Regulation of inducible nitric oxide synthase mRNA levels by differentiation and cytokines in human keratinocytes

Inducible nitric oxide synthase (iNOS) transcription is regulated by cytokines and immune stimuli in various cell types. However, there are few data available on iNOS expression and regulation in keratinocytes, even though it can play a role in keratinocyte proliferation during inflammation following wound healing. Our studies demonstrated a differentiation-dependent regulation of iNOS transcription in human keratinocytes from epidermis but not in buccal mucosal cells, which are less differentiated. Different interferon (IFN) types (alpha and gamma) regulated skin keratinocyte iNOS mRNA levels in different ways, predominantly in a differentiation-dependent manner. TGF beta 1 and IFN alpha can antagonize IFN gamma related iNOS induction. However, the antagonistic effects of IFN alpha on IFN gamma differ from those of TGF beta 1. Our studies demonstrate: (a) the presence of iNOS mRNA in human keratinocytes; (b) inducibility of iNOS mRNA by different cytokines; and (c) antagonism between certain cytokines in induction of iNOS mRNA. Further studies are needed to determine biological and therapeutical relevance of our findings. (C) 1996 Academic Press, Inc.