Centrosomal P4.1-associated protein (CPAP) is a novel regulator of ESCRT pathway function during multivesicular body formation and endosome maturation

Previously, we have shown that Centrosomal P4.1-associated protein (CPAP) is a positive regulator of endocytic vesicle transport (EVT) pathway, and it promotes lysosomal targeting of ligand-bound EGFR. Here, we show that recruitment of TSG101, an ESCRT-I protein, to endosome is the mechanism by which CPAP facilitates EVT. While CPAP depletion disrupts the Rab5-to-Rab7 conversion and endosome maturation processes, it does not interact with these GTPases. We found that CPAP not only co-immunoprecipitates with TSG101, but also colocalizes with TSG101 as well as ESCRT 0 protein HRS on the early endosomes. Although CPAP-TSG101 interaction occurs under quiescent state, this interaction is more robust during EVT progression. TSG101 recruitment to endosome and Rab5-to-Rab7 conversion were restored in CPAP depleted cells upon overexpression of HRS suggesting that CPAP functions upstream of TSG101, but in parallel to HRS, and bridges ESCRT 0 and ESCRT I components. Our results reveal a novel ESCRT dependent regulatory role for the centriole biogenesis protein CPAP in endosome maturation.