A specific mode of microsatellite instability is a crucial biomarker in adult T-cell leukaemia/lymphoma patients

HTLV-1 bZIP factor impairs DNA mismatch repair system

Adult T-cell leukemia (ATL) is a peripheral T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1). Microsatellite instability (MSI) has been observed in ATL cells. Although MSI results from impaired mismatch repair (MMR) pathway, no null mutations in the genes encoding MMR factors are detectable in ATL cells. Thus, it is unclear whether or not impairment of MMR causes the MSI in ATL cells. HTLV-1 bZIP factor (HBZ) protein interacts with numerous host transcription factors and significantly contributes to disease pathogenesis and progression. Here we investigated the effect of HBZ on MMR in normal cells. The ectopic expression of HBZ in MMR-proficient cells induced MSI, and also suppressed the expression of several MMR factors. We then hypothesized that the HBZ compromises MMR by interfering with a transcription factor, nuclear respiratory factor 1 (NRF-1), and identified the consensus NRF-1 binding site at the promoter of the gene encoding MutS homologue 2 (MSH2), an essential MMR factor. The luciferase reporter assay revealed that NRF-1 overexpression enhanced MSH2 promoter activity, while co-expression of HBZ reversed this enhancement. These results supported the idea that HBZ suppresses the transcription of MSH2 by inhibiting NRF-1. Our data demonstrate that HBZ causes impaired MMR, and may imply a novel oncogenesis driven by HTLV-1.

Looking beyond the cytogenetics in haematological malignancies: decoding the role of tandem repeats in DNA repair genes

BACKGROUND

In cancer research, one of the most significant findings was to characterize the DNA repair deficiency as carcinogenic. Amongst the various repair mechanisms, mismatch repair (MMR) and direct reversal of DNA damage systems are designated as multilevel safeguards in the human genome. Defects in these elevate the rate of mutations and results in dire consequences like cancer. Of the several molecular signatures in human genome, tandem repeats (TRs) appear at various frequencies in the exonic, intronic, and regulatory regions of the DNA. Hypervariability among these repeats in the coding and non-coding regions of the genes is well characterized for solid tumours, but its significance in haematologic malignancies remains to be explored. The purpose of our study was to elucidate the role of nucleotide repeat instability in the coding and non-coding regions of 10 different repair genes in myeloid and lymphoid cell lines compared to the control samples.

METHODS AND RESULTS

We selected MMR deficient extensively studied microsatellite instable colorectal cancer (HCT116), and MMR proficient breast cancer (MCF-7) cells along with underemphasized haematologic cancer cell lines to decipher the hypermutability of tandem repeats. A statistically significant TR variation was observed for MSH2 and MSH6 genes in 4 and 3 of the 6 cell lines respectively. KG1 (AML) and Daudi (Burkitt's lymphoma) were found to have compromised DNA repair competency with highly unstable nucleotide repeats.

CONCLUSION

Taken together, the results suggest that mutable TRs in intronic and non-intronic regions of repair genes in blood cancer might have a tumorigenic role. Since this is a pilot study on cell lines, high throughput research in large cohorts can be undertaken to reveal novel diagnostic markers for unexplained blood cancer patients with normal karyotypes or otherwise with karyotypic defects.

STR Profiling Reveals Tumor Genome Instability in Primary Mediastinal B-Cell Lymphoma

Primary mediastinal B-cell lymphoma (PMBCL) is the only non-Hodgkin’s lymphoma variant responding to immune checkpoint inhibitor (ICI) therapy, approximately in half of the cases; however, no molecular markers predicting a response to ICI therapy in PMBCL have been described so far. In this study, we assessed the incidence of the loss of heterozygosity (LOH), elevated microsatellite alteration at selected tetranucleotides (EMAST), and microsatellite instability (MSI) in the tumor genomes of 72 patients with PMBCL undergoing high-dose chemotherapy treatment at the National Research Center for Hematology (Moscow, Russia). Tumor DNA was isolated from biopsy samples taken at diagnosis. Control DNA was isolated from the blood of patients in complete remission or from buccal epithelium. STR-profiles for LOH and EMAST were assessed by PCR with COrDIS Plus multiplex kit (Gordiz Ltd., Moscow, Russia). LOH was detected in 37 of 72 patients (51.4%). EMAST was found in 40 patients (55.5%); 24 had a combination of EMAST with LOH. MSI-high was not found, while MSI-low was detected only in one patient. The association of certain genetic lesions with the clinical outcome in patients receiving treatment according to the standard clinical protocol R-Da-EPOCH-21 has been estimated (58 patients out of 72) and no associations with the worst overall or event-free survival were found.

DNA repair pathways as guardians of the genome: Therapeutic potential and possible prognostic role in hematologic neoplasms

DNA repair pathways, which are also identified as guardians of the genome, protect cells from frequent damage that can lead to DNA breaks. The most deleterious types of damage are double-strand breaks (DSBs), which are repaired by homologous recombination (HR) and non-homologous end joining (NHEJ). Single strand breaks (SSBs) can be corrected through base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR). Failure to restore DNA lesions or inappropriately repaired DNA damage culminates in genomic instability and changes in the regulation of cellular functions. Intriguingly, particular mutations and translocations are accompanied by special types of leukemia. Besides, expression patterns of certain repair genes are altered in different hematologic malignancies. Moreover, analysis of mutations in key mediators of DNA damage repair (DDR) pathways, as well as investigation of their expression and function, may provide us with emerging biomarkers of response/resistance to treatment. Therefore, defective DDR pathways can offer a rational starting point for developing DNA repair-targeted drugs. In this review, we address genetic alterations and gene/protein expression changes, as well as provide an overview of DNA repair pathways.

Recent advances in genetic predisposition to pediatric acute lymphoblastic leukemia

Introduction: Historically, the majority of childhood cancers, including acute lymphoblastic leukemia (ALL), were not thought to have a hereditary basis. However, recent germline genomic studies have revealed that at least 5 - 10% of children with cancer (and approximately 3 - 4% of children with ALL) develop the disease due to an underlying genetic predisposition.Areas covered: This review discusses several recently identified ALL predisposing conditions and provides updates on other more well-established syndromes. It also covers topics related to the evaluation and management of children and family members at increased ALL risk.Expert opinion: Germline predisposition is gaining recognition as an important risk factor underlying the development of pediatric ALL. The challenge now lies in how best to capitalize on germline genetic information to improve ALL diagnosis, treatment, and perhaps even prevention.

Correlations between microsatellite instability and the biological behaviour of tumours

Purpose

Microsatellites are widely distributed repetitive DNA motifs, accounting for approximately 3% of the genome. Due to mismatch repair system deficiency, insertion or deletion of repetitive units often occurs, leading to microsatellite instability. In this review, we aimed to explore the relationship between MSI and biological behaviour of colorectal carcinoma, gastric carcinoma, lymphoma/leukaemia and endometrial carcinoma, as well as the application of frameshift peptide vaccines in cancer therapy.

Methods

The relevant literature from PubMed and Baidu Xueshu were reviewed in this article. The ClinicalTrials.gov database was searched for clinical trials related to the specific topic.

Results

Microsatellite instability is divided into three subtypes: high-level, low-level microsatellite instability, and stable microsatellites. The majority of tumour patients with high-level microsatellite instability often show a better efficacy and prognosis than those with low-level microsatellite instability or stable microsatellites. In coding regions, especially for genes involved in tumourigenesis, microsatellite instability often results in inactivation of proteins and contributes to tumourigenesis. Moreover, the occurrence of microsatellite instability in coding regions can also cause the generation of frameshift peptides that are thought to be unknown and novel to the individual immune system. Thus, these frameshift peptides have the potential to be biomarkers to raise tumour-specific immune responses.

Conclusion

MSI has the potential to become a key predictor for evaluating the degree of malignancy, efficacy and prognosis of tumours. Clinically, MSI patterns will provide more valuable information for clinicians to create optimal individualized treatment strategies based on frameshift peptides vaccines.

Differential genomic destabilisation in human cells with pathogenic MSH2 mutations introduced by genome editing

Repeat destabilisation is variously associated with human disease. In neoplastic diseases, microsatellite instability (MSI) has been regarded as simply reflecting DNA mismatch repair (MMR) deficiency. However, several discrepancies have been pointed out. Firstly, the MSI⁺ phenotype is not uniform in human neoplasms. Established classification utilises the frequency of microsatellite changes, i.e. MSI-H (high) and -L (low), the former regarded as an authentic MMR-defective phenotype. In addition, we have observed the qualitatively distinct modes of MSI, i.e. Type A and Type B. One discrepancy we previously pointed out is that tumours occurring in MMR gene knockout mice exhibited not drastic microsatellite changes typical in MSI-H tumours (i.e. Type B mode) but minor and more subtle alterations (i.e. Type A mode). In the present study, MSH2 mutations reported in Lynch syndrome (LS) kindred have been introduced into HeLa cells using the CRISPR/Cas9 system. The established mutant clones clearly exhibited MMR-defective phenotypes with alkylating agent-tolerance and elevated mutation frequencies. Nevertheless, microsatellites were not markedly destabilised as in MSI-H tumours occurring in LS patients, and all the observed alterations were uniformly Type A, which confirms the results in mice. Our findings suggest added complexities to the molecular mechanisms underlying repeat destabilisation in human genome.