MAP Kinases Erk1/2 Phosphorylate Sterol Regulatory Element-binding Protein (SREBP)-1a at Serine 117 in Vitro

Roth, Günther E.; Kotzka, Jörg; Kremer, L.; Lehr, Stefan; Lohaus, Christiane; Meyer, Helmut E.; Krone, Wilhelm; Müller‐Wieland, Dirk

doi:10.1074/jbc.m005425200

Cited by 147 publications

(117 citation statements)

References 25 publications

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“…Gel shift assays using nuclear extracts prepared from untreated and the cytokine oncostatin M-treated Hep G2 cells revealed that an as yet unidentified complex, which appears with the administration of oncostatin M and disappears with U0126, is bound to the sterol-independent regulatory element in the LDL receptor promoter region Ϫ17 to Ϫ1 (30). Furthermore, it has been demonstrated that MAP kinases phosphorylate both SREBPs and Sp1, which coordinately regulate LDL receptor gene expression, and augment their transcriptional activities (31)(32)(33). We found that CDCA as well as PMA indeed activates the MAP kinase cascade (Fig.…”

Section: Discussionmentioning

confidence: 63%

Bile Acids Enhance Low Density Lipoprotein Receptor Gene Expression via a MAPK Cascade-mediated Stabilization of mRNA

Nakahara

Fujii²,

Maloney³

et al. 2002

Journal of Biological Chemistry

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Recent studies have indicated that bile acids regulate the expression of several genes involved in bile acid and lipid metabolism as ligands for the farnesoid X receptor (FXR). We report here that bile acids are directly able to govern cholesterol metabolism by a novel mechanism. We show that chenodeoxycholic acid (CDCA) enhances low density lipoprotein (LDL) receptor gene expression in human cultured cell lines (HeLa, Hep G2, and Caco-2). The proteolytic activation of sterol regulatory elementbinding protein-2 (SREBP-2), a major regulator for LDL receptor gene expression, is not affected by CDCA. Both deoxycholic acid and lithocholic acid as well as CDCA, but not ursodeoxycholic acid, increase the mRNA level for the LDL receptor, even when Hep G2 cells are cultured with 25-hydroxycholesterol, a potent suppressor of gene expression for the LDL receptor. Although it seems possible that FXR might be involved in genetic regulation, both reporter assays with a reporter gene containing the LDL receptor promoter as well as Northern blot analysis reveal that FXR is not involved in the process. On the other hand, inhibition of mitogen-activated protein (MAP) kinase activities, which are found to be induced by CDCA, abolishes the CDCA-mediated up-regulation of LDL receptor gene expression. We further demonstrate that CDCA stabilizes LDL receptor mRNA and that the MAP kinase inhibitors accelerate its turnover. Taken together, these results indicate that bile acids increase LDL uptake and the intracellular cholesterol levels through the activation of MAP kinase cascades in conjunction with a down-regulation of bile acid biosynthesis by FXR. This work opens up a new avenue for developing pharmaceutical interventions that lower plasma LDL by stabilizing LDL receptor mRNA.Bile acids are synthesized from cholesterol in the liver and secreted as either taurine or glycine conjugates into bile. They are required for the efficient absorption of dietary fats and lipid-soluble vitamins in the gut. In humans, more than 90% of bile acids released into the duodenum are reabsorbed and returned to the liver, after which they are secreted again into bile. The catabolism of cholesterol to bile acid and their excretion are the main mechanisms for cholesterol elimination from the body and thus play important roles in cholesterol homeostasis. Elevated concentrations of cholesterol within the liver promote bile acid synthesis through an increase in cholesterol 7␣-hydroxylase (CYP7a1) activity at the transcription level, the rate-limiting enzyme of the pathway. On the other hand, CYP7a1 expression is repressed by bile acids. Thus, CYP7a1 is under the influence of both feed forward and feedback regulation (1, 2).CYP7a1 expression in rodents but not in humans (3, 4) is regulated by two nuclear receptors, the liver X receptor ␣ (LXR␣) 1 and FXR, both of which are abundantly expressed in the liver. LXR␣ is activated by cholesterol derivatives such as 24(S),25-epoxycholesterol and 24(S)-hydroxycholesterol and binds to a response element in the CYP7a...

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Section: Discussionmentioning

confidence: 63%

Bile Acids Enhance Low Density Lipoprotein Receptor Gene Expression via a MAPK Cascade-mediated Stabilization of mRNA

Nakahara

Fujii²,

Maloney³

et al. 2002

Journal of Biological Chemistry

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“…Previously, we demonstrated that the SREBP transcription factors are targets of intracellular signaling pathways and substrates of Erk1 and Erk2 (8,9). Furthermore, in SREBP-1a, we identified Ser-117 as a major Erk-MAPK phosphorylation site (16). By using the same protein chemistry approach, we have identified in this study serine residues 432 and 455 as major phosphorylation sites of Erk in SREBP-2-NT.…”

Section: Discussionmentioning

confidence: 69%

Insulin-activated Erk-mitogen-activated Protein Kinases Phosphorylate Sterol Regulatory Element-binding Protein-2 at Serine Residues 432 and 455 in Vivo

Kotzka

Lehr

Roth

et al. 2004

Journal of Biological Chemistry

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102

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The transcription factor sterol regulatory element binding protein (SREBP)-2 plays a pivotal role in lipid metabolism. Previously, we have shown that the mature form of SREBP-2 is a substrate of Erk-mitogen-activated protein kinases (MAPK). The aim of the present study was to identify Erk-specific phosphorylation sites. Using a protein chemistry approach, we could identify Ser-432 and Ser-455 as major phosphorylation sites. Further characterization by electrophoretic mobility shift assay and promoter reporter gene analyses revealed that phosphorylation does not influence protein/DNA interaction, but enhances trans-activity. In intact cells, SREBP-2 is phosphorylated by insulin, which seems to be related to their bio-responses on low density lipoprotein receptor activity. These results suggest that activation of Erk-MAPK pathways by hormones such as insulin might be related to a novel regulatory principle of SREBP-2.Sterol regulatory element binding proteins (SREBPs) 1 are a family of basic helix-loop-helix transcription factors that are embedded as precursor proteins in the endoplasmic reticulum and nuclear envelope. To date, three SREBP isoforms have been detected: SREBP-1a, SREBP-1c (shorter splicing variant of SREBP-1a), as well as SREBP-2 (1-5). SREBP-2 is a major regulator of cholesterol homeostasis, whereas SREBP-1c regulates predominantly de novo synthesis of fatty acids. In contrast, SREBP-1a seems to influence both lipogenic and cholesterogenic enzymes (6).Activation of SREBPs initiated by cellular cholesterol depletion is mediated by sequential cleavage (7). As a result, the amino-terminal domain of the protein translocates into the nucleus and activates transcription of target genes. Beside this mechanism, which controls the abundance of activated SREBPs in the cell, we have demonstrated that trans-activity of the N-terminal domain of SREBPs is regulated directly by extra cellular stimuli, e.g. by hormones such as insulin (8, 9). Moreover, in these studies, we have shown that the N-terminal domains of SREBP-1a, SREBP-1c, and SREBP-2 are substrates of the extracellular signal-regulated kinase (Erk) subfamily of mitogen-activated protein kinases (MAPK). In this study, we have identified Ser-432 and Ser-455 as the major phosphorylation sites of Erk-MAPK in SREBP-2 using protein chemistry methodology. This phosphorylation has no influence on DNA interaction but affects trans-activity of SREBP-2. Accordingly, in cells, activation of low density lipoprotein (LDL) receptor gene by insulin is coupled to the identified Erk-specific phosphorylation sites in SREBP-2.

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“…Early observations indicated that SREBP1a is phosphorylated in vivo (14). Subsequently, it has been suggested that both SREBP1 and SREBP2 are phosphorylated by various protein kinases, both in vivo and in vitro (15)(16)(17). We were interested in mapping the major phosphorylated residues in SREBP1, especially those found in the Ser͞Thr͞Gly-rich C terminus of the mature protein (Fig.…”

Section: Resultsmentioning

confidence: 99%

Hyperphosphorylation regulates the activity of SREBP1 during mitosis

Bengoechea-Alonso

Punga

Ericsson

2005

Proc. Natl. Acad. Sci. U.S.A.

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The sterol regulatory element-binding protein (SREBP) family of transcription factors controls the biosynthesis of cholesterol and other lipids, and lipid synthesis is critical for cell growth and proliferation. We were, therefore, interested in the expression and activity of SREBPs during the cell cycle. We found that the expression of a number of SREBP-responsive promoter-reporter genes were induced in a SREBP-dependent manner in cells arrested in G 2͞M. In addition, the mature forms of SREBP1a and SREBP1c were hyperphosphorylated in mitotic cells, giving rise to a phosphoepitope recognized by the mitotic protein monoclonal-2 (MPM-2) antibody. In contrast, SREBP2 was not hyperphosphorylated in mitotic cells and was not recognized by the MPM-2 antibody. The MPM-2 epitope was mapped to the C terminus of mature SREBP1, and the mitosis-specific hyperphosphorylation of SREBP1 depended on this domain of the protein. The transcriptional and DNA-binding activity of SREBP1 was enhanced in cells arrested in G 2͞M, and these effects depended on the C-terminal domain of the protein. In part, these effects could be explained by our observation that mature SREBP1 was stabilized in G 2͞M. In agreement with these observations, we found that the synthesis of cholesterol was increased in G 2͞M-arrested cells. Thus, our results demonstrate that the activity of mature SREBP1 is regulated by phosphorylation during the cell cycle, suggesting that SREBP1 may provide a link between lipid synthesis, proliferation, and cell growth.cell cycle ͉ cholesterol ͉ phosphorylation ͉ proliferation M embers of the sterol regulatory element-binding protein (SREBP) family of transcription factors control cholesterol and lipid metabolism and play critical roles in insulin signaling and during adipocyte differentiation (1). Two genes, srebf1 and srebf2, encode three different SREBPs (SREBP1a, SREBP1c, and SREBP2) (2). SREBPs are synthesized as large precursor proteins that are inserted into the nuclear and endoplasmic reticulum (ER) membranes and are transcriptionally inactive. In sterol-depleted cells, SREBP cleavage-activating protein (SCAP) escorts SREBP to the Golgi apparatus where SREBP is processed sequentially by two membrane-associated proteases, resulting in the release of the mature form of the protein (3, 4). This transcriptionally active fragment of SREBP is translocated to the nucleus and binds to the promoters of SREBP target genes. Most of these genes are involved in the control of lipid biosynthesis and metabolism (5). In sterolloaded cells, the SCAP͞SREBP complex is trapped in the ER as a result of sterol-induced binding of SCAP to Insigs, which are resident proteins of the ER membrane (6, 7).It is well established that the synthesis of membrane lipids is critical for cell growth and proliferation (8, 9). Here, we report that the expression of a number of SREBP-responsive promoterreporter genes are induced in a SREBP-dependent manner in cells arrested in G 2 ͞M. In addition, the mature forms of SREBP1a and SREBP1c are hyperphosphory...

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MAP Kinases Erk1/2 Phosphorylate Sterol Regulatory Element-binding Protein (SREBP)-1a at Serine 117 in Vitro

Cited by 147 publications

References 25 publications

Bile Acids Enhance Low Density Lipoprotein Receptor Gene Expression via a MAPK Cascade-mediated Stabilization of mRNA

Bile Acids Enhance Low Density Lipoprotein Receptor Gene Expression via a MAPK Cascade-mediated Stabilization of mRNA

Insulin-activated Erk-mitogen-activated Protein Kinases Phosphorylate Sterol Regulatory Element-binding Protein-2 at Serine Residues 432 and 455 in Vivo

Hyperphosphorylation regulates the activity of SREBP1 during mitosis

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