We present evidence for a specific role of p53 in the mitochondria-associated cellular dysfunction and behavioral abnormalities of Huntington's disease (HD). Mutant huntingtin (mHtt) with expanded polyglutamine (polyQ) binds to p53 and upregulates levels of nuclear p53 as well as p53 transcriptional activity in neuronal cultures. The augmentation is specific, as it occurs with mHtt but not mutant ataxin-1 with expanded polyQ. p53 levels are also increased in the brains of mHtt transgenic (mHtt-Tg) mice and HD patients. Perturbation of p53 by pifithrin-alpha, RNA interference, or genetic deletion prevents mitochondrial membrane depolarization and cytotoxicity in HD cells, as well as the decreased respiratory complex IV activity of mHtt-Tg mice. Genetic deletion of p53 suppresses neurodegeneration in mHtt-Tg flies and neurobehavioral abnormalities of mHtt-Tg mice. Our findings suggest that p53 links nuclear and mitochondrial pathologies characteristic of HD.

SUMMARY Comparative analyses have identified genomic regions potentially involved in human evolution, but do not directly assess function. Human accelerated regions (HARs) represent conserved genomic loci with elevated divergence in humans. If some HARs regulate human-specific social and behavioral traits, then mutations would likely impact cognitive and social disorders. Strikingly, rare biallelic point mutations–identified by whole genome and targeted “HAR-ome” sequencing–showed a significant excess in individuals with ASD whose parents share common ancestry compared to familial controls, suggesting a contribution in 5% of consanguineous ASD cases. Using chromatin interaction sequencing, massively parallel reporter assays (MPRA), and transgenic mice, we identified disease-linked, biallelic HAR mutations in active enhancers for CUX1, PTBP2, GPC4, CDKL5, and other genes implicated in neural function, ASD, or both. Our data provide genetic evidence that specific HARs are essential for normal development, consistent with suggestions that their evolutionary changes may have altered social and/or cognitive behavior.

Besides its role in glycolysis, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) initiates a cell death cascade 1-9 . Diverse apoptotic stimuli activate inducible nitric oxide synthase (iNOS) or neuronal NOS (nNOS), with the generated nitric oxide (NO) S-nitrosylating GAPDH, abolishing its catalytic activity and conferring on it the ability to bind to Siah1, an E3-ubiquitin-ligase with a nuclear localization signal (NLS). The GAPDH-Siah1 protein complex, in turn, translocates to the nucleus and mediates cell death; these processes are blocked by procedures that interfere with GAPDH-Siah1 binding. Nuclear events induced by GAPDH to kill cells have been obscure. Here we show that nuclear GAPDH is acetylated at Lys 160 by the acetyltransferase p300/CREB binding protein (CBP) through direct protein interaction, which in turn stimulates the acetylation and catalytic activity of p300/CBP. Consequently, downstream targets of p300/CBP, such as p53 (refs 10 -15 ), are activated and cause cell death. A dominant-negative mutant GAPDH with the substitution of Lys 160 to Arg (GAPDH-K160R) prevents activation of p300/CBP, blocks induction of apoptotic genes and decreases cell death. Our findings reveal a pathway in which NO-induced nuclear GAPDH mediates cell death through p300/CBP.10Correspondence and requests for materials should be addressed A.S. or S.H.S (E-mail: asawa1@jhmi.edu; E-mail: ssnyder@jhmi.edu). 8 Current address: Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA. 9 These authors contributed equally to this work. AUTHOR CONTRIBUTIONS Ni.S. and M.R.H. were primarily responsible for experimental design and work, data analysis and preparation of figures, and helped to write the manuscript; M.K., M.C., B.-I.B., Ne.S. and B.T. contributed to data acquisition and analysis; T.D. and V.D. helped with the data analysis, provided technical assistance and material support; S.H.S and A.S. supervised the project and wrote the manuscript.Note: Supplementary Information is available on the Nature Cell Biology website. COMPETING FINANCIAL INTERESTSThe authors declare no competing financial interests. -(3-(aminomethyl)benzyl)acetamidine (1400W), a selective iNOS inhibitor (Fig. 1a). To ascertain whether p300 and/or CBP are physiologically responsible for GAPDH acetylation in intact cells, we depleted p300 and CBP by RNA interference (RNAi). Depletion of either protein decreased GAPDH acetylation, which was abolished following depletion of both CBP and p300 (Fig. 1b). We also observed acetylation of GAPDH by p300 in vitro ( Supplementary Information, Fig. S1a). Moreover, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometric analysis of nuclear GAPDH in HEK293 cells following apoptotic stress revealed acetylation at Lys 160 ( Supplementary Information, Fig. S1b, c). To confirm the site of acetylation in intact cells, we transfected HEK293 cells with GAPDH or a mutant GAPDH (GAPDH-K160R). We observed acetylation of wild-type but not the K160R mutant GAPDH (Fi...