BRYOSTATIN-1 INDUCES UBIQUITIN COOH-TERMINAL HYDROLASE IN ACUTE LYMPHOBLASTIC-LEUKEMIA CELLS

It has been previously reported that Bryostatin 1 (Bryo1) induces diff erentiation of the human acute lymphoblastic leukemia (ALL) cell line, Reh, to a monocytoid B-cell stage. In this study we demonstrate that a novel protein, ubiquitin COOH-terminal hydrolase (UCH-L1), is associ ated with this differentiation. Reh cells were treated with 200 nmol/l of Bryo1 for 72 h and analyzed for changes in morphology surface immu nophenotype, acid phosphatase and terminal deoxynucleotidyl transferas e, Protein patterns of the parent and differentiated cells. by two-dim ensional polyacrylamide gel electrophoresis (2D PAGE), were studied. B ryo1-treated cells expressed morphologic, phenotypic and enzymatic fea tures of the monocytoid B-cell stage, The UCH-L1 enzyme (MW-pI 34-5.3) was detected by 2 D PAGE in the differentiated, but not in parent cel ls. The presence of UCH-L1 in the Bryo1-treated cells was further conf irmed by immunoblotting of 2 D PAGE using UCH-L1 polyclonal antibody. Ubiquitin expression was studied in parent and Bryo1-treated cells and was compared with 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated cells, Both agents, TPA and Bryo1, increased the level of ubiquitin ex pression as detected by flow cytometry. Sodium borohydride. an inhibit or of UCH-L1, inhibited the Bryo1-induced differentiating effect on Re h cells, To date, the mechanism by which Bryol, exerts its B-cell diff erentiating effect is not fully understood. This study shows that UCH- L1 expression may play a major role in Bryo1-induced differentiation i n pre-B-ALL.