Studies of the differentiation of promyelocytic cells by phorbol ester. II. A methylation inhibitor, 3-deazaadenosine, inhibits the induction of specific differentiation proteins. Lack of effect on early and late phosphorylation events.

Cells of the promyelocytic leukemic line, HL-60, differentiate into macrophage-like cells in response to phorbol-12-myristate-13-acetate (phorbol ester). We have shown that this process is associated with expression of motility functions and induction of specific changes in the synthesis of discrete proteins. In the present study we show that a methylation inhibitor, 3-deazaadenosine, inhibits the phorbol ester induction of the differentiation functions, adherence and motility. These effects were associated with interference in the expression of membrane proteins indicative of the acquisition of macrophage-like characteristics by HL-60 cells. Of particular importance was the observation that the methylation inhibitor preferentially arrested the induction of one differentiation, protein m10 (pI approximately equal to 7, 28 kDa). The selective effect of 3-deazaadenosine is further supported by observations in this study which show that the methylation inhibitor did not affect other cellular and biochemical effects of phorbol ester in these cells. Most significantly, 3-deazaadenosine did not inhibit the induction of phosphorylation in pp17 and pp27, which was previously shown to be a rapid event associated with initiation of differentiation in HL-60 cells by phorbol ester (Feuerstein, N. and Cooper, H. (1983) J. Biol. Chem. 258, 10786-10793). Furthermore, later elevated phosphorylation of other proteins as well as the arrest of cell growth induced by phorbol ester were also unimpeded by the methylation inhibitor. These results indicate that the methylation inhibitor did not interfere with the transduction of the phorbol ester signal at an early step so as to block all the subsequent events in this sequence, but rather its effect was selectively associated with interference in later events in the sequence of differentiation. It is proposed that transmethylation events might be specifically involved in the induction and expression of discrete proteins during the differentiation of these leukemic cells but not in the initial propagation of the signal produced by phorbol ester binding.