EXPRESSION AND REGULATION OF INTERFERON-GAMMA-INDUCED TRYPTOPHAN CATABOLISM IN CULTURED SKIN FIBROBLASTS

Interferon-gamma (IFN-gamma)-induced, indoleamine dioxygenase-catalyze d tryptophan catabolism was studied in cultured human foreskin fibrobl asts using the increase in cellular kynurenine synthesis as an index o f gene expression. The time courses of the inhibition of IFN-gamma-ind uced kynurenine synthesis by actinomycin D and cycloheximide showed th at the indoleamine dioxygenase gene was transcribed as early as 2 h an d translated as early as 5 h after initiation of IFN treatment. Expres sion was completely inhibited by the Ser/Thr kinase inhibitor, H-7 (66 mu M), during the first 2 h after IFN-gamma treatment. Prolonged pret reatment of cells with high concentrations of staurosporine (380 nM) o r genestein (610 mu M) inhibited expression by 38% and 53%, respective ly. Genestein also inhibited expression when it was added to cultures between 8 and 24 h after IFN-gamma treatment. The expression of kynure nine synthesis was inhibited by A23817 during the first 4 h after IFN treatment by mechanisms that were independent of cyclooxygenase, calmo dulin, and calcineurin. Exogenous gangliosides (bovine brain gangliosi des and purified GM(1)) inhibited IDO expression throughout the first 24 h after IFN-gamma treatment by mechanisms that did not involve effe cts on Ca2+ channels. Other biologic response modifiers, including pho rbol myristic acetate, arachidonic acid, lipopolysaccharide, analogs o f cAMP and cGMP, W-7, and sphingosine, did not induce IDO in the absen ce of IFN-gamma, nor did they modulate IFN-gamma-induced expression. T hese results indicate that the expression of kynurenine synthesis is m odulated at the transcriptional and posttranscriptional levels by prot ein tyrosine kinase and by a Ser/Thr kinase with properties distinctly different from those of conventional protein kinase C. The capacity f or attenuation of this IFN-gamma-induced response over its entire time course by many effecters and through multiple cellular signaling path ways may represent a mechanism for finetuning the level of oxidative t ryptophan metabolism to meet the needs of a particular cytostatic or a ntiproliferative response.