Fbxo22-mediated KDM4B degradation determines selective estrogen receptor modulator activity in breast cancer

Potential role of Fbxo22 in resistance to endocrine therapy in breast cancer with invasive lobular carcinoma

BACKGROUND

Invasive lobular carcinoma (ILC) is distinct from invasive ductal carcinoma (IDC) in terms of their hormonal microenvironments that may require different therapeutic strategies. We previously reported that selective estrogen receptor modulator (SERM) function requires F-box protein 22 (Fbxo22). Here, we investigated the role of Fbxo22 as a potential biomarker contributing to the resistance to endocrine therapy in ILC.

METHODS

A total of 302 breast cancer (BC) patients including 150 ILC were recruited in the study. Fbxo22 expression and clinical information were analyzed to elucidate whether Fbxo22 negativity could be a prognostic factor or there were any correlations among clinical variables and SERM efficacy.

RESULTS

Fbxo22 negativity was significantly higher in ILC compared with IDC (58.0% vs. 27.0%, P < 0.001) and higher in postmenopausal patients than premenopausal patients (64.1% vs. 48.2%, P = 0.041). In the ILC cohort, Fbxo22-negative patients had poorer overall survival (OS) than Fbxo22-positive patients, with 10-year OS rates of 77.4% vs. 93.6% (P = 0.055). All patients treated with SERMs, Fbxo22 negativity resulted in a poorer outcome, with 10-year OS rates of 81.3% vs. 92.3% (P = 0.032). In multivariate analysis regarding recurrence-free survival (RFS) in ILC patients, Fbxo22 status was independently predictive of survival as well as lymph node metastasis.

CONCLUSION

Fbxo22 negativity significantly impacts on survival in BC patients with IDC and ILC, and the disadvantage was enhanced among ILC postmenopausal women or patients treated with SERMs. The findings suggest that different therapeutic strategies might be needed according to the different histopathological types when considering adjuvant endocrine therapy.

Targeting FBXO22 enhances radiosensitivity in non-small cell lung cancer by inhibiting the FOXM1/Rad51 axis

Radioresistance is a major constraint on the efficacy of lung cancer radiotherapy, but its mechanism has not been fully elucidated. Here, we found that FBXO22 was aberrantly highly expressed in lung cancer and that FBXO22 knockdown increased the radiosensitivity of lung cancer cells. Mechanistically, FBXO22 promoted Rad51 gene transcription by increasing the level of FOXM1 at the Rad51 promoter, thereby inducing the formation of lung cancer radioresistance. Furthermore, we found that deguelin, a potential inhibitor of FBXO22, enhanced radiosensitivity in an FBXO22/Rad51-dependent manner and was safely tolerated in vivo. Collectively, our results illustrate that FBXO22 induces lung cancer radioresistance by activating the FOXM1/Rad51 axis and provide preclinical evidence for the clinical translation of this critical target.

A CRISPR activation screen identifies FBXO22 as an E3 ligase supporting targeted protein degradation

Targeted protein degradation (TPD) represents a potent chemical biology paradigm that leverages the cellular degradation machinery to pharmacologically eliminate specific proteins of interest. Although multiple E3 ligases have been discovered to facilitate TPD, there exists a compelling requirement to diversify the pool of E3 ligases available for such applications. This expansion will broaden the scope of potential protein targets, accommodating those with varying subcellular localizations and expression patterns. In this study, we describe a CRISPR-based transcriptional activation screen focused on human E3 ligases, with the goal of identifying E3 ligases that can facilitate heterobifunctional compound-mediated target degradation. This approach allows us to address the limitations associated with investigating candidate degrader molecules in specific cell lines that either lack or have low levels of the desired E3 ligases. Through this approach, we identified a candidate proteolysis-targeting chimera (PROTAC), 22-SLF, that induces the degradation of FKBP12 when the FBXO22 gene transcription is activated. 22-SLF induced the degradation of endogenous FKBP12 in a FBXO22-dependent manner across multiple cancer cell lines. Subsequent mechanistic investigations revealed that 22-SLF interacts with C227 and/or C228 in FBXO22 to achieve the target degradation. Finally, we demonstrated the versatility of FBXO22-based PROTACs by effectively degrading another endogenous protein BRD4. This study uncovers FBXO22 as an E3 ligase capable of supporting ligand-induced protein degradation through electrophilic PROTACs. The platform we have developed can readily be applied to elucidate protein degradation pathways by identifying E3 ligases that facilitate either small molecule-induced or endogenous protein degradation.

Fbxo22 inhibits metastasis in triple-negative breast cancer through ubiquitin modification of KDM5A and regulation of H3K4me3 demethylation

The importance of Fbxo22 in carcinogenesis has been highly documented. Here, we discussed downstream regulatory factors of Fbxo22 in TNBC. RNA-sequencing was conducted for identifying differentially expressed genes, followed by construction of a regulatory network. Expression patterns of Fbxo22/KDM5A in TNBC were determined by their correlation with the prognosis analyzed. Then, regulation mechanisms between Fbxo22 and KDM5A as well as between KDM5A and H3K4me3 were assayed. After silencing and overexpression experiments, the significance of Fbxo22 in repressing tumorigenesis in vitro and in vivo was explored. Fbxo22 was poorly expressed, while KDM5A was highly expressed in TNBC. Patients with elevated Fbxo22, decreased KDM5A, or higher p16 had long overall survival. Fbxo22 reduced the levels of KDM5A by ubiquitination. KDM5A promoted histone H3K4me3 demethylation to downregulate p16 expression. Fbxo22 reduced KDM5A expression to enhance p16, thus inducing DNA damage as well as reducing tumorigenesis and metastasis in TNBC. Our study validated FBXO22 as a tumor suppressor in TNBC through ubiquitination of KDM5A and regulation of p16.

LONRF2 is a protein quality control ubiquitin ligase whose deficiency causes late-onset neurological deficits

Protein misfolding is a major factor of neurodegenerative diseases. Post-mitotic neurons are highly susceptible to protein aggregates that are not diluted by mitosis. Therefore, post-mitotic cells may have a specific protein quality control system. Here, we show that LONRF2 is a bona fide protein quality control ubiquitin ligase induced in post-mitotic senescent cells. Under unperturbed conditions, LONRF2 is predominantly expressed in neurons. LONRF2 binds and ubiquitylates abnormally structured TDP-43 and hnRNP M1 and artificially misfolded proteins. Lonrf2-/- mice exhibit age-dependent TDP-43-mediated motor neuron (MN) degeneration and cerebellar ataxia. Mouse induced pluripotent stem cell-derived MNs lacking LONRF2 showed reduced survival, shortening of neurites and accumulation of pTDP-43 and G3BP1 after long-term culture. The shortening of neurites in MNs from patients with amyotrophic lateral sclerosis is rescued by ectopic expression of LONRF2. Our findings reveal that LONRF2 is a protein quality control ligase whose loss may contribute to MN degeneration and motor deficits.

The crosstalk between ubiquitination and endocrine therapy

Endocrine therapy (ET), also known as hormone therapy, refers to the treatment of tumors by regulating and changing the endocrine environment and hormone levels. Its related mechanism is mainly through reducing hormone levels and blocking the binding of hormones to corresponding receptors, thus blocking the signal transduction pathway to stimulate tumor growth. However, with the application of ET, some patients show resistance to ET, which is attributed to abnormal accumulation of hormone receptors (HRs) and the production of multiple mutants of HRs. The targeted degradation of abnormal accumulation protein mediated by ubiquitination is an important approach that regulates the protein level and function of intracellular proteins in eukaryotes. Here, we provide a brief description of the traditional and novel drugs available for ET in this review. Then, we introduce the link between ubiquitination and ET. In the end, we elaborate the clinical application of ET combined with ubiquitination-related molecules. KEY MESSAGES: • A brief description of the traditional and novel drugs available for endocrine therapy (ET). • The link between ubiquitination and ET. • The clinical application of ET combined with ubiquitination-related molecules.

FBXO22 promotes leukemogenesis by targeting BACH1 in MLL-rearranged acute myeloid leukemia

BACKGROUND

Selectively targeting leukemia stem cells (LSCs) is a promising approach in treating acute myeloid leukemia (AML), for which identification of such therapeutic targets is critical. Increasing lines of evidence indicate that FBXO22 plays a critical role in solid tumor development and therapy response. However, its potential roles in leukemogenesis remain largely unknown.

METHODS

We established a mixed lineage leukemia (MLL)-AF9-induced AML model with hematopoietic cell-specific FBXO22 knockout mice to elucidate the role of FBXO22 in AML progression and LSCs regulation, including self-renewal, cell cycle, apoptosis and survival analysis. Immunoprecipitation combined with liquid chromatography-tandem mass spectrometry analysis, Western blotting and rescue experiments were performed to study the mechanisms underlying the oncogenic role of FBXO22.

RESULTS

FBXO22 was highly expressed in AML, especially in MLL-rearranged (MLLr) AML. Upon FBXO22 knockdown, human MLLr leukemia cells presented markedly increased apoptosis. Although conditional deletion of Fbxo22 in hematopoietic cells did not significantly affect the function of hematopoietic stem cells, MLL-AF9-induced leukemogenesis was dramatically abrogated upon Fbxo22 deletion, together with remarkably reduced LSCs after serial transplantations. Mechanistically, FBXO22 promoted degradation of BACH1 in MLLr AML cells, and overexpression of BACH1 suppressed MLLr AML progression. In line with this, heterozygous deletion of BACH1 significantly reversed delayed leukemogenesis in Fbxo22-deficient mice.

CONCLUSIONS

FBXO22 promotes MLLr AML progression by targeting BACH1 and targeting FBXO22 might be an ideal strategy to eradicate LSCs without influencing normal hematopoiesis.

KDM4 Demethylases: Structure, Function, and Inhibitors

KDM4 histone demethylases mainly catalyze the removal of methyl marks from H3K9 and H3K36 to epigenetically regulate chromatin structure and gene expression. KDM4 expression is strictly regulated to ensure proper function in a myriad of biological processes, including transcription, cellular proliferation and differentiation, DNA damage repair, immune response, and stem cell self-renewal. Aberrant expression of KDM4 demethylase has been documented in many types of blood and solid tumors, and thus, KDM4s represent promising therapeutic targets. In this chapter, we summarize the current knowledge of the structures and regulatory mechanisms of KDM4 proteins and our understanding of their alterations in human pathological processes with a focus on development and cancer. We also review the reported KDM4 inhibitors and discuss their potential as therapeutic agents.

Pharmacokinetic Study of Conjugated Equine Estrogens in Healthy Chinese Postmenopausal Women Using a Parallel Two-Column LC-MS/MS Method

BACKGROUND AND OBJECTIVE: Postmenopausal women often require estrogen supplementation to improve menopausal and postmenopausal vasomotor symptoms and maintain hormonal balance. Conjugated equine estrogens extracted from the urine of pregnant mares are commonly used to provide this estrogen replacement therapy. The complex composition of this mixture of animal sulfated metabolites makes its bioanalysis challenging such that its detailed pharmacokinetics has not been fully characterized. The purpose of this work is to reveal the pharmacokinetic behavior of conjugated equine estrogens in healthy Chinese postmenopausal women by a parallel two-column LC-MS/MS method.

METHODS

An open-label study was carried out in 35 Chinese healthy postmenopausal women who received a single dose of Premarin^® 0.625 mg. A high-throughput column-switching liquid chromatography-tandem mass spectrometry method was developed to determine four conjugated estrogens and two unconjugated estrogens formed by hydrolysis in vivo. The method multiplexes two high-performance liquid chromatography systems into one mass spectrometer and incorporates the positive/negative ion switching acquisition mode of mass spectrometry to significantly increase analysis efficiency. Pharmacokinetics was determined using non-compartmental methods.

RESULTS

Both conjugated and unconjugated estrogens can be analyzed simultaneously in a single run with an analysis time of 13.0 minutes in the column-switching liquid chromatography-tandem mass spectrometry method as opposed to 23.0 minutes in a single-column liquid chromatography-tandem mass spectrometry system. The exposures (maximum concentration and area under the curve) of estrone and equilin in Chinese women were higher than those in the North American women.

CONCLUSIONS

The fully validated assay was successfully applied to a pharmacokinetic study in healthy postmenopausal Chinese women after oral administration of a conjugated equine estrogen tablet. This study suggests that Chinese postmenopausal women achieve the same level of unconjugated estrogens in plasma at a lower dose of conjugated equine estrogens than North American women.

Targeting matrix metalloproteinases by E3 ubiquitin ligases as a way to regulate the tumor microenvironment for cancer therapy

The tumor microenvironment (TME) plays an important role in neoplastic development. Matrix metalloproteinases (MMPs) are critically involved in tumorigenesis by modulation of the TME and degradation of the extracellular matrix (ECM) in a large variety of malignancies. Evidence has revealed that dysregulated MMPs can lead to ECM damage, the promotion of cell migration and tumor metastasis. The expression and activities of MMPs can be tightly regulated by TIMPs, multiple signaling pathways and noncoding RNAs. MMPs are also finely controlled by E3 ubiquitin ligases. The current review focuses on the molecular mechanism by which MMPs are governed by E3 ubiquitin ligases in carcinogenesis. Due to the essential role of MMPs in oncogenesis, they have been considered the attractive targets for antitumor treatment. Several strategies that target MMPs have been discovered, including the use of small-molecule inhibitors, peptides, inhibitory antibodies, natural compounds with anti-MMP activity, and RNAi therapeutics. However, these molecules have multiple disadvantages, such as poor solubility, severe side-effects and low oral bioavailability. Therefore, it is necessary to discover the novel inhibitors that suppress MMPs for cancer therapy. Here, we discuss the therapeutic potential of targeting E3 ubiquitin ligases to inhibit MMPs. We hope this review will stimulate the discovery of novel therapeutics for the MMP-targeted treatment of a variety of human cancers.

Host F-Box Protein 22 Enhances the Uptake of Brucella by Macrophages and Drives a Sustained Release of Proinflammatory Cytokines through Degradation of the Anti-Inflammatory Effector Proteins of Brucella

Brucella species are intracellular bacterial pathogens, causing the worldwide zoonotic disease brucellosis. Brucella invades professional and nonprofessional phagocytic cells, followed by resisting intracellular killing and establishing a replication permissive niche. Brucella also modulates the innate and adaptive immune responses of the host for its chronic persistence. The complex intracellular cycle of Brucella depends in a major way on multiple host factors, but limited information is available on host and bacterial proteins that play an essential role in the invasion, intracellular replication, and modulation of host immune responses. By employing a small interfering RNA (siRNA) screening, we identified a role for the host protein FBXO22 in the Brucella-macrophage interaction. FBXO22 is the key element in the SCF E3 ubiquitination complex, where it determines the substrate specificity for ubiquitination and degradation of various host proteins. Downregulation of FBXO22 by siRNA or the CRISPR-Cas9 system resulted in diminished uptake of Brucella into macrophages, which was dependent on NF-κB-mediated regulation of phagocytic receptors. FBXO22 expression was upregulated in Brucella-infected macrophages, which resulted in induction of phagocytic receptors and enhanced production of proinflammatory cytokines through NF-κB. Furthermore, we found that FBXO22 recruits the effector proteins of Brucella, including the anti-inflammatory proteins TcpB and OMP25, for degradation through the SCF complex. We did not observe any role for another F-box-containing protein of the SCF complex, β-TrCP, in the Brucella-macrophage interaction. Our findings unravel novel functions of FBXO22 in host-pathogen interaction and its contribution to pathogenesis of infectious diseases.

Pan-Cancer Analyses Reveal Oncogenic Role and Prognostic Value of F-Box Only Protein 22

The F-box protein 22 (FBXO22), an F-box E3 ligase, has been identified to be critically involved in carcinogenesis. However, a systematic assessment of the role of FBXO22 across human cancers is lacking. Here, we performed a pan-cancer analysis to explore the role of FBXO22 in 33 cancer types using multiomic data from The Cancer Genome Atlas (TCGA). First, we found that high FBXO22 expression in multiple cancers was closely associated with poor overall survival and relapse-free survival. Next, we identified ten proteins that interact with FBXO22 and 13 of its target substrates using the STRING database and a literature search to explore the regulatory role of FBXO22 in tumorigenesis. Genes encoding these proteins were found to be significantly enriched in cell cycle negative regulation and ubiquitination pathways. This was confirmed in nonsmall cell lung cancer A549 cells, where FBXO22 overexpression enhanced cyclin-dependent kinase 4 (CDK4) protein levels and promoted cell proliferation. Similarly, overexpression or interference of FBXO22 changed the protein level of one of its substrates, PTEN. Additionally, we found that FBXO22 mutations were accompanied by altered substrate expression, especially in uterine corpus endometrial carcinoma and lung adenocarcinoma; endometrial carcinoma patients with FBXO22 genetic alterations also had better overall and relapse-free survival. Notably, FBXO22 methylation levels were also decreased in most tumors, and hypomethylation of FBXO22 was associated with poor overall survival, relapse-free interval, and progression-free interval in pancreatic adenocarcinoma. Finally, we analyzed the correlation between the abundance of tumor infiltrating lymphocytes (TILs) and FBXO22 expression, copy number variation, and methylation. Multiple algorithms revealed that high FBXO22 expression was associated with lower TIL levels, especially in lung adenocarcinoma, lung squamous cell carcinoma, and sarcoma. Taken together, our findings demonstrate that FBXO22 degrades tumor suppressor genes by ubiquitination and inhibits the cell cycle to promote nonsmall cell lung cancer progression. Our study also provides a relatively comprehensive understanding of the oncogenic role of FBXO22 in different tumors.

Global identification of phospho-dependent SCF substrates reveals a FBXO22 phosphodegron and an ERK-FBXO22-BAG3 axis in tumorigenesis

SKP1-CUL1-F-box (SCF) ubiquitin ligases play fundamental roles in cellular functions. Typically, substrate phosphorylation is required for SCF recognition and subsequent degradation. However, phospho-dependent substrates remain largely unidentified. Here, using quantitative phoshoproteome approach, we performed a system-wide investigation of phospho-dependent SCF substrates. This strategy identified diverse phospho-dependent candidates. Biochemical verification revealed a mechanism by which SCF^FBXO22 recognizes the motif XXPpSPXPXX as a conserved phosphodegron to target substrates for destruction. We further demonstrated BAG3, a HSP70 co-chaperone, is a bona fide substrate of SCF^FBXO22. FBXO22 mediates BAG3 ubiquitination and degradation that requires ERK-dependent BAG3 phosphorylation at S377. FBXO22 depletion or expression of a stable BAG3 S377A mutant promotes tumor growth via defects in apoptosis and cell cycle progression in vitro and in vivo. In conclusion, our study identified broad phosphorylation-dependent SCF substrates and demonstrated a phosphodegron recognized by FBXO22 and a novel ERK-FBXO22-BAG3 axis involved in tumorigenesis.

KDM4 Involvement in Breast Cancer and Possible Therapeutic Approaches

Breast cancer (BC) is the second leading cause of cancer death in women, although recent scientific and technological achievements have led to significant improvements in progression-free disease and overall survival of patients. Genetic mutations and epigenetic modifications play a critical role in deregulating gene expression, leading to uncontrolled cell proliferation and cancer progression. Aberrant histone modifications are one of the most frequent epigenetic mechanisms occurring in cancer. In particular, methylation and demethylation of specific lysine residues alter gene accessibility via histone lysine methyltransferases (KMTs) and histone lysine demethylases (KDMs). The KDM family includes more than 30 members, grouped into six subfamilies and two classes based on their sequency homology and catalytic mechanisms, respectively. Specifically, the KDM4 gene family comprises six members, KDM4A-F, which are associated with oncogene activation, tumor suppressor silencing, alteration of hormone receptor downstream signaling, and chromosomal instability. Blocking the activity of KDM4 enzymes renders them "druggable" targets with therapeutic effects. Several KDM4 inhibitors have already been identified as anticancer drugs in vitro in BC cells. However, no KDM4 inhibitors have as yet entered clinical trials due to a number of issues, including structural similarities between KDM4 members and conservation of the active domain, which makes the discovery of selective inhibitors challenging. Here, we summarize our current knowledge of the molecular functions of KDM4 members in BC, describe currently available KDM4 inhibitors, and discuss their potential use in BC therapy.

Mechanisms of JARID1B Up-Regulation and Its Role in Helicobacter pylori-Induced Gastric Carcinogenesis

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide. Helicobacter pylori infection can induce GC through a serial cascade of events, with emerging evidence suggesting the important role of epigenetic alterations in the development and progression of the disease. Here, we report on mechanisms responsible for Jumonji AT-rich interactive domain1B (JARID1B) upregulation in GC and its role in the malignant transformation induced by H. pylori infection. We found that upregulation of JARID1B was associated with poorer prognosis, greater tumor purity, and less immune cell infiltration into the tumor. Mechanistically, we showed that the upregulation of JARID1B in human GC was attributed to JARID1B amplification and its induction by H. pylori infection. Furthermore, we identified miR-29c as a negative regulator of JARID1B in GC. H. pylori caused downregulation of miR-29c in human GC and thereby contributed to JARID1B upregulation through relieving posttranscriptional regulation. Functionally, we showed that knockdown of JARID1B reduced GC cell proliferation induced by H. pylori infection. Subsequently, cyclinD1 (CCND1), a key molecule in GC, was shown to be a target gene of JARID1B. In conclusion, these results suggest that JARID1B may be an oncogene upregulated in human GC and could represent a novel therapeutic target to prevent malignant transformation induced by H. pylori infection.

Suppression of Estrogen Receptor Alpha Inhibits Cell Proliferation, Differentiation and Enhances the Chemosensitivity of P53-Positive U2OS Osteosarcoma Cell

Osteosarcoma is a highly malignant musculoskeletal tumor that is commonly noticed in adolescent children, young children, and elderly adults. Due to advances in surgery, chemotherapy and imaging technology, survival rates have improved to 70–80%, but chemical treatments do not enhance patient survival; in addition, the survival rate after chemical treatments is still low. The most obvious clinical feature of osteosarcoma is new bone formation, which is called “sun burst”. Estrogen receptor alpha (ERα) is an essential feature of osteogenesis and regulates cell growth in various tumors, including osteosarcoma. In this study, we sought to investigate the role of ERα in osteosarcoma and to determine if ERα can be used as a target to facilitate the chemosensitivity of osteosarcoma to current treatments. The growth rate of each cell clone was assayed by MTT and trypan blue cell counting, and cell cycle analysis was conducted by flow cytometry. Osteogenic differentiation was induced by osteogenic induction medium and quantified by ARS staining. The effects of ERα on the chemoresponse of OS cells treated with doxorubicin were evaluated by colony formation assay. Mechanistic studies were conducted by examining the levels of proteins by Western blot. The role of ERα on OS prognosis was investigated by an immunohistochemical analysis of OS tissue array. The results showed an impaired growth rate and a decreased osteogenesis ability in the ERα-silenced P53(+) OS cell line U2OS, but not in P53(−) SAOS2 cells, compared with the parental cell line. Cotreatment with tamoxifen, an estrogen receptor inhibitor, increased the sensitivity to doxorubicin, which decreased the colony formation of P53(+) U2OS cells. Cell cycle arrest in the S phase was observed in P53(+) U2OS cells cotreated with low doses of doxorubicin and tamoxifen, while increased levels of apoptosis factors indicated cell death. Moreover, patients with ER−/P53(+) U2OS showed better chemoresponse rates (necrosis rate > 90%) and impaired tumor sizes, which were compatible with the findings of basic research. Taken together, ERα may be a potential target of the current treatments for osteosarcoma that can control tumor growth and improve chemosensitivity. In addition, the expression of ERα in osteosarcoma can be a prognostic factor to predict the response to chemotherapy.

The transcription co-factor JAB1/COPS5, serves as a potential oncogenic hub of human chondrosarcoma cells in vitro

Chondrosarcoma (CS) is the second most common skeletal malignancy in humans. High-grade CS is aggressive and extremely resistant to chemo- and radio-therapies. The lack of effective treatment options warrants the development of novel therapies. The evolutionarily conserved transcriptional co-factor JAB1 (also known as COPS5/CSN5) has emerged as a novel regulator of tumorigenesis. JAB1 overexpression occurs in many common cancers and is associated with poor prognosis. However, the role of JAB1 in CS pathogenesis was completely unknown. To study JAB1's function in CS, we performed shRNA knockdown (KD) of JAB1 in two high-grade human CS cell lines, SW1353 and Hs819.T, and observed significantly decreased proliferation and colony formations, and increased apoptosis in both CS cell lines upon JAB1-KD. Interestingly, we found that endogenous JAB1 interacted with endogenous SOX9, a potent oncogene and a master regulator of skeletogenesis, in chondrosarcoma cells, but not in primary chondrocytes. JAB1 also binds to the same SOX9-mediated chondrocyte-specific enhancer elements in CS cells. Furthermore, we found that a recently developed, novel, potent, and JAB1-specific small molecule inhibitor, CSN5i-3, can significantly increase apoptosis, drastically alter the activities of several signaling pathways, and modulates the expression of specific Cullin-ring-ligases (CRLs) in CS cells. Finally, our RNA-sequencing analysis in JAB1-KD CS cells identified a total of 2945 differentially expressed genes. Gene set enrichment analysis revealed that JAB1 regulates several essential pathways such as DNA damage response and cell cycle regulation. In conclusion, our study showed that JAB1 might regulate a distinct pro-tumorigenic regulatory network to promote chondrosarcoma pathogenesis.

The KDM4B-CCAR1-MED1 axis is a critical regulator of osteoclast differentiation and bone homeostasis

Bone undergoes a constant and continuous remodeling process that is tightly regulated by the coordinated and sequential actions of bone-resorbing osteoclasts and bone-forming osteoblasts. Recent studies have shown that histone demethylases are implicated in osteoblastogenesis; however, little is known about the role of histone demethylases in osteoclast formation. Here, we identified KDM4B as an epigenetic regulator of osteoclast differentiation. Knockdown of KDM4B significantly blocked the formation of tartrate-resistant acid phosphatase-positive multinucleated cells. Mice with myeloid-specific conditional knockout of KDM4B showed an osteopetrotic phenotype due to osteoclast deficiency. Biochemical analysis revealed that KDM4B physically and functionally associates with CCAR1 and MED1 in a complex. Using genome-wide chromatin immunoprecipitation (ChIP)-sequencing, we revealed that the KDM4B–CCAR1–MED1 complex is localized to the promoters of several osteoclast-related genes upon receptor activator of NF-κB ligand stimulation. We demonstrated that the KDM4B–CCAR1–MED1 signaling axis induces changes in chromatin structure (euchromatinization) near the promoters of osteoclast-related genes through H3K9 demethylation, leading to NF-κB p65 recruitment via a direct interaction between KDM4B and p65. Finally, small molecule inhibition of KDM4B activity impeded bone loss in an ovariectomized mouse model. Taken together, our findings establish KDM4B as a critical regulator of osteoclastogenesis, providing a potential therapeutic target for osteoporosis.

TP53/p53-FBXO22-TFEB controls basal autophagy to govern hormesis

Preconditioning with a mild stressor such as fasting is a promising way to reduce severe side effects from subsequent chemo- or radiotherapy. However, the underlying mechanisms have been largely unexplored. Here, we demonstrate that the TP53/p53-FBXO22-TFEB (transcription factor EB) axis plays an essential role in this process through upregulating basal macroautophagy/autophagy. Mild stress-activated TP53 transcriptionally induced FBXO22, which in turn ubiquitinated KDM4B (lysine-specific demethylase 4B) complexed with MYC-NCOR1 suppressors for degradation, leading to transcriptional induction of TFEB. Upregulation of autophagy-related genes by increased TFEB dramatically enhanced autophagic activity and cell survival upon following a severe stressor. Mitogen-induced AKT1 activation counteracted this process through the phosphorylation of KDM4B, which inhibited FBXO22-mediated ubiquitination. Additionally, fbxo22^-/- mice died within 10 h of birth, and their mouse embryonic fibroblasts (MEFs) showed a lowered basal autophagy, whereas FBXO22-overexpressing mice were resistant to chemotherapy. Taken together, these results suggest that TP53 upregulates basal autophagy through the FBXO22-TFEB axis, which governs the hormetic effect in chemotherapy.Abbreviations: BBC3/PUMA: BCL2 binding component 3; CDKN1A/p21: cyclin dependent kinase inhibitor 1A; ChIP-seq: chromatin immunoprecipitation followed by sequencing; DDB2: damage specific DNA binding protein 2; DRAM: DNA damage regulated autophagy modulator; ESR/ER: estrogen receptor 1; FMD: fasting mimicking diet; HCQ: hydroxychloroquine; KDM4B: lysine-specific demethylase 4B; MAP1LC3/LC3: microtubule associated protein 1 light chain 3 alpha; MEFs: mouse embryonic fibroblasts; MTOR: mechanistic target of rapamycin kinase; NCOR1: nuclear receptor corepressor 1; SCF: SKP1-CUL-F-box protein; SQSTM1: sequestosome 1; TFEB: transcription factor EB.

Systematic analysis of the expression and prognosis relevance of FBXO family reveals the significance of FBXO1 in human breast cancer

Background

Breast cancer (BC) remains a prevalent and common form of cancer with high heterogeneity. Making efforts to explore novel molecular biomarkers and serve as potential disease indicators, which is essential to effectively enhance the prognosis and individualized treatment of BC. FBXO proteins act as the core component of E3 ubiquitin ligase, which play essential regulators roles in multiple cellular processes. Recently, research has indicated that FBXOs also play significant roles in cancer development. However, the molecular functions of these family members in BC have not been fully elucidated.

Methods

In this research, we investigated the expression data, survival relevance and mutation situation of 10 FBXO members (FBXO1, 2, 5, 6, 16, 17, 22, 28, 31 and 45) in patients with BC from the Oncomine, GEPIA, HPA, Kaplan–Meier Plotter, UALCAN and cBioPortal databases. The high transcriptional levels of FBXO1 in different subtypes of BC were verified by immunohistochemical staining and the specific mutations of FBXO1 were obtained from COSMIC database. Top 10 genes with the highest correlation to FBXO1 were identified through cBioPortal and COXPRESdb tools. Additionally, functional enrichment analysis, PPI network and survival relevance of FBXO1 and co-expressed genes in BC were obtained from DAVID, STRING, UCSC Xena, GEPIA, bc-GenExMiner and Kaplan–Meier Plotter databases. FBXO1 siRNAs were transfected into MCF-7 and MDA-MB-231 cell lines. Expression of FBXO1 in BC cell lines was detected by western-blot and RT-qPCR. Cell proliferation was detected by using CCK-8 kit and colony formation assay. Cell migration was detected by wound‐healing and transwell migration assay.

Results

We found that FBXO2, FBXO6, FBXO16 and FBXO17 were potential favorable prognostic factors for BC. FBXO1, FBXO5, FBXO22, FBXO28, FBXO31 and FBXO45 may be the independent poor prognostic factors for BC. All of them were correlated to clinicopathological staging. Moreover, knockdown of FBXO1 in MCF7 and MDA-MB-231 cell lines resulted in decreased cell proliferation and migration in vitro. We identified that FBXO1 was an excellent molecular biomarker and therapeutic target for different molecular typing of BC.

Conclusion

This study implies that FBXO1, FBXO2, FBXO5, FBXO6, FBXO16, FBXO17, FBXO22, FBXO28, FBXO31 and FBXO45 genes are potential clinical targets and prognostic biomarkers for patients with different molecular typing of BC. In addition, the overexpression of FBXO1 is always found in breast cancer and predicts disadvantageous prognosis, implicating it could as an appealing therapeutic target for breast cancer patients.

Tamoxifen induces stem-like phenotypes and multidrug resistance by altering epigenetic regulators in ERα+ breast cancer cells

Background

To understand the mechanism underlying tamoxifen-induced multidrug resistance (MDR) and stem-like phenotypes in breast cancer cells, we treated the MCF-7 cells with 4-hydroxy-tamoxifen (TAM) for 6 months continuously and established MCF-7 tamoxifen resistance (TR) phenotypes.

Methods

In the present study, the following methods were used: cell viability assay, colony formation, cell cycle analysis, ALDEFLUOR assay, mammosphere formation assay, chromatin immunoprecipitation (ChIP) assay, PCR array, western blot analysis and quantitative reverse transcription polymerase chain reaction (QRT-PCR).

Results

The expression of ERα was significantly higher in MCF7-TR cells when compared with parental MCF-7 cells. MCF7-TR cells exposed to TAM showed a significant increase in the proliferation and rate of colony formation. The number of cancer stem cells was higher in MCF7-TR cells as observed by the increase in the number of ALDH+ cells. Furthermore, the number of mammospheres formed from the FACS-sorted ALDH+ cells was higher in MCF7-TR cells. Using PCR array analysis, we were able to identify that the long-term exposure of TAM leads to alterations in the epigenetic and MDR stem cell marker genes. Furthermore, western blot analysis demonstrated elevated levels of Notch-1 expression in MCF-TR cells compared with MCF-7 cells. Chromatin immunoprecipitation (ChIP) assay revealed that Notch-1 enhanced the cyclin D1 expression significantly in these cells. In addition, we observed that MCF7-TR cells were resistant to doxorubicin but not the MCF-7 cells.

Conclusions

In the present study, we conclude that the treatment with tamoxifen induces multiple epigenetic alterations that lead to the development of MDR and stem-like phenotypes in breast cancers. Therefore, our study provides better insights to develop novel treatment regime to control the progression of breast cancer.

Age-related copy number variations and expression levels of F-box protein FBXL20 predict ovarian cancer prognosis

About 70% of ovarian cancer (OvCa) cases are diagnosed at advanced stages (stage III/IV) with only 20–40% of them survive over 5 years after diagnosis. A reliably screening marker could enable a paradigm shift in OvCa early diagnosis and risk stratification. Age is one of the most significant risk factors for OvCa. Older women have much higher rates of OvCa diagnosis and poorer clinical outcomes. In this article, we studied the correlation between aging and genetic alterations in The Cancer Genome Atlas Ovarian Cancer dataset. We demonstrated that copy number variations (CNVs) and expression levels of the F-Box and Leucine-Rich Repeat Protein 20 (FBXL20), a substrate recognizing protein in the SKP1-Cullin1-F-box-protein E3 ligase, can predict OvCa overall survival, disease-free survival and progression-free survival. More importantly, FBXL20 copy number loss predicts the diagnosis of OvCa at a younger age, with over 60% of patients in that subgroup have OvCa diagnosed at age less than 60 years. Clinicopathological studies further demonstrated malignant histological and radiographical features associated with elevated FBXL20 expression levels. This study has thus identified a potential biomarker for OvCa prognosis.

Emerging role of FBXO22 in carcinogenesis

The F-box protein 22 (FBXO22), one of F-box proteins, has been identified to be critically involved in carcinogenesis. FBXO22 promotes proliferation in breast cancer and lung cancer, but suppresses migration and metastasis. FBXO22 exerts oncogenetic functions via promoting the ubiquitination and degradation of its substrates, including KDM4A, KDM4B, methylated p53, p21, KLF4, LKB1, Snail, CD147, Bach1, PTEN, and HDM2. FBXO22 is also regulated by several regulatory factors such as p53, miR-155, SNHG14, and circ_0006282. In this review, we summarize the regulatory factors and downstream targets of FBXO22 in cancers, discuss its functions in tumorigenesis, and further highlight the alteration of FBXO22 expression in a variety of human malignancies. Finally, we provide novel insights for future perspectives on targeting FBXO22 as a promising strategy for cancer therapy.

FBXO22, an epigenetic multiplayer coordinating senescence, hormone signaling, and metastasis

Ubiquitin‐dependent protein degradation has been implicated in the control of various cellular processes such as cell cycle control, transcriptional regulation, DNA damage repair, and apoptosis, many of which are involved in the initiation, progression, metastasis, and drug resistance of cancers. E3 ubiquitin ligases are known to be the second most prevalent cancer‐related functional gene family next to protein kinases. Of these, FBXO22, an F‐box receptor subunit of SCF E3 ligase, has recently been proposed to play a critical role in multiple aspects related to cancer development and therapy response. Firstly, FBXO22 is a key regulator of senescence induction through ubiquitylation of p53 for degradation. FBXO22 also acts as a molecular switch for the antagonistic and agonistic actions of selective estrogen receptor modulators (SERM) and determines the sensitivity of breast cancer to SERM by ubiquitylating KDM4B complexed with unliganded or SERMs‐bound estrogen receptor (ER). Furthermore, FBXO22 binds to Bach1, a pro‐metastatic transcription factor, suppressing Bach1‐driven metastasis of lung adenocarcinoma, and loss of FBXO22 facilitates metastasis. These findings, as well as other reports, unveiled strikingly important roles of FBXO22 in cancer development and therapeutic strategy. In this review, we summarize recent findings of how FBXO22 regulates major cancer suppression pathways.

The crucial p53-dependent oncogenic role of JAB1 in osteosarcoma in vivo

Osteosarcoma (OS) is the most common primary bone cancer and ranks amongst the leading causes of cancer mortality in young adults. Jun activation domain binding protein 1 (JAB1) is overexpressed in many cancers and has recently emerged as a novel target for cancer treatment. However, the role of JAB1 in osteosarcoma was virtually unknown. In this study, we demonstrate that JAB1-knockdown in malignant osteosarcoma cell lines significantly reduced their oncogenic properties, including proliferation, colony formation, and motility. We also performed RNA-sequencing analysis in JAB1-knockdown OS cells and identified 4110 genes that are significantly differentially expressed. This demonstrated for the first time that JAB1 regulates a large and specific transcriptome in cancer. We also found that JAB1 is overexpressed in human OS and correlates with a poor prognosis. Moreover, we generated a novel mouse model that overexpresses Jab1 specifically in osteoblasts upon a TP53 heterozygous sensitizing background. Interestingly, by 13 months of age, a significant proportion of these mice spontaneously developed conventional OS. Finally, we demonstrate that a novel, highly specific small molecule inhibitor of JAB1, CSN5i-3, reduces osteosarcoma cell viability and has specific effects on the ubiquitin-proteasome system in OS. Thus, we show for the first time that the overexpression of JAB1 in vivo can result in accelerated spontaneous tumor formation in a p53-dependent manner. In summary, JAB1 might be a unique target for the treatment of osteosarcoma and other cancers.

Overcoming Endocrine Resistance in Breast Cancer

Estrogen receptor-positive (ER+) breast cancer is the most common breast cancer subtype. Treatment of ER+ breast cancer comprises interventions that suppress estrogen production and/or target the ER directly (overall labeled as endocrine therapy). While endocrine therapy has considerably reduced recurrence and mortality from breast cancer, de novo and acquired resistance to this treatment remains a major challenge. An increasing number of mechanisms of endocrine resistance have been reported, including somatic alterations, epigenetic changes, and changes in the tumor microenvironment. Here, we review recent advances in delineating mechanisms of resistance to endocrine therapies and potential strategies to overcome such resistance.

FBXO22 degrades nuclear PTEN to promote tumorigenesis

Nuclear localization of PTEN is essential for its tumor suppressive role, and loss of nuclear PTEN is more prominent than cytoplasmic PTEN in many kinds of cancers. However, nuclear PTEN-specific regulatory mechanisms were rarely reported. Based on the finding that nuclear PTEN is more unstable than cytoplasmic PTEN, here we identify that F-box only protein 22 (FBXO22) induces ubiquitylation of nuclear but not cytoplasmic PTEN at lysine 221, which is responsible for the degradation of nuclear PTEN. FBXO22 plays a tumor-promoting role by ubiquitylating and degrading nuclear PTEN. In accordance, FBXO22 is overexpressed in various cancer types, and contributes to nuclear PTEN downregulation in colorectal cancer tissues. Cumulatively, our study reports the mechanism to specifically regulate the stability of nuclear PTEN, which would provide the opportunity for developing therapeutic strategies aiming to achieve complete reactivation of PTEN as a tumor suppressor.

Loss of nuclear PTEN is associated with aggressive cancers. Here the authors show that nuclear PTEN is more susceptible to ubiquitin-mediated proteasomal degradation than cytoplasmic PTEN, and identify FBXO22 ubiquitinates and degrades nuclear PTEN to promote tumorigenesis.

Long noncoding RNA SNHG14 promotes osteosarcoma progression via miR-433-3p/FBXO22 axis

Long noncoding RNA small nucleolus RNA host gene 14 (SNHG14) has been shown to exert oncogenic functions in seceral cancers, but its role in osteosarcoma still unclear. In this present study, we found that SNHG14 was significantly upregulated in osteosarcoma tissues and cell lines. Knockdown SNHG14 expression significantly inhibited osteosarcoma cell proliferation through inducing apoptosis. Further functional assays revealed that SNHG14 knockdown dramatically suppressed cell migration and invasion. Bioinformatics analysis and luciferase assays identified that microRNA-433-3p (miR-433-3p) was a direct target of SNHG14, and directly targeted F-box only protein 22 (FBXO22). Mechanistic analysis demonstrated that SNHG14 acted as a ceRNA in modulating osteosarcoma proliferation, migration and invasion by decoying miR-433-3p to upregulate FBXO22 expression. We also observed that knockdown of FBXO22 and SNHG14 and overexpression of miR-433-3p both dramatically suppressed osteosarcoma cell proliferation, migration and invasion, but induced cell apoptosis. Moreover, the suppresive effect of SNHG14 knockdown on osteosarcoma cell proliferation, invasion and migration was attenuated by miR-433-3p inhibitor. Our findings demonstrated that SNHG14 promoted osteosarcoma progression by acting as a ceRNA for miR-433-3p to regulate FBXO22 expression, suggesting that SNHG14 may serve as a potential therapeutic target in osteosarcoma patients.

Emerging roles of F-box proteins in cancer drug resistance

Chemotherapy continues to be a major treatment strategy for various human malignancies. However, the frequent emergence of chemoresistance compromises chemotherapy efficacy leading to poor prognosis. Thus, overcoming drug resistance is pivotal to achieve enhanced therapy efficacy in various cancers. Although increased evidence has revealed that reduced drug uptake, increased drug efflux, drug target protein alterations, drug sequestration in organelles, enhanced drug metabolism, impaired DNA repair systems, and anti-apoptotic mechanisms, are critically involved in drug resistance, the detailed resistance mechanisms have not been fully elucidated in distinct cancers. Recently, F-box protein (FBPs), key subunits in Skp1-Cullin1-F-box protein (SCF) E3 ligase complexes, have been found to play critical roles in carcinogenesis, tumor progression, and drug resistance through degradation of their downstream substrates. Therefore, in this review, we describe the functions of FBPs that are involved in drug resistance and discuss how FBPs contribute to the development of cancer drug resistance. Furthermore, we propose that targeting FBPs might be a promising strategy to overcome drug resistance and achieve better treatment outcome in cancer patients. Lastly, we state the limitations and challenges of using FBPs to overcome chemotherapeutic drug resistance in various cancers.

HERC2 regulates RPA2 by mediating ATR-induced Ser33 phosphorylation and ubiquitin-dependent degradation

Replication protein A (RPA) binds to and stabilizes single-stranded DNA and is essential for the genome stability. We reported that an E3 ubiquitin ligase, HERC2, suppresses G-quadruplex (G4) DNA by regulating RPA-helicase complexes. However, the precise mechanism of HERC2 on RPA is as yet largely unknown. Here, we show essential roles for HERC2 on RPA2 status: induction of phosphorylation and degradation of the modified form. HERC2 interacted with RPA through the C-terminal HECT domain. Ubiquitination of RPA2 was inhibited by HERC2 depletion and rescued by reintroduction of the C-terminal fragment of HERC2. ATR-mediated phosphorylation of RPA2 at Ser33 induced by low-level replication stress was inhibited by depletion of HERC2. Contrary, cells lacking HERC2 catalytic residues constitutively expressed an increased level of Ser33-phosphorylated RPA2. HERC2-mediated ubiquitination of RPA2 was abolished by an ATR inhibitor, supporting a hypothesis that the ubiquitinated RPA2 is a phosphorylated subset. Functionally, HERC2 E3 activity has an epistatic relationship with RPA in the suppression of G4 when judged with siRNA knockdown experiments. Together, these results suggest that HERC2 fine-tunes ATR-phosphorylated RPA2 levels through induction and degradation, a mechanism that could be critical for the suppression of secondary DNA structures during cell proliferation.

Discovery of novel natural compound inhibitors targeting estrogen receptor α by an integrated virtual screening strategy

Estrogen receptor (ER) is a nuclear hormone receptor and plays an important role in mediating the cellular effects of estrogen. ER can be classified into two receptors: estrogen receptor alpha (ERα) and beta (ERβ), and the former is expressed in 50~80% of breast tumors and has been extensively investigated in breast cancer for decades. Excessive exposure to estrogen can obviously stimulate the growth of breast cancers primarily mediated by ERα, and thus anti-estrogen therapies by small molecules are of concern to clinicians and pharmaceutical industry in the treatment of ERα-positive breast cancers. Although a series of estrogen receptor modulators have been developed, these drugs can lead to resistance and side effects. Therefore, the development of small molecule inhibitors with high target specificity has been intensified. In this pursuit, an integrated computer-aided virtual screening technique, including molecular docking and pharmacophore model screening, was used to screen traditional Chinese medicine (TCM) databases. The compounds with high docking scores and fit values were subjected to ADME (adsorption, distribution, metabolism, excretion) and toxicity prediction, and ten hits were identified as potential inhibitors targeting ERα. Molecular docking was used to investigate the binding modes between ERα and three most potent hits, and molecular dynamic simulations were chosen to explore the stability of these complexes. The rank of the predicted binding free energies evaluated by MM/GBSA is consistent with the docking score. These novel scaffolds discovered in the present study can be used as critical starting point in the drug discovery process for treating ERα-positive breast cancer. Graphical abstract .

FBXW10 promotes hepatocarcinogenesis in male patients and mice

Hepatocellular carcinoma (HCC) is reported to associate with abnormal expression of SCF E3 ubiquitin ligases. FBXW10, an F-box protein of the E3 ubiquitin ligases, was abnormally regulated in HCC patients. However, whether FBXW10 is associated with HCC has not yet been evaluated. Here, we analyzed the associations between overall survival and various risk factors in 191 HCC tissues. Univariate and multivariate analyses demonstrated that FBXW10 was an independent risk factor related to HCC prognosis. The results showed that FBXW10, gender and tumor state were strongly associated with overall survival in HCC patients. Furthermore, high expression of FBXW10 was associated with poor survival among male HCC patients but not female HCC patients. FBXW10 was more highly expressed in male HCC tissues and more strongly related to vascular invasion in male HCC patients. Consistent with these findings, the male FBXW10-Tg(+) mice were more susceptible to tumorigenesis, changes in regenerative capacity, and liver injury and inflammation but not changes in liver function than FBXW10-Tg(–) mice. FBXW10 promoted cell proliferation and migration in HCC cell lines. Our findings reveal that FBXW10, an independent risk factor for HCC, promotes hepatocarcinogenesis in male patients, and is also a potential prognostic marker in male patients with HCC.

The Histone Demethylase Enzymes KDM3A and KDM4B Co-Operatively Regulate Chromatin Transactions of the Estrogen Receptor in Breast Cancer

Many estrogen receptor (ER)-positive breast cancers develop resistance to endocrine therapy but retain canonical receptor signalling in the presence of selective ER antagonists. Numerous co-regulatory proteins, including enzymes that modulate the chromatin environment, control the transcriptional activity of the ER. Targeting ER co-regulators has therefore been proposed as a novel therapeutic approach. By assessing DNA-binding dynamics in ER-positive breast cancer cells, we have identified that the histone H3 lysine 9 demethylase enzymes, KDM3A and KDM4B, co-operate to regulate ER activity via an auto-regulatory loop that facilitates the recruitment of each co-activating enzyme to chromatin. We also provide evidence that suggests that KDM3A primes chromatin for deposition of the ER pioneer factor FOXA1 and recruitment of the ER-transcriptional complex, all prior to ER recruitment, therefore establishing an important mechanism of chromatin regulation involving histone demethylases and pioneer factors, which controls ER functionality. Importantly, we show via global gene-expression analysis that a KDM3A/KDM4B/FOXA1 co-regulated gene signature is enriched for pro-proliferative and ER-target gene sets, suggesting that abrogation of this network could be an efficacious therapeutic strategy. Finally, we show that depletion of both KDM3A and KDM4B has a greater inhibitory effect on ER activity and cell growth than knockdown of each individual enzyme, suggesting that targeting both enzymes represents a potentially efficacious therapeutic option for ER-driven breast cancer.

FBXO22 mediates polyubiquitination and inactivation of LKB1 to promote lung cancer cell growth

Liver kinase B1 (LKB1) regulates both cell growth and energy metabolism. Inactivated mutations of LKB1, observed in 20–30% of nonsmall cell lung cancers (NSCLC), contribute significantly to lung cancer malignancy progression. However, the upstream signalings regulating LKB1 activity remain incompletely understood. Here, we present evidence that FBXO22 interacts with and promotes polyubiquitination of LKB1. More intriguingly, FBXO22 mediates Lys-63-linked LKB1 polyubiquitination and inhibits kinase activity of LKB1. Furthermore, over-expression of FBXO22 promotes NSCLC cell growth through inhibiting LKB1-AMPK-mTOR signaling in vitro and in vivo. Clinically, FBXO22 is highly expressed in human lung adenocarcinoma and high FBXO22 expression predicts significant poor prognosis. Our study provides new insights into the upstream regulation of LKB1 activation and identifies FBXO22 as a potential therapeutic target for lung cancer treatment.

SCFFBXO22 targets HDM2 for degradation and modulates breast cancer cell invasion and metastasis

Human homolog of mouse double minute 2 (HDM2) is an oncogene frequently overexpressed in cancers with poor prognosis, but mechanisms of controlling its abundance remain elusive. In an unbiased biochemical search, we discovered Skp1-Cullin 1-FBXO22-ROC1 (SCF^FBXO22) as the most dominating HDM2 E3 ubiquitin ligase from human proteome. The results of protein decay rate analysis, ubiquitination, siRNA-mediated silencing, and coimmunoprecipitation experiments support a hypothesis that FBXO22 targets cellular HDM2 for ubiquitin-dependent degradation. In human breast cancer cells, FBXO22 knockdown (KD) increased cell invasiveness, which was driven by elevated levels of HDM2. Moreover, mouse 4T1 breast tumor model studies revealed that FBXO22 KD led to a significant increase of breast tumor cell metastasis to the lung. Finally, low FBXO22 expression is correlated with worse survival and high HDM2 expression in human breast cancer. Altogether, these findings suggest that SCF^FBXO22 targets HDM2 for degradation and possesses inhibitory effects against breast cancer tumor cell invasion and metastasis.

A temperature-sensitive phase-change hydrogel of tamoxifen achieves the long-acting antitumor activation on breast cancer cells

Background: Breast cancer is one of the foremost threats to female health nowadays. Tamoxifen, an antagonist of estrogen receptor-α (ERα), is the first choice for endocrine-dependent breast cancer (ERα-positive breast cancer) treatment. However, ERα has an important function in the normal physical regulation of estrogen, and current oral administration of tamoxifen has potential side effects on normal endocrine secretion. In the present work, we aim to develop novel approaches to increase the antitumor effect of tamoxifen on breast cancer cells and decrease the potential side effects in the human body during treatment. Methods: A temperature-sensitive phase-change hydrogel for tamoxifen (Tam-Gel) was generated. After establishing subcutaneous tumors formed by MCF-7, an ERα-positive breast cancer cell line, in nude mice, an intratumoral injection of Tam-Gel was performed to examine whether Tam-Gel facilitated the slow-release or antitumor effect of tamoxifen. A metastatic breast cancer model was established using the intrahepatic growth of MCF-7 cells in immunodeficient rats. Results: Tam-Gel can transform from liquid to hydrogel at room temperature. An intratumoral injection of Tam-Gel facilitated the slow-release or antitumor effect of tamoxifen. Once Tam-Gel, but not Tam-Sol, was administered by intratumoral injection, it significantly decreased the uptake of radionuclide probes (¹⁸F-fluoroestradiol or ¹⁸F-fluorodeoxyglucose) by cells in rats' livers and the intrahepatic growth of MCF-7 cells in rats' livers. Conclusion: A novel slow-release system was successfully prepared to facilitate the long-term release of tamoxifen in breast cancer tissues, and achieved an antitumor effect in the long term.

KDM4B: A Nail for Every Hammer?

Epigenetic changes are well-established contributors to cancer progression and normal developmental processes. The reversible modification of histones plays a central role in regulating the nuclear processes of gene transcription, DNA replication, and DNA repair. The KDM4 family of Jumonj domain histone demethylases specifically target di- and tri-methylated lysine 9 on histone H3 (H3K9me3), removing a modification central to defining heterochromatin and gene repression. KDM4 enzymes are generally over-expressed in cancers, making them compelling targets for study and therapeutic inhibition. One of these family members, KDM4B, is especially interesting due to its regulation by multiple cellular stimuli, including DNA damage, steroid hormones, and hypoxia. In this review, we discuss what is known about the regulation of KDM4B in response to the cellular environment, and how this context-dependent expression may be translated into specific biological consequences in cancer and reproductive biology.