A genome-wide survey of RAS transformation targets

An important aspect of multi-step tumorigenesis is the mutational activatio n of genes of the RAS family, particularly in sporadic cancers of the pancr eas, colon, lung and myeloid system(1). RAS genes encode small GTP-binding proteins that affect gene expression in a global way by acting as major swi tches in signal transduction processes, coupling extracellular signals with transcription factors(2-4). Oncogenic farms of RAS are locked in their act ive state and transduce signals essential for transformation, angiogenesis, invasion and metastasis via downstream pathways involving the RAF/MEK/ERK cascade of cytoplasmic kinases, the small GTP-binding proteins RAC and RHO, phosphatidylinositol 3-kinase and others(5,6). We have used subtractive su ppression hybridization (SSH), a PCR-based cDNA subtraction technique(7), t o contrast differential gene expression profiles in immortalized, non-tumor igenic rat embryo fibroblasts and in HRAS-transformed cells. Sequence and e xpression analysis of more than 1,200 subtracted cDNA fragments revealed tr anscriptional stimulation or repression of 104 ESTs, 45 navel sequences and 244 known genes in HRAS-transformed cells compared with normal cells. Furt hermore, we identified common and distinct targets in cells transformed by mutant HRAS, KRAS and NRAS, as well as 61 putative target genes controlled by the RAF/MEK/ERK pathway in reverted cells treated with the MEK-specific inhibitor PD 98059.