Deregulation of members of the
transforming growth factor (
TGF)-beta signaling pathway occurs often in
colon cancers and is believed to affect the formation of primary
colon cancer. Mutational inactivation of
TGFBR2 is the most common genetic event affecting the
TGF-beta signaling pathway and occurs in approximately 20-30% of all
colon cancers. By mating Fabpl(4xat-132) Cre mice with
Tgfbr2(flx/flx) mice, we have generated a mouse model that is null for
Tgfbr2 in the colonic epithelium, and in this model system, we have assessed the effect of loss of
TGF-beta signaling in vivo on
colon cancer formation induced by
azoxymethane (AOM). We have observed a significant increase in the number of AOM-induced
adenomas and
adenocarcinomas in the Fabpl(4xat-132) Cre
Tgfbr2(flx/flx) mice compared with
Tgfbr2(flx/flx) mice, which have intact
TGF-beta receptor type II (
TGFBR2) in the colon epithelium, and we have found increased proliferation in the
neoplasms occurring in the Fabpl(4xat-132) Cre
Tgfbr2(flx/flx) mice. These results implicate the loss of
TGF-beta-mediated growth inhibition as one of the in vivo mechanisms through which
TGFBR2 inactivation contributes to
colon cancer formation. Thus, we have demonstrated that loss of
TGFBR2 in colon epithelial cells promotes the establishment and progression of AOM-induced
colon neoplasms, providing evidence from an in vivo model system that
TGFBR2 is a tumor suppressor gene in the colon.