UBTD1 regulates ceramide balance and endolysosomal positioning to coordinate EGFR signaling

Abstract

To adapt in an ever-changing environment, cells must integrate physical and chemical signals and translate them into biological meaningful information through complex signaling pathways. By combining lipidomic and proteomic approaches with functional analysis, we have shown that UBTD1 (Ubiquitin domain-containing protein 1) plays a crucial role in both the EGFR (Epidermal Growth Factor Receptor) self-phosphorylation and its lysosomal degradation. On the one hand, by modulating the cellular level of ceramides through ASAH1 (N-Acylsphingosine Amidohydrolase 1) ubiquitination, UBTD1 controls the ligand-independent phosphorylation of EGFR. On the other hand, UBTD1, via the ubiquitination of SQSTM1/p62 (Sequestosome 1) and endolysosome positioning, participates in the lysosomal degradation of EGFR. The coordination of these two ubiquitin-dependent processes contributes to the control of the duration of the EGFR signal. Moreover, we showed that UBTD1 depletion exacerbates EGFR signaling and induces cell proliferation emphasizing a hitherto unknown function of UBTD1 in EGF-driven cell proliferation. IntroductionAll living organisms perceive variations in their environment and translate them into intracellular signals via signaling pathways. In multicellular organisms, disturbances in this signal transduction mechanism induce inappropriate cell behavior and are associated with a plethora of diseases including cancer. Cellular signaling can be viewed as a finely tuned "space-time continuum" [1]. Receptors activated by their ligands at the plasma membrane are endocytosed, then moved along endocytic compartments to be routed to the lysosomes for final degradation or recycled back to the cell surface. Thus, the signal delivered to the cell is the sum of the signals emitted by the activated receptor at the plasma membrane and during its intracellular trafficking [2]. The responsiveness of these processes requires fast and accurate control in space and time, which is mainly ensured by post-translational modification (PTM) of proteins. Broadly, several aspects of cell signaling and receptor trafficking are regulated by proteolytic or non-proteolytic ubiquitination [2-6].Protein ubiquitination is a PTM that results in the covalent attachment of one or more ubiquitin to lysine residues of the substrate [7][8][9]. Ubiquitin conjugation occurs in a sequential three-step enzymatic process involving E1 (ubiquitin activation), E2 (ubiquitin conjugation), and E3 (ubiquitin ligation). In this hierarchical framework, there are only two E1s, over 30 E2s and hundreds of E3s in human, illustrating the large spectrum of E2s that contrasts with the high specificity of E3s in the recognition of substrates [10,11]. While the interaction of E3s with their substrates confers specificity to the system, E2s are more versatile and are commonly considered as "ubiquitin carriers" with an auxiliary rather than control role.However, the modulation of the functionality of E2/E3 complexes by scaffold proteins has been poorly investigated and few proteins ...

USP17 is required for peripheral trafficking of lysosomes

“…In addition, RNF26 depletion blocks EGF trafficking to the perinuclear cloud from the cell periphery, as well as EGFR degradation upon EGF engagement, and it redistributes the transferrin receptor (TfR) toward the cell periphery (Jongsma et al, 2016). Two subsequent studies have also indicated RNF26 facilitates the targeting of EGFR to the lysosome for degradation (Cremer et al, 2021;Torrino et al, 2021). We have shown that USP17 is required for clathrin-mediated endocytosis of EGFR and TfR, and that USP17 depletion also blocks EGFR degradation upon EGF engagement, although it blocks its endocytosis, rather than its subsequent targeting to the lysosome (Jaworski et al, 2014).…”