A variant of DNA polymerase beta is not cancer specific

DNA polymerase beta (pol beta) carries out base-excision repair (BER) required for DNA maintenance, replication, and recombination in eukaryotic cells. A variant characterized by a deletion of exon 11, an 87-bp region in the catalytic domain (pol betadelta208-236), was previously described as a possible cause of genomic instability in cancer. The variant form was hypothesized to act in a dominant negative fashion, due to the fact that the variant inhibits the gap filling and DNA binding activities of the wild-type pol beta protein. DNA polymerase beta transcripts were analyzed in 8 breast cancer cell lines, snap-frozen benign breast tissues from 10 women, and lymphocytes from 10 normal controls, using reverse-transcription polymerase chain reaction (RT-PCR) and three separate primer pairs. The exon 10-12 splice site (variant) was identified using a primer designed to span the spliced exons and by sequencing RT-PCR products that included exon 10, exon 11 (if present), and exon 12. In all of the samples tested, we found both the wild-type and exon 11 87-bp deleted variant mRNAs expressed. We conclude that expression of the DNA polymerase beta variant (pol betadelta208-236) is ubiquitous and not breast cancer specific.