Targeting E3 ubiquitin ligases and their adaptors as a therapeutic strategy for metabolic diseases.

Posttranslational modification of proteins via ubiquitination determines their activation, translocation, dysregulation, or degradation. This process targets a large number of cellular proteins, affecting all biological pathways involved in the cell cycle, development, growth, and differentiation. Thus, aberrant regulation of ubiquitination is likely associated with several diseases, including various types of metabolic diseases. Among the ubiquitin enzymes, E3 ubiquitin ligases are regarded as the most influential ubiquitin enzymes due to their ability to selectively bind and recruit target substrates for ubiquitination. Continued research on the regulatory mechanisms of E3 ligases and their adaptors in metabolic diseases will further stimulate the discovery of new targets and accelerate the development of therapeutic options for metabolic diseases. In this review, based on recent discoveries, we summarize new insights into the roles of E3 ubiquitin ligases and their adaptors in the pathogenesis of metabolic diseases by highlighting recent evidence obtained in both human and animal model studies.

Hepatocyte Kctd17 Inhibition Ameliorates Glucose Intolerance and Hepatic Steatosis Caused by Obesity-induced Chrebp Stabilization.

BACKGROUND & AIMS: Obesity predisposes to type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD), but underlying mechanisms are incompletely understood. Potassium channel tetramerization domain-containing protein 17 (Kctd17) levels are increased in livers from obese mice and humans. In this study, we investigated the mechanism of increased Kctd17 and whether it is causal to obesity-induced metabolic complications. METHODS: We transduced Rosa26-LSL-Cas9 knockin mice with AAV8-TBG-Cre (Control), AAV8-U6-Kctd17 sgRNA-TBG-Cre (L-Kctd17), AAV8-U6-Oga sgRNA-TBG-Cre (L-Oga), or AAV8-U6-Kctd17/Oga sgRNA-TBG-Cre (DKO). We fed mice a high-fat diet (HFD) and assessed for hepatic glucose and lipid homeostasis. We generated Kctd17, O-GlcNAcase (Oga), or Kctd17/Oga-knockout hepatoma cells by CRISPR-Cas9, and Kctd17-directed antisense oligonucleotide to test therapeutic potential in vivo. We analyzed transcriptomic data from patients with NAFLD. RESULTS: Hepatocyte Kctd17 expression was increased in HFD-fed mice due to increased Srebp1c activity. HFD-fed L-Kctd17 or Kctd17 antisense oligonucleotide-treated mice show improved glucose tolerance and hepatic steatosis, whereas forced Kctd17 expression caused glucose intolerance and hepatic steatosis even in lean mice. Kctd17 induced Oga degradation, resulting in increasing carbohydrate response element-binding protein (Chrebp) protein, so concomitant Oga knockout negated metabolic benefits of hepatocyte Kctd17 deletion. In patients with NAFLD, KCTD17 messenger RNA was positively correlated with expression of Chrebp target and other lipogenic genes. CONCLUSIONS: Srebp1c-induced hepatocyte Kctd17 expression in obesity disrupted glucose and lipid metabolism by stabilizing Chrebp, and may represent a novel therapeutic target for obesity-induced T2D and NAFLD.

Emerging roles of PHLPP phosphatases in metabolism.

Over the last decades, research has focused on the role of pleckstrin homology (PH) domain leucine-rich repeat protein phosphatases (PHLPPs) in regulating cellular signaling via PI3K/Akt inhibition. The PKB/Akt signaling imbalances are associated with a variety of illnesses, including various types of cancer, inflammatory response, insulin resistance, and diabetes, demonstrating the relevance of PHLPPs in the prevention of diseases. Furthermore, identification of novel substrates of PHLPPs unveils their role as a critical mediator in various cellular processes. Recently, researchers have explored the increasing complexity of signaling networks involving PHLPPs whereby relevant information of PHLPPs in metabolic diseases was obtained. In this review, we discuss the current knowledge of PHLPPs on the well-known substrates and metabolic regulation, especially in liver, pancreatic beta cell, adipose tissue, and skeletal muscle in relation with the stated diseases. Understanding the context-dependent functions of PHLPPs can lead to a promising treatment strategy for several kinds of metabolic diseases. [BMB Reports 2021; 54(9): 451-457].

Interaction of BRAF-induced ETS factors with mutant TERT promoter in papillary thyroid cancer.

Synergistic effects of BRAFV600E and TERT promoter mutations on the poor clinical outcomes in papillary thyroid cancer (PTC) have been demonstrated. The potential mechanism of this phenomenon has been proposed: MAPK pathway activation by the BRAFV600E mutation may upregulate E-twenty six (ETS) transcription factors, increasing TERT expression by binding to the ETS-binding site generated by the TERT promoter mutation; however, it has not yet been fully proven. This article provides transcriptomic insights into the interaction between BRAFV600E and TERT promoter mutations mediated by ETS factors in PTC. RNA sequencing data on 266 PTCs from The Cancer Genome Atlas and 65 PTCs from our institute were analyzed for gene expression changes and related molecular pathways, and the results of transcriptomic analyses were validated by in vitro experiments. TERT mRNA expression was increased by the coexistence of BRAFV600E and TERT promoter mutations (fold change, 16.17; q-value = 7.35 × 10-12 vs no mutation). In the ETS family of transcription factors, ETV1, ETV4 and ETV5 were upregulated by the BRAFV600E/MAPK pathway activation. These BRAFV600E-induced ETS factors selectively bound to the mutant TERT promoter. The molecular pathways activated by BRAFV600E were further augmented by adding the TERT promoter mutation, and the pathways related to immune responses or adhesion molecules were upregulated by TERT expression. The mechanism of the synergistic effect between BRAFV600E and TERT promoter mutations on cancer invasiveness and progression in PTC may be explained by increased TERT expression, which may result from the BRAF-induced upregulation of several ETS transcription factors.

Hepatic Elovl6 gene expression is regulated by the synergistic action of ChREBP and SREBP-1c.

Elongation of very long chain fatty acids protein 6 (ELOVL6), a rate-limiting enzyme for the elongation of saturated and monounsaturated fatty acids with 12, 14, and 16 carbons, plays a key role in energy metabolism and insulin sensitivity. Hepatic Elovl6 expression is upregulated in the fasting-refeeding response and in leptin-deficient ob/ob mice. Mouse Elovl6 has been shown to be a direct target of sterol regulatory element binding protein-1 (SREBP-1) in response to insulin. In the present study, we demonstrated that mouse and human Elovl6 expression is under the direct transcriptional control of carbohydrate response element binding protein (ChREBP), a mediator of glucose-induced gene expression. Serial deletion and site-directed mutagenesis studies revealed functional carbohydrate response elements (ChoREs) in the mouse and human Elovl6 promoters and gel shift assays and chromatin immunoprecipitation assays confirmed the binding of ChREBP to the Elovl6-ChoRE sites. In addition, the ectopic co-expression of ChREBP and SREBP-1c in HepG2 cells synergistically stimulated Elovl6 promoter activity and this synergistic activation was abolished by mutating the Elovl6 promoter ChoREs. Taken together, these results suggest that the synergistic action of ChREBP and SREBP-1c is necessary for the maximal induction of Elovl6 expression in the liver.

The Unusual Suspect: Anemia-induced Systolic Anterior Motion of the Mitral Valve and Intraventricular Dynamic Obstruction in a Hyperdynamic Heart as Unexpected Causes of Exertional Dyspnea after Cardiac Surgery.

Dynamic left ventricular (LV) outflow tract obstruction is a characteristic feature of hypertrophic cardiomyopathy; however, it can also occur in association with hyperdynamic LV contraction and/or changes in the cardiac loading condition, even in a structurally normal or near-normal heart. Here, we report a case of anemia-induced systolic anterior motion of the mitral valve and the resultant intraventricular obstruction in a patient who underwent coronary artery bypass grafting and suffered from anemia associated with recurrent gastrointestinal bleeding.

The insect peptide CopA3 inhibits lipopolysaccharide-induced macrophage activation.

We recently demonstrated that the insect peptide CopA3 (LLCIALRKK), a disulfide-linked dimeric peptide, exerts antimicrobial and anti-inflammatory activities in a mouse colitis model. Here, we examined whether CopA3 inhibited activation of macrophages by LPS. Exposure of an unseparated mouse peritoneal cell population or isolated peritoneal macrophages to LPS markedly increased secretion of IL-6 and TNF-α; these effects were significantly inhibited by CopA3 treatment. The inhibitory effect of CopA3 was also evident in murine macrophage cell line, RAW 264.7. Western blotting revealed that LPS-induced activation of STAT1 and STAT5 in macrophages was significantly inhibited by CopA3. Inhibition of JAK (STAT1/STAT5 kinase) with AG490 markedly reduced the production of IL-6 and TNF-α in macrophages. Collectively, these observations suggest that CopA3 inhibits macrophage activation by inhibiting activating phosphorylations of the transcription factors, STAT1 and STAT5, and blocking subsequent production of IL-6 and TNF-α and indicate that CopA3 may be useful as an immune-modulating agent.