Genetic and epigenetic inactivation of mitotic checkpoint genes hBUB1 and hBUBR1 and their relationship to survival.

Sequence alterations of mitotic checkpoint genes, hBUB1 and hBUBR1, were examined, and their gene transcripts were quantified using on-line, real-time quantitative reverse transcription-PCR in surgically resected human colorectal cancers and their neighboring normal tissues. Our results reveal a new hBUB1 missense mutation (Ala130Ser) but not any hBUBR1 coding sequence mutations. hBUB1 and hBUBR1 mRNA levels were reduced to < 10% of the neighboring normal tissues in 3 of 103 and 3 of 109 carcinomas, respectively, and to < 50% in 7 and 7 carcinomas, whereas the overall expression levels were markedly higher in cancers than in normal tissues. Carcinomas with reduced hBUB1 and/or hBUBR1 mRNA levels, as well as the colon carcinoma harboring the hBUB1 mutation, were associated with lymph node metastasis (P < 0.005) and shorter relapse-free survival after surgery (P = 0.006). Thus, hBUB1 and hBUBR1 may contribute to a specific driving force in tumor metastasis and progression as a result of nonmutational, as well as mutational, inactivation.