Impaired Expression of the DNA Repair Factor DDB2 in Human Myeloid Leukemias.

Recent studies have suggested that chromosomal deletions might represent a mechanism of inactivation of DNA repair system in various hematological malignancies, including myeloid leukemias. However, the precise mechanisms remain unclear. Damaged DNA binding protein-2 (DDB2), a DNA repair factor induced by tumor suppressor p53, plays an important role in the nucleotide excision repair of UV-damaged DNA. Despite frequent mutations of p53 in human leukemic cells, the role of DDB2 on the leukemogenesis is unkown. In this study, we examined expression of DDB2 mRNA in four human myeloid leukemia cell lines (K562, KG1, HL60, and MEG01) and in fresh leukemic cells obtained from 4 patients with myeloid leukemias. In all leukemia cells, expression of DDB2 mRNA was remarkably decreased as compared to that of CD34 cells We then assayed DDB2-dependent DNA repairing activity in the leukemic cells using specific antibodies against photoproducts, and found that DNA repairing activity was reduced. When a plasmid encoding DDB2 gene (pCV-DDB2) was transduced into K562 cells, the DNA repairing activity was significantly restored. Finally we tested the expression of DDB2 mRNA in five myeloid leukemias obtained from patients, and found loss of DDB2 expression in four patients. These results suggested that in human myeloid leukemias, suppression of DDB2 expression may contribute to accumulation of gene mutation through the dysfunction of DNA repair.