Protein kinaseCδ-calmodulin crosstalk regulates epidermal growth factor receptor exit from early endosomes

We have recently shown that calmodulin antagonist W13 interferes with the trafficking of the epidermal growth factor receptor (EGFR) and regulates the mitogen-activated protein kinase (MAPK) signaling pathway. In the present study, we demonstrate that in cells in which calmodulin is inhibited, protein kinase C (PKC) inhibitors rapidly restore EGFR and transferrin trafficking through the recycling compartment, although onward transport to the degradative pathway remains arrested. Analysis of PKC isoforms reveals that inhibition of PKCdelta with rottlerin or its down-modulation by using small interfering RNA is specifically responsible for the release of the W13 blockage of EGFR trafficking from early endosomes. The use of the inhibitor Go 6976, specific for conventional PKCs (alpha, beta, and gamma), or expression of dominant-negative forms of PKCA, xi, or epsilon did not restore the effects of W13. Furthermore, in cells treated with W13 and rottlerin, we observed a recovery of brefeldin A tubulation, as well as transport of dextran-fluorescein isothiocyanate toward the late endocytic compartment. These results demonstrate a specific interplay between calmodulin and PKCdelta in the regulation of the morphology of and trafficking from the early endocytic compartment.