ONCOGENE-INDUCED BASEMENT-MEMBRANE INVASIVENESS IN HUMAN MAMMARY EPITHELIAL-CELLS

Expression of the intermediate filament protein vimentin, and loss of the cellular adhesion protein uvomorulin (E-cadherin) have been associ ated with increased invasiveness of established human breast cancer ce ll lines in vitro and in vivo. In the current study, we have further e xamined these relationships in oncogenically transformed human mammary epithelial cells. A normal human mammary epithelial strain, termed 18 4, was previously immortalized with benzo[a]pyrene, and two distinct s ublines were derived (A1N4 and 184B5). These sublines were infected wi th retroviral vectors containing a single or two oncogenes of the nucl ear, cytoplasmic, and plasma membrane-associated type (v-ras(H), v-ras (Ki), v-mos, SV40T and c-myc). All infectants have been previously sho wn to exhibit some aspects of phenotypic transformation. In the curren t study, cellular invasiveness was determined in vitro using Matrigel, a reconstituted basement membrane extract. Lineage-specific differenc es were observed with respect to low constitutive invasiveness and inv asive changes after infection with ras, despite similar ras-induced tr ansformation of each line. Major effects on cellular invasiveness were observed after infection of the cells with two different oncogenes (v -ras(H) + SV40T and v-ras(H) + v-mos). In contrast, the effects of sin gle oncogenes were only modest or negligible. All oncogenic infectants demonstrated increased attachment to laminin, but altered secretion o f the 72 kDa and 92 kDa gelatinases was not associated with any aspect of malignant progression. Each of the two highly invasive double onco gene transformants were vimentin-positive and uvomorulin-negative, a p henotype indicative of the epithelial-mesenchymal transition (EMT) pre viously associated with invasiveness of established human breast cance r cell lines, Weakly invasive untransformed mammary epithelial cells i n this study were positive for both vimentin and uvomorulin, suggestin g that uvomorulin may over-ride the otherwise vimentin-associated inva siveness.