Abstract
Human lysosomal acid lipase (LAL) is a hydrolase required for the cleavage of cholesteryl esters and triglycerides derived from plasma lipoproteins. It is shown here that during monocyte to macrophage differentiation, the expression of LAL-mRNA is induced. This induction is dependent on protein kinase C activity and protein synthesis. The cell type-specific increase in LAL expression is further investigated in the THP-1 cell line with respect to transcriptional regulation. The human monocytic leukemia cell line THP-1 differentiates into macrophage-like cells when treated with phorbol esters. In order to determine the cis-acting elements necessary for both basal and phorbol 12-myristate-13 acetate (PMA)-enhanced promoter activity, we performed deletion analysis and reporter gene assays. A PMA responsive element has been identified between −182 bp and −107 bp upstream of the major transcription start site. Gel mobility shift assays demonstrated that binding of Sp1 and AP-2 to the LAL promoter is increased by PMA in THP-1 cells. Co-transfections with expression plasmids for Sp1 and AP-2 further emphasized the important role of these transcription factors in both basal and PMA-enhanced LAL expression. Our data suggest that differentiation dependent increase of lysosomal acid lipase (LAL) expression in THP-1 cells is mediated by a concerted action of Sp1 and AP-2. —Ries, S., C. Büchler, T. Langmann, P. Fehringer, C. Aslanidis, and G. Schmitz. Transcriptional regulation of lysosomal acid lipase in differentiating monocytes is mediated by transcription factors Sp1 and AP-2. J. Lipid Res. 1998. 39: 2125–2134.
Highlights
Human lysosomal acid lipase (LAL) is a hydrolase required for the cleavage of cholesteryl esters and triglycerides derived from plasma lipoproteins
Free cholesterol is released from lysosomes, which leads to activation of acyl-CoA:cholesterol acyltransferase (ACAT) and Abbreviations: LAL, lysosomal acid lipase; M-CSF, macrophagecolony stimulating factor; phorbol 12myristate-13 acetate (PMA), phorbol 12-myristate-13-acetate; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; SR-A, scavenger receptor type A; EGR, early growth response; PKC, protein kinase C; TSS, transcriptional start site; TATAbox binding protein (TBP), TATA-box binding protein
We allowed the probe to hybridize to 10 g of total cellular RNA from monocytes and monocyte-derived macrophages cultivated in the presence of 50 ng/ml human recombinant M-CSF for 7 days, or to a negative control
Summary
Human lysosomal acid lipase (LAL) is a hydrolase required for the cleavage of cholesteryl esters and triglycerides derived from plasma lipoproteins. The human monocytic leukemia cell line THP-1 differentiates into macrophage-like cells when treated with phorbol esters. Our data suggest that differentiation dependent increase of lysosomal acid lipase (LAL) expression in THP-1 cells is mediated by a concerted action of Sp1 and AP-2.—Ries, S., C. The human leukemia cell line THP-1 may be induced toward a macrophage like state by culture with phorbol esters; this is characterized by adherence, increased phagocytic activity, and the induction of lysozyme and non-specific esterase activities [14]. Free cholesterol is released from lysosomes, which leads to activation of acyl-CoA:cholesterol acyltransferase (ACAT) and Abbreviations: LAL, lysosomal acid lipase; M-CSF, macrophagecolony stimulating factor; PMA, phorbol 12-myristate-13-acetate; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; SR-A, scavenger receptor type A; EGR, early growth response; PKC, protein kinase C; TSS, transcriptional start site; TBP, TATA-box binding protein. Our data clearly indicate that transcriptional induction of LAL during monocyte to macrophage differentiation is mediated by a concerted action of transcription factors Sp1 and AP-2
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