Disruption of the Raf/MEK/ERK (MAPK) kinase pathway, either by RAS or BRAF mutation, was detected in approximately 62% of all CC and is therefore one of the most frequent defects in cholangiocellular carcinogenesis.
A tumor suppressor gene, p16, was found to harbor promoter methylation associated with the loss of protein expression in cancer cells, suggesting that p16 inactivation due to promoter methylation may be important for gastric tumorigenesis.
These findings provide what we believe is the first evidence for a role for Hunk in primary tumorigenesis and cell survival and identify this kinase as an essential effector of the HER2/neu oncogenic pathway.
A strong correlation was observed between the promoter methylation of RASSF1A gene but notp16 gene (both frequently inactivated by promoter methylation in lung cancer) and expression of DeltaDNMT3B4 in primary lung cancer, suggesting a role of DeltaDNMT3B in regulating promoter-specific methylation of common tumor suppressor genes in tumorigenesis.
Furthermore, knockdown of Bmi-1 expression in CD133(+) cells led to inhibition of cell growth, colony formation, cell invasion in vitro, and tumorigenesis in vivo, through up-regulation of p16(INK4A) and p14(ARF).
From the data, it can be argued that p16/CDKN2 and p53 mutations are relatively late occurrences in human oral tumorigenesis and that genetic alterations of the ras genes may not play a significant role in squamous neoplasia.
Our results suggest that epigenetic alterations of p16 and RAR-β have an important role in ovarian carcinogenesis and that mechanism along with methylation plays a significant role in downregulation of RAR-β gene in ovarian cancer.