Translocation of lipocortin (annexin) 1 to the membrane of U937 cells induced by phorbol ester, but not by dexamethasone.
1. Induction of lipocortin 1 secretion by dexamethasone has been demonstrated, although the secretory mechanism is still unknown. We have studied the effects of 12-tetradecanoyl phorbol 13-acetate (TPA) and/or dexamethasone on the expression, translocation, and secretion of lipocortin 1 in U937 cells. 2. The expression of lipocortin 1 and its mRNA increased during TPA-induced differentiation of U937 cells to a maximum of 1.9 fold and 8.2 fold, respectively, after 48 h. Both the protein and the mRNA levels decreased after 48 h. 3. TPA caused the translocation of lipocortin 1 from the cytosol to the membrane of U937 cells in a time-dependent manner, as determined by Western blot analysis. The translocation was concurrent with the differentiation of the cells. After 48 h of TPA treatment, 82.6 +/- 6.5% of lipocortin 1 was present in the membrane fraction compared to 41.6 +/- 1.7% in untreated cells. 4. The amount of lipocortin 1 that was externally bound (associated) with the membrane increased to 3.2 fold as the cytosol to membrane translocation of lipocortin 1 increased. 5. Dexamethasone decreased the externally bound lipocortin 1, but had no effect on the cytosol to membrane translocation. 6. This offers a model system with which the function and the secretion mechanism of lipocortin 1 can be studied. Our data is consistent with the hypothesis that the secretory mechanism is through an unknown pathway, involving the translocation of lipocortin 1 from the cytosol to the internal membranes, and then, its secretion to the external membrane.
Kang
S A
SA
Department of Biochemistry, University of Ulsan, Seoul, Korea.
Cho
Y J
YJ
Moon
H B
HB
Na
D S
DS
D000818:Animals; D017305:Annexin A1 / Q000378:metabolism*; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D017305:Annexin A1; D000893:Anti-Inflammatory Agents; D003907:Dexamethasone; D013755:Tetradecanoylphorbol Acetate