The role of mitogen-activated protein kinases and sterol receptor coactivator-1 in TGF-β-regulated expression of genes implicated in macrophage cholesterol uptake.

Rebecca C Salter,Dipak P Ramji,Tim G Ashlin,Pelagia Foka,Hayley Gallagher,Thomas S Davies,Daryn R Michael

doi:10.1038/srep34368

Rebecca C Salter, Dipak P Ramji + Show 5 more

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https://doi.org/10.1038/srep34368

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Abstract

The anti-atherogenic cytokine TGF-β inhibits macrophage foam cell formation by suppressing the expression of key genes implicated in the uptake of modified lipoproteins. We have previously shown a critical role for p38 MAPK and JNK in the TGF-β-mediated regulation of apolipoprotein E expression in human monocytes. However, the roles of these two MAPK pathways in the control of expression of key genes involved in the uptake of modified lipoproteins in human macrophages is poorly understood and formed the focus of this study. TGF-β activated both p38 MAPK and JNK, and knockdown of p38 MAPK or c-Jun, a key downstream target of JNK action, demonstrated their requirement in the TGF-β-inhibited expression of several key genes implicated in macrophage lipoprotein uptake. The potential role of c-Jun and specific co-activators in the action of TGF-β was investigated further by studies on the lipoprotein lipase gene. c-Jun did not directly interact with the minimal promoter region containing the TGF-β response elements and a combination of transient transfection and knock down assays revealed an important role for SRC-1. These studies provide novel insights into the mechanisms underlying the TGF-β-mediated inhibition of macrophage gene expression associated with the control of cholesterol homeostasis.

Highlights

In cultured macrophages and in mouse model systems[7,8,9,12,13]
This system was employed to investigate the potential role of the Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinases (MAPKs) pathways in TGF-βsignaling in relation to the expression of key genes implicated in the control of macrophage lipoprotein uptake
Western blot analysis showed that TGF-βincreased the levels of phosphorylated, activated forms of p38 MAPK and JNK, without affecting the total levels of these proteins, with maximal levels of activated protein typically attained at 24 h (Supplementary Fig. 1A,B)

Summary

Introduction

In cultured macrophages and in mouse model systems[7,8,9,12,13]. Numerous in vitro studies from our own and other laboratories have demonstrated that TGF-βnegatively regulates the expression of key genes implicated in cholesterol uptake such as LPL and scavenger receptors (SR)–A1, -B1 and CD367–9,12,13. Relatively little is known about the role of MAPKs in TGF-βsignaling in macrophages, in relation to the control of expression of key genes implicated in the regulation of cholesterol homeostasis and foam cell formation. As apoE is involved in the control of macrophage cholesterol efflux, the role of these two kinases in the TGF-β-mediated regulation of key genes implicated in the uptake of modified LDL, such as SR-A1, SR-B1, CD36 and LPL, remains to be determined. The purpose of this study was to investigate the role of these kinases in the TGF-β-mediated inhibition of expression of key genes implicated in the control of modified lipoprotein uptake by human macrophages together with the potential underlying mechanisms

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