Demonstration of a double-stranded DNA-stimulated protein kinase (DNA-PK) inhibitory activity in human HL-60 leukemia cells

A 41,000 protein, p41, was highly purified from human promyelocytic HL-60 cells by chromatography on GTP-agarose columns. The purified p41 inhibited phosphorylation of endogenous substrates present in partially purified DNA-PK from HL-60 or HeLa cells, as well as phosphorylation of recombinant protein τ mediated by the purified HeLa DNA-PX. The ability of p41 to inhibit DNA-PK was largely abolished by heating at 95°C for 30 min.