Induction of Low Density Lipoprotein Receptor (LDLR) Transcription by Oncostatin M Is Mediated by the Extracellular Signal-regulated Kinase Signaling Pathway and the Repeat 3 Element of the LDLR Promoter

Oncostatin M (OM) activates the transcription of the human low density lipoprotein receptor (LDLR) in HepG2 cells through a sterol-independent mechanism. Our previous studies showed that mutations within the repeat 3 sequence of the LDLR promoter significantly decreased OM activity on LDLR promoter luciferase reporter constructs that contain the sterol responsive element-1 (repeat 2) and Sp1 binding sites (repeats 1 and 3). In this study, we investigated the signal transduction pathways that are involved in OM-induced LDLR transcription. In HepG2 cells, OM induced a rapid increase in LDLR mRNA expression, with increases detected at 30 min and maximal induction at 1 h. This OM effect was not blocked by protein synthesis inhibitors, inhibitors of p38 kinase, phosphatidylinositol 3-kinase, or c-Jun N-terminal kinase, but OM activity was completely abolished by pretreating cells with inhibitors of the extracellular signal-regulated kinase (ERK) kinase (mitogen/ERK kinase (MEK)). To investigate whether the repeat 3 sequence of the LDLR promoter is the OM-responsive element that converts ERK activation at the promoter level, three luciferase reporters, pLDLR-TATA containing only the TATA-like elements of the promoter, pLDLR-R3 containing repeat 3 and the TATA-like elements, and pLDLR-234 containing repeats 1, 2, 3 and the TATA-like elements were constructed and transiently transfected into HepG2 cells. OM had no effect on the basal promoter construct pLDLR-TATA; however, including a single copy of repeat 3 sequence in the TATA vector (pLDLR-R3) resulted in a full OM response. The activity of OM on pLDLR-R3 was identical to that of pLDLR-234. Importantly, the ability of OM to increase luciferase activities in both pLDLR-R3- and pLDLR-234-transfected cells was blocked in a dose-dependent manner by inhibition of MEK. These results demonstrate that the mitogen-activated protein kinase MEK/ERK cascade is the essential signaling pathway by which OM activates LDLR gene transcription and provide the first evidence that the repeat 3 element is a new downstream target of ERK activation. Oncostatin M (OM) activates the transcription of the human low density lipoprotein receptor (LDLR) in HepG2 cells through a sterol-independent mechanism. Our previous studies showed that mutations within the repeat 3 sequence of the LDLR promoter significantly decreased OM activity on LDLR promoter luciferase reporter constructs that contain the sterol responsive element-1 (repeat 2) and Sp1 binding sites (repeats 1 and 3). In this study, we investigated the signal transduction pathways that are involved in OM-induced LDLR transcription. In HepG2 cells, OM induced a rapid increase in LDLR mRNA expression, with increases detected at 30 min and maximal induction at 1 h. This OM effect was not blocked by protein synthesis inhibitors, inhibitors of p38 kinase, phosphatidylinositol 3-kinase, or c-Jun N-terminal kinase, but OM activity was completely abolished by pretreating cells with inhibitors of the extracellular signal-regulated kinase (ERK) kinase (mitogen/ERK kinase (MEK)). To investigate whether the repeat 3 sequence of the LDLR promoter is the OM-responsive element that converts ERK activation at the promoter level, three luciferase reporters, pLDLR-TATA containing only the TATA-like elements of the promoter, pLDLR-R3 containing repeat 3 and the TATA-like elements, and pLDLR-234 containing repeats 1, 2, 3 and the TATA-like elements were constructed and transiently transfected into HepG2 cells. OM had no effect on the basal promoter construct pLDLR-TATA; however, including a single copy of repeat 3 sequence in the TATA vector (pLDLR-R3) resulted in a full OM response. The activity of OM on pLDLR-R3 was identical to that of pLDLR-234. Importantly, the ability of OM to increase luciferase activities in both pLDLR-R3- and pLDLR-234-transfected cells was blocked in a dose-dependent manner by inhibition of MEK. These results demonstrate that the mitogen-activated protein kinase MEK/ERK cascade is the essential signaling pathway by which OM activates LDLR gene transcription and provide the first evidence that the repeat 3 element is a new downstream target of ERK activation. The transcription of the human low density lipoprotein receptor (LDLR) 1The abbreviations used are: LDLR, low density lipoprotein receptor; ERK, extracellular signal-regulated kinase; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; IL, interleukin; JNK, c-Jun N-terminal kinase; LIF, leukemia inhibitory factor; MAP, mitogen-activated protein; MEK, MAPK/ERK kinase; OM, oncostatin M; SRE-1, sterol response element-1; SREBP, SRE-1-binding protein; STAT, signal transducer and activator of transcription; PI, phosphatidylinositol; bp, base pair(s).1The abbreviations used are: LDLR, low density lipoprotein receptor; ERK, extracellular signal-regulated kinase; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; IL, interleukin; JNK, c-Jun N-terminal kinase; LIF, leukemia inhibitory factor; MAP, mitogen-activated protein; MEK, MAPK/ERK kinase; OM, oncostatin M; SRE-1, sterol response element-1; SREBP, SRE-1-binding protein; STAT, signal transducer and activator of transcription; PI, phosphatidylinositol; bp, base pair(s). gene is under the control of intracellular cholesterol and other non-sterol mediators. Cholesterol regulates LDLR transcription through a negative feedback mechanism (1Goldstein J.L. Basu S.K. Brown M.S. Methods Enzymol. 1983; 98: 241-260Crossref PubMed Scopus (1278) Google Scholar, 2Goldstein J.L. Brown M.S. Nature. 1990; 343: 425-430Crossref PubMed Scopus (4516) Google Scholar). When cellular cholesterol levels rise, LDLR transcription is reduced. When cellular cholesterol storage is depleted, LDLR transcription is activated. The promoter region and the cis-acting elements that are responsible for the basal and the cholesterol-controlled transcription of LDLR have been localized to three GC-rich imperfect 16-bp direct repeats (3Sudhof T.C. Van der Westhuyzen D.R. Goldstein J.L. Brown M.S. Russell D.W. J. Biol. Chem. 1987; 262: 10773-10779Abstract Full Text PDF PubMed Google Scholar, 4Dawson P.A. Hofmann S.L. Van der Westhuyzen D.R. Sudhof T.C. Brown M.S. Goldstein J.L. J. Biol. Chem. 1988; 263: 3372-3379Abstract Full Text PDF PubMed Google Scholar, 5Sudhof T.C. Russell D.W. Brown M.S. Goldstein J.L. Cell. 1987; 48: 1061-1069Abstract Full Text PDF PubMed Scopus (135) Google Scholar). The three repeats lie within 100 bp upstream of the transcriptional start site. Repeats 1 and 3 contain Sp1 binding sites that support the basal transcriptional activity of LDLR. Interference of Sp1 binding to either repeat severely decreases basal transcription. Cholesterol regulation is mediated through a 10-bp sequence (5′-ATCACCCCAC-3′) within repeat 2 designated sterol responsive element-1 (SRE-1) (6Smith J.R. Osborne T.F. Goldstein J.L. Brown M.S. J. Biol. Chem. 1990; 265: 2306-2310Abstract Full Text PDF PubMed Google Scholar, 7Briggs M.R. Yokoyama C. Wang X. Brown M.S. Goldstein J.L. J. Biol. Chem. 1993; 268: 14490-14496Abstract Full Text PDF PubMed Google Scholar). Under low intracellular cholesterol conditions, the SRE-1-binding proteins SREBP1 and SREBP2 bind to the SRE-1 sequence and interact synergistically with Sp1 in repeat 3, leading to the activation of LDLR transcription (8Wang X. Briggs M.R. Hua X. Yokoyama C. Goldstein J.L. Brown M.S. J. Biol. Chem. 1993; 268: 14497-14504Abstract Full Text PDF PubMed Google Scholar, 9Wang X. Sato R. Brown M.S. Hua X. Goldstein J.L. Cell. 1994; 77: 53-62Abstract Full Text PDF PubMed Scopus (853) Google Scholar, 10Yokoyama C. Wang X. Briggs M.R. Admon A. Wu J. Hua X. Goldstein J.L. Brown M.S. Cell. 1993; 75: 187-197Abstract Full Text PDF PubMed Scopus (785) Google Scholar, 11Sanchez H.B. Yieh L. Osborne T.F. J. Biol. Chem. 1995; 270: 1161-1169Abstract Full Text Full Text PDF PubMed Scopus (272) Google Scholar). In addition to the SRE-1 site, another cis-acting element, designated FP1, was recently described that is located upstream of the repeat 1 sequence (–145 to –126) (12Mehta K.D. Chang R. Underwood J. Wise J. Kumar A. J. Biol. Chem. 1996; 271: 33616-33622Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar). The FP1 site participates in LDLR transcription only under conditions of sterol depletion. In addition to cholesterol and its derivatives, LDLR transcription is also subject to regulation by physiological non-sterol mediators, including growth hormone (13Rudling M. Norstedt G. Olivecrona H. Reihner E. Gustafsson J. Angelin B. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 6983-6987Crossref PubMed Scopus (234) Google Scholar, 14Rudling M. Angelin B. Proc. Natl. Acad. Sci. U. S. A. 1998; 90: 8851-8855Crossref Scopus (58) Google Scholar), hepatocyte growth factor (15Pak Y.K. Kanuck M.P. Berrios D. Briggs M.R. Cooper A.D. Ellsworth J.L. J. Lipid Res. 1996; 37: 985-998Abstract Full Text PDF PubMed Google Scholar), cytokines (16Stopeck A.T. Nicholson A.C. Mancini F.P. Haijar D.P. J. Biol. Chem. 1993; 268: 17489-17494Abstract Full Text PDF PubMed Google Scholar), and some pharmaceuticals (17Block L.H. Keul R. Crabos M. Ziesche R. Roth M. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 4097-4101Crossref PubMed Scopus (15) Google Scholar). The increased transcription of the LDLR gene induced by these agents has been ascribed to activation of protein kinase C, protein kinase A, and an increase in intracellular Ca2+ (18Kumar A. Chambers T.C. Cloud-Heflin B.A. Mehta K.D. J. Lipid Res. 1997; 38: 2240-2248Abstract Full Text PDF PubMed Google Scholar, 19Auwerx J.H. Chait A. Wolfbauer G. Deeb S.S. Mol. Cell. Biol. 1989; 9: 2298-2302Crossref PubMed Scopus (44) Google Scholar). However, the cis-acting elements in the LDLR promoter and the transcription factors that are responsible for regulation by cholesterol-independent pathways have not been elucidated. Our laboratory has been involved in characterizing the mechanism by which the cytokine oncostatin M (OM) activates LDLR transcription. OM, a member of the interleukin-6 family of cytokines, is a strong inducer of LDLR transcription in HepG2 cells and in mouse liver (20Grove R.I. Mazzucco C.E. Radka S.F. Shoyab M. Kiener P.A. J. Biol. Chem. 1991; 266: 18194-18199Abstract Full Text PDF PubMed Google Scholar, 21Liu J. Grove R.I. Vestal R.E. Cell Growth Differ. 1994; 5: 1333-1338PubMed Google Scholar, 22Liu J. Streiff R. Vestal R.E. Briggs M.R. J. Lipid Res. 1997; 38: Full Text PDF PubMed Google Scholar, J. Vestal R.E. D. Biol. 1997; PubMed Scopus Google Scholar). The mechanism of OM induction is we have that mutations within the SRE-1 site that abolished cholesterol regulation had no effect on OM of LDLR transcription. mutations within the repeat 3 sequence severely OM activity J. Streiff R. Vestal R.E. Briggs M.R. J. Lipid Res. 1997; 38: Full Text PDF PubMed Google Scholar). In to and the factors that OM-induced LDLR transcription by with the repeat 3 in the we the signal transduction pathways and that are involved in LDLR transcription. signaling pathways by OM and its cytokines interleukin-6 and leukemia inhibitory factor the transducer and activator of transcription pathway S. B.A. G. S. 1994; 263: PubMed Scopus Google and the protein kinase pathway B. D.P. S.K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, C. A.C. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). of OM to its activates 1, 2, and in transcription into by The 1, 3, and or and into the bind to This signaling pathway is responsible for OM-induced transcription of the kinase J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar), and for proteins C. J. J. C. E. Mol. Cell. Biol. 1994; PubMed Scopus Google Scholar, J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). However, the pathway not to involved in LDLR transcription no binding sites in the OM-responsive region of the LDLR promoter to of 3 or with LDLR promoter reporter constructs not basal or promoter activity J. Streiff R. Vestal R.E. Briggs M.R. J. Lipid Res. 1997; 38: Full Text PDF PubMed Google Scholar). in the we on the kinase Our in this demonstrate that LDLR transcription is also by the kinase inhibitors that signaling we demonstrate that inhibition of ERK activation by its upstream kinase, MEK, OM-induced LDLR mRNA also demonstrate that the activity of OM on the LDLR promoter is mediated through the repeat 3 we that the inhibition of ERK activation abolished OM activity on the LDLR These for the first an ERK responsive cis-acting element in the LDLR promoter and provide the first evidence that the repeat 3 sequence is a downstream target of kinase activation. The human HepG2 was and was in essential with human OM was by Cholesterol and and the were The was The was The p38 kinase was of The to were The and were The pLDLR-234 was constructed by a of the LDLR promoter by of (3Sudhof T.C. Van der Westhuyzen D.R. Goldstein J.L. Brown M.S. Russell D.W. J. Biol. Chem. 1987; 262: 10773-10779Abstract Full Text PDF PubMed Google into vector To construct the pLDLR-TATA a to LDLR promoter sequence to was with and sites at the and and was the and sites of The vector pLDLR-R3 was constructed by of a containing the LDLR promoter sequence to with and sites at the and into The repeat 3 sequence is were in and cellular was to the of was used to the LDLR mRNA described The were first to a human LDLR J. Streiff R. Vestal R.E. Briggs M.R. J. Lipid Res. 1997; 38: Full Text PDF PubMed Google and and with a human to that of were in of were by the of in these studies to of HepG2 cells in were into of 30 2 1 1 and and by through a were for 30 min at and at of 30 of protein were through a and to a The used to the and were first blocked in and in for 2 and with the containing at the of 1 at The ERK The used to and were blocked in containing for 2 and in containing and at a at was a and HepG2 cells were transiently transfected with by the of J. Streiff R. Vestal R.E. Briggs M.R. J. Lipid Res. 1997; 38: Full Text PDF PubMed Google Scholar). To demonstrate sterol-independent cells transfected with pLDLR-234 vector were in containing and cholesterol 1 the studies of kinase inhibitors, of inhibitors at the were 1 OM was of OM cells were with and with of reporter The luciferase of was with luciferase and the luciferase activity was in a activity of was to luciferase activity was activity to for were for and at three were for reporter The of OM-induced LDLR gene in HepG2 cells was by was cells that were with OM for 30 min to h. OM induced a rapid increase in LDLR mRNA This increase was detected 30 min OM addition to the cells, a maximal of at 1 and to at with GAPDH, showed that of cells with OM for 1 increased LDLR mRNA to an of with cells. The rapid of OM on LDLR mRNA that OM LDLR transcription in the of new protein To investigate this HepG2 cells were first with the protein synthesis inhibitors, and for 1 to addition of OM to the cells. of protein synthesis with that of protein synthesis in HepG2 cells was blocked by these inhibitors at the that the protein synthesis inhibitors had on the basal LDLR mRNA The LDLR mRNA was decreased in cells of but was significantly increased in of and of cells. However, the OM-induced of LDLR mRNA was not by of the LDLR mRNA was This that activation of LDLR transcription by OM not new protein kinase pathways have been to by OM and its pathway S. B.A. G. S. 1994; 263: PubMed Scopus Google Scholar, C. J. J. C. E. Mol. Cell. Biol. 1994; PubMed Scopus Google Scholar), kinase pathway B. D.P. S.K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, C. A.C. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), and H. H. H. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). previous studies the of in LDLR transcription J. Streiff R. Vestal R.E. Briggs M.R. J. Lipid Res. 1997; 38: Full Text PDF PubMed Google Scholar), we the on and the In cells, extracellular are through three kinase including kinase extracellular signal-regulated kinase (ERK) J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google the c-Jun N-terminal kinase M. A. A. M. 1993; PubMed Scopus Google Scholar), and kinase J. L. 1994; 265: PubMed Scopus Google Scholar). To which kinase pathway is involved in OM-induced LDLR mRNA expression, HepG2 cells were with OM for 1 in the or the of inhibitors and p38 kinase and was and the of LDLR mRNA was by The showed that the inhibitors, and were in OM-induced LDLR mRNA The of the OM activity was by at 1 and at In at to 100 which has been to completely activity H. H. H. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), had no The p38 kinase not OM activity at its A. J. R. T.F. 1995; PubMed Scopus Google but OM activity at 3). The of the kinase JNK, in OM-induced LDLR transcription was by has been to the of and ERK at 1998; PubMed Scopus Google Scholar). The pathway is to with an of activation of ERK by is with an of of cells with to the OM-induced increase in LDLR mRNA only This effect at of that the inhibitory activity of was mediated through its effect on ERK activation activation. The is a that Van P.A. J. Biol. Chem. 1998; 263: Full Text Full Text PDF Scopus Google Scholar). the activity of and 1 on other ERK, and showed a of D.R. A. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google on LDLR mRNA expression, the dose-dependent inhibitory effect of on OM activity was a OM activity with an of with inhibition at and This is in with its effect on MEK. The basal of LDLR mRNA was decreased by the These results demonstrate that inhibition of activity OM induction of LDLR inhibitors of p38 kinase and kinase only OM activity at these we that the kinase MEK/ERK cascade is the signaling pathway through which OM activates LDLR transcription. and are the only of and E. H. D. J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google Scholar). activates ERK by on both and of of kinase activity ERK activation. that ERK and that only the ERK was to OM-induced activation of in OM the of of and In the of and was increased by OM increase was detected at a maximal of at and to inhibition of OM-induced ERK activation was by This that OM activates both and and that this activation OM-induced LDLR transcription. Our was to the promoter region and the cis-acting element that the downstream target of the MEK/ERK by we localized the OM response to the LDLR promoter region to which repeats 1, 2, and 3 and the TATA-like studies of repeat showed that OM activity was only repeat 3 was J. Streiff R. Vestal R.E. Briggs M.R. J. Lipid Res. 1997; 38: Full Text PDF PubMed Google Scholar). To that repeat 3 is the response element that OM in the we constructed luciferase reporter that contain LDLR promoter TATA-like with or repeat was by of the LDLR promoter sequence to to the transcription start site into the luciferase the LDLR promoter sequence to The effect of OM on pLDLR-TATA and pLDLR-R3 was with its effect on pLDLR-234. These reporters, with the vector were transiently transfected into HepG2 cells and luciferase activity and activity were a that the basal promoter activities and the response to OM of the three reporter a low of luciferase activity and showed no response to a single copy of repeat 3 with the TATA sequence (pLDLR-R3) increased the basal of luciferase activity a promoter that was responsive to OM increased luciferase activity in cells to an to that in pLDLR-234-transfected cells. the results and that OM increased pLDLR-234 and pLDLR-R3 promoter activities and These provide strong evidence that the OM effect on the LDLR promoter is mediated through the repeat 3 whether ERK activation by inhibition of the ability of OM to increase the activity of the LDLR HepG2 cells were transfected with pLDLR-234 or was to the cells at for 1 by a dose-dependent inhibition of OM of both the full promoter and the promoter containing a single copy of repeat 3 (pLDLR-R3) The of that blocked OM-induced LDLR promoter activity is in a to that of inhibition of OM-induced LDLR mRNA These that an transcription activator is involved in LDLR transcription through with the repeat 3 to investigate whether the repeat 3 element in the LDLR promoter only OM signaling or whether is used by other of the family of cytokines, the activities of and on pLDLR-234 and pLDLR-R3 were and with OM in the or the of the the cytokines at increased LDLR promoter and activities were by The of these cytokines to increase LDLR promoter activity was in the OM LIF, which is with to kinase in HepG2 cells B. D.P. S.K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar). bind to and intracellular signaling by of the kinase family of the pathway and the has an essential in the activation of kinase, which and activates the ERK upstream and MEK, in activates and by of and in has been that OM activates and C. A.C. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google E. H. R. J. J. Biol. Chem. 1997; PubMed Scopus Google Scholar, M. M. J. A.C. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar, J. 1994; PubMed Scopus Google Scholar), we were in the downstream of this signaling cascade that a in the of LDLR transcription. inhibitors that signal we that the inhibitors and are in OM-induced LDLR inhibitors of 3-kinase, JNK, and p38 kinase had or no The inhibitory of p38 kinase at on OM-induced LDLR mRNA was to its on MEK, the OM-induced ERK activation detected by was also by at not The of on OM activity is to that for its inhibition of These provide evidence that the MEK/ERK cascade is the essential signaling pathway by which OM activates LDLR transcription. The of ERK activation in OM-induced LDLR transcription is also by the of these of ERK by OM was detected within a at min and to by This was by an increase in LDLR mRNA LDLR mRNA levels to 30 min of to OM, a maximal at 1 and decreased The of ERK activation and LDLR transcription that these by OM are of the essential of ERK activation in OM-induced LDLR transcription a which cis-acting element in the LDLR promoter is the downstream target of ERK we have localized the OM response to the LDLR promoter region to which repeats 1, 2, and 3 and the TATA-like within the repeat 3 sequence of pLDLR-234 significantly OM activity J. Streiff R. Vestal R.E. Briggs M.R. J. Lipid Res. 1997; 38: Full Text PDF PubMed Google Scholar). In this study, we demonstrate that OM activity is mediated through the repeat 3 OM had no effect on the basal LDLR promoter to that the TATA-like the 16-bp repeat 3 sequence to the basal promoter to is in the promoter the OM response that with the promoter Importantly, the OM-induced of pLDLR-234 and pLDLR-R3 were both by the These results for the first a region in the LDLR promoter that to kinase activation and demonstrate that the repeat 3 element is a new downstream target of the MEK/ERK cis-acting elements that the of the cytokines on gene transcription have been These S. J. Cell Biol. 1997; PubMed Scopus Google Scholar), binding site S. B.A. G. S. 1994; 263: PubMed Scopus Google Scholar), and E. H. R. J. J. Biol. Chem. 1997; PubMed Scopus Google Scholar, M. B. 1998; PubMed Google Scholar). In this study, we demonstrate that OM, and are of LDLR transcription through the repeat 3 These that the repeat 3 sequence a responsive element that the of OM and its cytokines on of a ERK to the a of transcription including of the and R. Cell Biol. 1996; PubMed Scopus Google Scholar, A.D. 1995; PubMed Scopus Google Scholar, R. J. 1998; Scopus Google Scholar). of by ERK the binding of and the of a at the response element of the in an activation of transcription of the gene H. M. C. C. J. 1995; PubMed Scopus Google Scholar). of the of the ERK or with the repeat 3 sequence not sequence Sp1 and the are the only transcription factors that have been to bind to the repeat 3 Sp1 was to by a protein kinase, but this not the and of binding or transcription S. Res. 1993; Google Scholar). the other a showed that Sp1 in leukemia cells was by protein kinase A, and the Sp1 binding and activities were also by protein kinase C. S. J. R.I. J. Biol. Chem. 1997; PubMed Scopus Google Scholar). have the that Sp1 is by ERK or an ERK OM in a increased transcriptional activity of LDLR However, we not OM-induced in Sp1 binding by or in the of the Sp1 by J. Streiff R. Vestal R.E. Briggs M.R. J. Lipid Res. 1997; 38: Full Text PDF PubMed Google Scholar). the at that blocked ERK activation had no effect on Sp1 binding activity not is whether Sp1 is by ERK or downstream at Sp1 binding This the of Sp1 to interact with other transcription factors or an a direct or of activation by OM, this factor either with Sp1 a or bind to the repeat 3 LDLR transcription. These are under Kumar A. A. Chambers T.C. Mehta K.D. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google that LDLR transcription was mediated through ERK activation. However, of the of with OM on LDLR transcription that these cytokines LDLR transcription through the of OM in LDLR mRNA is that of OM activity a at 1 and a increase in LDLR mRNA induced by was not and levels to increase cholesterol has no effect on OM induction of LDLR mRNA or on LDLR promoter but cholesterol abolished the increase in LDLR mRNA the activity of which on LDLR mRNA was by at of the OM-induced LDLR mRNA was not significantly by at and was at that p38 kinase involved in but not a in OM-induced LDLR transcription. the effect of on the LDLR promoter was within a reporter construct containing a of the LDLR is not region of the LDLR promoter was responsible for the effect whether the element is the cis-acting element that to ERK activation. These the of ERK activation in both OM-induced and LDLR that ERK activation involved both in and cholesterol-independent regulation of LDLR transcription. In we have that the kinase MEK/ERK cascade is the essential signaling pathway by which OM activates LDLR gene transcription. The repeat 3 sequence of the LDLR promoter not only an Sp1 binding site that basal transcription but also is an OM-responsive element that converts ERK activation at the LDLR promoter These results provide for characterizing the transcriptional that LDLR transcription of the at and R. Briggs at for M. and at for the C. at for the p38 kinase and Streiff for the