Spy1 Is Frequently Overexpressed in Malignant Gliomas and Critically Regulates the Proliferation of Glioma Cells

The role of ubiquitin-specific peptidases in glioma progression

The balance between ubiquitination and deubiquitination is crucial for protein stability, function and location under physiological conditions. Dysregulation of E1/E2/E3 ligases or deubiquitinases (DUBs) results in malfunction of the ubiquitin system and is involved in many diseases. Increasing reports have indicated that ubiquitin-specific peptidases (USPs) play a part in the progression of many kinds of cancers and could be good targets for anticancer treatment. Glioma is the most common malignant tumor in the central nervous system. Clinical treatment for high-grade glioma is unsatisfactory thus far. Multiple USPs are dysregulated in glioma and have the potential to be therapeutic targets. In this review, we collected studies on the roles of USPs in glioma progression and summarized the mechanisms of USPs in glioma tumorigenesis, malignancy and chemoradiotherapy resistance.

RINGO/Speedy proteins, a family of non-canonical activators of CDK1 and CDK2

Cyclin-dependent kinases (CDKs) require the binding to a regulatory subunit to acquire enzymatic activity, and cyclins are the canonical CDK activators. However, there are specific situations in which CDKs can be activated by non-cyclin proteins that are less characterized. This review focuses on the family of RINGO/Speedy proteins, which have no sequence amino acid homology to cyclins but can bind to and activate CDK1 and CDK2. Interestingly, RINGO/Speedy proteins can activate CDKs under conditions in which CDK-cyclin complexes would not be active, and there is evidence that RINGO/Speedy-activated CDKs can phosphorylate different sites than the cyclin-activated CDKs. RINGO/Speedy proteins were originally described in Xenopus oocytes, but their roles in mammalian cells have also been addressed. We will summarize the properties of RINGO/Speedy proteins and how they trigger CDK activation, and discuss recent studies that characterized their physiological functions. In particular, studies using genetically modified mice have shown that RingoA, also known as Spy1, plays a key role in meiosis regulation. Emerging evidence also suggests a potential role for RingoA/Spy1 in cancer.

Screening critical genes associated with malignant glioma using bioinformatics analysis

Malignant gliomas are high‑grade gliomas, which are derived from glial cells in the spine or brain. To examine the mechanisms underlying malignant gliomas in the present study, the expression profile of GSE54004, which included 12 grade II astrocytomas, 33 grade III astrocytomas and 98 grade IV astrocytomas, was downloaded from the Gene Expression Omnibus. Using the Limma package in R, the differentially expressed genes (DEGs) in grade III, vs. grade II astrocytoma, grade IV, vs. grade II astrocytoma, and grade IV, vs. grade III astrocytoma were analyzed. Venn diagram analysis and enrichment analyses were performed separately for the DEGs using VennPlex software and the Database for Annotation, Visualization and Integrated Discovery. Protein‑protein interaction (PPI) networks were visualized using Cytoscape software, and subsequent module analysis of the PPI networks was performed using the ClusterONE tool. Finally, glioma‑associated genes and glioma marker genes among the DEGs were identified using the CTD database. A total of 27, 1,446 and 776 DEGs were screened for the grade III, vs. grade II, grade IV, vs. grade II, and grade IV, vs. grade III astrocytoma comparison groups, respectively. Functional enrichment analyses showed that matrix metalloproteinase 9 (MMP9) and chitinase 3‑like 1 (CHI3L1) were enriched in the extracellular matrix and extracellular matrix structural constituent, respectively. In the PPI networks, annexin A1 (ANXA1) had a higher degree and MMP9 had interactions with vascular endothelial growth factor A (VEGFA). There were 10 common glioma marker genes between the grade IV, vs. grade II and the grade IV, vs. grade III comparison groups, including MMP9, CHI3L1, VEGFA and S100 calcium binding protein A4 (S100A4). This suggested that MMP9, CHI3L1, VEGFA, S100A4 and ANXA1 may be involved in the progression of malignant gliomas.

Structural basis of divergent cyclin-dependent kinase activation by Spy1/RINGO proteins

Cyclin-dependent kinases (Cdks) are principal drivers of cell division and are an important therapeutic target to inhibit aberrant proliferation. Cdk enzymatic activity is tightly controlled through cyclin interactions, posttranslational modifications, and binding of inhibitors such as the p27 tumor suppressor protein. Spy1/RINGO (Spy1) proteins bind and activate Cdk but are resistant to canonical regulatory mechanisms that establish cell-cycle checkpoints. Cancer cells exploit Spy1 to stimulate proliferation through inappropriate activation of Cdks, yet the mechanism is unknown. We have determined crystal structures of the Cdk2-Spy1 and p27-Cdk2-Spy1 complexes that reveal how Spy1 activates Cdk. We find that Spy1 confers structural changes to Cdk2 that obviate the requirement of Cdk activation loop phosphorylation. Spy1 lacks the cyclin-binding site that mediates p27 and substrate affinity, explaining why Cdk-Spy1 is poorly inhibited by p27 and lacks specificity for substrates with cyclin-docking sites. We identify mutations in Spy1 that ablate its ability to activate Cdk2 and to proliferate cells. Our structural description of Spy1 provides important mechanistic insights that may be utilized for targeting upregulated Spy1 in cancer.

Direct interactions with both p27 and Cdk2 regulate Spy1-mediated proliferation in vivo and in vitro

Families of cyclin-like proteins have emerged that bind and activate cyclin dependent kinases (Cdk)s, directing the phosphorylation of noncanonical Cdk substrates. One of these proteins, Spy1, has demonstrated the unique ability to directly bind and activate both Cdk1 and Cdk2, as well as binding and promoting the degradation of at least one Cdk inhibitor, p27(Kip1). Spy1 accelerates somatic cell growth and proliferation and is implicated in a number of human cancers including the breast, brain and liver. Herein we isolate key residues mediating the direct interaction with p27. We use mutants of Spy1 to determine the physiological role of direct interactions with distinct binding partners Cdk2 and p27. We demonstrate that disrupting the direct interaction with either Spy1 binding partner decreased endogenous activity of Cdk2, as well as Spy1-mediated proliferation. However, only the direct interaction with p27 was essential for Spy1-mediated effects on p27 stability. In vivo neither mutation completely prevented tumorigenesis, although each mutation slowed the rate of Spy1-mediated tumorigenesis and decreased overall tumor volumes. This work supports the conclusion that direct interaction with both p27 and Cdk2 contribute to Spy1-mediated effects on cell growth. It is important to elucidate the dynamics of these interactions and to consider these data when assessing functional outcomes.

Spy1 induces de-ubiquitinating of RIP1 arrest and confers glioblastoma's resistance to tumor necrosis factor (TNF-α)-induced apoptosis through suppressing the association of CLIPR-59 and CYLD

Glioblastoma multiforme (GBM), a grade-IV glioma, is resistant to TNF-α induced apoptosis. CLIPR-59 modulates ubiquitination of RIP1, thus promoting Caspase-8 activation to induce apoptosis by TNF-α. Here we reported that CLIPR-59 was down-regulated in GBM cells and high-grade glioma tumor samples, which was associated with decreased cancer-free survival. In GBM cells, CLIPR-59 interacts with Spy1, resulting in its decreased association with CYLD, a de-ubiquitinating enzyme. Moreover, experimental reduction of Spy1 levels decreased GBM cells viability, while increased the lysine-63-dependent de-ubiquitinating activity of RIP1 via enhancing the binding ability of CLIPR-59 and CYLD in GBM, thus promoting Caspase-8 and Caspase-3 activation to induce apoptosis by TNF-α. These findings have identified a novel Spy1-CLIPR-59 interplay in GBM cell's resistance to TNF-α-induced apoptosis revealing a potential target in the intervention of malignant brain tumors.

Spy1 Protein Mediates Phosphorylation and Degradation of SCG10 Protein in Axonal Degeneration

Axon loss is a destructive consequence of a wide range of neurological diseases without a clearly defined mechanism. Recent data demonstrate that SCG10 is a novel axonal maintenance factor and that rapid SCG10 loss after injury requires JNK activity; how JNK induces degradation of SCG10 is not well known. Here we showed that SCG10 was a binding partner of Spy1, a Speedy/RINGO family protein, which participated in cellular response to sciatic nerve injury. During the early stage of axonal injury, Spy1 expression was inversely correlated with SCG10. Spy1 mediated SCG10 phosphorylation and degradation partly in a JNK-dependent manner. Inhibition of Spy1 attenuated SCG10 phosphorylation and delayed injury-induced axonal degeneration. Taken together, these data suggest that Spy1 is an important regulator of SCG10 and can be targeted in future axo-protective therapeutics.

The role of FoxJ2 in the migration of human glioma cells

Previous studies have demonstrated that FoxJ2 (forkhead box J2) is a member of Forkhead Box transcription factors and acts as an important prognostic indicator in human breast cancer. Our study aimed to assess the expression and function in human glioma. Western blot analysis and immunohistochemistry were performed in human glioma tissues. Low FoxJ2 expression was observed in 80 samples and its level was correlated with the grade of malignancy. A strongly positive correlation was observed between FoxJ2 and E-cadherin. Overexpression of FoxJ2 increased E-cadherin expression and decreased vimentin expression. The wound healing and transwell assays showed that overexpression of FoxJ2 significantly inhibited their migration in U87 cells. Consistent with this, knockdown of FoxJ2 promoted cellular motility. In a word, FoxJ2 suppressed cell migration and invasion in glioma, which might be a potential novel molecular targeted therapy for surgery and immune treatment.

The cyclin-like protein Spy1 regulates growth and division characteristics of the CD133+ population in human glioma

The heterogeneity of brain cancers, as most solid tumors, complicates diagnosis and treatment. Identifying and targeting populations of cells driving tumorigenesis is a top priority for the cancer biology field. This is not a trivial task; considerable variance exists in the driving mutations, identifying markers, and evolutionary pressures influencing initiating cells in different individual tumors. Despite this, the ability to self-renew and differentiate must be conserved to reseed a heterogeneous tumor mass. Focusing on one example of a tumor-initiating cell population, we demonstrate that the atypical cyclin-like protein Spy1 plays a role in balancing the division properties of glioma cells with stemness properties. This mechanistic insight may provide new opportunities for therapeutic intervention of brain cancer.

Glycinamide ribonucleotide formyl transferase is frequently overexpressed in glioma and critically regulates the proliferation of glioma cells

AIMS

Current treatments for the most common form of brain tumor, glioma, are disappointing in their effectiveness. Low expression levels of GART, an enzyme in the core nucleotide metabolism, significantly correlate with chemosensitivity, conferring a survival advantage to tumor cells. Our study aimed to explore the expression and function of GART in glioma.

METHODS

Immunohistochemical and Western blot analysis were performed in 70 cases of human gliomas and normal brain tissues. We mainly used cell growth assay and multicellular tumor spheroid formation assay to evaluate the proliferation and chemosensitivity of glioma cells.

RESULTS

High GART expression (most cancer cells cytoplasm stained) was observed in 70 specimens and was related to the grade of malignancy. We also reviewed each grade of tumors separately and investigated whether GART expression predicted patient survival within each subgroup. In brief, GART overexpression was significantly associated with overall survival (P=0.03). Interestingly, transfecting cells with GART-siRNA suppressed proliferation and enhanced temozolomide (TMZ)-induced apoptosis in glioma cells.

CONCLUSION

The current results showed that GART expression was associated with glioma grade and that high GART protein expression might be related to poor outcome.

Temporal-spatial expressions of Spy1 in rat sciatic nerve after crush

As a novel cell cycle protein, Spy1 enhances cell proliferation, promotes the G1/S transition as well as inhibits apoptosis in response to UV irradiation. Spy1 levels are tightly regulated during mammary development, and overexpression of Spy1 accelerates tumorigenesis in vivo. But little is known about the role of Spy1 in the pathological process of damage and regeneration of the peripheral nervous system. Here we established a rat sciatic nerve crush (SNC) model to examine the spatiotemporal expression of Spy1. Spy1 expression was elevated gradually after sciatic nerve crush and peaked at day 3. The alteration was due to the increased expression of Spy1 in axons and Schwann cells after SNC. Spy1 expression correlated closely with Schwann cells proliferation in sciatic nerve post injury. Furthermore, Spy1 largely localized in axons in the crushed segment, but rarely co-localized with GAP43. These findings suggested that Spy1 participated in the pathological process response to sciatic nerve injury and may be associated with Schwann cells proliferation and axons regeneration.