Thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs. In Caucasians, four variant TPMT alleles have been detected in over 80% of individuals with low or intermediate TPMT activity. The wild-type allele is designated as TPMT*1 and the mutant alleles are designated TPMT*2 through TPMT*8. The frequency of these alleles in different ethnic groups has not been well defined. In this study, one hundred individuals, from each of the Indonesian, Thai and Philippine populations, together with 249 Taiwanese, were analysed by polymerase chain reaction-restriction fragment length polymorphism and direct sequencing methods. The results showed that the allelic frequencies of TPMT*3C were 0.6% for Taiwanese and 1% for Filipino, Thai and Indonesian populations, respectively. One Filipino with a Caucasian parent was found to be heterozygous for the TPMT*2 allele. This study provides the first analysis of the allele frequency distribution of all known TPMT mutations in South-east Asian populations.

Although the oncogenic functions of activating BRAF mutations have been clearly demonstrated in human cancer, their roles in nontransformed epithelial cells remain largely unclear. Investigating the cellular response to the expression of mutant BRAF in nontransformed epithelial cells is fundamental to the understanding of the roles of BRAF in cancer pathogenesis. In this study, we used two nontransformed cyst108 and RK3E epithelial cell lines as models in which to compare the phenotypes of cells expressing BRAF WT and BRAF V600E . We found that transfection of the BRAF V600E , but not the BRAF WT , expression vector suppressed cellular proliferation and induced apoptosis in both cell types. BRAF V600E generated reactive oxygen species, induced DNA double-strand breaks, and caused subsequent DNA damage response as evidenced by an increased number of pCHK2 and ␥H2AX nuclear foci as well as the up-regulation of pCHK2, p53, and p21. Because BRAF and KRAS (alias Ki-ras) mutations have been correlated with GLUT1 up-regulation, which encodes glucose transporter-1, we demonstrated here that expression of BRAF V600E , but not BRAF WT , was sufficient to up-regulate GLUT1. Taken together, our findings provide new insights into mutant BRAF-induced oncogenic stress that is manifested by DNA damage and growth arrest by activating the pCHK2-p53-p21 pathway in nontransformed cells, while it also confers tumor-promoting phenotypes such as the up-regulation of GLUT1 that contributes to enhanced glucose metabolism that characterizes tumor cells.

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