The XBP1-MARCH5-MFN2 Axis Confers ER Stress Resistance by Coordinating Mitochondrial Fission and Mitophagy in Melanoma

Background: Melanoma cells are relatively resistant to ER stress, which contributes to tumor progression under stressful conditions and renders tolerance to ER stress-inducing therapeutic agents. Mitochondria are tightly interconnected with ER. However, whether mitochondria play a role in regulating ER stress resistance in melanoma remains elusive. Methods: : Integrative bioinformatics was employed to figure out the implication of mitochondria in the resistance of melanoma cells to ER stress. A panel of biochemical assays and pre-clinical xenograft mouse model were used to investigate the role of mitochondrial fission and mitophagy in affecting ER stress sensitivity and the underlying mechanisms. Results: : Our integrative bioinformatics analysis revealed that the down-regulation of mitochondrial genes was highly correlated with UPR activation in melanoma. Then we proved that mitochondrial fission and mitophagy were prominently induced in melanoma cells upon ER stress. Pharmacological inhibition of either mitochondrial fission or mitophagy effectively restored the sensitivity of melanoma cells to ER stress both in vitro and in vivo . Mechanistically, the down-regulation of MFN2 was essential for rendering the resistance by promoting mitochondrial fission and mitophagy. XBP1-mediated transcriptional up-regulation of E3 ligase MARCH5 contributed to the ubiquitination and degradation of MFN2 in ER stress-resistant cells, whereas the impaired transduction of this axis indicated the fragile to ER stress. Finally, the relationships among UPR pathway molecules, MARCH5 and mitochondrial genes were confirmed in both publicly accessible databases and tumor specimens. Conclusions: Together, our findings demonstrate a novel regulatory axis that links mitochondrial fission and mitophagy to the resistance to ER stress. Targeting mitochondrial quality control machinery can be exploited as an approach to reinforce the efficacy of ER stress-inducing agents against cancer.