ABSTRACT
Interferon regulatory factor-1 (IRF-1) has been recognized as an important tumor suppressor and growth regulatory transcription factor, which is also involved in cell differentiation. In this study we investigated the role of IRF-1 in phorbol 12-myristate 13-acetate (PMA)-induced monocyte/macrophage differentiation of human monoblastic U937 cells. For this purpose U937 cells were stably transfected with a vector overexpressing IRF-1 antisense mRNA (U937 IRF-1A cells) and with the SV-40 empty vector (U937-SV40 e.v. cells). We report here that U937 and U937-SV40 e.v. cells differentiated into macrophage-like cells upon PMA stimulation and showed IRF-1 up-regulation. On the contrary, U937 IRF-1A cells stimulated with PMA kept an undifferentiated phenotype and proliferated actively. A direct correlation between induction of IRF-1 and up-regulation of IRF-1 gene targets such as ornithine decarboxylase (ODC) and WAF-1/CIP-1 was also observed in U937 cells. On the other hand U937 IRF-1A cells down-regulated ODC and did not express WAF-1. Results show that IRF-1 plays a pivotal role in PMA-induced monocyte/macrophage differentiation.
Subject(s)
DNA-Binding Proteins/physiology , Macrophages/cytology , Monocytes/cytology , Phosphoproteins/physiology , Cell Differentiation/immunology , Cyclin-Dependent Kinase Inhibitor p21 , Cyclins/metabolism , Cyclins/physiology , DNA-Binding Proteins/metabolism , Gene Expression Regulation/immunology , Humans , Interferon Regulatory Factor-1 , Interferon-gamma/metabolism , Interferon-gamma/physiology , Macrophages/drug effects , Macrophages/enzymology , Monocytes/drug effects , Monocytes/enzymology , Ornithine Decarboxylase/metabolism , Ornithine Decarboxylase/physiology , Phosphoproteins/metabolism , Tetradecanoylphorbol Acetate/analogs & derivatives , Tetradecanoylphorbol Acetate/pharmacology , Transcription Factors/metabolism , Transcription Factors/physiology , Tumor Cells, Cultured , U937 Cells/enzymology , U937 Cells/metabolismABSTRACT
AO 1535 is a semisynthetic monoglycosylceramide derived from O-glycosilated sphingosine, with a chemical structure similar to the glycolipids present in many mammalian tissues. In the epidermis monoglycosylceramides contribute to consolidate the structure of cutaneous layers. It has been recently shown that sphingosine and its derivatives are potent inhibitors of Protein kinase C, and block the 'respiratory burst' of phagocitic cells. In macrophages, like in neutrophils, the reactive oxygen intermediates are produced by a membrane associated enzymatic complex, NADPH-oxidase, which is activated by Protein kinase C. This study demonstrates that AO 1535 is able to inhibit the production of reactive oxygen intermediates in human monocytes and macrophages stimulated by phorbol ester and chemotactic tetrapeptide, suggesting a potential clinical application of AO 1535 in the treatment of inflammatory dermatoses.
