Sirt3 Pharmacologically Promotes Insulin Sensitivity through PI3/AKT/mTOR and Their Downstream Pathway in Adipocytes

Sirtuin-3 (Sirt3) is a major mitochondrial deacetylase enzyme that regulates multiple metabolic pathways, and its expression is decreased in diabetes type 1 and type 2 diabetes. This study aimed to elucidate Sirt3′s molecular mechanism in regulating insulin sensitivity in adipocytes that can contribute to the effort of targeting Sirt3 for the treatment of obesity and type 2 diabetes. We found that the Sirt3 activator honokiol (HNK) induced adipogenesis compared to the control, in contrast to Sirt3 inhibitor, 3-TYP. Accordingly, HNK increased expression of adipocyte gene markers, gene-involved lipolysis and glucose transport (GLUT4), while 3-TYP reduced expression of those genes. Interestingly, 3-TYP caused an increase in gene expression of adipocyte-specific cytokines including IL6, resistin, and TNF-α. However, changes in adipocyte-specific cytokines in HNK treated cells were not significant. In addition, HNK stimulated insulin pathway by promoting insulin receptor beta (IRβ) and PI3K/AKT/mTOR pathways, resulting in an increase in phosphorylation of the forkhead family FoxO1/FoxO3a/FoxO4 and glycogen synthase kinase-3 (GSK-3β), opposing 3-TYP. In line with these findings, HNK increased free fatty acid and glucose uptake, contrary to 3-TYP. In conclusion, Sirt3 activator-HNK induced adipogenesis and lipolysis reduced adipocytes specific cytokines. Intriguingly, HNK activated insulin signaling pathway and increased free fatty acid as well as glucose uptake and transport, in sharp contrast to 3-TYP. These results indicate that, via insulin signaling regulation, Sirt3 activation by HNK improves insulin resistance, while Sirt3 inhibition by 3-TYP might precipitate insulin resistance.

RELT stains prominently in B-cell lymphomas and binds the hematopoietic transcription factor MDFIC

Receptor Expressed in Lymphoid Tissues (RELT) is a human tumor necrosis factor receptor superfamily member (TNFRSF) that is expressed most prominently in cells and tissues of the hematopoietic system. RELL1 and RELL2 are two homologs that physically interact with RELT and co-localize with RELT at the plasma membrane. This study sought to further elucidate the function of RELT by identifying novel protein interactions with RELT family members. The transcription factor MyoD family inhibitor domain-containing (MDFIC) was identified in a yeast two-hybrid genetic screen using RELL1 as bait. MDFIC co-localizes with RELT family members at the plasma membrane; this co-localization was most prominently observed with RELL1 and RELL2. In vitro co-immunoprecipitation (Co-IP) was utilized to demonstrate that MDFIC physically interacts with RELT, RELL1, and RELL2. Co-IP using deletion mutants of MDFIC and RELT identified regions important for physical association between MDFIC and RELT family members and a computational analysis revealed that RELT family members are highly disordered proteins. Immunohistochemistry of normal human lymph nodes revealed RELT staining that was most prominent in macrophages. Interestingly, the level of RELT staining significantly increased progressively in low and high-grade B-cell lymphomas versus normal lymph nodes. RELT co-staining with CD20 was observed in B-cell lymphomas, indicating that RELT is expressed in malignant B cells. Collectively, these results further our understanding of RELT-associated signaling pathways, the protein structure of RELT family members, and provide preliminary evidence indicating an association of RELT with B-cell lymphomas.

•

RELT family members physically interact with MDFIC.

•

RELT is expressed in human lymph nodes, with prominent expression in macrophages.

•

RELT is expressed in malignant B cells associated with B-cell lymphomas.

•

RELT is a highly disordered protein.

Sirt3 regulates adipogenesis and adipokine secretion via its enzymatic activity

The purpose of this research was to identify if Sirt3 plays a role in marrow adipogenesis and adipokines secretion, especially adiponectin using bone marrow-derived stroma (ST2) cell model. Sirt3 overexpression leads to a significant increase in adipogenesis compared to controls. The induction of adipogenesis by Sirt3 is associated with increased gene expression of adipocyte markers as well as adiponectin/adipokines. In sharp contrast, the inhibition of Sirt3 exhibited significantly decreased adipogenesis, adipocyte markers, and adiponectin/adipokines compared to the controls. Interestingly, perilipin 1 (Plin 1) expression was decreased in Sirt3 induction but increased in Sirt3 inhibition. One hundred and fifteen mitochondrial acetylated peptides from 67 mitochondrial proteins had lower levels of acetylation in adipocytes induced by Sirt3 overexpression (Sirt3OE) compared to the control. Of the 67 proteins less enriched in acetylation, 22 acetylated proteins were decreased by more than twofold. These proteins are considered potential Sirt3 substrates in adipogenesis. In conclusion, Sirt3 has a novel, important role in modulating adipogenesis and adiponectin/adipokine expression. The connection axis among Sirt3-adipogenesis-adipokines was linked to its substrates by mass spectrometry analysis. These findings contribute to the efforts of revealing Sirt3 functions and Sirt3 usage as a potential target for treatment of metabolic homeostasis and diseases including type 2 diabetes.

Genistein Combined Polysaccharide (GCP) Can Inhibit Intracrine Androgen Synthesis in Prostate Cancer Cells

Our group and others have previously shown that genistein combined polysaccharide (GCP), an aglycone isoflavone-rich extract with high bioavailability and low toxicity, can inhibit prostate cancer (CaP) cell growth and survival as well as androgen receptor (AR) activity. We now elucidate the mechanism by which this may occur using LNCaP and PC-346C CaP cell lines; GCP can inhibit intracrine androgen synthesis in CaP cells. UPLC-MS/MS and qPCR analyses demonstrated that GCP can mediate a ~3-fold decrease in testosterone levels (p < 0.001) and cause decreased expression of intracrine androgen synthesis pathway enzymes (~2.5-fold decrease of 3βHSD (p < 0.001), 17βHSD (p < 0.001), CYP17A (p < 0.01), SRB1 (p < 0.0001), and StAR (p < 0.01)), respectively. Reverse-phase HPLC fractionation and bioassay identified three active GCP fractions. Subsequent NMR and LC-MS analysis of the fraction with the highest level of activity, fraction 40, identified genistein as the primary active component of GCP responsible for its anti-proliferative, pro-apoptotic, and anti-AR activity. GCP, fraction 40, and genistein all mediated at least a ~2-fold change in these biological activities relative to vehicle control (p < 0.001). Genistein caused similar decreases in the expression of 17βHSD and CYP17A (2.5-fold (p < 0.001) and 1.5-fold decrease (p < 0.01), respectively) compared to GCP, however it did not cause altered expression of the other intracrine androgen synthesis pathway enzymes; 3βHSD, SRB1, and StAR. Our combined data indicate that GCP and/or genistein may have clinical utility and that further pre-clinical studies are warranted.

RELT stains prominently in B cell lymphomas and binds proteins associated with leukemia

Receptor Expressed in Lymphoid Tissues (RELT) is a human TNFR that is expressed prominently in the hematopoietic system and negatively regulates T-cell activation in mice. RELT has two identified homologous binding partners, RELL1 and RELL2. This study sought to further elucidate the function of RELT by identifying novel protein interactions with RELT family members and to study the localization of RELT in both normal and diseased tissues. A yeast two-hybrid screen identifed Phospholipid Scramblase 1 (PLSCR1) and MyoD family inhibitor domain-containing protein (MDFIC) as potential RELT-family member binding proteins that were confirmed by in vitro co-immunoprecipitations. PLSCR1 has been demonstrated to possess anti-leukemic properties, and RELT expression results in an altered cellular localization of PLSCR1 as determined by immunofluorescence (IF). The MDFIC gene encodes for a transcription factor and is located proximally to regions of chromosome 7 (7q31.1) frequently lost in AML patients. MDFIC was observed to co-localize with RELL1 at the plasma membrane and co-localize with RELT in intracellular compartments as determined by IF. Since RELT, PLSCR1 and MDFIC are prominently expressed in the hematopoietic system, we sought to characterize the expression of RELT in both normal lymph nodes and B cell lymphomas. Immunohistochemistry revealed a higher intensity of RELT staining in germinal centers in comparison to surrounding lymph node regions. Interestingly, the level of RELT staining increased progressively in low and high-grade B cell lymphomas versus normal lymph nodes. Collectively, these results further our understanding of proteins that interact with RELT and identify an association of RELT with B cell lymphomas.

Abstract 2820: Use of a genetically engineered mouse model and RNA sequencing to identify genes that are aberrantly regulated by mutant p53 in prostate cells following irradiation

Our group has previously demonstrated that the Trp53 R270H mutation can drive prostate cancer (CaP) initiation in a genetically engineered mouse model, and that the human equivalent, TP53 R273H, can promote development of castration resistant growth of LNCaP cells as well as resistance to commonly used therapeutic agents. The primary objective of the current study was to identify genes that may contribute to the development of these gain-of-function phenotypes.

Wildtype mice and mice that were heterozygous or homozygous for the Trp53 R270H mutation (referred to as Trp53 +/+, Trp53 +/ R270H, or Trp53 R270H/R270H, respectively) that were ~3 months old were exposed to 5 Gy radiation to activate and stabilize p53, consequently increasing its expression. Mouse prostates were harvested 6 hours post-irradiation and either processed for subsequent histological/immunohistochemistry (IHC) analysis or snap-frozen for subsequent RNA extraction and transcriptome profiling with RNA-Sequencing (RNA-Seq) analysis. P53 expression was determined by IHC. RNA-Seq data were processed to quantify transcript levels and to assess differential gene expression between the 3 groups.

PIN lesions were observed in 3-month-old Trp53 R270H/R270H mice prostates, but not in Trp53 +/+ or Trp53 +/ R270H mice prostates. IHC analysis demonstrated that p53 was stabilized in the majority of prostate cells from Trp53 +/+, Trp53 +/ R270H, or Trp53 R270H/R270H mice 6 hours post-irradiation. RNA-Seq analysis of RNA isolated from irradiated mice prostates identified 1,444 genes that were differentially expressed in Trp53 +/+ versus Trp53 R270H/R270H mice prostate cells, and 796 genes that were differentially expressed in Trp53 +/+ versus Trp53 +/ R270H mice. Statistically significant differences in gene expression between the 3 groups were observed for 1,378 genes, including a number of p53 target genes, such as Cdkn1a, Bax, Bcl2, Kras, Mdm2, and Id4.

Our data identify multiple genes that may contribute to prostate cancer initiation and/or progression through p53 gain-of-function and loss-of-function mechanisms. It is possible that further analysis of these genes may lead to the development of new therapies and/or biomarkers for prostate cancer patients as well as guide the usage of currently available therapies in men at risk of developing CaP and CaP patients who harbor TP53 mutations.

Citation Format: Ruth L. Vinall, Qian Chen, George Talbott, Neil Hubbard, Clifford Tepper, Alexander Borowsky. Use of a genetically engineered mouse model and RNA sequencing to identify genes that are aberrantly regulated by mutant p53 in prostate cells following irradiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2820. doi:10.1158/1538-7445.AM2017-2820

RELT binds HIC and induces apoptosis by a mechanism distinct from TNFR1

Receptor Expressed in Lymphoid Tissues (RELT) is a human Tumor Necrosis Factor Receptor (TNFR) that is expressed most prominently in cells and tissues of the hematopoietic system. RELT has two identified homologous binding partners RELL1 and RELL2. This study sought to further elucidate the function of RELT by identifying novel protein interactions with RELT family members. Human I-mfa domain-containing protein (HIC), also known as MDFIC, was identified in a yeast two-hybrid genetic screen using RELL1 as bait. HIC is a transcription factor that was initially identified to differentially regulate HTLV and HIV gene expression. HIC is now known to regulate many other cellular processes and the hic gene is located proximally to regions of chromosome 7 (7q31.1) frequently lost in Acute Myeloid Leukemia (AML) patients. HIC physically interacts with both RELT and RELL1, as determined by in vitro co-immunoprecipitations. HIC co-localizes with RELL1 at the plasma membrane and co-localizes with RELT in intracellular compartments. Deletion mutants of RELT were utilized to determine regions of RELT required for both the activation of p38 and the induction of apoptosis in HEK-293 cells, two previously described functions of RELT. Co-immunoprecipitation experiments utilizing the deletion mutants indicate that regions of RELT proximal to the plasma membrane are sufficient for physical interaction with HIC. Overexpression of RELT induces cleavage of PARP and Caspase-3 as determined by western blotting. Interestingly, induction of apoptotic morphology by RELT overexpression was not prevented if signaling by FADD or Caspase-8 was blocked, indicating RELT induces apoptosis by a pathway distinct from death-domain containing TNFRs such as TNFR1.

Metformin Inhibits Hepatic mTORC1 Signaling via Dose-Dependent Mechanisms Involving AMPK and the TSC Complex

Metformin is the most widely prescribed drug for the treatment of type 2 diabetes. However, knowledge of the full effects of metformin on biochemical pathways and processes in its primary target tissue, the liver, is limited. One established effect of metformin is to decrease cellular energy levels. The AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) are key regulators of metabolism that are respectively activated and inhibited in acute response to cellular energy depletion. Here we show that metformin robustly inhibits mTORC1 in mouse liver tissue and primary hepatocytes. Using mouse genetics, we find that at the lowest concentrations of metformin that inhibit hepatic mTORC1 signaling, this inhibition is dependent on AMPK and the tuberous sclerosis complex (TSC) protein complex (TSC complex). Finally, we show that metformin profoundly inhibits hepatocyte protein synthesis in a manner that is largely dependent on its ability to suppress mTORC1 signaling.

Spatial control of the TSC complex integrates insulin and nutrient regulation of mTORC1 at the lysosome

mTORC1 promotes cell growth in response to nutrients and growth factors. Insulin activates mTORC1 through the PI3K-Akt pathway, which inhibits the TSC1-TSC2-TBC1D7 complex (the TSC complex) to turn on Rheb, an essential activator of mTORC1. However, the mechanistic basis of how this pathway integrates with nutrient-sensing pathways is unknown. We demonstrate that insulin stimulates acute dissociation of the TSC complex from the lysosomal surface, where subpopulations of Rheb and mTORC1 reside. The TSC complex associates with the lysosome in a Rheb-dependent manner, and its dissociation in response to insulin requires Akt-mediated TSC2 phosphorylation. Loss of the PTEN tumor suppressor results in constitutive activation of mTORC1 through the Akt-dependent dissociation of the TSC complex from the lysosome. These findings provide a unifying mechanism by which independent pathways affecting the spatial recruitment of mTORC1 and the TSC complex to Rheb at the lysosomal surface serve to integrate diverse growth signals.

Antibodies against CD14 protect primates from endotoxin-induced shock

Lipopolysaccharide (LPS), residing in the outer membrane of all gram-negative bacteria, is considered a major initiating factor of the gram-negative septic shock syndrome in humans. LPS forms a complex with the LPS binding protein (LBP) in plasma, and LPS-LBP complexes engage a specific receptor, CD14, on the surface of myeloid cells, leading to the production of potent proinflammatory cytokines. The major goal of this study was to test the importance of the CD14 pathway in vivo in a primate model that is similar to human septic shock. Primates were pretreated with one of two different inhibitory anti-CD14 mAbs, then challenged with intravenous endotoxin (375 microg/kg/h) for 8 h. The anti-CD14 treatment regimens were successful in preventing profound hypotension, reducing plasma cytokine levels (TNF-alpha, IL-1beta, IL-6, and IL-8), and inhibiting the alteration in lung epithelial permeability that occurred in animals treated with LPS and an isotype-matched control antibody. These results demonstrate for the first time the importance of the CD14 pathway in a primate model that is similar to human septic shock. Inhibition of the CD14 pathway represents a novel therapeutic approach to treating this life-threatening condition.