Oncogenic Ras and Akt signaling contribute to glioblastoma formation by differential recruitment of existing mRNAs to polysomes.

In order to determine the global effects of oncogenic Ras and Akt signaling pathways on translational efficiencies, we compared the gene expression profiles of total cellular mRNA and mRNA associated with polysomes. We found that the immediate effect of Ras and Akt signaling blockade on transcription was relatively modest; however, the profile of mRNA associated with polysomes was substantially altered. These observations indicate that the immediate effect of Ras and Akt signaling regulates the recruitment of specific mRNAs to ribosomes to a far greater extent than they regulate the production of mRNAs by transcriptional effects. The mRNAs most affected are those encoding proteins that regulate growth, transcription regulation, cell to cell interactions, and morphology. These data support a model whereby Ras and Akt signaling primarily lead to cellular transformation by altering the transcriptome and producing a radical shift in the composition of mRNAs associated with actively translating polysomes.