Polycystin-1 is a microtubule-driven desmosome-associated component in polarized epithelial cells.

In this study, we have analyzed the expression and localization of polycystin-1 in intestinal epithelial cells, a system lacking primary cilia. Polycystin-1 was found to be expressed in the epithelium of the small intestine during development and levels remained elevated in the adult. Dual-labelling indirect immunofluorescence revealed polycystin-1 at sites of cell-cell contact co-localizing with the desmosomes both in situ as well as in polarized Caco-2/15 cells. In unpolarized cultures of Caco-2/15 cells, polycystin-1 was recruited to the cell surface early during initiation of cell junction assembly. In isolated Caco-2/15 cells and HIEC-6 cell cultures, where junctional complexes are absent, polycystin-1 was found predominantly associated with the cytoskeletal elements of the intermediate filaments and microtubule networks. More precisely, polycystin-1 was seen as brightly labelled puncta decorating the keratin-18 positive filaments as well as the beta-tubulin positive microtubules, which was particularly obvious in the lamellipodia. Treatment with the microtubule-disrupting agent, nocodazole, eliminated the microtubule association of polycystin-1 but did not seem to affect its association with keratin or the desmosomes. Taken together these data suggest that polycystin-1 is involved with the establishment of cell-cell junctions in absorptive intestinal epithelial cells and exploits the microtubule-based machinery in order to be transported to the plasma membrane.

Repressed E-cadherin expression in the lower crypt of human small intestine: a cell marker of functional relevance.

In epithelia, abnormal expression of E-cadherin is related to pathologies involving a loss of cell polarization and/or differentiation. However, recent observations suggest that E-cadherin could also be repressed under physiological conditions, such as in some epithelial stem cell lineages. In the present work, we have analyzed E-cadherin expression in human intestinal epithelial cell progenitors and investigated its potential role. E-cadherin expression was analyzed along the crypt-villus axis by immunofluorescence on cryosections of small intestine. E-cadherin was found to be differentially expressed, being significantly weaker in the cells located at the bottom of the crypts. Surprisingly, neither the E-cadherin protein nor transcript were detected in a normal human intestinal epithelial (HIEC) crypt cell model isolated in our laboratory, whereas other E-cadherin-related components such as catenins and APC were present. Forced expression of E-cadherin in HIEC cells increased membrane-associated beta-catenin and was accompanied by the appearance of junction-like structures at the cell-cell interface. Functionally, cell kinetics and p21Cip levels were found to be altered in the E-cadherin expressing HIEC cells as compared to controls. Furthermore, a significant reduction of the migration abilities and an increase in sensitivity to anoikis were also observed. These results suggest that down-regulated expression of E-cadherin is a human intestinal crypt base cell-related feature that appears to be of functional relevance for the maintenance of the progenitor cell population.