Role Of SREBP-1 Research Articles

SREBP1 as a potential biomarker predicts levothyroxine efficacy of differentiated thyroid cancer

BackgroundSREBP1 is a well-known transcript factor regulating lipogenesis. It has been reported to play an important role in tumor progress in recent years. However, the roles of SREBP1 in differentiated thyroid cancer (DTC) are uncertain. Based on this, we aimed to investigate the expression of SREBP1 and the influence of SREBP1 on DTC patients. MethodsqRT-PCR and immunohistochemistry were used to detect the expression of SREBPs in DTC tissues and the adjacent normal tissues. The following methods, including the MTS, colony-forming assay, flow cytometry and Hoechst staining were used to detect the biological function of thyroid cancer cells based on SREBP1 interference or not. Resultsthe expression of SREBP1 was significantly different among DTCs, thyroid nodules and the adjacent normal tissues. Briefly, SREBP1 was upregulated follow with the malignancy, but there was no significant difference of SREBP2 between thyroid nodules and the adjacent normal tissues. Further, the ROC curve showed that SREBP1 has higher diagnostic value than SREBP2. SREBP1 expression was significantly related to the tumor size and lymph node metastasis in DTCs. In vitro, the proliferation of thyroid cancer cells was suppressed obviously after interfered with SREBP1, and the apoptotic cells was increased. Further, SREBP1 expression was also associated with the short-term efficacy of levothyroxine in DTC patients. Conclusionthis is the first time to report that SREBP1 is an oncogene and a pro-proliferation factor in thyroid cancer, indicating that SREBP1 may serve as a potential biomarker and therapeutic target in thyroid cancer.

Abstract LB-245: 9cis-retinoid UAB30 by inhibiting aberrant fatty acid metabolism protects against UVB-induced skin inflammation and carcinogenesis

Abstract Tumor cells are characterized by aberrant energy metabolism such as an accelerated glycolytic flux and enhanced de novo fatty acid (FA) synthesis which underlie the pathogenesis of aggressive cancer growth. Increased FA synthesis that commensurates with high metabolic demand of cancer cells could be targeted for the prevention or therapeutic intervention of cancer pathogenesis. Retinoids, are well known to inhibit cell proliferation and induce cellular differentiation/apoptosis in various tumor cell types. However, their use is often limited due to severe adverse effects including hyperlipidemia. We have developed 9cUAB30, a selective retinoid X receptors (RXR) agonist with potential anti-carcinogenic effects. Interestingly, it does not manifest hyperlipidemia both in experimental animals and in humans. Here, we demonstrate that chronic administration of 9cUAB30 to Ptch+/-/SKH1 mice diminishes expression of enzymes involved in de novo fatty acid synthesis as well as in UVB-induced inflammatory response. The metabolic analysis of tumor adjacent skin revealed that 9cUAB30 decreases levels of cutaneous saturated fatty acids as well as medium and long chain acetyl carnitines. Additionally, 9cUAB30 inhibits de novo lipid synthesis by inhibiting transcription factor, sterol regulatory element-binding protein 1 (SREBP-1). UVB-induced cutaneous inflammatory response was characterized by an increase in skin bi-fold thickness and edema as well as by augmented levels of pro-inflammatory cytokines/chemokines. 9cUAB30 administered soon after UVB irradiation, significantly diminished these inflammatory responses. Our data confirm that 9cUAB30 decreased the SREBP1-mediated transcription regulation of inflammasome components and its downstream pro-inflammatory cytokines/chemokines such as IL-1β and IL18. 9cUAB30 mediated alterations of UVB-induced pro-inflammatory signaling were identical to those mediated by fatostatin, a potent inhibitor of SREBP1 activation and these data further confirm the role of SREBP1 in UVB-induced inflammation. The molecular mechanism associated with anti-inflammatory response of 9cUAB30 was confirmed in skin tumor cells which are known to secrete pro-inflammatory cytokines to develop a tumor growth condusive micro-environment. Treatment of human squamous cell carcinoma A431 and SCC13 cells with 9cUAB30 (10, 20 and 30 μM) resulted in the downregulation of multiple proteins involved in de novo FA synthesis. The expression of Acetyl-CoA carboxylase 1 (ACC1), ATP citrate lyase (ACLY) and fatty acid synthase (FASN) was significantly reduced in these SCC cells, but not in normal keratinocyte (KerCT). 9cUAB30 reduced the expression of Sirt1 and Sirt2, deacetylases required for the activation of acetyl-CoA synthetase (AceCS1) and Acetyl-CoA production. The expression of CPT1B and CPT2, but not CPT1A (a critical enzyme required for FA β-oxidation) were also decreased. Additionally, 9cUAB30 was instrumental in decreasing the levels of ACADL, ACADM, HADHA and Sirtulin-3. These changes in FA driven energy metabolism underlie the reduced pathogenesis of xenograft tumors in nude mice. In summary, these data demonstrate a novel mechanism by which 9cUAB30 targets lipid metabolism-driven pro-inflammatory and pro-cancer signaling pathways to block the pathogenesis of skin cancer. Citation Format: Mahendra P. Kashyap, Mohammad Waseem, Changzhao Li, Mohd Shameel Iqbal, Venkatram R. Atigadda, Craig A. Elmets, Mohammad Athar. 9cis-retinoid UAB30 by inhibiting aberrant fatty acid metabolism protects against UVB-induced skin inflammation and carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-245.

CVB3 Nonstructural 2A Protein Modulates SREBP1a Signaling via the MEK/ERK Pathway.

Coxsackievirus B3 (CVB3) is the predominant pathogen of viral myocarditis. In our previous study, we found that CVB3 caused abnormal lipid accumulation in host cells. However, the underlying mechanisms by which CVB3 disrupts and exploits the host lipid metabolism are not well understood. Sterol regulatory element binding protein 1 (SREBP1) is the major transcriptional factor in lipogenic genes expression. In this study, we demonstrated that CVB3 infection and nonstructural 2A protein upregulated and activated SREBP1a at the transcriptional level. Deletion analysis of SREBP1a promoter revealed that two regions, -1821/-1490 and -312/+217, in this promoter were both required for its activation by 2A. These promoter regions possessed several binding motifs for transcription factor SP1. Next, we used SP1-specific small interfering RNAs (siRNAs) to confirm that SP1 might be the essential factor in SREBP1a upregulation by 2A. Furthermore, we showed that MEK/ERK pathway was involved in the activation of SREBP1a by 2A and that blocking this signaling pathway with the specific inhibitor U0126 attenuated SREBP1a activation and lipid accumulation by 2A. Finally, we showed that inhibition of SREBP1 with siRNAs attenuated lipid accumulation induced by CVB3 infection and reduced virus replication. Moreover, inhibition of the MEK/ERK pathway also led to reduction of SREBP1a activation, lipid accumulation, and virus replication during CVB3 infection. Taken together, these data demonstrate that CVB3 nonstructural 2A protein activates SREBP1a at the transcription level through a mechanism involving MEK/ERK signaling pathway and SP1 transcription factor, which promotes cellular lipid accumulation and benefits virus replication.IMPORTANCE Coxsackievirus B3 (CVB3) infection is the leading cause of viral myocarditis, but effective vaccines and antiviral therapies against CVB3 infection are still lacking. It is important to understand the precise interactions between host and virus for the rational design of effective therapies. During infection, CVB3 disrupts and exploits host lipid metabolism to promote excessive lipid accumulation, which benefits virus replication. SREBP1 is the master regulator of cellular lipid metabolism. Here, we report that one of the viral nonstructural proteins, 2A, upregulates and activates SREBP1a. Furthermore, we find that inhibition of SREBP1 decreases CVB3 virus replication. These results reveal the regulation of SREBP1a expression by 2A and the roles of SREBP1 in lipid accumulation and viral replication during CVB3 infection. Our findings provide a new insight into CVB3 host interactions and inform a potential novel therapeutic target for this important pathogen.

Egg-Yolk Sphingomyelin and Phosphatidylcholine Attenuate Cholesterol Absorption in Caco-2 Cells.

Phospholipids have been shown to modulate intestinal cholesterol absorption in cells and animals, a process that is regulated by several transporter proteins. Of these proteins, Niemann-Pick C1-Like 1 (NPC1L1) is a major contributor to this process. The mechanism by which phospholipids modulate cholesterol absorption remains unknown. Here, we evaluate the effects of egg-yolk phospholipids on cholesterol absorption and transport in human colon carcinoma cell line (Caco-2 cells) and on the expression of NPC1L1 and others proteins associated with cholesterol absorption (ABCG5, ABCG8, ABCA1, ACAT2, MTP, CAV-1, ANX-2). The roles of SREBP-1 and SREBP-2 in this process were also investigated. The results show that egg-yolk sphingomyelin (CerPCho) and phosphatidylcholine (PtdCho) inhibit cholesterol transport in the Caco-2 monolayer in a dose-dependent manner. These might be due to the decrease of the cholesterol solubility in micelles as well as to the increases in the micellar sizes and the bile acid-binding capacity. Furthermore, the treatments with egg-yolk CerPCho or PtdCho at 1.2 mmol/L reduced the expression levels of NPC1L1 protein to 21 or 22%, respectively, and its mRNA to 9 or 31% of that in the control group (p < 0.05). Moreover, there was a general inhibitory effect of egg-yolk PtdCho and CerPCho on the mRNA levels of SREBP-1, and SREBP-2. These results suggest that the inhibitory effect of egg-yolk CerPCho and PtdCho on cholesterol transport might be due to their interference with the physicochemical properties of micelles and their regulations on the expression of the NPC1L1 gene.

Stable SREBP-1a knockdown decreases the cell proliferation rate in human preadipocyte cells without inducing senescence

Sterol regulatory element binding proteins (SREBP), encoded by the Srebf1 and Srebf2 genes, are important regulators of genes involved in cholesterol and fatty acid metabolism. Whereas SREBP-2 controls the cholesterol synthesis, SREBP-1 proteins (-1a and -1c) function as the central hubs in lipid metabolism. Despite the key function of these transcription factors to promote adipocyte differentiation, the roles of SREBP-1 proteins during the preadipocyte state remain unknown. Here, we evaluate the role of SREBP-1 in preadipocyte proliferation using RNA interference technology. Knockdown of the SREBP-1a gene decreased the proliferation rate in human SGBS preadipocyte cell strain without inducing senescence. Furthermore, our data identified retinoblastoma binding protein 8 and cyclin-dependent kinase inhibitor 3 genes as new potential SREBP-1 targets, in addition to cyclin-dependent kinase inhibitor 1A which had already been described as a gene regulated by SREBP-1a. These data suggested a new role of SREBP-1 in adipogenesis via regulation of preadipocyte proliferation.

Abstract 5169: Roles of lipogenesis in cancer stem-like cells at early stage of breast cancer

Abstract Ductal carcinoma in situ (DCIS) is considered an early stage of breast cancer and it is the precursor of invasive breast carcinoma. However, the transition from normal breast epithelial cells to DCIS is still not clearly elucidated. In order to determine the role of lipogenesis in normal to DCIS transition, we investigated the roles of SREBP1, a major transcription regulator of lipogenesis and its downstream lipogenic genes such as ACLY, ACC1 and FAS, by isolating cancer stem-like cells (CSCs) from DCIS.com cell line which forms typical DCIS lesions in animals by using the well-established cell surface markers, CD24−/CD44+/ESA+. We found that lipid synthesis was significantly upregulated in CSCs from DCIS.com in contrast to the corresponding population from normal breast epithelial cells (MCF10A). Furthermore, we found that this elevation of lipogenesis is indeed caused by the overexpression of SREBP1 which co-ordinately induces the overexpression of the downstream lipogenic genes. The CSCs obtained from DCIS.com were also found to be more tumorigenic than the parental cells as shown by the limiting dilution analysis. To determine the role of elevated level of SREBP1 and lipogenesis in the transition of normal breast epithelial cells to DCIS phenotype, we overexpressed SREBP1 in MCF10A and examined the transforming properties. Our in vitro data showed that MCF10A-SREBP1 cells indeed expressed a significantly higher level of SREBP1 and other lipogenic genes and this elevated level of lipogenesis resulted in the increased cell proliferation, increased mammospheres forming ability and enhanced cellular growth in 3D culture. These data suggest that increased lipogenesis in breast CSCs plays critical roles in DCIS formation. We also examined the effects of Resveratrol on CSCs from DCIS.com. Resveratrol significantly reduced the total lipid content by inhibiting SREBP1 and in turn other lipogenic genes and induced a series of pro-apoptotic genes such as DAPK2 and BNIP3 causing the death of CSCs from DCIS. The mammosphere forming ability of CSCs from DCIS was also blocked by Resveratrol. We also observed that Resveratrol indeed significantly suppressed the formation of DCIS by inhibiting lipogenesis and by upregulating DAPK2 and BNIP3 in our animal model of human DCIS. Collectively, our results indicate that lipogenic genes ACLY, ACC-1, FAS and SREBP1 are significantly up regulated in early stage of breast tumorigenesis and they confer proliferative and growth advantages to these cells. Lipogenesis targeting effect of Resveratrol on CSCs from DCIS provides us with a strong rationale to use this agent for chemo-prevention against DCIS. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5169. doi:1538-7445.AM2012-5169

Transcription of the mitochondrial citrate carrier gene: Role of SREBP-1, upregulation by insulin and downregulation by PUFA

In this study we investigated the transcriptional role of the sterol regulatory element (SRE) present in the promoter of the mitochondrial citrate carrier (CIC). We show that wild-type (but not mutated) CIC SRE cloned in front of the luciferase promoter confers transcriptional activation of the gene reporter. We also demonstrate that insulin activates, and polyunsaturated fatty acids (PUFA) inhibit, the gene reporter activity driven by the CIC promoter containing wild-type (but not mutated) SRE. Finally, both insulin treatment and overexpression of SRE binding protein (SREBP-1) increase the CIC transcript and protein levels, whereas PUFA have an opposite effect. These results show that SRE/SREBP-1 play a role in the transcriptional regulation of CIC by insulin and PUFA.