3 The frequency of TAT down-regulation was significantly higher in HCC with loss of TAT allele (25/27,
92.6%) than that in HCC without TAT deletion (3/23, 13.0%, P < 0.001), suggesting that the down-regulation of TAT was associated with the loss of the TAT allele. Interestingly, homo-deletion of TAT alleles was detected in two cases, H12 and H36. Loss of both copies of genomic material of the TAT gene was confirmed by both southern blot analysis and PCR. The weak TAT band observed in H12T and H36T (Fig. 1C) might be caused by nontumor DNA contamination or the heterogeneity of the tumor. The homo-deleted regions in H12 and H36 were several kilobases and larger than 30 kb affecting a neighbor gene GST3, respectively. Identification of genes within the homo-deleted region is a useful strategy to isolate a tumor selleck compound library suppressor gene. To date, the majority of classical tumor suppressor genes (TSG), including APC, CDKN2A (p16)
and RB1, have been identified by the delineation of homozygous deletions.17-19 Down-regulation of TAT was detected in 28/50 (56%) of 50 primary HCCs by RT-PCR. A similar frequency of TAT down-regulation (77/138, 55.8%) was detected in 148 primary HCCs by IHC, compared with their paired nontumor liver tissues. The down-regulation of TAT was not only associated with the loss of TAT allele, but also DNA hypermethylation in the 5′-CGI of Tolmetin TAT. It has been well documented that DNA methylation of CpG islands located near gene promoters affects this website the transcription of specific genes.20, 21 Aberrant DNA methylation of two genes located at 16q22.1, E-cadherin and TAT, have been reported in pretumorous conditions and HCCs.22, 23 Methylation of one TAT allele could be detected in all 50 adjacent nontumor liver samples, indicating that one TAT allele was inactivated in early development. Loss of the active (unmethylated) allele of TAT, which was detected in 18/50 (36%) of HCCs, might be one of the major mechanisms of TAT inactivation. Statistical analysis further confirmed that the down-regulation
of TAT was significantly associated with both TAT deletion and methylation (P < 0.001). The functional study provided the first evidence that TAT has strong tumor-suppressive ability, including the inhibition of foci formation, colony formation in soft agar, and tumor formation in nude mice. A mechanism study found that the tumor-suppressive effect of TAT was associated with its proapoptotic effect. The apoptosis induced by TAT was mediated through the intrinsic mitochondrial pathway because caspase-9, but not caspase-8, was activated. A molecular study found that the proapoptotic effect of TAT was triggered by the stimulation of apoptotic agents such as STS. Before STS treatment, the apoptotic index between TAT-7703 and Vec-7703 was similar.