Interplay between p53-family, their regulators, and PARPs in DNA repair

USP10 as a Potential Therapeutic Target in Human Cancers

Deubiquitination is a major form of post-translational protein modification involved in the regulation of protein homeostasis and various cellular processes. Deubiquitinating enzymes (DUBs), comprising about five subfamily members, are key players in deubiquitination. USP10 is a USP-family DUB featuring the classic USP domain, which performs deubiquitination. Emerging evidence has demonstrated that USP10 is a double-edged sword in human cancers. However, the precise molecular mechanisms underlying its different effects in tumorigenesis remain elusive. A possible reason is dependence on the cell context. In this review, we summarize the downstream substrates and upstream regulators of USP10 as well as its dual role as an oncogene and tumor suppressor in various human cancers. Furthermore, we summarize multiple pharmacological USP10 inhibitors, including small-molecule inhibitors, such as spautin-1, and traditional Chinese medicines. Taken together, the development of specific and efficient USP10 inhibitors based on USP10’s oncogenic role and for different cancer types could be a promising therapeutic strategy.

Deubiquitinating enzymes (DUBs): Regulation, homeostasis, and oxidative stress response

Ubiquitin signaling is a conserved, widespread, and dynamic process in which protein substrates are rapidly modified by ubiquitin to impact protein activity, localization, or stability. To regulate this process, deubiquitinating enzymes (DUBs) counter the signal induced by ubiquitin conjugases and ligases by removing ubiquitin from these substrates. Many DUBs selectively regulate physiological pathways employing conserved mechanisms of ubiquitin bond cleavage. DUB activity is highly regulated in dynamic environments through protein-protein interaction, posttranslational modification, and relocalization. The largest family of DUBs, cysteine proteases, are also sensitive to regulation by oxidative stress, as reactive oxygen species (ROS) directly modify the catalytic cysteine required for their enzymatic activity. Current research has implicated DUB activity in human diseases, including various cancers and neurodegenerative disorders. Due to their selectivity and functional roles, DUBs have become important targets for therapeutic development to treat these conditions. This review will discuss the main classes of DUBs and their regulatory mechanisms with a particular focus on DUB redox regulation and its physiological impact during oxidative stress.

Spatial regulation of the KH domain RNA-binding protein Rnc1 mediated by a Crm1-independent nuclear export system in Schizosaccharomyces pombe

RNA-binding proteins (RBPs) play important roles in the posttranscriptional regulation of gene expression, including mRNA stability, transport and translation. Fission yeast rnc1+ encodes a K Homology (KH)-type RBP, which binds and stabilizes the Pmp1 MAPK phosphatase mRNA thereby suppressing the Cl- hypersensitivity of calcineurin deletion and MAPK signaling mutants. Here, we analyzed the spatial regulation of Rnc1 and discovered a putative nuclear export signal (NES)Rnc1 , which dictates the cytoplasmic localization of Rnc1 in a Crm1-independent manner. Notably, mutations in the NESRnc1 altered nucleocytoplasmic distribution of Rnc1 and abolished its function to suppress calcineurin deletion, although the Rnc1 NES mutant maintains the ability to bind Pmp1 mRNA. Intriguingly, the Rnc1 NES mutant destabilized Pmp1 mRNA, suggesting the functional importance of the Rnc1 cytoplasmic localization. Mutation in Rae1, but not Mex67 deletion or overproduction, induced Rnc1 accumulation in the nucleus, suggesting that Rnc1 is exported from the nucleus to the cytoplasm via the mRNA export pathway involving Rae1. Importantly, mutations in the Rnc1 KH-domains abolished the mRNA-binding ability and induced nuclear localization, suggesting that Rnc1 may be exported from the nucleus together with its target mRNAs. Collectively, the functional Rae1-dependent mRNA export system may influence the cytoplasmic localization and function of Rnc1.

Targeting Deubiquitinating Enzymes in Glioblastoma Multiforme: Expectations and Challenges

Glioblastoma (GBM) is regarded as the most common primary intracranial neoplasm. Despite standard treatment with tumor resection and radiochemotherapy, the outcome remains gloomy. It is evident that a combination of oncogenic gain of function and tumor-suppressive loss of function has been attributed to glioma initiation and progression. The ubiquitin-proteasome system is a well-orchestrated system that controls the fate of most proteins by striking a dynamic balance between ubiquitination and deubiquitination of substrates, having a profound influence on the modulation of oncoproteins, tumor suppressors, and cellular signaling pathways. In recent years, deubiquitinating enzymes (DUBs) have emerged as potential anti-cancer targets due to their targeting several key proteins involved in the regulation of tumorigenesis, apoptosis, senescence, and autophagy. This review attempts to summarize recent studies of GBM-associated DUBs, their roles in various cellular processes, and discuss the relation between DUBs deregulation and gliomagenesis, especially how DUBs regulate glioma stem cells pluripotency, microenvironment, and resistance of radiation and chemotherapy through core stem-cell transcriptional factors. We also review recent achievements and progress in the development of potent and selective reversible inhibitors of DUBs, and attempted to find a potential GBM treatment by DUBs intervention.

Identification of O-GlcNAc modification targets in mouse retinal pericytes: implication of p53 in pathogenesis of diabetic retinopathy

Hyperglycemia is the primary cause of the majority of diabetes complications, including diabetic retinopathy (DR). Hyperglycemic conditions have a detrimental effect on many tissues and cell types, especially the retinal vascular cells including early loss of pericytes (PC). However, the mechanisms behind this selective sensitivity of retinal PC to hyperglycemia are undefined. The O-linked β-N-acetylglucosamine (O-GlcNAc) modification is elevated under hyperglycemic condition, and thus, may present an important molecular modification impacting the hyperglycemia-driven complications of diabetes. We have recently demonstrated that the level of O-GlcNAc modification in response to high glucose is variable in various retinal vascular cells. Retinal PC responded with the highest increase in O-GlcNAc modification compared to retinal endothelial cells and astrocytes. Here we show that these differences translated into functional changes, with an increase in apoptosis of retinal PC, not just under high glucose but also under treatment with O-GlcNAc modification inducers, PUGNAc and Thiamet-G. To gain insight into the molecular mechanisms involved, we have used click-It chemistry and LC-MS analysis and identified 431 target proteins of O-GlcNAc modification in retinal PC using an alkynyl-modified GlcNAc analog (GlcNAlk). Among the O-GlcNAc target proteins identified here 115 of them were not previously reported to be target of O-GlcNAc modification. We have identified at least 34 of these proteins with important roles in various aspects of cell death processes. Our results indicated that increased O-GlcNAc modification of p53 was associated with an increase in its protein levels in retinal PC. Together our results suggest that post-translational O-GlcNAc modification of p53 and its increased levels may contribute to selective early loss of PC during diabetes. Thus, modulation of O-GlcNAc modification may provide a novel treatment strategy to prevent the initiation and progression of DR.

Sequence and structural analyses of nuclear export signals in the NESdb database

We compiled >200 nuclear export signal (NES)-containing CRM1 cargoes in a database named NESdb. We analyzed the sequences and three-dimensional structures of natural, experimentally identified NESs and of false-positive NESs that were generated from the database in order to identify properties that might distinguish the two groups of sequences. Analyses of amino acid frequencies, sequence logos, and agreement with existing NES consensus sequences revealed strong preferences for the Φ1-X(3)-Φ2-X(2)-Φ3-X-Φ4 pattern and for negatively charged amino acids in the nonhydrophobic positions of experimentally identified NESs but not of false positives. Strong preferences against certain hydrophobic amino acids in the hydrophobic positions were also revealed. These findings led to a new and more precise NES consensus. More important, three-dimensional structures are now available for 68 NESs within 56 different cargo proteins. Analyses of these structures showed that experimentally identified NESs are more likely than the false positives to adopt α-helical conformations that transition to loops at their C-termini and more likely to be surface accessible within their protein domains or be present in disordered or unobserved parts of the structures. Such distinguishing features for real NESs might be useful in future NES prediction efforts. Finally, we also tested CRM1-binding of 40 NESs that were found in the 56 structures. We found that 16 of the NES peptides did not bind CRM1, hence illustrating how NESs are easily misidentified.

Pinworm and TNKS inhibitors, an eccentric duo to derail the oncogenic WNT pathway

The WNT/β-catenin pathway underlies many human cancers through mutations in the APC, β-catenin, and Axin genes. Activation of WNT signalling can also occur due to the localization of glycogen synthase kinase 3β(GSK3β) to the multivesicular bodies, which prevents the degradation of β-catenin. This leads to accumulation of β-catenin within the cytoplasmic matrix and nucleus of cancer cells, which triggers the transactivation of genes involved in cell proliferation, including various oncogenes. Recent research into the mechanistic regulations of molecule homeostasis and identification of new small-targeted inhibitors has provided further insights into the WNT signalling pathway and its role in human cancers. Novel WNT inhibitors target unsuspected cellular enzymes, such as tankyrases, or casein kinase 1α/γ, which controls the destruction of β-catenin and GSK3β. These could lead to the identification of new biomarkers and WNT-targeted inhibitors for the treatment of cancer.

Priming and potentiation of DNA damage response by fibronectin in human colon cancer cells and tumor-derived myofibroblasts

We have previously shown that the genotoxin-induced apoptosis in mouse embryo fibroblasts was enhanced by the extracellular matrix protein fibronectin (FN). In the present study, we tested the hypothesis that FN regulates the DNA damage response (DDR) signaling pathways in HCT116 (p53-wt) and HT29 (p53-mut) human colon cancer cells and tumor-derived myofibroblasts. DNA damage recognition mechanisms were analyzed by immunofluorescence staining, cell cycle analysis and immunoblotting addressed at specific molecular sensors and executors involved in the DDR pathways. The results show that FN, but not collagen type IV or Matrigel, initiates and potentiates the DDR to the anticancer drug cisplatin in an α5 integrin and cell cycle-dependent manner (S and G2/M phases) in human colon cancer cells. Accordingly, we demonstrate that adhesion of HCT116 cells to FN upregulated the expression of α5 integrin FN receptors at the cell surface. These FN-induced DDR pathways include the concerted phosphorylation of histone H2AX on Ser139 detected as nuclear foci (γ-H2AX, 15 and 25 kDa forms), of ataxia telangiectasia mutated (ATM-Ser1981), checkpoint kinase 2 (CHK2-Thr68, 62 and 67 kDa) and p53-Ser15. These FN-induced γ-H2AX signals were interrupted or attenuated by selective inhibitors acting on the DDR pathway kinases, including wortmannin (targeting the phosphatidylinositol-3-kinase-related protein kinases, PIKK), KU55933 (ATM), NU7026 (DNA-dependent protein kinase catalytic subunit, DNA-PK-cs) and SP600125 (JNK2, stress activated protein kinase/c-Jun N-terminal kinase-2). Adhesion to FN also potentiated the γ-H2AX signals and the cytotoxic effects of cisplatin in human colon tumor-derived myofibroblasts. These data provide evidence that FN promotes DNA damage recognition and chemosensitization to cisplatin via the potentiation of the DNA damage signaling responses in human colon cancer cells and tumor-derived myofibroblasts.