INDUCTION OF APOPTOTIC NUCLEI BY INTERFERON-GAMMA AND BY PREDESQUAMININ CULTURED KERATINOCYTES

Predesquamin is a glycoprotein found in the transition layer and the l ower stratum corneum of human epidermis, Interferon-gamma (IFN-gamma) induces the synthesis of predesquamin by keratinocytes in culture, We now show ultrastructurally that exogenous addition of either predesqua min or IFN-gamma to cultured keratinocytes induces apoptotic nuclei wi th condensed chromatin. Degradation of cellular DNA is also evident as a ladder pattern in an agarose gel. After incubation with both predes quamin and IFN-gamma (but not either alone), the mobility of plasmid D NA in a gel shows retardation specific for guanine residues, This bind ing to the DNA may impart to it a conformational change that facilitat es access by endogenous cellular nucleases. In epidermal cells culture d with IFN-gamma supplementation, we also show by RT-PCR that there is an upregulation of the genes c-myc, p53, gadd45, dsRNA-activated prot ein kinase, and 2'-5'-oligo(A)-dependent RNase, which have all been im plicated in apoptosis in other cell types. These results are pertinent to the mechanism of occurrence of apoptosis in the epidermis in vivo, where predesquamin and IFN-gamma are endogenous, Programmed cell deat h is an inherent step in the terminal differentiation and desquamation of the epidermis.