Expression regulation of MAO isoforms in monocytic cells in response to Th2 cytokines.
BACKGROUND
Th2-cytokines, such as interleukins-4 and -13 (IL-4, IL-13), have been identified as alternative stimuli of monocytes/macrophages. We have recently profiled the gene-expression pattern of IL-4-treated human peripheral monocytes and found that 15-lipoxygenase-1 (15-LOX1) and monoamine oxidase A (MAO-A) are among the five most strongly upregulated gene products in IL-4-treated cells. Transfection of monocytic cells (U937) with 15-LOX1 also induced MAO-A expression. These data suggested that 15-LOX1 products might play a role in the IL4-induced signaling cascade leading to expression of MAO-A in human monocytes.


METHODS
To test this hypothesis we incubated wild-type and 15-LOX1-transfected U937 cells with different concentrations of either IL-4 or 15-LOX-products [13S-H(p)ODE, 15S-H(p)ETE] and quantified the expression of 15-LOX1, MAO-A, and MAO-B by activity assays and real-time RT-PCR.


RESULTS
Wild-type U937 cells express neither MAO-A nor MAO-B, but after three days of IL4 treatment, MAO-A mRNA was detected. A similar isoform-specific expression of MAO-A mRNA was observed when U937 cells were transfected with 15-LOX1 or when the cells were incubated with primary 15-LOX1 products (hydroperoxy fatty acids) or H2O2. In contrast, the corresponding hydroxy fatty acids were ineffective.


CONCLUSIONS
These data indicate that increased intracellular peroxide concentrations (oxidative stress) induce MAO-A expression in monocytes/macrophages, which normally do not express the enzyme. Our findings also suggest that IL-4-induced upregulation of MAO-A expression in human peripheral monocytes may proceed via 15-LOX1-dependent and 15-LOX1-independent pathways. The biological role of MAO-A expression for monocyte function is discussed.
Chaitidis
Pavlos
P
Institute of Biochemistry, University Medicine Berlin Charité, Berlin, Germany.
Billett
Ellen
E
Kuban
Ralf J
RJ
Ungethuem
Ute
U
Kuhn
Hartmut
H
D001093:Arachidonate 15-Lipoxygenase / Q000378:metabolism; D045744:Cell Line, Tumor; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D015847:Interleukin-4 / Q000494:pharmacology*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D019787:Linoleic Acid / Q000378:metabolism; D008995:Monoamine Oxidase / Q000235:genetics / Q000378:metabolism*; D009000:Monocytes / Q000187:drug effects* / Q000201:enzymology*; D018418:Th2 Cells / Q000378:metabolism*
D007527:Isoenzymes; D015847:Interleukin-4; D019787:Linoleic Acid; D001093:Arachidonate 15-Lipoxygenase; D008995:Monoamine Oxidase