Small and large intestine express a truncated Dab1 isoform that assembles in cell-cell junctions and co-localizes with proteins involved in endocytosis

Disabled-1 (Dab1) is an essential intracellular adaptor protein in the reelin pathway. Our previous studies in mice intestine showed that Dab1 transmits the reelin signal to cytosolic signalling pathways. Here, we determine the Dab1 isoform expressed in rodent small and large intestine, its subcellular location and co-localization with clathrin, caveolin-1 and N-Wasp. PCR and sequencing analysis reveal that rodent small and large intestine express a Dab1 isoform that misses three (Y198, Y200and Y220) of the five tyrosine phosphorylation sites present in brain Dab1 isoform (canonical) and contains nuclear localization and export signals. Western blot assays show that both, crypts, which shelter progenitor cells, and enterocytes express the same Dab1 isoform, suggesting that epithelial cell differentiation does not regulate intestinal generation of alternatively spliced Dab1 variants. They also reveal that the canonical and the intestinal Dab1 isoforms differ in their total degree of phosphorylation. Immunostaining assays show that in enterocytes Dab1 localizes at the apical and lateral membranes, apical vesicles, close to adherens junctions and desmosomes, as well as in the nucleus; co-localizes with clathrin and with N-Wasp but not with caveolin-1, and in Caco-2 cells Dab1 localizes at cell-to-cell junctions by a Ca2+-dependent process. In conclusion, the results indicate that in rodent intestine a truncated Dab1 variant transmits the reelin signal and may play a role in clathrin-mediated apical endocytosis and in the control of cell-to-cell junctions assembly. A function of intestinal Dab1 variant as a nucleocytoplasmic shuttling protein is also inferred from its sequence and nuclear location

Proper E-cadherin membrane location in colon requires Dab2 and it modifies by inflammation and cancer

We reported that Disabled‐2 (Dab2) is located at the apical membrane in suckling rat intestine. Here, we discovered that, in colon of suckling and adult mouse and of adult human, Dab2 is only at lateral crypt cell membrane and colocalized with E‐cadherin. Dab2 depletion in Caco‐2 cells led to E‐cadherin internalization indicating that its membrane location requires Dab2. In mice, we found that 3 days of dextran sulfate sodium‐induced colitis increased Dab2/E‐cadherin colocalization, which was decreased as colitis progressed to 6 and 9 days. In agreement, Dab2/E‐cadherin colocalization increased in human mild and severe ulcerative colitis and in polyps, being reduced in colon adenocarcinomas, which even showed epithelial Dab2 absence and E‐cadherin delocalization. Epithelial Dab2 decrement preceded that of E‐cadherin. We suggest that Dab2, by inhibiting E‐cadherin internalization, stabilizes adherens junctions, and its absence from the epithelium may contribute to development of colon inflammation and cancer