then morphogenetic behavior of cell clones was examined.

When cell clones were seeded on Matrigel, they formed round or zonal clusters on day 1; however, they failed to develop into a salivary gland morphogenesis. Semithin sections of cell clones cultured on Matrigel exhibited multicellular aggregates on day 1, whereas on days 2 and 3, these cells lost both cell-Matrigel and cell-cell interactions and eventually entered crisis. In an attempt to understand the mechanism involved in this phenomenon, we investigated proteolytic enzymes and their inhibitors secreted by cell clones. Although cell clones produced almost identical levels of gelatinases, they released increased amounts of plasminogen activators as compared with a neoplastic human salivary gland cell line, which had already been demonstrated to differentiate into acinar cells when cultured on Matrigel. Obvious difference of expression level of tissue inhibitor of metalloproteinases-1 was not observed in these cells, however, NS-SV-DC produced a relatively small amount of endothelial-type plasminogen activator inhibitor as compared with NS-SV-MC. Neutralization of excess plasminogen activators by exogenously added serine protease inhibitors corrected the aberrant in vitro morphogenesis of NS-SV-DC, but not of NS-SV-MC, and allowed NS-SV-DC to form glandular-like structures.