The maintenance of DNA sequence integrity is critical to avoid accumulation of cancer-causing mutations. Inactivation of DNA Mismatch Repair (MMR) genes (e.g., MLH1 and MSH2) is common among many cancers, including colorectal cancer (CRC) and is the driver of classic microsatellite instability (MSI) in tumors. Somatic MSH3 alterations have been linked to a specific form of MSI called elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) that is associated with patient poor prognosis and elevated among African American (AA) rectal cancer patients. Genetic variants of MSH3 and their pathogenicity vary among different populations, such as among AA, which are not well-represented in publicly available databases. Targeted exome sequencing of MSH3 among AA CRC samples followed by computational bioinformatic pipeline and molecular dynamic simulation analysis approach confirmed six identified MSH3 variants (c.G1237A, c.C2759T, c.G1397A, c.G2926A, c.C3028T, c.G3241A) that corresponded to MSH3 amino-acid changes (p.E413K; p.S466N; p.S920F; p.E976K; p.H1010Y; p.E1081K). All identified MSH3 variants were non-synonymous, novel, pathogenic, and show loss or gain of hydrogen bonding, ionic bonding, hydrophobic bonding, and disulfide bonding and have a deleterious effect on the structure of MSH3 protein. Some variants were located within the ATPase site of MSH3, affecting ATP hydrolysis that is critical for MSH3′s function. Other variants were in the MSH3-MSH2 interacting domain, important for MSH3’s binding to MSH2. Overall, our data suggest that these variants among AA CRC patients affect the function of MSH3 making them pathogenic and likely contributing to the development or advancement of CRC among AA. Further clarifying functional studies will be necessary to fully understand the impact of these variants on MSH3 function and CRC development in AA patients.

维持 DNA 序列完整性对于避免致癌突变的积累至关重要。DNA 错配修复 (MMR) 基因（例如MLH1和MSH2）失活在包括结直肠癌 (CRC) 在内的许多癌症中很常见，并且是肿瘤中经典微卫星不稳定性 (MSI) 的驱动因素。体细胞MSH3改变与一种特殊形式的 MSI 相关，这种 MSI 称为选定四核苷酸重复序列微卫星改变升高 (EMAAST)，这种改变与患者不良预后相关，并且在非裔美国人 (AA) 直肠癌患者中升高。MSH3的遗传变异及其致病性在不同人群中有所不同，例如 AA 人群，这些人群在公开数据库中没有得到很好的体现。对 AA CRC 样本中的MSH3进行靶向外显子测序，然后通过计算生物信息学流程和分子动态模拟分析方法确认了六种已识别的MSH3变体（c.G1237A、c.C2759T、c.G1397A、c.G2926A、c.C3028T、c.G3241A）对应于 MSH3 氨基酸变化（p.E413K；p.S466N；p.S920F；p.E976K；p.H1010Y；p.E1081K）。所有已鉴定的MSH3变体都是非同义的、新颖的、致病性的，并且显示出氢键、离子键、疏水键和二硫键的丢失或增加，并对 MSH3 蛋白的结构产生有害影响。一些变异位于 MSH3 的 ATP 酶位点内，影响对 MSH3 功能至关重要的 ATP 水解。其他变体位于 MSH3-MSH2 相互作用域，对于 MSH3 与 MSH2 的结合很重要。总体而言，我们的数据表明，AA CRC 患者中的这些变异影响 MSH3 的功能，使其具有致病性，并可能促进 AA CRC 的发展或进展。为了充分了解这些变异对 AA 患者 MSH3 功能和 CRC 发展的影响，需要进一步阐明功能研究。