| Summary: | 碩士 === 國立臺灣大學 === 微生物學研究所 === 85 ===
The infection of Epstein-Barr vrus (EBV) has been considered to be closely associated with the development of nasopharyngeal carcinoma (NPC) . BHRF1 is one of EBV early genes expressed in the lytic cycle, and it is a structural and functional homolog of the cellular proto-oncogene bcl-2. Since expression of BHRF1 can block apoptosis, it is hypothesized that BHRF1 may be associated with the carcinogenesis of NPC. Thus, using RT-PCR and Southern blotting to detect the expression of BHRF1 in NPC biopsies, 23 out of 27 (85.2%) NPC biopsies and 15 out of 17 (88.2%) metastatic NPC biopsies were shown the expression of BHRF1 mRNA. In contrast, only 1 out of 25 (4%) control biopsies expressed the transcript of BHRF1. In addition, expression of two latent genes, EBNA1 and LMP2A, and other lytic gene, BZLF1, was also detected. The data indicated the expression rates of EBNA1, LMP2A and BZLF1 in the primary and metastatic NPC biopsies were betweeen 74.1% and 88.2%, similar to those of BHRF1. The expression of four EBV genes was detected at the same time in more than half of the NPC biopsies in our study. In contrast, expression in the control biopsies was almost restricted to the latent genes, and expression of the lytic genes was rarely detected. Therefore, expression of the EBV lytic genes is a striking feature for most NPC biopsies compared to the control biopsies.
E. coli-expressed BHRF1 fusion protein was used as antigen to detect specific antibody in sera by western blot blotting. There were 56 out of 94 (59.6%) NPC patients, 13 out of 87 (14.9%) patients with discomfort around nasopharynx, and 3 out 53 (5.7%) patients with other cancers positive for IgA antibody to the BHRF1 protein. The positive rate for NPC patients was significantly high. When compared to the positive rates of antibody neutralizing DNase activity and anti-VGA IgA antibody in sera of NPC patients, the rate of anti-BHRF1 antibody was the lowest one. However, some NPC patients only contained the anti-BHRF1 antibody. Therefore, anti-BHRF1 IgA antibody may not be the best screening marker for NPC, but it can be used as an accessory marker.
Finally, to identify any differences of the BHRF1 DNA sequences between NPC and other sources, the open reading frame (ORF) of BHRF1 from 3 NPC biopsies and 3 control biopsies were cloned and sequenced. Compared to the published sequences of EBV from B95-8, BHRF1 nucleotide sequences in NPC did not show many variations. Furthermore, no specific nucleotide conversion was detected in NPC biopsies. Properties of the new amino acids resulted from the nucleotide changes were very similar to those of the old amino acids. Therefore, conserved and significant mutations of BHRF1 ORF were not detected in NPC biopsies.
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