Molecular and cellular mechanisms involved in transepithelial transport

Conclusions

Our current understanding of vesicular transport across polarized epithelial cells is largely derived from studies of various cell lines in vitro and rat liver in vivo. It may be assumed that the basic mechanisms and cellular machineries which control membrane protein sorting, coated pit-mediated internalization, membrane fusion and fission, play important roles in the phenomenon of selective transcytosis. At the present, however, no general rules have been established that explain the traffic of different membrane proteins and ligands across specific epithelial cell types. For example, the pattern of protein movement that seems to represent a default pathway in certain cell types appears to be signal-mediated in others.

The dissection at the molecular level of the components involved in transepithelial traffic of membrane proteins will require complementary experimental approaches, including the isolation of specific transcytotic carrier vesicles, their biochemical characterization, the reconstitution of the various steps in cell-free systems, and analysis of the traffic patterns of transcytotic proteins in different cell types after transfection and in transgenic animals.