Telomere Elongation and Mismatch Repair Deficiency Distinguish MSI Colorectal Cancer Cell Lines

Microsatellite instability (MSI) is a hallmark of mismatch repair (MMR) deficiency and characterizes a distinct subset of colorectal cancers (CRC). In parallel, telomere length dynamics have emerged as important contributors to genomic stability and tumorigenesis. However, the relationship between MSI status, MMR protein expression, and telomere maintenance remains poorly defined. This study aimed to investigate the association between MSI status and telomere length in CRC cell lines and to evaluate the expression of key MMR proteins (MLH1, MSH2, MSH6, PMS2) to elucidate molecular differences between MSI and microsatellite stable (MSS) phenotypes. A panel of CRC cell lines with known MSI and MSS statuses was used. Telomere length was quantified using real-time quantitative PCR (qPCR) based on the T/S ratio method. MSI status was confirmed via PCR using mononucleotide repeat markers. Western blotting was performed to assess protein expressions of MLH1, MSH2, MSH6, and PMS2. β-actin served as a loading control. qPCR analysis revealed that MSI cell lines exhibited significantly longer telomeres compared to MSS lines (P < 0.05). Western blot results showed reduced or absent expression of MLH1 and PMS2 in MSI cell lines, confirming MMR deficiency. In contrast, MSS cell lines maintained normal expression of all tested MMR proteins. These findings suggest a link between defective MMR function and altered telomere dynamics in MSI-CRC. MSI CRC cell lines exhibit telomere elongation and loss of key MMR proteins, highlighting distinct molecular features compared to MSS counterparts. These insights may inform future strategies for personalized CRC diagnostics and therapeutics, particularly in the context of telomere-targeted or immunomodulatory treatments.