USP32 regulates late endosomal transport and recycling through deubiquitylation of Rab7

Deletion of the deISGylating enzyme USP18 enhances tumour cell antigenicity and radiosensitivity

BACKGROUND

Interferon (IFN) signalling pathways, a key element of the innate immune response, contribute to resistance to conventional chemotherapy, radiotherapy, and immunotherapy, and are often deregulated in cancer. The deubiquitylating enzyme USP18 is a major negative regulator of the IFN signalling cascade and is the predominant human protease that cleaves ISG15, a ubiquitin-like protein tightly regulated in the context of innate immunity, from its modified substrate proteins in vivo.

METHODS

In this study, using advanced proteomic techniques, we have significantly expanded the USP18-dependent ISGylome and proteome in a chronic myeloid leukaemia (CML)-derived cell line. USP18-dependent effects were explored further in CML and colorectal carcinoma cellular models.

RESULTS

Novel ISGylation targets were characterised that modulate the sensing of innate ligands, antigen presentation and secretion of cytokines. Consequently, CML USP18-deficient cells are more antigenic, driving increased activation of cytotoxic T lymphocytes (CTLs) and are more susceptible to irradiation.

CONCLUSIONS

Our results provide strong evidence for USP18 in regulating antigenicity and radiosensitivity, highlighting its potential as a cancer target.

Ubiquitomics: An Overview and Future

Covalent attachment of ubiquitin, a small globular polypeptide, to protein substrates is a key post-translational modification that determines the fate, function, and turnover of most cellular proteins. Ubiquitin modification exists as mono- or polyubiquitin chains involving multiple ways how ubiquitin C-termini are connected to lysine, perhaps other amino acid side chains, and N-termini of proteins, often including branching of the ubiquitin chains. Understanding this enormous complexity in protein ubiquitination, the so-called 'ubiquitin code', in combination with the ∼1000 enzymes involved in controlling ubiquitin recognition, conjugation, and deconjugation, calls for novel developments in analytical techniques. Here, we review different headways in the field mainly driven by mass spectrometry and chemical biology, referred to as "ubiquitomics", aiming to understand this system's biological diversity.

Focus on the morphogenesis, fate and the role in tumor progression of multivesicular bodies

Multivesicular bodies (MVBs) are endosome organelles that are gradually attracting research attention. Initially, MVBs were considered as important components of the endosomal-lysosomal degradation pathway. In recent years, with an increase in extracellular vesicle (EV) research, the biogenesis, fate, and pathological effects of MVBs have been increasingly studied. However, the mechanisms by which MVBs are sorted to the lysosome and plasma membrane remain unclear. In addition, whether the trafficking of MVBs can determine whether exosomes are released from cells, the factors are involved in cargo loading and regulating the fate of MVBs, and the roles that MVBs play in the development of disease are unknown. Consequently, this review focuses on the mechanism of MVB biogenesis, intraluminal vesicle formation, sorting of different cargoes, and regulation of their fate. We also discuss the mechanisms of emerging amphisome-dependent secretion and degradation. In addition, we highlight the contributions of MVBs to the heterogeneity of EVs, and their important roles in cancer. Thus, we attempt to unravel the various functions of MVBs in the cell and their multiple roles in tumor progression.

The Role of Deubiquitinating Enzymes in the Various Forms of Autophagy

Deubiquitinating enzymes (DUBs) have an essential role in several cell biological processes via removing the various ubiquitin patterns as posttranslational modification forms from the target proteins. These enzymes also contribute to the normal cytoplasmic ubiquitin pool during the recycling of this molecule. Autophagy, a summary name of the lysosome dependent self-degradative processes, is necessary for maintaining normal cellular homeostatic equilibrium. Numerous forms of autophagy are known depending on how the cellular self-material is delivered into the lysosomal lumen. In this review we focus on the colorful role of DUBs in autophagic processes and discuss the mechanistic contribution of these molecules to normal cellular homeostasis via the possible regulation forms of autophagic mechanisms.

Role of Deubiquitinases in Human Cancers: Potential Targeted Therapy

Deubiquitinases (DUBs) are involved in various cellular functions. They deconjugate ubiquitin (UBQ) from ubiquitylated substrates to regulate their activity and stability. Studies on the roles of deubiquitylation have been conducted in various cancers to identify the carcinogenic roles of DUBs. In this review, we evaluate the biological roles of DUBs in cancer, including proliferation, cell cycle control, apoptosis, the DNA damage response, tumor suppression, oncogenesis, and metastasis. This review mainly focuses on the regulation of different downstream effectors and pathways via biochemical regulation and posttranslational modifications. We summarize the relationship between DUBs and human cancers and discuss the potential of DUBs as therapeutic targets for cancer treatment. This review also provides basic knowledge of DUBs in the development of cancers and highlights the importance of DUBs in cancer biology.

SKIP-HOPS recruits TBC1D15 for a Rab7-to-Arl8b identity switch to control late endosome transport

The endolysosomal system fulfils a myriad of cellular functions predicated on regulated membrane identity progressions, collectively termed maturation. Mature or “late” endosomes are designated by small membrane‐bound GTPases Rab7 and Arl8b, which can either operate independently or collaborate to form a joint compartment. Whether, and how, Rab7 and Arl8b resolve this hybrid identity compartment to regain functional autonomy is unknown. Here, we report that Arl8b employs its effector SKIP to instigate inactivation and removal of Rab7 from select membranes. We find that SKIP interacts with Rab7 and functions as its negative effector, delivering the cognate GAP, TBC1D15. Recruitment of TBC1D15 to SKIP occurs via the HOPS complex, whose assembly is facilitated by contacts between Rab7 and the KMI motif of SKIP. Consequently, SKIP mediates reinstatement of single identity Arl8b sub‐compartment through an ordered Rab7‐to‐Arl8b handover, and, together with Rab7's positive effector RILP, enforces spatial, temporal and morphological compartmentalization of endolysosomal organelles.

Rabs in Signaling and Embryonic Development

Rab GTPases play key roles in various cellular processes. They are essential, among other roles, to membrane trafficking and intracellular signaling events. Both trafficking and signaling events are crucial for proper embryonic development. Indeed, embryogenesis is a complex process in which cells respond to various signals and undergo dramatic changes in their shape, position, and function. Over the last few decades, cellular studies have highlighted the novel signaling roles played by Rab GTPases, while numerous studies have shed light on the important requirements of Rab proteins at various steps of embryonic development. In this review, we aimed to generate an overview of Rab contributions during animal embryogenesis. We first briefly summarize the involvement of Rabs in signaling events. We then extensively highlight the contribution of Rabs in shaping metazoan development and conclude with new approaches that will allow investigation of Rab functions in vivo.

CK19 stabilizes CFTR at the cell surface by limiting its endocytic pathway degradation

Protein interactions that stabilize the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) at the apical membranes of epithelial cells have not yet been fully elucidated. We identified keratin 19 (CK19 or K19) as a novel CFTR-interacting protein. CK19 overexpression stabilized both wild-type (WT)-CFTR and Lumacaftor (VX-809)-rescued F508del-CFTR (where F508del is the deletion of the phenylalanine residue at position 508) at the plasma membrane (PM), promoting Cl- secretion across human bronchial epithelial (HBE) cells. CK19 prevention of Rab7A-mediated lysosomal degradation was a key mechanism in apical CFTR stabilization. Unexpectedly, CK19 expression was decreased by ∼40% in primary HBE cells from homogenous F508del patients with CF relative to non-CF controls. CK19 also positively regulated multidrug resistance-associated protein 4 expression at the PM, suggesting that this keratin may regulate the apical expression of other ATP-binding cassette proteins as well as CFTR.-Hou, X., Wu, Q., Rajagopalan, C., Zhang, C., Bouhamdan, M., Wei, H., Chen, X., Zaman, K., Li, C., Sun, X., Chen, S., Frizzell, R. A., Sun, F. CK19 stabilizes CFTR at the cell surface by limiting its endocytic pathway degradation.