To study the early alterations in carcinogenesis, we determined apoptosis and proliferation in rat mucin depleted foci (MDF), precancerous lesions in the colon under basal conditions and 24 h after treatment with 1,2-dimethylhydrazine (DMH), which induces apoptosis in the colon. Spontaneous apoptosis in MDF was higher than in normal mucosa (Apoptotic Index was 1.61 ± 0.30 and 0.21 ± 0.02 in MDF and normal mucosa, respectively, mean ± SE, p < 0.05). DMH (30 and 75 mg/kg) increased apoptosis in both normal mucosa and MDF (up to 20 times higher compared to basal levels in normal mucosa, but only two times in MDF). MDF had a higher and deregulated pattern of proliferation along the crypt compared to normal mucosa. After DMH, proliferation in normal mucosa was significantly depressed, but it did not vary in MDF. Survivin-Birc5 regulating apoptosis and proliferation was significantly over-expressed (RT-qPCR and immunohistochemistry experiments) in MDF vs. normal mucosa, but did not vary in response to DMH. The expression of the pro-apoptotic protein Bak did not vary in normal mucosa and MDF. Since inflammation is present in MDF, which may hamper apoptosis, we studied the effect of pre-treatment with aspirin (600 ppm in the diet for 10 days). No significant effects of aspirin were observed. In conclusion, MDF had a higher spontaneous apoptosis and proliferation coupled with a reduced response to apoptotic stimuli from cytotoxic compounds. Survivin over-expression in MDF indicates that this is an early event in colon carcinogenesis and suggests that down-regulation of Survivin may represent a strategy for cancer prevention.
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