Induction of New Proteins by Gamma Interferon in Cultured Human Keratinocytes

Human epidermal keratinocytes incubated with recombinant gamma interferon (r-IFN-γ) show, on two-dimensional gel electrophoresis, both the appearance of new proteins and the loss of others. Among [35S]methionine-labeled proteins, which are induced in an actinomycin- or α-amanitin-sensitive manner, is a prominent group with an apparent relative molecular mass of 53,000 and pI of 5.3–5.8. The synthesis of these proteins continues for at least 4 days in the presence of gamma interferon (IFN-γ). Over the concentration range tested, up to 670 pM, there is no inhibition of protein synthesis, so the appearance of these proteins cannot be explained by overall inhibition of protein synthesis. Furthermore, at 4pM we found only minor inhibition of DNA (21%) and RNA (29%) synthesis. Half-maximal induction of the prominent 53 kD proteins occurs at an interferon concentration of 0.8–3.5pM which may be compared with a range of 1.5–30pM for HLA-DR induction. The same prominent proteins are also induced by type I interferons. The 53kD protein complex appears to consist of at least 4 different proteins, one of which is phosphorylated and another one of which is not induced in fibroblasts treated with IFN-γ. We could obtain no evidence that the proteins were related by glycosylation. The presence of these proteins provides a sensitive means of identifying keratinocytes responding to interferons. Lack of these proteins in normal epidermis indicates that interferon does not play a major role in the control of keratinocyte behavior in sound skin.