RESUMO
FDPS (farnesyl diphosphate synthase) catalyses the formation of farnesyl diphosphate, a key intermediate in the synthesis of cholesterol and isoprenylated cellular metabolites. FDPS is also the molecular target of nitrogen-containing bisphosphonates, which are used as bone-antiresorptive drugs in various disorders. In the present study, we characterized the sterol-response element and NF-Y (nuclear factor Y)-binding site in the human FDPS promoter. Using a luciferase assay, electrophoretic mobility-shift assay and chromatin immunoprecipitation assay, we demonstrated that these elements are responsible for the transcription of the FDPS gene, and that its transcriptional activation is mediated by SREBP-2 (sterol-regulatory-element-binding protein 2) and NF-Y. We also investigated whether sterol-mediated FDPS expression is involved in the cell proliferation induced by zoledronic acid, an FDPS inhibitor. We show that the SREBP-2- and NF-Y-mediated regulation of FDPS gene transcription modulates cell proliferation. These results suggest that SREBP-2 and NF-Y are required to trigger cell proliferation through the induction of FDPS expression and that the pharmacological action of zoledronic acid is involved in this pathway.
Assuntos
Fator de Ligação a CCAAT/metabolismo , Geraniltranstransferase/genética , Hepatoblastoma/genética , Hepatoblastoma/metabolismo , Neoplasias Hepáticas/genética , Neoplasias Hepáticas/metabolismo , Proteína de Ligação a Elemento Regulador de Esterol 2/metabolismo , Sequência de Bases , Sítios de Ligação/genética , Conservadores da Densidade Óssea/farmacologia , Fator de Ligação a CCAAT/antagonistas & inibidores , Fator de Ligação a CCAAT/genética , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Sequência Conservada , Primers do DNA/genética , DNA de Neoplasias/genética , DNA de Neoplasias/metabolismo , Difosfonatos/farmacologia , Técnicas de Silenciamento de Genes , Geraniltranstransferase/biossíntese , Hepatoblastoma/patologia , Humanos , Imidazóis/farmacologia , Neoplasias Hepáticas/patologia , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Regiões Promotoras Genéticas , RNA Interferente Pequeno/genética , Homologia de Sequência do Ácido Nucleico , Proteína de Ligação a Elemento Regulador de Esterol 2/antagonistas & inibidores , Proteína de Ligação a Elemento Regulador de Esterol 2/genética , Esteróis/metabolismo , Ativação Transcricional , Transfecção , Ácido ZoledrônicoRESUMO
Liver X receptor alpha (LXRalpha) is a member of the nuclear receptor superfamily that is activated by oxysterols, and plays a pivotal role in regulating the metabolism, transport and uptake of cholesterol. Here, we demonstrate that LXRalpha also regulates the low-density lipoprotein receptor (LDLR) gene, which mediates the endocytic uptake of LDL cholesterol in the liver. An LXR agonist induced the expression of LDLR in cultured hepatoblastoma cells. Moreover, the LDLR promoter contained an LXR response element that was recognized by LXRalpha/RXRalpha (retinoid X receptor alpha) heterodimers in hepatoblastoma cells. These results suggest a novel pathway whereby LXRalpha might modulate cholesterol metabolism.