Studies on the mechanism of Drs-mediated apoptosis and tumor suppression by gene-knockout mouse

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Drs protein associates with ASY/Nogo-B, an apoptosis-inducing protein in the endoplasmic reticulum, and sequentially activate caspases (-12,-9, and -3) to induce apoptosis in human cancer cells. Malignant tumors were generated in about 30% of the drs KO mice, indicating that drs contributes to the suppression of malignant tumor formation. In this study, we investigated the physiological roles of drs and the mechanism of tumor suppression by this gene by using drs KO mice and cells. The following results were obtained.1.Re-introduction of drs by retrovirus vector into a lung cancer cell line derived from a lung adenocarcinoma of a drs KO mouse caused suppression of tumorigenicity in nude mouse and elevation of apoptosis mediated by activation of caspase-12,-9, and -3.2.drs KO embryonic fibroblasts (MEF) also showed enhanced sensitivity to transformation by v-src oncogene.3.Autophagy induced by low serum conditions was suppressed in drs KO MEF cells. Analyses with electron microscope and GFP-LC3 showed that drs is involved in the maturation process from autophagosomes to autolysosomes.4.Drs associates with Rab24, which is involved in the autophagosome maturation, and colocalized with Rab24 on the autolysosomes during the late phase of autophagy induced by low serum.5.Drs interacts with stress-inducible GADD34. Experiments with KO MEF cells, showed that drs and GADD34 are involved in survival in energy-depletion conditions and anti-viral defense via suppression of mTOR pathway.These results idicate that drs is involved in the regulatuion of autophagy as well as apoptosis. Furthermore, drs plays a role in cell survival in stress conditions and anti-viral defense. By using KO mice and KO cells, we are going to clarify the physiological function of drs and the molecular mechanism of tumor suppression by drs.