Indoleamine 2,3-dioxygenase participates in the interferon-gamma-induced cell death process in cultured bovine luteal cells.
Interferon-gamma (IFNG) induces apoptotic cell death in bovine luteal cells, but the pathway(s) involved in this process are not well defined. Evidence supporting the involvement of an IFNG-inducible enzymatic pathway that degrades tryptophan in IFNG-induced death of bovine luteal cells is presented in this study. The IFNG-inducible enzyme indoleamine 2,3-dioxygenase (INDO) catalyzes the first step in a metabolic pathway that degrades tryptophan. In the first experiment, RT-PCR revealed the presence of INDO mRNA in luteal cells treated with IFNG, but not in untreated cells. To determine whether INDO participates in IFNG-induced death of bovine luteal cells, an experiment was performed to test the effect of 1-methyl-D-tryptophan (1-MT), an inhibitor of INDO, on IFNG-induced DNA fragmentation in luteal cells. Single-cell gel electrophoresis and microscopic image analysis revealed that 1-MT inhibited DNA fragmentation induced by IFNG. To determine whether supplementation of cell cultures with additional tryptophan could also protect luteal cells from IFNG-induced DNA fragmentation, luteal cells were cultured in the presence of IFNG, and L-tryptophan was added to cultures to achieve final concentrations that were 5-, 10-, or 25-fold higher than the concentration of L-tryptophan found in nonsupplemented culture medium. Supplementation of IFNG-treated luteal cell cultures with elevated concentrations of tryptophan also prevented IFNG-induced DNA fragmentation. We conclude that INDO participates in IFNG-induced death of bovine luteal cells, through a mechanism that involves degradation of tryptophan, thereby reducing tryptophan concentrations to a point insufficient to meet luteal cells needs.
Cannon
Matthew J
MJ
Department of Animal Sciences, The Ohio State University/Ohio Agricultural Research and Development Center, Wooster, Ohio 44691, USA.
Pate
Joy L
JL
D000818:Animals; D002417:Cattle; D016923:Cell Death / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D053938:DNA Fragmentation / Q000187:drug effects; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000235:genetics / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology*; D008184:Luteal Cells / Q000166:cytology* / Q000201:enzymology*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014364:Tryptophan / Q000494:pharmacology
D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D012333:RNA, Messenger; D007371:Interferon-gamma; D014364:Tryptophan