SKP2 inactivation suppresses prostate tumorigenesis by mediating JARID1B ubiquitination

Discovery of an efficacious KDM5B PROTAC degrader GT-653 up-regulating IFN response genes in prostate cancer

Epigenetic alterations promote cancer development by regulating the expression of various oncogenes and anti-oncogenes. Histone methylation modification represents a pivotal area in epigenetic research and numerous publications have demonstrated that aberrant histone methylation is highly correlated with tumorigenesis and development. As a key histone demethylase, lysine-specific demethylase 5B (KDM5B) demethylates lysine 4 of histone 3 (H3K4) and serves as a transcriptional repressor of certain tumor suppressor genes. Meanwhile, KDM5B inhibits STING-induced intrinsic immune response of tumor cells or recruits SETDB1 through non-enzymatic function to silence reverse transcription elements to promote immune escape. The conventional small molecule inhibitors can only inhibit the enzymatic function of KDM5B with no effect on the non-enzymatic function. In the article, we present the development of the first series of KDM5B degraders based on CPI-455 to inhibit the non-enzymatic function. Among them, GT-653 showed optimal KDM5B degradation efficiency in a ubiquitin proteasome-dependent manner. GT-653 efficiently reduced KDM5B protein levels without affecting KDM5B transcription. Interestingly, GT-653 increased H3K4me3 levels and activated the type-I interferon signaling pathway in 22RV1 cells without significant phenotypic response on cell proliferation.

Co-targeting SKP2 and KDM5B inhibits prostate cancer progression by abrogating AKT signaling with induction of senescence and apoptosis

BACKGROUND

Prostate cancer (PCa) is the second-leading cause of cancer mortalities in the United States and is the most commonly diagnosed malignancy in men. While androgen deprivation therapy (ADT) is the first-line treatment option to initial responses, most PCa patients invariably develop castration-resistant PCa (CRPC). Therefore, novel and effective treatment strategies are needed. The goal of this study was to evaluate the anticancer effects of the combination of two small molecule inhibitors, SZL-P1-41 (SKP2 inhibitor) and PBIT (KDM5B inhibitor), on PCa suppression and to delineate the underlying molecular mechanisms.

METHODS

Human CRPC cell lines, C4-2B and PC3 cells, were treated with small molecular inhibitors alone or in combination, to assess effects on cell proliferation, migration, senescence, and apoptosis.

RESULTS

SKP2 and KDM5B showed an inverse regulation at the translational level in PCa cells. Cells deficient in SKP2 showed an increase in KDM5B protein level, compared to that in cells expressing SKP2. By contrast, cells deficient in KDM5B showed an increase in SKP2 protein level, compared to that in cells with KDM5B intact. The stability of SKP2 protein was prolonged in KDM5B depleted cells as measured by cycloheximide chase assay. Cells deficient in KDM5B were more vulnerable to SKP2 inhibition, showing a twofold greater reduction in proliferation compared to cells with KDM5B intact (p < 0.05). More importantly, combined inhibition of KDM5B and SKP2 significantly decreased proliferation and migration of PCa cells as compared to untreated controls (p < 0.005). Mechanistically, combined inhibition of KDM5B and SKP2 in PCa cells abrogated AKT activation, resulting in an induction of both cellular senescence and apoptosis, which was measured via Western blot analysis and senescence-associated β-galactosidase (SA-β-Gal) staining.

CONCLUSIONS

Combined inhibition of KDM5B and SKP2 was more effective at inhibiting proliferation and migration of CRPC cells, and this regimen would be an ideal therapeutic approach of controlling CRPC malignancy.

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.

Effect of ubiquitin protease system on DNA damage response in prostate cancer (Review)

Genomic instability is an essential hallmark of cancer, and cellular DNA damage response (DDR) defects drive tumorigenesis by disrupting genomic stability. Several studies have identified abnormalities in DDR-associated genes, and a dysfunctional ubiquitin-proteasome system (UPS) is the most common molecular event in metastatic castration-resistant prostate cancer (PCa). For example, mutations in Speckle-type BTB/POZ protein-Ser119 result in DDR downstream target activation deficiency. Skp2 excessive upregulation inhibits homologous recombination repair and promotes cell growth and migration. Abnormally high expression of a deubiquitination enzyme, ubiquitin-specific protease 12, stabilizes E3 ligase MDM2, which further leads to p53 degradation, causing DDR interruption and genomic instability. In the present review, the basic pathways of DDR, UPS dysfunction, and its induced DDR alterations mediated by genomic instability, and especially the potential application of UPS and DDR alterations as biomarkers and therapeutic targets in PCa treatment, were described.

Lysosome-dependent FOXA1 ubiquitination contributes to luminal lineage of advanced prostate cancer

Changes in FOXA1 (forkhead box protein A1) protein levels are well associated with prostate cancer (PCa) progression. Unfortunately, direct targeting of FOXA1 in progressive PCa remains challenging due to variations in FOXA1 protein levels, increased FOXA1 mutations at different stages of PCa, and elusive post-translational FOXA1 regulating mechanisms. Here, we show that SKP2 (S-phase kinase-associated protein 2) catalyzes K6- and K29-linked polyubiquitination of FOXA1 for lysosomal-dependent degradation. Our data indicate increased SKP2:FOXA1 protein ratios in stage IV human PCa compared to stages I-III, together with a strong inverse correlation (r = -0.9659) between SKP2 and FOXA1 levels, suggesting that SKP2-FOXA1 protein interactions play a significant role in PCa progression. Prostate tumors of Pten/Trp53 mice displayed increased Skp2-Foxa1-Pcna signaling and colocalization, whereas disruption of the Skp2-Foxa1 interplay in Pten/Trp53/Skp2 triple-null mice demonstrated decreased Pcna levels and increased expression of Foxa1 and luminal positive cells. Treatment of xenograft mice with the SKP2 inhibitor SZL P1-41 decreased tumor proliferation, SKP2:FOXA1 ratios, and colocalization. Thus, our results highlight the significance of the SKP2-FOXA1 interplay on the luminal lineage in PCa and the potential of therapeutically targeting FOXA1 through SKP2 to improve PCa control.

A truncated and catalytically inactive isoform of KDM5B histone demethylase accumulates in breast cancer cells and regulates H3K4 tri-methylation and gene expression

KDM5B histone demethylase is overexpressed in many cancers and plays an ambivalent role in oncogenesis, depending on the specific context. This ambivalence could be explained by the expression of KDM5B protein isoforms with diverse functional roles, which could be present at different levels in various cancer cell lines. We show here that one of these isoforms, namely KDM5B-NTT, accumulates in breast cancer cell lines due to remarkable protein stability relative to the canonical PLU-1 isoform, which shows a much faster turnover. This isoform is the truncated and catalytically inactive product of an mRNA with a transcription start site downstream of the PLU-1 isoform, and the consequent usage of an alternative ATG for translation initiation. It also differs from the PLU-1 transcript in the inclusion of an additional exon (exon-6), previously attributed to other putative isoforms. Overexpression of this isoform in MCF7 cells leads to an increase in bulk H3K4 methylation and induces derepression of a gene cluster, including the tumor suppressor Cav1 and several genes involved in the interferon-alpha and -gamma response. We discuss the relevance of this finding considering the hypothesis that KDM5B may possess regulatory roles independent of its catalytic activity.

The KDM5B and KDM1A lysine demethylases cooperate in regulating androgen receptor expression and signalling in prostate cancer

Histone H3 lysine 4 (H3K4) methylation is key epigenetic mark associated with active transcription and is a substrate for the KDM1A/LSD1 and KDM5B/JARID1B lysine demethylases. Increased expression of KDM1A and KDM5B is implicated in many cancer types, including prostate cancer (PCa). Both KDM1A and KDM5B interact with AR and promote androgen regulated gene expression. For this reason, there is great interested in the development of new therapies targeting KDM1A and KDM5B, particularly in the context of castrate resistant PCa (CRPC), where conventional androgen deprivation therapies and androgen receptor signalling inhibitors are no longer effective. As there is no curative therapy for CRPC, new approaches are urgently required to suppress androgen signalling that prevent, delay or reverse progression to the castrate resistant state. While the contribution of KDM1A to PCa is well established, the exact contribution of KDM5B to PCa is less well understood. However, there is evidence that KDM5B is implicated in numerous pro-oncogenic mechanisms in many different types of cancer, including the hypoxic response, immune evasion and PI3/AKT signalling. Here we elucidate the individual and cooperative functions of KDM1A and KDM5B in PCa. We show that KDM5B mRNA and protein expression is elevated in localised and advanced PCa. We show that the KDM5 inhibitor, CPI-455, impairs androgen regulated transcription and alternative splicing. Consistent with the established role of KDM1A and KDM5B as AR coregulators, we found that individual pharmacologic inhibition of KDM1A and KDM5 by namoline and CPI-455 respectively, impairs androgen regulated transcription. Notably, combined inhibition of KDM1A and KDM5 downregulates AR expression in CRPC cells. Furthermore, combined KDM1A and KDM5 inhibition impairs PCa cell proliferation and invasion more than individual inhibition of KDM1A and KDM5B. Collectively our study has identified individual and cooperative mechanisms involving KDM1A and KDM5 in androgen signalling in PCa. Our findings support the further development of KDM1A and KDM5B inhibitors to treat advanced PCa. Further work is now required to confirm the therapeutic feasibility of combined inhibition of KDM1A and KDM5B as a novel therapeutic strategy for targeting AR positive CRPC.

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.

Role of K63-linked ubiquitination in cancer

Ubiquitination is a critical type of post-translational modifications, of which K63-linked ubiquitination regulates interaction, translocation, and activation of proteins. In recent years, emerging evidence suggest involvement of K63-linked ubiquitination in multiple signaling pathways and various human diseases including cancer. Increasing number of studies indicated that K63-linked ubiquitination controls initiation, development, invasion, metastasis, and therapy of diverse cancers. Here, we summarized molecular mechanisms of K63-linked ubiquitination dictating different biological activities of tumor and highlighted novel opportunities for future therapy targeting certain regulation of K63-linked ubiquitination in tumor.

Circ_0087960 stabilizes KDM5B by reducing SKP2 mediated ubiquitination degradation and promotes osteogenic differentiation in periodontal ligament stem cells

Background

Periodontitis is a common chronic oral disease among the world. Periodontal ligament stem cells (PDLSCs) has been proved to be a promising tool for the treatment of periodontitis due to their capability of generating periodontal tissues. Circ_0087960 and KDM5B have been shown to participate in the process of osteogenic differentiation with unclear function and mechanism.

Methods

Circ_0087960 and KDM5B expressions were detected during the osteogenic induction of PDLSCs. The functions of circ_0087960 and KDM5B were validated by manipulating their expression with shRNA. ChIP and luciferase reporter assays were used to prove the KDM5B-based osteogenic gene regulation. Co-IP assay was used to determine the interaction between SKP2 and KDM5B. In vivo ubiquitination assay was used to test the modification of KDM5B by SKP2. RNA pull-down was used to demonstrate the interaction between circ_0087960 and KDM5B.

Results

Circ_0087960 and KDM5B were found to be upregulated in the osteogenic differentiation of PDLSCs and promote the expression of related genes. KDM5B could directly bind and promote the expression of Runx2, ALP and OCN. KDM5B protein level in PDLSCs was controlled by SKP2-mediated protein ubiquitination and degradation. Circ_0087960 was identified to bind to KDM5B protein and protect it against SKP2-induced protein degradation, leading to the upregulation of osteogenic genes.

Conclusion

Circ_0087960 and KDM5B could be applied as promising therapeutic methods to stimulate the osteogenic differentiation of PDLSCs, expanding their capability in the treatment of periodontitis.

The association of prostatic lipids with progression, racial disparity and discovery of biomarkers in prostate cancer

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This study performed lipid profiling on human PCa and BPT tissues matched with patient's age and race, pathological grades and clinical stages.

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The human prostatic lipid profiles were widely associated with the pathogenesis, progression and racial disparity of PCa.

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Neutral lipids had greater impact on pathogenesis, progression and racial disparity of PCa as compared to phospholipids. Cholesteryl ester is the only lipid class significantly higher in PCa than in BPT in all population and stratified AA and CA populations.

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A panel of prostatic lipid parameters in each study population were identified as diagnostic and prognostic biomarkers with high sensitivity, specificity and accuracy simultaneously.

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Lipid profiling on mouse prostatic tissue from mouse PCa model further confirmed the roles of prostatic lipids on the pathogenesis, progression and discovery of diagnostic and prognostic biomarkers of PCa. In addition, this animal model was excellent to investigate prognostic lipid biomarkers in differentiation of indolent from aggressive PCa.

Background

It remains under-investigated whether prostatic lipid profiles are associated with pathogenesis, progression, racial disparity, and discovery of biomarkers in prostate cancer (PCa).

Methods

The electrospray ionization-tandem mass spectrometry was applied to quantitate prostatic lipids in human and mouse PCa and non-cancer prostatic tissues. Biostatistics and bioinformatics were used to compare the concentrations of prostatic lipids at levels of total lipid, group, class and individual species between PCa and benign prostatic tissues, between races, and among pathological conditions of PCa.

Results

Prostatic concentrations of total lipids as well as neutral lipids were significantly higher in PCa than in benign prostatic tissues in all population and Caucasian American population, but not in African American population. The prostatic phospholipid were not statistically different between PCa and benign prostatic tissues in all study populations. Cholesteryl ester is the only lipid class significantly higher in PCa than in benign prostatic tissues in all study populations. A panel of prostatic lipid parameters in each study population was identified as diagnostic and prognostic biomarkers with >60% of sensitivity, specificity and accuracy simultaneously. Lipid profiling on mouse prostatic tissues further confirmed correlation of prostatic lipid profiles to the pathogenesis and progression of PCa. In addition, a few prostatic lipids in mouse can serve as prognostic biomarkers in differentiation of indolent from aggressive PCa.

Conclusion

The prostatic lipids are widely associated with the pathogenesis, progression and racial disparity of PCa. A panel of prostatic lipids can serve as diagnostic, prognostic and race-specific biomarkers for PCa.

Post-Translational Modifications That Drive Prostate Cancer Progression

While a protein primary structure is determined by genetic code, its specific functional form is mostly achieved in a dynamic interplay that includes actions of many enzymes involved in post-translational modifications. This versatile repertoire is widely used by cells to direct their response to external stimuli, regulate transcription and protein localization and to keep proteostasis. Herein, post-translational modifications with evident potency to drive prostate cancer are explored. A comprehensive list of proteome-wide and single protein post-translational modifications and their involvement in phenotypic outcomes is presented. Specifically, the data on phosphorylation, glycosylation, ubiquitination, SUMOylation, acetylation, and lipidation in prostate cancer and the enzymes involved are collected. This type of knowledge is especially valuable in cases when cancer cells do not differ in the expression or mutational status of a protein, but its differential activity is regulated on the level of post-translational modifications. Since their driving roles in prostate cancer, post-translational modifications are widely studied in attempts to advance prostate cancer treatment. Current strategies that exploit the potential of post-translational modifications in prostate cancer therapy are presented.

JARID1B promotes colorectal cancer proliferation and Wnt/β-catenin signaling via decreasing CDX2 level

BACKGROUND

Jumonji AT-rich interactive domain 1B(JARID1B) has been shown to be upregulated in many human cancers and plays a critical role in the development of cancers cells. Nevertheless, its functional role in colorectal cancer (CRC) progression is not fully understood.

METHODS

Herein, JARID1B expression levels were detected in clinical CRC samples by western blotting and qRT-PCR. DLD-1 cells with JARID1B knockdown or overexpression by stably transfected plasmids were used in vitro and in vivo study. Colony formation, 5-ethynyl-20-deoxyuridine (EdU) and Real Time Cellular Analysis (RTCA) assays were used to detect cell proliferation and growth. Transcriptome and CHIP assays were used to examine the molecular biology changes and molecular interaction in these cells. Nude mice was utilized to study the correlation of JARID1B and tumor growth in vivo.

RESULTS

Here, we first observed that JARID1B was significantly upregulated in CRC tissue compared to adjacent normal tissues. In CRC patients, JARID1B high expression was positively relation with poor overall survival. Multivariate analyses revealed that high JARID1B expression was an independent predictive marker for the poor prognosis of CRC. In addition, we found that JARID1B promoted CRC cells proliferation by Wnt/β-catenin signaling pathway. Further studies demonstrated CDX2 as a downstream target of JARID1B, and our data demonstrated that CDX2 is crucial for JARID1B -mediated Wnt/β-catenin signaling pathway. Mechanistically, we demonstrated that JARID1B regulated CDX2 expression through demethylation of H3K4me3.

CONCLUSIONS

CDX2 inhibited by JARID1B-derived H3K4me3 methylation promoted cells proliferation of CRC via Wnt/β-catenin signaling pathway. Therefore, our studies provided a novel insight into the role of JARID1B in CRC cells proliferation and potential new molecular target for treating CRC. Video abstract.

KDM5B Is Essential for the Hyperactivation of PI3K/AKT Signaling in Prostate Tumorigenesis

KDM5B (lysine[K]-specific demethylase 5B) is frequently upregulated in various human cancers including prostate cancer. KDM5B controls H3K4me3/2 levels and regulates gene transcription and cell differentiation, yet the contributions of KDM5B to prostate cancer tumorigenesis remain unknown. In this study, we investigated the functional role of KDM5B in epigenetic dysregulation and prostate cancer progression in cultured cells and in mouse models of prostate epithelium-specific mutant Pten/Kdm5b. Kdm5b deficiency resulted in a significant delay in the onset of prostate cancer in Pten-null mice, whereas Kdm5b loss alone caused no morphologic abnormalities in mouse prostates. At 6 months of age, the prostate weight of Pten/Kdm5b mice was reduced by up to 70% compared with that of Pten mice. Pathologic analysis revealed Pten/Kdm5b mice displayed mild morphologic changes with hyperplasia in prostates, whereas age-matched Pten littermates developed high-grade prostatic intraepithelial neoplasia and prostate cancer. Mechanistically, KDM5B governed PI3K/AKT signaling in prostate cancer in vitro and in vivo. KDM5B directly bound the PIK3CA promoter, and KDM5B knockout resulted in a significant reduction of P110α and PIP3 levels and subsequent decrease in proliferation of human prostate cancer cells. Conversely, KDM5B overexpression resulted in increased PI3K/AKT signaling. Loss of Kdm5b abrogated the hyperactivation of AKT signaling by decreasing P110α/P85 levels in Pten/Kdm5b mice. Taken together, our findings reveal that KDM5B acts as a key regulator of PI3K/AKT signaling; they also support the concept that targeting KDM5B is a novel and effective therapeutic strategy against prostate cancer. SIGNIFICANCE: This study demonstrates that levels of histone modification enzyme KDM5B determine hyperactivation of PI3K/AKT signaling in prostate cancer and that targeting KDM5B could be a novel strategy against prostate cancer.

Targeting histone demethylase KDM5B for cancer treatment

KDM5B (Lysine-Specific Demethylase 5B) erases the methyl group from H3K4me2/3, which performs wide regulatory effects on chromatin structure, and represses the transcriptional function of genes. KDM5B functions as an oncogene and associates with human cancers closely. Targeting KDM5B has been a promising direction for curing cancer since the emergence of potent KDM5B inhibitor CPI-455. In this area, most reported KDM5B inhibitors are Fe (Ⅱ) chelators, which also compete with the cofactor 2-OG in the active pockets. Besides, Some KDM5B inhibitors have been identified through high throughput screening or biochemical screening. In this reviewing article, we summarized the pioneering progress in KDM5B to provide a comprehensive realization, including crystal structure, transcriptional regulation function, cancer-related functions, development of inhibitors, and SAR studies. We hope to provide a comprehensive overview of KDM5B and the development of KDM5B inhibitors.

Histone Demethylase KDM5B as a Therapeutic Target for Cancer Therapy

Lysine-specific demethylase 5B (KDM5B/PLU1/JARID1B) is found to be overexpressed in numerous malignancies, including breast, lung, skin, liver, and prostate cancer. Identification of molecules targeting the KDM5B enzyme could be a potential lead in cancer research. Although many KDM5B inhibitors with promising outcomes have been developed so far, its further application in clinical practice is limited due to toxicity and lack of target specificity. Here, we summarize the significance of targeting KDM5B in anticancer therapy and report the molecular docking studies of some known anti-viral agents, decitabine, entecavir, abacavir, penciclovir, and 3-deazaneplanocin A in the catalytic domain JmjC of KDM5B. These studies show the repurposing potential of identified anti-viral agents in cancer therapy.

Phosphorylation of the histone demethylase KDM5B and regulation of the phenotype of triple negative breast cancer

Epigenetic modifications are known to play critical roles in the expression of genes related to differentiation and dedifferentiation. Histone lysine demethylase KDM5B (PLU-1) catalyzes the demethylation of histone H3 on Lys 4 (H3K4), which results in the repression of gene expression. KDM5B is involved in regulation of luminal and basal cell specific gene expression in breast cancers. However, the mechanisms by which KDM5B is regulated in breast cancer, in particular in response to post-translational signals is not well-defined. Here, we demonstrate that KDM5B is phosphorylated at Ser1456 by the cyclin-dependent kinase 1 (CDK1). Phosphorylation of KDM5B at Ser1456 attenuated the occupancy of KDM5B on the promoters of pluripotency genes. Moreover, KDM5B inhibited the expression of pluripotency genes, SOX2 and NANOG, and decreased the stem cell population in triple-negative breast cancer cell lines (TNBC). We previously reported that the tumor suppressor HEXIM1 is a mediator of KDM5B recruitment to its target genes, and HEXIM1 is required for the inhibition of nuclear hormone receptor activity by KDM5B. Similarly, HEXIM1 is required for regulation of pluripotency genes by KDM5B.

Genetic heterogeneity within collective invasion packs drives leader and follower cell phenotypes

Collective invasion, the coordinated movement of cohesive packs of cells, has become recognized as a major mode of metastasis for solid tumors. These packs are phenotypically heterogeneous and include specialized cells that lead the invasive pack and others that follow behind. To better understand how these unique cell types cooperate to facilitate collective invasion, we analyzed transcriptomic sequence variation between leader and follower populations isolated from the H1299 non-small cell lung cancer cell line using an image-guided selection technique. We now identify 14 expressed mutations that are selectively enriched in leader or follower cells, suggesting a novel link between genomic and phenotypic heterogeneity within a collectively invading tumor cell population. Functional characterization of two phenotype-specific candidate mutations showed that ARP3 enhances collective invasion by promoting the leader cell phenotype and that wild-type KDM5B suppresses chain-like cooperative behavior. These results demonstrate an important role for distinct genetic variants in establishing leader and follower phenotypes and highlight the necessity of maintaining a capacity for phenotypic plasticity during collective cancer invasion.

A Derivate of Benzimidazole-Isoquinolinone Induces SKP2 Transcriptional Inhibition to Exert Anti-Tumor Activity in Glioblastoma Cells

We have previously shown that compound-7g inhibits colorectal cancer cell proliferation and survival by inducing cell cycle arrest and PI3K/AKT/mTOR pathway blockage. However, whether it has the ability to exert antitumor activity in other cancer cells and what is the exact molecular mechanism for its antiproliferation effect remained to be determined. In the present study, compound-7g exhibited strong activity in suppressing proliferation and growth of glioblastoma cells. The inhibitor selectively downregulated F-box protein SKP2 expression and upregulated cell cycle inhibitor p27, and then resulted in G1 cell cycle arrest. Mechanism analysis revealed that compound-7g also provokes the down-regulation of E2F-1, which acts as a transcriptional factor of SKP2. Further results indicated that compound-7g induced an increase of LC3B-II and p62, which causes a suppression of fusion between autophagosome and lysosome. Moreover, compound-7g mediated autophagic flux blockage promoted accumulation of ubiquitinated proteins and then led to endoplasmic reticulum stress. Our study thus demonstrated that pharmacological inactivation of E2F-1-SKP2-p27 axis is a promising target for restricting cancer progression.

High Skp2 expression is associated with a mesenchymal phenotype and increased tumorigenic potential of prostate cancer cells

Skp2 is a crucial component of SCFSkp2 E3 ubiquitin ligase and is often overexpressed in various types of cancer, including prostate cancer (PCa). The epithelial-to-mesenchymal transition (EMT) is involved in PCa progression. The acquisition of a mesenchymal phenotype that results in a cancer stem cell (CSC) phenotype in PCa was described. Therefore, we aimed to investigate the expression and localization of Skp2 in clinical samples from patients with PCa, the association of Skp2 with EMT status, and the role of Skp2 in prostate CSC. We found that nuclear expression of Skp2 was increased in patients with PCa compared to those with benign hyperplasia, and correlated with high Gleason score in PCa patients. Increased Skp2 expression was observed in PCa cell lines with mesenchymal and CSC-like phenotype compared to their epithelial counterparts. Conversely, the CSC-like phenotype was diminished in cells in which SKP2 expression was silenced. Furthermore, we observed that Skp2 downregulation led to the decrease in subpopulation of CD44+CD24- cancer stem-like cells. Finally, we showed that high expression levels of both CD24 and CD44 were associated with favorable recurrence-free survival for PCa patients. This study uncovered the Skp2-mediated CSC-like phenotype with oncogenic functions in PCa.

Translocator Protein PET Imaging in a Preclinical Prostate Cancer Model

PURPOSE

The identification and targeting of biomarkers specific to prostate cancer (PCa) could improve its detection. Given the high expression of translocator protein (TSPO) in PCa, we investigated the use of [¹⁸F]VUIIS1008 (a novel TSPO-targeting radioligand) coupled with positron emission tomography (PET) to identify PCa in mice and to characterize their TSPO uptake.

PROCEDURES

Pten^pc-/-, Trp53^pc-/- prostate cancer-bearing mice (n = 9, 4-6 months old) were imaged in a 7T MRI scanner for lesion localization. Within 24 h, the mice were imaged using a microPET scanner for 60 min in dynamic mode following a retro-orbital injection of ~ 18 MBq [¹⁸F]VUIIS1008. Following imaging, tumors were harvested and stained with a TSPO antibody. Regions of interest (ROIs) were drawn around the tumor and muscle (hind limb) in the PET images. Time-activity curves (TACs) were recorded over the duration of the scan for each ROI. The mean activity concentrations between 40 and 60 min post radiotracer administration between tumor and muscle were compared.

RESULTS

Tumor presence was confirmed by visual inspection of the MR images. The uptake of [¹⁸F]VUIIS1008 in the tumors was significantly higher (p < 0.05) than that in the muscle, where the percent injected dose per unit volume for tumor was 7.1 ± 1.6 % ID/ml and that of muscle was < 1 % ID/ml. In addition, positive TSPO expression was observed in tumor tissue analysis.

CONCLUSIONS

The foregoing preliminary data suggest that TSPO may be a useful biomarker of PCa. Therefore, using TSPO-targeting PET ligands, such as [¹⁸F]VUIIS1008, may improve PCa detectability and characterization.

AKT Inhibition Modulates H3K4 Demethylase Levels in PTEN-Null Prostate Cancer

Hyperactivated AKT kinase due to loss of its negative regulator PTEN influences many aspects of cancer biology, including chromatin. AKT primarily regulates acetyl-CoA production and phosphorylates many histone-modulating enzymes, resulting in their activation or inhibition. Therefore, understanding the therapeutic impact of AKT inhibition on chromatin-related events is essential. Here, we report that AKT inhibition in prostate-specific PTEN knockout mice significantly induces di- and trimethylation of H3K4 with concomitant reduction in H3K9 acetylation. Mechanistically, we observed that AKT inhibition reduces expression of the H3K4 methylation-specific histone demethylases KDM5 family, especially KDM5B expression at transcriptional levels. Furthermore, we observed that AKT negatively regulates miR-137 levels, which transcriptionally represses KDM5B expression. Overexpression of miR-137 significantly reduced KDM5B and increased H3K4 methylation levels but failed to change AKT phosphorylation. Overall, we observed that AKT transcriptionally regulates KDM5B mainly via repression of miR-137. Our data identify a mechanism by which AKT kinase modulates the prostate cancer epigenome through regulating H3K4 methylation. Additional studies on AKT inhibition-mediated induction of H3K4 methylation will help in designing strategies to enhance the therapeutic efficacy of PI3K/AKT inhibitors.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

Jumonji AT-rich interactive domain 1B promotes the growth of pancreatic tumors via the phosphatase and tensin homolog/protein kinase B signaling pathway

Jumonji AT-rich interactive domain 1B (JARID1B) has been revealed to remove methyl residues from methylated lysine 4 on histone H3 (H3K4) and has also been reported to be associated with the progression of numerous types of tumor. However, its roles and mechanisms in pancreatic cancer (PC) remain unknown. The present study demonstrated that JARID1B is elevated in PC and is associated with the growth of pancreatic tumors. Overexpression of JARID1B significantly promoted the proliferation in vitro and tumor formation in vivo of PC cells. Furthermore, silencing the expression of JARID1B in other PC cells revealed opposite effects. Further research revealed that JARID1B exerted its function through modulation of H3K4me3 at the phosphatase and tensin homolog (PTEN) gene promoter which was associated with inactive PTEN transcription. To the best of our knowledge, the present study was the first to demonstrate that JARID1B promotes the growth of PC and that targeting JARID1B may be a useful strategy to suppress the progression of PC.

KDM5B demethylates H3K4 to recruit XRCC1 and promote chemoresistance

Chemotherapy is the main treatment for human cancers including gastric cancer. However, in response to chemotherapeutic drugs, tumor cells can develop drug resistance by reprogramming intracellular metabolic and epigenetic networks to maintain their intrinsic homeostasis. Previously, we have established cisplatin-resistant gastric cancer cells as a drug resistant model, and elucidated the XRCC1 as the core DNA repair mechanism of drug resistance. This study investigated the regulation of XRCC1 by lysine demethylase 5B (KDM5B) in drug resistance. We found that the methylation level of H3K4 decreased significantly in drug-resistant cells. The chemical inhibitor of H3K4 demethylases, JIB-04, restored the methylation of H3K4 and blocked the co-localization of XRCC1 and γH2AX, eventually improved drug sensitivity. We further found that the expression level of KDM5B increased significantly in drug-resistant cells. Knockdown of KDM5B increased the methylation level of H3K4 and blocked the localization of XRCC1 to the DNA damage site, leads to increased drug sensitivity. In the sensitive cells, overexpression of KDM5B suppressed H3K4 methylation levels, which resulted to resistance to cisplatin. Moreover, we found that the posttranslational modification of KDM5B is responsible for its high expression in drug-resistant cells. Through mass spectrometry screening and co-immunoprecipitation validation, we found that the molecular chaperone HSP90 forms a complex with KDM5B in drug resistance cells. Interestingly, HSP90 inhibitor 17-AAG induced KDM5B degradation in a time-and-dose-dependent manner, indicating that HSP90 protected KDM5B from protein degradation. Targeting inhibition of HSP90 and KDM5B reversed drug resistance both in vitro and in vivo. Taken together, molecular chaperon HSP90 interacted with KDM5B to protect it from ubiquitin-dependent proteasomal degradation. Increased KDM5B demethylated H3K4 and facilitated the recruitment of XRCC1 to repair damaged DNA. Therefore, inhibition of HSP90 or KDM5B represented a novel approach to reverse chemoresistance in human cancers.

Epigenetic Regulation in Prostate Cancer Progression

Purpose of Review

An important number of newly identified molecular alterations in prostate cancer affect gene encoding master regulators of chromatin biology epigenetic regulation. This review will provide an updated view of the key epigenetic mechanisms underlying prostate cancer progression, therapy resistance, and potential actionable mechanisms and biomarkers.

Recent Findings

Key players in chromatin biology and epigenetic master regulators has been recently described to be crucially altered in metastatic CRPC and tumors that progress to AR independency. As such, epigenetic dysregulation represents a driving mechanism in the reprograming of prostate cancer cells as they lose AR-imposed identity.

Summary

Chromatin integrity and accessibility for transcriptional regulation are key features altered in cancer progression, and particularly relevant in nuclear hormone receptor-driven tumors like prostate cancer. Understanding how chromatin remodeling dictates prostate development and how its deregulation contributes to prostate cancer onset and progression may improve risk stratification and treatment selection for prostate cancer patients.

Histone demethylase lysine demethylase 5B in development and cancer

Histone methylation is one of the most important chromatin posttranslational modifications. It has a range of influences on nuclear functions including epigenetic inheritance, transcriptional regulation and the maintenance of genome integrity. Changes in histone methylation status take part in various physiological and pathological processes. KDM5B (lysine demethylase 5B, also called JARID1B or PLU-1) encodes the histone H3 lysine4 (H3K4) demethylase and exhibits a strong transcriptional repression activity. KDM5B plays a role in cell differentiation, stem cell self-renewal and other developmental progresses. Recent studies showed that KDM5B expression was increased in breast, bladder, lung, prostate and many other tumors and promotes tumor initiation, invasion and metastasis. Given its association with tumor progression and prognosis of cancer patients, KDM5B was proposed to be a novel target for the prevention and treatment of human cancers. In this review, we will summarize recent advances in our understanding of the regulation and function of KDM5B in development and cancer.

Rottlerin exerts its anti-tumor activity through inhibition of Skp2 in breast cancer cells

Studies have investigated the tumor suppressive role of rottlerin in carcinogenesis. However, the molecular mechanisms of rottlerin-induced anti-tumor activity are largely unclear. Skp2 (S-phase kinase associated protein 2) has been validated to play an oncogenic role in a variety of human malignancies. Therefore, inactivation of Skp2 could be helpful for the treatment of human cancers. In the current study, we explore whether rottlerin could inhibit Skp2 expression, leading to inhibition of cell growth, migration and invasion in breast cancer cells. We found that rottlerin treatment inhibited cell growth, induced apoptosis and cell cycle arrest. We also revealed that rottlerin suppressed cell migration and invasion in breast cancer cells. Mechanically, we observed that rottlerin significantly down-regulated the expression of Skp2 in breast cancer cells. Importantly, overexpression of Skp2 abrogated rottlerin-mediated tumor suppressive activity, whereas down-regulation of Skp2 enhanced rottlerin-triggered anti-tumor function. Strikingly, we identified that rottlerin exhibited its anti-tumor potential partly through inactivation of Skp2 in breast cancer. Our findings indicate that rottlerin could be a potential safe agent for the treatment of breast cancer.

MMP7 interacts with ARF in nucleus to potentiate tumor microenvironments for prostate cancer progression in vivo

ARF couples with TP53 in a canonical signaling pathway to activate cellular senescence for tumor suppressive function under oncogenic insults. However, the mechanisms on aberrant elevation of ARF in cancers are still poorly understood. We previously showed that ARF (p14^ARF in human and p19^Arf in mouse) elevation correlates with PTEN loss and stabilizes SLUG to reduce cell adhesion in prostate cancer (PCa). Here we report that ARF is essential for MMP7 expression, E-Cadherin decrease and the anchorage loss to the extracellular matrix (ECM) in PCa in vitro and in vivo. We found that Mmp7 is aberrantly elevated in cytosol and nucleus of malignant prostate tumors of Pten/Trp53 mutant mice. Interestingly, p19^Arf deficiency strikingly decreases Mmp7 levels but increases E-Cadherin in Pten/Trp53/p19^Arf mice. ARF knockdown markedly reduces MMP7 in human PCa cells. Conversely, tetracycline-inducible expression of ARF increases MMP7 with a decrease of E-Cadherin in PCa cells. Importantly, MMP7 physically binds ARF to show the co-localization in nucleus. Co-expression of MMP7 and ARF promotes cell migration, and MMP7 knockdown decreases wound healing in PCa cells. Furthermore, MMP7 elevation correlates with ARF expression in advanced human PCa. Our findings reveal for the first time that the crosstalk between ARF and MMP7 in nucleus contributes to ECM network in tumor microenvironments in vivo, implicating a novel therapeutic target for advanced PCa treatment.

SIRT6-dependent cysteine monoubiquitination in the PRE-SET domain of Suv39h1 regulates the NF-κB pathway

Sirtuins are NAD⁺-dependent deacetylases that facilitate cellular stress response. They include SirT6, which protects genome stability and regulates metabolic homeostasis through gene silencing, and whose loss induces an accelerated aging phenotype directly linked to hyperactivation of the NF-κB pathway. Here we show that SirT6 binds to the H3K9me3-specific histone methyltransferase Suv39h1 and induces monoubiquitination of conserved cysteines in the PRE-SET domain of Suv39h1. Following activation of NF-κB signaling Suv39h1 is released from the IκBα locus, subsequently repressing the NF-κB pathway. We propose that SirT6 attenuates the NF-κB pathway through IκBα upregulation via cysteine monoubiquitination and chromatin eviction of Suv39h1. We suggest a mechanism based on SirT6-mediated enhancement of a negative feedback loop that restricts the NF-κB pathway.

Sirtuins are involved in the regulation of responses to diverse types of cellular stress. Here the authors describe the SirT6-dependent cysteine monoubiquitination of the histone methyltransferase Suv39h1 as part of a regulatory circuit for the NF-κB pathway.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

miR-19b attenuates H2O2-induced apoptosis in rat H9C2 cardiomyocytes via targeting PTEN

Myocardial ischemia-reperfusion (I-R) injury lacks effective treatments. The miR-17-92 cluster plays important roles in regulating proliferation, apoptosis, cell cycle and other pivotal processes. However, their roles in myocardial I-R injury are largely unknown. In this study, we found that miR-19b was the only member of the miR-17-92 cluster that was downregulated in infarct area of heart samples from a murine model of I-R injury. Meanwhile, downregulation of miR-19b was also detected in H₂O₂-treated H9C2 cells in vitro mimicking oxidative stress occurring during myocardial I-R injury. Using flow cytometry and Western blot analysis, we found that overexpression of miR-19b decreased H₂O₂-induced apoptosis and improved cell survival, while downregulation of that had inverse effects. Furthermore, PTEN was negatively regulated by miR-19b at the protein level while silencing PTEN could completely block the aggravated impact of miR-19b inhibitor on H₂O₂-induced apoptosis in H9C2 cardiomyocytes, indicating PTEN as a downstream target of miR-19b controlling H₂O₂-induced apoptosis. These data indicate that miR-19b overexpression might be a novel therapy for myocardial I-R injury.

Matrine derivative YF-18 inhibits lung cancer cell proliferation and migration through down-regulating Skp2

Lung cancer is the leading cause of cancer related death which needs novel drugs to improve patient outcomes. In this study, we examined the ability of YF-18, a novel matrine derivative to inhibit the growth and migration of lung cancer cells. By cell cycle analysis, wound healing and transwell assays, we found that YF-18 induced G2/M cell cycle arrest and inhibited migration of lung cancer cells in a dose-dependent manner. Further results indicated that YF-18 inhibited cell proliferation and migration through down-regulating Skp2 and up-regulating its substrates, p27 and E-cadherin. Moreover, YF-18 inhibited A549-luciferase cell xenograft tumor growth in a dose-dependent manner. The findings indicate that YF-18 bears therapeutic potentials for lung cancer.

Dysregulated expression of SKP2 and its role in hematological malignancies

S-phase kinase-associated protein 2 (SKP2) is a well-studied F-box protein and a critical part of the Skp1-Cul1-Fbox (SCF) E3 ligase complex. It controls cell cycle by regulating the expression level of p27 and p21 through ubiquitination and proteasomal degradation. SKP2-mediated loss of p27Kip1 is associated with poor clinical outcome in various types of cancers including hematological malignancies. It is however well established that SKP2 is an oncogene, and its targeting may be an attractive therapeutic strategy for the management of hematological malignancies. In this article, we have highlighted the recent findings from our group and other investigators regarding the role of SKP2 in the pathogenesis of hematological malignancies.

MYC Modulation around the CDK2/p27/SKP2 Axis

MYC is a pleiotropic transcription factor that controls a number of fundamental cellular processes required for the proliferation and survival of normal and malignant cells, including the cell cycle. MYC interacts with several central cell cycle regulators that control the balance between cell cycle progression and temporary or permanent cell cycle arrest (cellular senescence). Among these are the cyclin E/A/cyclin-dependent kinase 2 (CDK2) complexes, the CDK inhibitor p27^KIP1 (p27) and the E3 ubiquitin ligase component S-phase kinase-associated protein 2 (SKP2), which control each other by forming a triangular network. MYC is engaged in bidirectional crosstalk with each of these players; while MYC regulates their expression and/or activity, these factors in turn modulate MYC through protein interactions and post-translational modifications including phosphorylation and ubiquitylation, impacting on MYC's transcriptional output on genes involved in cell cycle progression and senescence. Here we elaborate on these network interactions with MYC and their impact on transcription, cell cycle, replication and stress signaling, and on the role of other players interconnected to this network, such as CDK1, the retinoblastoma protein (pRB), protein phosphatase 2A (PP2A), the F-box proteins FBXW7 and FBXO28, the RAS oncoprotein and the ubiquitin/proteasome system. Finally, we describe how the MYC/CDK2/p27/SKP2 axis impacts on tumor development and discuss possible ways to interfere therapeutically with this system to improve cancer treatment.

SKP2 loss destabilizes EZH2 by promoting TRAF6-mediated ubiquitination to suppress prostate cancer

EZH2 is crucial for the progression of prostate cancer (PCa) and castration-resistant prostate cancer (CRPC) through upregulation and activation of progenitor genes, as well as androgen receptor (AR)-target genes. However, the mechanisms by which EZH2 is regulated in PCa and CRPC remain elusive. Here we report that EZH2 is post-transcriptionally regulated by SKP2 in vitro in cultured cells and in vivo in mouse models. We observed aberrant upregulation of Skp2, Ezh2 and histone H3 lysine 27 trimethylation (H3K27me3) in both Pten null mouse embryonic fibroblasts (MEFs) and Pten null mouse prostate tissues. Loss of Skp2 resulted in a striking decrease of Ezh2 levels in Pten/Trp53 double-null MEFs and in prostate tumors of Pten/Trp53 double-null mutant mice. SKP2 knockdown decreased EZH2 levels in human PCa cells through upregulation of TRAF6-mediated and lysine(K) 63-linked ubiquitination of EZH2 for degradation. Ectopic expression of TRAF6 promoted the K63-linked ubiquitination of EZH2 to decrease EZH2 and H3K27me3 levels in PCa cells. In contrast, TRAF6 knockdown resulted in a reduced EZH2 ubiquitination with an increase of EZH2 and H3K27me3 levels in PCa cells. Furthermore, the catalytically dead mutant TRAF6 C70A abolished the TRAF6-mediated polyubiquitination of recombinant human EZH2 in vitro. Most importantly, a concurrent elevation of Skp2 and Ezh2 was found in CRPC tumors of Pten/Trp53 mutant mice, and expression levels of SKP2 and EZH2 were positively correlated in human PCa specimens. Taken together, our findings revealed a novel mechanism on EZH2 ubiquitination and an important signaling network of SKP2-TRAF6-EZH2/H3K27me3, and targeting SKP2-EZH2 pathway may be a promising therapeutic strategy for CRPC treatment.

Flavokawain A induces deNEDDylation and Skp2 degradation leading to inhibition of tumorigenesis and cancer progression in the TRAMP transgenic mouse model

S phase kinase-associated protein 2 (Skp2) has been shown to be required for spontaneous tumor development that occurs in the retinoblastoma protein (pRb) deficient mice. Here we have demonstrated that flavokawain A (FKA), a novel chalcone from the kava plant, selectively inhibited the growth of pRb deficient cell lines and resulted in a proteasome-dependent and ubiquitination-mediated Skp2 degradation. Degradation of Skp2 by FKA was found to be involved in a functional Cullin1, but independent of Cdh1 expression. Further studies have demonstrated that FKA docked into the ATP binding pocket of the precursor cell-expressed developmentally down-regulated 8 (NEDD8)-activating enzyme (NAE) complex, inhibited NEDD8 conjugations to both Cullin1 and Ubc12 in PC3 cells and Ubc12 NEDDylation in an in vitro assay. Finally, dietary feeding of the autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) mice with FKA inhibited the formation of high-grade prostatic intra-epithelial neoplasia lesions (HG-PIN) and prostate adenocarcinomas, reduced the tumor burden and completely abolished distant organ metastasis. Immunohistochemistry studies revealed that dietary FKA feeding resulted in marked anti-proliferative and apoptotic effects via down-regulation of Skp2 and NEDD8 and up-regulation of p27/Kip1 in the prostate of TRAMP mice. Our findings therefore provide evidence that FKA is a promising NEDDylation inhibitor for targeting Skp2 degradation in prostate cancer prevention and treatment.

Curcumin inhibits cell growth and invasion and induces apoptosis through down-regulation of Skp2 in pancreatic cancer cells

Natural polyphenol compound curcumin has been found to exhibit its anticancer activity in a variety of human malignancies including pancreatic cancer (PC). However, the underlying mechanism has not been fully understood. Accumulating evidence has demonstrated that Skp2 (S-phase kinase associated protein 2) plays an oncogenic role in the development and progression of human cancers. In this study, we aim to explore the molecular basis of curcumin-induced cell growth inhibition in PC cells.Multiple methods such as CTG assay, Flow cytometry, clonogenic assay, wound healing assay, Transwell invasion assay, Western blotting, and transfection were performed to validate the oncogenic role of curcumin in PC cells. We found that curcumin suppressed cell growth, clonogenic potential, migration and invasion, and induced cell apoptosis and cell cycle arrest. Moreover, we observed thatover-expression of Skp2 significantly promoted cell growth, whereas down-regulation of Skp2 with siRNAs inhibited cell growth. The molecular basis of curcumin-mediated cell growth inhibition we identified is that curcumin significantly suppressed Skp2 expression and subsequently induced p21 expression. These findings suggested thattargeting Skp2 by curcumin could be a promising therapeutic strategy for the treatment of PC patients.

Curcumin suppresses cell growth and invasion and induces apoptosis by down-regulation of Skp2 pathway in glioma cells

Studies have demonstrated that curcumin exerts its tumor suppressor function in a variety of human cancers including glioma. However, the exact underlying molecular mechanisms remain obscure. Emerging evidence has revealed that Skp2 (S-phase kinase associated protein 2) plays an oncogenic role in tumorigenesis. Therefore, we aim to determine whether curcumin suppresses the Skp2 expression, leading to the inhibition of cell growth, invasion, induction of apoptosis, and cell cycle arrest. To this end, we conducted multiple methods such as MTT assay, Flow cytometry, Wound healing assay, invasion assay, RT-PCR, Western blotting, and transfection to explore the functions and molecular insights of curcumin in glioma cells. We found that curcumin significantly inhibited cell growth, suppressed cell migration and invasion, induced apoptosis and cell cycle arrest in glioma cells. Furthermore, we observed that overexpression of Skp2 promoted cell growth, migration, and invasion, whereas depletion of Skp2 suppressed cell growth, migration, and invasion and triggered apoptosis in glioma cells. Mechanistically, we defined that curcumin markedly down-regulated Skp2 expression and subsequently up-regulated p57 expression. Moreover, our results demonstrated that curcumin exerts its antitumor activity through inhibition of Skp2 pathway. Collectively, our findings suggest that targeting Skp2 by curcumin could be a promising therapeutic approach for glioma prevention and therapy.

The G1 phase E3 ubiquitin ligase TRUSS that gets deregulated in human cancers is a novel substrate of the S-phase E3 ubiquitin ligase Skp2

E3 ubiquitin ligases have been implicated in the ubiquitination and proteasome-mediated degradation of several key regulators of cell cycle. Owing to their pleotropic behavior, E3 ubiquitin ligases are tightly regulated both at transcriptional and post-translational levels. The E3 ubiquitin ligase TRUSS (tumor necrosis factor receptor-associated ubiquitous scaffolding and signaling protein) which negatively regulates c-Myc, are found down-regulated in most human cancer cell lines. However, the mechanism of regulation of intracellular levels of TRUSS remains elusive. Here we show that TRUSS is expressed majorly during the G1 phase of cell cycle and its level starts to decline with the expression of S-phase specific E3 ligase Skp2. Enforced expression of Skp2 led to a marked increase in the ubiquitination of TRUSS after its phosphorylation by GSK3β and followed by rapid proteolytic degradation. Our co-immunoprecipitation studies suggested a direct interaction between Skp2 and TRUSS through the LRR motif of Skp2. Interestingly, the human tumor samples that exhibited elevated expression of Skp2, showed relatively poor expression of TRUSS. Further, enforced expression of HBx, the oncoprotein of Hepatitis B virus which is known to stabilize c-Myc and enhance its oncogenic potential, led to the intracellular accumulation of TRUSS as well as c-Myc. Apparently, HBx also interacted with TRUSS which negatively impacted the TRUSS-c-Myc and TRUSS-Skp2 interactions leading to stabilization of TRUSS. Thus, the present study suggests that TRUSS is a novel substrate of E3 ligase Skp2 and that disruption of TRUSS-Skp2 interaction by viral oncoproteins could lead to pathophysiological sequelae.

JARID1B promotes metastasis and epithelial-mesenchymal transition via PTEN/AKT signaling in hepatocellular carcinoma cells

JARID1B is a member of the family of JmjC domain-containing proteins that removes methyl residues from methylated lysine 4 on histone H3 lysine 4 (H3K4). JARID1B has been proposed as an oncogene in many types of tumors; however, its role and underlying mechanisms in hepatocellular carcinoma (HCC) remain unknown. Here we show that JARID1B is elevated in HCC and its expression level is positively correlated with metastasis. In addition Kaplan-Meier survival analysis showed that high expression of JARID1B was associated with decreased overall survival of HCC patients. Overexpression of JARID1B in HCC cells increased proliferation, epithelial-mesenchymal transition, migration and invasion in vitro, and enhanced tumorigenic and metastatic capacities in vivo. In contrast, silencing JARID1B in aggressive and invasive HCC cells inhibited these processes. Mechanistically, we found JARID1B exerts its function through modulation of H3K4me3 at the PTEN gene promoter, which was associated with inactive PTEN transcription. PTEN overexpression blocked JARID1B-driven proliferation, EMT, and metastasis. Our results, for the first time, portray a pivotal role of JARID1B in stimulating metastatic behaviors of HCC cells. Targeting JARID1B may thus be a useful strategy to impede HCC cell invasion and metastasis.

Co-targeting hexokinase 2-mediated Warburg effect and ULK1-dependent autophagy suppresses tumor growth of PTEN- and TP53-deficiency-driven castration-resistant prostate cancer

Currently, no therapeutic options exist for castration-resistant prostate cancer (CRPC) patients who have developed resistance to the second generation anti-androgen receptor (AR) axis therapy. Here we report that co-deletion of Pten and p53 in murine prostate epithelium, often observed in human CRPC, leads to AR-independent CRPC and thus confers de novo resistance to second generation androgen deprivation therapy (ADT) in multiple independent yet complementary preclinical mouse models. In contrast, mechanism-driven co-targeting hexokinase 2 (HK2)-mediated Warburg effect with 2-deoxyglucose (2-DG) and ULK1-dependent autophagy with chloroquine (CQ) selectively kills cancer cells through intrinsic apoptosis to cause tumor regression in xenograft, leads to a near-complete tumor suppression and remarkably extends survival in Pten-/p53-deficiency-driven CRPC mouse model. Mechanistically, 2-DG causes AMPK phosphorylation, which in turn inhibits mTORC1-S6K1 translation signaling to preferentially block anti-apoptotic protein MCL-l synthesis to prime mitochondria-dependent apoptosis while simultaneously activates ULK1-driven autophagy for cell survival to counteract the apoptotic action of anti-Warburg effect. Accordingly, inhibition of autophagy with CQ sensitizes cancer cells to apoptosis upon 2-DG challenge. Given that 2-DG is recommended for phase II clinical trials for prostate cancer and CQ has been clinically used as an anti-malaria drug for many decades, the preclinical results from our proof-of-principle studies in vivo are imminently translatable to clinical trials to evaluate the therapeutic efficacy by the combination modality for a subset of currently incurable CRPC harboring PTEN and TP53 mutations.

Histone H3K4 trimethylation: dynamic interplay with pre-mRNA splicing

Histone H3 lysine 4 trimethylation (H3K4me3) is often stated as a mark of transcriptionally active promoters. However, closer study of the positioning of H3K4me3 shows the mark locating primarily after the first exon at the 5′ splice site and overlapping with a CpG island in mammalian cells. There are several enzyme complexes that are involved in the placement of the H3K4me3 mark, including multiple protein complexes containing SETD1A, SETD1B, and MLL1 enzymes (writers). CXXC1, which is associated with SETD1A and SETD1B, target these enzymes to unmethylated CpG islands. Lysine demethylases (KDM5 family members, erasers) demethylate H3K4me3. The H3K4me3 mark is recognized by several proteins (readers), including lysine acetyltransferase complexes, chromatin remodelers, and RNA bound proteins involved in pre-mRNA splicing. Interestingly, attenuation of H3K4me3 impacts pre-mRNA splicing, and inhibition of pre-mRNA splicing attenuates H3K4me3.

Arsenic Trioxide Inhibits Cell Growth and Invasion via Down- Regulation of Skp2 in Pancreatic Cancer Cells

Arsenic trioxide (ATO) has been found to exert anti-cancer activity in various human malignancies. However, the molecular mechanisms by which ATO inhibits tumorigenesis are not fully elucidated. In the current study, we explored the molecular basis of ATO-mediated tumor growth inhibition in pancreatic cancer cells. We used multiple approaches such as MTT assay, wound healing assay, Transwell invasion assay, annexin V-FITC, cell cycle analysis, RT-PCR and Western blotting to achieve our goal. We found that ATO treatment effectively caused cell growth inhibition, suppressed clonogenic potential and induced G2-M cell cycle arrest and apoptosis in pancreatic cancer cells. Moreover, we observed a significant down-regulation of Skp2 after treatment with ATO. Furthermore, we revealed that ATO regulated Skp2 downstream genes such as FOXO1 and p53. These findings demonstrate that inhibition of Skp2 could be a novel strategy for the treatment of pancreatic cancer by ATO.

Roles of ubiquitination and SUMOylation on prostate cancer: mechanisms and clinical implications

The initiation and progression of human prostate cancer are highly associated with aberrant dysregulations of tumor suppressors and proto-oncogenes. Despite that deletions and mutations of tumor suppressors and aberrant elevations of oncogenes at the genetic level are reported to cause cancers, emerging evidence has revealed that cancer progression is largely regulated by posttranslational modifications (PTMs) and epigenetic alterations. PTMs play critical roles in gene regulation, cellular functions, tissue development, diseases, malignant progression and drug resistance. Recent discoveries demonstrate that ubiquitination and SUMOylation are complicated but highly-regulated PTMs, and make essential contributions to diseases and cancers by regulation of key factors and signaling pathways. Ubiquitination and SUMOylation pathways can be differentially modulated under various stimuli or stresses in order to produce the sustained oncogenic potentials. In this review, we discuss some new insights about molecular mechanisms on ubiquitination and SUMOylation, their associations with diseases, oncogenic impact on prostate cancer (PCa) and clinical implications for PCa treatment.