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Functional analysis of mutations within the kinase activation segment of B-Raf in human colorectal tumors.

2003; National Institutes of Health; Volume: 63; Issue: 23 Linguagem: Inglês

Tsuneo Ikenoue, Yohko Hikiba, Fumihiko Kanai, Yasuo Tanaka, Jun Imamura, Takaaki Imamura, Miki Ohta, Hideaki Ijichi, Keisuke Tateishi, Takayuki Kawakami, Jun Aragaki, Masayuki Matsumura, Takao Kawabe, Masao Omata,

Cytokine Signaling Pathways and Interactions

Mutations in the B-Raf gene have been reported in a number of human cancers, including colorectal carcinoma. More than 80% of the B-Raf mutations were V599E. Although other mutations have been reported, their functional consequences were unclear. Here, we examined the effect of colon tumor-associated B-Raf mutations within the kinase activation segment, including V599E, on extracellular signal-regulated kinase (Erk) and nuclear factor kappaB (NFkappaB) signaling, and on the transformation of NIH3T3 fibroblasts. Among the six mutations examined, only the B-Raf V599E and K600E mutations greatly increased Erk and NFkappaB signaling, and the transformation of NIH3T3 cells. The B-Raf F594L mutation moderately elevated Erk signaling and NIH3T3 transformation, but did not significantly increase NFkappaB signaling. Although the basal kinase activity of the B-Raf T598I mutant was comparable with that of wild-type, its oncogenic Ras-induced kinase activity was decreased to 60% of wild-type activity. The B-Raf D593V and G595R mutants showed severely reduced kinase activity and affected neither NFkappaB signaling nor NIH3T3 transforming activity. These results suggest that the B-Raf activation segment mutations other than V599E reported in colorectal tumors do not necessarily contribute to carcinogenesis by increasing kinase and transforming activities.