TUR (TPA-U937-Resistant) is a stably transfected cell line generated by Ralf Hass and Masanori Hirano in 1992 from U-937 (ATCC CRL-1593.2)
, a monoblastoid cell line.
U-937 cells were transfected by electroporation with the pMG2neoPA plasmid containing the neomycin resistant gene and then selected in medium containing G418 and 12-O-tetradecanoylphorbol-13-acetate (TPA).
TUR cells have remained resistant to both G418 and TPA after culture in the absence of these agents for over 100 passages.
The cell line retains monocytic properties but does not differentiate along the macrophage pathway by phorbal ester treatment.
While treatment of human U-937 myeloid leukemia cells with TPA is associated with growth arrest and induction of monocytic differentiation, the TUR cell line is unresponsive to the growth-inhibitory effects of this agent.
The TUR variant is defective in TPA-induced signaling events upstream to activation of Raf-1 kinase.
Expression of major histocompatibility complex (MHC) Class II antigens on U937 and TPA-treated U937 cells is barely detectable.
However, 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.
TUR cells continue to proliferate in the presence of TPA although increasing concentrations of TPA continuously reduces the proliferative capacity of the cells.
Unlike U-937 cells, exposure to TPA did not induce detectable levels of internucleosomal DNA fragmentation or the generation of apoptotic bodies.