Search

OTUD1 is a deubiquitinating enzyme involved in many cellular processes including cancer and innate, immune signaling pathways. Here, we perform a proximity labeling-based interactome study that identifies OTUD1 largely present in the translation and RNA metabolism protein complexes. Biochemical analysis validates OTUD1 association with ribosome subunits, elongation factors and the E3 ubiquitin ligase ZNF598 but not with the translation initiation machinery. OTUD1 catalytic activity suppresses polyA triggered ribosome stalling through inhibition of ZNF598-mediated RPS10 ubiquitination and stimulates formation of polysomes. Finally, analysis of gene expression suggests that OTUD1 regulates the stability of rare codon rich mRNAs by antagonizing ZNF598.

The RAS pathway is among the most frequently activated signaling nodes in cancer. However, the mechanisms that alter RAS activity in human pathologies are not entirely understood. The most prevalent post-translational modification within the GTPase core domain of NRAS and KRAS is ubiquitination at lysine 128 (K128), which is significantly decreased in cancer samples compared to normal tissue. Here, we found that K128 ubiquitination creates an additional binding interface for RAS GTPase-activating proteins (GAPs), NF1 and RASA1, thus increasing RAS binding to GAP proteins and promoting GAP-mediated GTP hydrolysis. Stimulation of cultured cancer cells with growth factors or cytokines transiently induces K128 ubiquitination and restricts the extent of wild-type RAS activation in a GAP-dependent manner. In KRAS mutant cells, K128 ubiquitination limits tumor growth by restricting RAL/ TBK1 signaling and negatively regulating the autocrine circuit induced by mutant KRAS. Reduction of K128 ubiquitination activates both wild-type and mutant RAS signaling and elicits a senescence-associated secretory phenotype, promoting RAS-driven pancreatic tumorigenesis. Synopsis: RAS family protein ubiquitination at several residues regulates RAS signaling activity and stability. This study shows that monoubiquitination of KRAS and NRAS at lysine 128 (K128) enhances RAS binding to GTPase-activating proteins to restrict RAS activity, a mechanism that is dysregulated in cancer tissues. K128 monoubiquitination of KRAS or NRAS creates an additional interface that facilitates binding to the GTPase activating proteins RASA1 and NF1. The level of KRAS and NRAS ubiquitination at K128 is decreased in cancer samples compared to normal tissue. K128 ubiquitination of wild-type RAS proteins constrains downstream MAPK signalling in a GAP-dependent manner. K128 ubiquitination of the oncogenic KRAS-G12D mutant suppresses the RAL-TBK1 axis and inhibits the autocrine circuit induced by mutant KRAS. Reduction of K128 monoubiquitination activates wild-type and mutant RAS signaling and elicits a senescence-associated secretory phenotype, promoting RAS-driven tumorigenesis. [ABSTRACT FROM AUTHOR]

Simple Summary: In comparison to other neoplasias, Multiple Myeloma is extremely sensitive to changes in protein homeostasis. Therefore, proteasome inhibitors are highly efficient and widely used for this disease. Genetic alterations of the PSMC genes, such as the ones shown in this manuscript, affect this Multiple Myeloma vulnerability and, therefore, play a key role in the physiopathogenesis and resistance to proteasome inhibitors. By different modes of action, those alterations are likely to increase the proteolytic capacity of cancer cells. Even though they occur in low frequencies, they can serve as biomarkers to predict and monitor a patient's response to proteasome inhibitors over time and might be useful to guide therapy. For the treatment of Multiple Myeloma, proteasome inhibitors are highly efficient and widely used, but resistance is a major obstacle to successful therapy. Several underlying mechanisms have been proposed but were only reported for a minority of resistant patients. The proteasome is a large and complex machinery. Here, we focus on the AAA ATPases of the 19S proteasome regulator (PSMC1-6) and their implication in PI resistance. As an example of cancer evolution and the acquisition of resistance, we conducted an in-depth analysis of an index patient by applying FISH, WES, and immunoglobulin-rearrangement sequencing in serial samples, starting from MGUS to newly diagnosed Multiple Myeloma to a PI-resistant relapse. The WES analysis uncovered an acquired PSMC2 Y429S mutation at the relapse after intensive bortezomib-containing therapy, which was functionally confirmed to mediate PI resistance. A meta-analysis comprising 1499 newly diagnosed and 447 progressed patients revealed a total of 36 SNVs over all six PSMC genes that were structurally accumulated in regulatory sites for activity such as the ADP/ATP binding pocket. Other alterations impact the interaction between different PSMC subunits or the intrinsic conformation of an individual subunit, consequently affecting the folding and function of the complex. Interestingly, several mutations were clustered in the central channel of the ATPase ring, where the unfolded substrates enter the 20S core. Our results indicate that PSMC SNVs play a role in PI resistance in MM. [ABSTRACT FROM AUTHOR]