Inhibiting the role of Skp2 suppresses cell proliferation and tumorigenesis of human gastric cancer cells via the upregulation of p27kip1

Implication of protein post translational modifications in gastric cancer

Gastric cancer (GC) is one of the most common and highly lethal malignant tumors worldwide, and its occurrence and development are regulated by multiple molecular mechanisms. Post-translational modifications (PTM) common forms include ubiquitylation, phosphorylation, acetylation and methylation. Emerging research has highlighted lactylation and glycosylation. The diverse realm of PTM and PTM crosstalk is linked to many critical signaling events involved in neoplastic transformation, carcinogenesis and metastasis. This review provides a comprehensive overview of the impact of PTM on the occurrence and progression of GC. Specifically, aberrant PTM have been shown to alter the proliferation, migration, and invasion capabilities of GC cells. Moreover, PTM are closely associated with resistance to chemotherapeutic agents in GC. Notably, this review also discusses the phenomenon of PTM crosstalk, highlighting the interactions among PTM and their roles in regulating signaling pathways and protein functions. Therefore, in-depth investigation into the mechanisms of PTM and the development of targeted therapeutic strategies hold promise for advancing early diagnosis, treatment, and prognostic evaluation of GC, offering novel insights and future research directions.

Hypoxia-induced S-phase kinase-interacting protein 2 knockdown repressed the progression of melanoma through extracellular signal-regulated kinase 1/2 pathway

Objective

Hypoxia intensely drives the development of malignant tumors, including skin cutaneous melanoma (SKCM). S-phase kinase-interacting protein 2 (SKP2) is known to participate in the progression of human tumors. The purpose of this study is to explore whether SKP2 acts as a hypoxic response gene during SKCM progression.

Material and Methods

SKP2 expression in SKCM tissues was analyzed using The Cancer Genome Atlas database. Anoxic experiments were conducted to simulate an anoxic environment. 5-Ethynyl-2'-deoxyuridine and colony formation assays were used to evaluate SKCM cell growth. Scratch healing and Transwell assays were applied to measure the migration and invasion abilities of SKCM cells. An immunoblotting assay was used to detect the levels of extracellular signal-regulated kinase (ERK)1/2 pathway proteins. In addition, the ERK-specific agonist LM22B-10 was added to confirm whether the ERK1/2 signaling pathway is required for SKP2-mediated SKCM progression under hypoxic conditions.

Results

SKP2 was significantly upregulated in SKCM tissues and closely related to adverse outcomes in patients. Moreover, SKP2 levels increased in SKCM cells under normoxic conditions and further elevated under hypoxic conditions. SKP2 deficiency led to the reduced proliferation, migration, and invasion potential of cells under hypoxic conditions. Mechanically, SKP2 silencing blocked the ERK1/2 pathway in hypoxic cells, and the activation of the ERK1/2 pathway rescued the suppression effect of SKP2 on the hypoxia-induced progression of SKCM.

Conclusion

SKP2 deficiency repressed the hypoxic-induced progression of SKCM through the ERK1/2 pathway. This novel discovery regarding the SKP2/ERK1/2 axis might provide new insights into the pathogenesis of SKCM.

Prognostic significance of p27 in colorectal cancer: a meta-analysis and bioinformatics analysis

Background

In the past, numerous investigations have delved into the influence of p27 (p27kip) on the prognosis and clinicopathological characteristics of colorectal cancer (CRC), yielding conclusions that are not universally statistically significant, thus rendering the discourse rather contentious.

Methods

We collected available articles published before August 2024 and extracted data to analyze the association between the expression of p27 and the prognosis and clinicopathological features of CRC. In addition, we used Gene Expression Profiling Interactive Analysis (GEPIA), University of Alabama at Birmingham's Cancer Data Analysis Portal (UALCAN), and the Human Protein Atlas (HPA) to validate our results.

Results

Through an extensive examination of four prominent databases, a total of 21 original articles encompassing a cohort of 3,378 patients were identified. The findings indicated that a low expression of p27 could lead to shorter overall survival (OS) [hazard ratio (HR) = 0.44, 95% confidence interval (95%CI) = 0.31-0.61, Z = 4.89, p = 0.000] and disease-free survival (DFS) (HR = 0.40, 95%CI = 0.28-0.59, Z = 4.75, p = 0.000). In addition, a low expression of p27 predisposed tumors to the right colon [odds ratio (OR) = 0.61, 95%CI = 0.46-0.82, Z = 3.32, p = 0.001] and limited tumor differentiation (OR = 0.56, 95%CI = 0.41-0.77, Z = 3.62, p = 0.000), but had no effect on TNM staging (OR = 0.80, 95%CI = 0.52-1.22, Z = 1.05, p = 0.295), lymph node metastasis (OR = 0.90, 95%CI = 0.25-3.28, Z = 0.16, p = 0.876), and tumor size (OR = 0.94, 95%CI = 0.54-1.65, Z = 0.21, p = 0.835). The results from GEPIA and UALCAN showed that p27 had no effect on TNM staging, lymph node metastasis, DFS, and OS; moreover, there was no expression difference between tumor tissues and normal tissues. The findings from the HPA indicated that there was lower expression of p27 in tumor tissues compared with normal tissues.

Conclusion

Although inconsistent results were reached with the bioinformatics analysis from this meta-analysis, it was confirmed that a low expression of p27 can adversely affect the prognosis of patients with CRC and make a meaningful impact on a part of the clinicopathological features in the meta-analysis with abundant data. In the future, predicting the prognosis of patients with CRC and guiding treatment might emerge as a significant objective.

Role for the F-box proteins in heart diseases

The maintenance of cardiac homeostasis necessitates proper protein turnover, which is regulated by the ubiquitin-proteasome system. F-box proteins are one type of E3 ubiquitin ligases, and accumulating evidence suggests that dysregulation of FBPs exacerbates heart diseases. Therefore, in this review, we summarized the F-box proteins present in the heart, which can be divided into three types based on their repeated sequences, namely FBXO (Fbxo32, Fbxo25, Fbxo44, Fbxo27 and Fbxo28), FBXW (Fbxw7 and Fbxw5), and FBXL (Fbxl1, Fbxl10, Fbxl16 and Fbxl2). Moreover, the physiological and pathological roles and the functional mechanisms of these F-box proteins were elucidated within the cardiac context, providing new theories and strategies for the prevention and treatment of heart diseases.

Role of F-box proteins in human upper gastrointestinal tumors

Protein ubiquitination and degradation is an essential physiological process in almost all organisms. As the key participants in this process, the E3 ubiquitin ligases have been widely studied and recognized. F-box proteins, a crucial component of E3 ubiquitin ligases that regulates diverse biological functions, including cell differentiation, proliferation, migration, and apoptosis by facilitating the degradation of substrate proteins. Currently, there is an increasing focus on studying the role of F-box proteins in cancer. In this review, we present a comprehensive overview of the significant contributions of F-box proteins to the development of upper gastrointestinal tumors, highlighting their dual roles as both carcinogens and tumor suppressors. We delve into the molecular mechanisms underlying the involvement of F-box proteins in upper gastrointestinal tumors, exploring their interactions with specific substrates and their cross-talks with other key signaling pathways. Furthermore, we discuss the implications of F-box proteins in radiotherapy resistance in the upper gastrointestinal tract, emphasizing their potential as clinical therapeutic and prognostic targets. Overall, this review provides an up-to-date understanding of the intricate involvement of F-box proteins in human upper gastrointestinal tumors, offering valuable insights for the identification of prognostic markers and the development of targeted therapeutic strategies.

Inhibitors Targeting the F-BOX Proteins

F-box proteins are involved in multiple cellular processes through ubiquitylation and consequent degradation of targeted substrates. Any significant mutation in F-box protein-mediated proteolysis can cause human malformations. The various cellular processes F-box proteins involved include cell proliferation, apoptosis, invasion, angiogenesis, and metastasis. To target F-box proteins and their associated signaling pathways for cancer treatment, researchers have developed thousands of F-box inhibitors. The most advanced inhibitor of FBW7, NVD-BK M120, is a powerful P13 kinase inhibitor that has been proven to bring about apoptosis in cancerous human lung cells by disrupting levels of the protein known as MCL1. Moreover, F-box Inhibitors have demonstrated their efficacy for treating certain cancers through targeting particular mutated proteins. This paper explores the key studies on how F-box proteins act and their contribution to malignancy development, which fabricates an in-depth perception of inhibitors targeting the F-box proteins and their signaling pathways that eventually isolate the most promising approach to anti-cancer treatments.

LncRNA POU6F2-AS2 contributes to malignant phenotypes and paclitaxel resistance by promoting SKP2 expression in stomach adenocarcinoma

This study aimed to investigate the role and mechanism of POU6F2-AS2 in the development of gastric cancer. POU6F2-AS2 expression was considerably higher in clinical stomach adenocarcinoma (STAD) tissues and gastric cancer cell lines (MKN-28 and MGC-803) than in neighbouring normal tissues and gastric mucosa epithelial cells (GES-1). POU6F2-AS2 overexpression resulted in a low overall survival probability, progression-free survival probability and post progression survival probability, as well as increased cell viability, migration and invasion of gastric cancer cells, thereby inhibiting apoptosis. Based on RNA pull-down, cycloheximide and MG132 incubation experiments, POU6F2-AS2 promoted SKP2 by stabilizing NONO expression. In addition, in vivo silencing of POU6F2-AS2 in gastric cancer cells can inhibit tumour progression and produce a synergistic antitumour effect when combined with paclitaxel. POU6F2-AS2 is overexpressed in STAD, which is attributed to a bad prognosis. In vitro and in vivo experiments have confirmed that the POU6F2-AS2/NONO/SKP2 axis promotes STAD progression, and that the silencing of POU6F2-AS2 plays a synergistic antitumour effect when combined with paclitaxel. Therefore, POU6F2-AS2 may be potentially developed as a target to inhibit STAD and reduce chemoresistance.

UPS: Opportunities and challenges for gastric cancer treatment

Gastric cancer remains the fourth most frequently diagnosed malignancy and the fifth leading cause of cancer-related mortality worldwide owning to the lack of efficient drugs and targets for therapy. Accumulating evidence indicates that UPS, which consists of E1, E2, and E3 enzymes and proteasome, plays an important role in the GC tumorigenesis. The imbalance of UPS impairs the protein homeostasis network during development of GC. Therefore, modulating these enzymes and proteasome may be a promising strategy for GC target therapy. Besides, PROTAC, a strategy using UPS to degrade the target protein, is an emerging tool for drug development. Thus far, more and more PROTAC drugs enter clinical trials for cancer therapy. Here, we will analyze the abnormal expression enzymes in UPS and summarize the E3 enzymes which can be developed in PROTAC so that it can contribute to the development of UPS modulator and PROTAC technology for GC therapy.

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).

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.

Pine needle hexane extract promote cell cycle arrest and premature senescence via p27KIP1 upregulation gastric cancer cells

Pinus densiflora sieb. et zucc.(pine needle) is a traditional medicine used in several East Asian countries. However, the efficacy of pine needle has rarely been reported. In this study showed that the anti-proliferative effects and the mechanisms of hexane layer of pine needle MeOH extract (PNH) on gastric cancer cells. At first, PNH inhibited the proliferation of gastric cancer cells in a dose-dependent manner. Moreover, PNH treatment induced G1 phase cell cycle arrest through the increased p27^KIP1 expression and decreased cyclin dependent kinase (CDKs) activity. Furthermore, PNH treatment induced premature senescence without oncogenic stress, through the expression of p27^KIP1 and Skp2. Taken together, these results showed that PNH inhibited gastric cancer cell proliferation through the induction of G1-cell cycle arrest and premature senescence via induced p27^KIP1 expression, as controlled by Skp2 reduction. Also, PNH could be a candidate for anti-gastric cancer treatment and may be useful in the development of anti-gastric cancer drugs.

Chemical probes of Skp2-mediated p27 ubiquitylation and degradation

Skp2 is a member of the F-box family of proteins that serve as substrate-specific adaptors in Skp1-CUL1-ROC1-F-box (SCF) E3 ubiquitin ligases. Skp2 (Fbxl1) directly binds to the tumor suppressor p27 in the context of the SCF^Skp2 E3 ubiquitin ligase to ubiquitylate and target-phosphorylated p27 for proteasomal degradation. As p27 is a powerful suppressor of growth in a variety of cells, and as Skp2 is also overexpressed in many human cancers, Skp2 is considered an oncogene and an intriguing drug target. However, despite 20 years of investigation, a valid chemical inhibitor of Skp2-mediated degradation of p27 has not been identified. Recently, an increasing number of compounds designed to have this bioactivity have been reported. Here, we conduct a meta-analysis of the evidence regarding bioactivity, structure, and medicinal chemistry in order to evaluate and compare these Skp2 inhibitor compounds. Despite chemically diverse compounds with a wide array of Skp2-mediated p27 ubiquitylation inhibition properties reported by several independent groups, no current chemical probe formally qualifies as a validated pharmaceutical hit compound. This finding suggests that our knowledge of the structural biochemistry of the Skp2-p27 complex remains incomplete and highlights the need for novel modes of inquiry.

Role of p27Kip1 as a transcriptional regulator

The protein p27Kip1 is a member of the Cip/Kip family of cyclin-dependent kinase (Cdk) inhibitors. It interacts with both the catalytic and the regulatory subunit (cyclin) and introduces a region into the catalytic cleave of the Cdk inducing its inactivation. Its inhibitory capacity can be modulated by specific tyrosine phosphorylations. p27Kip1 also behaves as a transcriptional regulator. It associates with specific chromatin domains through different transcription factors. ChIP on chip, ChIP-seq and expression microarray analysis allowed the identification of the transcriptional programs regulated by p27Kip1. Thus, important cellular functions as cell division cycle, respiration, RNA processing, translation and cell adhesion, are under p27Kip1 regulation. Moreover, genes involved in pathologies as cancer and neurodegeneration are also regulated by p27Kip1, suggesting its implication in these pathologies. The carboxyl moiety of p27Kip1 can associate with different proteins, including transcriptional regulators. In contrast, its NH2-terminal region specifically interacts with cyclin-Cdk complexes. The general mechanistic model of how p27Kip1 regulates transcription is that it associates by its COOH region to the transcriptional regulators on the chromatin and by the NH2-domain to cyclin-Cdk complexes. After Cdk activation it would phosphorylate the specific targets on the chromatin leading to gene expression. This model has been demonstrated to apply in the transcriptional regulation of p130/E2F4 repressed genes involved in cell cycle progression. We summarize in this review our current knowledge on the role of p27Kip1 in the regulation of transcription, on the transcriptional programs under its regulation and on its relevance in pathologies as cancer and neurodegeneration.

Amentoflavone suppresses tumor growth in ovarian cancer by modulating Skp2

AIM

Ovarian cancer is one of most common malignancies in women and is associated with high reoccurrence rate and poor prognosis. This study is designed to investigate the anti-tumor effects of amentoflavone (AF), one of the major active ingredients of S. tamariscina, against ovarian cancer.

MATERIALS AND METHODS

Human ovarian cancer cell lines SKOV3 and OVCAR-3 were used in this study. The effect of AF on cell viability was examined by CCK-8 assay. Cell apoptosis and cell cycle distribution was determined by flow cytometry. ROS generation was detected using fluorescent staining. Expression of signaling molecules was determined by western blots. Xenograft model was established to evaluate the therapeutic efficacy of AF in vivo.

KEY FINDINGS

Our results showed that AF could significantly suppress cell proliferation, induce apoptosis and block cell cycle progression. Mechanistically, downregulation of S-phase kinase protein 2 (Skp2) by AF contributed to its anti-tumor effect against ovarian cancer. Furthermore, our results showed that AF repressed the expression of Skp2 through ROS/AMPK/mTOR signaling. The anti-tumor effect of AF against ovarian cancer was also confirmed in a xenograft animal model.

SIGNIFICANCE

Overall, our present findings highlighted the potential of AF in the treatment of ovarian cancer. Moreover, our study also provided a new elucidation regarding the anti-tumor mechanisms of AF.

RETRACTED: Physcion 8-O-β-glucopyranosideregulates cell cycle, apoptosis, and invasion in glioblastoma cells through modulating Skp2

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief, following the initial request of the corresponding author. The journal has further requested the author to provide explanations for the figure similarities with papers previously published by different authors. However, the author was not able to fulfil the request. The panels U251/PG+Skp2 cDNA from Figure 4E and U251/Vehicle from Figure 6D appear similar to the panels SOX2 shRNA from Figure 3D and CoCl2 from Figure 6B of the article previously published by Yan-tao Han, Xue-hong Chen, Hui Gao, Jun-li Ye and Chun-bo Wang in Acta Pharmacologica Sinica 37(2) (2016) 264–275 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4753366/. The panel U251/PG from Figure 6B appears similar to the panel KYSE30/miR-370 mimic + PIM1 vector from Figure 5D of the article previously published by Yantao Han, Xiuwei Yang, Ning Zhao, Jianjun Peng, Hui Gao and Xia Qiu in the American Journal of Cancer Research 6(12) (2016) 2755–2771 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5199752/.