ROLE OF UBIQUITIN CARBOXYL-TERMINAL HYDROLASE IN THE DIFFERENTIATION OF HUMAN ACUTE LYMPHOBLASTIC-LEUKEMIA CELL-LINE, REH

We have previously demonstrated that the phorbol ester 12-O-tetradecan oylphorbol 13-acetate (TPA), induces differentiation of the acute lymp hoblastic leukemia cell line, Reh, to a mature non-dividing state. Ass ociated with this differentiation is the expression of ubiquitin carbo xyl terminal hydrolase (UCH-LI). To investigate the role of UCH-L1 in TPA-induced Reh differentiation and apoptosis, molecular and chemical inhibition was used. Molecularly, a sequence-specific antisense oligod eoxynucleotide (AODN) directed against UCH-L1 transcript was used to i nhibit the expression of the gene. In addition, its complementary sens e oligo deoxynucleotide (SODN) was used to indicate the specificity of AODN action. Chemically, sodium borohydride (NaBH4), an inhibitor of UCH-L, was used to block the transcript product. TPA-induced changes i n Reh cell growth and morphology, UCH-L1 protein expression, apoptosis contour, surface phenotype, and enzymatic profile were assessed in th e presence or absence of NaBH,, AODN or SODN. As previously reported, TPA induced Reh cells to differentiate into monocytoid B lymphocytes a nd stimulated the apoptotic pathway. However, adding NaBH4 or AODN inh ibited the TPA effect on all parameters measured except apoptosis. The sequence in which NaBH, or AODN were added in relation to TPA did not affect any of the response variables measured. The use of SODN did no t influence any of the parameters measured, indicating the specificity of the action. Thus, we conclude that UCH-L1 is involved in the diffe rentiation process of the lymphoblastic leukemia cell line, Reh. Our d ata suggest that TPA-induced apoptosis of Reh cells has a separate pat hway from that of differentiation or that UCH-L1 expression is indepen dent of the apoptotic pathway.