Participation of mouse DNA polymerase ι in strand-biased mutagenic bypass of UV photoproducts and suppression of skin cancer

doi:10.1073/pnas.0605247103

Participation of mouse DNA polymerase ι in strand-biased mutagenic bypass of UV photoproducts and suppression of skin cancer

*Department of Pharmacology and Toxicology and James Graham Brown Cancer Center, University of Louisville, Louisville, KY 40202-1786;
^†Laboratory of Molecular Genetics and Laboratory of Structural Biology, and
^§Biostatistics Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709; and
^‡Harvard Medical School–Partners Healthcare Center for Genetics and Genomics and Harvard Medical School, Boston, MA 02115

Edited by Richard B. Setlow, Brookhaven National Laboratory, Upton, NY, and approved September 28, 2006 (received for review June 22, 2006)

Abstract

DNA polymerase ι (pol ι) is a conserved Y family enzyme that is implicated in translesion DNA synthesis (TLS) but whose cellular functions remain uncertain. To test the hypothesis that pol ι performs TLS in cells, we compared UV-induced mutagenesis in primary fibroblasts derived from wild-type mice to mice lacking functional pol η, pol ι, or both. A deficiency in mouse DNA polymerase η (pol η) enhanced UV-induced Hprt mutant frequencies. This enhanced UV-induced mutagenesis and UV-induced mutagenesis in wild-type cells were strongly diminished in cells deficient in pol ι, indicating that pol ι participates in the bypass of UV photoproducts in cells. Moreover, a clear strand bias among UV-induced base substitutions was observed in wild-type cells that was diminished in pol η- and pol ι-deficient mouse cells and abolished in cells deficient in both enzymes. These data suggest that these enzymes bypass UV photoproducts in an asymmetric manner. To determine whether pol ι status affects cancer susceptibility, we compared the UV-induced skin cancer susceptibility of wild-type mice to mice lacking functional pol η, pol ι, or both. Although pol ι deficiency alone had no effect, UV-induced skin tumors in pol η-deficient mice developed 4 weeks earlier in mice concomitantly deficient in pol ι. Collectively, these data reveal functions for pol ι in bypassing UV photoproducts and in delaying the onset of UV-induced skin cancer.

Footnotes

^¶To whom correspondence should be addressed. E-mail: kunkel{at}niehs.nih.gov
Author contributions: C.A.D., A.B.C., and Q.L. contributed equally to this work; C.A.D., A.B.C., Q.L., R.K., W.G.M., and T.A.K. designed research; C.A.D., A.B.C., Q.L., and T.Y. performed research; C.A.D., A.B.C., Q.L., G.E.K., T.Y., R.K., W.G.M., and T.A.K. analyzed data; and C.A.D., A.B.C., Q.L., G.E.K., T.Y., R.K., W.G.M., and T.A.K. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
Abbreviations:

pol ι,

DNA polymerase ι;

TLS,

translesion synthesis;

TG,

thioguanine;

TGr,

TG resistant;

XP,

xeroderma pigmentosum