A functional RNAi screen identifies hexokinase 1 as a modifier of type II apoptosis.

Tumor necrosis factor alpha (TNF-alpha) signals through NF-kappaB, JNK, and caspase modules to drive physiological responses that range from inflammation to apoptosis. The balance between the individual modules determines the nature of the response, and deregulated TNF signaling has been implicated in numerous pathological conditions. We used a quantitative high-throughput RNA interference assay to probe the entire complement of human kinases and phosphatases for gene products that tilt the balance of TNF signal transduction in favor of cell death or cell viability. Of all gene products tested, loss of hexokinase 1 resulted in the greatest elevations in TNF-dependent death. In secondary assays, we demonstrated that hexokinase 1 does not alter TNF-dependent activation of NF-kappaB or JNK modules. Instead, hexokinase 1 modifies the induction of caspase-driven cell death. Specifically, we showed that hexokinase 1 inhibits the formation of active, pro-apoptotic caspases in response to extrinsic inducers of apoptosis. These data are the first loss-of-function reports to examine the involvement of hexokinase 1 in the transduction of cell death signals and indicate that hexokinases are critical determinants of the viability of cells in response to extrinsic apoptotic cues.