Project description:SIRT7 is a member of the mammalian sirtuin family of NAD+ dependent deacylases, and interacts with RNA polymerase I and UBF to regulate rDNA transcription. Various studies in mammalian cells and human clinical data have linked SIRT7 to cancer. However studies differ as to whether SIRT7 is oncogenic or tumor suppressive. Here we analyzed SIRT7 knockout mice and found SIRT7 deficiency caused sub-Mendelian birth numbers and a reduction in body size. Moreover, at 18 month of age, roughly 60 % of the SIRT7 knockout mice develop hepatocellular carcinoma (HCC), in many cases leading to suspected metastasis. Several HCC associated genes were up-regulated in livers of mice as young as 6 months of age, particularly targets of the proto-oncogene, c- MYC. Indeed SIRT7 interacts with MYC at endogenous protein levels and also represses MYC activity. Our findings thus show that SIRT7 acts as a tumor suppressor in vivo, and may suggest novel strategies to treat liver cancer. The mRNAs from 3 replicates of mouse Wildtype liver compared to 3 replicates of mouse liver lacking SIRT7
Project description:Male Sirt7 KO mice exhibit an lifespan extension and increased FGF21 expression in liver. To reveal the mechanism of the increase of hepatic FGF21 expression in aged male Sirt7 KO mice, we performed RNA-seq analysis of the liver.
Project description:Sirtuin proteins regulate diverse cellular pathways that influence genomic stability, metabolism, and ageing. SIRT7 is a mammalian sirtuin whose biochemical activity, molecular targets, and physiologic functions have been unclear. Here we show that SIRT7 is an NAD+-dependent, histone H3 acetyl-lysine 18 (H3K18Ac) deacetylase that stabilizes the transformed state of cancer cells. Genome-wide binding studies reveal that SIRT7 binds to promoters of a specific set of gene targets, where it deacetylates H3K18Ac and promotes transcriptional repression. The spectrum of SIRT7 target genes is defined in part by interaction of SIRT7 with the cancer-related ETS transcription factor ELK4, and comprises numerous genes with links to tumour suppression. Notably, selective hypoacetylation of H3K18Ac has recently been linked to oncogenic transformation, and in patients, is associated with aggressive tumour phenotypes and poor prognosis. We find that deacetylation of H3K18Ac by SIRT7 is necessary for maintaining essential features of human cancer cells including anchorage independent growth and escape from contact inhibition. Moreover, SIRT7 is necessary for a global hypoacetylation of H3K18Ac associated with cellular transformation by viral oncoproteins. Finally, SIRT7 depletion markedly reduces the tumourigenicity of human cancer cell xenografts in mice. Together, our work establishes SIRT7 as the first known site-specific H3K18Ac deacetylase and demonstrates a pivotal role for SIRT7 in chromatin regulation, cellular transformation programs, and tumour formation in vivo. SIRT7 ChIP-seq was performed in K562 cell lines under normal conditions. Two replicates were performed for both the SIRT7 ChIP as well as input control.
Project description:SIRT7 is a member of the mammalian sirtuin family of NAD+ dependent deacylases, and interacts with RNA polymerase I and UBF to regulate rDNA transcription. Various studies in mammalian cells and human clinical data have linked SIRT7 to cancer. However studies differ as to whether SIRT7 is oncogenic or tumor suppressive. Here we analyzed SIRT7 knockout mice and found SIRT7 deficiency caused sub-Mendelian birth numbers and a reduction in body size. Moreover, at 18 month of age, roughly 60 % of the SIRT7 knockout mice develop hepatocellular carcinoma (HCC), in many cases leading to suspected metastasis. Several HCC associated genes were up-regulated in livers of mice as young as 6 months of age, particularly targets of the proto-oncogene, c- MYC. Indeed SIRT7 interacts with MYC at endogenous protein levels and also represses MYC activity. Our findings thus show that SIRT7 acts as a tumor suppressor in vivo, and may suggest novel strategies to treat liver cancer.
Project description:SIRT7 is an NAD+-dependent protein deacetylase with important roles in ribosome biogenesis and cell proliferation. Previous studies have established that SIRT7 is associated with RNA polymerase I, interacts with pre-rRNA and promotes rRNA synthesis. Here we show that SIRT7 is also associated with snoRNAs that are involved in pre-rRNA processing and rRNA maturation. Knockdown of SIRT7 impairs U3 snoRNA-dependent early cleavage steps that are necessary for generation of 18S rRNA. Mechanistically, SIRT7 deacetylates U3-55k, a core component of the U3 snoRNP complex, and reversible acetylation of U3-55k modulates the association of U3-55k with U3 snoRNA. Deacetylation by SIRT7 enhances U3-55k binding to U3 snoRNA, which is a prerequisite for pre-rRNA processing. Under stress conditions, SIRT7 is released from nucleoli, leading to hyperacetylation of U3-55k and attenuation of prerRNA processing. The results reveal a multifaceted role of SIRT7 in ribosome biogenesis, regulating both transcription and processing of rRNA. CLIP-seq was performed in Flag-SIRT7-293T cells.
Project description:SIRT7 is a member of the mammalian sirtuin family and functions as a NAD+-dependent deacylase. Studies in culture cells and human clinical data have implicated the role of SIRT7 in tumorigenesis. However, controversies were raised as to whether SIRT7 is oncogenic or tumor suppressive. Here we show that SIRT7 deficiency led to aneuploidy and aging-phenotypes, including senescence and nucleolin expansion. SIRT7 knockout mice were susceptible to DSS-induced colitis and alcohol-derived DNA damage, in advance led to intestinal epithelial barrier disruption. Devoid of SIRT7 aggravated the susceptibility of colorectal cancer incidence in APCMin/+ mouse model with further dysregulated Wnt signaling. Our findings indicated a tumor suppressive role of SIRT7 in vivo, novel strategies design for activating SIRT7 in treating colon cancer may be reappraised.
Project description:To investigate the specific roles of SIRT7 in the development of HCC, we employed large-scale gene expression analysis to identify the molecular signature that may affect enabling characteristics of cancer cells. Differentially expressed genes were analyzed on the Hep3B cells transfected with SIRT7 shRNAs, and recapitulated molecular signatures that related to hallmarks of cancer.
Project description:Sirtuin proteins regulate diverse cellular pathways that influence genomic stability, metabolism, and ageing. SIRT7 is a mammalian sirtuin whose biochemical activity, molecular targets, and physiologic functions have been unclear. Here we show that SIRT7 is an NAD+-dependent, histone H3 acetyl-lysine 18 (H3K18Ac) deacetylase that stabilizes the transformed state of cancer cells. Genome-wide binding studies reveal that SIRT7 binds to promoters of a specific set of gene targets, where it deacetylates H3K18Ac and promotes transcriptional repression. The spectrum of SIRT7 target genes is defined in part by interaction of SIRT7 with the cancer-related ETS transcription factor ELK4, and comprises numerous genes with links to tumour suppression. Notably, selective hypoacetylation of H3K18Ac has recently been linked to oncogenic transformation, and in patients, is associated with aggressive tumour phenotypes and poor prognosis. We find that deacetylation of H3K18Ac by SIRT7 is necessary for maintaining essential features of human cancer cells including anchorage independent growth and escape from contact inhibition. Moreover, SIRT7 is necessary for a global hypoacetylation of H3K18Ac associated with cellular transformation by viral oncoproteins. Finally, SIRT7 depletion markedly reduces the tumourigenicity of human cancer cell xenografts in mice. Together, our work establishes SIRT7 as the first known site-specific H3K18Ac deacetylase and demonstrates a pivotal role for SIRT7 in chromatin regulation, cellular transformation programs, and tumour formation in vivo.
Project description:Sirtuins are key players in the response to oxidative, metabolic and genotoxic stress, and are involved in genome stability, metabolic homeostasis and aging. Originally described as NAD+-dependent deacetylases, some sirtuins are also characterized by poorly understood mono-ADP-ribosyltransferase (MADPRT) activity. Here we report that the deacetylase SirT7 is a dual sirtuin as it also features auto-MADPRT activity. Molecular and structural evidence suggests that this novel activity occurs at a second previously undefined active site that is physically separated in another domain. Specific abrogation of this activity alters SirT7 chromatin distribution, suggesting a role for this modification in SirT7 chromatin binding specificity and localization. Our studies uncover an epigenetic pathway by which ADP-ribosyl-SirT7 is recognized by the ADP-ribose reader macroH2A1.1, a histone variant involved in chromatin organization, metabolism and differentiation. Glucose starvation (GS) boosts this interaction and promotes SirT7 re-localization intergenic regions in a macroH2A1-dependent manner, which is required for specific up- or downregulation of a subset of nearby genes upon GS in primary cells and in vivo in the livers of calorie-restricted (CR) Wt and SirT7-/- mice. The level of expression of these genes decreases with age in SirT7-deficient mice, reinforcing the link between Sirtuins, CR and aging. Our work provides a novel perspective about sirtuin duality and suggests a key role for SirT7/macroH2A1.1 axis in mammalian glucose homeostasis, calorie restriction signaling and aging.
Project description:Human mesenchymal stem cell (hMSC) senescence contributes to the imbalance of tissue homeostasis during aging. However, the connection between Sirtuin 7 (SIRT7) and hMSC homeostasis remains unclear. Here, we discovered a pivotal role of SIRT7 in protecting hMSC from senescence. We detected a decreased expression of SIRT7 during hMSC aging, while overexpression of which reversed premature hMSC senescence phenotypes. Mechanistically, we proved SIRT7 as a novel interacting protein of the heterochromatin complex, whose deficiency disrupted heterochromatin organization, thereby contributing to the derepression of the retrotransposon Long Interspersed Element 1 (LINE1 or L1). SIRT7-deficient hMSCs accumulated LINE1 in cytoplasm stimulating innate immune response by activated the cyclic GMP-AMP synthase (cGAS) and its downstream signaling effector stimulator of interferon genes (STING). Moreover, reverse-transcriptase inhibitors (RTis), such as Lamivudine (3TC), attenuated these senescence phenotypes of SIRT7-deficient hMSCs. Taken together, our findings identify SIRT7-heterochromatin via LINE1-cGAS/STING influence innate immune response, which contributes more comprehensive understanding of the physiological and function of SIRT7 and help us to find novel targets for the treatment of aging and aging relative diseases.