SYSTEMATIC BIOCHEMICAL ANALYSIS OF SOMATIC MISSENSE MUTATIONS IN DNA POLYMERASE β FOUND IN PROSTATE CANCER REVEAL ALTERATION OF ENZYMATIC FUNCTION

DNA polymerase b is essential for short- patch base excision repair. We have previously identified 20 somatic pol b mutations in prostate tumors, many of them missense. In the current article we describe the effect of all of these somatic missense pol b mutations (p.K27N, p.E123K, p.E232K, p.P242R, p.E216K, p.M236L, and the triple mutant p.P261L/T292A/I298T) on the biochemical properties of the polymerase in vitro, following bacterial expression and purification of the respective enzymatic variants. We report that all missense somatic pol b mutations significantly affect enzyme function. Two of the pol b variants reduce catalytic efficiency, while the remaining five missense mutations alter the fidelity of DNA synthesis. Thus, we conclude that a significant proportion (9 out of 26; 35%) of prostate cancer patients have functionally important somatic mutations of pol b. Many of these missense mutations are clonal in the tumors, and/or are associated with loss of heterozygosity and microsatellite instability. These results suggest that interfering with normal polymerase b function may be a frequent mechanism of prostate tumor progression. Furthermore, the availability of detailed structural information for pol b allows understanding of the potential mechanistic effects of these mutants on polymerase function. Hum Mutat 32:415-423, 2011. & 2011 Wiley-Liss, Inc.