Characterization of Human DNase I Family Endonucleases and Activation of DNase γ during Apoptosis

We describe here the characterization of the so far identified human DNase I family DNases, DNase I, DNase X, DNase γ, and DNAS1L2. The DNase I family genes are found to be expressed with different tissue specificities and suggested to play unique physiological roles. All the recombinant DNases are shown to be Ca2+/Mg2+-dependent endonucleases and catalyze DNA hydrolysis to produce 3'-OH/5'-P ends. High activities for DNase I, DNase X, and DNase γ are observed under neutral conditions, whereas DNAS1L2 shows its maximum activity at acidic pH. These enzymes have also some other peculiarities: different sensitivities to G-actin, aurintricarboxylic acid, and metal ions are observed. Using a transient expression system in HeLa S3 cells, the possible involvement of the DNases in apoptosis was examined. The ectopic expression of each DNase has no toxic effect on the host cells; however, extensive DNA fragmentation is observed only in DNase γ-transfected cells after the induction of apoptosis. Furthermore, DNase γ is revealed to be located at the perinuclear region in living cells, and to translocate into the nucleus during apoptosis. Our results demonstrate that DNase I, DNase X, DNase γ, and DNAS1L2 have similar but unique endonuclease activities, and that among DNase I family DNases, DNase γ is capable of producing apoptotic DNA fragmentation in mammalian cells.