Involvement of DNA polymerase β overexpression in the malignant transformation induced by benzo[a]pyrene.

To explore the relationship between DNA polymerase β (pol β) overexpression and benzo[a]pyrene (BaP) carcinogenesis. Firstly, mouse embryonic fibroblasts that express wild-type level of DNA polymerase β (pol β cell) and high level of pol β (pol β oe cell) were treated by various concentrations of BaP to determine genetic instability induced by BaP under differential expression levels of pol β. Secondly, malignant transformation of pol β cells by low concentration of BaP (20 μM) was determined by soft agar colony formation assay and transformation focus assay. Thirdly, the mRNA and protein levels of BaP-transformed pol β cells (named pol β-T cells) was measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and western blot, and the genetic instability of these cells were examined by HPRT gene mutation assay and random amplified polymorphic DNA (RAPD) assay. Pol β cells were successfully transformed into malignant pol β-T cells by an exposure to low concentration of BaP for 6 months. Pol β-T cells exhibited increased levels of pol β gene expression, HPRT gene mutation frequency and polymorphisms of RAPD products that were comparable to those of pol β oe cells. Pol β overexpression and its-associated genetic instability may play a key role in BaP carcinogenesis.