Acquired FANCA dysfunction and cytogenetic instability in adult acute myelogenous leukemia

Abstract

Myelodysplastic and leukemic stem cell clones that evolve in children and adults with Fanconi anemia universally bear complex cytogenetic abnormalities. The abnormalities are generally recurring deletions or chromosomal loss and involve precisely the same chromosomes with the same frequency as has been described in marrow cells from patients with secondary acute leukemia induced by alkylating agents. Reasoning that acquired Fanconi anemia protein dysfunction might contribute to cytogenetic instability in secondary acute myelogenous leukemia (AML) cells, we analyzed leukemic cells bearing characteristic complex cytogenetic defects obtained from a 68-year-old man whose lymphoblasts showed no evidence of Fanconi anemia. Unlike the lymphoblasts, this myeloid leukemia cell line (UoC-M1) was hypersensitive to mitomycin-C (MMC) and diepoxybutane (DEB) and exhibited a marked decrease in nuclear FANCA, FANCG, and FANCD2-L. Retroviral transduction of FANCA significantly reduced MMC sensitivity but FANCF, FANCG, and FANCC did not. Overexpression of FANCA restored levels of both FANCA and FANCG, whereas overexpression of FANCG or IntroductionA variety of molecular defects have been discovered in patients with myeloproliferative syndromes and acute myelogenous leukemia, many of which result in the activation of autonomous signal transduction pathways for growth and survival. [1][2][3][4][5] Although oncogenic mutations in such pathways are sufficient to induce myeloproliferative disorders in transgenic mice, 2,3 the development of acute leukemia requires additional mutations that ultimately interfere with myeloid differentiation. 6 The risk of this second type of mutation would be necessarily enhanced by cytogenetic instability, a manifestation of which in the leukemic clone would be multiple cytogenetic defects. That such complex cytogenetic defects universally occur in the myeloid leukemic clones of children with Fanconi anemia, a cytogenetic instability syndrome, supports this notion. In fact, because the clonal abnormalities found in this clinical context exactly recapitulate those found in patients with secondary myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML), 7,8 and high-risk MDS, 9 we hypothesized that acquired Fanconi anemia (FA) protein dysfunction might serve as a progression factor for the evolution of cytogenetically unstable AML clones, even in patients without hereditary evidence of Fanconi anemia. To test this notion, we examined a variety of AML cells and cell lines, including a cell line from a 68-year-old patient with cytogenetic defects characteristic of secondary AML. The patient's lymphoblasts were normal, but the leukemic cell population exhibited hypersensitivity to mitomycin C, a feature of Fanconi anemia. Nuclear FANCC, FANCG, and FANCA levels were markedly reduced, and retroviral complementation indicated that the leukemic cells exhibited a secondary defect of FANCA function. Because lymphoblasts from this same patient showed normal levels of nuclear Fanconi proteins, we propo...

Deletion and reduced expression of the Fanconi anemia FANCA gene in sporadic acute myeloid leukemia

“…16 In fact, either a germline FA gene mutation or a somatic mutation in a stem cell may constitute a progression factor in a pathway that leads in some cases to chromosomal instability and cancer. 16,26 The three cases with FANCA gene deletions in which diagnostic cytogenetics was available had a very complex karyotype, which is consistent with this hypothesis. Further studies looking at both tumor and germline DNA from sporadic AML cases are required to determine whether FANCA or other FA gene mutations represent germline or somatic mutations.…”

“…In cell lysates from primary AML blasts, 11 out of 15 cases also had aberrant profiles. Further evidence that disruption of the FA pathway may be implicated in the etiology of some sporadic AML cases is provided by Lensch et al, 26 who reported a case of acquired cytogenetic instability in a 68-year-old man with AML and demonstrated FANCA dysfunction in tumor cells, while lymphoblastoid cells from the same individual had normal FANCA function.…”

“…The high incidence of AML in FA homozygotes and the evidence for deficiency of FA proteins and their complexes in sporadic AML, 25,26 have led us to examine the role of inactivation of the FA pathway in the development of sporadic AML. We selected the FANCA gene for analysis since mutations in this gene account for 70% of all cases of FA.…”

Fanconi anaemia genes and susceptibility to cancer

“…A follow-up study of this cell line showed that the MMC sensitivity could be corrected by transfection with the FANCF gene, and that FANCF expression in these cells was silenced not by mutation, but by extensive methylation of its promoter region . Hypersensitivity to MMC and inactivation of the FA pathway with loss of FANCD2 ubiquitination and reduced amounts of nuclear FA proteins was reported in another AML cell line (Lensch et al, 2003). In this case, MMC sensitivity was partially corrected by transduction with the FANCA gene, but no mutation or methylation of FANCA was detected, so the basis of this acquired FANCA dysfunction was unresolved.…”

Inherited mutations impair responses to environmental carcinogens: Cancer prevention in mutation carriers

“…Mutations in Fanconi genes contribute to a subset of sporadic AML [26][27][28]. In heterozygous carriers, lymphocytes show increased sensitivity to mutagens, but are not blocked in G2 phase as in full Fanconi Anemia [29,30].…”