Platelet-derived growth factor stimulates membrane lipid synthesis through activation of phosphatidylinositol 3-kinase and sterol regulatory element-binding proteins

DHCR24 in Tumor Diagnosis and Treatment: A Comprehensive Review

As an important nutrient in the human body, cholesterol can not only provide structural components for the body's cells, but also can be transformed into a variety of active substances to regulate cell signaling pathways. As an important cholesterol synthase, DHCR24 participates in important regulatory processes in the body. The application of DHCR24 in tumor clinical diagnosis and treatment also attracts much attention. This article reviews the structure and regulatory characteristics of DHCR24, and the research of DHCR24 on tumor progression. We summarize the possible mechanisms of DHCR24 promoting tumor progression through reactive oxygen species (ROS), p53, Ras and PI3K-AKT pathways. Through our review, we hope to provide more research ideas and reference value for the application of DHCR24 in tumor prevention and treatment.

3β-hydroxysteroid-Δ24 reductase dampens anti-viral innate immune responses by targeting K27 ubiquitination of MAVS and STING

IMPORTANCE

The precise regulation of the innate immune response is essential for the maintenance of homeostasis. MAVS and STING play key roles in immune signaling pathways activated by RNA and DNA viruses, respectively. Here, we showed that DHCR24 impaired the antiviral response by targeting MAVS and STING. Notably, DHCR24 interacts with MAVS and STING and inhibits TRIM21-triggered K27-linked ubiquitination of MAVS and AMFR-triggered K27-linked ubiquitination of STING, restraining the activation of MAVS and STING, respectively. Together, this study elucidates how one cholesterol key enzyme orchestrates two antiviral signal transduction pathways.

Lipid metabolic disturbance induced by triphenyl phosphate and hydroxy metabolite in HepG2 cells

Triphenyl phosphate (TPHP) has been widely used as flame retardants and been detected with increasing frequency in environment. TPHP can transform into mono-hydroxylated phosphate (OH-TPHP) and diester diphenyl phosphate (DPHP) through biotransformation. So far, information on the cytotoxicity and molecular regulatory mechanisms of TPHP metabolites are still limit. This study investigated the adverse effects of TPHP, OH-TPHP, and DPHP in HepG2 cells in terms of cell proliferation, lactate dehydrogenase release, reactive oxygen species generation, and mitochondrial membrane potential. The transcriptomic changes were measured using RNA sequencing, and bioinformatics characteristics including biological functions, signal pathways and protein-protein interaction were analyzed to explore the potential molecular mechanisms. Results displayed that the order of cytotoxicity was OH-TPHP> TPHP> DPHP. The prioritized biological functions changes induced by TPHP and OH-TPHP were correlated with lipid metabolism. Significant lipid accumulation was observed as confirmed by increased total cholesterol and triglycerides contents, and enhanced oil red O staining. Enrichment of PPARα/γ and down-stream genes suggested the participation of PPARs signal pathway in lipid metabolism disorder. In addition, TPHP and OH-TPHP induced endoplasmic reticulum stress (ERS), which was further confirmed by the ERS inhibitor experiment. In general, TPHP and OH-TPHP had obvious cytotoxic effects in HepG2 cells. PPARs signal pathway and endoplasmic reticulum stress may be involved in the lipid metabolism disorder induced by TPHP and OH-TPHP.

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.

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.

The long-term effect of mTOR inhibition on lipid and glucose metabolism in tuberous sclerosis complex: data from the Dutch TSC registry

Background

MTOR inhibition is an effective treatment for many manifestations of tuberous sclerosis complex. Because mTOR inhibition is a disease modifying therapy, lifelong use will most likely be necessary. This study addresses the long-term effects of mTOR inhibitors on lipid and glucose metabolism and aims to provide better insight in the incidence and time course of these metabolic adverse effects in treated TSC patients.

Methods

All patients who gave informed consent for the nationwide TSC Registry and were ever treated with mTOR inhibitors (sirolimus and/or everolimus) were included. Lipid profiles, HbA1c and medication were analysed in all patients before and during mTOR inhibitor treatment.

Results

We included 141 patients, the median age was 36 years, median use of mTOR inhibitors 5.1 years (aimed serum levels 3.0–5.0 µg/l). Total cholesterol, LDL- and HDL-cholesterol levels at baseline were similar to healthy reference data. After start of mTOR inhibition therapy, total cholesterol, LDL-cholesterol and triglycerides increased significantly and were higher compared to healthy reference population. Mean total cholesterol levels increased by 1.0 mmol/L after 3–6 months of mTOR inhibition therapy but did not increase further during follow-up. In this study, 2.5% (3/118) of patients developed diabetes (defined as an HbA1c ≥ 48 mmol/mol) during a median follow-up of 5 years.

Conclusions

Hypercholesterolemia is a frequent side effect of mTOR inhibition in TSC patients, and predominantly occurs within the first year of treatment. Although hyperglycemia is a frequent side effect in other indications for mTOR inhibition, incidence of diabetes mellitus in TSC patients was only 2.5%. This may reflect the difference of mTOR inhibition in patients with normal mTOR complex pathway function versus patients with overactive mTOR complex signaling due to a genetic defect (TSC patients).

Transcriptome-wide analysis reveals gluten-induced suppression of small intestine development in young chickens

Wheat gluten is an increasingly common ingredient in poultry diets but its impact on the small intestine in chicken is not fully understood. This study aimed to identify effects of high-gluten diets on chicken small intestines and the variation of their associated transcriptional responses by age. A total of 120 broilers (Ross Strain) were used to perform two animal experiments consisting of two gluten inclusion levels (0% or 25%) by bird’s age (1 week or 4 weeks). Transcriptomics and histochemical techniques were employed to study the effect of gluten on their duodenal mucosa using randomly selected 12 broilers (3 chicks per group). A reduction in feed intake and body weight gain was found in the broilers fed a high-gluten containing diet at both ages. Histochemical photomicrographs showed a reduced villus height to crypt depth ratio in the duodenum of gluten-fed broilers at 1 week. We found mainly a significant effect on the gene expression of duodenal mucosa in gluten-fed broilers at 1 week (289 differentially expressed genes [DEGs]). Pathway analyses revealed that the significant DEGs were mainly involved in ribosome, oxidative phosphorylation, and peroxisome proliferator-activated receptor (PPAR) signaling pathways. These pathways are involved in ribosome protein biogenesis, oxidative phosphorylation and fatty acid metabolism, respectively. Our results suggest a pattern of differential gene expression in these pathways that can be linked to chronic inflammation, suppression of cell proliferation, cell cycle arrest and apoptosis. And via such a mode of action, high-gluten inclusion levels in poultry diets could lead to the observed retardation of villi development in the duodenal mucosa of young broiler chicken.

Targeting stearoyl-CoA desaturase in solid tumors

Cancer cells are demarcated from normal cells by distinct biological hallmarks, including the reprogramming of metabolic processes. One of the key players involved in metabolic reprogramming is stearoyl-CoA desaturase (SCD), which converts saturated fatty acids to monounsaturated fatty acids in an oxygen-dependent reaction that is crucial for maintaining fatty acid homeostasis. As such, SCD has been identified as a potential therapeutic target in numerous types of cancers, and its inhibition suppresses cancer cell growth in vitro and in vivo. This review summarizes the evidence implicating SCD in cancer progression and proposes novel therapeutic strategies for targeting SCD in solid tumors.

Enhanced Autophagic Flux, Suppressed Apoptosis and Reduced Macrophage Infiltration by Dasatinib in Kidneys of Obese Mice

Obesity causes renal changes (ORC), characterized by defective renal autophagy, lipogenesis, enhanced macrophage infiltration and apoptosis. We hypothesize that Dasatinib, a tyrosine kinase inhibitor, may ameliorate changes associated with obesity. We the mice with either Obesogenic diet (OD) or a standard basal diet. After 12 weeks, the mice received either vehicle or Dasatinib 4 mg/kg/d for an additional four weeks. We examined serum creatinine, urea, lipid profile and renal cortical mRNA expression for lipogenesis marker SREBP1, inflammatory macrophage marker iNOS and fibrosis markers; TGFβ and PDGFA genes; immunohistochemical (IHC) staining for CD68; inflammatory macrophage marker and ASMA; fibrosis marker, LC3 and SQSTM1/P62; autophagy markers and western blotting (WB) for caspase-3; and, as an apoptosis marker, LC3II/I and SQSTM1/P62 in addition to staining for H&E, PAS, Sirius red and histopathological scoring. Dasatinib attenuated renal cortical mRNA expression for SREBP1, iNOS, PDGFA and TGFβ and IHC staining for CD68, ASMA and SQSTM1/P62 and WB for caspase-3 and SQSTM1/P62, while elevating LC3 expression. Moreover, Dasatinib ameliorated ORC; glomerulosclerosis, glomerular expansion, tubular dilatation, vacuolation and casts; inflammatory cellular infiltration; and fibrosis. Dasatinib is a promising therapy for ORC by correcting autophagy impairment, attenuating lipogenesis, apoptosis and macrophage infiltration by inducing antifibrotic activity.

MiR-15a-5p Confers Chemoresistance in Acute Myeloid Leukemia by Inhibiting Autophagy Induced by Daunorubicin

Anthracyclines remain a cornerstone of induction chemotherapy for acute myeloid leukemia (AML). Refractory or relapsed disease due to chemotherapy resistance is a major obstacle in AML management. MicroRNAs (miRNAs) have been observed to be involved in chemoresistance. We previously observed that miR-15a-5p was overexpressed in a subgroup of chemoresistant cytogenetically normal AML patients compared with chemosensitive patients treated with daunorubicin and cytarabine. MiR-15a-5p overexpression in AML cells reduced apoptosis induced by both drugs in vitro. This study aimed to elucidate the mechanisms by which miR-15a-5p contributes to daunorubicin resistance. We showed that daunorubicin induced autophagy in myeloid cell lines. The inhibition of autophagy reduced cell sensitivity to daunorubicin. The overexpression of miR-15a-5p decreased daunorubicin-induced autophagy. Conversely, the downregulation of miR-15a-5p increased daunorubicin-induced autophagy. We found that miR-15a-5p targeted four genes involved in autophagy, namely ATG9a, ATG14, GABARAPL1 and SMPD1. Daunorubicin increased the expression of these four genes, and miR-15a-5p counteracted this regulation. Inhibition experiments with the four target genes showed the functional effect of miR-15a-5p on autophagy. In summary, our results indicated that miR-15a-5p induces chemoresistance in AML cells through the abrogation of daunorubicin-induced autophagy, suggesting that miR-15a-5p could be a promising therapeutic target for chemoresistant AML patients.

PDGF receptor mutations in human diseases

PDGFRA and PDGFRB are classical proto-oncogenes that encode receptor tyrosine kinases responding to platelet-derived growth factor (PDGF). PDGFRA mutations are found in gastrointestinal stromal tumors (GISTs), inflammatory fibroid polyps and gliomas, and PDGFRB mutations drive myofibroma development. In addition, chromosomal rearrangement of either gene causes myeloid neoplasms associated with hypereosinophilia. Recently, mutations in PDGFRB were linked to several noncancerous diseases. Germline heterozygous variants that reduce receptor activity have been identified in primary familial brain calcification, whereas gain-of-function mutants are present in patients with fusiform aneurysms, Kosaki overgrowth syndrome or Penttinen premature aging syndrome. Functional analysis of these variants has led to the preclinical validation of tyrosine kinase inhibitors targeting PDGF receptors, such as imatinib, as a treatment for some of these conditions. This review summarizes the rapidly expanding knowledge in this field.

Overexpression of Human Syndecan-1 Protects against the Diethylnitrosamine-Induced Hepatocarcinogenesis in Mice

Simple Summary

Syndecan-1 is a Janus-faced proteoglycan: depending on the type of cancer, it can promote or inhibit the development of tumors. Our previous in vitro experiments revealed that transfection of human syndecan-1 (hSDC1) into hepatoma cells, initiating hepatocyte-like differentiation. To further confirm the antitumor action of hSDC1 in the context of liver carcinogenesis, mice transgenic for albumin promoter-driven hSDC1 were created with exclusive expression of hSDC1 in the liver. Indeed, hSDC1 interfered with the development of liver cancer in diethylnitrosamine (DEN)-induced hepatocarcinogenesis experiments. The mechanism was found to be related to lipid metabolism that plays an important role in the induction of nonalcoholic liver cirrhosis. Nonalcoholic fatty liver disease is known to promote the development of cancer; therefore, the oncoprotective effect of hSDC1 may be mediated by a beneficial modulation of lipid metabolism.

Abstract

Although syndecan-1 (SDC1) is known to be dysregulated in various cancer types, its implication in tumorigenesis is poorly understood. Its effect may be detrimental or protective depending on the type of cancer. Our previous data suggest that SDC1 is protective against hepatocarcinogenesis. To further verify this notion, human SDC1 transgenic (hSDC1^+/+) mice were generated that expressed hSDC1 specifically in the liver under the control of the albumin promoter. Hepatocarcinogenesis was induced by a single dose of diethylnitrosamine (DEN) at an age of 15 days after birth, which resulted in tumors without cirrhosis in wild-type and hSDC1^+/+ mice. At the experimental endpoint, livers were examined macroscopically and histologically, as well as by immunohistochemistry, Western blot, receptor tyrosine kinase array, phosphoprotein array, and proteomic analysis. Liver-specific overexpression of hSDC1 resulted in an approximately six month delay in tumor formation via the promotion of SDC1 shedding, downregulation of lipid metabolism, inhibition of the mTOR and the β-catenin pathways, and activation of the Foxo1 and p53 transcription factors that lead to the upregulation of the cell cycle inhibitors p21 and p27. Furthermore, both of them are implicated in the regulation of intermediary metabolism. Proteomic analysis showed enhanced lipid metabolism, activation of motor proteins, and loss of mitochondrial electron transport proteins as promoters of cancer in wild-type tumors, inhibited in the hSDC1^+/+ livers. These complex mechanisms mimic the characteristics of nonalcoholic steatohepatitis (NASH) induced human liver cancer successfully delayed by syndecan-1.

Can Dasatinib Ameliorate the Hepatic changes, Induced by Long Term Western Diet, in Mice?

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a worldwide disease that progresses into steatohepatitis (NASH) that has no current effective treatment. This study aimed, for the first time, to investigate the effect of Dasatinib; a tyrosine kinase inhibitor showing anti-PDGFR activity with a macrophage modulating efficacy, on NASH.

METHODS

NASH was induced, in C57BL/6 mice by western diet (WD). Control groups received either DMSO or Dasatinib. After 12 weeks, WD-fed mice received DMSO, Dasatinib (4 mg/kg) or Dasatinib (8 mg/kg) once daily, for four weeks. Serum was examined for ALT and lipid profile. Immunohistochemical staining for SREBP1 (lipogenesis marker), iNOS, arginase-1, CD68, CD163 (macrophage polarization markers), TGF-β (fibrosis marker) and ASMA (a marker for activated hepatic stellate cell), hepatic mRNA expression for SREBP-1, iNOS, arginase-1, TGF-β and PDGFA genes; and western blotting for phosphorylated PDGFR α and β, SREBP1, iNOS, arginase-1, IL1α, COX2, TGF-β and ASMA were performed. Liver sections were stained also for H & E, Oil red O and Sirius red.

RESULTS

Dasatinib could ameliorate the WD-induced disturbance of serum ALT, lipid profile and significantly reduced hepatic expression of PDGFA, phosphorylated PDGFR α and β, IL1α, COX2, SREBP-1, iNOS, CD68, TGF-β and ASMA but increased expression for arginase-1 and CD163 (M2 macrophage markers). Moreover, Dasatinib reduced the steatosis, inflammation, hepatocellular ballooning, hepatic fibrosis and the high NAFLD activity scoring induced by WD.

CONCLUSION

Dasatinib can prevent the progression of WD-induced NASH by attenuating lipogenesis, and inducing M2 macrophage polarization with antifibrotic activity.

Fatty Acid Synthase: An Emerging Target in Cancer

In recent years, lipid metabolism has garnered significant attention as it provides the necessary building blocks required to sustain tumor growth and serves as an alternative fuel source for ATP generation. Fatty acid synthase (FASN) functions as a central regulator of lipid metabolism and plays a critical role in the growth and survival of tumors with lipogenic phenotypes. Accumulating evidence has shown that it is capable of rewiring tumor cells for greater energy flexibility to attain their high energy requirements. This multi-enzyme protein is capable of modulating the function of subcellular organelles for optimal function under different conditions. Apart from lipid metabolism, FASN has functional roles in other cellular processes such as glycolysis and amino acid metabolism. These pivotal roles of FASN in lipid metabolism make it an attractive target in the clinic with several new inhibitors currently being tested in early clinical trials. This article aims to present the current evidence on the emergence of FASN as a target in human malignancies.

The balance of protein farnesylation and geranylgeranylation during the progression of nonalcoholic fatty liver disease

Protein prenylation is an essential posttranslational modification and includes protein farnesylation and geranylgeranylation using farnesyl diphosphate or geranylgeranyl diphosphate as substrates, respectively. Geranylgeranyl diphosphate synthase is a branch point enzyme in the mevalonate pathway that affects the ratio of farnesyl diphosphate to geranylgeranyl diphosphate. Abnormal geranylgeranyl diphosphate synthase expression and activity can therefore disrupt the balance of farnesylation and geranylgeranylation and alter the ratio between farnesylated and geranylgeranylated proteins. This change is associated with the progression of nonalcoholic fatty liver disease (NAFLD), a condition characterized by hepatic fat overload. Of note, differential accumulation of farnesylated and geranylgeranylated proteins has been associated with differential stages of NAFLD and NAFLD-associated liver fibrosis. In this review, we summarize key aspects of protein prenylation as well as advances that have uncovered the regulation of associated metabolic patterns and signaling pathways, such as Ras GTPase signaling, involved in NAFLD progression. Additionally, we discuss unique opportunities for targeting prenylation in NAFLD/hepatocellular carcinoma with agents such as statins and bisphosphonates to improve clinical outcomes.

HSF1 Regulates Mevalonate and Cholesterol Biosynthesis Pathways

Heat shock factor 1 (HSF1) is an essential transcription factor in cellular adaptation to various stresses such as heat, proteotoxic stress, metabolic stress, reactive oxygen species, and heavy metals. HSF1 promotes cancer development and progression, and increased HSF1 levels are frequently observed in multiple types of cancers. Increased activity in the mevalonate and cholesterol biosynthesis pathways, which are very important for cancer growth and progression, is observed in various cancers. However, the functional role of HSF1 in the mevalonate and cholesterol biosynthesis pathways has not yet been investigated. Here, we demonstrated that the activation of RAS-MAPK signaling through the overexpression of H-Ras^V12 increased HSF1 expression and the cholesterol biosynthesis pathway. In addition, the activation of HSF1 was also found to increase cholesterol biosynthesis. Inversely, the suppression of HSF1 by the pharmacological inhibitor KRIBB11 and short-hairpin RNA (shRNA) reversed H-Ras^V12-induced cholesterol biosynthesis. From the standpoint of therapeutic applications for hepatocellular carcinoma (HCC) treatment, HSF1 inhibition was shown to sensitize the antiproliferative effects of simvastatin in HCC cells. Overall, our findings demonstrate that HSF1 is a potential target for statin-based HCC treatment.

Stearoyl-CoA Desaturase 1 as a Therapeutic Target for the Treatment of Cancer

A distinctive feature of cancer cells of various origins involves alterations of the composition of lipids, with significant enrichment in monounsaturated fatty acids. These molecules, in addition to being structural components of newly formed cell membranes of intensely proliferating cancer cells, support tumorigenic signaling. An increase in the expression of stearoyl-CoA desaturase 1 (SCD1), the enzyme that converts saturated fatty acids to ∆9-monounsaturated fatty acids, has been observed in a wide range of cancer cells, and this increase is correlated with cancer aggressiveness and poor outcomes for patients. Studies have demonstrated the involvement of SCD1 in the promotion of cancer cell proliferation, migration, metastasis, and tumor growth. Many studies have reported a role for this lipogenic factor in maintaining the characteristics of cancer stem cells (i.e., the population of cells that contributes to cancer progression and resistance to chemotherapy). Importantly, both the products of SCD1 activity and its direct impact on tumorigenic pathways have been demonstrated. Based on these findings, SCD1 appears to be a significant player in the development of malignant disease and may be a promising target for anticancer therapy. Numerous chemical compounds that exert inhibitory effects on SCD1 have been developed and preclinically tested. The present review summarizes our current knowledge of the ways in which SCD1 contributes to the progression of cancer and discusses opportunities and challenges of using SCD1 inhibitors for the treatment of cancer.

Metabolic features and regulation in cell senescence

Organismal aging is accompanied by a host of progressive metabolic alterations and an accumulation of senescent cells, along with functional decline and the appearance of multiple diseases. This implies that the metabolic features of cell senescence may contribute to the organism’s metabolic changes and be closely linked to age-associated diseases, especially metabolic syndromes. However, there is no clear understanding of senescent metabolic characteristics. Here, we review key metabolic features and regulators of cellular senescence, focusing on mitochondrial dysfunction and anabolic deregulation, and their link to other senescence phenotypes and aging. We further discuss the mechanistic involvement of the metabolic regulators mTOR, AMPK, and GSK3, proposing them as key metabolic switches for modulating senescence.

Yarrow supercritical extract exerts antitumoral properties by targeting lipid metabolism in pancreatic cancer

Metabolic reprogramming is considered a hallmark of cancer. Currently, the altered lipid metabolism in cancer is a topic of interest due to the prominent role of lipids regulating the progression of various types of tumors. Lipids and lipid-derived molecules have been shown to activate growth regulatory pathways and to promote malignancy in pancreatic cancer. In a previous work, we have described the antitumoral properties of Yarrow (Achillea Millefolium) CO₂ supercritical extract (Yarrow SFE) in pancreatic cancer. Herein, we aim to investigate the underlaying molecular mechanisms by which Yarrow SFE induces cytotoxicity in pancreatic cancer cells. Yarrow SFE downregulates SREBF1 and downstream molecular targets of this transcription factor, such as fatty acid synthase (FASN) and stearoyl-CoA desaturase (SCD). Importantly, we demonstrate the in vivo effect of Yarrow SFE diminishing the tumor growth in a xenograft mouse model of pancreatic cancer. Our data suggest that Yarrow SFE can be proposed as a complementary adjuvant or nutritional supplement in pancreatic cancer therapy.

A KLF6-driven transcriptional network links lipid homeostasis and tumour growth in renal carcinoma

Transcriptional networks are critical for the establishment of tissue-specific cellular states in health and disease, including cancer. Yet, the transcriptional circuits that control carcinogenesis remain poorly understood. Here we report that Kruppel like factor 6 (KLF6), a transcription factor of the zinc finger family, regulates lipid homeostasis in clear cell renal cell carcinoma (ccRCC). We show that KLF6 supports the expression of lipid metabolism genes and promotes the expression of PDGFB, which activates mTOR signalling and the downstream lipid metabolism regulators SREBF1 and SREBF2. KLF6 expression is driven by a robust super enhancer that integrates signals from multiple pathways, including the ccRCC-initiating VHL-HIF2A pathway. These results suggest an underlying mechanism for high mTOR activity in ccRCC cells. More generally, the link between super enhancer-driven transcriptional networks and essential metabolic pathways may provide clues to the mechanisms that maintain the stability of cell identity-defining transcriptional programmes in cancer.

Transcriptomic analysis of the liver of cholesterol-fed rabbits reveals altered hepatic lipid metabolism and inflammatory response

Rabbits are a suitable animal model for atherosclerosis due to their sensitivity to dietary cholesterol. Moreover, rabbits have lipoprotein profiles that are more similar to humans than those of other laboratory animals. However, little is known about the transcriptomic information related to atherosclerosis in rabbits. We aimed to determine the changes in the livers of rabbits fed a normal chow diet (control) or high cholesterol diet (HCD) by histological examinations and RNA sequencing analysis. Compared with the control group, the lipid levels and small LDL subfractions in plasma were increased, and aortic atherosclerotic plaques were formed in the HCD group. Most importantly, HCD resulted in lipid accumulation and inflammation in the livers. Transcriptomic analysis of the liver showed that HCD induces 1183 differentially expressed genes (DEGs) that mainly participate in the regulation of inflammation and lipid metabolism. Furthermore, the signaling pathways involved in inflammation and lipid metabolism were enriched by KEGG pathway analysis. In addition, hepatic DEGs of the HCD group were further validated by real-time PCR. These results suggest that HCD causes liver lipid accumulation and inflammatory response. Although the relationships between these hepatic changes and atherogenesis need further investigation, these findings provide a fundamental framework for future research on human atherosclerosis using rabbit models.

HBP1 phosphorylation by AKT regulates its transcriptional activity and glioblastoma cell proliferation

The HMG-box protein 1 (HBP1) is a transcriptional regulator and a potential tumor suppressor that controls cell proliferation, differentiation and oncogene-mediated senescence. In a previous study, we showed that AKT activation through the PI3K/AKT/FOXO pathway represses HBP1 expression at the transcriptional level in human fibroblasts as well as in cancer cell lines. In the present study, we investigated whether AKT could also regulate HBP1 directly. First, AKT1 phosphorylated recombinant human HBP1 in vitro on three conserved sites, Ser380, Thr484 and Ser509. In living cells, we confirmed the phosphorylation of HBP1 on residues 380 and 509 using phospho-specific antibodies. HBP1 phosphorylation was induced by growth factors, such as EGF or IGF-1, which activated AKT. Conversely, it was blocked by treatment of cells with an AKT inhibitor (MK-2206) or by AKT knockdown. Next, we observed that HBP1 transcriptional activity was strongly modified by mutating its phosphorylation sites. The regulation of target genes such as DNMT1, P47phox, p16^INK4A and cyclin D1 was also affected. HBP1 had previously been shown to limit glioma cell growth. Accordingly, HBP1 silencing by small-hairpin RNA increased human glioblastoma cell proliferation. Conversely, HBP1 overexpression decreased cell growth and foci formation. This effect was amplified by mutations that prevented phosphorylation by AKT, and blunted by mutations that mimicked phosphorylation. In conclusion, our results suggest that HBP1 phosphorylation by AKT blocks its functions as transcriptional regulator and tumor suppressor.

Targeting stearoyl-CoA desaturase 1 to repress endometrial cancer progression

Stearoyl-CoA desaturase 1 (SCD1) is an established molecular target in many primary tumors including breast, lung, pancreatic, colon and hepatocellular carcinomas. However, its potential role in supporting endometrial cancer growth and progression has not yet been determined. In this study, we evaluated the value of SCD1 as a candidate therapeutic target in human endometrial cancer. Compared with secretory and post-menopausal endometrium, SCD1 was highly expressed in normal endometrium of proliferative phase, endometrial hyperplasia and endometrial carcinoma, while was absent or low expression in non-malignant control stromal cells and adjacent normal endometrium. Knockdown of SCD1 significantly repressed endometrial cancer cell growth and induced cell apoptosis. Both short hairpin RNA targeted knockdown and chemical inhibitor of SCD1 suppressed the foci formation of AN3CA, a metastatic endometrial cell line. Xenograft model further demonstrated that reduced SCD1 expression impaired endometrial cancer growth in vivo. Taken together, these findings indicate that SCD1 is a potentially therapeutic target in human endometrial cancer. Inhibiting lipid metabolism in cancer cells would be a promising strategy for anti-cancer therapy.

Targeting the lipid metabolic axis ACSL/SCD in colorectal cancer progression by therapeutic miRNAs: miR-19b-1 role

An abnormal acyl-CoA synthetase/stearoyl-CoA desaturase (ACSL/SCD) lipid network fuels colon cancer progression, endowing cells with invasive and migratory properties. Therapies against this metabolic network may be useful to improve clinical outcomes. Because micro-RNAs (miRNAs/miRs) are important epigenetic regulators, we investigated novel miRNAs targeting this pro-tumorigenic axis; hence to be used as therapeutic or prognostic miRNAs. Thirty-one putative common miRNAs were predicted to simultaneously target the three enzymes comprising the ACSL/SCD network. Target validation by quantitative RT-PCR, Western blotting, and luciferase assays showed miR-544a, miR-142, and miR-19b-1 as major regulators of the metabolic axis, ACSL/SCD Importantly, lower miR-19b-1 expression was associated with a decreased survival rate in colorectal cancer (CRC) patients, accordingly with ACSL/SCD involvement in patient relapse. Finally, miR-19b-1 regulated the pro-tumorigenic axis, ACSL/SCD, being able to inhibit invasion in colon cancer cells. Because its expression correlated with an increased survival rate in CRC patients, we propose miR-19b-1 as a potential noninvasive biomarker of disease-free survival and a promising therapeutic miRNA in CRC.

Aβ inhibits SREBP-2 activation through Akt inhibition

We previously demonstrated that oligomeric amyloid β₄₂ (oAβ₄₂) inhibits the mevalonate pathway impairing cholesterol synthesis and protein prenylation. Enzymes of the mevalonate pathway are regulated by the transcription factor SREBP-2. Here, we show that in several neuronal types challenged with oAβ₄₂, SREBP-2 activation is reduced. Moreover, SREBP-2 activation is also decreased in the brain cortex of the Alzheimer's disease (AD) mouse model, TgCRND8, suggesting that SREBP-2 may be affected in vivo early in the disease. We demonstrate that oAβ₄₂ does not affect enzymatic cleavage of SREBP-2 per se, but may impair SREBP-2 transport from the endoplasmic reticulum (ER) to the Golgi. Trafficking of SREBP-2 from the ER to the Golgi requires protein kinase B (Akt) activation. oAβ₄₂ significantly reduces Akt phosphorylation and this decrease is responsible for the decline in SREBP-2 activation. Overexpression of constitutively active Akt prevents the effect of oAβ₄₂ on SREBP-2 and the downstream inhibition of cholesterol synthesis and protein prenylation. Our work provides a novel mechanistic link between Aβ and the mevalonate pathway, which will impact the views on issues related to cholesterol, isoprenoids, and statins in AD. We also identify SREBP-2 as an indirect target of Akt in neurons, which may play a role in the cross-talk between AD and diabetes.

Unsaturated Fatty Acids Maintain Cancer Cell Stemness

Investigation of the metabolic regulation of cancer stem cells is an emerging field that offers promising approaches for identifying and targeting recalcitrant stem cell populations. In this issue of Cell Stem Cell, Li et al. (2017) indicate that increased lipid desaturation is essential to stem-like characteristics in ovarian cancer cells.

Complementary ACSL isoforms contribute to a non-Warburg advantageous energetic status characterizing invasive colon cancer cells

Metabolic reprogramming is one of cancer hallmarks. Here, we focus on functional differences and individual contribution of acyl coA synthetases (ACSL) isoforms to the previously described ACSL/stearoyl-CoA desaturase (ACSL1/ACSL4/SCD) metabolic network causing invasion and poor prognosis in colorectal cancer (CRC). ACSL4 fuels proliferation and migration accompanied by a more glycolytic phenotype. Conversely, ACSL1 stimulates invasion displaying a lower basal respiratory rate. Acylcarnitines elevation, polyunsaturated fatty acids (PUFA) lower levels, and monounsaturated fatty acids (MUFA) upregulation characterize the individual overexpression of ACSL1, ACSL4 and SCD, respectively. However, the three enzymes simultaneous overexpression results in upregulated phospholipids and urea cycle derived metabolites. Thus, the metabolic effects caused by the network are far from being caused by the individual contributions of each enzyme. Furthermore, ACSL/SCD network produces more energetically efficient cells with lower basal respiration levels and upregulated creatine pathway. These features characterize other invasive CRC cells, thus, ACSL/SCD network exemplifies specific metabolic adaptations for invasive cancer cells.

Atorvastatin Decreases HBx-Induced Phospho-Akt in Hepatocytes via P2X Receptors

Hepatocellular carcinoma (HCC) is rated as the fifth most common malignancy and third in cancer-related deaths worldwide. Statins, HMG-CoA reductase inhibitors, are potent cholesterol-lowering drugs, and recent epidemiologic evidence suggests that statins prevent aggressive HCC development. Previous experiments revealed that statins downregulate phosphorylated Akt (pAkt). Here, it is demonstrated that atorvastatin decreases nuclear pAkt levels in pancreatic and lung cancer cell lines within minutes, and this rapid effect is mediated by the purinergic P2X receptors. Akt is upregulated by hepatitis viruses and has oncogenic activity in HCC; therefore, we tested the possibility that the P2X-Akt pathway is important for the anticipated anticancer effects of statins in hepatocytes. Atorvastatin decreased hepatitis B virus X protein- and insulin-induced pAkt and pGsk3β (Ser9) levels. Furthermore, Akt-induced lipogenesis was counteracted by atorvastatin, and these statin-induced effects were dependent on P2X receptors. Statin also decreased proliferation and invasiveness of hepatocytes. These data provide mechanistic evidence for a P2X receptor-dependent signaling pathway by which statins decrease pAkt, its downstream phosphorylation target pGsk3β, and lipogenesis in hepatocytes.Implications: The Akt pathway is deregulated and may act as a driver in HCC development; the P2X-Akt signaling pathway may have a role in anticancer effects of statins. Mol Cancer Res; 15(6); 714-22. ©2017 AACR.

PDGF-induced fibroblast growth requires monounsaturated fatty acid production by stearoyl-CoA desaturase

Stearoyl-coenzyme A desaturase (SCD) catalyzes the Δ9-cis desaturation of saturated fatty acids (SFA) to generate monounsaturated fatty acids (MUFA). This enzyme is highly up-regulated by platelet-derived growth factor (PDGF) in human fibroblasts. Accordingly, the analysis of cellular fatty acids by gas chromatography showed that PDGF significantly increased the proportion of MUFA, particularly palmitoleate, in cellular lipids. To further analyze the role of SCD in fibroblasts, we used small hairpin RNA targeting SCD (shSCD), which decreased the MUFA content. SCD down-regulation blunted the proliferation of fibroblasts in response to PDGF. This was confirmed using a pharmacological inhibitor of SCD. In addition, proliferation was blocked by palmitate and stearate (two SCD substrates) but not by palmitoleate and oleate (two SCD products). In the presence of an equal amount of oleate, palmitate had no effect on cell proliferation. SCD inhibition or down-regulation did not decrease PDGF receptor activity or signaling. However, by measuring plasma membrane lipid lateral diffusion by fluorescence recovery after photobleaching, we showed that the modulation of the MUFA/SFA ratio by PDGF and SCD inhibitor was related to modifications of membrane fluidity. Altogether, our data suggest that SCD is required for the response of normal fibroblasts to growth factors.

The interplay between cell signalling and the mevalonate pathway in cancer

The mevalonate (MVA) pathway is an essential metabolic pathway that uses acetyl-CoA to produce sterols and isoprenoids that are integral to tumour growth and progression. In recent years, many oncogenic signalling pathways have been shown to increase the activity and/or the expression of MVA pathway enzymes. This Review summarizes recent advances and discusses unique opportunities for immediately targeting this metabolic vulnerability in cancer with agents that have been approved for other therapeutic uses, such as the statin family of drugs, to improve outcomes for cancer patients.

A link between lipid metabolism and epithelial-mesenchymal transition provides a target for colon cancer therapy

The alterations in carbohydrate metabolism that fuel tumor growth have been extensively studied. However, other metabolic pathways involved in malignant progression, demand further understanding. Here we describe a metabolic acyl-CoA synthetase/stearoyl-CoA desaturase ACSL/SCD network causing an epithelial-mesenchymal transition (EMT) program that promotes migration and invasion of colon cancer cells. The mesenchymal phenotype produced upon overexpression of these enzymes is reverted through reactivation of AMPK signaling. Furthermore, this network expression correlates with poorer clinical outcome of stage-II colon cancer patients. Finally, combined treatment with chemical inhibitors of ACSL/SCD selectively decreases cancer cell viability without reducing normal cells viability. Thus, ACSL/SCD network stimulates colon cancer progression through conferring increased energetic capacity and invasive and migratory properties to cancer cells, and might represent a new therapeutic opportunity for colon cancer treatment.

Stearoyl CoA desaturase-1: New insights into a central regulator of cancer metabolism

The processes of cell proliferation, cell death and differentiation involve an intricate array of biochemical and morphological changes that require a finely tuned modulation of metabolic pathways, chiefly among them is fatty acid metabolism. The critical participation of stearoyl CoA desaturase-1 (SCD1), the fatty acyl Δ9-desaturing enzyme that converts saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA), in the mechanisms of replication and survival of mammalian cells, as well as their implication in the biological alterations of cancer have been actively investigated in recent years. This review examines the growing body of evidence that argues for a role of SCD1 as a central regulator of the complex synchronization of metabolic and signaling events that control cellular metabolism, cell cycle progression, survival, differentiation and transformation to cancer.

Genistein upregulates LDLR levels via JNK-mediated activation of SREBP-2

Background

Genistein has been proved in vitro and in vivo to lower LDLR level. It is also widely consumed and implicated for its anti-atherogenic effects. However, the molecular mechanism by which genistein lowers the LDL level is still unknown.

Objective

To understand the anti-atherogenic molecular mechanism of action, genistein was investigated for its impact on the expression of LDLR, the receptor for LDL cholesterol, and related signaling pathways in a human hepatoma cell line.

Design

HepG2 cell was used for the experiments. Genistein with different concentrations was diluted in media and was incubated for 24 h or more as indicated. Protein levels were measured by western blotting, and mRNA expression was detected by RT-qPCR. Chromatin immunoprecipitation assay (CHIP) assay was used to determine protein binding levels, and luciferase assay was used to measure promoter activity.

Result

Genistein increased the mRNA and protein levels of LDLR in a time-dependent manner. Genistein increased the transcriptional activity of the LDLR promoter containing the reporter gene (pLDLR-luc, −805 to +50). But the sterol regulatory element deletion mutant construct failed to be activated by genistein. Genistein increased the nuclear fraction of SREBP-2 and the DNA-binding activity of SREBP-2 to LDLR promoter, as assessed by CHIP. The genistein-phosphorylated JNK inhibitor (SP600126) abolished the genistein-stimulated levels of LDLR and the nuclear SREBP-2. The addition of cholesterol up to 5 µg/mL for 24 h did not affect the effect of genistein on LDLR protein expression. Even the addition of 40 µM genistein increased the cholesterol uptake by more than 10% in the human hepatoma cell line.

Conclusion

Our data support the idea that genistein may have anti-atherogenic effects by activating JNK signals and SREBP-2 processing, which is followed by the upregulation of LDLR.

SLC20A2 Deficiency in Mice Leads to Elevated Phosphate Levels in Cerbrospinal Fluid and Glymphatic Pathway-Associated Arteriolar Calcification, and Recapitulates Human Idiopathic Basal Ganglia Calcification

Idiopathic basal ganglia calcification is a brain calcification disorder that has been genetically linked to autosomal dominant mutations in the sodium-dependent phosphate co-transporter, SLC20A2. The mechanisms whereby deficiency of Slc20a2 leads to basal ganglion calcification are unknown. In the mouse brain, we found that Slc20a2 was expressed in tissues that produce and/or regulate cerebrospinal fluid, including choroid plexus, ependyma and arteriolar smooth muscle cells. Haploinsufficient Slc20a2 +/- mice developed age-dependent basal ganglia calcification that formed in glymphatic pathway-associated arterioles. Slc20a2 deficiency uncovered phosphate homeostasis dysregulation characterized by abnormally high cerebrospinal fluid phosphate levels and hydrocephalus, in addition to basal ganglia calcification. Slc20a2 siRNA knockdown in smooth muscle cells revealed increased susceptibility to high phosphate-induced calcification. These data suggested that loss of Slc20a2 led to dysregulated phosphate homeostasis and enhanced susceptibility of arteriolar smooth muscle cells to elevated phosphate-induced calcification. Together, dysregulated cerebrospinal fluid phosphate and enhanced smooth muscle cell susceptibility may predispose to glymphatic pathway-associated arteriolar calcification.

The Inflammatory Transcription Factors NFκB, STAT1 and STAT3 Drive Age-Associated Transcriptional Changes in the Human Kidney

Human kidney function declines with age, accompanied by stereotyped changes in gene expression and histopathology, but the mechanisms underlying these changes are largely unknown. To identify potential regulators of kidney aging, we compared age-associated transcriptional changes in the human kidney with genome-wide maps of transcription factor occupancy from ChIP-seq datasets in human cells. The strongest candidates were the inflammation-associated transcription factors NFκB, STAT1 and STAT3, the activities of which increase with age in epithelial compartments of the renal cortex. Stimulation of renal tubular epithelial cells with the inflammatory cytokines IL-6 (a STAT3 activator), IFNγ (a STAT1 activator), or TNFα (an NFκB activator) recapitulated age-associated gene expression changes. We show that common DNA variants in RELA and NFKB1, the two genes encoding subunits of the NFκB transcription factor, associate with kidney function and chronic kidney disease in gene association studies, providing the first evidence that genetic variation in NFκB contributes to renal aging phenotypes. Our results suggest that NFκB, STAT1 and STAT3 underlie transcriptional changes and chronic inflammation in the aging human kidney.

The structure and function of human kidneys deteriorate steadily with age, yet little is known about the underlying causes of kidney aging. In this work, we first used a genomics approach to identify candidate regulators of gene expression changes in the aging human kidney and identified inflammation-related transcription factors NFκB, STAT1 and STAT3 as the top candidate regulators. We found that kidney aging is associated with activation of NFκB, STAT1 and STAT3 in the renal parenchyma, and that the gene expression signatures evoked by activation of these transcription factors in human renal epithelial cells mimics age-associated gene expression changes in the kidney. Furthermore, we identified specific genetic variants in the NFκB transcription factor genes RELA and NFKB1 that associate with renal function and chronic kidney disease in humans, implicating NFκB as a potential contributor to the pathogenesis of chronic kidney disease and renal dysfunction in old age. Our findings suggest that activation of the inflammatory transcription factors STAT1, STAT3 and NFκB underlie transcriptional changes and reduced renal function in the elderly.

Stearoyl-CoA desaturase 1 and paracrine diffusible signals have a major role in the promotion of breast cancer cell migration induced by cancer-associated fibroblasts

Background:

Despite the recognised contribution of the stroma to breast cancer development and progression, the effective targeting of the tumor microenvironment remains a challenge to be addressed. We previously reported that normal fibroblasts (NFs) and, notably, breast cancer-associated fibroblasts (CAFs) induced epithelial-to-mesenchymal transition and increases in cell membrane fluidity and migration in well- (MCF-7) and poorly-differentiated (MDA-MB-231) breast cancer cells. This study was designed to better define the role played, especially by CAFs, in promoting breast tumor cell migration.

Methods:

Fibroblast/breast cancer cell co-cultures were set up to investigate the influence of NFs and CAFs on gene and protein expression of Stearoyl-CoA desaturase 1 (SCD1), the main enzyme regulating membrane fluidity, as well as on the protein level and activity of its transcription factor, the sterol regulatory element-binding protein 1 (SREBP1), in MCF-7 and MDA-MB-231 cells. To assess the role of SREBP1 in the regulation of SCD1 expression, the desaturase levels were also determined in tumor cells treated with an SREBP1 inhibitor. Migration was evaluated by wound-healing assay in SCD1-inhibited (by small-interfering RNA (siRNA) or pharmacologically) cancer cells and the effect of CAF-conditioned medium was also assessed. To define the role of stroma-derived signals in cancer cell migration speed, cell-tracking analysis was performed in the presence of neutralising antibodies to hepatocyte growth factor, transforming growth factor-β or basic fibroblast growth factor.

Results:

A two to three fold increase in SCD1 mRNA and protein expression has been induced, particularly by CAFs, in the two cancer cell lines that appear to be dependent on SREBP1 activity in MCF-7 but not in MDA-MB-231 cells. Both siRNA-mediated and pharmacological inhibition of SCD1 impaired tumor cells migration, also when promoted by CAF-released soluble factors. Fibroblast-triggered increase in cancer cell migration speed was markedly reduced or abolished by neutralising the above growth factors.

Conclusion:

These results provide further insights in understanding the role of CAFs in promoting tumor cell migration, which may help to design new stroma-based therapeutic strategies.

Idiopathic basal ganglia calcification-associated PDGFRB mutations impair the receptor signalling

Platelet-derived growth factors (PDGF) bind to two related receptor tyrosine kinases, which are encoded by the PDGFRA and PDGFRB genes. Recently, heterozygous PDGFRB mutations have been described in patients diagnosed with idiopathic basal ganglia calcification (IBGC or Fahr disease), a rare inherited neurological disorder. The goal of the present study was to determine whether these mutations had a positive or negative impact on the PDGFRB activity. We first showed that the E1071V mutant behaved like wild-type PDGFRB and may represent a polymorphism unrelated to IBGC. In contrast, the L658P mutant had no kinase activity and failed to activate any of the pathways normally stimulated by PDGF. The R987W mutant activated Akt and MAP kinases but did not induce the phosphorylation of signal transducer and activator of transcription 3 (STAT3) after PDGF stimulation. Phosphorylation of phospholipase Cγ was also decreased. Finally, we showed that the R987W mutant was more rapidly degraded upon PDGF binding compared to wild-type PDGFRB. In conclusion, PDGFRB mutations associated with IBGC impair the receptor signalling. PDGFRB loss of function in IBGC is consistent with recently described inactivating mutations in the PDGF-B ligand. These results raise concerns about the long-term safety of PDGF receptor inhibition by drugs such as imatinib.

PDGF-D expression is down-regulated by TGFβ in fibroblasts

Transforming growth factor-β (TGFβ) is a key mediator of fibrogenesis. TGFβ is overexpressed and activated in fibrotic diseases, regulates fibroblast differentiation into myofibroblasts and induces extracellular matrix deposition. Platelet-derived growth factor (PDGF) is also a regulator of fibrogenesis. Some studies showed a link between TGFβ and PDGF in certain fibrotic diseases. TGFβ induces PDGF receptor alpha expression in scleroderma fibroblasts. PDGF-C and -D are the most recently discovered ligands and also play a role in fibrosis. In this study, we report the first link between TGFβ and PDGF-D and -C ligands. In normal fibroblasts, TGFβ down-regulated PDGF-D expression and up-regulated PDGF-C expression at the mRNA and protein levels. This phenomenon is not limited to TGFβ since other growth factors implicated in fibrosis, such as FGF, EGF and PDGF-B, also regulated PDGF-D and PDGF-C expression. Among different kinase inhibitors, only TGFβ receptor inhibitors and the IκB kinase (IKK) inhibitor BMS-345541 blocked the effect of TGFβ. However, activation of the classical NF-κB pathway was not involved. Interestingly, in a model of lung fibrosis induced by either bleomycin or silica, PDGF-D was down-regulated, which correlates with the production of TGFβ and other fibrotic growth factors. In conclusion, the down-regulation of PDGF-D by TGFβ and other growth factors may serve as a negative feedback in the network of cytokines that control fibrosis.

Lupin peptides lower low-density lipoprotein (LDL) cholesterol through an up-regulation of the LDL receptor/sterol regulatory element binding protein 2 (SREBP2) pathway at HepG2 cell line

Previous experiments in suitable animal models and in mild hypercholesterolemic individuals have shown that the consumption of lupin proteins may be useful for controlling total and low-density lipoprotein (LDL) cholesterol levels. With the objective of providing evidence that peptides deriving from the hydrolysis of lupin proteins may be responsible of the observed activities and for investigating the mechanism of action, HepG2 cells were treated with lupin peptides obtained by either pepsin (P) or trypsin (T) hydrolysis, and molecular and functional investigations were performed on the LDL receptor/SREBP2 pathway. For the first time, this paper provides experimental evidence that lupin peptides are able to interfere with the HMGCoAR activity, up-regulating the LDL receptor (136 and 84% vs the control for P and T peptides, respectively, at 1 mg/mL) and SREBP2 proteins (148 and 73% vs the control for P and T peptides, respectively, at 1 mg/mL) via the activation of PI3K/Akt/GSK3β pathways and increasing the LDL uptake at HepG2 cell line (40 and 50% vs the control for P and T peptides, respectively, at 1 mg/mL). These results may be useful in explaining the activities observed in vivo in animals and humans treated with lupin protein.

The expression of the tumour suppressor HBP1 is down-regulated by growth factors via the PI3K/PKB/FOXO pathway

Growth factors inactivate the FOXO (forkhead box O) transcription factors through PI3K (phosphoinositide 3-kinase) and PKB (protein kinase B). By comparing microarray data from multiple model systems, we identified HBP1 (high-mobility group-box protein 1) as a novel downstream target of this pathway. HBP1 mRNA was down-regulated by PDGF (platelet-derived growth factor), FGF (fibroblast growth factor), PI3K and PKB, whereas it was up-regulated by FOXO factors. This observation was confirmed in human and murine fibroblasts as well as in cell lines derived from leukaemia, breast adenocarcinoma and colon carcinoma. Bioinformatics analysis led to the identification of a conserved consensus FOXO-binding site in the HBP1 promoter. By luciferase activity assay and ChIP, we demonstrated that FOXO bound to this site and regulated the HBP1 promoter activity in a PI3K-dependent manner. Silencing of HBP1 by shRNA increased the proliferation of human fibroblasts in response to growth factors, suggesting that HBP1 limits cell growth. Finally, by analysing a transcriptomics dataset from The Cancer Genome Atlas, we observed that HBP1 expression was lower in breast tumours that had lost FOXO expression. In conclusion, HBP1 is a novel target of the PI3K/FOXO pathway and controls cell proliferation in response to growth factors.

Glycogen Synthase Kinase 3 Inactivation Induces Cell Senescence through Sterol Regulatory Element Binding Protein 1-Mediated Lipogenesis in Chang Cells

BACKGROUND

Enhanced lipogenesis plays a critical role in cell senescence via induction of expression of the mature form of sterol regulatory element binding protein 1 (SREBP1), which contributes to an increase in organellar mass, one of the indicators of senescence. We investigated the molecular mechanisms by which signaling molecules control SREBP1-mediated lipogenesis and senescence.

METHODS

We developed cellular models for stress-induced senescence, by exposing Chang cells, which are immortalized human liver cells, to subcytotoxic concentrations (200 µM) of deferoxamine (DFO) and H2O2.

RESULTS

In this model of stress-induced cell senescence using DFO and H2O2, the phosphorylation profile of glycogen synthase kinase 3α (GSK3α) and β corresponded closely to the expression profile of the mature form of SREBP-1 protein. Inhibition of GSK3 with a subcytotoxic concentration of the selective GSK3 inhibitor SB415286 significantly increased mature SREBP1 expression, as well as lipogenesis and organellar mass. In addition, GSK3 inhibition was sufficient to induce senescence in Chang cells. Suppression of GSK3 expression with siRNAs specific to GSK3α and β also increased mature SREBP1 expression and induced senescence. Finally, blocking lipogenesis with fatty acid synthase inhibitors (cerulenin and C75) and siRNA-mediated silencing of SREBP1 and ATP citrate lyase (ACL) significantly attenuated GSK3 inhibition-induced senescence.

CONCLUSION

GSK3 inactivation is an important upstream event that induces SREBP1-mediated lipogenesis and consequent cell senescence.

Cytosolic functions of MORC2 in lipogenesis and adipogenesis

Microrchidia (MORC) family CW-type zinc finger 2 (MORC2) has been shown to be involved in several nuclear processes, including transcription modulation and DNA damage repair. However, its cytosolic function remains largely unknown. Here, we report an interaction between MORC2 and adenosine triphosphate (ATP)-citrate lyase (ACLY), an enzyme that catalyzes the formation of acetyl-coA and plays a central role in lipogenesis, cholesterogenesis, and histone acetylation. Furthermore, we demonstrate that MORC2 promotes ACLY activation in the cytosol of lipogenic breast cancer cells and plays an essential role in lipogenesis, adipogenesis and differentiation of 3T3-L1 preadipocytic cells. Consistently, the expression of MORC2 is induced during the process of 3T3-L1 adipogenic differentiation and mouse mammary gland development at a stage of increased lipogenesis. This observation was accompanied by a high ACLY activity. Together, these results demonstrate a cytosolic function of MORC2 in lipogenesis, adipogenic differentiation, and lipid homeostasis by regulating the activity of ACLY.

The potential of ¹¹C-acetate PET for monitoring the Fatty acid synthesis pathway in Tumors

Positron emission tomography (PET) is a molecular imaging modality that provides the opportunity to rapidly and non-invasively visualize tumors derived from multiple organs. In order to do so, PET utilizes radiotracers, such as ¹⁸F-FDG and ¹¹C-acetate, whose uptake coincides with altered metabolic pathways within tumors. Increased expression and activity of enzymes in the fatty acid synthesis pathway is a frequent hallmark of cancer cells. As a result, this pathway has become a prime target for therapeutic intervention. Although multiple drugs have been developed that both directly and indirectly interfere with fatty acid synthesis, an optimal means to assess their efficacy is lacking. Given that ¹¹Cacetate is directly linked to the fatty acid synthesis pathway, this probe provides a unique opportunity to monitor lipogenic tumors by PET. Herein, we review the relevance of the fatty acid synthesis pathway in cancer. Furthermore, we address the potential utility of ¹¹C-acetate PET in imaging tumors, especially those that are not FDG-avid. Last, we discuss several therapeutic interventions that could benefit from ¹¹C-acetate PET to monitor therapeutic response in patients with certain types of cancers.

Desmosterol and DHCR24: unexpected new directions for a terminal step in cholesterol synthesis

3β-Hydroxysterol Δ(24)-reductase (DHCR24) catalyzes the conversion of desmosterol to cholesterol. This ultimate step of cholesterol biosynthesis appears to be remarkable in its diverse functions and the number of diseases it is implicated in from vascular disease to Hepatitis C virus (HCV) infection to cancer to Alzheimer's disease. This review summarizes the present knowledge on the DHCR24 gene, sterol Δ(24)-reductase protein and the regulation of both. In addition, the functions of desmosterol, DHCR24 and their roles in human diseases are discussed. It is apparent that DHCR24 exerts more complex effects than what would be expected based on the enzymatic activity of sterol Δ(24)-reduction alone, such as its influence in modulating oxidative stress. Increasing information about DHCR24 membrane association, processing, enzymatic regulation and interaction partners will provide further fundamental insights into DHCR24 and its many and varied biological roles.

Phosphatidylinositol 3-kinase is involved in Toll-like receptor 4-mediated BST-2/tetherin regulation

BST-2 is a virus restriction factor whose expression is principally induced by IFNα through the type I IFN receptor. However, expression of BST-2 is modulated by mitogens, notably the TLR4 agonist - LPS, via mechanisms that are poorly understood. In this study, the role of TLR4 pathway on BST-2 expression was examined. We demonstrate that the TLR4/PI3K signaling pathway regulates both constitutive and LPS-induced BST-2 expression. LPS stimulation induces BST-2 expression in a manner dependent on TLR4/TRIF/IRF3 pathway. Genetic deletion or pharmacological inhibition of signaling through TLR4, as well as, the deletion of the TRIF and IRF3 genes blunts BST-2 induction by LPS. However, MYD88-/- cells have enhanced BST-2 levels and respond to LPS-mediated induction of BST-2. High level of BST-2 in MYD88 null cells is dependent on IFNβ since antibody-mediated neutralization of IFNβ synthesis results in reduced BST-2 levels in these cells. Similar to the effect of MYD88, inhibition of PI3K activity elevates basal BST-2 level and augments LPS-induced BST-2 expression. Importantly, BST-2 regulation via TLR4 and PI3K is transcriptionally controlled. We discovered that actinomycin D-mediated blocking of gene transcription and inhibition of protein synthesis with cycloheximide result in impairment of BST-2 mRNA expression. Taken together, our results demonstrate that activation of TLR4 results in TRIF/IRF3-mediated positive regulation of BST-2 or MYD88/PI3K-directed negative regulation of BST-2. Thus, our findings enlist BST-2 as one of the genes regulated by PI3K downstream of TLR4 and identify the TLR4/PI3K signaling as a novel pathway that controls BST-2 expression.

PDGFRA alterations in cancer: characterization of a gain-of-function V536E transmembrane mutant as well as loss-of-function and passenger mutations

Activating mutations in the platelet-derived growth factor (PDGF) receptor alpha (PDGFRA) have been described in patients with gastrointestinal stromal tumors or myeloid malignancies associated with hypereosinophilia. These patients respond well to imatinib mesylate, raising the question as to whether patients with a PDGF receptor mutation in other tumor types should receive a tyrosine kinase inhibitor treatment. We characterized 10 novel somatic point mutations in PDGFRA that have been reported in isolated cases of glioblastoma, melanoma, acute myeloid leukemia, peripheral nerve sheath tumors and neuroendocrine carcinoma. The PDGFRA transmembrane domain mutation V536E stimulated Ba/F3 cell growth and signaling via ERK and STAT5 in the absence of ligand. This mutant, identified in glioblastoma, was strongly inhibited by imatinib. Modeling suggested that the mutation modulates the packing of the transmembrane domain helices in the receptor dimer. By contrast, two mutations in highly conserved residues affected the receptor traffic to the cell surface or kinase activity, thereby preventing the response to PDGF. The other mutations had no significant impact on the receptor activity. This functional analysis matched the predictions of SIFT and PolyPhen for only five mutations and these algorithms do not discriminate gain from loss of function. Finally, an E996K variant that had been identified in a melanoma cell line was not expressed in these cells. Altogether, several newly identified PDGFRA mutations do not activate the receptor and may therefore represent passenger mutations. Our results also underline the importance of characterizing novel kinase alterations in cancer patients.

Oxysterols in cancer cell proliferation and death

Oxysterols have been shown to interfere with proliferation and cause the death of many cancer cell types, such as leukaemia, glioblastoma, colon, breast and prostate cancer cells, while they have little or no effect on senescent cells. The mechanisms by which oxysterols may influence proliferation are manifold: they control the transcription and the turnover of the key enzyme in cholesterol synthesis, 3-hydroxy-3-methylglutaryl CoA reductase, by binding to Insig-1, Insig-2 and liver X receptors. Oxysterols are thought to be generated in proportion to the rate of cholesterol synthesis. Although there is no consensus about the mechanism by which these oxysterols are generated in vivo, it clearly has to be ubiquitous. The 25- and the 27-cholesterol hydroxylases, present in almost all tissues, are possible candidates. Cholesterol uptake from lipoproteins, intracellular vesicle transport and lipid transfer are also modified by oxysterols. Oxysterols interfere with ERK, hedgehog and wnt pathways of proliferation and differentiation. When administered in vitro to cancer cell lines, oxysterols invariably both slow down proliferation and provoke cell death. Perhaps is it sufficient to stop proliferation of a cancer to provoke its eradication. Therefore, the two facets of oxysterol action that seem important for cancer treatment, cytostaticity and cytotoxicity, will be discussed.

FGFR3 stimulates stearoyl CoA desaturase 1 activity to promote bladder tumor growth

Fibroblast growth factor receptor 3 (FGFR3) belongs to a family of receptor tyrosine kinases that control cell proliferation, differentiation, and survival. Aberrant activation of FGFR3 via overexpression or mutation is a frequent feature of bladder cancer; however, its molecular and cellular consequences and functional relevance to carcinogenesis are not well understood. Through transcriptional profiling of bladder carcinoma cells subjected to short hairpin RNA knockdown of FGFR3, we identified a gene-signature linking FGFR3 signaling with de novo sterol and lipid biosynthesis and metabolism. We found that FGFR3 signaling promotes the cleavage and activation of the master transcriptional regulator of lipogenesis, sterol regulatory element-binding protein 1(SREBP1/SREBF1), in a PI3K-mTORC1-dependent fashion. In turn, SREBP1 regulates the expression of key lipogenic enzymes, including stearoyl CoA desaturase 1 (SCD1/SCD). SCD1 is the rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids and is crucial for lipid homeostasis. In human bladder cancer cell lines expressing constitutively active FGFR3, knockdown of SCD1 by siRNA markedly attenuated cell-cycle progression, reduced proliferation, and induced apoptosis. Furthermore, inducible knockdown of SCD1 in a bladder cancer xenograft model substantially inhibited tumor progression. Pharmacologic inhibition of SCD1 blocked fatty acid desaturation and also exerted antitumor activity in vitro and in vivo. Together, these findings reveal a previously unrecognized role of FGFR3 in regulating lipid metabolism to maintain tumor growth and survival, and also identify SCD1 as a potential therapeutic target for FGFR3-driven bladder cancer.