Effects of cytokines on the gamma interferon-induced tryptophanyl-tRNA synthetase expression by human keratinocytes

Incubation of human keratinocytes with gamma interferon (gamma-IFN) has been shown to potently induce the synthesis of a 53 kDa protein which was recently identified as tryptophanyl-tRNA synthetase (TRS). However, in spite of the high sensitivity of cultured keratinocytes to TRS induction by gamma-IFN, the study of inflammatory skin lesions has allowed the detection of the protein only in a few cases, suggesting regulatory mechanisms from soluble endogenous mediators with antagonistic activity on the induction of TRS by gamma-IFN. Among these mediators, we wondered whether cytokines selected for possible anti-inflammatory activity and potentially derived from activated resident skin cells, such as IL-4, IL-10, TNF-alpha and TGF-beta, may be involved in the modulation of the keratinocyte TRS expression. To assess this possibility, we investigated the modulation of the synthesis of TRS by human cultured keratinocytes upon stimulation by various gamma-IFN/cytokine combinations. The effects were evaluated by immunoblotting assay revealed by enhanced chemiluminescence, with the aid of a specific antibody to the TRS protein. Results failed to demonstrate any effect of the tested cytokines, whether on the basal level of the TRS, or on the gamma-IFN-induced enzyme expression in keratinocytes. It is thus unlikely that such cytokines can account for the infrequency of the TRS detection in inflammatory skin processes. Further investigations of alternative working hypothesis should help elucidate the regulation of TRS in human keratinocytes.