Dataset Information

Regulation of lipoprotein lipase mRNA content in 3T3-L1 cells by tumour necrosis factor.

ABSTRACT: Tumour necrosis factor (TNF) was previously shown to suppress lipoprotein lipase (LPL) synthesis and activity in 3T3-L1 adipocytes. The present study examined the effect of TNF on amounts of mRNA for LPL in 3T3-L1 cells. Northern-blot analysis of polyadenylated RNA using a cDNA probe to guinea-pig LPL identified two predominant species of LPL message, 3.7 and 3.9 kilobases in size. The steady-state amounts of these mRNAs increased 10-fold upon expression of the adipocyte phenotype. A single dose of 1.5 nM-TNF decreased LPL mRNA by approx. 60% in 17 h with a corresponding decrease in LPL activity, an effect that was reversed 48 h after exposure to TNF. The results demonstrate that TNF reversibly down-regulates LPL mRNA in fully differentiated 3T3-L1 adipocytes. Cells induced to differentiate in the presence of 1.5 nM-TNF exhibited a delayed time course for development of the adipocyte phenotype, as judged by attenuation of the normal increase in LPL mRNA that occurs with differentiation.

SUBMITTER: Cornelius P

PROVIDER: S-EPMC1148772 | biostudies-other | 1988 Feb

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:Tumour necrosis factor alpha (TNF-alpha) regulates the transport of myo-inositol in 3T3-L1 adipocytes. Treating 3T3-L1 adipocytes with TNF-alpha decreases Na+/myo-inositol co-transporter (SMIT) mRNA levels and myo-inositol accumulation in a concentration-and time-dependent manner. TNF-alpha decreases the V'max for high-affinity myo-inositol transport with little change in the K'm. Studies with actinomycin D suggest that RNA synthesis is required for the TNF-alpha-induced effect on SMIT mRNA levels. In contrast with the effect of TNF-alpha, hyperosmolarity increases SMIT mRNA levels and myo-inositol accumulation in 3T3-L1 adipocytes. Hyperosmolarity increases SMIT gene expression as evidenced by the inhibition of hyperosmotic induction of SMIT mRNA levels by actinomycin D, and of myo-inositol accumulation by actinomycin D and cycloheximide. TNF-alpha and osmotic stress have previously been shown to activate similar signal transduction pathways in mammalian cells. In 3T3-L1 adipocytes, both TNF-alpha and hyperosmolarity increase mitogen-activated protein kinase kinase pathway activity; however, with the possible exception of c-Jun N-terminal kinase, this pathway does not seem to regulate SMIT mRNA levels or myo-inositol accumulation. TNF-alpha activates nuclear factor kappaB (NF-kappaB) in 3T3-L1 adipocytes but, unlike the effect of TNF-alpha on cultured endothelial cells, NF-kappaB does not seem to contribute to the regulation by TNF-alpha of SMIT gene expression in 3T3-L1 adipocytes. Therefore other signal transduction pathways must be considered in the regulation by TNF-alpha of SMIT mRNA levels and activity. Thus TNF-alpha and hyperosmolarity have opposing effects on SMIT mRNA levels and activity in 3T3-L1 adipocytes. Because myo-inositol in the form of phosphoinositides is an important component of membranes and signal transduction pathways, the regulation of myo-inositol metabolism by TNF-alpha might represent another mechanism by which TNF-alpha regulates adipocyte function.

Project description:In obesity, high levels of tumor necrosis factor ? (TNF?) stimulate lipolysis in adipocytes, leading to hyperlipidemia and insulin resistance. Thiazolidinediones (TZDs), the insulin-sensitizing drugs, antagonize TNF?-induced lipolysis in adipocytes, thereby increasing insulin sensitivity in diabetes patients. The cellular target of TZDs is peroxisome proliferator-activated receptor ? (PPAR?), a nuclear receptor that controls many adipocyte functions. As a transcription factor, PPAR? is closely modulated by coregulators, which include coactivators and corepressors. Previous studies have revealed that in macrophages, the insulin-sensitizing effect of PPAR? may involve suppression of proinflammatory gene expression by recruiting the corepressor complex that contains corepressors and histone deacetylases (HDACs). Therefore, we investigated whether the corepressor complex is involved in TZD-mediated suppression of TNF?-induced lipolysis in 3T3-L1 adipocytes. Trichostatin A (TSA), a pan HDAC inhibitor (HDACI) that inhibits class I and II HDACs, was used to examine the involvement of HDACs in the actions of TZDs. TSA alone increased basal lipolysis and attenuated TZD-mediated suppression of TNF?-induced lipolysis. Increased basal lipolysis may in part result from class I HDAC inhibition because selective class I HDACI treatment had similar results. However, attenuation of TZD-mediated TNF? antagonism may be specific to TSA and related hydroxamate-based HDACI rather than to HDAC inhibition. Consistently, corepressor depletion did not affect TZD-mediated suppression. Interestingly, TSA treatment greatly reduced PPAR? levels in differentiated adipocytes. Finally, extracellular signal-related kinase 1/2 (ERK1/2) mediated TNF?-induced lipolysis, and TZDs suppressed TNF?-induced ERK phosphorylation. We determined that TSA increased basal ERK phosphorylation, and attenuated TZD-mediated suppression of TNF?-induced ERK phosphorylation, consistent with TSA's effects on lipolysis. These studies suggest that TSA, through down-regulating PPAR?, attenuates TZD-mediated suppression of TNF?-induced ERK phosphorylation and lipolysis in adipocytes.

Dataset Information

Regulation of lipoprotein lipase mRNA content in 3T3-L1 cells by tumour necrosis factor.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets