mTOR dependent transformed human cells have a distinct set of essential genes from bcr-abl transformed cells

Constitutively active intracellular signaling drives and sustains cancer growth. The mTOR kinase integrates multiple inputs sensing nutrient, energy and growth factor levels to promote protein synthesis and anabolic metabolism, and is hyperactivated in a broad range of cancers. The bcr-abl kinase is a fusion protein generated by chromosomal translocation and gives rise to chronic myeloid leukemia and a small sub-set of leukemias. Using an in vitro transformed murine cell model, we performed shRNA knockdown of 25 genes previously shown to be essential for mTOR dependent oncogenic growth and survival. None of the genes were essential in the bcr-abl transformed line. Interrogation of this gene set in human cancer cell lines revealed that many of these genes were essential in cells dependent on mTOR signaling (defined by sensitivity to pharmacological mTOR inhibition). However, none of the genes were essential in bcr-abl transformed K562 cells that are insensitive to mTOR inhibition. Thus there is a clear divide between cells transformed via bcr-abl directed oncogenesis and other modes of transformation where mTOR, due to its central role in regulating cell growth and metabolism, is recruited as part of an oncogenic program. These validated hits represent a set of genes essential for executing critical functions downstream of mTOR and may be novel therapeutic targets for cancer.