The PX-RICS-14-3-3ζ/θ Complex Couples N-cadherin-β-Catenin with Dynein-Dynactin to Mediate Its Export from the Endoplasmic Reticulum

We have recently shown that beta-catenin-facilitated export of cadherins from the endoplasmic reticulum requires PX-RICS, a beta-catenin-interacting GTPase-activating protein for Cdc42. Here we show that PX-RICS interacts with isoforms of 14-3-3 and couples the N-cadherin-beta-catenin complex to the microtubule-based molecular motor dynein-dynactin. Similar to knockdown of PX-RICS, knockdown of either 14-3-3 zeta or -theta resulted in the disappearance of N-cadherin and beta-catenin from the cell-cell boundaries. Furthermore, we found that PX-RICS and 14-3-3 zeta/theta are present in a large multiprotein complex that contains dynein-dynactin components as well as N-cadherin and beta-catenin. Both RNAi- and dynamitin-mediated inhibition of dynein-dynactin function also led to the absence of N-cadherin and beta-catenin at the cell-cell contact sites. Our results suggest that the PX-RICS-14-3-3 zeta/theta complex links the N-cadherin-beta-catenin cargo with the dynein-dynactin motor and thereby mediates its endoplasmic reticulum export.