Alterations of BLU, a candidate tumor suppressor gene on chromosome 3p21.3, in human nasopharyngeal carcinoma.

Abstract

Nonrandom allelic loss on chromosome 3p is a common event in nasopharyngeal carcinoma (NPC) with the implication that certain tumor suppressor gene(s) in this region are involved in the pathogenesis of these tumors. The BLU gene, located at 3p21.3, has recently been identified as a candidate tumor suppressor gene due to the occurrence of missense mutations and loss of its expression in lung cancer. To investigate the involvement of BLU gene in NPC, we examined both genetic and epigenetic changes of BLU in NPC primary tumors and cell lines. No pathogenic mutations were detected in the entire coding region of this gene in 45 primary NPC tumors and 5 NPC cell lines. While BLU was expressed in 100% (15 of 15) of noncancerous nasopharyngeal epithelia, its transcripts were missing in all 5 NPC cell lines, and absent or reduced mRNA levels were observed in 78% (28 of 36) of the primary tumors. In the NPC cell lines, loss of BLU expression correlated with hypermethylation of the CpG island promoter sequence, and expression was restored after treatment with 5'-aza-2'-deoxycytidine. Methylation specific PCR analysis revealed that the BLU promoter was highly methylated in 74% (17 of 23) of primary tumors in which BLU was downregulated, whereas only 2 of 9 non-neoplastic nasopharyngeal epithelia exhibited hypermethylation in the BLU promoter region. The high incidence of BLU alterations suggests that it may be one of the critical tumor suppressor genes on chromosome 3p21.3 involved in the development of NPC.