Effect of tumor necrosis factor and interferon-gamma on platelet-derived growth factor (PDGF) A and B gene expression in THP-1 monocytic cells

Abstract

Platelet-derived growth factor (PDGF) is a potent mitogen of mesenchymal cells. A and B chains of PDGF are transcribed in atherosclerotic plaques but details of the mechanism of the expression of either chains in vivo are not understood. It has been suggested that differentiated macrophages, which are the major origin of foam cells, but not monocytes hardly secrete PDGF in vitro. In the present study, we investigated the effect of 1) tumor necrosis factor-alpha (TNF-alpha), a macrophage derived cytokine which promote the differentiation from monocytes to macrophages, and 2) interferon-gamma (IFN-gamma), a T cell derived macrophage activating factor, on the production and mRNA expression of PDGF A and B chains in a human monocytic leukemia cell line THP-1. THP-1 cells were cultured in the presence of one of the experimental cytokines with or without the addition of phorbol 12-myristate 13-acetate (PMA). PMA is known to induce the differentiation of monocytes (including THP-1 cells) to macrophages within a period of 24 hours. Thus the treatment of THP-1 cells with a cytokine and/or PMA in vitro was expected to mimic the effect of the cytokine during the differentiation of monocytes to macrophages in vivo. Unstimulated THP-1 cells expressed no detectable amount of PDGF A or B mRNA. The treatment of THP-1 cells with PMA resulted in the strong expression of both PDGF A and B mRNAs. Stimulated with TNF-alpha (50 U/ml) on day 0, THP-1 cells expressed PDGF A mRNA significantly from 1 up to 3 days after the treatment, whereas the expression of PDGF B and mRNA was only weakly detected on day 2. The maximum signal of PDGF A mRNA was ten times stronger than that of PDGF B mRNA. Within the same period, relatively small number of TNF-alpha treated THP-1 cells had differentiated to macrophages as detected by the reduction of nitro blue tetrazolium (NBT) (35% of total cells) and by the counting of adherent cells (35% of total cells). THP-1 cells simultaneously treated with TNF-alpha and PMA strongly expressed PDGF A and B gene. Most remarkably, the expression of PDGF B mRNA was greatly enhanced with compared to the treatment with PMA alone. In addition, TNF-alpha augmented the secretion of PDGF proteins in PMA stimulated THP-1 cells. In contrast, INF gamma per se had no effect on PDGF gene expression, NBT reducing activity and cell adherence in unstimulated THP-1 cells.(ABSTRACT TRUNCATED AT 400 WORDS)