Targeting Smurf1 to block PDK1-Akt signaling in KRAS-mutated colorectal cancer.

The phosphoinositide 3-kinase (PI3K)-Akt axis is one of the most frequently activated pathways and is demonstrated as a therapeutic target in Kirsten rat sarcoma viral oncogene homolog (KRAS)-mutated colorectal cancer (CRC). Targeting the PI3K-Akt pathway has been a challenging undertaking through the decades. Here we unveiled an essential role of E3 ligase SMAD ubiquitylation regulatory factor 1 (Smurf1)-mediated phosphoinositide-dependent protein kinase 1 (PDK1) neddylation in PI3K-Akt signaling and tumorigenesis. Upon growth factor stimulation, Smurf1 immediately triggers PDK1 neddylation and the poly-neural precursor cell expressed developmentally downregulated protein 8 (poly-Nedd8) chains recruit methyltransferase SET domain bifurcated histone lysine methyltransferase 1 (SETDB1). The cytoplasmic complex of PDK1 assembled with Smurf1 and SETDB1 (cCOMPASS) consisting of PDK1, Smurf1 and SETDB1 directs Akt membrane attachment and T308 phosphorylation. Smurf1 deficiency dramatically reduces CRC tumorigenesis in a genetic mouse model. Furthermore, we developed a highly selective Smurf1 degrader, Smurf1-antagonizing repressor of tumor 1, which exhibits efficient PDK1-Akt blockade and potent tumor suppression alone or combined with PDK1 inhibitor in KRAS-mutated CRC. The findings presented here unveil previously unrecognized roles of PDK1 neddylation and offer a potential strategy for targeting the PI3K-Akt pathway and KRAS mutant cancer therapy.

Deubiquitylase OTUD3 regulates integrated stress response to suppress progression and sorafenib resistance of liver cancer.

The integrated stress response (ISR) is activated in response to intrinsic and extrinsic stimuli, playing a role in tumor progression and drug resistance. The regulatory role and mechanism of ISR in liver cancer, however, remain largely unexplored. Here, we demonstrate that OTU domain-containing protein 3 (OTUD3) is a deubiquitylase of eukaryotic initiation factor 2α (eIF2α), antagonizing ISR and suppressing liver cancer. OTUD3 decreases interactions between eIF2α and the kinase EIF2ΑK3 by removing K27-linked polyubiquitylation on eIF2α. OTUD3 deficiency in mice leads to enhanced ISR and accelerated progression of N-nitrosodiethylamine-induced hepatocellular carcinoma. Additionally, decreased OTUD3 expression associated with elevated eIF2α phosphorylation correlates with the progression of human liver cancer. Moreover, ISR activation due to decreased OTUD3 expression renders liver cancer cells resistant to sorafenib, while the combined use of the ISR inhibitor ISRIB significantly improves their sensitivity to sorafenib. Collectively, these findings illuminate the regulatory mechanism of ISR in liver cancer and provide a potential strategy to counteract sorafenib resistance.

The deubiquitinase OTUD1 inhibits colonic inflammation by suppressing RIPK1-mediated NF-κB signaling.

The E3 ubiquitin ligase (E3)-mediated ubiquitination and deubiquitinase (DUB)-mediated deubiquitination processes are closely associated with the occurrence and development of colonic inflammation. Ovarian tumor deubiquitinase 1 (OTUD1) is involved in immunoregulatory functions linked to infectious diseases. However, the effect of OTUD1 on intestinal immune responses during colonic inflammatory disorders such as inflammatory bowel disease (IBD) remains unclear. Here, we show that loss of OTUD1 in mice contributes to the pathogenesis of dextran sulfate sodium (DSS)-induced colitis via excessive release of proinflammatory cytokines. In addition, bone marrow transplantation experiments revealed that OTUD1 in hematopoietic cells plays a dominant role in protection against colitis. Mechanistically, OTUD1 physically interacts with receptor-interacting serine/threonine-protein kinase 1 (RIPK1) and selectively cleaves K63-linked polyubiquitin chains from RIPK1 to inhibit the recruitment of NF-κB essential modulator (NEMO). Moreover, the expression of OTUD1 in mucosa samples from ulcerative colitis (UC) patients was lower than that in mucosa samples from healthy controls. Furthermore, we demonstrate that the UC-associated OTUD1 G430V mutation abolishes the ability of OTUD1 to inhibit RIPK1-mediated NF-κB activation and intestinal inflammation. Taken together, our study unveils a previously unexplored role of OTUD1 in moderating intestinal inflammation by inhibiting RIPK1-mediated NF-κB activation, suggesting that the OTUD1-RIPK1 axis could be a potential target for the treatment of IBD.

Global Screening of LUBAC and OTULIN Interacting Proteins by Human Proteome Microarray.

Linear ubiquitination is a reversible posttranslational modification, which plays key roles in multiple biological processes. Linear ubiquitin chain assembly complex (LUBAC) catalyzes linear ubiquitination, while the deubiquitinase OTULIN (OTU deubiquitinase with linear linkage specificity, FAM105B) exclusively cleaves the linear ubiquitin chains. However, our understanding of linear ubiquitination is restricted to a few substrates and pathways. Here we used a human proteome microarray to detect the interacting proteins of LUBAC and OTULIN by systematically screening up to 20,000 proteins. We identified many potential interacting proteins of LUBAC and OTULIN, which may function as regulators or substrates of linear ubiquitination. Interestingly, our results also hint that linear ubiquitination may have broad functions in diverse pathways. In addition, we recognized lymphocyte activation gene-3 (LAG3, CD223), a transmembrane receptor that negatively regulates lymphocyte functions as a novel substrate of linear ubiquitination in the adaptive immunity pathway. In conclusion, our results provide searchable, accessible data for the interacting proteins of LUBAC and OTULIN, which broaden our understanding of linear ubiquitination.

OTULIN allies with LUBAC to govern angiogenesis by editing ALK1 linear polyubiquitin.

OTULIN coordinates with LUBAC to edit linear polyubiquitin chains in embryonic development, autoimmunity, and inflammatory diseases. However, the mechanism by which angiogenesis, especially that of endothelial cells (ECs), is regulated by linear ubiquitination remains unclear. Here, we reveal that constitutive or EC-specific deletion of Otulin resulted in arteriovenous malformations and embryonic lethality. LUBAC conjugates linear ubiquitin chains onto Activin receptor-like kinase 1 (ALK1), which is responsible for angiogenesis defects, inhibiting ALK1 enzyme activity and Smad1/5 activation. Conversely, OTULIN deubiquitinates ALK1 to promote Smad1/5 activation. Consistently, embryonic survival of Otulin-deficient mice was prolonged by BMP9 pretreatment or EC-specific ALK1Q200D (constitutively active) knockin. Moreover, mutant ALK1 from type 2 hereditary hemorrhagic telangiectasia (HHT2) patients exhibited excessive linear ubiquitination and increased HOIP binding. As such, a HOIP inhibitor restricted the excessive angiogenesis of ECs derived from ALK1G309S-expressing HHT2 patients. These results show that OTULIN and LUBAC govern ALK1 activity to balance EC angiogenesis.

Deubiquitinating enzyme 4 facilitates chemoresistance in glioblastoma by inhibiting P53 activity.

Glioblastoma is a malignant primary brain tumor with poor prognosis with a median survival of only 12-15 months. The high mortality rate of this disease is mainly due to the chemoresistance resulting from various reasons. Ubiquitin-specific protease 4 (USP4) has recently been found to be elevated in various types of cancer through regulating P53 activity. However, whether USP4 is responsible for chemoresistance in glioblastoma is not clear. In the present study, the expression of USP4 in glioblastoma tissues and cell lines, as well as its association with temozolomide (TMZ) chemoresistance was analyzed. The results demonstrated that USP4 was significantly upregulated in glioblastoma tissues and cell lines at the mRNA and protein levels. Notably, USP4 knockdown alone did not affect glioblastoma cell viability; however, when USP4 knockdown cells were treated with TMZ, the cell viability was decreased significantly. In addition, the results revealed that cleaved poly(ADP-ribose) polymerase level increased when USP4 was knocked down in glioblastoma cells treated with TMZ. It was also observed that P53 was increased in U251 and U87 cells with USP4 knockdown. Following treatment with a P53 specific inhibitor, the results suggested that USP4 mediated chemoresistance through inhibiting apoptosis in a P53-dependent manner. In conclusion, the data revealed the critical role of USP4 in TMZ resistance in glioblastoma and provided new insight for future drug development for the treatment of this disease.