Interferon‐γ up‐regulates a unique set of proteins in human keratinocytes

Abstract

Treatment of proliferating and quiescent primary human keratinocytes with interferon-γ (IFN-γ) (100 U/ml, 23.5 h) followed by two-dimensional gel analysis revealed three proteins, IGUP I-3421 (M_r= 48 200, pI= 6.06); IGUP I-3524 (M_r= 56 900, pI= 5.92), a protein homologous to peptidechain-release factor and tryptophanyl-tRNA syntetase; and IGUP I-5111 (M_r= 30400, pI= 5.76) recorded in the keratinocyte protein database (Celis et al., 1991, 1992) that are highly and specifically up-regulated by IFN-γ among several agents tested including 14 other cytokines, second messengers [dibutyryl cAMP (Bt₂cAMP), dibutyryl cGMP (Bt₂cGMP)] and compounds known to affect keratinocytes [4β-phorbol 12-myristate 13-acetate (PMA), retinoic acid, Ca²⁺, dexamethasone, lipopolysaccharides, foetal calf serum]. Protein IGUP I-5111 was selected for further studies as its level is affected by simian-virus-40 transformation and because peptide sequences were available in the microsequence database. The cDNA was cloned from a fibroblast cDNA library using degenerate oligodeoxyribonucleotides and expressed in AMA cells using the vaccinia virus expression system. Database searches indicated that the predicted protein, which migrated with the AMA variant of keratinocyte protein IEF SSP 5111, is novel although it exhibits weak similarity to cytoskeletal proteins. IGUP I-5111 contains the RGD sequence found in many extracellular glycoprotein ligands of the integrin receptor family and it is found at least partially in the culture supernatant. Considering the presence of IFN-γ in psoriatic plaques as well as its putative involvement in the pathophysiology of the disease it was of interest to determine whether the set of proteins was up-regulated in these cells. Two-dimensional gel analysis of the protein phenotype of non-cultured, unfractionated psoriatic keratinocytes failed to reveal up-regulation of any of the three IFN-γ-induced proteins suggesting that the effect of IFN-γin vivo may be modulated by the activity of other cytokine(s) or growth factor(s). Psoriatic keratinocytes were equally sensitive to IFN-γ as their normal counterparts.