Naa10p Inhibits Beige Adipocyte-Mediated Thermogenesis through N-α-acetylation of Pgc1α.

Diet-induced obesity can be caused by impaired thermogenesis of beige adipocytes, the brown-like adipocytes in white adipose tissue (WAT). Promoting brown-like features in WAT has been an attractive therapeutic approach for obesity. However, the mechanism underlying beige adipocyte formation is largely unknown. N-α-acetyltransferase 10 protein (Naa10p) catalyzes N-α-acetylation of nascent proteins, and overexpression of human Naa10p is linked to cancer development. Here, we report that both conventional and adipose-specific Naa10p deletions in mice result in increased energy expenditure, thermogenesis, and beige adipocyte differentiation. Mechanistically, Naa10p acetylates the N terminus of Pgc1α, which prevents Pgc1α from interacting with Pparγ to activate key genes, such as Ucp1, involved in beige adipocyte function. Consistently, fat tissues of obese human individuals show higher NAA10 expression. Thus, Naa10p-mediated N-terminal acetylation of Pgc1α downregulates thermogenic gene expression, making inhibition of Naa10p enzymatic activity a potential strategy for treating obesity.

The Role of N-α-acetyltransferase 10 Protein in DNA Methylation and Genomic Imprinting.

Genomic imprinting is an allelic gene expression phenomenon primarily controlled by allele-specific DNA methylation at the imprinting control region (ICR), but the underlying mechanism remains largely unclear. N-α-acetyltransferase 10 protein (Naa10p) catalyzes N-α-acetylation of nascent proteins, and mutation of human Naa10p is linked to severe developmental delays. Here we report that Naa10-null mice display partial embryonic lethality, growth retardation, brain disorders, and maternal effect lethality, phenotypes commonly observed in defective genomic imprinting. Genome-wide analyses further revealed global DNA hypomethylation and enriched dysregulation of imprinted genes in Naa10p-knockout embryos and embryonic stem cells. Mechanistically, Naa10p facilitates binding of DNA methyltransferase 1 (Dnmt1) to DNA substrates, including the ICRs of the imprinted allele during S phase. Moreover, the lethal Ogden syndrome-associated mutation of human Naa10p disrupts its binding to the ICR of H19 and Dnmt1 recruitment. Our study thus links Naa10p mutation-associated Ogden syndrome to defective DNA methylation and genomic imprinting.

O-GlcNAcylation regulates EZH2 protein stability and function.

O-linked N-acetylglucosamine (GlcNAc) transferase (OGT) is the only known enzyme that catalyzes the O-GlcNAcylation of proteins at the Ser or Thr side chain hydroxyl group. OGT participates in transcriptional and epigenetic regulation, and dysregulation of OGT has been implicated in diseases such as cancer. However, the underlying mechanism is largely unknown. Here we show that OGT is required for the trimethylation of histone 3 at K27 to form the product H3K27me3, a process catalyzed by the histone methyltransferase enhancer of zeste homolog 2 (EZH2) in the polycomb repressive complex 2 (PRC2). H3K27me3 is one of the most important histone modifications to mark the transcriptionally silenced chromatin. We found that the level of H3K27me3, but not other H3 methylation products, was greatly reduced upon OGT depletion. OGT knockdown specifically down-regulated the protein stability of EZH2, without altering the levels of H3K27 demethylases UTX and JMJD3, and disrupted the integrity of the PRC2 complex. Furthermore, the interaction of OGT and EZH2/PRC2 was detected by coimmunoprecipitation and cosedimentation experiments. Importantly, we identified that serine 75 is the site for EZH2 O-GlcNAcylation, and the EZH2 mutant S75A exhibited reduction in stability. Finally, microarray and ChIP analysis have characterized a specific subset of potential tumor suppressor genes subject to repression via the OGT-EZH2 axis. Together these results indicate that OGT-mediated O-GlcNAcylation at S75 stabilizes EZH2 and hence facilitates the formation of H3K27me3. The study not only uncovers a functional posttranslational modification of EZH2 but also reveals a unique epigenetic role of OGT in regulating histone methylation.

TET1 suppresses cancer invasion by activating the tissue inhibitors of metalloproteinases.

Tumor suppressor gene silencing through cytosine methylation contributes to cancer formation. Whether DNA demethylation enzymes counteract this oncogenic effect is unknown. Here, we show that TET1, a dioxygenase involved in cytosine demethylation, is downregulated in prostate and breast cancer tissues. TET1 depletion facilitates cell invasion, tumor growth, and cancer metastasis in prostate xenograft models and correlates with poor survival rates in breast cancer patients. Consistently, enforced expression of TET1 reduces cell invasion and breast xenograft tumor formation. Mechanistically, TET1 suppresses cell invasion through its dioxygenase and DNA binding activities. Furthermore, TET1 maintains the expression of tissue inhibitors of metalloproteinase (TIMP) family proteins 2 and 3 by inhibiting their DNA methylation. Concurrent low expression of TET1 and TIMP2 or TIMP3 correlates with advanced node status in clinical samples. Together, these results illustrate a mechanism by which TET1 suppresses tumor development and invasion partly through downregulation of critical gene methylation.

Autophagy-related gene 7 is downstream of heat shock protein 27 in the regulation of eye morphology, polyglutamine toxicity, and lifespan in Drosophila.

BACKGROUND: Autophagy and molecular chaperones both regulate protein homeostasis and maintain important physiological functions. Atg7 (autophagy-related gene 7) and Hsp27 (heat shock protein 27) are involved in the regulation of neurodegeneration and aging. However, the genetic connection between Atg7 and Hsp27 is not known. METHODS: The appearances of the fly eyes from the different genetic interactions with or without polyglutamine toxicity were examined by light microscopy and scanning electronic microscopy. Immunofluorescence was used to check the effect of Atg7 and Hsp27 knockdown on the formation of autophagosomes. The lifespan of altered expression of Hsp27 or Atg7 and that of the combination of the two different gene expression were measured. RESULTS: We used the Drosophila eye as a model system to examine the epistatic relationship between Hsp27 and Atg7. We found that both genes are involved in normal eye development, and that overexpression of Atg7 could eliminate the need for Hsp27 but Hsp27 could not rescue Atg7 deficient phenotypes. Using a polyglutamine toxicity assay (41Q) to model neurodegeneration, we showed that both Atg7 and Hsp27 can suppress weak, toxic effect by 41Q, and that overexpression of Atg7 improves the worsened mosaic eyes by the knockdown of Hsp27 under 41Q. We also showed that overexpression of Atg7 extends lifespan and the knockdown of Atg7 or Hsp27 by RNAi reduces lifespan. RNAi-knockdown of Atg7 expression can block the extended lifespan phenotype by Hsp27 overexpression, and overexpression of Atg7 can extend lifespan even under Hsp27 knockdown by RNAi. CONCLUSIONS: We propose that Atg7 acts downstream of Hsp27 in the regulation of eye morphology, polyglutamine toxicity, and lifespan in Drosophila.