Fhit-Deficient Hematopoietic Stem Cells Survive Hydroquinone Exposure Carrying Precancerous Changes

Abstract

The fragile FHIT gene is among the first targets of DNA damage in preneoplastic lesions, and recent studies have shown that Fhit protein is involved in surveillance of genome integrity and checkpoint response after genotoxin exposure. We now find that Fhit-deficient hematopoietic cells, exposed to the genotoxin hydroquinone, are resistant to the suppression of stem cell in vitro colony formation observed with wild-type (Wt) hematopoietic cells. In vivo-transplanted, hydroquinone-exposed, Fhit-deficient bone marrow cells also escaped the bone marrow suppression exhibited by Wt-transplanted bone marrow. Comparative immunohistochemical analyses of bone marrow transplants showed relative absence of Bax in Fhit-deficient bone marrow, suggesting insensitivity to apoptosis; assessment of DNA damage showed that occurrence of the oxidized base 8-hydroxyguanosine, a marker of DNA damage, was also reduced in Fhit-deficient bone marrow, as was production of intracellular reactive oxygen species. Treatment with the antioxidant N -acetyl-L-cysteine relieved hydroquinoneinduced suppression of colony formation by Wt hematopoietic cells, suggesting that the decreased oxidative damage to Fhitdeficient cells, relative to Wt hematopoietic cells, accounts for the survival advantage of Fhit-deficient bone marrow. Homology-dependent recombination repair predominated in Fhit-deficient cells, although not error-free repair, as indicated by a higher incidence of 6-thioguanine-resistant colonies. Tissues of hydroquinone-exposed Fhit-deficient bone marrow-transplanted mice exhibited preneoplastic alterations, including accumulation of histone H2AX-positive DNA damage. The results indicate that reduced oxidative stress, coupled with efficient but not error-free DNA damage repair, allows unscheduled long-term survival of genotoxin-exposed Fhitdeficient hematopoietic stem cells carrying deleterious mutations. [Cancer Res 2008;68(10):3662-70]

Nit1 and Fhit tumor suppressor activities are additive

“…We have reported previously that Fhit is involved in the DNA damage response through modulation of checkpoint proteins (Ishii et al, 2008; Okumura et al, in press). To determine if Nit1 may also have a role in responses to DNA damage, we examined the expression of γH2AX and pChk2 in wt, Fhit −/− and DKO non-neoplastic tissues of treated and non NMBA-treated mice; pChk2 and γH2AX were expressed in NMBA-treated Fhit −/− , non-treated and treated DKO forestomach tissues, but not in untreated Fhit −/− tissue (Fig.…”

A knockdown with smoke model reveals FHIT as a repressor of Heme oxygenase 1

“…A reduction in intracellular levels of ROS are detected in FHIT negative BMCs relative to wild-type, and this reduction in ROS accumulation is linked to failure to induce apoptosis as the phenotype is reversed with application of the antioxidant N-acetyl-L-cysteine. 1,5,[7][8][9]69 Several studies that connect Fhit expression to increased sensitivity to anti-cancer drugs may also serve to substantiate the link between Fhit function and oxidative stress. Re-expression of Fhit in Fhit-negative cancerderived cell lines increases sensitivity to mitomycin C (MMC), camptothecin (CPT), and cisplatin.…”

Common fragile sites and genomic instability

“…Examination of cells that have lost FHIT revealed that the protein has some functional roles in response to DNA damage (Saldivar et al, 2010). In particular, kidney epithelial cells established from Fhit-/-mice exhibited >2-fold increased chromosome breaks at fragile sites vs. corresponding Fhit+/+ cells (Turner et al, 2002), and the frequency of mutations following replicative and oxidative stress in Fhit-deficient cells was 2 to 5-fold greater than in Fhit-expressing cells (Ishii et al, 2008;Ottey et al, 2004). Despite these findings and strong evidence that Fhit acts as a tumor suppressor (Joannes et al, 2010;Pekarsky et al, 1998;Siprashvili et al, 1997) it has been proposed that deletions within the FHIT locus are secondary alterations rather than cancer-driving mutations (Bignell et al, 2010).…”