APOPTOSIS INDUCED BY GLIOTOXIN IS PRECEDED BY PHOSPHORYLATION OF HISTONE H3 AND ENHANCED SENSITIVITY OF CHROMATIN TO NUCLEASE DIGESTION

The fungal toxin gliotoxin induces apoptotic I-ell death in a variety of cells. Apoptosis induced in thymocytes by gliotoxin is rapid, and D NA fragmentation is observable within 4 h treatment. Apoptosis induced by gliotoxin is calcium independent and unaffected by protein synthes is inhibitors. We have previously shown that gliotoxin results in phos phorylation of a 16.3-kDa protein within 10 min treatment of thymocyte s. Here we show that this protein is histone HS and phosphorylation oc curs on Ser-10. Cyclic AMP levels and activity of protein kinase A (PK A) are raised in cells treated with gliotoxin. Apoptosis is inhibited by genistein which also inhibits PKA and histone H3 phosphorylation. A poptosis is also inhibited by a number of specific inhibitors of PKA s uggesting apoptosis induced by gliotoxin is modulated by this kinase. The agents forskolin and cholera toxin do not induce rapid phosphoryla tion of H3 although some increase in phosphorylation of H3 does occur after 8 h with these agents. Forskolin and cholera toxin also induce a poptosis but over a longer time course than gliotoxin. In all cases le vels of apoptosis correlate with degree of H3 phosphorylation. Cells: treated with gliotoxin show an early sensitivity to micrococcal nuclea se and DNase I digestion indicating a functional relationship between DNA fragmentation and H3 phosphorylation.