TY - JOUR
T1 - Constitutive and modulated expression of the human α1 antitrypsin gene. Different transcriptional initiation sites used in three different cell types
AU - Hafeez, Waseem
AU - Ciliberto, Gennaro
AU - Perlmutter, David H.
PY - 1992
Y1 - 1992
N2 - α1,-Antitrypsin (α1 AT) is plasma glycoprotein that constitutes the principle inhibitor of neutrophil elastase in tissue fluids. It has been considered a prototype for liver-derived acute phase proteins in that its concentration in plasma increases three- to fourfold during the host response to inflammation/tissue injury. However, recent studies have shown that α1 AT is expressed in several types of extrahepatic cells, including mononuclear phagocytes and enterocytes, and that there are distinct transcriptional units used in hepatocytes and at least one extrahepatic cell type, blood monocytes. In this study, we have used a combination of ribonuclease protection assays, primer elongation analysis, and transcriptional run-on assays to further characterize mechanisms of basal and modulated α1 AT gene expression in hepatocytes, enterocytes, and macrophages. The hepatoma cell line HepG2, intestinal epithelial cell line Caco2, and primary cultures of human peripheral blood monocytes were used as examples of the cell types. The results indicate that there are three macrophage-specific transcriptional initiation sites upstream from a single hepatocyte-specific transcriptional initiation site. Macrophages use these sites during basal and modulated expression. Hepatoma cells use the hepatocyte-specific transcriptional initiation site during basal and modulated expression but also switch on transcription from the upstream macrophage transcriptional initiation sites during modulation by the acute phase mediator interleukin 6 (IL-6). Caco2 cells use the hepatocyte-specific transcriptional initiation site during basal expression. There is a marked increase in the use of this site and an increase in the rate of transcriptional elongation of α1 AT mRNA during differentiation of Cacol cells from crypt-type to villous-type enterocytes. Caco2 cells also switch on transcription from the upstream macrophage transcriptional initiation sites during modulation by IL-6. These results provide further evidence that there are differences in the mechanisms of constitutive and regulated expression of the α1 AT gene in at least three different cell types, HepG2-derived hepatocytes, Caco2-derived enterocytes and mononuclear phagocytes.
AB - α1,-Antitrypsin (α1 AT) is plasma glycoprotein that constitutes the principle inhibitor of neutrophil elastase in tissue fluids. It has been considered a prototype for liver-derived acute phase proteins in that its concentration in plasma increases three- to fourfold during the host response to inflammation/tissue injury. However, recent studies have shown that α1 AT is expressed in several types of extrahepatic cells, including mononuclear phagocytes and enterocytes, and that there are distinct transcriptional units used in hepatocytes and at least one extrahepatic cell type, blood monocytes. In this study, we have used a combination of ribonuclease protection assays, primer elongation analysis, and transcriptional run-on assays to further characterize mechanisms of basal and modulated α1 AT gene expression in hepatocytes, enterocytes, and macrophages. The hepatoma cell line HepG2, intestinal epithelial cell line Caco2, and primary cultures of human peripheral blood monocytes were used as examples of the cell types. The results indicate that there are three macrophage-specific transcriptional initiation sites upstream from a single hepatocyte-specific transcriptional initiation site. Macrophages use these sites during basal and modulated expression. Hepatoma cells use the hepatocyte-specific transcriptional initiation site during basal and modulated expression but also switch on transcription from the upstream macrophage transcriptional initiation sites during modulation by the acute phase mediator interleukin 6 (IL-6). Caco2 cells use the hepatocyte-specific transcriptional initiation site during basal expression. There is a marked increase in the use of this site and an increase in the rate of transcriptional elongation of α1 AT mRNA during differentiation of Cacol cells from crypt-type to villous-type enterocytes. Caco2 cells also switch on transcription from the upstream macrophage transcriptional initiation sites during modulation by IL-6. These results provide further evidence that there are differences in the mechanisms of constitutive and regulated expression of the α1 AT gene in at least three different cell types, HepG2-derived hepatocytes, Caco2-derived enterocytes and mononuclear phagocytes.
KW - Acute phase proteins
KW - Enterocytes
KW - Hepatocytes
KW - Mononuclear phagocytes
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U2 - 10.1172/JCI115705
DO - 10.1172/JCI115705
M3 - Article
C2 - 1556183
AN - SCOPUS:0026652705
SN - 0021-9738
VL - 89
SP - 1214
EP - 1222
JO - Journal of Clinical Investigation
JF - Journal of Clinical Investigation
IS - 4
ER -