RESUMO
A study was made of the effect of the oxidizing agent potassium chromate (K2CrO4, PC) on cultured dermal fibroblasts of a healthy donor and three patients with rheumatoid arthritis (RA). Characteristics of the rRNA gene (RG) complex-RG copy number, active RG (ARG) dosage, and 18S rRNA content--were determined for each cell line. In cells of the healthy donor, oxidative stress caused by low doses of PC (2-4 microM, 1-4 h) induced an early response, including a 50-80% increase in total RNA and rRNA. An appreciable activation of the nucleolus was observed cytochemically, by silver staining and morphometry. The early response grew considerably lower with the increasing passage number and/or PC concentration. Exposure to 6-12 microM PC for 24 h led to a progressive cell death (late response). The existence and intensity of the early response correlated positively with the cell survival during further culturing. Cells of the RA patients displayed almost no early response even at early passages: total RNA did not increase, and rRNA increased by no more than 10%. Cell disruption (apoptosis) during further culturing was more intense than in the line originating from the healthy donor. The apoptosis intensity characterized by the increase in the content of DNA fragments in the culture medium and in the caspase 3 activity, was inversely proportional to the ARG dosage in the genome. The results provide the first quantitative characterization of the early and late responses of cells to PC-induced oxidative stress and suggest a role of the ARG dosage in cell survival in stress.