Interaction with DNA polymerase η is required for nuclear accumulation of REV1 and suppression of spontaneous mutations in human cells

Defects in the gene encoding human Pol eta result in xeroderma pigmentosum variant (XP-V), an inherited cancer-prone syndrome. Pol eta catalyzes efficient and accurate translesion DNA synthesis (TLS) past UV-induced lesions. In addition to Pol eta, human cells have multiple TLS polymerases such as Pol iota, Pol kappa, Pol zeta and REV1. REV1 physically interacts with other TLS polymerases, but the physiological relevance of the interaction remains unclear. Here we developed an antibody that detects the endogenous REV1 protein and found that human cells contain about 60,000 of REV1 molecules per cell as well as Pol eta. In un-irradiated cells, formation of nuclear foci by ectopically expressed REV1 was enhanced by the co-expression of Pol eta. Importantly, the endogenous REV1 protein accumulated at the UV-irradiated areas of nuclei in Pol eta-expressing cells but not in Pol eta-deficient XP-V cells. UV-irradiation induced nuclear foci of REV1 and Pol eta proteins in both S-phase and G1 cells, suggesting that these proteins may function both during and outside S phase. We reconstituted XP-V cells with wild-type Pol eta or with Pol eta mutants harboring substitutions in phenylalanine residues critical for interaction with REV1. The REV1 interaction-deficient Pol eta mutant failed to promote REV1 accumulation at sites of UV-irradiation, yet (similar to wild-type Pol eta) corrected the UV sensitivity of XP-V cells and suppressed UV-induced mutations. Interestingly however, spontaneous Mutations of XP-V cells were only partially suppressed by the REV1-interaction deficient mutant of Pol eta. Thus, Pol eta-REV1 interactions prevent spontaneous mutations, probably by promoting accurate TLS past endogenous DNA lesions, while the interaction is dispensable for accurate Pol eta-mediated TLS of UV-induced lesions. (C) 2008 Elsevier BY. All rights reserved.