SUPPRESSION OF THE METASTATIC PHENOTYPE OF A MOUSE SKIN CARCINOMA CELL-LINE INDEPENDENT OF E-CADHERIN EXPRESSION AND CORRELATED WITH REDUCED LEVELS OF HA-RAS ONCOGENE PRODUCTS

The HaCa4 cell line, derived from a mouse skin carcinoma induced by Ha rvey murine sarcoma virus, is highly tumorigenic when injected into nu de mice and produces multiple metastases in the lungs. HaCa4 cells exp ress high levels of viral Ha-ras oncogene products, anomalously synthe size the embryonic/simple epithelial keratin K8, and have lost the exp ression of the cell-cell adhesion receptor E-cadherin (E-CD). E-CD (+) cell clones (E62 and E24), obtained by transfection of an exogenous E -CD cDNA into HaCa4 cells, had a decreased ability to migrate through type IV collagen matrices. However, the E-CD (+) E62 clone remained as metastatic as the parental cell line, whereas the E24 clone, which do es not take up the exogenous cDNA but spontaneously switches on the en dogenous E-CD gene, suppressed the metastatic phenotype although it ma intained its tumorigenicity. E24 cells had fivefold to sixfold lower l evels of viral Ha-I-as mRNA and p21 protein than the other cell lines. In addition, they did not synthesize K8 but rather switched on kerati n K19. The comparison of E-CD proteins synthesized by E62 and E24 cell lines revealed no structural or functional differences because both l ocalized at cell-cell contacts and associated with alpha-catenin, beta -catenin, and plakoglobin. Furthermore, E-CD was still expressed in me tastatic lung nodules produced by E62 cells. These results suggest tha t suppression of the metastatic phenotype in E24 cells occurs independ ently of E-CD expression and correlates with decreased levels of the o ncogenic ras p21 protein. (C) 1996 Wiley-Liss, Inc.