Interleukin-6 stimulates LDL receptor gene expression via activation of sterol-responsive and Sp1 binding elements

Inflammatory or malignant diseases are associated with elevated levels of c ytokines and abnormal low density lipoprotein (LDL) cholesterol metabolism, In the acute-phase response to myocardial injury or other trauma or surger y, total and LDL cholesterol levels are markedly decreased. We investigated the effects of the proinflammatory cytokine interleukin (IL)-6 on LDL rece ptor (LDL-R) function and gene expression in HepG2 cells. IL-6 dose-depende ntly increased the binding, internalization, and degradation of I-125-LDL, IL-6-stimulated HepG2 cells revealed increased steady-state levels of LDL-R tnRNA, In HepG2 cells transiently transfected with reporter gene construct s harboring the sequence of the LDL-R promoter extending from nucleotide -1 563 (or from nucleotide -234) through -58 relative to the translation start site, IL-6 dose-dependently increased promoter activity. In the presence o f LDL, a similar relative stimulatory effect of IL-6 was observed. Studies using a reporter plasmid with a functionally disrupted sterol-responsive el ement (SRE)-1 revealed a reduced stimulatory response to IL-6. In gel-shift assays, nuclear extracts of IL-6-treated HepG2 cells showed an induced bin ding of SRE binding protein (SREBP)-1a and SRE binding protein(SREBP)-2 to the SRE-1 that was independent of the cellular sterol content and an induce d binding of Spl and Sp3 to repeat 3 of the LDL-R promoter. Our data indica te that IL-6 induces stimulation of the LDL-R gene, resulting in enhanced g ene transcription and LDL-R activity. This effect is sterol independent and involves, on the molecular level, activation of nuclear factors binding to SRE-1 and the Sp1 binding site in repeat 2 and repeat 3 of the LDL-R promo ter, respectively.