SARA and RNF11 interact with each other and ESCRT-0 core proteins and regulate degradative EGFR trafficking

Smad anchor for receptor activation (SARA) is highly enriched on endocytic membranes via binding to phosphatidylinositol 3-phosphates through its FYVE (Fab1p-YOTB-Vps27p-EEA1) domain. SARA was originally identified as a protein that recruits non-phosphorylated SMAD2/3 to the activated TGFβ receptors for phosphorylation, but later reports suggested a regulatory role in endocytic trafficking. Here we demonstrate that the ubiquitin ligase RNF11 is a SARA-interacting protein residing on early and late endosomes, as well as the fast recycling compartment. RNF11 and SARA interact with the ESCRT-0 subunits STAM2 and Eps15b, but only RNF11 associates with the core subunit Hrs. Both gain- and loss-of-function perturbation of RNF11 and SARA levels result in delayed degradation of epidermal growth factor (EGF)-activated EGF receptor (EGFR), while loss-of-function sustained/enhanced EGF-induced ERK1/2 phosphorylation. These findings suggest that RNF11 and SARA are functional components of the ESCRT-0 complexes. Moreover, SARA interacts with clathrin, the ESCRT-I subunit Tsg101 and ubiquitinated cargo exhibiting all the properties of Hrs concerning ESCRT-0 function, indicating that it could substitute Hrs in some ESCRT-0 complexes. These results suggest that RNF11 and SARA participate structurally and functionally in the ESCRT-dependent lysosomal degradation of receptors. As a consequence, the negative influence that perturbation of RNF11 and SARA levels exerts on the lysosomal degradation of EGFRs could underscore the reported overexpression of RNF11 in several cancers. In these cancers, deficient termination of the oncogenic signaling of mutated receptors, such as the EGFRs, through suboptimal lysosomal degradation could contribute to the process of malignant transformation.