We screened for genetic alterations of
adenomatous polyposis coli (APC) and
beta-catenin genes in 17 frozen specimens from 12 cases of sporadic
desmoid tumors and then subdivided these cases into two groups according to the results of mutational analysis. We further examined
mRNA expression of
beta-catenin and
cyclin D1 by TaqMan PCR and compared the
mRNA expression within both groups. Single-strand conformation polymorphism analysis followed by
DNA direct sequencing revealed
beta-catenin mutation in 3 of 12 cases (6 of 17 specimens), whereas no APC missense mutations in the mutation cluster region were found. TaqMan PCR revealed extremely higher
mRNA expression of
beta-catenin and
cyclin D1 in
desmoid tumors, compared with those of normal skeletal muscles. In the
beta-catenin mutated group,
cyclin D1 mRNA expression was significantly higher than that of the
beta-catenin wild-type group (p = 0.0120, Mann-Whitney U test). In addition, in the
beta-catenin mutated group,
beta-catenin mRNA expression was also significantly higher than that of the
beta-catenin wild-type group (p = 0.0036, Mann-Whitney U test). All cases of
desmoid tumors showed detectable
beta-catenin nuclear expression immunohistochemically. These results suggest that a continuously elevated
beta-catenin protein level caused by the
beta-catenin mutation itself may have a stronger power that can transactivate transcription in vivo. Furthermore, the results provide a possible association between higher
beta-catenin mRNA expression and mutated
beta-catenin in sporadic
desmoid tumors. This may suggest that the
beta-catenin gene may be up-regulated by mutated or continuously elevated
beta-catenin protein, that is, the
beta-catenin gene may also be one of the targeted genes in the APC-
beta-catenin-Tcf pathway.