The Skp2-SCF E3 ligase regulates Akt ubiquitination, glycolysis, herceptin sensitivity, and tumorigenesis

Periostin overexpression is associated with worse prognosis in nasopharyngeal carcinoma from endemic area: a cohort study

Purpose

Nasopharyngeal carcinoma (NPC) is a heterogeneous disease. We searched for genes that function in cell adhesion in GSE12452, a published transcriptomic database. We found that POSTN, which encodes periostin (POSTN), was significantly upregulated in NPC tumorigenesis. Herein, we sought to analyze the expression of POSTN and its prognostic significances in patients with NPC.

Materials and methods

In this single-institution retrospective study, we determined and analyzed POSTN expression by immunohistochemistry and H-score method, respectively, in 124 patients with NPC. The results indicated that POSTN expression was correlated with the clinicopathologic features, disease-specific survival (DSS), distant metastasis-free survival (DMFS), and local recurrence-free survival (LRFS) of NPC. We performed univariate and multivariate analyses to determinate the statistical significance.

Results

High POSTN expression was significantly associated with lymph node metastasis (p=0.004) and advanced American Joint Committee on Cancer (AJCC) stage (p=0.006). In univariate analysis, high POSTN expression served as a significant prognostic factor for worse DSS (p=0.0002), DMFS (p=0.0138), and LRFS (p=0.0028). In multivariate Cox regression analyses, which was adjusted for AJCC stages, POSTN expression was independently associated with cancer-related death (HR: 2.311; 95% CI: 1.327-4.027; p=0.003) and local tumor recurrence (HR: 3.187; 95% CI: 1.108-4.408; p=0.024).

Conclusion

High POSTN expression is associated with tumor aggressiveness and worse clinical outcomes in NPC, indicating that it may be a potential prognostic biomarker and a therapeutic target.

Complex role of SIRT6 in NF-κB pathway regulation

The NF-κB pathway regulates cell physiology under stress conditions. We have recently described a novel NF-κB regulatory mechanism, by which SIRT6 induces cysteine monoubiquitination of the methyltransferase SUV39H1. This causes SUV39H1 dissociation from the gene encoding the NF-κB inhibitor IκBα,  increasing its expression and leading to NF-κB pathway inactivation.

USP18 promotes breast cancer growth by upregulating EGFR and activating the AKT/Skp2 pathway

Recent studies have suggested that ubiquitin-specific peptidase (USP)18 may act as an oncogene in various types of cancer. Although the role of USP18 in breast cancer cell lines has been elucidated, the underlying mechanisms and clinical role of USP18 in breast cancer are currently not well understood. The bioinformatics analysis and experimental results of the present study demonstrated that aberrant promoter methylation led to increased expression of USP18 in breast cancer. In addition, correlation analysis suggested that a negative correlation between methylation and USP18 mRNA expression was observed in The Cancer Genome Atlas database. USP18 promoted cell proliferation, colony formation and cell cycle progression in vitro. Furthermore, the Gene Set Enrichment Analysis results demonstrated that USP18 may be negatively associated with apoptosis in patients with breast cancer. Bioinformatics analysis results indicated that USP18 was also revealed to be associated with the protein kinase B (AKT) signaling pathway and mammary tumorigenesis in vivo. In addition, the results indicated that USP18 may promote the epidermal growth factor (EGF)-mediated EGF receptor (EGFR)/AKT/S‑phase kinase-associated protein 2 (Skp2) pathway by upregulating EGFR and Skp2 in a AKT/forkhead box O3-dependent manner in breast cancer. The results of bioinformatics analysis revealed that increased USP18 expression was associated with a higher TNM stage and unfavorable prognosis in clinical patients. USP18 was also significantly enhanced in patients with human epidermal growth factor receptor 2-positive breast cancer; furthermore, Kaplan‑Meier curve demonstrated that combining USP18 and Skp2 expression improved prognostic capability in breast cancer. Taken together, these results suggested that USP18 may serve a key role in breast cancer development by upregulating EGFR and subsequently activating the AKT/Skp2 feedback loop pathway. The role of USP18 in breast cancer provides a novel insight into the clinical application of the USP18/AKT/Skp2 pathway.

F-box proteins involved in cancer-associated drug resistance

The ubiquitin proteasome system (UPS) regulated human biological processes through the appropriate and efficient proteolysis of cellular proteins. F-box proteins are the vital components of SKP1-CUL1-FBP (SCF)-type E3 ubiquitin ligases that determine substrate specificity. As F-box proteins have the ability to control the degradation of several crucial protein targets associated with drug resistance, the dysregulation of these proteins may lead to induction of chemoresistance in cancer cells. Chemotherapy is one of the most conventional therapeutic approaches of treatment of patients with cancer. However, its exclusive application in clinical settings is restricted due to the development of chemoresistance, which typically results treatment failure. Therefore, overcoming drug resistance is considered as one of the most critical issues that researchers and clinician associated with oncology face. The present review serves to provide a comprehensive overview of F-box proteins and their possible targets as well as their correlation with the chemoresistance and chemosensitization of cancer cells. The article also presents an integrated representation of the complex regulatory mechanisms responsible for chemoresistance, which may lay the foundation to explore sensible candidate drugs for therapeutic intervention.

S-phase kinase-associated protein 2 is involved in epithelial-mesenchymal transition in methotrexate-resistant osteosarcoma cells

Osteosarcoma (OS), a common worldwide primary aggressive bone malignancy, arises from primitive transformed cells of mesenchymal origin and usually attacks adolescents and young adults. Methotrexate (MTX) is the anti-folate drug used as a pivotal chemotherapeutic agent in the treatment of OS. However, patients with OS often develop drug resistance, leading to poor treatment outcomes. In the present study, in order to explore the underlying mechanisms responsible for MTX resistance, we established MTX-resistant OS cells using the U2OS and MG63 cell lines and examined whether MTX-resistant OS cells underwent epithelial-mesenchymal transition (EMT) by Transwell assay, wound healing assay, MTT assay, RT-PCR and western blot analysis. We found that the viability of the MTX-resistant cells remained relatively unaltered following further treatment with MTX compared to the parental cells. The resistant cells appeared to possess a mesenchymal phenotype, with an elongated and more spindle-like shape, and acquired enhanced invasive, migratory and attachment abilities. The measurement of EMT markers also supported EMT transition in the MTX-resistant OS cells. Our result further demonstrated that the overexpression of S-phase kinase-associated protein 2 (Skp2) was closely involved in the resistance of OS cells to MTX and in the acquirement of EMT properties. Thus, the pharmacological inhibition of Skp2 may prove to be a novel therapeutic strategy with which to overcome drug resistance in OS.

New Insights into Protein Kinase B/Akt Signaling: Role of Localized Akt Activation and Compartment-Specific Target Proteins for the Cellular Radiation Response

Genetic alterations driving aberrant activation of the survival kinase Protein Kinase B (Akt) are observed with high frequency during malignant transformation and cancer progression. Oncogenic gene mutations coding for the upstream regulators or Akt, e.g., growth factor receptors, RAS and phosphatidylinositol-3-kinase (PI3K), or for one of the three Akt isoforms as well as loss of the tumor suppressor Phosphatase and Tensin Homolog on Chromosome Ten (PTEN) lead to constitutive activation of Akt. By activating Akt, these genetic alterations not only promote growth, proliferation and malignant behavior of cancer cells by phosphorylation of various downstream signaling molecules and signaling nodes but can also contribute to chemo- and radioresistance in many types of tumors. Here we review current knowledge on the mechanisms dictating Akt’s activation and target selection including the involvement of miRNAs and with focus on compartmentalization of the signaling network. Moreover, we discuss recent advances in the cross-talk with DNA damage response highlighting nuclear Akt target proteins with potential involvement in the regulation of DNA double strand break repair.

Skp2-dependent reactivation of AKT drives resistance to PI3K inhibitors

The PI3K-AKT kinase signaling pathway is frequently deregulated in human cancers, particularly breast cancer, where amplification and somatic mutations of PIK3CA occur with high frequency in patients. Numerous small-molecule inhibitors targeting both PI3K and AKT are under clinical evaluation, but dose-limiting toxicities and the emergence of resistance limit therapeutic efficacy. Various resistance mechanisms to PI3K inhibitors have been identified, including de novo mutations, feedback activation of AKT, or cross-talk pathways. We found a previously unknown resistance mechanism to PI3K pathway inhibition that results in AKT rebound activation. In a subset of triple-negative breast cancer cell lines, treatment with a PI3K inhibitor or depletion of PIK3CA expression ultimately promoted AKT reactivation in a manner dependent on the E3 ubiquitin ligase Skp2, the kinases IGF-1R (insulin-like growth factor 1 receptor) and PDK-1 (phosphoinositide-dependent kinase-1), and the cell growth and metabolism-regulating complex mTORC2 (mechanistic target of rapamycin complex 2), but was independent of PI3K activity or PIP₃ production. Resistance to PI3K inhibitors correlated with the increased abundance of Skp2, ubiquitylation of AKT, cell proliferation in culture, and xenograft tumor growth in mice. These findings reveal a ubiquitin signaling feedback mechanism by which PI3K inhibitor resistance may emerge in aggressive breast cancer cells.

A novel reporter for real-time, quantitative imaging of AKT-directed K63-poly-ubiquitination in living cells

Post-translational K63-linked poly-ubiquitination of AKT is required for its membrane recruitment and phosphorylation dependent activation in response to growth-factor stimulation. Current assays for target specific poly-ubiquitination involve cumbersome enzymatic preparations and semi-quantitative readouts. We have engineered a reporter that can quantitatively and in a target specific manner report on AKT-directed K63-polyubiquitination (K63UbR) in live cells. The reporter constitutes the AKT-derived poly-ubiquitination substrate peptide, a K63 poly-ubiquitin binding domain (UBD) as well as the split luciferase protein complementation domains. In cells, wherein signaling events upstream of AKT are activated (e.g. either EGFR or IGFR), poly-ubiquitination of the reporter leads to a stearic constraint that prevents luciferase complementation. However, upon inhibition of growth factor receptor signaling, loss of AKT poly-ubiquitination results in a decrease in interaction between the target peptide and the UBD, allowing for reconstitution of the split luciferase domains and therefore increased bioluminescence in a quantitative and dynamic manner. The K63UbR was confirmed to be suitable for high throughput screen (HTS), thus providing an excellent tool for small molecule or siRNA based HTS to discover new inhibitors or identify novel regulators of this key signaling node. Furthermore, the K63UbR platform could be adapted for non-invasive monitoring of additional target specific K63-polyubiquitination events in live cells.

Pim kinase isoforms: devils defending cancer cells from therapeutic and immune attacks

Pim kinases are being implicated in oncogenic process in various human cancers. Pim kinases primarily deal with three broad categories of functions such as tumorigenesis, protecting cells from apoptotic signals and evading immune attacks. Here in this review, we discuss the regulation of Pim kinases and their expression, and how these kinases defend cancer cells from therapeutic and immune attacks with special emphasis on how Pim kinases maintain their own expression during apoptosis and cellular transformation, defend mitochondria during apoptosis, defend cancer cells from immune attack, defend cancer cells from therapeutic attack, choose localization, self-regulation, activation of oncogenic transcription, metabolic regulation and so on. In addition, we also discuss how Pim kinases contribute to tumorigenesis by regulating cellular transformation and glycolysis to reinforce the importance of Pim kinases in cancer and cancer stem cells.

Quinacrine upregulates p21/p27 independent of p53 through autophagy-mediated downregulation of p62-Skp2 axis in ovarian cancer

We have previously shown that the anti-malarial compound Quinacrine (QC) inhibits ovarian cancer (OC) growth by modulating autophagy. In the present study we extended these studies to identify the molecular pathways regulated by QC to promote apoptosis independent of p53 status in OC. QC exhibited strong anti-cancer properties in OC cell lines in contrast to other anti-malarial autophagy inhibiting drugs. QC treatment selectively upregulated cell cycle inhibitor p21, and downregulated F box protein Skp2 and p62/SQSTM1 expression independent of p53 status. Genetic downregulation of key autophagy protein ATG5 abolished QC-mediated effects on both cell cycle protein p21/Skp2 as well as autophagic cargo protein p62. Furthermore, genetic silencing of p62/SQSTM1 resulted in increased sensitivity to QC-mediated apoptosis, downregulated Skp2 mRNA and increased accumulation of p21 expression. Likewise, genetic knockdown of Skp2 resulted in the upregulation of p21 and p27 and increased sensitivity of OC cells to QC treatment. In contrast, transient overexpression of exogenous p62-HA plasmid rescued the QC-mediated Skp2 downregulation indicating the positive regulation of Skp2 by p62. Collectively, these data indicate that QC-mediated effects on cell cycle proteins p21/Skp2is autophagy-dependent and p53-independent in high grade serious OC cells.

TRAF6 regulates proliferation of stromal cells in the transition and peripheral zones of benign prostatic hyperplasia via Akt/mTOR signaling

BACKGROUND

Increased prostatic smooth muscle tone and hyperplastic growth contribute to urethral obstruction and voiding symptoms in benign prostatic hyperplasia (BPH). It has been suggested that different proliferative potential of stromal cells between transition zone (TZ) and adjoining regions of the prostate plays a significant role in the development of BPH. However, the molecular mechanisms of this hyperplastic process remain unclear. We found tumor necrosis factor receptor-associated factor 6 (TRAF6) highly expressed in TZ stromal cells compared to peripheral zone (PZ) stromal cells by gene array analyzes. Therefore, we aim to study the potential mechanisms of stromal TRAF6 in promoting BPH progression.

METHODS

Stromal cells obtained from BPH-derived primary cultures. The TRAF6-siRNA vector were constructed and transfected into cultured human BPH primary TZ stromal cells, and TRAF6-overexpressing vector were constructed and transfected into cultured human BPH primary PZ stromal cells. Stromal cells were recombined with BPH-1 cells then subcutaneously inoculated into the kidney capsule of male nude mice. Cell proliferation was evaluated by CCK-8 assay. Multiple proteins in the Akt/mTOR pathway were assessed using western blot.

RESULTS

TRAF6 levels were increased in TZ stroma compared with PZ stroma of BPH. The in vitro cell culture and in vivo cell recombination revealed that selective downregulation of TRAF6 in TZ stromal cells led to suppression of the proliferation, while upregulation of TRAF6 in PZ stromal cells enhanced the proliferation. We found that the Phosphorylation and Ubiquitination of Akt as well as the Phosphorylation of mTOR, P70^S6K were decreased when TRAF6 was downregulated in primary cultured TZ stromal cells of BPH.

CONCLUSIONS

TRAF6 can promote the proliferation of stromal cells of BPH via Akt/mTOR signaling. Our results may make stromal TRAF6 responsible for zonal characteristic of BPH and as a promising therapeutic strategy for BPH treatment.

Ubiquitin ligases in oncogenic transformation and cancer therapy

The cellular response to external stress signals and DNA damage depends on the activity of ubiquitin ligases (E3s), which regulate numerous cellular processes, including homeostasis, metabolism and cell cycle progression. E3s recognize, interact with and ubiquitylate protein substrates in a temporally and spatially regulated manner. The topology of the ubiquitin chains dictates the fate of the substrates, marking them for recognition and degradation by the proteasome or altering their subcellular localization or assembly into functional complexes. Both genetic and epigenetic alterations account for the deregulation of E3s in cancer. Consequently, the stability and/or activity of E3 substrates are also altered, in some cases leading to downregulation of tumour-suppressor activities and upregulation of oncogenic activities. A better understanding of the mechanisms underlying E3 regulation and function in tumorigenesis is expected to identify novel prognostic markers and to enable the development of the next generation of anticancer therapies. This Review summarizes the oncogenic and tumour-suppressor roles of selected E3s and highlights novel opportunities for therapeutic intervention.

The sweet trap in tumors: aerobic glycolysis and potential targets for therapy

Metabolic change is one of the hallmarks of tumor, which has recently attracted a great of attention. One of main metabolic characteristics of tumor cells is the high level of glycolysis even in the presence of oxygen, known as aerobic glycolysis or the Warburg effect. The energy production is much less in glycolysis pathway than that in tricarboxylic acid cycle. The molecular mechanism of a high glycolytic flux in tumor cells remains unclear. A large amount of intermediates derived from glycolytic pathway could meet the biosynthetic requirements of the proliferating cells. Hypoxia-induced HIF-1α, PI3K-Akt-mTOR signaling pathway, and many other factors, such as oncogene activation and tumor suppressor inactivation, drive cancer cells to favor glycolysis over mitochondrial oxidation. Several small molecules targeting glycolytic pathway exhibit promising anticancer activity both in vitro and in vivo. In this review, we will focus on the latest progress in the regulation of aerobic glycolysis and discuss the potential targets for the tumor therapy.

Lysine demethylase 2A promotes stemness and angiogenesis of breast cancer by upregulating Jagged1

Alterations of histone methylation dynamically regulated by methyltransferases and demethylases are frequently found in human cancers. Here, we showed that expression of lysine demethylase 2A (KDM2A) is markedly increased in human breast cancer and its overexpression is associated with tumor progression and poor prognosis. Knockdown of KDM2A in breast cancer cells reduced proliferation but not viability. Gene set enrichment analysis revealed that inhibition of KDM2A down-regulates angiogenic genes with concurrent reduction of Jagged1 (JAG1), NOTCH1 and HEY1 in the NOTCH signaling. Chromatin immunoprecipitation- quantitative polymerase chain reaction (ChIP-qPCR) demonstrated the binding of KDM2A to the JAG1 promoter and the increase of methylation of Lys-36 of histone H3 (H3K36) in KDM2A-depleted MDA-MB-231 cells. Tumorsphere formation was significantly reduced in KDM2A-depleted cells which could be reversed by ectopic expression of JAG1. A selective KDM2A inhibitor daminozide also decreased the number of tumorsphere and the number of CD24-/CD44hi cells. In addition, daminozide acted synergistically with cisplatin in cell killing. We identified SOX2 as a direct transcriptional target of KDM2A to promote cancer stemness. Depletion of KDM2A in MDA-MB-231 cells attenuated NOTCH activation and tube formation in co-cultured endothelial cells. Two pro-angiogenic factors JAG1 and PDGFA are key mediators for KDM2A to enhance angiogenesis. Finally, inhibition of KDM2A significantly decreased tumor growth and angiogenesis in orthotopic animal experiments. Collectively, we conclude that KDM2A functions as an oncogene in breast cancer by upregulating JAG1 to promote stemness, chemoresistance and angiogenesis.

Assessing the clinical utility of genomic expression data across human cancers

Cancer molecular profiling provides better understanding of tumor mechanisms and helps to improve the existing cancer management. Here we present the gene expression signatures from ∼9000 human tumors with clinical information across 32 malignancies from The Cancer Genome Atlas project (TCGA). Major predictors from the RNA sequencing data that were significantly correlated with cancer survival were identified. The expression level of these prognostic genes revealed significant genomic pathways that were clinically relevant to survival outcomes across human cancers. Furthermore, it is shown that in most cancer types, combinations of these genomic signatures with clinical information might yield improved predictions. Thus, with respect to clinical utility, our study reveals the promising values of genomic data from the pan-cancer perspective.

Paeoniflorin exerts antitumor effects by inactivating S phase kinase-associated protein 2 in glioma cells

Paeoniflorin (PF), a natural compound isolated from Paeoniae radix, has been shown to exert antitumor effects in various types of human cancers including glioma. However, the mechanism of action is not well understood. S-phase kinase-associated protein (Skp)2 functions as an oncogene in many cancers. In the present study, we investigated whether Skp2 mediates the anti-glioma activity of PF. We found that PF inhibited glioma cell proliferation, migration and invasion, and induced G2/M arrest and apoptosis. Skp2 expression was downregulated in glioma cells treated with PF. PF-induced antitumor effects in glioma cells were abolished by Skp2 overexpression but were enhanced by RNA interference of Skp2. Moreover, PF treatment inhibited U87 cell-derived tumor growth in a xenograft mouse model. These results demonstrate that PF exerts its antitumor effects in part by inhibiting Skp2 expression in glioma cells and could be a promising therapeutic agent for glioma therapy.

Novel Insights Into E3 Ubiquitin Ligase in Cancer Chemoresistance

Drug resistance can obstruct successful cancer chemotherapy. The ubiquitin-proteasome pathway has emerged as a crucial player that controls steady-state protein levels regulating multiple biological processes, such as cell cycle, cellular proliferation, apoptosis, and DNA damage response, which are involved in oncogenesis, cancer development, prognosis, and drug resistance. E3 ligases perform the final step in the ubiquitination cascade, and determine which protein becomes ubiquitylated by specifically binding the substrate protein. They are promising drug targets thanks to their ability to regulate protein stability and functions. Although patient survival has increased in recent years with the availability of novel agents, chemoresistance remains a major problem in cancer management. E3 ligases attract increasing attention with advances in chemoresistance knowledge. To explore the role of E3 ligase in cancer chemotherapy resistance and the underlying mechanism, we summarize the growing number of E3 ligases and their substrate proteins, which have emerged as crucial players in cancer chemoresistance and targeted therapies.

FBXO2, a novel marker for metastasis in human gastric cancer

FBXO2 belongs to the F-box family of proteins, is a cytoplasmic protein and ubiquitin ligase F-box protein with specificity for high-mannose glycoproteins. Recently published studies indicate that other members of the F-box family, such as SKP2 and FBXW7, are involved in the development of gastric cancer. The role of FBXO2 in the process of tumorigenesis, including gastric cancer, is still unknown. In this study, we show that the level of FBXO2 is highly correlated with lymph node metastasis, and that overall survival (OS) of patients with high FBXO2 expression is significantly shorter than patients with low FBXO2 expression. FBXO2 promoted the proliferation and migration of human gastric cancer cells, whereas knockdown of FBXO2 by siRNA led to a decrease in those activities. Down-regulating FBXO2 reduced epithelial-mesenchymal transition (EMT) in gastric cancer cells, with increased expression of E-cadherin and decreased expression of N-cadherin and vimentin. In summary, our findings suggest that FBXO2-regulated EMT led to carcinogenicity in gastric cancer and may be a novel target in the diagnosis and treatment of gastric cancer.

t-Darpp Activates IGF-1R Signaling to Regulate Glucose Metabolism in Trastuzumab-Resistant Breast Cancer Cells

Purpose: Increased glycolysis and glucose dependence is a hallmark of malignancy that enables tumors to maximize cell proliferation. In HER2⁺ cancers, an increase in glycolytic capacity is associated with trastuzumab resistance. IGF-1R activation and t-Darpp overexpression both confer trastuzumab resistance in breast cancer. We therefore investigated a role for IGF-1R and t-Darpp in regulating glycolytic capacity in HER2⁺ breast cancers.Experimental Design: We examined the relationship between t-Darpp and IGF-1R expression in breast tumors and their respective relationships with patient survival. To assess t-Darpp's metabolic effects, we used the Seahorse flux analyzer to measure glucose metabolism in trastuzumab-resistant SK-BR-3 cells (SK.Her^R) that have high endogenous t-Darpp levels and SK.tDrp cells that stably overexpress exogenous t-Darpp. To investigate t-Darpp's mechanism of action, we evaluated t-Darpp:IGF-1R complexes by coimmunoprecipitation and proximity ligation assays. We used pathway-specific inhibitors to study the dependence of t-Darpp effects on IGF-1R signaling. We used siRNA knockdown to determine whether glucose reliance in SK.Her^R cells was mediated by t-Darpp.Results: In breast tumors, PPP1R1B mRNA levels were inversely correlated with IGF-1R mRNA levels and directly associated with shorter overall survival. t-Darpp overexpression was sufficient to increase glucose metabolism in SK.tDrp cells and essential for the glycolytic phenotype of SK.Her^R cells. Recombinant t-Darpp stimulated glucose uptake, glycolysis, and IGF-1R-Akt signaling in SK-BR-3 cells. Finally, t-Darpp stimulated IGF-1R heterodimerization with ErbB receptors and required IGF-1R signaling to confer its metabolic effects.Conclusions: t-Darpp activates IGF-1R signaling through heterodimerization with EGFR and HER2 to stimulate glycolysis and confer trastuzumab resistance. Clin Cancer Res; 24(5); 1216-26. ©2017 AACR.

Targeting protein quality control pathways in breast cancer

The efficient production, folding, and secretion of proteins is critical for cancer cell survival. However, cancer cells thrive under stress conditions that damage proteins, so many cancer cells overexpress molecular chaperones that facilitate protein folding and target misfolded proteins for degradation via the ubiquitin-proteasome or autophagy pathway. Stress response pathway induction is also important for cancer cell survival. Indeed, validated targets for anti-cancer treatments include molecular chaperones, components of the unfolded protein response, the ubiquitin-proteasome system, and autophagy. We will focus on links between breast cancer and these processes, as well as the development of drug resistance, relapse, and treatment.

F-box proteins in epigenetic regulation of cancer

Epigenetic abnormalities are now realized as important as genetic alterations in contributing to the initiation and progression of cancer. Recent advancements in the cancer epigenetics field have identified extensive alterations of the epigenetic network in human cancers, including histone modifications and DNA methylation. F-box proteins, the substrate receptors of SCF (SKP1-Cullin1-F-box protein) E3 ubiquitin ligases, can directly and indirectly affect the balance of epigenetic regulation. In this brief review, we discuss our current understanding of F-box proteins in cellular epigenetic regulation and how dysregulation of these processes contribute to cancer development.

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.

Composition and Regulation of the Cellular Repertoire of SCF Ubiquitin Ligases

SCF (Skp1-Cullin-F-box) ubiquitin ligases comprise several dozen modular enzymes that have diverse roles in biological regulation. SCF enzymes share a common catalytic core containing Cul1⋅Rbx1, which is directed toward different substrates by a variable substrate receptor (SR) module comprising 1 of 69 F-box proteins bound to Skp1. Despite the broad cellular impact of SCF enzymes, important questions remain about the architecture and regulation of the SCF repertoire, including whether SRs compete for Cul1 and, if so, how this competition is managed. Here, we devise methods that preserve the in vivo assemblages of SCF complexes and apply quantitative mass spectrometry to perform a census of these complexes (the "SCFome") in various states. We show that Nedd8 conjugation and the SR exchange factor Cand1 have a profound effect on shaping the SCFome. Together, these factors enable rapid remodeling of SCF complexes to promote biased assembly of SR modules bound to substrate.

The Glycolytic Switch in Tumors: How Many Players Are Involved?

Reprogramming of cellular metabolism is a hallmark of cancers. Cancer cells more readily use glycolysis, an inefficient metabolic pathway for energy metabolism, even when sufficient oxygen is available. This reliance on aerobic glycolysis is called the Warburg effect, and promotes tumorigenesis and malignancy progression. The mechanisms of the glycolytic shift in tumors are not fully understood. Growing evidence demonstrates that many signal molecules, including oncogenes and tumor suppressors, are involved in the process, but how oncogenic signals attenuate mitochondrial function and promote the switch to glycolysis remains unclear. Here, we summarize the current information on several main mediators and discuss their possible mechanisms for triggering the Warburg effect.

The roles of ubiquitin modifying enzymes in neoplastic disease

The initial experiments performed by Rose, Hershko, and Ciechanover describing the identification of a specific degradation signal in short-lived proteins paved the way to the discovery of the ubiquitin mediated regulation of numerous physiological functions required for cellular homeostasis. Since their discovery of ubiquitin and ubiquitin function over 30years ago it has become wholly apparent that ubiquitin and their respective ubiquitin modifying enzymes are key players in tumorigenesis. The human genome encodes approximately 600 putative E3 ligases and 80 deubiquitinating enzymes and in the majority of cases these enzymes exhibit specificity in sustaining either pro-tumorigenic or tumour repressive responses. In this review, we highlight the known oncogenic and tumour suppressive effects of ubiquitin modifying enzymes in cancer relevant pathways with specific focus on PI3K, MAPK, TGFβ, WNT, and YAP pathways. Moreover, we discuss the capacity of targeting DUBs as a novel anticancer therapeutic strategy.

S-phase kinase-associated protein 2 promotes cell growth and motility in osteosarcoma cells

Skp2 (S-phase kinase-associated protein 2) plays an oncogenic role in a variety of human cancers. However, the function of Skp2 in osteosarcoma (OS) is elusive. Therefore, in the current study, we explore whether Skp2 exerts its oncogenic function in OS. The cell growth, apoptosis, invasion and cell cycle were measured in OS cells after Skp2 overexpression. We found that overexpression of Skp2 enhanced cell growth, and inhibited cell apoptosis in OS cells. Moreover, we observed that upregulation of Skp2 accelerated cell cycle progression in OS cells. Furthermore, the ability of migration and invasion was enhanced in Skp2 overexpressing OS cells. Mechanically, our Western blotting data suggested that Skp2 decreased the expression of E-cadherin, Foxo1, p21, and p57, but increased MMP-9 in OS cells. In conclusion, our study demonstrated that Skp2 exhibited an oncogenic function in OS cells, suggesting that inhibition of Skp2 may be a novel approach for the treatment of OS.

Increased mitochondrial fusion allows the survival of older animals in diverse C. elegans longevity pathways

Mitochondria are dynamic organelles that undergo fusion and fission events. Mitochondrial dynamics are required for mitochondrial viability and for responses to changes in bioenergetic status. Here we describe an insulin-signaling and SCFLIN-23-regulated pathway that controls mitochondrial fusion in Caenorhabditis elegans by repressing the expression of the mitochondrial proteases SPG-7 and PPGN-1. This pathway is required for mitochondrial fusion in response to physical exertion, and for the associated extension in lifespan. We show that diverse longevity pathways exhibit increased levels of elongated mitochondria. The increased mitochondrial fusion is essential for longevity in the diverse longevity pathways, as inhibiting mitochondrial fusion reduces their lifespans to wild-type levels. Our results suggest that increased mitochondrial fusion is not a major driver of longevity, but rather is essential to allow the survival of older animals beyond their normal lifespan in diverse longevity pathways.Mitochondria can undergo shape changes as a result of fusion and fission events. Here the authors describe how insulin signalling regulates mitochondrial fusion in C. elegans, and show that mitochondrial fusion is necessary, but not sufficient, for longevity of worms with mutations that increase lifespan.

Epidermal Growth Factor Receptor activation promotes ADA3 acetylation through the AKT-p300 pathway

The ADA3 (Alteration/Deficiency in Activation 3) protein is an essential adaptor component of several Lysine Acetyltransferase (KAT) complexes involved in chromatin modifications. Previously, we and others have demonstrated a crucial role of ADA3 in cell cycle progression and in maintenance of genomic stability. Recently, we have shown that acetylation of ADA3 is key to its role in cell cycle progression. Here, we demonstrate that AKT activation downstream of Epidermal Growth Factor Receptor (EGFR) family proteins stimulation leads to phosphorylation of p300, which in turn promotes the acetylation of ADA3. Inhibition of upstream receptor tyrosine kinases (RTKs), HER1 (EGFR)/HER2 by lapatinib and the accompanying reduction of phospho-AKT levels led to a decrease in p300 phosphorylation and ADA3 protein levels. The p300/PCAF inhibitor garcinol also destabilized the ADA3 protein in a proteasome-dependent manner and an ADA3 mutant with K→R mutations exhibited a marked increase in half-life, consistent with opposite role of acetylation and ubiquitination of ADA3 on shared lysine residues. ADA3 knockdown led to cell cycle inhibitory effects, as well as apoptosis similar to those induced by lapatinib treatment of HER2+ breast cancer cells, as seen by accumulation of CDK inhibitor p27, reduction in mitotic marker pH3(S10), and a decrease in the S-phase marker PCNA, as well as the appearance of cleaved PARP. Taken together our results reveal a novel RTK-AKT-p300-ADA3 signaling pathway involved in growth factor-induced cell cycle progression.

TGF-β promotes PI3K-AKT signaling and prostate cancer cell migration through the TRAF6-mediated ubiquitylation of p85α

Transforming growth factor-β (TGF-β) is a pluripotent cytokine that regulates cell fate and plasticity in normal tissues and tumors. The multifunctional cellular responses evoked by TGF-β are mediated by the canonical SMAD pathway and by noncanonical pathways, including mitogen-activated protein kinase (MAPK) pathways and the phosphatidylinositol 3'-kinase (PI3K)-protein kinase B (AKT) pathway. We found that TGF-β activated PI3K in a manner dependent on the activity of the E3 ubiquitin ligase tumor necrosis factor receptor-associated factor 6 (TRAF6). TRAF6 polyubiquitylated the PI3K regulatory subunit p85α and promoted the formation of a complex between the TGF-β type I receptor (TβRI) and p85α, which led to the activation of PI3K and AKT. Lys⁶³-linked polyubiquitylation of p85α on Lys⁵¹³ and Lys⁵¹⁹ in the iSH2 (inter-Src homology 2) domain was required for TGF-β-induced activation of PI3K-AKT signaling and cell motility in prostate cancer cells and activated macrophages. Unlike the activation of SMAD pathways, the TRAF6-mediated activation of PI3K and AKT was not dependent on the kinase activity of TβRI. In situ proximity ligation assays revealed that polyubiquitylation of p85α was evident in aggressive prostate cancer tissues. Thus, our data reveal a molecular mechanism by which TGF-β activates the PI3K-AKT pathway to drive cell migration.

Mechanical cue-induced YAP instructs Skp2-dependent cell cycle exit and oncogenic signaling

Mechanical tensions are usually generated during development at spatially defined regions within tissues. Such physical cues dictate the cellular decisions of proliferation or cell cycle arrest. Yet, the mechanisms by which mechanical stress controls the cell cycle are not yet fully understood. Here, we report that mechanical cues function upstream of Skp2 transcription in human breast cancer cells. We found that YAP, the mechano-responsive oncogenic Hippo signaling effector, directly promotes Skp2 transcription. YAP inactivation induces cell cycle exit (G0) by down-regulating Skp2, causing p21/p27 to accumulate. Both Skp2 reconstitution and p21/p27 depletion can rescue the observed defect in cell cycle progression. In the context of a tissue-mimicking 3D culture system, Skp2 inactivation effectively suppresses YAP-driven oncogenesis and aberrant stiff 3D matrix-evoked epithelial tissue behaviors. Finally, we also found that the expression of Skp2 and YAP is positively correlated in breast cancer patients. Our results not only reveal the molecular mechanism by which mechanical cues induce Skp2 transcription, but also uncover a role for YAP-Skp2 oncogenic signaling in the relationship between tissue rigidity and cancer progression.

AKT/PKB Signaling: Navigating the Network

The Ser and Thr kinase AKT, also known as protein kinase B (PKB), was discovered 25 years ago and has been the focus of tens of thousands of studies in diverse fields of biology and medicine. There have been many advances in our knowledge of the upstream regulatory inputs into AKT, key multifunctional downstream signaling nodes (GSK3, FoxO, mTORC1), which greatly expand the functional repertoire of AKT, and the complex circuitry of this dynamically branching and looping signaling network that is ubiquitous to nearly every cell in our body. Mouse and human genetic studies have also revealed physiological roles for the AKT network in nearly every organ system. Our comprehension of AKT regulation and functions is particularly important given the consequences of AKT dysfunction in diverse pathological settings, including developmental and overgrowth syndromes, cancer, cardiovascular disease, insulin resistance and type 2 diabetes, inflammatory and autoimmune disorders, and neurological disorders. There has also been much progress in developing AKT-selective small molecule inhibitors. Improved understanding of the molecular wiring of the AKT signaling network continues to make an impact that cuts across most disciplines of the biomedical sciences.

MicroRNA-508-5p suppresses metastasis in human gastric cancer by targeting S-phase kinase‑associated protein 2

S-phase kinase-associated protein 2 (SKP2), a potent oncogene was revealed to be upregulated in gastric cancer (GC) tissue samples, in which SKP2 was inversely correlated with microRNA (miR)‑508‑5p transcripts. In present study, the functional effect of miR‑508‑5p on SKP2 and its metastatic potential were investigated in SGC‑7901 GC cells. Significant downregulation of the miR‑508‑5p transcript was associated with the progression of GC. Furthermore, the overexpression of miR‑508‑5p was demonstrated to inhibit the proliferation, migration and invasion of SGC‑7901 cells, as well as induced cell apoptosis and cell cycle arrest at the G0/G1 phase in vitro. The overexpression of miR‑508‑5p was able to downregulate the expression of the SKP2 oncogene, through a mechanism by which miR‑508‑5p directly targeted the SKP2 gene. Thus, regulating transcriptional and post‑transcriptional SKP2 expression, as demonstrated using luciferase reporter assays, reverse transcription‑quantitative polymerase chain reaction analysis and immunoblotting assays. The results of the present study identified that miR‑508‑5p functionally affects the SKP2 gene and reduces metastatic potential in GC, suggesting a novel role of miR‑508‑5p in the regulation of SKP2 and cell cycle.

Inhibition of Skp2 suppresses the proliferation and invasion of osteosarcoma cells

Osteosarcoma (OS) is a common bone tumor that mainly affects children and young adults. S-phase kinase‑associated protein 2 (Skp2) has been characterized to play a critical oncogenic role in a variety of human malignancies. However, the biological function of Skp2 in OS remains largely obscure. In the present study, we elucidated the role of Skp2 in cell growth, cell cycle, apoptosis and migration in OS cells. We found that depletion of Skp2 inhibited cell growth in both MG-63 and SW 1353 cells. Moreover, we observed that depletion of Skp2 triggered cell apoptosis in two OS cell lines. Furthermore, downregulation of Skp2 induced cell cycle arrest in the G0/G1 phase in OS cells. Notably, our wound healing assay results revealed that inhibition of Skp2 suppressed cell migration in OS cells. Invariably, our western blot results demonstrated that depletion of Skp2 in OS cells inhibited activation of pAkt and increased p27 expression in OS cells, suggesting that Skp2 exerted its oncogenic function partly through the regulation of Akt and p27. Our findings revealed that targeting Skp2 could be a promising therapeutic strategy for the treatment of OS.

Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Hippo Signaling Suppresses Cell Ploidy and Tumorigenesis through Skp2

Polyploidy can lead to aneuploidy and tumorigenesis. Here, we report that the Hippo pathway effector Yap promotes the diploid-polyploid conversion and polyploid cell growth through the Akt-Skp2 axis. Yap strongly induces the acetyltransferase p300-mediated acetylation of the E3 ligase Skp2 via Akt signaling. Acetylated Skp2 is exclusively localized to the cytosol, which causes hyper-accumulation of the cyclin-dependent kinase inhibitor p27, leading to mitotic arrest and subsequently cell polyploidy. In addition, the pro-apoptotic factors FoxO1/3 are overly degraded by acetylated Skp2, resulting in polyploid cell division, genomic instability, and oncogenesis. Importantly, the depletion or inactivation of Akt or Skp2 abrogated Hippo signal deficiency-induced liver tumorigenesis, indicating their epistatic interaction. Thus, we conclude that Hippo-Yap signaling suppresses cell polyploidy and oncogenesis through Skp2.

Associations among Metabolism, Circadian Rhythm and Age-Associated Diseases

Accumulating epidemiological studies have implicated a strong link between age associated metabolic diseases and cancer, though direct and irrefutable evidence is missing. In this review, we discuss the connection between Warburg effects and tumorigenesis, as well as adaptive responses to environment such as circadian rhythms on molecular pathways involved in metabolism. We also review the central role of the sirtuin family of proteins in physiological modulation of cellular processes and age-associated metabolic diseases. We also provide a macroscopic view of how the circadian rhythm affects metabolism and may be involved in cell metabolism reprogramming and cancer pathogenesis. The aberrations in metabolism and the circadian system may lead to age-associated diseases directly or through intermediates. These intermediates may be either mutated or reprogrammed, thus becoming responsible for chromatin modification and oncogene transcription. Integration of circadian rhythm and metabolic reprogramming in the holistic understanding of metabolic diseases and cancer may provide additional insights into human diseases.

Phosphorylation by mTORC1 stablizes Skp2 and regulates its oncogenic function in gastric cancer

Background

Both mTOR and Skp2 play critical roles in gastric cancer (GC) tumorigenesis. However, potential mechanisms for the association between these two proteins remains unidentified.

Methods

The regulatory role for mTORC1 in Skp2 stability was tested using ubiquitination assay. The functions of p-Skp2 (phosphorylation of Skp2) were studied in vitro and in vivo. Expression of p-Skp2 and p-mTOR (phosphorylation of mTOR) were shown in GC lines and in 169 human primary GC tissues.

Results

mTORC1 can directly interact with Skp2 and phosphorylated Skp2 at Ser64, which sequentially protect Skp2 from ubiquitination and degradation. Furthermore, the phospho-deficient p-Skp2 (S64) mutant significantly suppresses GC cell proliferation and tumorigenesis. The expression of p-Skp2 was associated with p-mTOR in GC cell lines and tissues. Interestingly, the combination of p-Skp2 and p-mTOR was a better predictor of survival than either factor alone.

Conclusion

The mTORC1 function to regulate Skp2 by Ser64 phosphorylation may represent an oncogenic event in GC tumorigenesis. Moreover, our study also indicates that Skp2 Ser64 expression is a potential indicator in the treatment of GC patients using mTORC1 inhibitor.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0649-0) contains supplementary material, which is available to authorized users.

USP49 negatively regulates tumorigenesis and chemoresistance through FKBP51-AKT signaling

The AKT pathway is a fundamental signaling pathway that mediates multiple cellular processes, such as cell proliferation and survival, angiogenesis, and glucose metabolism. We recently reported that the immunophilin FKBP51 is a scaffolding protein that can enhance PHLPP-AKT interaction and facilitate PHLPP-mediated dephosphorylation of AKT at Ser473, negatively regulating AKT activation. However, the regulation of FKBP51-PHLPP-AKT pathway remains unclear. Here we report that a deubiquitinase, USP49, is a new regulator of the AKT pathway. Mechanistically, USP49 deubiquitinates and stabilizes FKBP51, which in turn enhances PHLPP's capability to dephosphorylate AKT Furthermore, USP49 inhibited pancreatic cancer cell proliferation and enhanced cellular response to gemcitabine in a FKBP51-AKT-dependent manner. Clinically, decreased expression of USP49 in patients with pancreatic cancer was associated with decreased FKBP51 expression and increased AKT phosphorylation. Overall, our findings establish USP49 as a novel regulator of AKT pathway with a critical role in tumorigenesis and chemo-response in pancreatic cancer.

IL-17A promotes the proliferation of human nasopharyngeal carcinoma cells through p300-mediated Akt1 acetylation

Interleukin (IL)-17A is a T helper (Th)17 cell-secreted cytokine that is able to induce various inflammatory responses. There is emerging evidence that IL-17A is generated in the cancer microenvironment of human nasopharyngeal carcinoma (NPC). However, the role of IL-17A in NPC remains unclear. Thus, the present study aimed to examine the direct influence of IL-17A stimulation on the proliferation of human NPC cells and identify the underlying molecular mechanisms. Furthermore, E1A binding protein p300 (p300)-mediated AKT serine/threonine kinase 1 (Akt1) acetylation and its role in regulating the proliferation of NPC cells was investigated. The results of the current study demonstrated that IL-17A stimulation in vitro increased the proliferation of human NPC cells. Furthermore, Akt1 acetylation was identified to be enhanced in human NPC cells induced by IL-17A. Additionally, p300 induction was demonstrated to be required for Akt1 acetylation in human NPC cells following exposure to IL-17A. Functionally, p300-mediated Akt1 acetylation contributed to the proliferation of human NPC cells stimulated by IL-17A. In conclusion, the results of the present demonstrate a novel activity of IL-17A that promotes human NPC cell proliferation via p300-mediated Akt1 acetylation. This may provide a potential strategy for the treatment of patients with NPC through the inhibition of IL-17A or its receptors.

Skp2 deficiency restricts the progression and stem cell features of castration-resistant prostate cancer by destabilizing Twist

Castration-resistant prostate cancer (CRPC) remains a major clinical challenge because of the lack of effective targeted therapy for its treatment. The mechanism underlying how CRPC gains resistance toward hormone depletion and other forms of chemotherapy is poorly understood. Research on understanding the factors that drive these processes is desperately needed to generate new therapies to cure the disease. Here, we discovered a fundamental role of S-phase protein kinase 2 (Skp2) in the formation and progression of CRPC. In transgenic adenocarcinoma mouse prostate model, Skp2 depletion leads to a profound repression of prostate tumor growth and distal metastasis and substantially prolonged overall survival. We revealed that Skp2 regulates CRPC through Twist-mediated oncogenic functions including epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC) acquisitions. Mechanistically, Skp2 interacted with Twist and promoted the non-degradative ubiquitination of Twist. Consequently, Skp2 stabilized Twist protein expression by preventing proteasomal degradation of Twist by β-TrCP. We found that Twist overexpression augments CSC self-renewal and population and that Skp2 inhibition reverts Twist's effects on CSC regulation. Furthermore, genetically depleting or pharmacologically inactivating Skp2 synergistically re-sensitized CRPC cells toward chemotherapies such as paclitaxel or doxorubicin. Together, this study uncovering Skp2-mediated Twist stabilization and oncogenic functions in CRPC offers new knowledge on how CRPC progresses and acquires chemoresistance during tumor progression. It provides proof of principle that Skp2 targeting is a promising approach to combat metastatic CRPC by targeting Twist and CSCs.

Induction of G2M Arrest by Flavokawain A, a Kava Chalcone, Increases the Responsiveness of HER2-Overexpressing Breast Cancer Cells to Herceptin

HER2/neu positive breast tumors predict a high mortality and comprise 25%-30% of breast cancer. We have shown that Flavokawain A (FKA) preferentially reduces the viabilities of HER2-overexpressing breast cancer cell lines (i.e., SKBR3 and MCF7/HER2) versus those with less HER2 expression (i.e., MCF7 and MDA-MB-468). FKA at cytotoxic concentrations to breast cancer cell lines also has a minimal effect on the growth of non-malignant breast epithelial MCF10A cells. FKA induces G2M arrest in cell cycle progression of HER2-overexpressing breast cancer cell lines through inhibition of Cdc2 and Cdc25C phosphorylation and downregulation of expression of Myt1 and Wee1 leading to increased Cdc2 kinase activities. In addition, FKA induces apoptosis in SKBR3 cells by increasing the protein expression of Bim and BAX and decreasing expression of Bcl₂, BclX/L, XIAP, and survivin. FKA also downregulates the protein expression of HER-2 and inhibits AKT phosphorylation. Herceptin plus FKA treatment leads to an enhanced growth inhibitory effect on HER-2 overexpressing breast cancer cell lines through downregulation of Myt1, Wee1, Skp2, survivin, and XIAP. Our results suggest FKA as a promising and novel apoptosis inducer and G2 blocking agent that, in combination with Herceptin, enhances for the treatment of HER2-overexpressing breast cancer.

Metabolic Reprogramming by the PI3K-Akt-mTOR Pathway in Cancer

In the past decade, there has been a resurgence of interest in elucidating how metabolism is altered in cancer cells and how such dependencies can be targeted for therapeutic gain. At the core of this research is the concept that metabolic pathways are reprogrammed in cancer cells to divert nutrients toward anabolic processes to facilitate enhanced growth and proliferation. Importantly, physiological cellular signaling mechanisms normally tightly regulate the ability of cells to gain access to and utilize nutrients, posing a fundamental barrier to transformation. This barrier is often overcome by aberrations in cellular signaling that drive tumor pathogenesis by enabling cancer cells to make critical cellular decisions in a cell-autonomous manner. One of the most frequently altered pathways in human cancer is the PI3K-Akt-mTOR signaling pathway. Here, we describe mechanisms by which this signaling network is responsible for controlling cellular metabolism. Through both the post-translational regulation and the induction of transcriptional programs, the PI3K-Akt-mTOR pathway coordinates the uptake and utilization of multiple nutrients, including glucose, glutamine, nucleotides, and lipids, in a manner best suited for supporting the enhanced growth and proliferation of cancer cells. These regulatory mechanisms illustrate how metabolic changes in cancer are closely intertwined with oncogenic signaling pathways that drive tumor initiation and progression.

The Emerging Role of Non-traditional Ubiquitination in Oncogenic Pathways

The addition of ubiquitin to a target protein has long been implicated in the process of degradation and is the primary mediator of protein turnover in the cell. Recently, however, many non-proteolytic functions of ubiquitination have emerged as key regulators of cellular homeostasis. In this review, we will describe the various non-traditional functions of ubiquitination, with particular focus on how they can be used as signaling entities in cancer formation and progression. Elaboration of this topic can lead to a better understanding of oncogenic mechanisms, as well as the discovery of novel druggable proteins within the ubiquitin pathway.

A novel read-through transcript JMJD7-PLA2G4B regulates head and neck squamous cell carcinoma cell proliferation and survival

Recent findings on the existence of oncogenic fusion genes in a wide array of solid tumors, including head and neck squamous cell carcinoma (HNSCC), suggests that fusion genes have become attractive targets for cancer diagnosis and treatment. In this study, we showed for the first time that a read-through fusion gene JMJD7-PLA2G4B is presented in HNSCC, splicing neighboring jumonji domain containing 7 (JMJD7) and phospholipase A2, group IVB (PLA2G4B) genes together. Ablation of JMJD7-PLA2G4B significantly inhibited proliferation of HNSCC cells by promoting G1 cell cycle arrest and increased starvation-induced cell death compared to JMJD7-only knockdown HNSCC cells. Mechanistically, we found that JMJD7-PLA2G4B modulates phosphorylation of Protein Kinase B (AKT) to promote HNSCC cell survival. Moreover, JMJD7-PLA2G4B also regulated an E3 ligase S-phase kinase-associated protein 2 (SKP2) to control the cell cycle progression from G1 phase to S phase by inhibiting Cyclin-dependent kinase inhibitor 1 (p21) and 1B (p27) expression. Our study provides novel insights into the oncogenic control of JMJD7-PLA2G4B in HNSCC cell proliferation and survival, and suggests that JMJD7-PLA2G4B may serve as an important therapeutic target and prognostic marker for HNSCC development and progression.

Perspectives of Reprogramming Breast Cancer Metabolism

Reprogramming of cellular metabolism is one of the hallmarks of breast cancer. Breast cancer cells remodel metabolic network to maintain their transformed state and survive in a harsh tumor microenvironment. Dysregulated metabolism further interacts with cellular signaling and epigenetics to promote breast cancer development. Meanwhile, breast cancer stem cells exhibit unique metabolic features, which are critical for therapeutic resistance and tumor recurrence. Besides, aberrant metabolism of breast cancer cells reshapes tumor microenvironment, such as promoting cancer vascularization and sabotaging tumor immunity, to accelerate tumor progression. These special metabolic traits not only open vulnerabilities of breast cancer by targeting essential metabolic pathways but also provide promising diagnostic and prognostic biomarkers to facilitate clinical investigations. Studies in the last few decades have significantly advanced our understanding of mechanisms underlying the reprogramming of breast cancer metabolism and metabolic regulation of breast cancer biology. Targeting tumor metabolism serves as a potentially effective therapeutic approach to suppress breast cancer.

NOTCH1 and SOX10 are Essential for Proliferation and Radiation Resistance of Cancer Stem-Like Cells in Adenoid Cystic Carcinoma

PURPOSE

Although the existence of cancer stem cells (CSC) in adenoid cystic carcinoma (ACC) has been proposed, lack of assays for their propagation and uncertainty about molecular markers prevented their characterization. Our objective was to isolate CSC from ACC and provide insight into signaling pathways that support their propagation.

EXPERIMENTAL DESIGN

To isolate CSC from ACC and characterize them, we used ROCK inhibitor-supplemented cell culture, immunomagnetic cell sorting, andin vitro/in vivoassays for CSC viability and tumorigenicity.

RESULTS

We identified in ACC CD133-positive CSC that expressed NOTCH1 and SOX10, formed spheroids, and initiated tumors in nude mice. CD133(+)ACC cells produced activated NOTCH1 (N1ICD) and generated CD133(-)cells that expressed JAG1 as well as neural differentiation factors NR2F1, NR2F2, and p27Kip1. Knockdowns ofNOTCH1, SOX10, and their common effectorFABP7had negative effects on each other, inhibited spheroidogenesis, and induced cell death pointing at their essential roles in CSC maintenance. Downstream effects ofFABP7knockdown included suppression of a broad spectrum of genes involved in proliferation, ribosome biogenesis, and metabolism. Among proliferation-linked NOTCH1/FABP7 targets, we identified SKP2 and its substrate p27Kip1. A γ-secretase inhibitor, DAPT, selectively depleted CD133(+)cells, suppressed N1ICD and SKP2, induced p27Kip1, inhibited ACC growthin vivo, and sensitized CD133(+)cells to radiation.

CONCLUSIONS

These results establish in the majority of ACC the presence of a previously uncharacterized population of CD133(+)cells with neural stem properties, which are driven by SOX10, NOTCH1, and FABP7. Sensitivity of these cells to Notch inhibition and their dependence on SKP2 offer new opportunities for targeted ACC therapies.

Resveratrol inhibits Hexokinases II mediated glycolysis in non-small cell lung cancer via targeting Akt signaling pathway

Deregulation of glycolysis was often observed in human cancer cells. In the present study, we reported resveratrol, a small polyphenol, which has been intensively studied in various tumor models, has a profound anti-tumor effect on human non-small cell lung cancer (NSCLC) via regulation of glycolysis. Resveratrol impaired hexokinase II (HK2)-mediated glycolysis, and markedly inhibited anchorage-dependent and -independent growth of NSCLC cells. Exposure to resveratrol decreased EGFR and downstream kinases Akt and ERK1/2 activation. Moreover, we revealed that resveratrol impaired glucose metabolism by mainly inhibiting expression of HK2 mediated by the Akt signaling pathway, and exogenous overexpression of constitutively activated Akt1 in NSCLC cells substantially rescued resveratrol-induced glycolysis suppression. The in vivo data indicated that resveratrol obviously suppressed tumor growth in a xenograft mouse model. Our results suggest targeting HK2 or metabolic enzymes appears to be a new approach for clinical NSCLC prevention or treatment.