UC Davis

Background/aim

The Akt signaling pathway mediates a potent anti-apoptotic signal in pancreatic cancer and inhibition of this pathway has become an attractive mechanism to increase the efficacy of traditional chemotherapies. Autophagy is a lysosomal catabolic pathway by which eukaryotic cells recycle macromolecules and organelles. Although autophagy may function as a survival mechanism under metabolic stress conditions, it also serves as an alternate route to programmed cell death distinct from apoptosis. In the present study, we examined the role of autophagy in Akt-mediated regulation of cell death in pancreatic cancer.

Materials and methods

Mia-PaCa-2 and PANC-1 human pancreatic cancer cell lines were used in our experiments. The small-molecule inhibitor A-443654 was used to inhibit Akt, and rapamycin was used to inhibit mTOR. Autophagy was inhibited with Chloroquine and 3-methyladenine. Autophagy was assessed by immunoblotting for light chain-3 (LC-3) processing as well as fluorescence microscopy for autophagosome formation following transfection with a LC-3/GFP construct. Cell death was determined by fluorescence-activated cell sorting (FACS) with quantitation of the sub-G0 content.

Results

Inhibition of either Akt or mTOR induced autophagy; inhibition of Akt but not of mTOR led to traditional caspase-mediated apoptosis. When autophagy was inhibited, cell death was abrogated following Akt, but not mTOR, inhibition.

Conclusion

The Akt signaling pathway regulates both autophagy and apoptosis through divergent pathways; mTOR mediates autophagy signaling but appears to be un-involved in cell death. Autophagy appears to play a role in the regulation of cell survival by Akt, but only when proximal signaling pathways not involving mTOR are simultaneously activated.