p53 mediated regulation of coactivator associated arginine methyltransferase 1 (CARM1) expression is critical for suppression of adipogenesis

Deciphering adipose development: Function, differentiation and regulation

The overdevelopment of adipose tissues, accompanied by excess lipid accumulation and energy storage, leads to adipose deposition and obesity. With the increasing incidence of obesity in recent years, obesity is becoming a major risk factor for human health, causing various relevant diseases (including hypertension, diabetes, osteoarthritis and cancers). Therefore, it is of significance to antagonize obesity to reduce the risk of obesity-related diseases. Excess lipid accumulation in adipose tissues is mediated by adipocyte hypertrophy (expansion of pre-existing adipocytes) or hyperplasia (increase of newly-formed adipocytes). It is necessary to prevent excessive accumulation of adipose tissues by controlling adipose development. Adipogenesis is exquisitely regulated by many factors in vivo and in vitro, including hormones, cytokines, gender and dietary components. The present review has concluded a comprehensive understanding of adipose development including its origin, classification, distribution, function, differentiation and molecular mechanisms underlying adipogenesis, which may provide potential therapeutic strategies for harnessing obesity without impairing adipose tissue function.

Regulation of adipogenesis by histone methyltransferases

Epigenetic regulation is a critical component of lineage determination. Adipogenesis is the process through which uncommitted stem cells or adipogenic precursor cells differentiate into adipocytes, the most abundant cell type of the adipose tissue. Studies examining chromatin modification during adipogenesis have provided further understanding of the molecular blueprint that controls the onset of adipogenic differentiation. Unlike histone acetylation, histone methylation has context dependent effects on the activity of a transcribed region of DNA, with individual or combined marks on different histone residues providing distinct signals for gene expression. Over half of the 42 histone methyltransferases identified in mammalian cells have been investigated in their role during adipogenesis, but across the large body of literature available, there is a lack of clarity over potential correlations or emerging patterns among the different players. In this review, we will summarize important findings from studies published in the past 15 years that have investigated the role of histone methyltransferases during adipogenesis, including both protein arginine methyltransferases (PRMTs) and lysine methyltransferases (KMTs). We further reveal that PRMT1/4/5, H3K4 KMTs (MLL1, MLL3, MLL4, SMYD2 and SET7/9) and H3K27 KMTs (EZH2) all play positive roles during adipogenesis, while PRMT6/7 and H3K9 KMTs (G9a, SUV39H1, SUV39H2, and SETDB1) play negative roles during adipogenesis.

A CRISPR-Cas9 library screening identifies CARM1 as a critical inhibitor of ferroptosis in hepatocellular carcinoma cells

Ferroptosis is an iron-catalyzed form of regulated cell death that results from the accumulation of lipid peroxidation products and reactive oxygen species to a lethal content. However, the transcriptional regulation of ferroptosis is not well understood. Sorafenib, a standard drug for hepatocellular carcinoma (HCC), induces ferroptosis in HCC cells. In this study, we conducted a CRISPR-Cas9 library screening targeting epigenetic factors and identified coactivator-associated arginine methyltransferase 1 (CARM1) as a critical inhibitor of ferroptosis. CARM1 depletion intensified Sorafenib-induced ferroptosis, resulting in decreased cell viability, reduced cellular glutathione level, increased lipid peroxidation, and altered mitochondrial crista structure. Additionally, we investigated a CARM1 inhibitor (CARM1i) as a potential ferroptosis inducer. Combining the CARM1i with Sorafenib enhanced the induction of ferroptosis. Notably, both CARM1 knockdown and CARM1i showed cooperative effects with Sorafenib in inhibiting HCC growth in mice. The underlying mechanism involves CARM1-catalyzed H3R26me2a on the promoter of glutathione peroxidase 4, leading to its transcriptional activation and subsequent ferroptosis inhibition. Furthermore, Sorafenib treatment induced the transcription of CARM1 through the MDM2-p53 axis. In summary, our findings establish CARM1 as a critical ferroptosis inhibitor and highlight the potential of CARM1is as novel ferroptosis inducers, providing promising therapeutic strategies for HCC treatment.

PRMT4 Facilitates White Adipose Tissue Browning and Thermogenesis by Methylating PPARγ

Obesity is a global health threat, and the induction of white adipose tissue (WAT) browning presents a promising therapeutic method for it. Recent publications revealed the essential role of protein arginine methyltransferase 4 (PRMT4) in lipid metabolism and adipogenesis, but its involvement in WAT browning has not been investigated. Our initial studies found that the expression of PRMT4 in adipocytes was upregulated in cold-induced WAT browning but downregulated in obesity. Besides, PRMT4 overexpression in inguinal adipose tissue accelerated WAT browning and thermogenesis to protect against high-fat diet-induced obesity and metabolic disruptions. Mechanistically, our work demonstrated that PRMT4 methylated peroxisome proliferator-activated receptor-γ (PPARγ) on Arg240 to enhance its interaction with the coactivator PR domain-containing protein 16 (PRDM16), leading to the increased expression of thermogenic genes. Taken together, our results uncover the essential role of the PRMT4/PPARγ/PRDM16 axis in the pathogenesis of WAT browning.

ARTICLE HIGHLIGHTS

Protein arginine methyltransferase 4 (PRMT4) expression was upregulated during cold exposure and negatively correlated with body mass of mice and humans. PRMT4 overexpression in inguinal white adipose tissue of mice improved high-fat diet-induced obesity and associated metabolic impairment due to enhanced heat production. PRMT4 methylated peroxisome proliferator-activated receptor-γ on Arg240 and facilitated the binding of the coactivator PR domain-containing protein 16 to initiate adipose tissue browning and thermogenesis. PRMT4-dependent methylation of peroxisome proliferator-activated receptor-γ on Arg240 is important in the process of inguinal white adipose tissue browning.

Unraveling the complexity of histone-arginine methyltransferase CARM1 in cancer: From underlying mechanisms to targeted therapeutics

Coactivator-associated arginine methyltransferase 1 (CARM1), a type I protein arginine methyltransferase (PRMT), has been widely reported to catalyze arginine methylation of histone and non-histone substrates, which is closely associated with the occurrence and progression of cancer. Recently, accumulating studies have demonstrated the oncogenic role of CARM1 in many types of human cancers. More importantly, CARM1 has been emerging as an attractive therapeutic target for discovery of new candidate anti-tumor drugs. Therefore, in this review, we summarize the molecular structure of CARM1 and its key regulatory pathways, as well as further discuss the rapid progress in better understanding of the oncogenic functions of CARM1. Moreover, we further demonstrate several representative targeted CARM1 inhibitors, especially focusing on demonstrating their designing strategies and potential therapeutic applications. Together, these inspiring findings would shed new light on elucidating the underlying mechanisms of CARM1 and provide a clue on discovery of more potent and selective CARM1 inhibitors for the future targeted cancer therapy.

Emphasis on Adipocyte Transformation: Anti-Inflammatory Agents to Prevent the Development of Cancer-Associated Adipocytes

Of the various cell types in the tumor microenvironment (TME), adipocytes undergo a dynamic transformation when activated by neighboring cancer cells. Although these adipocytes, known as cancer-associated adipocytes (CAAs), have been reported to play a crucial role in tumor progression, the factors that mediate their transformation remain elusive. In this review, we discuss the hypothesis that inflammatory signals involving NF-ĸB activation can induce lipolysis and adipocyte dedifferentiation. This provides a mechanistic understanding of CAA formation and introduces the concept of preventing adipocyte transformation via anti-inflammatory agents. Indeed, epidemiological studies indicate a higher efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) in obese patients with cancer, suggesting that NSAIDs can modulate the TME. Inhibition of cyclooxygenase-2 (COX-2) and prostaglandin production leads to the suppression of inflammatory signals such as NF-ĸB. Thus, we suggest the use of NSAIDs in cancer patients with metabolic disorders to prevent the transformation of TME components. Moreover, throughout this review, we attempt to expand our knowledge of CAA transformation to improve the clinical feasibility of targeting CAAs.

p53 regulates lipid metabolism in cancer

Reprogrammed cell metabolism is a well-accepted hallmark of cancer. Metabolism changes provide energy and precursors for macromolecule biosynthesis to satisfy the survival needs of cancer cells. The specific changes in different aspects of lipid metabolism in cancer cells have been focused in recent years. These changes can affect cell growth, proliferation, differentiation and motility through affecting membranes synthesis, energy homeostasis and cell signaling. The tumor suppressor p53 plays vital roles in the control of cell proliferation, senescence, DNA repair, and cell death in cancer through various transcriptional and non-transcriptional activities. Accumulating evidences indicate that p53 also regulates cellular metabolism, which appears to contribute to its tumor suppressive functions. Particularly the role of p53 in regulating lipid metabolism has gained more and more attention in recent decades. In this review, we summarize recent advances in the function of p53 on lipid metabolism in cancer. Further understanding and research on the role of p53 in lipid metabolism regulation will provide a potential therapeutic window for cancer treatment.

PRMT4 inhibitor TP-064 impacts both inflammatory and metabolic processes without changing the susceptibility for early atherosclerotic lesions in male apolipoprotein E knockout mice

BACKGROUND AND AIMS

Atherosclerotic cardiovascular disease is a metabolic and inflammatory disorder. In vitro studies have suggested that protein arginine methyltransferase 4 (PRMT4) may act as a transcriptional coactivator to modulate inflammatory and metabolic processes. Here we investigated the potential anti-atherogenic effect of PRMT4 inhibitor TP-064 in vivo.

METHODS

Male apolipoprotein E knockout mice fed a high cholesterol/high fat Western-type diet were intraperitoneally injected three times a week with 2.5 mg/kg (low dose) or 10 mg/kg (high dose) TP-064 or with DMSO control.

RESULTS

TP-064 induced a dose-dependent decrease in lipopolysaccharide-induced ex vivo blood monocyte Tnfα secretion (p < 0.05 for trend) in the context of unchanged blood monocyte concentrations and neutrophilia induction (p < 0.01 for trend). A dose-dependent decrease in gonadal white adipose tissue expression levels of PPARγ target genes was detected, which translated into a reduced body weight gain after high dose TP-064 treatment (p < 0.05). TP-064 treatment also dose-dependently downregulated gene expression of the glycogen metabolism related protein G6pc in the liver (p < 0.001 for trend). In addition, a trend towards lower plasma insulin and higher blood glucose levels was observed, which was paralleled by a reduction in hepatic mRNA expression levels of the insulin-responsive genes Fasn (-55%; p < 0.001) and Gck (-47%; p < 0.001) in high dose-treated mice. Plasma triglyceride levels were reduced by high dose TP-064 treatment (-30%; p < 0.05). However, no change was observed in the size or composition of aortic root atherosclerotic lesions.

CONCLUSIONS

The PRMT4 inhibitor TP-064 impacts both inflammatory and metabolic processes without changing atherosclerosis susceptibility of male apolipoprotein E knockout mice.

Mechanisms Mediating the Regulation of Peroxisomal Fatty Acid Beta-Oxidation by PPARα

In mammalian cells, two cellular organelles, mitochondria and peroxisomes, share the ability to degrade fatty acid chains. Although each organelle harbors its own fatty acid β-oxidation pathway, a distinct mitochondrial system feeds the oxidative phosphorylation pathway for ATP synthesis. At the same time, the peroxisomal β-oxidation pathway participates in cellular thermogenesis. A scientific milestone in 1965 helped discover the hepatomegaly effect in rat liver by clofibrate, subsequently identified as a peroxisome proliferator in rodents and an activator of the peroxisomal fatty acid β-oxidation pathway. These peroxisome proliferators were later identified as activating ligands of Peroxisome Proliferator-Activated Receptor α (PPARα), cloned in 1990. The ligand-activated heterodimer PPARα/RXRα recognizes a DNA sequence, called PPRE (Peroxisome Proliferator Response Element), corresponding to two half-consensus hexanucleotide motifs, AGGTCA, separated by one nucleotide. Accordingly, the assembled complex containing PPRE/PPARα/RXRα/ligands/Coregulators controls the expression of the genes involved in liver peroxisomal fatty acid β-oxidation. This review mobilizes a considerable number of findings that discuss miscellaneous axes, covering the detailed expression pattern of PPARα in species and tissues, the lessons from several PPARα KO mouse models and the modulation of PPARα function by dietary micronutrients.

Arsenic exposure increased expression of HOTAIR and LincRNA-p21 in vivo and vitro

Arsenic is an environmental contaminant, its multiple effects on human tend to increase the rate of disease, cancer and other health problems. Some of long non-coding RNAs (lncRNAs) can be induced in major cellular processes such as necrosis, proliferation, and mutation. While the toxicity of arsenic is well established, the association between arsenic exposure and long non-coding RNAs has not been studied enough. This study investigated the association between arsenic and the expression of HOTAIR and LincRNA-p21 in vivo and vitro. In epidemiological studies, the expression of HOTAIR and LincRNA-p21 was increased after long-term arsenic exposure. HOTAIR and LincRNA-p21 expression were positively linked to monomethylarsenic acid (MMA), dimethylarsenic acid (DMA), inorganic arsenic (iAs), total arsenic (tAs), and MMA% and negatively linked to secondary methylation index (SMI). In A549 cells, arsenic exposure resulted in enhanced HOTAIR and LincRNA-p21 expression dose-dependently. The expression of HOTAIR was considerably high in the presence of NaAsO₂ and MMA but showed no difference in DMA compared with control group. And LincRNA-p21 expression was increased in the presence of NaAsO₂, MMA, and DMA. The expression of HOTAIR and LincRNA-p21 induced by iAs was much higher than that induced by MMA and DMA. Compared with the control group, treatment of A549 cells with NaAsO₂/S-adenosylmethionine (SAM) and NaAsO₂/glutathione (GSH) combination increased HOTAIR and LincRNA-p21 expression. The expression of LincRNA-p21 in combination of NaAsO₂/GSH was significantly decreased compared with NaAsO₂ alone. Besides, in the presence of arsenic, both of HOTAIR and LincRNA-p21 were upregulated significantly when P53 was knocked down. We revealed that inorganic arsenic, its methylated metabolites, and arsenic metabolism efficiency affect the expression of HOTAIR and LincRNA-p21.

Aging-associated skeletal muscle defects in HER2/Neu transgenic mammary tumor model

BACKGROUND

Loss of skeletal muscle volume and resulting in functional limitations are poor prognostic markers in breast cancer patients. Several molecular defects in skeletal muscle including reduced MyoD levels and increased protein turn over due to enhanced proteosomal activity have been suggested as causes of skeletal muscle loss in cancer patients. However, it is unknown whether molecular defects in skeletal muscle are dependent on tumor etiology.

METHODS

We characterized functional and molecular defects of skeletal muscle in MMTV-Neu (Neu+) mice (n= 6-12), an animal model that represents HER2+ human breast cancer, and compared the results with well-characterized luminal B breast cancer model MMTV-PyMT (PyMT+). Functional studies such as grip strength, rotarod performance, and ex vivo muscle contraction were performed to measure the effects of cancer on skeletal muscle. Expression of muscle-enriched genes and microRNAs as well as circulating cytokines/chemokines were measured. Since NF-κB pathway plays a significant role in skeletal muscle defects, the ability of NF-κB inhibitor dimethylaminoparthenolide (DMAPT) to reverse skeletal muscle defects was examined.

RESULTS

Neu+ mice showed skeletal muscle defects similar to accelerated aging. Compared to age and sex-matched wild type mice, Neu+ tumor-bearing mice had lower grip strength (202±6.9 vs. 179±6.8 g grip force, p=0.0069) and impaired rotarod performance (108±12.1 vs. 30±3.9 seconds, P<0.0001), which was consistent with reduced muscle contractibility (p<0.0001). Skeletal muscle of Neu+ mice (n=6) contained lower levels of CD82+ (16.2±2.9 vs 9.0±1.6) and CD54+ (3.8±0.5 vs 2.4±0.4) muscle stem and progenitor cells (p<0.05), suggesting impaired capacity of muscle regeneration, which was accompanied by decreased MyoD, p53 and miR-486 expression in muscles (p<0.05). Unlike PyMT+ mice, which showed skeletal muscle mitochondrial defects including reduced mitochondria levels and Pgc1β, Neu+ mice displayed accelerated aging-associated changes including muscle fiber shrinkage and increased extracellular matrix deposition. Circulating "aging factor" and cachexia and fibromyalgia-associated chemokine Ccl11 was elevated in Neu+ mice (1439.56±514 vs. 1950±345 pg/ml, p<0.05). Treatment of Neu+ mice with DMAPT significantly restored grip strength (205±6 g force), rotarod performance (74±8.5 seconds), reversed molecular alterations associated with skeletal muscle aging, reduced circulating Ccl11 (1083.26 ±478 pg/ml), and improved animal survival.

CONCLUSIONS

These results suggest that breast cancer subtype has a specific impact on the type of molecular and structure changes in skeletal muscle, which needs to be taken into consideration while designing therapies to reduce breast cancer-induced skeletal muscle loss and functional limitations.

The Intricate Role of p53 in Adipocyte Differentiation and Function

For more than three decades, numerous studies have demonstrated the function of p53 in cell cycle, cellular senescence, autophagy, apoptosis, and metabolism. Among diverse functions, the essential role of p53 is to maintain cellular homeostatic response to stress by regulating proliferation and apoptosis. Recently, adipocytes have been studied with increasing intensity owing to the increased prevalence of metabolic diseases posing a serious public health concern and because metabolic dysfunction can directly induce tumorigenesis. The prevalence of metabolic diseases has steadily increased worldwide, and a growing interest in these diseases has led to the focus on the role of p53 in metabolism and adipocyte differentiation with or without metabolic stress. However, our collective understanding of the direct role of p53 in adipocyte differentiation and function remains insufficient. Therefore, this review focuses on the newly discovered roles of p53 in adipocyte differentiation and function.

Regulation of metabolic reprogramming by tumor suppressor genes in pancreatic cancer

Background

Pancreatic cancer continues to be one of the most aggressive malignant tumors. Work in recent years in cancer molecular biology has revealed that metabolic reprogramming is an additional hallmark of cancer that is involved in the pathogenesis of cancers, and is intricately linked to gene mutations.

Main text

However, though oncogenes such as KRAS and c-Myc play important roles in the process, and have been extensively studied, no substantial improvements in the prognosis of pancreatic cancer have seen. Therefore, some scientists have tried to explain the mechanisms of abnormal cancer metabolism from the perspective of tumor suppressor genes. In this paper, we reviewed researches about how metabolic reprogramming was regulated by tumor suppressor genes in pancreatic cancer and their clinical implications.

Conclusion

Abnormal metabolism and genetic mutations are mutually causal and complementary in tumor initiation and development. A clear understanding of how metabolic reprogramming is regulated by the mutated genes would provide important insights into the pathogenesis and ultimately treatment of pancreatic cancer.

The CARM1-p300-c-Myc-Max (CPCM) transcriptional complex regulates the expression of CUL4A/4B and affects the stability of CRL4 E3 ligases in colorectal cancer

The transcription factor c-Myc and two cullin family members CUL4A/4B function as oncogenes in colorectal cancer. Our recent publication reveals that c-Myc specifically activates the expression of CUL4A/4B through binding to their promoters. However, the underlying mechanism of how c-Myc actions in this process is still unknown. Using mass spectrometry and immunoprecipitation assays, we identified c-Myc formed a transcriptional complex with its partner Max (Myc-associated factor X), a histone acetyltransferase p300 and a coactivator associated arginine methyltransferase 1 (CARM1) in the present study. Knockdown or overexpression of the components of CARM1-p300-c-Myc-Max (CPCM) complex resulted in a decrease or increase of CUL4A/4B levels, respectively. Individual knockdown or inhibition of CPCM components decreased cell proliferation, colony formation, and cell invasion. Biochemically, knockdown or inhibition of CPCM components decreased their occupancies on the promoters of CUL4A/4B and resulted in their downregulation. Importantly, inhibition of CPCM components also caused a decrease of CRL4 E3 ligase activities and eventually led to an accumulation of ST7 (suppression of tumorigenicity 7), the specific substrate of CRL4 E3 ligases in colorectal cancer. Moreover, the in vivo tumor formation results indicated that knockdown or inhibition of CPCM components significantly decreased the tumor volumes. Together, our results suggest that the CPCM complex mediates explicitly the expression of CUL4A/4B, and thus affects the stability of CRL4 E3 ligases and the ubiquitination of ST7. These results provide more options by targeting the CPCM components to inhibit tumor growth in the therapy of colorectal cancer.

Protein Arginine Methyltransferase 4 Regulates Adipose Tissue Lipolysis in Type 1 Diabetic Mice

PURPOSE

Hypertriglyceridemia is considered to be driven by increased lipolysis in type 1 diabetes mellitus (T1DM). However, information regarding the transcriptional circuitry that governs lipolysis remains incomplete in T1DM. Protein arginine methyltransferase 4 (PRMT4), a transcriptional coactivation factor, promotes autophagy and may play an important role in lipolysis. We wonder whether activated lipolysis in T1DM is regulated by PRMT4.

MATERIALS AND METHODS

Recombinant adeno-associated virus was adopted to overexpress PRMT4 in adipose tissue of mice. Streptozotocin (150 mg/kg) was injected intraperitoneally into mice to induce T1DM. Plasma insulin, triglycerides, free fatty acids (FFAs) levels were determined using commercial assay kits. Differentiated adipocytes were applied to verify the regulation of PRMT4 on lipolysis.

RESULTS

Elevated serum triglycerides and FFAs were observed in PRMT4-overexpressed T1DM mice. We also observed that PRMT4 over-expression induced the decrease of fat pads weights and adipocyte sizes. Moreover, expression levels of lipolysis-related molecules, including ATGL, HSL, and MAGL, and HSL phosphorylation levels were increased in PRMT4-overexpressed mice when compared to those of control mice. In vitro, PRMT4 promoted FFAs release and activated HSL phosphorylation, whereas PRMT4 knockdown inhibited these processes.

CONCLUSION

PRMT4 promotes lipolysis and increases serum triglyceride in T1DM.

p53 Functions in Adipose Tissue Metabolism and Homeostasis

As a tumor suppressor and the most frequently mutated gene in cancer, p53 is among the best-described molecules in medical research. As cancer is in most cases an age-related disease, it seems paradoxical that p53 is so strongly conserved from early multicellular organisms to humans. A function not directly related to tumor suppression, such as the regulation of metabolism in nontransformed cells, could explain this selective pressure. While this role of p53 in cellular metabolism is gradually emerging, it is imperative to dissect the tissue- and cell-specific actions of p53 and its downstream signaling pathways. In this review, we focus on studies reporting p53’s impact on adipocyte development, function, and maintenance, as well as the causes and consequences of altered p53 levels in white and brown adipose tissue (AT) with respect to systemic energy homeostasis. While whole body p53 knockout mice gain less weight and fat mass under a high-fat diet owing to increased energy expenditure, modifying p53 expression specifically in adipocytes yields more refined insights: (1) p53 is a negative regulator of in vitro adipogenesis; (2) p53 levels in white AT are increased in diet-induced and genetic obesity mouse models and in obese humans; (3) functionally, elevated p53 in white AT increases senescence and chronic inflammation, aggravating systemic insulin resistance; (4) p53 is not required for normal development of brown AT; and (5) when p53 is activated in brown AT in mice fed a high-fat diet, it increases brown AT temperature and brown AT marker gene expression, thereby contributing to reduced fat mass accumulation. In addition, p53 is increasingly being recognized as crucial player in nutrient sensing pathways. Hence, despite existence of contradictory findings and a varying density of evidence, several functions of p53 in adipocytes and ATs have been emerging, positioning p53 as an essential regulatory hub in ATs. Future studies need to make use of more sophisticated in vivo model systems and should identify an AT-specific set of p53 target genes and downstream pathways upon different (nutrient) challenges to identify novel therapeutic targets to curb metabolic diseases.