Modulation of endocytic traffic in polarized Madin-Darby canine kidney cells by the small GTPase RhoA

Efficient postendocytic membrane traffic in polarized epithelial cells is t hought to be regulated in part by the actin cytoskeleton. RhoA modulates as semblies of actin in the cell, and it has been shown to regulate pinocytosi s and phagocytosis;,however, its effects on postendocytic traffic are large ly unexplored. To this end, we expressed wild-type RhoA (RhoAWT), dominant active RhoA (RhoAV14), and dominant inactive RhoA (RhoAN19) in Madin-Darby canine kidney (MDCK) cells expressing the polymeric immunoglobulin receptor . RhoAV14 expression stimulated the rate of apical and basolateral endocyto sis, whereas RhoAN19 expression decreased the rate from both membrane domai ns. Polarized basolateral recycling of transferrin was disrupted in RhoAV14 -expressing cells as a result of increased ligand release at the apical pol e of the cell. Degradation of basolaterally internalized epidermal growth f actor was slowed in RhoAV14-expressing cells. Although apical recycling of immunoglobulin A (IgA) was largely unaffected in cells expressing RhoAV14, transcytosis of basolaterally internalized IgA: was severely impaired. Morp hological and biochemical analyses demonstrated that a large proportion of IgA internalized from the basolateral pole of RhoAV14-expressing cells rema ined within basolateral early endosomes and was slow to exit these compartm ents. RhoAN19 and RhoAWT expression had little effect on these postendocyti c pathways. These results indicate that in polarized MDCK cells activated R hoA may modulate endocytosis from both membrane domains and postendocytic t raffic at the basolateral pole of the cell.