Galectin-3 expression in macrophages is signaled by Ras/MAP kinase pathway and up-regulated by modified lipoproteins.
To study the signaling pathway involved in the regulation of galectin-3 expression we used phorbol ester to stimulate macrophage differentiation of THP-1 cells. Treatment with phorbol 12-myristate 13-acetate (PMA) increased significantly the level of expression of galectin-3 in THP-1 cells. PMA-induced galectin-3 overexpression was blocked by: protein kinase C inhibitors staurosporine, calphostin C, and apigenin; tyrosine-specific protein kinase inhibitors genistein and tyrphostin A25; PD 98059, a selective inhibitor of mitogen-activated protein kinase (MAPK) kinase 1 (MEK1 or MKK1); and SB 203580, a specific inhibitor of p38 MAPK. Galectin-3 up-regulation was not affected by exposure to two inhibitors of cAMP-dependent protein kinase (PKA), H-89 and KT5720. Co-transfection of pPG3.5, a plasmid vector containing the rabbit galectin-3 promoter and the constructs pMCL-MKK1 N3 or pRC-RSV-MKK3Glu that constitutively express MKK1 and MKK3, raised the activity of galectin-3 promoter by 185% and 110%, respectively. Co-transfection with a Ha-Ras expression vector stimulated galectin-3 promoter activity approximately 10-fold. Expression of c-Jun or v-Jun raised the level of galectin-3 promoter activity more the three- and fourfold, respectively. Co-transfection of c-Jun and pPG3.5 5'-upstream deletion mutants resulted in a reduction of the galectin-3 promoter activity by 50% to 80%. Transfection of c-Jun, v-Jun or Ha-Ras increased significantly galectin-3 protein in THP-1 cells. These findings indicated that Ras/MEKK1/MKK1-dependent/AP-1 signal transduction pathway plays an important role in the expression of galectin-3 in PMA-stimulated macrophages. We further investigated the effect of modified lipoproteins on galectin-3 expression in macrophages. Murine resident peritoneal macrophages loaded with acetylated low-density lipoprotein (AcLDL) or oxidized LDL (OxLDL) showed increased galectin-3 protein and mRNA. These results showed that treatment of macrophages with PMA or modified lipoproteins results in galectin-3 overexpression. These findings may explain the enhanced expression of galectin-3 in atherosclerotic foam cells and suggest that Ras/MAPK signal transduction pathway is involved in controlling this gene.
Kim
Koanhoi
K
Department of Pathology and Microbiology, University of South Carolina-School of Medicine, Columbia, SC 29208, USA.
Mayer
Eugene P
EP
Nachtigal
Maurice
M
D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D037502:Galectin 3 / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects*; D016758:Genes, jun / Q000187:drug effects; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000502:physiology*; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008809:Mice, Inbred C3H; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D011817:Rabbits; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015854:Up-Regulation; D018631:ras Proteins / Q000378:metabolism*
D004791:Enzyme Inhibitors; D037502:Galectin 3; D016755:Proto-Oncogene Proteins c-jun; D017346:Protein Serine-Threonine Kinases; D011493:Protein Kinase C; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins; D013755:Tetradecanoylphorbol Acetate