The role of excision repair in the removal of transient benzo[a]pyrene-induced DNA lesions in Chinese hamster ovary cells

Abstract

In Chinese hamster ovary (CHO) cells, benzo[a]pyrene induces both persistent and transient lesions that are detected by alkaline sucrose gradient sedimentation analysis (ASG sites). The transient lesions disappear within 15 min while the persistent lesions can be detected for several hours following treatment. Although the persistent ASG sites are believed to be repaired by excision repair, the process responsible for the disappearance of the transient ASG sites is unknown. To determine the contribution of excision repair to the removal of these transient lesions, CHO cells were treated with benzo[a]pyrene (B(a)P) in the presence of the inhibitors of excision repair, araC and novobiocin. The results indicate that: (1) araC inhibits the removal of persistent, but not the transient B(a)P-induced ASG sites; (2) novobiocin, a putative inhibitor of the incision step of DNA excision repair, reduced the number of lesions detected immediately following treatment, indicating that many of these lesions may represent single-strand discontinuities generated during repair; and (3) the lesions detected in the presence of novobiocin disappear rapidly following treatment. Based on these results, we concluded that B(a)P-induced transient ASG sites are repaired by a process other than excision repair.