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

KCTD17-mediated Ras stabilization promotes hepatocellular carcinoma progression

BACKGROUND/AIMS

Potassium channel tetramerization domain containing 17 (KCTD17) protein, an adaptor for the cullin3 (Cul3) ubiquitin ligase complex, has been implicated in various human diseases; however, its role in hepatocellular carcinoma (HCC) remains elusive. Here, we aimed to elucidate the clinical features of KCTD17, and investigate the mechanisms by which KCTD17 affects HCC progression.

METHODS

We analyzed transcriptomic data from patients with HCC. Hepatocyte-specific KCTD17 deficient mice were treated with diethylnitrosamine (DEN) to assess its effect on HCC progression. Additionally, we tested KCTD17-directed antisense oligonucleotides for their therapeutic potential in vivo.

RESULTS

Our investigation revealed the upregulation of KCTD17 expression in both tumors from patients with HCC and mouse models of HCC, in comparison to non-tumor controls. We identified the leucine zipper-like transcriptional regulator 1 (Lztr1) protein, a previously identified Ras destabilizer, as a substrate for KCTD17-Cul3 complex. KCTD17-mediated Lztr1 degradation led to Ras stabilization, resulting in increased proliferation, migration, and wound healing in liver cancer cells. Hepatocyte-specific KCTD17 deficient mice or liver cancer xenograft models were less susceptible to carcinogenesis or tumor growth. Similarly, treatment with KCTD17-directed antisense oligonucleotides (ASO) in a mouse model of HCC markedly lowered tumor volume as well as Ras protein levels, compared to those in control ASO-treated mice.

CONCLUSION

KCTD17 induces the stabilization of Ras and downstream signaling pathways and HCC progression and may represent a novel therapeutic target for HCC.

Diabetes mellitus-Progress and opportunities in the evolving epidemic

Diabetes, a complex multisystem metabolic disorder characterized by hyperglycemia, leads to complications that reduce quality of life and increase mortality. Diabetes pathophysiology includes dysfunction of beta cells, adipose tissue, skeletal muscle, and liver. Type 1 diabetes (T1D) results from immune-mediated beta cell destruction. The more prevalent type 2 diabetes (T2D) is a heterogeneous disorder characterized by varying degrees of beta cell dysfunction in concert with insulin resistance. The strong association between obesity and T2D involves pathways regulated by the central nervous system governing food intake and energy expenditure, integrating inputs from peripheral organs and the environment. The risk of developing diabetes or its complications represents interactions between genetic susceptibility and environmental factors, including the availability of nutritious food and other social determinants of health. This perspective reviews recent advances in understanding the pathophysiology and treatment of diabetes and its complications, which could alter the course of this prevalent disorder.

The role of NAD-dependent deacetylase sirtuin-2 in liver metabolic stress through regulating pyruvate kinase M2 ubiquitination

NAD-dependent deacetylase Sirt2 is involved in mammalian metabolic activities, matching energy demand with energy production and expenditure, and is relevant to a variety of metabolic diseases. Here, we constructed Sirt2 knockout and adeno-associated virus overexpression mice and found that deletion of hepatic Sirt2 accelerated primary obesity and insulin resistance in mice with concomitant hepatic metabolic dysfunction. However, the key targets of Sirt2 are unknown. We identified the M2 isoform of pyruvate kinase (PKM2) as a key Sirt2 target involved in glycolysis in metabolic stress. Through yeast two-hybrid and mass spectrometry combined with multi-omics analysis, we identified candidate acetylation modification targets of Sirt2 on PKM2 lysine 135 (K135). The Sirt2-mediated deacetylation-ubiquitination switch of PKM2 regulated the development of glycolysis. Here, we found that Sirt2 deficiency led to impaired glucose tolerance and insulin resistance and induced primary obesity. Sirt2 severely disrupted liver function in mice under metabolic stress, exacerbated the metabolic burden on the liver, and affected glucose metabolism. Sirt2 underwent acetylation modification of lysine 135 of PKM2 through a histidine 187 enzyme active site-dependent effect and reduced ubiquitination of the K48 ubiquitin chain of PKM2. Our findings reveal that the hepatic glucose metabolism links nutrient state to whole-body energetics through the rhythmic regulation of Sirt2.

O-GlcNAcylation of RBM14 contributes to elevated cellular O-GlcNAc through regulation of OGA protein stability

Dysregulation of O-GlcNAcylation has emerged as a potential biomarker for several diseases, particularly cancer. The role of OGT (O-GlcNAc transferase) in maintaining O-GlcNAc homeostasis has been extensively studied; nevertheless, the regulation of OGA (O-GlcNAcase) in cancer remains elusive. Here, we demonstrated that the multifunctional protein RBM14 is a regulator of cellular O-GlcNAcylation. By investigating the correlation between elevated O-GlcNAcylation and increased RBM14 expression in lung cancer cells, we discovered that RBM14 promotes ubiquitin-dependent proteasomal degradation of OGA, ultimately mediating cellular O-GlcNAcylation levels. In addition, RBM14 itself is O-GlcNAcylated at serine 521, regulating its interaction with the E3 ligase TRIM33, consequently affecting OGA protein stability. Moreover, we demonstrated that mutation of serine 521 to alanine abrogated the oncogenic properties of RBM14. Collectively, our findings reveal a previously unknown mechanism for the regulation of OGA and suggest a potential therapeutic target for the treatment of cancers with dysregulated O-GlcNAcylation.

LncRNA Gm28382 promotes lipogenesis by interacting with miR-326-3p to regulate ChREBP signaling pathway in NAFLD

Long non-coding RNAs (lncRNAs) have been demonstrated to play vital roles in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). However, their biological roles and function mechanisms in NAFLD remain largely unknown. In this study, we found that Gm28382 may be a potential pathogenic lncRNA of NAFLD and highly expressed in NAFLD through RNA-seq. Overexpression of Gm28382 significantly enhanced the lipid accumulation in AML12 cells, whereas Gm28382 silencing reduced lipogenesis both in palmitic acid (PA)-induced AML12 cells and high fat diet (HFD)-induced mice. Then, bioinformatics were employed to speculate the potential interacting genes of Gm28382, and found that Gm28382 may regulate ChREBP expression through binding with miR-326-3p. Fluorescence in situ hybridization (FISH), dual luciferase reporter assay, immunofluorescence RNA pull-down and RNA immunoprecipitation (RIP) assays were used to validate the binding and targeting relationship of these genes, and we confirmed that Gm28382 competitively binds to miR-326-3p to increase ChREBP expression as a ceRNA. Mechanistically, overexpression of Gm28382 upregulated the ChREBP-mediated lipid synthesis signaling pathway, but the function was sabotaged by miR-326-3p deletion or ChREBP overexpression. Furthermore, in PA-challenged AML12 cells or HFD-induced mice, silencing of Gm28382 reversed the aberrant ChREBP signaling pathway and lipid accumulation, whereas ChREBP overexpression or liver-specific silencing of miR-326-3p blocked this function of Gm28382. Collectively, these findings reveal a critical role of Gm28382 in the promotion of lipogenesis in NAFLD by regulating the ChREBP signaling pathway through interaction with miR-326-3p, which could serve as a potential therapeutic target for NAFLD treatment.

Unmasking the enigma of lipid metabolism in metabolic dysfunction-associated steatotic liver disease: from mechanism to the clinic

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly defined as non-alcoholic fatty liver disease (NAFLD), is a disorder marked by the excessive deposition of lipids in the liver, giving rise to a spectrum of liver pathologies encompassing steatohepatitis, fibrosis/cirrhosis, and hepatocellular carcinoma. Despite the alarming increase in its prevalence, the US Food and Drug Administration has yet to approve effective pharmacological therapeutics for clinical use. MASLD is characterized by the accretion of lipids within the hepatic system, arising from a disarray in lipid provision (whether through the absorption of circulating lipids or de novo lipogenesis) and lipid elimination (via free fatty acid oxidation or the secretion of triglyceride-rich lipoproteins). This disarray leads to the accumulation of lipotoxic substances, cellular pressure, damage, and fibrosis. Indeed, the regulation of the lipid metabolism pathway is intricate and multifaceted, involving a myriad of factors, such as membrane transport proteins, metabolic enzymes, and transcription factors. Here, we will review the existing literature on the key process of lipid metabolism in MASLD to understand the latest progress in this molecular mechanism. Notably, de novo lipogenesis and the roles of its two main transcription factors and other key metabolic enzymes are highlighted. Furthermore, we will delve into the realm of drug research, examining the recent progress made in understanding lipid metabolism in MASLD. Additionally, we will outline prospective avenues for future drug research on MASLD based on our unique perspectives.

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.

The role of ChREBP in carbohydrate sensing and NAFLD development

Excessive sugar consumption and defective glucose sensing by hepatocytes contribute to the development of metabolic diseases including type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD). Hepatic metabolism of carbohydrates into lipids is largely dependent on the carbohydrate-responsive element binding protein (ChREBP), a transcription factor that senses intracellular carbohydrates and activates many different target genes, through the activation of de novo lipogenesis (DNL). This process is crucial for the storage of energy as triglycerides in hepatocytes. Furthermore, ChREBP and its downstream targets represent promising targets for the development of therapies for the treatment of NAFLD and T2DM. Although lipogenic inhibitors (for example, inhibitors of fatty acid synthase, acetyl-CoA carboxylase or ATP citrate lyase) are currently under investigation, targeting lipogenesis remains a topic of discussion for NAFLD treatment. In this Review, we discuss mechanisms that regulate ChREBP activity in a tissue-specific manner and their respective roles in controlling DNL and beyond. We also provide in-depth discussion of the roles of ChREBP in the onset and progression of NAFLD and consider emerging targets for NAFLD therapeutics.