The Catalytic Subunit of DNA-Dependent Protein Kinase Regulates Proliferation, Telomere Length, and Genomic Stability in Human Somatic Cells

Abstract

The DNA-dependent protein kinase (DNA-PK) complex is a serine/threonine protein kinase comprised of a 469-kDa catalytic subunit (DNA-PK_cs) and the DNA binding regulatory heterodimeric (Ku70/Ku86) complex Ku. DNA-PK functions in the nonhomologous end-joining pathway for the repair of DNA double-stranded breaks (DSBs) introduced by either exogenous DNA damage or endogenous processes, such as lymphoid V(D)J recombination. Not surprisingly, mutations in Ku70, Ku86, or DNA-PK_cs result in animals that are sensitive to agents that cause DSBs and that are also immune deficient. While these phenotypes have been validated in several model systems, an extension of them to humans has been missing due to the lack of patients with mutations in any one of the three DNA-PK subunits. The worldwide lack of patients suggests that during mammalian evolution this complex has become uniquely essential in primates. This hypothesis was substantiated by the demonstration that functional inactivation of either Ku70 or Ku86 in human somatic cell lines is lethal. Here we report on the functional inactivation of DNA-PK_cs in human somatic cells. Surprisingly, DNA-PK_cs does not appear to be essential, although the cell line lacking this gene has profound proliferation and genomic stability deficits not observed for other mammalian systems.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

The FISH and G-banding cytogenetic analyses were performed by LeAnn Oseth in the Cytogenetics Core Laboratory at the University of Minnesota, with support from Comprehensive Cancer Center NIH grant no. P30 CA077598-09. This work has been supported in part by grants HL079559 and GM069576 from the NIH to E.A.H.

We thank Anja-Katrin Bielinsky and members of our laboratory for their helpful comments on the manuscript. We are indebted to Bert Vogelstein (The Johns Hopkins University, Baltimore, MD) and the many members of his laboratory who were very generous with their reagents and advice.