COOPERATIVE EFFECTS OF V-MYC AND C-HA-RAS ONCOGENES ON GAP JUNCTIONALINTERCELLULAR COMMUNICATION AND TUMORIGENICITY IN RAT-LIVER EPITHELIAL-CELLS

The objective of this study was to isolate and partially characterize several rat liver epithelial cell clones containing myc, ras and myc/r as oncogenes in order to study their roles in apoptosis and to test th e hypothesis that gap junctional intercellular communication is necess ary for apoptosis in solid tissues and that the loss of junctional com munication leads to tumorigenesis, The co-transfection of the myc and ras oncogenes in the normal rat liver epithelial cell line (WB-F344) r esulted in a loss of functional channels and normal growth regulation; cell-cell communication was significantly decreased and tumorigenicit y determined in adult male F344 rats was induced. We examined cell gro wth properties, gap junctional intercellular communication (GJIC), usi ng the scrape-loading-dye transfer and fluorescence-redistribution-aft er-photobleaching assays, and tumorigenicity in a series of normal and v-myc-, c-Ha-ras- and v-myc/c-Ha-ras-transfected WB-F344 cell lines. The c-Ha-ras- and the v-myc/c-Ha-ras-transduced cell lines appeared di stinctly different from the other lines, having spindle-shaped morphol ogy, shorter generation time and contact insensitivity. On the other h and, the normal WB-F344 cell line and the v-myc-transduced cell line s howed excellent GJIC. Moreover, the c-Ha-ras-transduced cell lines dis played decreasing levels of GJIC associated with their increasing tumo rigenicity. The v-myc/c-Ha-ras-transformed cell lines showed the lowes t levels of GJIC and were also the most tumorigenic. These findings su ggest that the reduction of GJIC in c-Ha-ras- and v-myc/c-Ha-ras-trans formed WB-F344 cells is linked to their tumorigenic potential. These c ell lines should provide valuable tools to study the role of GJIC in a poptosis during tumorigenesis. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.