Autophagy pathways activated in response to PDT contribute to cell resistance against ROS damage.
Bottom Line: Paradoxically, genetic loss of MA improved clearance of oxidized proteins and reduced photokilling.We found that up-regulation of chaperone-mediated autophagy (CMA) in unstressed Atg(-/-) cells compensated for MA loss and increased cellular resistance to PDT.These results disclose a stress-specific recruitment of autophagy pathways with cytoprotective function and unravel CMA as the dominant defence mechanism against PDT.
Affiliation: Cell Death Research and Therapy Laboratory, Department of Molecular Cell Biology, Faculty of Medicine, Katholieke Universiteit Leuven, Leuven, Belgium.Show MeSH
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Mentions: Having shown that MA is stimulated following PDT in different cells, we decided to investigate the functional role of MA on PDT-mediated cell death in apoptosis-competent cells. Although the inhibitor of autophagosome formation 3MA  alone was not cytotoxic, its addition in cells exposed to PDT inhibited GFP-LC3 puncta formation (Fig. 3A), enhanced caspase 3 activation and PARP processing (Fig. 3B) and significantly increased apoptosis (Fig. 3C). An siRNA-mediated knockdown of Atg5, resulted in the reduction of the Atg5-Atg12 complex and the attenuation of MA stimulation after PDT as demonstrated by reduced LC3-conversion (Fig. 3D). Consistent with the results obtained with the inhibitor, Atg5 knockdown boosted caspase 3 cleavage and PARP processing, increased apoptotic SubG1 fraction (Fig. 3D and E) and enhanced overall photokilling (data not shown). Note that as compared to our previous studies in HeLa cells , the light dose used in this study was purposely milder (i.e. 2.7 J/cm2) in order to measure possible pro-death inducing effects of MA inhibition.
Affiliation: Cell Death Research and Therapy Laboratory, Department of Molecular Cell Biology, Faculty of Medicine, Katholieke Universiteit Leuven, Leuven, Belgium.