UP-REGULATION OF LYSYL OXIDASE IN SPONTANEOUS REVERTANTS OF H-RAS-TRANSFORMED RAT FIBROBLASTS

Neoplastic transformation mediated by ras oncogenes is associated with down-regulation of gene expression. We have constructed a subtracted complementary DNA library from preneoplastic rat 208F fibroblasts by h ybridizing with mRNA from a ras-transformed subclone. One of the compl ementary DNA clones identified by this approach encodes the 3' end of lysyl oxidase, the homologue of the mouse ras recision gene. Expressio n of lysyl oxidase was almost completely down-regulated in two clones of H-ras-transformed 208F cells (FE-8 and FE-56). We isolated a set of spontaneous phenotypic revertants of FE-8 cells (designated FSR) by c loning at limiting dilution. FSR revertant clones expressed high level s of lysyl oxidase and H-ras mRNA but grew only poorly in semisolid ag ar medium as opposed to anchorage-independent parental FE-8 cells. We obtained subclones of FSR cells which displayed again the transformed morphology of FE-8 cells but required anchorage for growth and continu ed to express high levels of lysyl oxidase mRNA. Thus, expression of l ysyl oxidase correlated with the suppression of anchorage-independent growth rather than with flat morphology. Lysyl oxidase might be a usef ul marker to distinguish between different aspects of reversion and tr ansformation.