MSH2, a crucial component of the DNA mismatch repair (MMR) system, is frequently implicated in the pathogenesis of colorectal cancer (CRC). Immunohistochemistry (IHC) utilizing anti-MSH2 antibodies enables the detection of MSH2 protein expression, offering a robust diagnostic tool for identifying MMR deficiencies in colorectal carcinoma. This review examines the molecular basis of MSH2, the development and application of anti-MSH2 antibodies, and their role in the diagnostic pathology of colon tumors.
Colorectal cancer is one of the leading causes of cancer-related morbidity and mortality worldwide. Deficiencies in the DNA mismatch repair (MMR) system, particularly involving the MSH2 protein, play a critical role in the tumorigenesis of a significant subset of these cancers. MSH2, encoded by the MSH2 gene located on chromosome 2p21, is essential for the recognition and repair of mismatched nucleotides during DNA replication. Loss of MSH2 function leads to microsatellite instability (MSI), a hallmark of Lynch syndrome and sporadic CRC cases. Anti-MSH2 antibodies, through immunohistochemical (IHC) techniques, provide a precise and reliable method for evaluating MSH2 expression in tumor tissues.
Molecular Basis of MSH2
MSH2 is a protein of 934 amino acids with a molecular weight of approximately 104 kDa. It forms a heterodimer with MSH6 (MutSα) or MSH3 (MutSβ), which are essential for initiating the MMR process. The MSH2-MSH6 complex primarily recognizes base-base mismatches and small insertion-deletion loops, while the MSH2-MSH3 complex is involved in the recognition of larger insertion-deletion loops. Mutations in the MSH2 gene disrupt these critical interactions, resulting in the accumulation of replication errors and genomic instability, which drive oncogenesis.
Development of Anti-MSH2 Antibodies
Anti-MSH2 antibodies are developed using recombinant MSH2 protein or specific MSH2 peptides as antigens. These antibodies can be polyclonal or monoclonal, with monoclonal antibodies offering higher specificity and consistency. The production process involves immunizing animals (e.g., mice, rabbits) with the MSH2 antigen, followed by hybridoma technology for monoclonal antibodies or serum extraction for polyclonal antibodies. These antibodies are then rigorously validated through western blotting, enzyme-linked immunosorbent assay (ELISA), and IHC to ensure their specificity and sensitivity.
Application in Immunohistochemistry
IHC using anti-MSH2 antibodies is a well-established method for assessing MSH2 expression in formalin-fixed, paraffin-embedded (FFPE) tissue sections. The procedure involves deparaffinization, antigen retrieval, blocking of non-specific binding sites, and incubation with the primary anti-MSH2 antibody. Visualization is achieved using a secondary antibody conjugated to an enzyme (e.g., horseradish peroxidase) that catalyzes a chromogenic reaction, producing a colorimetric signal at the site of antibody binding. Positive MSH2 staining is typically nuclear, reflecting the protein’s role in DNA repair.
Diagnostic Implications
The absence of MSH2 staining in tumor cells, with retained staining in adjacent normal tissue, indicates a loss of MSH2 function, suggestive of MMR deficiency. This loss can occur due to germline mutations (Lynch syndrome) or somatic hypermethylation of the MSH2 promoter. IHC for MSH2, alongside other MMR proteins (MLH1, MSH6, and PMS2), forms part of the diagnostic algorithm for CRC, guiding further genetic testing and therapeutic decisions. MMR deficiency detected by anti-MSH2 IHC correlates with a better prognosis and a higher likelihood of response to immunotherapy.
The utilization of anti-MSH2 antibodies in the diagnosis of colon tumors represents a critical advancement in molecular pathology. Their ability to reliably detect MSH2 protein loss provides valuable diagnostic, prognostic, and therapeutic information. As the understanding of MMR mechanisms and their implications in colorectal cancer evolves, the role of anti-MSH2 antibodies in clinical practice will continue to expand, underscoring the importance of ongoing research and development in this area.