Table 1. Classification of 22 missense BRAF mutations detected in human cancer samples as tested by Wan et al. [5].

Mutants were expressed as c-Myc-tagged fusion proteins in COS cells and classified as having either high, intermediate or impaired levels of BRAF kinase activity. The high and intermediate activity mutants have greater kinase activity than ^WTBRAF and stimulate ERK activation directly. Although these mutants also stimulate CRAF activity, siRNA (small interfering RNA) to CRAF indicates that this isoform does not account for the increased ERK activation. The impaired activity mutants have less activity than ^WTBRAF. In the case of three or four of these mutants, ERK activation is greater than that mediated by ^WTBRAF and this is thought to be mediated by CRAF. The fourth impaired mutant, D594V, does not stimulate CRAF or ERK activation and has a similar level of BRAF kinase activity as kinase-defective BRAF. The mechanism by which this mutant operates in cancer development is currently unclear