Search

Deubiquitylases (DUBs) are therapeutically amenable components of the ubiquitin machinery that stabilize substrate proteins. Their inhibition can destabilize oncoproteins that may otherwise be undruggable. Here, we screened for DUB vulnerabilities in multiple myeloma, an incurable malignancy with dependency on the ubiquitin proteasome system and identified OTUD6B as an oncogene that drives the G1/S-transition. LIN28B, a suppressor of microRNA biogenesis, is specified as a bona fide cell cycle-specific substrate of OTUD6B. Stabilization of LIN28B drives MYC expression at G1/S, which in turn allows for rapid S-phase entry. Silencing OTUD6B or LIN28B inhibits multiple myeloma outgrowth in vivo and high OTUD6B expression evolves in patients that progress to symptomatic multiple myeloma and results in an adverse outcome of the disease. Thus, we link proteolytic ubiquitylation with post-transcriptional regulation and nominate OTUD6B as a potential mediator of the MGUS-multiple myeloma transition, a central regulator of MYC, and an actionable vulnerability in multiple myeloma and other tumors with an activated OTUD6B-LIN28B axis.

Vorgeschichte: Ein 80-jähriger Patient mit einem myelodysplastischen Syndrom mit Blastenexzess (MDS-EB2) erhielt im Rahmen einer Phase-1-Studie (NCT02966782) Venetoclax, einen neuen Bcl-2-Antagonisten, der in verschiedenen Zelltypen eine Apoptose induziert. Der Patient hatte zum Studieneinschluss[zum vollständigen Text gelangen Sie über die oben angegebene URL], 47. Kongress der Deutschen Gesellschaft für Rheumatologie (DGRh), 33. Jahrestagung der Deutschen Gesellschaft für Orthopädische Rheumatologie (DGORh), 29. Jahrestagung der Gesellschaft für Kinder- und Jugendrheumatologie (GKJR)

Bone sarcomas are among the most common tumors in adolescents andyounger adults. Despite advances in treatment set-up a significant number of patients do not respond adequately to chemotherapeutic agents andare faced with a dismal prognosis despite mutilating surgical treatment.Neither can treatment response be predicted at initial diagnosis nor havenovel agents been included in first-line therapy of treatment-resistant tumors. The Wilms Tumor protein (WT1) is known to act as an oncogenein different sarcoma subtypes. However, its regulation or sarcoma-specificfunctions have not been described. Here, we identify WT1 as a resistancefactor to chemotherapy as a consequence of CDC14B/CDK1-USP9X-induced stabilization.For protein interaction studies and phospho-analysis we have used unbiased mass-spectrometric approaches. Immunoprecipitation, in vivoubiquitylation, Ubiquitin-sulfone assays as well as in vitro kinase assaysvalidated the screening results. We applied western blot, flow cytometryand immunofluorescence for further analysis. Genome editing by theCRISPR-Cas9 system was applied to produce specifically mutated U2OSosteosarcoma cells.In a first step, we have identified the deubiquitinase USP9X as a mitoticbinding partner of the dual phosphatase CDC14B. We confirmed that theUSP9X_Serine 2563 phosphorylation site is regulated by opposing activities of the CDC14B phosphatase and the mitotic kinase CDK1. Accordingly, USP9X proved to be phosphorylated at Serine 2563 exclusively inthe G2/M phase of the cell cycle resulting in USP9X activation. Using amass spectrometry-based proteome-wide ubiquitin screen we identifiedWT1 as a mitotic substrate of USP9X and demonstrated that the deubiquitylating and stabilizing effect on WT1 depends on the USP9X phosphorylation status at Serine 2563. WT1 has been described as a potent oncogene via p53 antagonism. In human osteosarcoma cells, that exhibited lowWT1 stability from genetic editing at the respective USP9X phosphorylation site, various p53-activating chemotherapeutic agents consequentlyinduced massive apoptosis.We identify the CDC14B/CDK1-USP9X-WT1 axis as a novel pathwayregulating sarcoma cell sensitivity to chemotherapeutic agents. Phosphorylation of USP9X at Serine 2563 might not only be used to predictresponse to chemotherapy (e.g. the VIDE protocol) but small moleculeinhibitors to this phosphosite may serve as a novel targeted therapy approach for treatment-resistant sarcoma patients

NIPA (nuclear interaction partner of ALK) is an F-box-like protein that monitors the timing of mitotic entry. Constitutively active NIPA delays mitotic entry by preventing accumulation of nuclear cyclin B1. Here, we have investigated the consequences of Nipa inactivation by using a conditional knockout strategy. Nipa-deficient animals are viable but show a lower birth rate and reduced body weight. Furthermore, Nipa-deficient males are sterile owing to a block of spermatogenesis during meiotic prophase. Whereas Nipa−/− mouse embryonic fibroblasts show no severe phenotype, Nipa−/− spermatocytes arrest during stage IV of the epithelial cycle with subsequent TUNEL-positive apoptosis resulting from improper synapsis, defects in the repair of DNA double-stranded breaks and synaptonemal complex formation. Moreover, we show nuclear accumulation of cyclin B1 with a subsequent premature increase in G2/M kinase activity in Nipa−/− spermatocytes. Together, these results reveal a novel role for NIPA in meiosis.

Introduction: Immunomodulatory drugs (IMiDs) as thalidomide, lenalidomide and pomalidomide, have immunomodulatory, anti-proliferative, anti-angiogenic and teratotoxic effects and are key treatment components for hematologic malignancies such as multiple myeloma (MM)and del(5q) myelodysplastic syndrome (MDS). IMiDs bind to Cereblon(CRBN), a substrate receptor of CRL4 ubiquitin ligases, to mediate anti-cancer and teratotoxic effects. Recently, IKZF1/3 and CK1-alpha wereidentified as substrates, which are degraded upon IMiD-induced bindingto CRBN. However, both the physiological function of CRBN, as well as acommon mechanism by which IMiDs exert their versatile effects, remainlargely elusive.