Regulation of apical transport in epithelial cells by a Gs class of heterotrimeric G protein.

The role of heterotrimeric GTP-binding proteins in signal transduction is well established. They might also be involved in vesicular transport. Here we show that in the epithelial cell line Madin-Darby Canine Kidney, transport of influenza haemagglutinin protein to the apical surface is stimulated and that of vesicular stomatitis virus glycoprotein to the basolateral surface is retarded by AlF(3-5) treatment. Treatment of cells with the reagents known to influence the Gi class of G proteins affected only the basolateral pathway whereas reagents acting on the Gs class of G proteins specifically affected the apical pathway. In permeabilized cells, antibodies raised against the N-terminal domain of the alpha-subunit of Gs inhibited the transport of haemagglutinin from the trans-Golgi network to apical surface but not between the endoplasmic reticulum and Golgi complex. These observations demonstrate involvement of a Gs class of heterotrimeric G proteins, besides that of the Gi, in vesicular transport. Moreover, the apical and the basolateral pathways in epithelial cells seem to be regulated by Gs and Gi proteins, respectively, in the trans-Golgi network.