The
integrin family of
adhesion receptors plays a major role in epithelial organization and function. Moreover, the altered expression and function of specific
integrins most likely contributes significantly to
carcinoma progression. The
integrin alpha 6 beta 4, the focus of this review, is a receptor for several members of the
laminin family and is preferentially expressed at the basal surface of most epithelia, where it contributes to basement membrane interactions. Mounting evidence suggests that the
alpha 6 beta 4 integrin plays a key role in
carcinoma cell biology. Several histopathological studies have established a correlation between
alpha 6 beta 4 integrin expression and
tumor progression. The importance of alpha 6 beta 4 expression in
tumors in underscored by the findings that invading fronts of several
carcinomas are enriched in the expression of
alpha 6 beta 4 integrin ligands, such as
laminin-1 and
laminin-5. The participation of the
alpha 6 beta 4 integrin in invasion is supported further by in vitro functional studies using
carcinoma cells that have been transfected with the beta 4
cDNA. The mechanisms by which alpha 6 beta 4 contributes to
tumor progression are probably related to its mechanical and signaling properties and are currently under intense study.