CML-152: Investigation of Short Tandem Repeat Instability of Mismatch Repair Genes in Hematologic Malignancies

Abstract

Context: In the present study, we sought answers to the following questions: 1. Do mutations in mismatch repair genes contribute substantially toward progression of hematologic malignancies? 2. Are blood cancers solely driven by chromosomal instabilities, or does microsatellite instability play a role in their causation? Objective: Recently, the concept of dark DNA is gaining momentum in cancer research. Short tandem repeats (STRs) are more prevalent in intronic regions, and due to their evolutionary relevance, tandem repeat hypervariability in both protein coding and non-coding regions is being investigated in various cancer subtypes. However, their occurrence in hematologic malignancies is highly debatable. Here, we evaluate the instability of certain STRs in 10 selective repair genes in various hematologic cell lines. Design: We selected MMR proficient/deficient, underemphasized hematologic cell lines (K562, Molt-4, Daudi, KG-1), along with extensively studied microsatellite instable colorectal (HCT116) and breast (MCF7) cancer cells to decipher the hypervariability of TRs. The primers were selected for gene sequence-specific intronic/exonic TRs. The splice sites were analyzed for individual markers. The TR instability was investigated via PCR and capillary electrophoresis-based fragment analysis. The two sample F-test was performed for statistical analysis. Results: The overall results suggest that TR hypermutability alongside chromosomal aberrations could be the underlying cause of myeloid and lymphoid malignancies. As per the ASSP online tool, the PCR products had cryptic splice sites, which could alter with expansion and loss of repeat sequences. A statistically significant TR variation was observed for MSH2, MSH4, and MSH6 (P Conclusion: Taken together, the mutable TRs in intronic and non-intronic regions of DNA repair genes in blood cancer cells might have a tumorigenic role. Although the repeat instabilities are causally reflected in treated patients, primary patient sample studied for such repeat variability can have huge diagnostic relevance.