Dysregulation or mislocalization of
cell adhesion molecules and their regulators, such as
E-cadherin,
beta-catenin, and
alpha-catenin, usually correlates with loss of polarity, dedifferentiation, invasive
tumor growth, and
metastasis. A subpopulation of
alpha-catenin-negative cells within the DLD-1
colorectal carcinoma cell line causes it to display a heterogeneous morphological makeup, thus providing an excellent model system in which to investigate the role of
alpha-catenin in
tumorigenesis. We re-established expression of
alpha-catenin protein in an
alpha-catenin-deficient subpopulation of the DLD-1 cell line and used it to demonstrate that loss of
alpha-catenin resulted in increased in vitro tumorigenic characteristics (increased soft
agarose colony formation, clonogenic survival after
suspension, and survival in
suspension). When the cells were used to form
tumor xenografts, those lacking
alpha-catenin showed faster growth rates because of increased cellular cycling but not increased
tumor microvascular recruitment.
alpha-Catenin-expressing cells were preferentially located in well perfused areas of xenografts when
tumors were formed from mixed
alpha-catenin-positive and -negative cells. We therefore evaluated the role of the ischemic tumor microenvironment on
alpha-catenin expression and demonstrated that cells lose expression of
alpha-catenin after prolonged exposure in vitro to
hypoglycemic conditions. Our findings illustrate that the tumor microenvironment is a potent modulator of
tumor suppressor expression, which has implications for localized nutrient deficiency and
ischemia-induced
cancer progression.