D-Akap2 Interacts With Rab4 And Rab11 Through Its Rgs Domains And Regulates Transferrin Recycling

Dual‐specificity A‐Kinase Anchoring Protein 2 (D‐AKAP2/AKAP10) has been linked genetically to heart disease and breast cancer, but its biological function has remained unknown. Besides PKA‐ and PDZ‐binding motifs, D‐AKAP2 has two tandem Regulator of G protein Signaling (RGS) domains with no known binding partners. In HeLa cells, D‐AKAP2 is primarily cytosolic but can localize to membranes of the endocytic recycling compartment where it co‐localizes with endocytosed transferrin. Rab4 and Rab11, two small GTPases known to regulate membrane recycling, co‐localize with D‐AKAP2 and recruit it to endosomes. Co‐expression of D‐AKAP2 and Rab11 causes both proteins to accumulate on enlarged endosomes. Co‐immunoprecipitation and co‐localization studies demonstrated that D‐AKAP2 forms protein complexes through the RGS domains with both Rabs, preferring GTP‐locked Rab4 and wild‐type Rab11. Yeast two‐hybrid analysis confirmed that the tandem RGS domains were sufficient for interactions with both Rabs. Knockdown of D‐AKAP2 by RNA interference causes the Rab11 compartment to become more condensed, tubular, and peripheral. These changes correspond to a significant increase in the rate of transferrin recycling, suggesting that the RGS domains of D‐AKAP2 act as novel Rab effectors that inhibit recycling from the Rab4/Rab11 compartment. This work was funded by the NIH (DK054441) and the American Cancer Society.