The phosphorylation-dependent regulation of nuclear SREBP1 during mitosis links lipid metabolism and cell growth

The roles and mechanisms of SREBP1 in cancer development and drug response

Cancer occurrence and development are closely related to increased lipid production and glucose consumption. Lipids are the basic component of the cell membrane and play a significant role in cancer cell processes such as cell-to-cell recognition, signal transduction, and energy supply, which are vital for cancer cell rapid proliferation, invasion, and metastasis. Sterol regulatory element-binding transcription factor 1 (SREBP1) is a key transcription factor regulating the expression of genes related to cholesterol biosynthesis, lipid homeostasis, and fatty acid synthesis. In addition, SREBP1 and its upstream or downstream target genes are implicated in various metabolic diseases, particularly cancer. However, no review of SREBP1 in cancer biology has yet been published. Herein, we summarized the roles and mechanisms of SREBP1 biological processes in cancer cells, including SREBP1 modification, lipid metabolism and reprogramming, glucose and mitochondrial metabolism, immunity, and tumor microenvironment, epithelial-mesenchymal transition, cell cycle, apoptosis, and ferroptosis. Additionally, we discussed the potential role of SREBP1 in cancer prognosis, drug response such as drug sensitivity to chemotherapy and radiotherapy, and the potential drugs targeting SREBP1 and its corresponding pathway, elucidating the potential clinical application based on SREBP1 and its corresponding signal pathway.

Lipid metabolism dynamics in cancer stem cells: potential targets for cancers

Cancer stem cells (CSCs) represent a small subset of heterogeneous cells within tumors that possess the ability to self-renew and initiate tumorigenesis. They serve as potential drivers for tumor initiation, metastasis, recurrence, and drug resistance. Recent research has demonstrated that the stemness preservation of CSCs is heavily reliant on their unique lipid metabolism alterations, enabling them to maintain their own environmental homeostasis through various mechanisms. The primary objectives involve augmenting intracellular fatty acid (FA) content to bolster energy supply, promoting β-oxidation of FA to optimize energy utilization, and elevating the mevalonate (MVA) pathway for efficient cholesterol synthesis. Additionally, lipid droplets (LDs) can serve as alternative energy sources in the presence of glycolysis blockade in CSCs, thereby safeguarding FA from peroxidation. Furthermore, the interplay between autophagy and lipid metabolism facilitates rapid adaptation of CSCs to the harsh microenvironment induced by chemotherapy. In this review, we comprehensively review recent studies pertaining to lipid metabolism in CSCs and provide a concise overview of the indispensable role played by LDs, FA, cholesterol metabolism, and autophagy in maintaining the stemness of CSCs.

MED15 is upregulated by HIF-2α and promotes proliferation and metastasis in clear cell renal cell carcinoma via activation of SREBP-dependent fatty acid synthesis

Emerging evidence has highlighted that dysregulation of lipid metabolism in clear cell renal cell carcinoma (ccRCC) is associated with tumor development and progression. HIF-2α plays an oncogenic role in ccRCC and is involved in abnormal lipid accumulation. However, the underlying mechanisms between these two phenomena remain unknown. Here, MED15 was demonstrated to be a dominant factor for HIF-2α-dependent lipid accumulation and tumor progression. HIF-2α promoted MED15 transcriptional activation by directly binding the MED15 promoter region, and MED15 overexpression significantly alleviated the lipid deposition inhibition and malignant tumor behavior phenotypes induced by HIF-2α knockdown. MED15 was upregulated in ccRCC and predicted poor prognosis. MED15 promoted lipid deposition and tumor progression in ccRCC. Mechanistic investigations demonstrated that MED15 acts as SREBP coactivator directly interacting with SREBPs to promote SREBP-dependent lipid biosynthesis enzyme expression, and promotes SREBP1 and SREBP2 activation through the PLK1/AKT axis. Overall, we describe a molecular regulatory network that links MED15 to lipid metabolism induced by the SREBP pathway and the classic HIF-2α pathway in ccRCC. Efforts to target MED15 or inhibit MED15 binding to SREBPs as a novel therapeutic strategy for ccRCC may be warranted.

AMP deaminase: A crucial regulator in nitrogen stress and lipid metabolism in Mucor circinelloides

Lipid biosynthesis is a significant metabolic response to nitrogen starvation in oleaginous fungi. The oleaginous fungus Mucor circinelloides copes with nitrogen stress by degrading AMP through AMP deaminase (AMPD). However, the mechanism of AMPD in regulating lipogenesis remains largely unclear. To elucidate the mechanism of AMPD in lipid synthesis in this M. circinelloides, we identified two genes (ampd1 and ampd2) encoding AMPD and constructed an ampd double knockout mutant. The engineered M. circinelloides strain elevated cell growth and lipid accumulation, as well as the content of oleic acid (OA) and gamma-linolenic acid (GLA). In addition to the expected increase in transcription levels of genes associated with lipid and TAG synthesis, we observed suppression of lipid degradation and reduced amino acid biosynthesis. This suggested that the deletion of AMPD genes induces the redirection of carbon towards lipid synthesis pathways. Moreover, the pathways related to nitrogen metabolism, including nitrogen assimilation and purine metabolism (especially energy level), were also affected in order to maintain homeostasis. Further analysis discovered that the transcription factors (TFs) related to lipid accumulation were also regulated. This study provides new insights into lipid biosynthesis in M. circinelloides, indicating that the trigger for lipid accumulation is not entirely AMPD-dependent and suggest that there may be additional mechanisms involved in the initiation of lipogenesis.

Let-7a-5p Regulates Animal Lipid Accumulation by Targeting Srebf2 and Thbs1 Signaling

Recently, the trend of obesity is becoming increasingly prevalent, and the underlying pathogenesis of obesity is complex and needs to be researched further. In this study, we report a decreased expression of let-7a-5p in the white adipose tissue (WAT) of animals with obesity. Using the RNA oligo, let-7a-5p over-expression or suppression-expression is achieved, impacting the proliferation and differentiation of preadipocytes in vitro. Srebf2 mechanistically interacts with the metabolic effect of let-7a-5p and participates in lipid accumulation by regulating Srebf2 downstream signaling. Moreover, let-7a-5p binds to Thbs1 to interact with the PI3K-AKT-mTOR pathway, down-regulating the phosphorylation levels of AKT, mTOR, and S6K1 to decrease lipid accumulation. In conclusion, our study highlights the physiological significance of let-7a-5p in lipid accumulation and suggests that the let-7a-5p/Srebf2 and let-7a-5p/Thbs1/PI3K-AKT-mTOR axes may represent potential mechanisms for controlling lipid accumulation in obesity.

Key events in cancer: Dysregulation of SREBPs

Lipid metabolism reprogramming is an important hallmark of tumor progression. Cancer cells require high levels of lipid synthesis and uptake not only to support their continued replication, invasion, metastasis, and survival but also to participate in the formation of biological membranes and signaling molecules. Sterol regulatory element binding proteins (SREBPs) are core transcription factors that control lipid metabolism and the expression of important genes for lipid synthesis and uptake. A growing number of studies have shown that SREBPs are significantly upregulated in human cancers and serve as intermediaries providing a mechanistic link between lipid metabolism reprogramming and malignancy. Different subcellular localizations, including endoplasmic reticulum, Golgi, and nucleus, play an indispensable role in regulating the cleavage maturation and activity of SREBPs. In this review, we focus on the relationship between aberrant regulation of SREBPs activity in three organelles and tumor progression. Because blocking the regulation of lipid synthesis by SREBPs has gradually become an important part of tumor therapy, this review also summarizes and analyzes several current mainstream strategies.

LncRNA HOXB-AS3 binding to PTBP1 protein regulates lipid metabolism by targeting SREBP1 in endometrioid carcinoma

Endometrial cancer (EC) is a malignant tumor with a high incidence in women, and the survival rate of high-risk patients decreases significantly after disease progression. The regulatory role of long non-coding RNAs (LncRNAs) in tumors has been widely appreciated, but there have been few studies in EC. To investigate the effect of HOXB-AS3 in EC, we used bioinformatics tools for prediction and collected clinical samples to detect the expression of HOXB-AS3. Colony formation assay, MTT assay, flow cytometry and apoptosis assay, and transwell assay were used to verify the role of HOXB-AS3 in EC. HOXB-AS3 was upregulated in EC, promoted the proliferation and invasive ability of EC cells, and inhibited apoptosis. In addition, the ROC curve illustrated its diagnostic value. We explored experiments via lentiviral transduction, FISH, Oil Red O staining, TC and FFA content detection, RNA-pulldown, RIP, and other mechanisms to reveal that HOXB-AS3 can bind to PTBP1 and co-regulate the expression of SREBP1, thereby regulating lipid metabolism in EC cells. To the best of our knowledge, this is the first study on HOXB-AS3 in disorders of lipid metabolism in EC. In addition, we believe HOXB-AS3 has the potential to be a neoplastic marker or a therapeutic target.

Integrative Proteomics and Phosphoproteomics Analysis of the Rat Adenohypophysis after GnRH Treatment

The regulation of mammalian reproductive activity is tightly dependent on the HPG axis crosstalk, in which several reproductive hormones play important roles. Among them, the physiological functions of gonadotropins are gradually being uncovered. However, the mechanisms by which GnRH regulates FSH synthesis and secretion still need to be more extensively and deeply explored. With the gradual completion of the human genome project, proteomes have become extremely important in the fields of human disease and biological process research. To explore the changes of protein and protein phosphorylation modifications in the adenohypophysis after GnRH stimulation, proteomics and phosphoproteomics analyses of rat adenohypophysis after GnRH treatment were performed by using TMT markers, HPLC classification, LC/MS, and bioinformatics analysis in this study. A total of 6762 proteins and 15,379 phosphorylation sites contained quantitative information. Twenty-eight upregulated proteins and fifty-three downregulated proteins were obtained in the rat adenohypophysis after GnRH treatment. The 323 upregulated phosphorylation sites and 677 downregulated phosphorylation sites found in the phosphoproteomics implied that a large number of phosphorylation modifications were regulated by GnRH and were involved in FSH synthesis and secretion. These data constitute a protein-protein phosphorylation map in the regulatory mechanism of "GnRH-FSH," which provides a basis for future studies on the complex molecular mechanisms of FSH synthesis and secretion. The results will be helpful for understanding the role of GnRH in the development and reproduction regulated by the pituitary proteome in mammals.

Loss of the Fbw7 tumor suppressor rewires cholesterol metabolism in cancer cells leading to activation of the PI3K-AKT signalling axis

The sterol regulatory-element binding proteins (SREBPs) are transcription factors controlling cholesterol and fatty acid synthesis and metabolism. There are three SREBP proteins, SREBP1a, SREBP1c and SREBP2, with SREBP1a being the strongest transcription factor. The expression of SREBP1a is restricted to rapidly proliferating cells, including cancer cells. The SREBP proteins are translated as large, inactive precursors bound to the endoplasmic reticulum (ER) membranes. These precursors undergo a two-step cleavage process that releases the amino terminal domains of the proteins, which translocate to the nucleus and function as transcription factors. The nuclear forms of the SREBPs are rapidly degraded by the ubiquitin-proteasome system in a manner dependent on the Fbw7 ubiquitin ligase. Consequently, inactivation of Fbw7 results in the stabilization of active SREBP1 and SREBP2 and enhanced expression of target genes. We report that the inactivation of Fbw7 in cancer cells blocks the proteolytic maturation of SREBP2. The same is true in cells expressing a cancer-specific loss-of-function Fbw7 protein. Interestingly, the activation of SREBP2 is restored in response to cholesterol depletion, suggesting that Fbw7-deficient cells accumulate cholesterol. Importantly, inactivation of SREBP1 in Fbw7-deficient cells also restores the cholesterol-dependent regulation of SREBP2, suggesting that the stabilization of active SREBP1 molecules could be responsible for the blunted activation of SREBP2 in Fbw7-deficient cancer cells. We suggest that this could be an important negative feedback loop in cancer cells with Fbw7 loss-of-function mutations to protect these cells from the accumulation of toxic levels of cholesterol and/or cholesterol metabolites. Surprisingly, we also found that the inactivation of Fbw7 resulted in the activation of AKT. Importantly, the activation of AKT was dependent on SREBP1 and on the accumulation of cholesterol. Thus, we suggest that the loss of Fbw7 rewires lipid metabolism in cancer cells to support cell proliferation and survival.

Posttranslational control of lipogenesis in the tumor microenvironment

Metabolic reprogramming of cancer cells within the tumor microenvironment typically occurs in response to increased nutritional, translation and proliferative demands. Altered lipid metabolism is a marker of tumor progression that is frequently observed in aggressive tumors with poor prognosis. Underlying these abnormal metabolic behaviors are posttranslational modifications (PTMs) of lipid metabolism-related enzymes and other factors that can impact their activity and/or subcellular localization. This review focuses on the roles of these PTMs and specifically on how they permit the re-wiring of cancer lipid metabolism, particularly within the context of the tumor microenvironment.

The SREBP-dependent regulation of cyclin D1 coordinates cell proliferation and lipid synthesis

The sterol regulatory-element binding protein (SREBP) family of transcription factors regulates cholesterol, fatty acid, and triglyceride synthesis and metabolism. However, they are also targeted by the ubiquitin ligase Fbw7, a major tumor suppressor, suggesting that they could regulate cell growth. Indeed, enhanced lipid synthesis is a hallmark of many human tumors. Thus, the SREBP pathway has recently emerged as a potential target for cancer therapy. We have previously demonstrated that one of these transcription factors, SREBP1, is stabilized and remains associated with target promoters during mitosis, suggesting that the expression of these target genes could be important as cells enter G1 and transcription is restored. Activation of cyclin D-cdk4/6 complexes is critical for the phosphorylation and inactivation of the retinoblastoma protein (Rb) family of transcriptional repressors and progression through the G1 phase of the cell cycle. Importantly, the cyclin D-cdk4/6-Rb regulatory axis is frequently dysregulated in human cancer. In the current manuscript, we demonstrate that SREBP1 activates the expression of cyclin D1, a coactivator of cdk4 and cdk6, by binding to an E-box in the cyclin D1 promoter. Consequently, inactivation of SREBP1 in human liver and breast cancer cell lines reduces the expression of cyclin D1 and attenuates Rb phosphorylation. Rb phosphorylation in these cells can be rescued by restoring cyclin D1 expression. On the other hand, expression of active SREBP1 induced the expression of cyclin D1 and increased the phosphorylation of Rb in a manner dependent on cyclin D1 and cdk4/6 activity. Inactivation of SREBP1 resulted in reduced expression of cyclin D1, attenuated phosphorylation of Rb, and reduced proliferation. Inactivation of SREBP1 also reduced the insulin-dependent regulation of the cyclin D1 gene. At the same time, SREBP1 is known to play an important role in supporting lipid synthesis in cancer cells. Thus, we propose that the SREBP1-dependent regulation of cyclin D1 coordinates cell proliferation with the enhanced lipid synthesis required to support cell growth.

Timosaponin A3 Inhibits Palmitate and Stearate through Suppression of SREBP-1 in Pancreatic Cancer

Timosaponin A3 (TA3) was demonstrated as a potent anticancer chemical by several studies. Although the effects of inhibiting growth, metastasis, and angiogenesis in various cancer cells were demonstrated through multiple mechanisms, the pharmacological mechanism of TA3 shown in pancreatic cancer (PC) is insufficient compared to other cancers. In this study, we aimed to explore the key molecular mechanisms underlying the growth inhibitory effects of TA3 using PC cells and a xenograft model. First, from the microarray results, we found that TA3 regulated INSIG-1 and HMGCR in BxPC-3 cells. Furthermore, we showed that inhibition of sterol regulatory element-binding protein-1 (SREBP-1) by TA3 reduced the fatty acid synthases FASN and ACC, thereby controlling the growth of BxPC-3 cells. We also tried to find mechanisms involved with SREBP-1, such as Akt, Gsk3β, mTOR, and AMPK, but these were not related to SREBP-1 inhibition by TA3. In the BxPC-3 xenograft model, the TA3 group had more reduced tumor formation and lower toxicity than the gemcitabine group. Interestingly, the level of the fatty acid metabolites palmitate and stearate were significantly reduced in the tumor tissue in the TA3 group. Overall, our study demonstrated that SREBP-1 was a key transcription factor involved in pancreatic cancer growth and it remained a precursor form due to TA3, reducing the adipogenesis and growth in BxPC-3 cells. Our results improve our understanding of novel mechanisms of TA3 for the regulation of lipogenesis and provide a new approach to the prevention and treatment of PC.

The effect of bile salt diet supplementation on genes related to fat metabolism in yellow-feathered broilers

Background and Aim:

As a new feed additive, bile acid (BA) can promote the absorption and transport of lipids and fat-soluble vitamins. In recent years, BAs have been widely used in animal feed to promote fat absorption. Therefore, this study aimed to investigate the effect of bile salt supplementation in the diet of yellow-feathered broilers on messenger RNA (mRNA) expression of sterol regulatory element-binding protein 1 (SREBF1), fatty acid synthase (FAS), acetyl-coenzyme A carboxylase (ACC), and fatty acid transport protein 4 (FATP4).

Materials and Methods:

Four hundred and twenty commercial male chicks were randomly divided into seven groups (with four replicates per group and 15 chickens per replicate). They were fed diets supplemented with bile salts at 0, 1.5, 2.5, 3.5, 4.5, 5.5 mg/kg, and 2 mg/kg tylosin for 30 days. Changes in SREBF1, fatty acid transporter 4, FAS, and acetyl-CoA carboxylase genes in intestinal mucosa and liver of yellow-feathered broilers were determined using a quantitative fluorescence polymerase chain reaction.

Results:

mRNA expression of SREBF1, FAS, ACC, and FATP4 in the small intestine decreased in chicks fed diets supplemented with 3.5 and 4.5 mg/kg bile salts (p<0.05) compared with the control group on 7 days and 14 d. The mRNA expressions of SREBF1, FAS, ACC, and FATP4 in liver tissue decreased in chicks fed diets supplemented with 4.5 and 5.5 mg/kg bile salts (p<0.05) compared to the control group on 7 days. The mRNA expression of SREBF1, FAS, ACC, and FATP4 in the liver at 14 days and the small intestine on 21 days also decreased in chicks fed diets supplemented with 4.5 mg/kg bile salts (p<0.05) compared to the control group. When contrasted with the control group on day 21, the mRNA expression of SRWBF1, FAS, ACC, and FATP4 detected in the liver was lower in chicks fed diets supplemented with bile salts (p<0.05).

Conclusion:

The dietary supplementation of bile salts at 4.5 mg/kg effectively regulates the expression of fat metabolism genes, such as SREBF1, FAS, ACC, and FATP4 mRNA. At this concentration, bile salts promote fat catabolism, inhibit fat synthesis, and play an essential role in improving the fat deposition of broilers.

Taraxasterol attenuates melanoma progression via inactivation of reactive oxygen species-mediated PI3K/Akt signaling pathway

Background: Taraxasterol (TX), a pentacyclic triterpene, is one of the main active constituents isolated from Taraxacum officinale. A growing number of studies have reported that TX exhibits a wide range of biological activities such as anti-oxidative, anti-inflammatory, and neuro-protective effects. Recently, TX has been demonstrated to be a potential drug candidate for treatment of some types of cancers. However, the specific role of TX in melanoma remains unclear.Purpose: In this study, we aimed at exploration of the effect of TX on melanoma cell viability, apoptosis, migration, invasion, and epithelial-mesenchymal transition (EMT) as well as the underlying mechanisms.Research design: A375 and SK-MEL-28 cells were treated with various concentrations of TX for different times. Cell viability was measured using CCK-8 assay. Cell apoptosis was determined by flow cytometry. Transwell assays were performed to measure cell migration and invasion. The expression of E-cadherin, α-catenin, N-cadherin, vimentin, p-PI3K, PI3K, p-Akt and Akt was detected using western blot.Results: The study showed that TX induced A375 and SK-MEL-28 cell apoptosis. Furthermore, exposure to TX inhibited A375 and SK-MEL-28 cell migration and invasion. Besides, the EMT process was reversed in A375 and SK-MEL-28 cells after TX treatment. We also observed that TX reduced the protein expression of p-PI3K and p-Akt; thus, inhibiting activity of the PI3K/Akt pathway in A375 and SK-MEL-28 cells. In addition, TX treatment increased the levels of reactive oxygen species (ROS) in A375 and SK-MEL-28 cells, and treatment with the ROS scavenger NAC significantly rescued TX-induced down-regulation of p-PI3K and p-Akt in A375 and SK-MEL-28 cells.Conclusions: In conclusion, our study demonstrated that TX induced ROS accumulation followed by inactivation of the PI3K/Akt pathway and subsequently attenuated melanoma progression, suggesting that TX may be a potential candidate for treatment of melanoma.

Suppressive role of E3 ubiquitin ligase FBW7 in type I diabetes in non-obese diabetic mice through mediation of ubiquitination of EZH2

The current study tried to uncover the molecular mechanism of E3 ubiquitin ligase F-box and WD repeat domain-containing 7 (FBW7) in a heritable autoimmune disease, type I diabetes (T1D). After streptozotocin-induced T1D model establishment in non-obese diabetic (NOD) mouse, the protein expression of FBW7, enhancer of zeste homolog 2 (EZH2), and Zinc finger and BTB domain containing 16 (ZBTB16) was quantified. Next, splenocytes and pancreatic beta cells were isolated to measure the production of pro-inflammatory cytokines in splenocytes, as well as islet beta-cell apoptosis. Additionally, the stability of EZH2 induced by FBW7 was analyzed by cycloheximide chase assay. The binding affinity of FBW7 and EZH2 and the consequence of ubiquitination were monitored by co-immunoprecipitation assay. Last, a chromatin immunoprecipitation assay was employed to analyze the accumulation of EZH2 and H3K27me3 at the ZBTB16 promoter region. Our study demonstrated downregulated FBW7 and ZBTB16 and upregulated EZH2 in diabetic NOD mice. Overexpression of FBW7 in the NOD mice inhibited pro-inflammatory cytokine release in the splenocytes and the apoptosis of islets beta cells. FBW7 destabilized EZH2 and accelerated ubiquitin-dependent degradation. EZH2 and H3K27me3 downregulated the ZBTB16 expression by accumulating in the ZBTB16 promoter and methylation. FBW7 upregulates the expression of ZBTB16 by targeting histone methyltransferase EZH2 thus reducing the occurrence of T1D.

Lipidomics reveals that sustained SREBP-1-dependent lipogenesis is a key mediator of gefitinib-acquired resistance in EGFR-mutant lung cancer

Patients with EGFR mutations in non-small cell lung cancer (NSCLC) have been greatly benefited from gefitinib, however, the therapeutic has failed due to the presence of acquired resistance. In this study, we show that gefitinib significantly induces downregulation of Sterol Regulator Element Binding (SREBP1) in therapy-sensitive cells. However, this was not observed in EGFR mutant NSCLC cells with acquired resistance. Lipidomics analysis showed that gefitinib could differently change the proportion of saturated phospholipids and unsaturated phospholipids in gefitinib-sensitive and acquired-resistant cells. Besides, levels of ROS and MDA were increased upon SREBP1 inhibition and even more upon gefitinib treatment. Importantly, inhibition of SREBP1 sensitizes EGFR-mutant therapy-resistant NSCLC to gefitinib both in vitro and in vivo models. These data suggest that sustained de novo lipogenesis through the maintenance of active SRBEP-1 is a key feature of acquired resistance to gefitinib in EGFR mutant lung cancer. Taken together, targeting SREBP1-induced lipogenesis is a promising approach to overcome acquired resistance to gefitinib in EGFR-mutant lung cancer.

Cell cycle dependence on the mevalonate pathway: Role of cholesterol and non-sterol isoprenoids

The mevalonate pathway is responsible for the synthesis of isoprenoids, including sterols and other metabolites that are essential for diverse biological functions. Cholesterol, the main sterol in mammals, and non-sterol isoprenoids are in high demand by rapidly dividing cells. As evidence of its importance, many cell signaling pathways converge on the mevalonate pathway and these include those involved in proliferation, tumor-promotion, and tumor-suppression. As well as being a fundamental building block of cell membranes, cholesterol plays a key role in maintaining their lipid organization and biophysical properties, and it is crucial for the function of proteins located in the plasma membrane. Importantly, cholesterol and other mevalonate derivatives are essential for cell cycle progression, and their deficiency blocks different steps in the cycle. Furthermore, the accumulation of non-isoprenoid mevalonate derivatives can cause DNA replication stress. Identification of the mechanisms underlying the effects of cholesterol and other mevalonate derivatives on cell cycle progression may be useful in the search for new inhibitors, or the repurposing of preexisting cholesterol biosynthesis inhibitors to target cancer cell division. In this review, we discuss the dependence of cell division on an active mevalonate pathway and the role of different mevalonate derivatives in cell cycle progression.

Impact of Sodium Glucose Cotransporter 2 Inhibitors on Nonalcoholic Fatty Liver Disease Complicated by Diabetes Mellitus

Sodium glucose cotransporter 2 (SGLT2), a type of membrane protein highly expressed in the kidney, can regulate plasma glucose through the glomerular filtration process by reabsorption from the kidney. SGLT2 inhibitors, which are newly developed oral antidiabetic drugs, can play a role in liver diseases by inhibiting SGLT2-mediated renal glucose reabsorption and inducing glycosuria. Nonalcoholic fatty liver disease (NAFLD) is the most common type of liver disease, resulting in severe liver dysfunction. During the progression of NAFLD, there are some hallmark complications, including lipid metabolism disorders, inflammation induction, and hepatocyte death. Herein, we review several SGLT2 inhibitors that are capable of protecting individuals with NAFLD from severe complications by inhibiting de novo lipogenesis, oxidative responses, inflammation induction, and hepatocyte death.

FBXW7 mediates high glucose‑induced SREBP‑1 expression in renal tubular cells of diabetic nephropathy under PI3K/Akt pathway regulation

Diabetic nephropathy (DN) is a severe complication of diabetes mellitus and lipid metabolism abnormality serves a key role in the pathogenesis of DN. Sterol regulatory element-binding protein 1 (SREBP-1) overexpression mediates aberrant lipid accumulation in renal tubular cells of DN. However, the exact mechanism involved in increased SREBP-1 has not been fully elucidated. The aim of the present study was to explore the mechanism involved in SREBP-1 upregulation. Diabetic mice and high glucose-cultured HKC cells were chosen to detect the expression of FBXW7 and SREBP-1 using immunohistochemistry, western blotting and PCR. The present study demonstrated that F-box and WD repeat domain containing 7 (FBXW7) expression was decreased in renal tubular cells of diabetic mice. Moreover, the co-expression of FBXW7 and SREBP-1 was observed in renal tubular cells, but not in the glomeruli. High glucose-induced the downregulation of FBXW7 expression in in vitro cultured HKC cells, which was accompanied by SREBP-1 upregulation. In addition, overexpression of FBXW7 in HKC cells led to SREBP-1 downregulation. By contrast, knockdown of FBXW7 caused SREBP-1 upregulation in HKC cells. It was found that the PI3K/Akt signaling pathway was activated in high glucose-stimulated HKC cells, and inhibition of PI3K/Akt pathway using LY294002 increased FBXW7 expression and decreased SREBP-1 expression. Taken together, the present results suggested that FBXW7 mediated high glucose-induced SREBP-1 expression in renal tubular cells of DN, under the regulation of the PI3K/Akt signaling pathway.

Pharmacological Properties of a Traditional Korean Formula Bojungchiseup-tang on 3T3-L1 Preadipocytes and High-Fat Diet-Induced Obesity Mouse Model

The global obesity epidemic has nearly doubled since 1980, and this increasing prevalence is threatening public health. It has been reported that natural products could contain potential functional ingredients that may assist in preventing obesity. Bojungchiseub-tang (BJT), mentioned in the Donguibogam as an herbal medication for the treatment of edema, a symptom of obesity, consists of eleven medicinal herbs. However, the pharmacological activity of BJT has not been investigated. The present study was designed to investigate the putative effect of BJT on the adipogenesis of 3T3-L1 cells and the weight gain of high-fat diet (HFD-) fed C57BL/6 mice. Oil Red O staining was conducted to examine the amount of lipids in 3T3-L1 adipocytes. Male C57BL/6 mice were divided into three groups: standard diet group (control, CON), 45% HFD group (HFD), and HFD supplemented with 10% of BJT (BJT). The expression levels of genes and proteins related to adipogenesis in cells, WAT, and liver were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot, respectively. We found that BJT treatment significantly decreased the protein and mRNA levels of peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα), and sterol regulatory element-binding protein 1 (SREBP1) in a dose-dependent manner in differentiated 3T3-L1 cells. Similar to the results of the in vitro experiment, BJT suppressed HFD-induced weight gain in an obese mouse model. In addition, BJT effectively reduced the HFD-induced epididymal adipose tissue weight/body weight index. BJT also downregulated the mRNA levels of PPARγ, C/EBPα, and SREBP1 in the epididymal adipose and liver tissue of HFD-fed obese mice. These findings suggest that BJT induces weight loss by affecting adipogenic transcription factors.

Down-Regulation of SREBP via PI3K/AKT/mTOR Pathway Inhibits the Proliferation and Invasion of Non-Small-Cell Lung Cancer Cells

Background

Lung cancer is one of the most common causes of cancer-related deaths worldwide, metabolic disorders are also a problem that puzzles mankind. SREBP is overexpressed in non-small-cell lung cancer (NSCLC) and is also a key regulator of lipid synthesis. However, the mechanisms by which SREBP regulates the proliferation, migration and invasion in NSCLC remain unclear.

Materials and Methods

CCK-8, colony formation assay, soft agar assay, scratch wound healing assay and transwell assays were performed to detect proliferation, and invasion in NSCLC cells, respectively. In addition, Western blotting assay, qPCR and immunofluorescence were applied to detect the expressions of SREBP1, SREBP2, ki-67, PCNA, Bax, bcl-2, E-cadherin, N-cadherin, Vimentin, PI3K, p-PI3k, AKT, p-AKT, mTOR, p-mTOR in NSCLC cells.

Results

In this study, downregulation of SREBP significantly inhibited the proliferation, migration and invasion of A549 and H1299 cells. Moreover, the method of piecewise inhibition was adopted to prove that SREBP is a downstream molecule of the PI3K/Akt/mTOR signaling pathway.

Conclusion

Our study indicated that downregulation of SREBP inhibited the growth in NSCLC cells via PI3K/AKT/mTOR signaling pathway. Thus, we suggested SREBP may serve as a potential target for the treatment of patients with NSCLC.

Regulatory Roles of SREBF1 and SREBF2 in Lipid Metabolism and Deposition in Two Chinese Representative Fat-Tailed Sheep Breeds

Simple Summary

Sterol regulatory element binding proteins (SREBPs) play the crucial role in regulating the cholesterol and fatty acid metabolism. However, it is unclear whether SREBPs are involved in the regulation of lipid metabolism in fat-tailed sheep. This study reveals the expression profiles of SREBF1 and SREBF2 in liver and adipose tissues of two Chinese representative fat-tailed sheep breeds, and provides a new insight for the regulatory role of SREBP1 and SREBP2 in fat metabolism and deposition in fat-tailed sheep.

Abstract

Sterol regulatory element binding proteins (SREBPs) can regulate the lipid homeostasis by regulating its target genes, which are crucial for the cholesterol and fatty acid metabolism. However, the transcriptional regulation role of SREBPs in fat-tailed sheep is unclear. In this study, two Chinese representative breeds of total 80 fat-tailed sheep were employed, serum triglyceride, total cholesterol (TC), non-esterified fatty acid (NEFA), high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and mRNA expressions of SREBF1 and SREBF2 in seven different adipose tissues and liver were examined in sheep at the ages of 4, 6, 8, 10, and 12 months, respectively. The subcellular localization and function of SREBP1/2 were predicted through bioinformatics approaches. The results demonstrated that serum TC and NEFA levels among breeds were significantly different, and most serum indices were dynamically altered in an age-dependent manner. The mRNA expression profiling of SREBF1 and SREBF2 are breed-specific with temporal and spatial expressions differences. Further analysis shows that SREBF1/2 transcriptional levels and tail traits are closely related. All investigations simplify that SREBF1/2 play a crucial role in lipid metabolism and deposition during growth and development of the fat-tailed sheep, which also provides a novel insight for revealing the genetic mechanism of different tail type and meat quality.

Lipids and cancer: Emerging roles in pathogenesis, diagnosis and therapeutic intervention

With the advent of effective tools to study lipids, including mass spectrometry-based lipidomics, lipids are emerging as central players in cancer biology. Lipids function as essential building blocks for membranes, serve as fuel to drive energy-demanding processes and play a key role as signaling molecules and as regulators of numerous cellular functions. Not unexpectedly, cancer cells, as well as other cell types in the tumor microenvironment, exploit various ways to acquire lipids and extensively rewire their metabolism as part of a plastic and context-dependent metabolic reprogramming that is driven by both oncogenic and environmental cues. The resulting changes in the fate and composition of lipids help cancer cells to thrive in a changing microenvironment by supporting key oncogenic functions and cancer hallmarks, including cellular energetics, promoting feedforward oncogenic signaling, resisting oxidative and other stresses, regulating intercellular communication and immune responses. Supported by the close connection between altered lipid metabolism and the pathogenic process, specific lipid profiles are emerging as unique disease biomarkers, with diagnostic, prognostic and predictive potential. Multiple preclinical studies illustrate the translational promise of exploiting lipid metabolism in cancer, and critically, have shown context dependent actionable vulnerabilities that can be rationally targeted, particularly in combinatorial approaches. Moreover, lipids themselves can be used as membrane disrupting agents or as key components of nanocarriers of various therapeutics. With a number of preclinical compounds and strategies that are approaching clinical trials, we are at the doorstep of exploiting a hitherto underappreciated hallmark of cancer and promising target in the oncologist's strategy to combat cancer.

Linking epigenetic dysregulation, mitochondrial impairment, and metabolic dysfunction in SBMA motor neurons

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disorder caused by a polyglutamine expansion in the androgen receptor (AR). Using gene expression analysis and ChIP sequencing, we mapped transcriptional changes in genetically engineered patient stem cell-derived motor neurons. We found that transcriptional dysregulation in SBMA can occur through AR-mediated histone modification. We detected reduced histone acetylation, along with decreased expression of genes encoding compensatory metabolic proteins and reduced substrate availability for mitochondrial function. Furthermore, we found that pyruvate supplementation corrected this deficiency and improved mitochondrial function and SBMA motor neuron viability. We propose that epigenetic dysregulation of metabolic genes contributes to reduced mitochondrial ATP production. Our results show a molecular link between altered epigenetic regulation and mitochondrial metabolism that contributes to neurodegeneration.

Comparative Whole-Transcriptome Profiling of Liver Tissue from Wistar Rats Fed with Diets Containing Different Amounts of Fat, Fructose, and Cholesterol

Differential expression of 30,003 genes was studied in the liver of female Wistar rats fed with isocaloric diets with the excess of fat, fructose, or cholesterol, or their combinations for 62 days using the method of whole-transcriptome profiling on a microchip. Relative mRNA expression levels of the Asah2, Crot, Crtc2, Fmo3, GSTA2, LOC1009122026, LOC102551184, NpY, NqO1, Prom1, Retsat, RGD1305464, Tmem104, and Whsc1 genes were also determined by RT-qPCR. All the tested diets affected differently the key metabolic pathways (KEGGs). Significant changes in the expression of steroid metabolism gene were observed in the liver of animals fed with the tested diets (except the high-fat high fructose diet). Both high-fat and high-fructose diets caused a significant decrease in the expression of squalene synthase (FDFT1 gene) responsible for the initial stage of cholesterol synthesis. On the contrary, in animals fed with the high-cholesterol diet (0.5% cholesterol), expression of the FDFT1 gene did not differ from the control group; however, these animals were characterized by changes in the expression of glucose and glycogen synthesis genes, which could lead to the suppression of glycogen synthesis and gluconeogenesis. At the same time, this group demonstrated different liver tissue morphology in comparison with the animals fed with the high-fructose high-fat diet, manifested as the presence of lipid vacuoles of a smaller size in hepatocytes. The high-fructose and high-fructose high-fat diets affected the metabolic pathways associated with intracellular protein catabolism (endocytosis, phagocytosis, proteasomal degradation, protein processing in the endoplasmic reticulum), tight junctions and intercellular contacts, adhesion molecules, and intracellular RNA transport. Rats fed with the high-fructose high-fat or high-cholesterol diets demonstrated consistent changes in the expression of the Crot, Prom1, and RGD1305464 genes, which reflected a coordinated shift in the regulation of lipid and carbohydrate metabolisms.

SREBP1 promotes 5-FU resistance in colorectal cancer cells by inhibiting the expression of caspase7

BACKGROUND

The role of lipid metabolism played in cancer cell growth attracts more attention. SREBP1 is a common lipid regulatory factor. It has been reported that SREBP1 can promote tumor cell resistance. The aim of this study was to investigate its role in chemoresistance of colorectal cancer (CRC).

METHODS

The expression of SREBP1 in CRC tissues was analyzed by immunohistochemistry. Using a viability assay, the sensitivity to 5-fluorouracil in two colon cancer cell lines (HT-29 and SW620) was measured and its correlation with different expression levels of SREBP1 protein by western blot was investigated.

RESULTS

The protein expression of SREBP1 in CRC tissues was higher than that in normal colon tissues. We found that over-expression of SREBP1 through SREBP1 gene transfection enhances the resistant of CRC cell lines to 5-FU, and SREBP1 silencing through SREBP1 shRNA transfection can promote apoptosis in 5-FU treated SW620 cells. Further study indicated that SREBP1 could inhibit the expression of caspase7 and reduce PARP1 cleavage fragments.

CONCLUSION

Our results suggest that SREBP1 protect the 5-FU treated CRC cells through caspase7 dependent PARP1 cleavage in apoptosis pathway and potentially provide a new target in the treatment of CRC.

The anti-obesity effects of Tongbi-san in a high-fat diet-induced obese mouse model

BACKGROUND

Recently, it has been noted that natural herbal medications may be effective in treating obesity. Tongbi-san (TBS) is a traditional medicine usually used for dysuria (i.e., painful urination), containing three herbs, Cyperus rotundus L., Citrus unshiu Markovich, and Poria cocos. In this study, we aimed to examine whether TBS can inhibit high-fat diet (HFD)-induced adipogenesis in the liver and epididymal adipose tissue of obese mice.

METHODS

Male C57BL/6 N mice were fed a normal diet, an HFD, an HFD plus orlistat 10 or 20 mg/kg, or an HFD plus TBS 50 or 100 mg/kg for 11 weeks. Body weight was checked weekly and histological tissue examinations were investigated. An expression of genes involved in adipogenesis was also assessed.

RESULTS

Oral administration of TBS significantly reduced body weight and decreased epididymal and visceral white adipose tissue (WAT) weight. In addition, we found that TBS enhanced the expression of the adenosine monophosphate-activated protein kinase (AMPK) and inhibited the expression of transcription factors, such as CCAAT/enhancer-binding proteins (C/EBPs), sterol regulatory element-binding protein 1 (SREBP1), and peroxisome proliferator-activated receptor γ (PPARγ) in the liver and epididymal WAT as measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR).

CONCLUSION

These findings demonstrate that the anti-obesity effects of TBS may be linked to the activation of AMPK.

SREBP1, targeted by miR-18a-5p, modulates epithelial-mesenchymal transition in breast cancer via forming a co-repressor complex with Snail and HDAC1/2

The progression of localized breast cancer to distant metastasis results in a poor prognosis and a high mortality rate. In this study, the contributions of miRNAs to tumor progression and the regulatory mechanisms leading to their expression alterations were investigated. Using highly lung-metastatic sub-lines from parental breast cancer cells, miRNA expression profiling revealed that the miR-17-92 cluster is significantly downregulated and the miR-18a-5p is the most evidently decreased. Ectopic expression and inhibition of miR-18a-5p demonstrated its capacity in suppressing migration and invasion of breast cancer cells. Further research identified sterol regulatory element binding transcription protein 1 (SREBP1), the master transcription factor that controls lipid metabolism, as a candidate target of miR-18a-5p. SREBP1 is overexpressed and strongly associated with worse clinical outcomes in breast cancer. Functionally SREBP1 promotes growth and metastasis of breast cancer both in vitro and in vivo. To unravel the underlying mechanism of SREBP1-mediated metastasis, mRNA profiling and subsequent gene set enrichment analyses (GSEA) were performed and SREBP1 was demonstrated to be significantly associated with epithelial-mesenchymal transition (EMT). Furthermore, SREBP1-mediated repression of E-cadherin was found to be deacetylation dependent and was augmented by recruiting Snail/HDAC1/2 repressor complex. In the light of these data, we propose that reduced expression of miR-18a-5p and concomitant overexpression of SREBP1 lead to induction of EMT states that in turn, promote breast cancer progression and metastasis. Taken together, our study reveals the crucial role of miR-18a-5p and SREBP1 in the EMT and metastasis, thus providing promising drug targets for tailored therapy in the advanced breast cancer setting.

Emerging role of lipid metabolism alterations in Cancer stem cells

BACKGROUND

Cancer stem cells (CSCs) or tumor-initiating cells (TICs) represent a small population of cancer cells with self-renewal and tumor-initiating properties. Unlike the bulk of tumor cells, CSCs or TICs are refractory to traditional therapy and are responsible for relapse or disease recurrence in cancer patients. Stem cells have distinct metabolic properties compared to differentiated cells, and metabolic rewiring contributes to self-renewal and stemness maintenance in CSCs.

MAIN BODY

Recent advances in metabolomic detection, particularly in hyperspectral-stimulated raman scattering microscopy, have expanded our knowledge of the contribution of lipid metabolism to the generation and maintenance of CSCs. Alterations in lipid uptake, de novo lipogenesis, lipid droplets, lipid desaturation, and fatty acid oxidation are all clearly implicated in CSCs regulation. Alterations on lipid metabolism not only satisfies the energy demands and biomass production of CSCs, but also contributes to the activation of several important oncogenic signaling pathways, including Wnt/β-catenin and Hippo/YAP signaling. In this review, we summarize the current progress in this attractive field and describe some recent therapeutic agents specifically targeting CSCs based on their modulation of lipid metabolism.

CONCLUSION

Increased reliance on lipid metabolism makes it a promising therapeutic strategy to eliminate CSCs. Targeting key players of fatty acids metabolism shows promising to anti-CSCs and tumor prevention effects.

Inactivation of SREBP-1a Phosphorylation Prevents Fatty Liver Disease in Mice: Identification of Related Signaling Pathways by Gene Expression Profiles in Liver and Proteomes of Peroxisomes

The key lipid metabolism transcription factor sterol regulatory element-binding protein (SREBP)-1a integrates gene regulatory effects of hormones, cytokines, nutrition and metabolites as lipids, glucose, or cholesterol via phosphorylation by different mitogen activated protein kinase (MAPK) cascades. We have previously reported the impact of SREBP-1a phosphorylation on the phenotype in transgenic mouse models with liver-specific overexpression of the N-terminal transcriptional active domain of SREBP-1a (alb-SREBP-1a) or a MAPK phosphorylation site-deficient variant (alb-SREBP-1a∆P; (S63A, S117A, T426V)), respectively. In this report, we investigated the molecular basis of the systemic observations by holistic analyses of gene expression in liver and of proteome patterns in lipid-degrading organelles involved in the pathogenesis of metabolic syndrome, i.e., peroxisomes, using 2D-DIGE and mass spectrometry. The differences in hepatic gene expression and peroxisomal protein patterns were surprisingly small between the control and alb-SREBP-1a mice, although the latter develop a severe phenotype with visceral obesity and fatty liver. In contrast, phosphorylation site-deficient alb-SREBP-1a∆P mice, which are protected from fatty liver disease, showed marked differences in hepatic gene expression and peroxisomal proteome patterns. Further knowledge-based analyses revealed that disruption of SREBP-1a phosphorylation resulted in massive alteration of cellular processes, including signs for loss of targeting lipid pathways.

Lipid Cell Biology: A Focus on Lipids in Cell Division

Cells depend on hugely diverse lipidomes for many functions. The actions and structural integrity of the plasma membrane and most organelles also critically depend on membranes and their lipid components. Despite the biological importance of lipids, our understanding of lipid engagement, especially the roles of lipid hydrophobic alkyl side chains, in key cellular processes is still developing. Emerging research has begun to dissect the importance of lipids in intricate events such as cell division. This review discusses how these structurally diverse biomolecules are spatially and temporally regulated during cell division, with a focus on cytokinesis. We analyze how lipids facilitate changes in cellular morphology during division and how they participate in key signaling events. We identify which cytokinesis proteins are associated with membranes, suggesting lipid interactions. More broadly, we highlight key unaddressed questions in lipid cell biology and techniques, including mass spectrometry, advanced imaging, and chemical biology, which will help us gain insights into the functional roles of lipids.

Physiological functions of FBW7 in cancer and metabolism

FBW7 is one of the most well characterized F-box proteins that serve as substrate recognition subunits of SCF (Skp1-Cullin 1-F-box proteins) E3 ubiquitin ligase complexes. SCF^FBW7 plays key roles in regulating cell cycle progression, differentiation, and stem cell maintenance largely through targeting a broad range of oncogenic substrates for proteasome-dependent degradation. The identification of an increasing number of FBW7 substrates for ubiquitination, and intensive in vitro and in vivo studies have revealed a network of signaling components controlled by FBW7 that contributes to metabolic regulation as well as its tumor suppressor role. Here we mainly focus on recent findings that highlight a critical role for FBW7 in cancer and metabolism.

Metabolism and Transcription in Cancer: Merging Two Classic Tales

Cellular plasticity, or the ability of a cancer cell to adapt to changes in the microenvironment, is a major determinant of cell survival and functionality that require the coordination of transcriptional programs with signaling and metabolic pathways. In this scenario, these pathways sense and integrate nutrient signals for the induction of coordinated gene expression programs in cancer. This minireview focuses on recent advances that shed light on the bidirectional relationship between metabolism and gene transcription, and their biological outcomes in cancer. Specifically, we will discuss how metabolic changes occurring in cancer cells impact on gene expression, both at the level of the epigenetic landscape and transcription factor regulation.

SREBP-1c as a molecular bridge between lipogenesis and cell cycle progression of clear cell renal carcinoma

Sterol regulatory element binding protein 1c (SREBP-1c) promotes lipogenesis and tumor growth in various cancers. It is well known that clear cell renal cell carcinoma (ccRCC), a major subtype of the kidney cancers, exhibits elevated lipid accumulation. However, it has not been fully understood how lipid metabolism might be associated with cell cycle regulation in ccRCC. In a recent issue, Lee et al. (Molecular and Cellular Biology (2017) pii: MCB.00265-17) demonstrate that SREBP-1c is up-regulated in ccRCC by ring finger protein 20 (RNF20) down-regulation, leading to aberrant lipid storage and pituitary tumor transforming gene 1 (PTTG1)-dependent cell cycle progression. These findings suggest that SREBP-1c serves as a molecular bridge between lipid metabolism and cell cycle control in ccRCC tumorigenesis.

SREBP-regulated lipid metabolism: convergent physiology - divergent pathophysiology

Cellular lipid metabolism and homeostasis are controlled by sterol regulatory-element binding proteins (SREBPs). In addition to performing canonical functions in the transcriptional regulation of genes involved in the biosynthesis and uptake of lipids, genome-wide system analyses have revealed that these versatile transcription factors act as important nodes of convergence and divergence within biological signalling networks. Thus, they are involved in myriad physiological and pathophysiological processes, highlighting the importance of lipid metabolism in biology. Changes in cell metabolism and growth are reciprocally linked through SREBPs. Anabolic and growth signalling pathways branch off and connect to multiple steps of SREBP activation and form complex regulatory networks. In addition, SREBPs are implicated in numerous pathogenic processes such as endoplasmic reticulum stress, inflammation, autophagy and apoptosis, and in this way, they contribute to obesity, dyslipidaemia, diabetes mellitus, nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, chronic kidney disease, neurodegenerative diseases and cancers. This Review aims to provide a comprehensive understanding of the role of SREBPs in physiology and pathophysiology at the cell, organ and organism levels.