title: High expression of IMPACT protein promotes resistance to indoleamine 2,3-dioxygenase-induced cell death.
abstract: Indoleamine 2,3-dioxygenase (IDO), a tryptophan degrading enzyme, is a potent immunomodulatory factor. IDO expression in fibroblasts selectively induces apoptosis in immune cells but not in primary skin cells. However, the mechanism(s) of this selective effect of IDO-induced low tryptophan environment is not elucidated. The aim of present study was to investigate whether the activity of general control non-derepressible-2(GCN2) kinase stress-responsive pathway and its known inhibitor, protein IMPACT homolog, in immune and skin cells are differentially regulated in response to IDO-induced low tryptophan environment. IDO-expressing human fibroblasts were co-cultured with Jurkat cells, human T cells, fibroblasts, or keratinocytes. Activation of GCN2 pathway was significantly higher in immune cells exposed to IDO-expressing environment relative to that of skin cells. In contrast, IMPACT was highly and constitutively expressed in skin cells while its expression was very low in stimulated T cells and undetectable in Jurkat cells. A significant IDO-induced suppressive as well as apoptotic effect was demonstrated in IMPACT knocked down fibroblasts co-cultured with IDO-expressing fibroblasts. Proliferation of Jurkat cells, stably transduced with IMPACT-expressing vector, was rescued significantly in tryptophan-deficient but not IDO-expressing environment. This may be due to the ability of IMPACT to recover the effects of IDO-mediated tryptophan depletion (GCN2 dependent) but not the effects of IDO-generated cytotoxic metabolites. These findings collectively suggest for the first time that high expression of protein IMPACT homolog in non-immune cells such as skin cells acts as a protective mechanism against IDO-induced GCN2 activation, therefore, makes them resistant to the amino acid-deprived environment caused by IDO.
authors.affiliation: BC Professional Fire Fighters' Burn and Wound Healing Research Laboratory, Department of Surgery, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Darya
authors.initials: D
authors.lastname: Habibi
authors.forename: Reza B
authors.initials: RB
authors.lastname: Jalili
authors.forename: Farshad
authors.initials: F
authors.lastname: Forouzandeh
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Ong
authors.forename: Aziz
authors.initials: A
authors.lastname: Ghahary
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects*; D002478:Cells, Cultured; D018920:Coculture Techniques; D017077:Culture Media, Conditioned / Q000737:chemistry; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000494:pharmacology*; D007371:Interferon-gamma / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells; D015603:Keratinocytes / Q000166:cytology / Q000502:physiology; D007737:Kynurenine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013601:T-Lymphocytes / Q000166:cytology / Q000502:physiology; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D014364:Tryptophan / Q000172:deficiency
chemical_list: D000998:Antiviral Agents; D017077:Culture Media, Conditioned; C497249:DDIT3 protein, human; C484600:IMPACT protein, human; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D034741:RNA, Small Interfering; D051742:Transcription Factor CHOP; D007737:Kynurenine; D007371:Interferon-gamma; D014364:Tryptophan; C529271:EIF2AK4 protein, human; D017346:Protein Serine-Threonine Kinases