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ATF4 inhibition by p62 represses stromal metabolic reprogramming and tumorigenesis

ABSTRACT: Tumors often undergo stress and need to reprogram their metabolism to survive and grow under nutrient challenging conditions. The stroma could play a critical role in this process by providing nutrients or signals to support the epithelial compartment of the tumor. Autophagy has been shown to play key roles both in the stroma and in the epithelium. However, how autophagy adaptors, such as p62, participate in the mechanisms whereby the stroma supports tumor progression is not yet fully understood. Here we show that p62 deficiency in stromal fibroblasts promotes resistance to glutamine deprivation through a metabolic reprogramming orchestrated by the direct control of ATF4 stability by p62-mediated polyubiquitination. This, in turn, activates the flux of glucose carbons through a pyruvate carboxylase-asparagine synthase cascade that results in asparagine-mediated stromal cell growth and tumor epithelial proliferation, independent of autophagy. This supports a new model in which p62 directly targets nuclear transcription factors to control metabolic reprograming in the microenvironment to repress tumorigenesis, and emerges as global tumor suppressor.

ORGANISM(S): Mus musculus

PROVIDER: GSE94343 | GEO | 2018/02/14

REPOSITORIES: GEO

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Project description:Huntington's disease (HD) is a dominantly inherited genetic disease caused by mutant huntingtin (htt) protein with expanded polyglutamine tracts. A neuropathological hallmark of HD is the presence of neuronal inclusions of mutant htt. p62 is an important regulatory protein in selective autophagy, a process by which aggregated proteins are degraded, and it is associated with several neurodegenerative disorders including HD. Here we investigated the effect of p62 depletion in three HD model mice: R6/2, HD190QG and HD120QG mice. We found that loss of p62 in these models led to longer lifespans and reduced nuclear inclusions, although cytoplasmic inclusions increased with polyglutamine length. In mouse embryonic fibroblasts (MEFs) with or without p62, mutant htt with a nuclear localization signal (NLS) showed no difference in nuclear inclusion between the two MEF types. In the case of mutant htt without NLS, however, p62 depletion increased cytoplasmic inclusions. Furthermore, to examine the effect of impaired autophagy in HD model mice, we crossed R6/2 mice with Atg5 conditional knockout mice. These mice also showed decreased nuclear inclusions and increased cytoplasmic inclusions, similar to HD mice lacking p62. These data suggest that the genetic ablation of p62 in HD model mice enhances cytoplasmic inclusion formation by interrupting autophagic clearance of polyQ inclusions. This reduces polyQ nuclear influx and paradoxically ameliorates disease phenotypes by decreasing toxic nuclear inclusions. Gene expression profiles were analyzed to examine the effects of p62 depletion in mouse with or without mutant huntingtin exon 1 To examine the effect of p62 depletion on the transcriptome of Huntington's disease model mice, we crossed p62 knockout mice with HD model mice. We extracted total RNA from the striatum of these mice at 8 weeks and used for a microaaray analysis. The samples are HD transgenic mice with p62 knockout (HD_p62KO), HD mice with normal p62 (HD_p62WT), non-HD-transgenic mice with p62 knockout (NT_p62KO), and non-HD-transgenic mice with normal p62 (NT_p62WT).

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ATF4 inhibition by p62 represses stromal metabolic reprogramming and tumorigenesis

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