| Summary: | 碩士 === 國立臺灣大學 === 醫學檢驗暨生物技術學研究所 === 103 === Colorectal cancer (CRC) is one of the most common causes of cancer death in the world and Taiwan. Most of CRC arise sporadically by the emergence of multiple chromosomal aberrations. In our previous study, a minimal deletion region (MDR) was delineated at 3p25.3-p26.3 by fine deletion mapping of chromosome 3 with 179 pairs of primary CRC tissues. By detecting the RNA transcripts of 9 genes in the MDR, the gene expression of Contactin 4 (CNTN4), a cell adhesion molecule, was remarkably down-regulated in 11 (91.6%) of 12 CRC cell lines and 22 (42.3%) of 52 primary tumors. The findings suggest that CNTN4 might be a novel CRC-associated tumor suppressor gene. In the present study, CNTN4-expression plasmid, pLAS3w-CNTN4, was constructed and then the single stable clones of CNTN4 re-expression in CRC cells, HCT116, were selected. Tumor suppressor activities of CNTN4 were identified by in vitro cell models and in vivo xenograft tumor mouse model. Ectopic expression of CNTN4 in HCT116 reduced cell proliferation, anchorage-dependent and anchorage-independent colony formation in vitro. CNTN4 expression also increased spontaneous apoptosis of HCT116 cells. However, ectopic expression of CNTN4 did not consistently affect the migration and invasion ability of HCT116 cells. Furthermore, we found that CNTN4 re-expression could suppress the tumorigenesis of subcutaneous xenograft in nude mice. The preliminary study of CNTN4 involved signaling pathway showed that CNTN4 could decrease the phosphorylated ERK1/2 in HCT116 cells. Taken together, the results support a role of CNTN4 as a novel tumor suppressor in colorectal tumorigenesis and progression. On the other hand, to identify other mechanisms of CNTN4 down-regulation expect genetic deletion in colorectal cancer, five colorectal cancer cell lines without CNTN4 expression were treated with DNA-demethylation agent, 5-aza-CdR. However, CNTN4 expression could not be restored after DNA demethylation. The result indicated that DNA type methylation might not the major mechanism of CNTN4 down-regulation in colorectal cancer.
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