Specific stimulation by phorbol esters of the phosphorylation of histones H2B and H4 in murine lymphocytes.

The effect of phorbol diesters on histone phosphorylation in BALB/c mouse lymphocytes, cells which do not respond to these agents with cell division, but with other biochemical and biological changes, was investigated. A technique for fractionating the proteins was used which was more powerful than those used previously in similar studies of phorbol diester effects on the metabolism of these proteins. Exposure of lymphocytes to tumor-promoting phorbol esters resulted in a rapid and specific increase in phosphorylation of the nuclear histone proteins H2B and H4. Within 2 hr, the phosphorylation of these two proteins rose to levels 6- to 8- and 2- to 4-fold greater, respectively, than those in control cells, when lymphocytes were exposed to 800 nM 12-O-tetradecanoylphorbol-13-acetate. Lower levels were observed with other phorbol analogues commensurate with their relative tumor-promoting abilities. Lymphocyte mitogens did not increase phosphorylation under the conditions used. The potential ability of the cell system used for defining early in vivo and in vitro phorbol diester effects, and those which are independent of cell division, is discussed.