Induction of tumor necrosis factor cv gene expression by lipoprotein lipase

In view of the suppressive effect of tumor necrosis factor a (TNFa) on lipoprotein lipase (LPL) and of the potential proatherogenic effects of these two macrophage secretory products, we have tested the possibility that LPL could modulate the production of T N F a . Treatment of macrophages with lipoprotein lipase induced tumor necrosis factor a gene expression and protein secretion. Maximal increase of T N F a mRNA levels occurred after a 3-h treatment with 200 ng/ml LPL. An additive effect of interferon y (IFNy) was observed on LPL-induced T N F a mRNA expression. De novo mRNA synthesis was required for induction of T N F a mRNA by LPL as no induction was observed when macrophages were pretreated with actinomycin D before adding LPL. We further established that LPL induced the transcription of the T N F a gene in macrophages. We also found that LPL caused the nuclear migration of one member of the NFkB family that appears to bind to a site in the murine T N F a gene promoter. Furthermore, we demonstrated that the treatment of macrophages with LPL increased the stability of T N F a mRNA.m These results show that the T N F a gene induction in response to LPL involves both transcriptional activation and the enhancement of T N F a mRNA stability. Overall, our data demonstrate a new role for LPL, that of modulating macrophage T N F a gene expression. This effect may represent one of the mechanisms by which LPL may favor the development of atherosclerosis.Renier, G., E. Skamene, J. B. DeSanctis, and D. Radzioch. Induction of tumor necrosis factor a gene expression by lipoprotein lipase. J. Lipid Res. 1994. 35: 271-278. scriptional activation, cell stimulation with LPS is associated with a release from translational blockage (3). These data indicate that LPS is a very powerful T N F a inducer as it augments both the transcription and the stability of the T N F a messenger. The rapid down-regulation of T N F a receptor expression (4) and the release of several secretory products, such as prostaglandin E2 (5), protect macrophages from the harmful effects of TNFa. Lipoprotein lipase (LPL) is a key enzyme in the metabolism of lipoproteins (6). It is constitutively expressed by macrophages (7) and synthesized by the parenchymal cells of various tissues (8-12). The demonstration of a suppressive effect of TNFa on LPL production (13) and the possibility that both macrophage cytokines may play a role in the development of atherosclerosis (14, 15) led us to investigate the possible effect of LPL on the regulation of TNFa mRNA gene expression in macrophages. Our results demonstrate that LPL can induce T N F a mRNA expression and that its effect involves transcriptional events as well as posttranscriptional modifications. These observations underline the importance of LPL in macrophage biology and define a novel mechanism of regulation of T N F a production. Supplementary key words gene expression macrophage MATERIALS AND METHODS TNFa is an important secretory product of macrophages directly involved in inflammatory reactions after a variety of bacterial infections (1). It has been well established that TNFa gene expression is tightly controlled both at the transcriptional and posttranscriptional levels (2, 3). Both the T N F a promoter and 3' untranslated region are involved in the response to lipopolysaccharide (LPS), the former at the transcriptional level and the latter at the translational level, leading to a synergistic effect on protein synthesis. LPS-mediated transcriptional activation of the T N F a gene has been shown to involve kB-type enhancers (2). In addition to LPS effects on tranReagents Fetal bovine serum (FBS) was purchased from Hyclone Lab. (Logan, UT). Dulbecco's minimal essential medium (DMEM) was obtained from ICN Biochemicals Inc., Costa Mesa, CA, and supplemented with 10% fetal bovine serum (FBS), 2 mM L-glutamine (ICN, Biochemicals Inc.) and penicillin-streptomycin (Flow, McLean, Abbreviations: LPL, lipoprotein lipase; T N F a , tumor necrosis factor a; IFNy, interferon y; LPS, lipopolysaccharide; GAPDH, glyceraldehyde-3-phosphate dehydrogenase. 'To whom correspondence and reprint requests should be addressed. Journal of Lipid Research Volume 35, 1994 271 by gest, on O cber 8, 2017 w w w .j.org D ow nladed fom VA). Actinomycin D (Dact), phospholipase A2 (PLA,) (200-400 U/mg protein) were purchased from Sigma Chemical Co. (St. Louis, MO). Recombinant murine IFNy was obtained from Amgen Biologicals (Thousand Oaks, CA).