Expression Of P53, Bcl-2, Bax And Survivin Proteins, And Its Relationships With Apoptosis During Hepatocarcinogenesis Of Tree Shrew Induced By Aflatoxin B₁

Objective To investigate the expression of apoptosis-related proteins, such as p53, bcl-2, bax and survivin during hepatocarcinogenesis induced by aflatoxin B1, and elucidate its relationship with apoptosis.Methods Tree shrews (Tupaia belangeri chinensis) were treated with or without aflatoxin B1. Liver biopsy was performed regularly during the experiment and the tissue samples were stored in formalin. The expression of p53, bcl-2, bax and survivin were detected in 35 HCC tissues, their corresponding 30th- and 60th- week liver biopsies and the corresponding tissues form 13 animals in control group control with the immunohistochemical S-P method.Terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) technique were applied to deterimine the apoptotic cells in all the tissues mentioned above.Results The exprssion rate of p53 protein in HCC and 60th-week biopsy was 71.4% (25/35) and 60% (21/35), respectively, with no significant difference between them (p>0.05). No expression of p53 protein in control tissues and 30th-week biopsy was detected. In HCC, there was no obviously significance in apoptotic index between p53-positive and p53-negative tissues (0.70±0.57% vs 0.72±0.31%; p>0.05). Bcl-2 expressed strongly in HCC tissues (40%;14/35), but weakly in 30th- and 60th-week biopsy (8.6%, 3/35;20%, 7/35, respectively). No expression of bcl-2 protein was observed in allthe tissues form control group. The expression of bax protein in control group, HCC and 30th- and 60th- week biopsy was similar to that of bcl-2, which was 0%(0/13), 71.4% (25/35), 5.7% (2/35) and 28.6% (10/25), respectively, (p<0.05). The average weighted scores for bcl-2 immunoreactivity in different types of tissues were in the following order: HCC > 60th-week > 30th-week > control group, so that was the average weighted scores for bax immunoreactivity. The obviously difference was not observed in the expression of survivin protein in HCC tissues, 30th- and 60th- week biopsies and tissues from control group, but the average weighted scores for survivin in HCC tissues was much higher than that of all other types of tissues (p<0.05).The apoptotic index of bcl-2-positive was significant higher than that of bcl-2-negative HCC (1.02 ± 0.50% vs 0.50 ± 0.40%;p<0.05). The similar result was also observed between bax-positive HCC and bax-negative HCC (0.74 ± 0.25% vs 0.24 ± 0.16%; p<0.05). The apoptotic index of bcl-2/bax-positive HCC was much higher than that of bcl-2/bax- negative HCC (1.02 ± 0.54% vs 0.25 ± 0.15%;p<0.01). The apoptotic index of survivin-positive HCC was lower than that of survivin-negative HCC (p<0.05). The expression of p53 was not correlated with that of bcl -2, bax and survivin , and the same result was seen between bcl-2 and survivin (p>0.05). There was positive relationship between the expression of bcl -2 and of bax . Conclusions The ratio of apoptosis was very low in normal hepatocellular cells and was increased in the process of hepatocarcinogenesis. In HCC, p53 probably plays important role in promoting liver cells proliferation but not in accelerating apoptosis. The expression of baxpromotes apoptosis, and the ratios of bcl-2 to bax reflects more exactly thedegree of apoptosis. The expression of bcl-2 was related to that of bax but not to that of survivin. The results suggest that there is a commonly or reciprocal active mechanism between the expression of bcl-2 and bax.