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Additional sex combs-like 1 (ASXL1) interacts with BRCA1-associated protein 1 (BAP1) deubiquitinase to oppose the polycomb repressive complex 1 (PRC1)-mediated histone H2A ubiquitylation. Germline BAP1 mutations are found in a spectrum of human malignancies, while ASXL1 mutations recurrently occur in myeloid neoplasm and are associated with poor prognosis. Nearly all ASXL1 mutations are heterozygous frameshift or nonsense mutations in the middle or to a less extent the C-terminal region, resulting in the production of C-terminally truncated mutant ASXL1 proteins. How ASXL1 regulates specific target genes and how the C-terminal truncation of ASXL1 promotes leukemogenesis are unclear. Here, we report that ASXL1 interacts with forkhead transcription factors FOXK1 and FOXK2 to regulate a subset of FOXK1/K2 target genes. We show that the C-terminally truncated mutant ASXL1 proteins are expressed at much higher levels than the wild-type protein in ASXL1 heterozygous leukemia cells, and lose the ability to interact with FOXK1/K2. Specific deletion of the mutant allele eliminates the expression of C-terminally truncated ASXL1 and increases the association of wild-type ASXL1 with BAP1, thereby restoring the expression of BAP1-ASXL1-FOXK1/K2 target genes, particularly those involved in glucose metabolism, oxygen sensing, and JAK-STAT3 signaling pathways. In addition to FOXK1/K2, we also identify other DNA-binding transcription regulators including transcription factors (TFs) which interact with wild-type ASXL1, but not C-terminally truncated mutant. Our results suggest that ASXL1 mutations result in neomorphic alleles that contribute to leukemogenesis at least in part through dominantly inhibiting the wild-type ASXL1 from interacting with BAP1 and thereby impairing the function of ASXL1-BAP1-TF in regulating target genes and leukemia cell growth.

The TET2 DNA dioxygenase regulates gene expression by catalyzing demethylation of 5-methylcytosine, thus epigenetically modulating the genome. TET2 does not contain a sequence-specific DNA-binding domain, and how it is recruited to specific genomic sites is not fully understood. Here we carried out a mammalian two-hybrid screen and identified multiple transcriptional regulators potentially interacting with TET2. The SMAD nuclear interacting protein 1 (SNIP1) physically interacts with TET2 and bridges TET2 to bind several transcription factors, including c-MYC. SNIP1 recruits TET2 to the promoters of c-MYC target genes, including those involved in DNA damage response and cell viability. TET2 protects cells from DNA damage-induced apoptosis dependending on SNIP1. Our observations uncover a mechanism for targeting TET2 to specific promoters through a ternary interaction with a co-activator and many sequence-specific DNA-binding factors. This study also reveals a TET2-SNIP1-c-MYC pathway in mediating DNA damage response, thereby connecting epigenetic control to maintenance of genome stability.

Peroxisomes account for ~35% of total H2O2 generation in mammalian tissues. Peroxisomal ACOX1 (acyl-CoA oxidase 1) is the first and rate-limiting enzyme in fatty acid β-oxidation and a major producer of H2O2 ACOX1 dysfunction is linked to peroxisomal disorders and hepatocarcinogenesis. Here, we show that the deacetylase sirtuin 5 (SIRT5) is present in peroxisomes and that ACOX1 is a physiological substrate of SIRT5. Mechanistically, SIRT5-mediated desuccinylation inhibits ACOX1 activity by suppressing its active dimer formation in both cultured cells and mouse livers. Deletion of SIRT5 increases H2O2 production and oxidative DNA damage, which can be alleviated by ACOX1 knockdown. We show that SIRT5 downregulation is associated with increased succinylation and activity of ACOX1 and oxidative DNA damage response in hepatocellular carcinoma (HCC). Our study reveals a novel role of SIRT5 in inhibiting peroxisome-induced oxidative stress, in liver protection, and in suppressing HCC development.

Enhanced glycolysis in cancer cells has been linked to cell protection from DNA damaging signals, although the mechanism is largely unknown. The 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) catalyzes the generation of fructose-2,6-bisphosphate, a potent allosteric stimulator of glycolysis. Intriguingly, among the four members of PFKFB family, PFKFB3 is uniquely localized in the nucleus, although the reason remains unclear. Here we show that chemotherapeutic agent cisplatin promotes glycolysis, which is suppressed by PFKFB3 deletion. Mechanistically, cisplatin induces PFKFB3 acetylation at lysine 472 (K472), which impairs activity of the nuclear localization signal (NLS) and accumulates PFKFB3 in the cytoplasm. Cytoplasmic accumulation of PFKFB3 facilitates its phosphorylation by AMPK, leading to PFKFB3 activation and enhanced glycolysis. Inhibition of PFKFB3 sensitizes tumor to cisplatin treatment in a xenograft model. Our findings reveal a mechanism for cells to stimulate glycolysis to protect from DNA damage and potentially suggest a therapeutic strategy to sensitize tumor cells to genotoxic agents by targeting PFKFB3.

Pathogens and inflammatory conditions rapidly induce the expression of immune-responsive gene 1 (IRG1) in cells of myeloid lineage. IRG1 encodes an aconitate decarboxylase (ACOD1) that produces the immunomodulatory metabolite itaconate (ITA). In addition to rapid intracellular accumulation, ITA is also secreted from the cell, but whether secreted ITA functions as a signaling molecule is unclear. Here, we identified ITA as an orthosteric agonist of the GPCR OXGR1, with an [EC.sub.50] of approximately 0.3 mM, which was in the same range as the physiological concentration of extracellular ITA upon macrophage activation. ITA activated OXGR1 to induce [Ca.sup.2+] mobilization, ERK phosphorylation, and endocytosis of the receptor. In a mouse model of pulmonary infection with bacterial Pseudomonas aeruginosa, ITA stimulated Oxgr1- dependent mucus secretion and transport in respiratory epithelium, the primary innate defense mechanism of the airway. Our study thus identifies ITA as a bona fide ligand for OXGR1 and the ITA/OXGR1 paracrine signaling pathway during the pulmonary innate immune response., Introduction Metabolic reprogramming is a fundamental mechanism for regulating the immune response in both innate and adaptive immune systems (1). Itaconate (ITA), a dicarboxylic acid, is one of the best [...]

Endothelin receptor A (ETAR) promotes tumorigenesis by stimulating cell proliferation, migration, and survival. However, the mechanism of ETAR in promoting tumor growth is largely unknown. In this study, we demonstrate that ETAR stimulates colon cell proliferation, migration, and tumorigenesis through the activation of YAP/TAZ, two transcription coactivators of the Hippo tumor suppressor pathway. Endothelin-1 treatment induced YAP/TAZ dephosphorylation, nuclear accumulation, and transcriptional activation in multiple colon cancer cells. ETAR stimulation acted via downstream G-protein Gαq/11 and Rho GTPase to suppress the Hippo pathway, thus leading to YAP/TAZ activation, which was required for ETAR-induced tumorigenesis. Overall, these results indicate a critical role of the YAP/TAZ axis in ETAR signaling. Cancer Res; 77(9); 2413-23. ©2017 AACR.

The thromboxane A2 receptor (TP) has been implicated in restenosis after vascular injury, which induces vascular smooth muscle cell (VSMC) migration and proliferation. However, the mechanism for this process is largely unknown. In this study, we report that TP signaling induces VSMC migration and proliferation through activating YAP/TAZ, two major downstream effectors of the Hippo signaling pathway. The TP-specific agonists [1S-[1α,2α(Z),3β(1E,3S*),4 α]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (I-BOP) and 9,11-dideoxy-9α,11α-methanoepoxy-prosta-5Z,13E-dien-1-oic acid (U-46619) induce YAP/TAZ activation in multiple cell lines, including VSMCs. YAP/TAZ activation induced by I-BOP is blocked by knockout of the receptor TP or knockdown of the downstream G proteins Gα12/13 Moreover, Rho inhibition or actin cytoskeleton disruption prevents I-BOP-induced YAP/TAZ activation. Importantly, TP activation promotes DNA synthesis and cell migration in VSMCs in a manner dependent on YAP/TAZ. Taken together, thromboxane A2 signaling activates YAP/TAZ to promote VSMC migration and proliferation, indicating YAP/TAZ as potential therapeutic targets for cardiovascular diseases.

The Hippo pathway plays a major role in organ size control, and its dysregulation contributes to tumorigenesis. The major downstream effectors of the Hippo pathway are the YAP/TAZ transcription co-activators, which are phosphorylated and inhibited by the Hippo pathway kinase LATS1/2. Here, we report a novel mechanism of TAZ regulation by the tight junction protein PARD3. PARD3 promotes the interaction between PP1A and LATS1 to induce LATS1 dephosphorylation and inactivation, therefore leading to dephosphorylation and activation of TAZ. The cytoplasmic, but not the tight junction complex associated, PARD3 is responsible for TAZ regulation. Our study indicates a potential molecular basis for cell growth-promoting function of PARD3 by modulating the Hippo pathway signaling in response to cell contact and cell polarity signals.

High aldehyde dehydrogenase (ALDH) activity is a marker commonly used to isolate stem cells, particularly breast cancer stem cells (CSCs). Here, we determined that ALDH1A1 activity is inhibited by acetylation of lysine 353 (K353) and that acetyltransferase P300/CBP-associated factor (PCAF) and deacetylase sirtuin 2 (SIRT2) are responsible for regulating the acetylation state of ALDH1A1 K353. Evaluation of breast carcinoma tissues from patients revealed that cells with high ALDH1 activity have low ALDH1A1 acetylation and are capable of self-renewal. Acetylation of ALDH1A1 inhibited both the stem cell population and self-renewal properties in breast cancer. Moreover, NOTCH signaling activated ALDH1A1 through the induction of SIRT2, leading to ALDH1A1 deacetylation and enzymatic activation to promote breast CSCs. In breast cancer xenograft models, replacement of endogenous ALDH1A1 with an acetylation mimetic mutant inhibited tumorigenesis and tumor growth. Together, the results from our study reveal a function and mechanism of ALDH1A1 acetylation in regulating breast CSCs.

Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in the pentose phosphate pathway (PPP) and plays an essential role in the oxidative stress response by producing NADPH, the main intracellular reductant. G6PD deficiency is the most common human enzyme defect, affecting more than 400 million people worldwide. Here, we show that G6PD is negatively regulated by acetylation on lysine 403 (K403), an evolutionarily conserved residue. The K403 acetylated G6PD is incapable of forming active dimers and displays a complete loss of activity. Knockdown of G6PD sensitizes cells to oxidative stress, and re-expression of wild-type G6PD, but not the K403 acetylation mimetic mutant, rescues cells from oxidative injury. Moreover, we show that cells sense extracellular oxidative stimuli to decrease G6PD acetylation in a SIRT2-dependent manner. The SIRT2-mediated deacetylation and activation of G6PD stimulates PPP to supply cytosolic NADPH to counteract oxidative damage and protect mouse erythrocytes. We also identified KAT9/ELP3 as a potential acetyltransferase of G6PD. Our study uncovers a previously unknown mechanism by which acetylation negatively regulates G6PD activity to maintain cellular NADPH homeostasis during oxidative stress.

Glucose-6-phosphate dehydrogenase (G6 PD) is a key enzyme in the pentose phosphate pathway ( PPP) and plays an essential role in the oxidative stress response by producing NADPH, the main intracellular reductant. G6 PD deficiency is the most common human enzyme defect, affecting more than 400 million people worldwide. Here, we show that G6 PD is negatively regulated by acetylation on lysine 403 ( K403), an evolutionarily conserved residue. The K403 acetylated G6 PD is incapable of forming active dimers and displays a complete loss of activity. Knockdown of G6 PD sensitizes cells to oxidative stress, and re-expression of wild-type G6 PD, but not the K403 acetylation mimetic mutant, rescues cells from oxidative injury. Moreover, we show that cells sense extracellular oxidative stimuli to decrease G6 PD acetylation in a SIRT2-dependent manner. The SIRT2-mediated deacetylation and activation of G6 PD stimulates PPP to supply cytosolic NADPH to counteract oxidative damage and protect mouse erythrocytes. We also identified KAT9/ ELP3 as a potential acetyltransferase of G6 PD. Our study uncovers a previously unknown mechanism by which acetylation negatively regulates G6 PD activity to maintain cellular NADPH homeostasis during oxidative stress. [ABSTRACT FROM AUTHOR]