hMYH cell cycle-dependent expression, subcellular localization and association with replication foci: evidence suggesting replication-coupled repair of adenine : 8-oxoguanine mispairs

The human MutY homolog, hMYH, is an adenine-specific DNA glycosylase that r emoves adenines or 2-hydroxyadenines mispaired with guanines or 8-oxoguanin es, In order to prevent mutations, this activity must be directed to the ne wly synthesized strand and not the template strand during DNA synthesis. Th e subcellular localization and expression of hMYH has been studied in serum -stimulated, proliferating MRC5 cells. Using specific antibodies, we demons trate that endogenous hMYH protein localized both to nuclei and mitochondri a, hMYH in the nuclei is distinctly distributed and co-localized with BrdU at replication foci and with proliferating cell nuclear antigen (PCNA), The levels of hMYH in the nucleus increased 3- to 4-fold during progression of the cell cycle and reached maximum levels in S phase compared to early G(1 ). Similar results were obtained for PCNA, while there were no notable chan ges in expression of 8-oxoguanine glycosylase or the human MutT homolog, MT H1, throughout the cell cycle. The cell cycle-dependent expression and loca lization of hMYH at sites of DNA replication suggest a role for this glycos ylase in immediate postreplication DNA base excision repair.