Skp2 inhibitor SKPin C1 decreased viability and proliferation of multiple myeloma cells and induced apoptosis

Long non-coding RNA Linc00657 up-regulates Skp2 to promote the progression of cervical cancer through lipid reprogramming and regulation of immune microenvironment

More and more evidence shows that long non-coding RNA (lncRNA) plays an important role in the biological behavior of many kinds of malignant tumors, but the specific function of lncRNA Linc00657 in cervical cancer is still unknown. The purpose of this study is to explore the effect of Linc00657 on the malignant progression of cervical cancer and its potential mechanism. In two kinds of cervical cancer cell lines and normal cervical epithelial cells, qRT-PCR showed increased expression of Linc00657 in cervical cancer cells. Through MTT, clone formation test, flow cytometry, wound healing test and Transwell test, it has been found that overexpression of Linc00657 could promote the proliferation,migration and invasion of cervical cancer cells，and inhibit apoptosis. Through the StarBase database, it was found that there may be a mutual regulatory relationship between Linc00657 and Skp2, and Skp2 may be the downstream target of Linc00657. QRT-PCR detection confirmed that the expression of Skp2 was increased in cervical cancer cells with overexpression of Linc00657. TIMER2 database found that Skp2 was associated with lipid metabolic enzymes and immune cell infiltration. It was found that Linc00657 knockdown inhibited tumor growth and metastasis and inhibited the expression of Skp2 in vivo. In short, our research shows that Linc00657 has carcinogenic properties in cervical cancer, and LINC00657 promotes the occurrence of cervical cancer by up-regulating the expression of Skp2. We predict that Linc00657/mir30s/Skp2 axis plays a role in the malignant progression of cervical cancer. In addition, Skp2 may participate in cancer immune response and promote lymph node metastasis of cervical cancer through lipid reprogramming. These findings also provide promising targets for the diagnosis and treatment of cervical cancer.

SKping cell cycle regulation: role of ubiquitin ligase SKP2 in hematological malignancies

SKP2 (S-phase kinase-associated protein 2) is a member of the F-box family of substrate-recognition subunits in the SCF ubiquitin-protein ligase complexes. It is associated with ubiquitin-mediated degradation in the mammalian cell cycle components and other target proteins involved in cell cycle progression, signal transduction, and transcription. Being an oncogene in solid tumors and hematological malignancies, it is frequently associated with drug resistance and poor disease outcomes. In the current review, we discussed the novel role of SKP2 in different hematological malignancies. Further, we performed a limited in-silico analysis to establish the involvement of SKP2 in a few publicly available cancer datasets. Interestingly, our study identified Skp2 expression to be altered in a cancer-specific manner. While it was found to be overexpressed in several cancer types, few cancer showed a down-regulation in SKP2. Our review provides evidence for developing novel SKP2 inhibitors in hematological malignancies. We also investigated the effect of SKP2 status on survival and disease progression. In addition, the role of miRNA and its associated families in regulating Skp2 expression was explored. Subsequently, we predicted common miRNAs against Skp2 genes by using miRNA-predication tools. Finally, we discussed current approaches and future prospective approaches to target the Skp2 gene by using different drugs and miRNA-based therapeutics applications in translational research.

Promoter methylation and enhanced SKP2 are associated with the downregulation of CDKN1C in cervical squamous cell carcinoma

PURPOSE

Cervical Squamous Cell Carcinoma (CSCC) is one of the significant causes of cancer deaths among women. Distinct genetic and epigenetic-altered loci, including chromosomal 11p15.5-15.4, have been identified. CDKN1C (Cyclin-Dependent Kinase Inhibitor 1C, p57KIP2), a member of the CIP/KIP family of cyclin-dependent kinase inhibitors (CDKIs), located at 11p15.4, is a putative tumor suppressor. Apart from transcriptional control, S-Phase Kinase Associated Protein 2 (SKP2), an oncogenic E3 ubiquitin ligase, regulates the protein turnover of CDKN1C. But the molecular status of CDKN1C in CSCC and the underlying mechanistic underpinnings have yet to be explored.

METHODS

TCGA and other publicly available datasets were analyzed to evaluate the expression of CDKN1C and SKP2. The expression (transcript/protein) was validated in independent CSCC tumors (n = 155). Copy number alteration and promoter methylation were correlated with the expression. Finally, in vitro functional validation was performed.

RESULTS

CDKN1C was down-regulated, and SKP2 was up-regulated at the transcript and protein levels in CSCC tumors and the SiHa cell line. Notably, promoter methylation (50%) was associated with the downregulation of the CDKN1C transcript. However, high expression of SKP2 was found to be associated with the decreased expression of CDKN1C protein. Independent treatments with 5-aza-dC, MG132, and SKP2i (SKPin C1) in SiHa cells led to an enhanced expression of CDKN1C protein, validating the mechanism of down-regulation in CSCC.

CONCLUSION

Collectively, CDKN1C was down-regulated due to the synergistic effect of promoter hyper-methylation and SKP2 over-expression in CSCC tumors, paving the way for further studies of its role in the pathogenesis of the disease.

Small-molecule compounds inhibiting S-phase kinase-associated protein 2: A review

S-phase kinase-associated protein 2 (Skp2) is a substrate-specific adaptor in Skp1-CUL1-ROC1-F-box E3 ubiquitin ligases and widely regarded as an oncogene. Therefore, Skp2 has remained as an active anticancer research topic since its discovery. Accordingly, the structure of Skp2 has been solved and numerous Skp2 inhibiting compounds have been identified. In this review, we would describe the structural features of Skp2, introduce the ubiquitination function of SCF^Skp2, and summarize the diverse natural and synthetic Skp2 inhibiting compounds reported to date. The IC₅₀ data of the Skp2 inhibitors or inhibiting compounds in various kinds of tumors at cellular levels implied that the cancer type, stage and pathological mechanisms should be taken into consideration when selecting Skp2-inhibiting compound for cancer treatment.

The Impact of SKP2 Gene Expression in Chronic Myeloid Leukemia

Introduction: The prognosis of chronic myeloid leukemia (CML) patients has been dramatically improved with the introduction of imatinib (IM), the first tyrosine kinase inhibitor (TKI). TKI resistance is a serious problem in IM-based therapy. The human S-phase kinase-associated protein 2 (SKP2) gene may play an essential role in the genesis and progression of CML. Aim of the study: We try to explore the diagnostic/prognostic impact of SKP2 gene expression to predict treatment response in first-line IM-treated CML patients at an early response stage. Patients and methods: The gene expression and protein levels of SKP2 were determined using quantitative RT-PCR and ELISA in 100 newly diagnosed CML patients and 100 healthy subjects. Results: SKP2 gene expression and SKP2 protein levels were significantly upregulated in CML patients compared to the control group. The receiver operating characteristic (ROC) analysis for the SKP2 gene expression level, which that differentiated the CML patients from the healthy subjects, yielded a sensitivity of 86.0% and a specificity of 82.0%, with an area under the curve (AUC) of 0.958 (p < 0.001). The ROC analysis for the SKP2 gene expression level, which differentiated optimally from the warning/failure responses, yielded a sensitivity of 70.59% and a specificity of 71.21%, with an AUC of 0.815 (p < 0.001). Conclusion: The SKP2 gene could be an additional diagnostic and an independent prognostic marker for predicting treatment responses in first-line IM-treated CML patients at an early time point (3 months).

Tyrphostin AG1024 Suppresses Coronaviral Replication by Downregulating JAK1 via an IR/IGF-1R Independent Proteolysis Mediated by Ndfip1/2_NEDD4-like E3 Ligase Itch

JAK1 depletion or downregulation was previously reported to account for coronavirus inhibition. Here, we found that AG1024, an IR (insulin receptor) and IGF-1R (insulin-like growth factor 1 receptor) inhibitor, diminishes JAK1 protein levels and exerts anti-coronaviral activities with EC50 values of 5.2 ± 0.3 μM against transmissible gastroenteritis coronavirus (TGEV) and 4.3 ± 0.3 μM against human flu coronavirus OC43. However, although the IR and IGF-1R signaling pathways are activated by insulin or IGF-1 in swine testis cells, they are not triggered upon TGEV infection. AG1024, therefore, inhibits coronaviral replication and downregulates JAK1 protein levels independently of IR and IGF-1R. Moreover, JAK1 proteolysis caused by AG1024 was found through activation of upstream Ndfip1/2 and its effector NEDD4-like E3 ligase Itch. In addition, ouabain, which was reported to mediate JAK1 proteolysis causing anti-coronaviral activity by activation of Ndfip1/2 and NEDD4 E3 ligase, additively inhibited anti-coronaviral activity and JAK1 diminishment in combination with AG1024. This study provides novel insights into the pharmacological effects of AG1024 and Itch E3 ligase mediated JAK1 proteolysis and identified Ndfip1/2 as a cognate effector for JAK1 proteolysis via the diversified E3 ligases NEDD4 and NEDD4-like Itch. These findings are expected to provide valued information for the future development of anti-viral agents.

Emerging Roles of SKP2 in Cancer Drug Resistance

More than half of all cancer patients receive chemotherapy, however, some of them easily acquire drug resistance. Resistance to chemotherapy has become a massive obstacle to achieve high rates of pathological complete response during cancer therapy. S-phase kinase-associated protein 2 (Skp2), as an E3 ligase, was found to be highly correlated with drug resistance and poor prognosis. In this review, we summarize the mechanisms that Skp2 confers to drug resistance, including the Akt-Skp2 feedback loop, Skp2-p27 pathway, cell cycle and mitosis regulation, EMT (epithelial-mesenchymal transition) property, enhanced DNA damage response and repair, etc. We also addressed novel molecules that either inhibit Skp2 expression or target Skp2-centered interactions, which might have vast potential for application in clinics and benefit cancer patients in the future.

Identification of the antidepressive properties of C1, a specific inhibitor of Skp2, in mice

We have reported that SMIP004, an inhibitor of S-phase kinase-associated protein 2 (Skp2), displays antidepressant-like activities in stress-naïve and chronically stressed mice. Here, we investigated the antidepressant-like effect of C1, another inhibitor of Skp2, in mouse models following acute or chronic drug administration at different doses and treatment times by using the tail suspension test (TST), forced swimming test (FST), and social interaction test (SIT). The time- and dose-dependent results showed that the antidepressant-like effect of C1 occurred 8 days after the drug treatment, and C1 produced antidepressant-like activities at the dose of 5 and 10 but not 1 mg/kg in male or female mice. C1 administration (5 mg/kg) also induced antidepressant-like effects in stress-naïve mice in a three-times administration mode within 24 h (24, 5, and 1 h before the test) but not in an acute administration mode (1 h before the test). The C1 and fluoxetine co-administration produced additive effect on depression-like behaviors in stress-naïve mice. The antidepressant-like effect of C1 was not associated with the change in locomotor activity, as no increased locomotor activity was observed in different treatment modes. Furthermore, the long-term C1 treatment (5 mg/kg) was found to ameliorate the depression-like behaviors in chronic social defeat stress-exposed mice, suggesting that C1 can produce antidepressant-like actions in stress conditions. Since C1 is a specific inhibitor of Skp2, our results demonstrate that inhibition of Skp2 might be a potential strategy for the treatment of depression, and Skp2 may be potential target for the development of novel antidepressants.

Designing high affinity target-binding peptides to HLA-E: a key membrane antigen of multiple myeloma

Multiple myeloma (MM) is a plasma cell malignancy that is currently incurable. Finding new targets and designing drugs are crucial for the treatment of MM. The two datasets (GSE6691 and GSE39754) are used to screen highly expressed antigen on MM cells. HLA-E was an ideal target for it was a hub gene, and also located in one of the key clusters. Highly expression of HLA-E mRNA on MM cells was also confirmed by real-time qPCR testing the MM patients' samples in Shengjing hospital. Crystal structure of HLA-E was obtained from Protein Data Bank (PDB ID: 3CDG) which was used to design targeting peptides with Molecular Operating Environment software. By analyzing interaction between CD94/NKG2A and HLA-E, a peptide with twelve amino acids was screened as a model peptide. Peptides library was constructed by randomly replaced non-key amino acid. Peptide-protein docking method was used to identify high affinity peptides. PEPTIDE 1-3 and model peptide were synthesized and identified the affinity to HLA-E by flow cytometer and confocal laser microscopy. At last, PEPTIDE3 (NALDEYCEDKNR) was found with the highest affinity. Taking all, HLA-E is a new treatment target, and PEPTIDE 3 is an ideal high affinity target-binding peptide candidate.

Skp2 in the ubiquitin-proteasome system: A comprehensive review

The ubiquitin-proteasome system (UPS) is a complex process that regulates protein stability and activity by the sequential actions of E1, E2 and E3 enzymes to influence diverse aspects of eukaryotic cells. However, due to the diversity of proteins in cells, substrate selection is a highly critical part of the process. As a key player in UPS, E3 ubiquitin ligases recruit substrates for ubiquitination specifically. Among them, RING E3 ubiquitin ligases which are the most abundant E3 ubiquitin ligases contribute to diverse cellular processes. The multisubunit cullin-RING ligases (CRLs) are the largest family of RING E3 ubiquitin ligases with tremendous plasticity in substrate specificity and regulate a vast array of cellular functions. The F-box protein Skp2 is a component of CRL1 (the prototype of CRLs) which is expressed in many tissues and participates in multiple cellular functions such as cell proliferation, metabolism, and tumorigenesis by contributing to the ubiquitination and subsequent degradation of several specific tumor suppressors. Most importantly, Skp2 plays a pivotal role in a plethora of cancer-associated signaling pathways. It enhances cell growth, accelerates cell cycle progression, promotes migration and invasion, and inhibits cell apoptosis among others. Hence, targeting Skp2 may represent a novel and attractive strategy for the treatment of different human cancers overexpressing this oncogene. In this review article, we summarized the known roles of Skp2 both in health and disease states in relation to the UPS.