Characterization of human TUR leukemia cells: continued cell cycle progression in the presence of phorbol ester is associated with resistance to apoptosis.

Human TUR leukemia cells were generated as a subclone of U937 monoblastoid leukemia cells. There was no obvious difference in the ultrastructure of both cell lines. Like in U937 cells, the expression of monocyte-specific surface markers such as CD14 was negligible in TUR cells. U937 cells and other human myeloid leukemia cell lines (HL-60, THP-1) can be induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) to differentiate along the monocytic pathway. In contrast, exposure to TPA had no effect on the induction of the differentiation program in TUR cells. Thus, the presence of leukocyte integrins including CD11 and CD18, which are significantly induced during TPA-induced differentiation of HL-60, U937 and THP-1 cells, remained nearly unchanged at low levels in both TUR and TPA-treated TUR cells. Furthermore, while expression of major histocompatibility complex (MHC) class II antigens on U937 and TPA-treated U937 cells is barely detectable, there was a significantly constitutive expression of MHC class II, particularly human lymphocyte antigen (HLA-DR) on the surface of TUR and TPA-treated TUR cells. Exposure of human myeloid leukemia cells to TPA is also associated with growth arrest resulting either in a retrodifferentiation process or in programmed cell death. In contrast, TUR cells continued to proliferate in the presence of TPA although the proliferative capacity was continuously reduced by increasing concentrations of TPA.(ABSTRACT TRUNCATED AT 250 WORDS)