RESUMO
Deletion of the long arm of chromosome 9, del(9q), is a recurring chromosomal aberration in acute myeloid leukemia (AML) that is frequently associated with t(8;21). The critical gene products affected by del(9q) are unknown but likely cooperate with the AML1/ETO fusion gene created by t(8;21) in leukemogenesis. In 43 AML samples with del(9q), we used high-density microsatellite markers to define the commonly deleted region (CDR) to less than 2.4 Mb. We found no homozygous loss at any locus tested. The CDR contains 7 known genes, FRMD3, UBQLN1, GKAP42, KIF27, HNRPK, SLC28A3, and NTRK2, and 4 novel genes, RASEF, C9orf103, C9orf64, and C9orf76. In addition, TLE1 and TLE4 are adjacent to the CDR. We performed a comprehensive mutational analysis of the coding regions of all these genes. No sequence variations absent in normal controls were seen in more than a single del(9q) AML sample. Expression of 7 of the 10 genes examined was significantly down-regulated in del(19q)AML as compared with the CD34-purified progenitors from normal individuals, a pattern distinct from that seen in AML samples with a normal karyotype. The results of our studies are consistent with a model of tumor suppression mediated by haploinsufficiency of critical genes in del(9q) AML.
Assuntos
Deleção Cromossômica , Cromossomos Humanos Par 9 , Genes Supressores de Tumor/fisiologia , Leucemia Mieloide/genética , Mutação , Doença Aguda , Cromossomos Humanos Par 5/genética , Cromossomos Humanos Par 8/genética , Estudos de Coortes , Primers do DNA , Humanos , Repetições de Microssatélites , Translocação Genética/genéticaRESUMO
BACKGROUND: Chromosomal translocations leading to chimeric oncoproteins are important in leukemogenesis, but how they form is unclear. We studied acute promyelocytic leukemia (APL) with the t(15;17) translocation that developed after treatment of breast or laryngeal cancer with chemotherapeutic agents that poison topoisomerase II. METHODS: We used long-range polymerase chain reaction and sequence analysis to characterize t(15;17) genomic breakpoints in therapy-related APL. To determine whether topoisomerase II was directly involved in mediating breaks of double-stranded DNA at the observed translocation breakpoints, we used a functional in vitro assay to examine topoisomerase II-mediated cleavage in the normal homologues of the PML and RARA breakpoints. RESULTS: Translocation breakpoints in APL that developed after exposure to mitoxantrone, a topoisomerase II poison, were tightly clustered in an 8-bp region within PML intron 6. In functional assays, this "hot spot" and the corresponding RARA breakpoints were common sites of mitoxantrone-induced cleavage by topoisomerase II. Etoposide and doxorubicin also induced cleavage by topoisomerase II at the translocation breakpoints in APL arising after exposure to these agents. Short, homologous sequences in PML and RARA suggested the occurrence of DNA repair by means of the nonhomologous end-joining pathway. CONCLUSIONS: Drug-induced cleavage of DNA by topoisomerase II mediates the formation of chromosomal translocation breakpoints in mitoxantrone-related APL and in APL that occurs after therapy with other topoisomerase II poisons.
