Aberrant transcripts of the FHIT gene are expressed in normal and leukaemic haemopoietic cells

Significance and implications of FHIT gene expression and promoter hypermethylation in acute lymphoblastic leukemia (ALL)

BACKGROUND

Fragile histidine triad (FHIT) has been documented to play a vital role in various cancers including acute lymphoblastic leukemia (ALL). Keeping in view the plausible role of FHIT gene, we aimed to examine DNA promoter hypermethylation and mRNA expression in ALL cases in Kashmir (North India).

METHODS

A total of 66 cases of ALL were analyzed for FHIT mRNA expression and promoter methylation by qRT-PCR and Methylation Specific-PCR (MS-PCR) respectively.

RESULTS

FHIT mRNA expression showed significantly decreased expression in ALL cases with mean fold change of 9.24 ± 5.44 as compared to healthy controls (p = 0.01). The pattern of FHIT deregulation in ALL cases differed significantly between decreased and increased expression (p < 0.0001). A threefold decreased expression was observed in 75% of ALL cases than healthy controls (- 3.58 ± 2.32). ALL patients with FHIT gene promoter hypermethylation presented significantly higher in 80% (53/66) of cases (p = 0.0005). The association of FHIT gene hypermethylation and its subsequent expression showed FHIT mRNA expression as significantly lower in ALL cases with hypermethylation (p = 0.0008). B-ALL cases exhibited a highly significant association between the methylation pattern and its mRNA expression (p = 0.000). In low range WBC group, a significant association was found between increased expression (26%) of the cases and methylated (4%)/unmethylated group 86% (p = 0.0006).

CONCLUSION

The present study conclude that FHIT gene hypermethylation and its altered expression may be linked in the pathogenesis of ALL and provide an evidence for the role of FHIT in the development of ALL.

Fragile histidine triad protein: structure, function, and its association with tumorogenesis

BACKGROUND

The human fragile histidine triad (FHIT) gene is a putative tumor suppressor gene, which is located at chromosome region 3p14.2. It was suggested that the loss of heterozygosity (LOH), homozygous deletions, and abnormal expression of the FHIT gene were involved in several types of human malignancies.

MATERIALS AND METHODS

To determine the role of FHIT in various cancers, we have performed structural and functional analysis of FHIT in detail.

RESULTS AND DISCUSSION

The protein FHIT catalyzes the Mg(2+) dependent hydrolysis of P1-5 cent-O-adenosine-P3-5 cent-O-adenosine triphosphate, Ap3A, to AMP, and ADP. The reaction is thought to follow a two-step mechanism. Histidine triad proteins, named for a motif related to the sequence H-cent-H-cent-H-cent-cent- (cent, a hydrophobic amino acid), belong to superfamily of nucleotide hydrolases and transferases. This enzyme acts on the R-phosphate of ribonucleotides, and contain a approximately 30-kDa domain that is typically a homodimer of approximately 15 kDa polypeptides with catalytic site.

CONCLUSION

Here we have gathered information is known about biological activities of FHIT, the structural and biochemical bases for their functions. Our approach may provide a comparative framework for further investigation of FHIT.

Expression and methylation status of the FHIT gene in acute myeloid leukemia and myelodysplastic syndrome

To clarify the role of fragile histidine triad (FHIT) in hematological malignancies, we examined the methylation status and the expression level of the FHIT gene in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) cells in comparison with the methylation of the p15(INK4B) gene. The FHIT methylation was found in 13 of 94 (13.8%) AML and 22 of 40 (55.0%) MDS cases, but not in normal mononuclear cells (MNCs). Both the frequency and density of methylation increased in the advanced-stages MDS and the relapsed AML cases. Although FHIT and p15(INK4B) methylations were not correlated in MDS and AML, increased FHIT methylation at the relapse in AML was associated with p15(INK4B) methylation. The median expression level in AML was significantly higher than in normal MNCs, although the median expression level in those with methylation was significantly lower than in those without methylation. Furthermore, the methylation level at relapse was significantly higher than at diagnosis in AML. These results suggested that FHIT methylation was accumulated through the disease progression of MDS and AML, and the role of the FHIT gene as a tumor suppressor seemed different in AML and MDS.

Alterations of common chromosome fragile sites in hematopoietic malignancies

Conditions of replication stress affect expression of all common fragile regions, including FRA3B (chromosome 3p14.2), FRA16D (16q23), FRA6E (6q26), FRA7G (7q31.2), and FRAXB (Xp22.3), and a number of cancer cell lines exhibit homozygous deletions in 2 or more common fragile regions. In 1996 the fragile histidine triad (FHIT) gene was isolated from the region encompassing the most active fragile FRA3B locus, and recently the WW domain-containing oxidoreductase gene (WWOX) was identified at FRA16D. These 2 fragile genes are altered or deleted in various epithelial tumors and exhibit tumor suppressor function. Aberration or absence of WWOX expression recently was detected in primary hematopoietic malignancies. The aberration resulted not only from genomic deletions but also possibly from epigenetic modifications associated with expression of fragility. Thus chromosomal aberrations at common fragile sites, in addition to the well-defined hallmark leukemia chromosome translocations, are involved in clinicopathological outcomes of hematopoietic malignancies.

Hypermethylation of the 5' CpG island of the FHIT gene is associated with hyperdiploid and translocation-negative subtypes of pediatric leukemia

The human FHIT (fragile histidine triad) gene is a putative tumor suppressor gene located at chromosome region 3p14.2. Previous studies have shown that loss of heterozygosity, homozygous deletions, and abnormal expression of the FHIT gene are involved in several types of human malignancies. A CpG island is present in the 5' promoter region of the FHIT gene, and methylation in this region correlates with loss of FHIT expression. To test whether aberrant methylation of the FHIT gene may play a role in pediatric leukemia, we assessed the FHIT methylation status of 10 leukemia cell lines and 190 incident population-based cases of childhood acute lymphocytic and myeloid leukemias using methylation-specific PCR. Conventional and fluorescence in situ hybridization cytogenetic data were also collected to examine aneuploidy, t(12, 21), and other chromosomal rearrangements. Four of 10 leukemia cell lines (40%) and 52 of 190 (27.4%) bone marrows from childhood leukemia patients demonstrated hypermethylation of the promoter region of FHIT. Gene expression analyses and 5-aza-2'-deoxycytidine treatment showed that promoter hypermethylation correlated with FHIT inactivation. Among primary leukemias, hypermethylation of FHIT was strongly correlated with acute lymphoblastic leukemia (ALL) histology (P = 0.008), high hyperdiploid (P < 0.0001), and translocation-negative (P < 0.0001) categories. Hyperdiploid B-cell ALLs were 23-fold more likely to be FHIT methylated compared with B-cell ALL harboring TEL-AML translocations. FHIT methylation was associated with high WBC counts at diagnosis, a known prognostic indicator. These results suggest that hypermethylation of the promoter region CpG island of the FHIT gene is a common event and may play an important role in the etiology and pathophysiology of specific cytogenetic subtypes of childhood ALL.

Alteration of the fragile histidine triad gene early in carcinogenesis: an update

An association between common chromosome fragile sites and frequent chromosomal deletions in cancer has been observed and led to the hypothesis that genes at fragile sites may play a role in tumor development. In 1996, the human fragile histidine triad gene, FHIT, was identified by positional cloning at 3p14.2, a chromosomal region spanning the carcinogen-sensitive, common fragile site FRA3B. FHIT gene is lost and inactivated in a large fraction of tumors and early in carcinogenesis. A group of ancestral cancerous cells that carry FHIT alterations, expanding in succeeding cell generations, exhibits a hallmark in carcinogenesis scenario.

Analysis of the tumour suppressor genes, FHIT and WT-1, and the tumour rejection genes, BAGE, GAGE-1/2, HAGE, MAGE-1, and MAGE-3, in benign and malignant neoplasms of the salivary glands

AIMS

Molecular genetic changes involved in tumorigenesis and malignant transformation of human tumours are novel targets of cancer diagnosis and treatment. This study aimed to analyse the expression of putative tumour suppressor genes, FHIT and WT-1, and tumour rejection genes, BAGE, GAGE-1/2, MAGE-1, MAGE-3, and HAGE (which are reported to be important in human cancers), in salivary gland neoplasms.

METHODS

Gene expression was analysed by reverse transcription polymerase chain reaction (RT-PCR) in normal salivary gland tissue and 44 benign and malignant salivary gland tumours.

RESULTS

Aberrant FHIT transcripts were found in one of 38 normal salivary glands, three of 28 adenomas, and two of 16 carcinomas. WT-1 mRNA was detectable in two adenomas and five carcinomas. Immunoblotting showed that WT-1 mRNA expression was associated with raised WT-1 protein concentrations. RT-PCR for detection of BAGE, GAGE, and MAGE gene expression was positive in two adenomas and nine carcinomas, but negative in normal salivary gland tissue. HAGE mRNA was found in two normal salivary glands, 11 benign, and eight malignant tumours.

CONCLUSIONS

FHIT mRNA splicing does not appear to be involved in the genesis of salivary gland neoplasms. The upregulation of WT-1 mRNA in tumours of epithelial/myoepithelial phenotype may imply a potential role of WT-1 in the genesis and/or cellular differentiation of these salivary gland tumours. The tumour rejection genes were more frequently, but not exclusively, expressed in malignant salivary gland tumours than in benign neoplasms, although none was suitable as a diagnostic marker of malignancy in salivary gland neoplasms.

Investigation of genetic susceptibility to non-small cell lung cancer by fragile site expression

Fragile sites are non-staining gaps and breaks in specific points of chromosomes that are inducible by various culture conditions. Previous studies have shown that various clastogenic agents increase expression of fragile sites. In this study, the expression of common fragile sites induced by aphidicolin was evaluated on prometaphase chromosomes obtained from peripheral blood lymphocytes. Chromosomal aberrations and fragile site expression of 60 individuals, including 20 patients with non-small cell lung cancer (NSCLC), 20 of their clinically healthy family members, and 20 age-matched normal healthy controls without history of any cancer type were studied. Both the proportion of damaged cells (P < 0.001) and the mean number of gaps and breaks per cell (P < 0.001) were significantly higher in both the patients and relatives' groups when compared with the control group. However, they were insignificant when the patients were compared to their relatives (P > 0.05). We determined four aphidicolin type common fragile sites in our study. These sites in patients with NSCLC and relatives were the following: 1p21, 2q33, 3p14, and 16q23. In these fragile sites, 2q33, 3p14, and 16q23 sites were statistically significant when compared with control group (P < 0.001, P < 0.0005, and P < 0.05, respectively). Consequently, we believe that fragile site studies may be helpful to detection of cancer risk.

The clinical significance of fragile sites on human chromosomes

Fragile X syndrome is now a well established common clinical entity and most of those who are aware of the condition probably know that it takes its name from a rare fragile site (FRAXA) on the X chromosome. This is the best known fragile site and its clinical significance is clear. Similar, but a little less known is FRAXE, a fragile site close to that associated with fragile X syndrome, but in this case associated with a mild form of non-specific X-linked mental retardation. These are the only two fragile sites that are unequivocally of clinical significance. A fragile site within the CBL2 oncogene on chromosome 11 has been mapped very close to the deletion breakpoint in a handful of patients with Jacobsen syndrome. It is doubtful that parents with FRA11B are at increased risk of having children with Jacobsen syndrome, but this cannot be ruled out. The common fragile sites have been implicated in oncogenesis since shortly after their discovery in the early 1980s. While a couple of these are within genes that have been implicated in cancer it is unclear whether either the fragile sites, or the genes in which they are located are important in cancer. It may be that the common fragile sites are regions of genomic instability and that this instability is increased in malignant cells, analogous to the enhanced instability seen at microsatellite loci in a number of tumours. Since we all have the common fragile sites there is no suggestion that they give anyone an increased risk of developing malignant disease. In dealing with patients who are found to have fragile sites, other than FRAXA, FRAXE and possibly FRA11B, considerable reassurance can be given that they are not at increased risk of having children with congenital disease or developing disease themselves because of their fragile sites.