Analysis of MICA gene transcripts in human rectal cancers

The human MHC class I chain-related gene A (MICA) encodes a protein which is an activator ligand for the NKG2D receptor on NK cells, CD8+ alpha beta T cells and gamma delta T cells. MICA expression is up-regulated upon cellular stress and its expression is correlated to infiltration of human NKG2D-bearing T cells into the tumors. It is assumed that the interaction of MICA-NKG2D ligand-receptor could play a significant role in induction of innate and adaptive responses against epithelial tumors, specifically those from the gastrointestinal tract. In this study MICA messenger RNA levels in human rectal carcinoma (Duke's stage B-D) and its normal adjacent tissue was analyzed in samples donated by 18 patients undergoing rectal tumor resection. Quantitative RT-PCR analysis from rectal tumors revealed that the overall expression of MICA at mRNA level differs extensively among individual tumors. In addition, invasive rectal tumors tend to up-regulate MICA whereas MICA mRNA levels were lower in early tumors. Differential transcription levels of MICA gene expression in rectal carcinomas at different stages is probably a strategy by tumors to escape confrontation with intraepithelial tumor-infiltrating T cells.