To clarify the roles of Bmi-1 in colorectal carcinoma, we examined the 
expression of Bmi-1 in 41 samples out of 46 colorectal carcinomas by reverse 
transcription-PCR, whereas all 46 were analyzed by immunostaining. In addition, 
we analyzed the expression patterns of Bmi-1 in association with p16INK4a and 
p14ARF (in mouse p19ARF) in a series of colorectal carcinomas. The level of 
Bmi-1 mRNA in the carcinoma tissues was significantly higher than those of the 
adjacent non-neoplastic colonic mucosal tissues. Immunohistochemistry for Bmi-1 
showed moderate or strong expression levels in 65% (30/46) of colorectal 
carcinomas. Colorectal carcinomas with moderate or strong Bmi-1 expression were 
more likely to have low levels of the INK4 locus proteins (p16INK4a/p14ARF) 
(P<0.07). These results suggested that modulation of Bmi-1 protein might be 
involved in human colorectal carcinogenesis by repressing the INK4a/ARF 
proteins.