[Analysis of suppressive roles of BLU gene at 3p21.3 in nasopharyngeal carcinoma].

ABSTRACT

BACKGROUND & OBJECTIVE: Nonrandom allelic loss at chromosome 3p21.3 is a common and early event in nasopharyngeal carcinoma (NPC), which implicates the presence of tumor suppressor genes (TSGs) that may be involved in the pathogenesis of NPCs. BLU gene, containing a MYND domain and located at 3p21.3, has been considered as a NPC associated candidate tumor suppressor gene (TSG) due to the occurrence of loss of its expression and aberrant promoter hypermethylation in most NPCs. This study was designed to construct expression vectors containing either wild type BLU gene and its mutants and to analyze the effect of BLU gene on proliferation of NPC cells by transfection assays. METHODS: The full-length cDNA of BLU gene was amplified by RT-PCR. The expression vectors containing various BLU mutants were constructed by site-directed mutagenesis by overlapping PCR. These mutants include a MYND domain deletion mutant, a Ser402Phe and del405Cys, del406Ser mutant, and a Gly160Arg mutant. The wild type BLU gene and the MYND domain deletion mutant were transfected into NPC cell lines CNE1 and CNE2. The effect on apoptosis was determined by TUNEL assay. Cellular proliferation of the stably-transfected cells was examined with cell growth curve and by colony formation assays. Tumorigenicity in nude mice of CNE2 stably-transfected with BLU was investigated. RESULTS: No significant difference in apoptosis index (AI) was observed between cells transfected with wild type or MYND domain deleted BLU gene and cells transfected with plasmid controls. Exogenous expression of wild type BLU gene had no effect on growth rate and colony formation ability of CNE1 and CNE2. BLU gene showed no suppressor ability in CNE2 tumorigenicity. CONCLUSION: Although BLU gene was frequently altered in NPCs, its suppressor role in NPC cells proliferation was not evident. Thus, the possibility of BLU gene as a TSG involved in NPC development remained to be elucidated by further studies.