GSE158833
Translational activation of ATF4 through mitochondrial anaplerotic metabolic pathways is required for DLBCL growth and survival
Cancer cells frequently hijack adaptive stress response signals/pathways to protect themselves from metabolic or genetic vulnerabilities, pointing to candidate therapeutic targets. Among these SIRT3 was recently identified as a non-oncogene addiction mechanism in DLBCL through its role in glutamine metabolism. Here, we investigated downstream signaling pathways linked to SIRT3 function in lymphoma.  We performed RNA-seq in DLBCL cells after SIRT3 knockdown and observed that ATF4 target genes were significantly downregulated in SIRT3 deficient cells. ATF4, a master regulator of cellular stress, was required to maintain proliferation and survival of DLBCL cells and its target genes were overexpressed in DLBCL patients as compared to normal germinal center B cells. Translation of ATF4 mRNA was inhibited in SIRT3 knockdown cells and expression of exogenous ATF4 partially rescued cell proliferation and viability inhibited by SIRT3 deficiency.  Accordingly, ATF4 protein was expressed at relatively lower levels SIRT3 deficient murine lymphomas, whereas its higher expression was associated with more severe disease.  We characterized mechanisms through which SIRT3 maintains ATF4 expression, downstream of its effects on glutamine entry into the TCA cycle and suppression of autophagy.  Specifically, loss of SIRT3 disrupted amino acid metabolism in DLBCL cells, with subsequent impairment of ATF4 response to metabolic stressors such as glutamine depletion. Collectively, the data suggest a key SIRT3-ATF4 axis maintains survival of DLBCL cells enabling them to optimize amino acid metabolism and cope with metabolic vulnerabilities possibly associated with their high proliferative rate. Overall design: RNAseq following shRNA knockdown of SIRT3 in DLBCL cell lines