Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 275, Issue 48, Pages 37474-37480Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M001012200
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Human thioredoxin (Trx) catalyzes intracellular disulfide reductions but has also co-cytokine activity with interleukins after leaderless secretion. A recombinant truncated form of thioredoxin with the 80 N-terminal residues (Trx80) was purified to homogeneity, We discovered that Trx80 by itself is a potent mitogenic cytokine stimulating growth of resting human peripheral blood mononuclear cells. No effect was seen by Trx, but Trx80 at 50-100 nm induced cell proliferation of human peripheral blood mononuclear cells in serum-free synthetic medium, measured as [H-3]thymidine incorporation after 72 h, with a maximum effect being comparable with that of 5 units/ml of interleukin-a. Trx80 lacked redox activity, but CD spectra suggested a secondary structure similar to Trx. Reduced Trx80 had an M-r of 25,000, indicating that it is a dimer in solution. We also developed two different sandwich enzyme-linked immunosorbent assays that distinguish between full-length Trx and Trx80 and determined plasma levels of Trx and Trx80 in blood donors. The levels of Trx80 varied from 2 to 175 ng/ml; in comparison levels of Trx varied from 16 to 55 ng/ml without correlation to Trx80, In conclusion, the naturally occurring Trx80 is a novel mitogenic cytokine for normal resting human blood mononuclear cells.
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