INCREASED CELL-SUBSTRATE ADHESION ACCOMPANIES CONDITIONAL REVERSION TO THE NORMAL PHENOTYPE IN RAS-ONCOGENE-TRANSFORMED NIH-3T3 CELLS

We recently reported (1991, Mol. Cell Biol. 11, 3699-3710) that deplet ion of c-myc protein by myc antisense sequences in ras-transformed NIH -3T3 cells reverses several of the malignant characteristics of these cells. These include transformed morphology, growth in soft agar, and ability to form tumors in athymic mice. In the present study we examin ed the same cells far in vitro adhesive behavior. Cells depleted of c- myc protein by antisense transfection showed no change in attachment t o fibronectin-coated dishes as compared to ras-transformed NIH-3T3 cel ls but had greatly increased resistance to trypsin/EDTA-mediated relea se from the substratum after attachment. In concomitant studies, the c ells were examined for fibronectin biosynthesis and cell surface fibro nectin. There was no overall change in fibronectin biosynthesis in the c-myc antisense transfected cells as compared to the ras-transformed NIH-3T3. However, immunofluorescence staining revealed increased amoun t of surface fibronectin associated with the antisense c-myc-expressin g transfectants. Taken together, these data indicate that the conditio nal reacquisition of the nonmalignant phenotype in ras-transformed NIH -3T3 cells by selected depletion of c-myc protein is associated with a n increase in cell-substrate adhesion. This, in turn, is associated wi th an increase in surface fibronectin. 1991 Academic Press, Inc.