CAST as a Tumor-Specific Suppressor in Colorectal Cancer: Discovery Through Integrative Analysis of Unannotated Isoforms, Proteomics, and Epigenetic Regulation

Colorectal cancer remains one of the leading causes of cancer-related mortality worldwide. Researchers used single-cell long-read sequencing, proteomics, and DNA methylation analysis to identify novel genes in colorectal cancer. Analysis of 29,429 isoforms from 3,262 cells revealed 3,338 new isoforms, with 3 candidates specific only to tumors. The CAST gene (Calpastatin) showed 63.1-fold higher expression in tumor tissue (2.62) compared to normal colon (0.03). Mutational analysis of 100 colorectal cancer samples revealed 8 deleterious mutations. Promoter methylation analysis of 393 tumor samples showed that 89.3% were hypomethylated, indicating gene reactivation. CAST expression was negatively correlated with promoter methylation and regulated by the miR-200 family.