Activation of LDL receptor gene expression in HepG2 cells by hepatocyte growth factor

Pak, Youngmi Kim; Kanuck, M P; Berrios, Daniel C.; Briggs, Mason; Cooper, Allen D.; Ellsworth, Jeff L.

doi:10.1016/s0022-2275(20)42009-7

Cited by 43 publications

(6 citation statements)

References 42 publications

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“…In our study with macrophages, however, tyrosine kinases did not appear to be involved in NF-κB transactivation, suggesting that SR gene expression might not be mediated by NF-κB. For the NF-κB activity assay we utilized the luciferase reporter construct bearing the E-selectin promoter [20], which contains three upstream NF-κB binding sites ; thus the expression of E-selectin should be induced by oxLDL or lysoPC through NF-κB activation. It should also be noted that the regulatory pathway of NF-κB activation observed in the present study might be limited to the case of E-selectin or to genes bearing multi-NF-κB binding sites in their promoter.…”

Section: Discussionmentioning

confidence: 80%

“…with pNF-κB-luc, a luciferase reporter construct with an Eselectin promoter (k730 to j52) containing three upstream NF-κB binding elements [20], and pHbNeo-β-gal [21] by calcium phosphate co-precipitation. The neomycin-resistant cells were selected using G418 (400 µg\ml).…”

Section: Figure 2 Oxldl Activates Nf-κb In Resting Macrophages In An Oxidationdependent Mannermentioning

confidence: 99%

“…In order to quantify NF-κB-mediated transcriptional activity, RAW264.7 cells were stably transfected with pNF-κB-luc [20] and pools of G418-resistant cells were obtained. This reporter construct contains three NF-κB-binding sites, and oxLDL was able to induce this promoter-mediated transcriptional activity.…”

Section: Oxldl Increases Nf-κb-mediated Transcriptional Activity In Resting Macrophagesmentioning

confidence: 99%

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Role of endocytosis in the transactivation of nuclear factor-κB by oxidized low-density lipoprotein

Han

Park

Pak

2000

Biochemical Journal

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Oxidized low-density lipoprotein (oxLDL) has been shown to modulate transactivation by the peroxisome proliferator-activated receptor (PPAR)-gamma and by nuclear factor-kappaB (NF-kappaB). In the present study, the oxLDL signalling pathways involved in NF-kappaB transactivation were investigated by utilizing a reporter construct driven by three upstream NF-kappaB binding sites, and various pharmacological inhibitors. OxLDL and its constituent lysophophatidylcholine (lysoPC) induced a rapid and transient increase in intracellular calcium and stimulated NF-kappaB transactivation in resting RAW264.7 macrophage cells in an oxidation-dependent manner. NF-kappaB activation by oxLDL or lysoPC was inhibited by inhibitors of protein kinase C or by a chelator of intracellular calcium. Tyrosine kinase or phosphatidylinositol 3-kinase inhibitors did not block NF-kappaB transactivation. Furthermore, oxLDL-induced NF-kappaB activity was abolished by PPAR-gamma ligands. When the endocytosis of oxLDL was blocked by cytochalasin B, NF-kappaB transactivation by oxLDL was synergistically increased, while PPAR transactivation was blocked. These results suggest that oxLDL activates NF-kappaB in resting macrophages via protein kinase C- and/or calcium-dependent pathways, and that this does not involve the endocytic processing of oxLDL. The endocytosis-dependent activation of PPAR-gamma by oxLDL may function as a route of inactivation of the oxLDL-induced NF-kappaB signal.

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Section: Discussionmentioning

confidence: 80%

Section: Figure 2 Oxldl Activates Nf-κb In Resting Macrophages In An Oxidationdependent Mannermentioning

confidence: 99%

Section: Oxldl Increases Nf-κb-mediated Transcriptional Activity In Resting Macrophagesmentioning

confidence: 99%

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Role of endocytosis in the transactivation of nuclear factor-κB by oxidized low-density lipoprotein

Han

Park

Pak

2000

Biochemical Journal

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“…Other investigators have proposed that cellular mito-gens and growth factors may increase LDL receptor expression in an SRE-dependent manner (28,29). Thus, hepatocyte growth factor increased LDL receptor expression in a cultured hepatocellular carcinoma cell line, HepG2, and also increased expression of a reporter gene driven by 3 tandem copies of repeats 2 and 3 (SRE-1 and Sp1, respectively) of the LDL receptor promoter (29). In addition, a point mutation in SRE-1 abolished insulin-and estradiol-induced increases in reporter gene expression driven by LDL receptor promoter fragments in HepG2 cells (28).…”

Section: Discussionmentioning

confidence: 99%

Sterol-independent, sterol response element-dependent, regulation of low density lipoprotein receptor gene expression

Makar

Lipsky

Cuthbert

1998

Journal of Lipid Research

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Stimulation with phorbol 12-myristate 13-acetate (PMA) and the calcium ionophore ionomycin increased native low density lipoprotein (LDL) receptor gene expression in the human leukemic T cell line Jurkat when cells were cultured in the absence of sterols and also increased nuclear accumulation of sterol regulatory element binding protein (SREBP)-1. PMA and ionomycin likewise increased LDL receptor mRNA levels when cells were cultured in the presence of suppressive concentrations of sterols, when neither SREBP-1 nor SREBP-2 was detectable in the nucleus. These findings indicated that mitogen-induced up-regulation of the LDL receptor gene could be independent of sterolregulated transcription factors. The involvement of sterol regulatory element (SRE)-1 was analyzed by transfection of LDL receptor promoter constructs. Promoter fragments of either the 5 1472 or 142 base pairs induced reporter gene expression after mitogenic stimulation when cells were cultured in the absence or presence of sterols. Mutation of the SRE-1 sequence in either construct abolished sterol-mediated regulation of transcription. However, mutation of the SRE-1 sequence in the 1472 base pair promoter fragment did not alter mitogenic induction of transcription, whereas mutation of SRE-1 in the 142 base pair promoter fragment completely prevented up-regulation of transcription. Taken together, these results demonstrate that the LDL receptor promoter contains at least one 5 SRE-independent as well as an SRE-dependent response element. Furthermore, the data suggest that the SRE-dependent response may not involve the action of either SREBP-1 or -2. Thus, mitogen-induced transcription of the LDL receptor promoter is regulated by diverse sterol-independent mechanisms.-

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“…Non-sterol regulation of LDL receptor gene expression is less well-characterized than sterol regulation. Growth factors and mitogenic stimuli, hormones, cytokines, signaling agonists and protein synthesis inhibitors may each increase LDL receptor mRNA levels in different model systems (28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42). Whereas some of these responses are considered related to sterol regulation (40,43), we have previously demonstrated that some of these responses are independent of sterols, independent of not only SREBPs but also of SRE-1 (17).…”

Section: Discussionmentioning

confidence: 99%

Multiple mechanisms, independent of sterol regulatory element binding proteins, regulate low density lipoprotein gene transcription

Makar

Lipsky

Cuthbert³

2000

Journal of Lipid Research

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Transcription of the LDL receptor gene is markedly enhanced in the Jurkat T cell line by stimulation with the combination of the phorbol ester phorbol 12-myristate 13-acetate (PMA) and the protein synthesis inhibitor cycloheximide (CHX). The DNA sequences necessary for this response were identified by analysis of Jurkat T cells permanently transfected with reporter gene expression vectors containing fragments of the LDL receptor promoter extending from 68 bp to 1472 bp 5 of the major transcription start site. The magnitude of the response of this array of promoter fragments to stimulation with PMA and CHX was similar to that previously observed with a ϳ 6.5 kb promoter fragment. However, the various promoter fragments differed with regard to the role of the sterol regulatory element-1 (SRE-1) sequence. Thus, whereas a 142 bp promoter mediated transcription stimulated by PMA and CHX independently of SRE-1, a shorter 115 bp promoter was absolutely dependent on SRE-1. Furthermore, internal deletion of promoter sequences from ؊ 142 bp to ؊ 113 bp from longer promoter constructs in which the SRE-1 was mutated prevented the induction of transcription by PMA and CHX. Electrophoretic mobility shift assays (EMSAs) demonstrated sequence-specific, stimulus-independent binding by Jurkat nuclear proteins to the novel response element mapped between ؊ 142 and ؊ 115. Even though the minimal 115 bp or 68 bp promoter fragment required an intact SRE-1 to respond to PMA and CHX, transcriptional induction persisted when nuclear levels of sterol regulatory element binding proteins (SREBPs) were made undetectable by culture in suppressive sterols. Taken together, these data indicate that non-sterol stimuli such as the combination of PMA and CHX induce LDL receptor gene transcription through at least two distinct promoter elements, neither of which requires the presence of SREBPs. However, the element proximal to the transcription start site is dependent on the SRE-1. -Makar, R. S. J., P. E. Lipsky, and J. A. Cuthbert. Multiple mechanisms, independent of sterol regulatory element binding proteins, regulate low density lipoprotein gene transcription.

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Activation of LDL receptor gene expression in HepG2 cells by hepatocyte growth factor

Cited by 43 publications

References 42 publications

Role of endocytosis in the transactivation of nuclear factor-κB by oxidized low-density lipoprotein

Role of endocytosis in the transactivation of nuclear factor-κB by oxidized low-density lipoprotein

Sterol-independent, sterol response element-dependent, regulation of low density lipoprotein receptor gene expression

Multiple mechanisms, independent of sterol regulatory element binding proteins, regulate low density lipoprotein gene transcription

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