Thioredoxin reductase is one of the selenoproteins in both promyelocytic and granulocytic HL-60 cells.

Human leukemia promyelocytic HL-60 cells differentiate into granulocytes when cultured with 1.25% dimethyl sulfoxide for 3 d. The radioactive Na2 75SeO3 incorporation and the amount of total proteins were interrelated in both promyelocytic and granulocytic HL-60. Promyelocytic cells had four times higher 75Se incorporation and 34% more protein synthesis than the granulocytic cells on the fifth culturing day. The enzyme activities of glutathione peroxidase (GSH-Px, E.C. 1.11.1.9) and thioredoxin reductase (TrxR, E.C. 1.6.4.5) in both types of cells increased significantly and approached steady stage on the third day. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE) analysis and autoradiography of the proteins from the cells revealed three proteins with molecular weights of 57, 28, and 21 kDa, respectively. These three 75Se-labeled proteins were present in both types of cells. The proteins from HL-60 cells were separated by DEAE-Sepharose and 2'5'-ADP-Sepharose columns. The purified 57-kDa protein had TrxR activity of 0.744 micromol 5'-thionitrobenzoic acid (TNB) formed/min/mg protein and two isoelectric points at pH 5.9 and 6.0. These results suggest that TrxR is one of the selenoproteins in both promyelocytic and granulocytic HL-60 cells.