Deletion of 6q27 in chronic lymphocytic leukemia and multiple myeloma detected by fluorescence in situ hybridization

Dact2 is involved in the regulation of epithelial-mesenchymal transition

Dishevelled-associated antagonist of beta-catenin 2 (Dact2) is involved in the regulation of intracellular signaling pathways during development. It negatively regulates the Nodal signaling pathway, possibly by promoting lysosomal degradation of Nodal receptors such as TGFBR1, and plays an inhibitory role during the re-epithelialization of skin wounds by attenuating transforming growth factor-β signaling. Dact2 is known to act as a functional tumor suppressor in colon cancer; reduced Dact2 can promote liver cancer progression and suppress gastric cancer proliferation, invasion, and metastasis by inhibiting Wnt signaling. Zebrafish is used as a model of cancer biology because it shows similar tumorigenesis and morphogenesis as in humans and gene manipulation in this organism is possible. This study was performed to explore phenotypic changes in Dact2 knockout zebrafish and investigate the function of Dact2. A 10-base pair deletion Dact2 knockout zebrafish was prepared using the CRISPR-Cas9 genome editing system. Dact2 knockout enhanced the expression of the MMP2 and MMP9 genes, which are related to tumor invasion and migration, and the Snail, VEGF, and ZEB genes, which are related to epithelial-mesenchymal transition (EMT). The absence of Dact2 also resulted in hyperplasia of the gastrointestinal epithelium, fibrosis in the pancreas and liver, increased proliferation of the pancreatic and hepatic bile ducts, and invasive proliferation into the pancreas. A wound healing assay confirmed that the absence of Dact2 enhanced EMT, thus accelerating wound healing. This study suggests that a loss of function of Dact2 impacts EMT-related gene regulation and tumor generation in a zebrafish knockout model, which is a useful model for exploring the mechanisms of these processes.

Upregulation of DACT2 suppresses proliferation and enhances apoptosis of glioma cell via inactivation of YAP signaling pathway

DACT2, one of the Dact gene family members, was shown to function as a tumor suppressor. However, its function in gliomas remains largely unknown. In this study, we investigated the role of DACT2, underlying molecular mechanisms and its clinical significance in glioma patients. Downexpression of DACT2 in gliomas compared with adjacent normal brain tissues was correlated with glioma grade and poor survival. Cox regression analysis revealed that the DACT2 is an independent prognostic indicator for glioma patients. Overexpression of DACT2 in glioma cells inhibited proliferation, cell cycle and enhanced apoptosis, sensitivity to temozolomide in vitro and suppressed tumor growth in vivo. Whereas knockdown of DACT2 induce opposite reaction. Mechanistically, overexpression of DACT2 resulted in upregulation of important signaling molecules such as p-YAP and p-β-catenin, and prevent YAP translocating into nucleus and sequestering in the cytoplasm to degrade. The study further proved that DACT2 can suppress YAP through Wnt/β-catenin signaling pathway. Collectively, these data indicate that DACT2 has a tumor suppressor function via inactivation of YAP pathway, providing a promising target for the treatment of gliomas.

PDCD2 functions in cancer cell proliferation and predicts relapsed leukemia

PDCD2 is an evolutionarily conserved eukaryotic protein with unknown function. The Drosophlia PDCD2 ortholog Zfrp8 has an essential function in fly hematopoiesis. Zfrp8 mutants exhibit marked lymph gland hyperplasia that results from increased proliferation of partially differentiated hemocytes, suggesting Zfrp8 may participate in cell growth. Based on the above observations we have focused on the role of PDCD2 in human cancer cell proliferation and hypothesized that aberrant PDCD2 expression may be characteristic of human malignancies. We report that PDCD2 is highly expressed in human acute leukemia cells as well as in normal hematopoietic progenitors. PDCD2 knockdown in cancer cells impairs their proliferation, but not viability relative to parental cells, supporting the notion that PDCD2 overexpression facilitates cancer cell growth. Prospective analysis of PDCD2 in acute leukemia patients indicates PDCD2 RNA expression correlates with disease status and is a significant predictor of clinical relapse. PDCD2's role in cell proliferation and its high expression in human malignancies make it an attractive, novel potential molecular target for new anti-cancer therapies.

6q deletion detected by fluorescence in situ hybridization using bacterial artificial chromosome in chronic lymphocytic leukemia

Deletions of the long arm of chromosome 6 are known to occur at relatively low frequency (3-6%) in chronic lymphocytic leukemia (CLL), and they are more frequently observed in 6q21. Few data have been reported regarding other bands on 6q involved by cytogenetic alterations in CLL. The cytogenetic study was performed in nuclei and metaphases obtained after stimulation with a combination of CpG-oligonucleotide DSP30 and interleukin-2. Four bacterial artificial chromosome (BAC) clones mapping regions in bands 6q16, 6q23, 6q25, 6q27 were used as probes for fluorescence in situ hybridization in 107 CLL cases in order to analyze the occurrence and localization of 6q aberrations. We identified 11 cases (10.2%) with 6q deletion of 107 patients studied with CLL. The trends of survival curves and the treatment-free intervals (TFI) of patients with deletion suggest a better outcome than the other cytogenetic risk groups. We observed two subgroups with 6q deletion as the sole anomaly: two cases with 6q16 deletion, and three cases with 6q25.2-27 deletion. There were differences of age, stage, and TFI between both subgroups. By using BAC probes, we observed that 6q deletion has a higher frequency in CLL and is linked with a good prognosis. In addition, it was observed that the deletion in 6q16 appears to be the most frequent and, if present as the only abnormality, it could be associated with a most widespread disease.

High-resolution genomic analysis in Waldenström's macroglobulinemia identifies disease-specific and common abnormalities with marginal zone lymphomas

Cytogenetic analyses have been historically limited in Waldenström's macroglobulinemia (WM) by the difficulty to obtain tumor metaphases. Thus, few recurrent karyotypic abnormalities have been reported and the molecular consequences of these imbalances are largely unknown. We used an array-based comparative genomic hybridization approach to better characterize the recurrent chromosome abnormalities associated with WM pathogenesis and to compare them with the publicly available findings in other B-cell neoplasias. The majority of the recurrent chromosome abnormalities identified in WM were shared with marginal zone lymphomas (MZL), as deletions of 6q23 and 13q14 and gains of 3q13-q28, 6p and 18q. On the other hand, gains of 4q and 8q were recurrently identified in WM but have not been described as being common abnormalities in MZL. The genetic consequences of these specific abnormalities remain elusive and further studies are critical to refine the search and to precise the molecular pathways affected by these abnormalities.

Genetic alteration associated with chronic lymphocytic leukemia

The genetics of B-cell chronic lymphocytic leukemia (B-CLL) differ considerably from most other forms of hematologic malignancy which are usually characterized by chromosome translocations. B-CLL typically contains chromosomal deletions and chromosomes 13q14 and 11q22-->q23 are the most common. These two regions appear to share a common ancestral origin (Auer et al., 2007b). Overall, chromosomal abnormalities can be found in the majority of patients with B-CLL when using sensitive techniques (Dohneret al., 2000) and possibly reflects an underlying predisposition, with a small but significant number of familial cases. Although single and consistent abnormalities are most common, multiple rearrangements can occur, often with disease progression (Feganetal., 1995; Dohner et al., 2000). Regions of recurrent deletion suggest the presence of tumor suppressor genes if following Knudson's theoretical 2-hit model. However, despite extensive sequencing analysis over the last decade and lack of pathogenic mutations identified, there has been a move away from this suggested hypothesis and alternative mechanisms of gene inactivation involving epigenetic silencing or haploinsufficiency may be considered as more likely in this disease. This review focuses on the common genetic abnormalities in B-CLL and relates them to some of the more recent hypotheses on inactivation of genes within these regions of deletion.

Chromosome band 6q deletion pattern in malignant lymphomas

Deletion of chromosome arm 6q is a frequent karyotypic alteration found in a variety of cancers and lymphoproliferative disorders, including leukemia and lymphomas. We characterized 6q deletions in 35 malignant lymphomas, using conventional and molecular cytogenetic approaches, to define the deletion pattern of 6q in different histological types. Conventional cytogenetics revealed a 6q deletion in 46% of lymphomas, including two cases that showed 6q deletion as the sole chromosome anomaly. Interphase FISH analysis demonstrated allelic loss of 6q regions in 33 out of 35 cases (94.2%); the deletions were discontinuous, involving nonadjacent molecular regions. Although 6q deletion is a common event in all types of lymphomas, specific deletion patterns seem to characterize different histological types, suggesting that different tumor suppressor genes play different roles in different types of lymphomas. Two specific 6q regions deleted in diffuse large B cell lymphomas but not in follicular lymphomas may be implicated in the clinical transformation.

Allelotyping of gastrointestinal nasal-type NK/T-cell lymphoma

Nasal-type natural killer/T-cell lymphoma (NKL) is a rare but distinct malignancy that often involves the mid-facial region and the gastrointestinal tract. This study is the first genome-wide allelotyping analysis on this rare lymphoma. We applied 382 microsatellite markers covering loci which spanned 22 autosomes to screen for allelic imbalances (AI) in six intestinal NKL. The most common chromosomal regions of allelic imbalances were found in 11p, 9q and 13q. Novel spots of allelic losses spots found at 2p21, 2q37.22, 18p11.21 and 18q12.1. In spite of presence of a few recurrent loci of imbalances, the allelotyping results show that NKL is heterogeneous.

Delineation of a minimal region of deletion at 6q16.3 in follicular lymphoma and construction of a bacterial artificial chromosome contig spanning a 6-megabase region of 6q16-q21

Regional deletions of 6q are frequent karyotypic alterations in malignant lymphoma and are associated with an adverse clinical outcome. One such region of recurrent deletion is 6q16-q21; however, the specific genes affected have not been identified. Our objective in this study was to identify cases with deletion of 6q16-q21 in follicular lymphoma and to define a minimal region of deletion. A physical map of 6q16.2-q21 was constructed using map information from both sequence-based and bacterial artificial chromosome (BAC) fingerprint-based maps. Forty-three BAC clones spanning a 6-Mb region of 6q16.2-q21 were identified and obtained from the RP-11 library. Selected BACs were fluorescence-labeled and hybridized to a series of 34 follicular lymphomas with a regional 6q deletion detected by G banding. Twenty-four cases with deletion of the 6q16.3 region were detected. A minimal deletion of 2.3 Mb was defined. Our study has identified a limited region of deletion of 6q16.3 that may implicate four known genes in follicular lymphoma and possibly in other cancers. A BAC contig spanning a 6-Mb region has been anchored to the 6q16.2-q21 region. This map represents a useful resource for gene identification in this region, not only in lymphoma but also in other neoplasms with 6q alterations.

A 2.6 Mb interval on chromosome 6q25.2-q25.3 is commonly deleted in human nasal natural killer/T-cell lymphoma

Natural killer (NK)/T-cell lymphoma is a special subtype of rare malignant lymphoma that is more prevalent in Asia than in America and Europe. This newly characterized haemato-lymphoid malignancy is highly aggressive and frequently present in nasal and upper aerodigestive sites. Several studies have reported the commonly deleted region of chromosome 6q21-25 in this particular type of lymphoma. To refine the smallest region of overlapping (SRO) deletion for localization of potential tumour suppressor (TS) genes, we performed loss of heterozygosity (LOH) and homozygosity mapping of deletion (HOMOD) analyses on 37 nasal and nasal-type NK/T-cell lymphoma patients using a panel of 25 microsatellite markers, covering the 6q21-q25 region. In all patients studied, LOH was detected in eight (89%) paired-sample patients, while hemizygous deletion was detected in three (11%) single-sample patients. Combination of the LOH and HOMOD results defined a distinct 3 Mb SRO on chromosome 6q25. Quantitative multiplex polymerase chain reaction analysis of 10 sequence-tagged sites further refined the putative TS-gene-containing region to a 2.6 Mb interval between TIAM2 and SNX9. Eighteen known genes/Unigene clusters and 25 hypothetical genes are located within this 2.6 Mb region, but none are previously identified TS genes. These results provide a framework for future positional cloning of novel TS gene(s) at 6q25.2-q25.3.

Value of comparative genomic hybridization and fluorescence in situ hybridization for molecular diagnostics in multiple myeloma

Chromosomal abnormalities, such as 13q deletions, are emerging as important prognostic factors in multiple myeloma. Fluorescence in situ hybridization (FISH) using specific DNA probes is the technique most widely used for the determination of genomic aberrations in this disease. The utility of comparative genomic hybridization (CGH) for molecular diagnostics in plasma cell malignancies has not been systematically analysed. We investigated tumour samples of patients with multiple myeloma (n = 43) or plasma cell leukaemia (n = 3) using CGH and FISH with five DNA probes localized to chromosome bands 1p22, 6q21, 11q22-q23, 13q14 and 17p13. By CGH, the most frequent genomic changes were gains on chromosomes 1q, 9q and 11q, as well as losses on chromosomes 13q, 6q, Xp and Xq. By FISH, trisomy 11q was identified at a similar frequency to the 13q deletion (42%). Compared with FISH data, the sensitivity of CGH was 80.7% and the specificity was 97.5%. Thirty-two aberrations found by FISH were not identified by CGH, mostly as a result of the proportion of cells carrying the respective aberrations, or because of the limited spatial resolution of CGH. Our data indicate that, for clinical molecular diagnostics in multiple myeloma, FISH with a disease-specific DNA probe set is superior to CGH analysis.

The human homologue of unc-93 maps to chromosome 6q27 - characterisation and analysis in sporadic epithelial ovarian cancer

BACKGROUND

In sporadic ovarian cancer, we have previously reported allele loss at D6S193 (62%) on chromosome 6q27, which suggested the presence of a putative tumour suppressor gene. Based on our data and that from another group, the minimal region of allele loss was between D6S264 and D6S149 (7.4 cM). To identify the putative tumour suppressor gene, we established a physical map initially with YACs and subsequently with PACs/BACs from D6S264 to D6S149. To accelerate the identification of genes, we sequenced the entire contig of approximately 1.1 Mb. Seven genes were identified within the region of allele loss between D6S264 and D6S149.

RESULTS

The human homologue of unc-93 (UNC93A) in C. elegans was identified to be within the interval of allele loss centromeric to D6S149. This gene is 24.5 kb and comprises of 8 exons. There are two transcripts with the shorter one due to splicing out of exon 4. It is expressed in testis, small intestine, spleen, prostate, and ovary. In a panel of 8 ovarian cancer cell lines, UNC93A expression was detected by RT-PCR which identified the two transcripts in 2/8 cell lines. The entire coding sequence was examined for mutations in a panel of ovarian tumours and ovarian cancer cell lines. Mutations were identified in exons 1, 3, 4, 5, 6 and 8. Only 3 mutations were identified specifically in the tumour. These included a c.452G>A (W151X) mutation in exon 3, c.676C>T (R226X) in exon 5 and c.1225G>A(V409I) mutation in exon 8. However, the mutations in exon 3 and 5 were also present in 6% and 2% of the normal population respectively. The UNC93A cDNA was shown to express at the cell membrane and encodes for a protein of 60 kDa.

CONCLUSIONS

These results suggest that no evidence for UNC93A as a tumour suppressor gene in sporadic ovarian cancer has been identified and further research is required to evaluate its normal function and role in the pathogenesis of ovarian cancer.

PDCD2 is a negative regulator of HCF-1 (C1)

Temperature sensitive mutations in host cell factor 1 (HCF-1) arrest cells in the middle of the G1 phase of the cycle. We have shown that the highly conserved C-terminal WYF domain of HCF-1 protein interacts with the MYND domain of the PDCD2 protein. This inter-action is conserved between human HCF-1 and HCF-2 and the C. elegans HCF. Overexpression of PDCD2, which interacts with the N-CoR/mSin3A corepressor complexes, suppresses cotransfected HCF-1 complement-ation of a temperature lesion in the endogenous HCF-1 protein. Overexpression of domains of either PDCD2 or HCF-1, which should interfere with interactions between these two proteins, enhances the complementation.

Chronic lymphocytic leukemia

Chronic lymphocytic leukemia continues to attract much basic and clinical research interest. Despite recent advances, the disease still has no established cure. Nonetheless, significant strides have been made in our understanding of the genetics, biology, and clinical staging of this disease. This understanding may improve our ability to segregate patients into subtypes that differ in their cytogenesis, propensity toward disease progression, or response to standard or innovative forms of therapy. Finally, several promising new modalities of treatment are being evaluated in clinical trials, involving novel drugs or drug-combinations, monoclonal antibodies, stem cell transplantation, or gene therapy.