Transcriptional networks of knockout cell lines identify functional specificities of H-Ras and N-Ras: significant involvement of N-Ras in biotic and defense responses

We characterized differential gene expression profiles of fibroblast cell lines harboring single or double-homozygous null mutations in H- ras and N- ras. Whereas the expression level of the individual H-, N- and K- ras genes appeared unaffected by the presence or absence of the other ras loci, significant differences were observed between the expression profiles of cells missing N- ras and/or H- ras. Absence of N- ras produced much stronger effects than absence of H- ras over the profile of the cellular transcriptome. N- ras −/− and H- ras −/− fibroblasts displayed rather antagonistic expression profiles and the transcriptome of H- ras −/− cells was significantly closer to that of wild-type fibroblasts than to that of N- ras −/− cells. Classifying all differentially expressed genes into functional categories suggested specific roles for H-Ras and N-Ras. It was particularly striking in N- ras −/− cells the upregulation of a remarkable number of immunity-related genes, as well as of several loci involved in apoptosis. Reverse-phase protein array assays demonstrated in the same N- ras −/− cells the overexpression and nuclear migration of tyrosine phosphorylated signal transducer and activator of transcription 1 (Stat1) which was concomitant with transcriptional activation mediated by interferon-stimulated response elements. Significantly enhanced numbers of apoptotic cells were also detected in cultures of N- ras −/− cells. Our data support the notion that different Ras isoforms play functionally distinct cellular roles and indicate that N-Ras is significantly involved in immune modulation/host defense and apoptotic responses