Abstract
Integrins are important mediators of cell-laminin interactions. In the small intestinal epithelium, which consists of spatially separated proliferative and differentiated cell populations located, respectively, in the crypt and on the villus, laminins and laminin-binding integrins are differentially expressed along the crypt-villus axis. One exception to this is the integrin alpha(6)beta(4), which is thought to be ubiquitously expressed by intestinal cells. However, in this study, a re-evaluation of the beta(4) subunit expression with different antibodies revealed that two forms of beta(4) exist in the human intestinal epithelium. Furthermore, we show that differentiated enterocytes express a full-length 205-kDa beta(4)A subunit, whereas undifferentiated crypt cells express a novel beta(4)A subunit that does not contain the COOH-terminal segment of the cytoplasmic domain (beta(4)A(ctd-)). This new form was not found to arise from alternative beta(4) mRNA splicing. Moreover, we found that these two beta(4)A forms can associate into alpha(6)beta(4)A complexes; however, the beta(4)A(ctd-) integrin expressed by the undifferentiated crypt cells is not functional for adhesion to laminin-5. Hence, these studies identify a novel alpha(6)beta(4)A(ctd-) integrin expressed in undifferentiated intestinal crypt cells that is functionally distinct.
Highlights
Epithelial cells are characterized by special structural features such as polarized morphology, specialized cell-cell contacts, and their attachment to an underlying basement membrane [1]
The integrin ␣64 has been reported to be present at the base of intestinal epithelial cells all along the crypt-villus axis suggesting that this laminin receptor is ubiquitously expressed by intestinal cells [31, 32, 36, 39]
The expression of the 4 subunit in intestinal cells was re-evaluated on the basis of the observation that antibodies directed to the COOH-terminal segment of the cytoplasmic domain of the molecule [40] detected the 4 subunit only in the villus cells of the intact small intestine, suggesting that two distinct forms of 4 may exist in the intestinal epithelium
Summary
Epithelial cells are characterized by special structural features such as polarized morphology, specialized cell-cell contacts, and their attachment to an underlying basement membrane [1]. The expression of the 4 subunit in intestinal cells was re-evaluated on the basis of the observation that antibodies directed to the COOH-terminal segment of the cytoplasmic domain of the molecule [40] detected the 4 subunit only in the villus cells of the intact small intestine, suggesting that two distinct forms of 4 may exist in the intestinal epithelium.
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