Analysis of lung tumorigenesis in chimeric mice indicates the Pulmonary adenoma resistance 2 (Par2) locus to operate in the tumor-initiation stage in a cell-autonomous manner: detection of polymorphisms in the Polı gene as a candidate for Par2

Abstract

The Pulmonary adenoma resistance 2 (Par2) locus of the BALB/cByJ mouse, located within 0.5 cM of chromosome 18, is responsible for reducing the mean multiplicity of urethane-induced lung tumors relative to those in C57BL/ 6J, A/J and C3H/HeJ mice. Thus, BALB/B6-Par2 congenic strain genetically identical to BALB/cByJ except carrying C57BL/6J Par2 alleles develops seven times more tumors than BALB/cByJ. To gain clues for identification of Par2 candidate genes, we analysed lung tumorigenesis in BALB/cByJ2BALB.B6-Par2 chimeric animals. Of 100 tumors induced by urethane in 16 chimeras, 82 originated from BALB.B6-Par2 cells, indicating the Par2 phenotype to be cell-autonomous. In addition, the BALB.B6-Par2-and BALB/cByJ-derived tumors were similar in mean size, implying that the phenotype is primarily expressed during initiation rather than in the promotion stage of carcinogenesis. Given these results, we surveyed a comprehensive mouse genome database and physically mapped Par2 within a 2.3 Mbp segment containing three known genes, Polı, Mbd2 and Dcc. Among those, the Polı seemed to be the most reasonable Par2 candidate, since it encodes an extremely error-prone DNA polymerase preferentially incorporating G or T opposite template T in vitro, reminiscent of the Kras2 activation because of an A to G or T point mutation within codon 61 with which most urethane-induced lung tumors are initiated. Indeed, our sequencing of Polı cDNAs from BALB/cByJ, C57BL/6J, A/J and C3H/ HeJ lungs revealed 21 BALB/cByJ-specific single-nucleotide polymorphisms in the coding region accompanied by seven amino-acid substitutions and an elevated frequency of alternative splicing, while no polymorphisms associated with tumor susceptibility were found for either Mbd2 or Dcc. Notably, we obtained evidence that BALB/cByJ Par2 alleles may selectively decrease the frequency of Kras2-mutated tumors compared with C57BL/6J alleles. Consequently, the Polı is an intriguing Par2 candidate clearly deserving further evaluation.

Pol ι Is a Candidate for the Mouse Pulmonary Adenoma Resistance 2 Locus, a Major Modifier of Chemically Induced Lung Neoplasia

“…2A, we have identified 10 amino acid-changing polymorphisms and two alternatively spliced exons in Pol between A/J and BALB/cJ mice. Among them, 9 amino acid polymorphisms and 1 alternative splicing variant were consistent with those reported previously (13). The newly observed amino acid changing polymorphism at codon 606 encodes a positively charged arginine (CGA) in BALB/cJ but a neutral Glutamine (CAA) in A/J (Fig.…”

“…Four known genes are located in this region, i.e., StarD6, Pol , Mbd2, and Dcc. Preliminary analysis of the polymorphisms in the Dcc and Pol genes were reported recently (11,13).…”

“…Its 5Ј-deoxyribose phosphate lyase activity and capability for filling short gaps implicate that this polymerase may play a role in certain base excision repair (BER) reactions (19). It may also play a role in lung tumorigenesis by affecting DNA adduct repair and thus Kras2 mutations that are found in a high proportion of mouse and human lung tumors (13,20).…”

UV-B Radiation Induces Epithelial Tumors in Mice Lacking DNA Polymerase η and Mesenchymal Tumors in Mice Deficient for DNA Polymerase ι

“…Previous reports have strongly indicated a genetic linkage between chemical-induced lung tumor formation and Pol deficiency in BALB/cJ and A/J mice (31,32,68). These findings have suggested that the Pol protein may be involved in preventing certain tumors.…”

Association of amino acid substitution polymorphisms in DNA repair genes TP53, POLI, REV1 and LIG4 with lung cancer risk

“…Interestingly, the mice counterpart for POLI, Poli, was recently identified as a strong candidate for the Par2 (pulmonary adenoma resistance 2) gene responsible for reducing the mean multiplicity of urethane-induced lung adenoma/adenocarcinoma. 27 POLI/Poli proteins undertake the error-prone translesion DNA synthesis in incorporating deoxynucleotides opposite highly distorting or noninstructional DNA lesions. Thus, interindividual differences in the activity of POLI/ Poli proteins due to polymorphisms might cause the interindividual differences in the probability of mutagenesis in both humans and mice.…”