Class I Rab11‐family interacting proteins are binding targets for the Rab14 GTPase

Background information. Rab11 and Rab14 are two related Rab GTPases that are believed to function in endosomal recycling and Golgi/endosome transport processes. We, and others, have identified a group of proteins that interact with Rab11 and function as Rab11 effectors, known as the Rab11‐FIPs (family interacting proteins). This protein family has been sub‐classified into two groups—class I FIPs FIP2, RCP (Rab coupling protein) and Rip11 (Rab11‐interacting protein)] and class II FIPs (FIP3 and FIP4). Results. In the present study we identify the class I FIPs as dual Rab‐binding proteins by demonstrating that they also interact with Rab14 in a GTP‐dependent manner. We show that these interactions are specific for the class I FIPs and that they occur via their C‐terminal regions, which encompass the previously described RBD (Rab11‐binding domain). Furthermore, we show that Rab14 significantly co‐localizes with the TfnR (transferrin receptor) and that Rab14 Q70L co‐localizes with Rab11a and with the class I FIPs on the ERC (endosomal recycling compartment) during interphase. Additionally, we show that during cytokinesis Rab14 localizes to the cleavage furrow/midbody. Conclusions. The data presented in the present study, which identifies the class I FIPs as the first putative effector proteins for the Rab14 GTPase, indicates greater complexity in the Rab‐binding specificity of the class I FIP proteins.