Macroautophagy (autophagy) is intimately linked with cell death and allows cells to evade apoptosis. This has prompted clinical trials to combine autophagy inhibitors with other drugs with the aim of increasing the likelihood of cancer cells dying. However, the molecular basis for such effects is unknown. Here, we describe a transcriptional mechanism that connects autophagy to apoptosis. The autophagy-regulating transcription factor, FOXO3a, is itself turned over by basal autophagy creating a potential feedback loop. Increased FOXO3a upon autophagy inhibition stimulates transcription of the pro-apoptotic BBC3/PUMA gene to cause apoptosis sensitization. This mechanism explains how autophagy inhibition can sensitize tumor cells to chemotherapy drugs and allows an autophagy inhibitor to change the action of an MDM2-targeted drug from growth inhibition to apoptosis, reducing tumor burden in vivo. Thus, a link between two processes mediated via a single transcription factor binding site in the genome can be leveraged to improve anti-cancer therapies.

Trisomy 21 (T21) causes Down syndrome (DS), affecting immune and neurological function by ill-defined mechanisms. Here we report a large metabolomics study of plasma and cerebrospinal fluid, showing in independent cohorts that people with DS produce elevated levels of kynurenine and quinolinic acid, two tryptophan catabolites with potent immunosuppressive and neurotoxic properties, respectively. Immune cells of people with DS overexpress IDO1, the rate-limiting enzyme in the kynurenine pathway (KP) and a known interferon (IFN)-stimulated gene. Furthermore, the levels of IFN-inducible cytokines positively correlate with KP dysregulation. Using metabolic tracing assays, we show that overexpression of IFN receptors encoded on chromosome 21 contribute to enhanced IFN stimulation, thereby causing IDO1 overexpression and kynurenine overproduction in cells with T21. Finally, a mouse model of DS carrying triplication of IFN receptors exhibits KP dysregulation. Together, our results reveal a mechanism by which T21 could drive immunosuppression and neurotoxicity in DS.

Trisomy 21 (T21) causes Down syndrome (DS), affecting immune and neurological function by unknown mechanisms. We report here the results of a large metabolomics study showing that people with DS produce elevated levels of kynurenine and quinolinic acid, two tryptophan catabolites with potent immunosuppressive and neurotoxic properties, respectively. We found that immune cells of people with DS overexpress IDO1, the rate-limiting enzyme in the kynurenine pathway (KP) and a known interferon (IFN)-stimulated gene. Furthermore, we found a positive correlation between levels of specific inflammatory cytokines and KP dysregulation.Using metabolic flux assays, we found that IFN stimulation causes IDO1 overexpression and kynurenine overproduction in cells with T21, dependent on overexpression of IFN receptors encoded on chromosome 21. Finally, KP dysregulation is conserved in a mouse model of DS carrying triplication of the IFN receptors. Altogether, these results reveal a mechanism by which T21 could drive immunosuppression and neurotoxicity in DS. 3 INTRODUCTION.

Highlights d A mouse model of Down syndrome displays lethal immune hypersensitivity d A heightened inflammatory response is associated with rapid wasting d Liver pathology is revealed in this mouse model and exacerbated by immune activation d JAK1 and JAK1/2 inhibitors provide therapeutic benefits in this mouse model

SUMMARY The transcriptional repressor ΔNp63α is a potent oncogene widely overexpressed in squamous cell carcinomas (SCCs) of diverse tissue origins, where it promotes malignant cell proliferation and survival. We report here the results of a genome-wide CRISPR screen to identify pathways controlling ΔNp63α-de- pendent cell proliferation, which revealed that the small GTPase RHOA blocks cell division upon ΔNp63α knockdown. After ΔNp63α depletion, RHOA activity is increased, and cells undergo RHOA-depen- dent proliferation arrest along with transcriptome changes indicative of increased TGF-β signaling. Mechanistically, ΔNp63α represses transcription of TGFB2, which induces a cell cycle arrest that is partially dependent on RHOA. Ectopic TGFB2 activates RHOA and impairs SCC proliferation, and TGFB2 neutralization restores cell proliferation during ΔNp63α depletion. Genomic data from tumors demonstrate inactivation of RHOA and the TGFBR2 receptor and DNp63a overexpression in more than 80% of lung SCCs. These results reveal a signaling pathway controlling SCC proliferation that is potentially amenable to pharmacological intervention.