An oncogenic JMJD6-DGAT1 axis tunes the epigenetic regulation of lipid droplet formation in clear cell renal cell carcinoma.

Characterized by intracellular lipid droplet accumulation, clear cell renal cell carcinoma (ccRCC) is resistant to cytotoxic chemotherapy and is a lethal disease. Through an unbiased siRNA screen of 2-oxoglutarate (2-OG)-dependent enzymes, which play a critical role in tumorigenesis, we identified Jumonji domain-containing 6 (JMJD6) as an essential gene for ccRCC tumor development. The downregulation of JMJD6 abolished ccRCC colony formation in vitro and inhibited orthotopic tumor growth in vivo. Integrated ChIP-seq and RNA-seq analyses uncovered diacylglycerol O-acyltransferase 1 (DGAT1) as a critical JMJD6 effector. Mechanistically, JMJD6 interacted with RBM39 and co-occupied DGAT1 gene promoter with H3K4me3 to induce DGAT1 expression. JMJD6 silencing reduced DGAT1, leading to decreased lipid droplet formation and tumorigenesis. The pharmacological inhibition (or depletion) of DGAT1 inhibited lipid droplet formation in vitro and ccRCC tumorigenesis in vivo. Thus, the JMJD6-DGAT1 axis represents a potential new therapeutic target for ccRCC.

Genome-wide Screening Identifies SFMBT1 as an Oncogenic Driver in Cancer with VHL Loss.

von Hippel-Lindau (VHL) is a critical tumor suppressor in clear cell renal cell carcinomas (ccRCCs). It is important to identify additional therapeutic targets in ccRCC downstream of VHL loss besides hypoxia-inducible factor 2α (HIF2α). By performing a genome-wide screen, we identified Scm-like with four malignant brain tumor domains 1 (SFMBT1) as a candidate pVHL target. SFMBT1 was considered to be a transcriptional repressor but its role in cancer remains unclear. ccRCC patients with VHL loss-of-function mutations displayed elevated SFMBT1 protein levels. SFMBT1 hydroxylation on Proline residue 651 by EglN1 mediated its ubiquitination and degradation governed by pVHL. Depletion of SFMBT1 abolished ccRCC cell proliferation in vitro and inhibited orthotopic tumor growth in vivo. Integrated analyses of ChIP-seq, RNA-seq, and patient prognosis identified sphingosine kinase 1 (SPHK1) as a key SFMBT1 target gene contributing to its oncogenic phenotype. Therefore, the pVHL-SFMBT1-SPHK1 axis serves as a potential therapeutic avenue for ccRCC.

The Roles of Cullin-2 E3 Ubiquitin Ligase Complex in Cancer.

Posttranslational protein modifications play an important role in regulating protein stability and cellular function. There are at least eight Cullin family members. Among them, Cullin-2 forms a functional E3 ligase complex with elongin B, elongin C, RING-box protein 1 (RBX1, also called ROC1), as well as the substrate recognition subunit (SRS) to promote the substrate ubiquitination and degradation. In this book chapter, we will review Cullin-2 E3 ligase complexes that include various SRS proteins, including von Hippel Lindau (pVHL), leucine-rich repeat protein-1 (LRR-1), preferentially expressed antigen of melanoma (PRAME), sex-determining protein FEM-1 and early embryogenesis protein ZYG-11. We will focus on the VHL signaling pathway in clear cell renal cell carcinoma (ccRCC), which may reveal various therapeutic avenues in treating this lethal cancer.

Cobalamin and folate protect mitochondrial and contractile functions in a murine model of cardiac pressure overload.

PGC-1α, a key regulator of energy metabolism, seems to be a relevant therapeutic target to rectify the energy deficit observed in heart failure (HF). Since our previous work has shown positive effects of cobalamin (Cb) on PGC-1α cascade, we investigate the protective role of Cb in pressure overload-induced myocardial dysfunction. Mice were fed with normal diet (ND) or with Cb and folate supplemented diet (SD) 3weeks before and 4weeks after transverse aortic constriction (TAC). At the end, left ventricle hypertrophy and drop of ejection fraction were significantly lower in SD mice than in ND mice. Alterations in mitochondrial oxidative capacity, fatty acid oxidation and mitochondrial biogenesis transcription cascade were markedly improved by SD. In SD-TAC mice, lower expression level of the acetyltransferase GCN5 and upregulation of the methyltransferase PRMT1 were associated with a lower protein acetylation and a higher protein methylation levels. This was accompanied by a sustained expression of genes involved in mitochondrial biogenesis transcription cascade (Tfam, Nrf2, Cox1 and Cox4) after TAC in SD mice, suggesting a preserved activation of PGC-1α; this could be at least partly due to corrected acetylation/methylation status of this co-activator. The beneficial effect of the treatment would not be due to an effect of Cb and folate on oxidative stress or on homocysteinemia, which were unchanged by SD. These results showed that Cb and folate could protect the failing heart by preserving energy status through maintenance of mitochondrial biogenesis. It reinforces the concept of a metabolic therapy of HF.

New Insights into Protein Hydroxylation and Its Important Role in Human Diseases.

Protein hydroxylation is a post-translational modification catalyzed by 2-oxoglutarate-dependent dioxygenases. The hydroxylation modification can take place on various amino acids, including but not limited to proline, lysine, asparagine, aspartate and histidine. A classical example of this modification is hypoxia inducible factor alpha (HIF-α) prolyl hydroxylation, which affects HIF-α protein stability via the Von-Hippel Lindau (VHL) tumor suppressor pathway, a Cullin 2-based E3 ligase adaptor protein frequently mutated in kidney cancer. In addition to protein stability regulation, protein hydroxylation may influence other post-translational modifications or the kinase activity of the modified protein (such as Akt and DYRK1A/B). In other cases, protein hydroxylation may alter protein-protein interaction and its downstream signaling events in vivo (such as OTUB1, MAPK6 and eEF2K). In this review, we highlight the recently identified protein hydroxylation targets and their pathophysiological roles, especially in cancer settings. Better understanding of protein hydroxylation will help identify novel therapeutic targets and their regulation mechanisms to foster development of more effective treatment strategies for various human cancers.

New orphan disease therapies from the proteome of industrial plasma processing waste- a treatment for aceruloplasminemia.

Plasma-derived therapeutic proteins are produced through an industrial fractionation process where proteins are purified from individual intermediates, some of which remain unused and are discarded. Relatively few plasma-derived proteins are exploited clinically, with most of available plasma being directed towards the manufacture of immunoglobulin and albumin. Although the plasma proteome provides opportunities to develop novel protein replacement therapies, particularly for rare diseases, the high cost of plasma together with small patient populations impact negatively on the development of plasma-derived orphan drugs. Enabling therapeutics development from unused plasma fractionation intermediates would therefore constitute a substantial innovation. To this objective, we characterized the proteome of unused plasma fractionation intermediates and prioritized proteins for their potential as new candidate therapies for human disease. We selected ceruloplasmin, a plasma ferroxidase, as a potential therapy for aceruloplasminemia, an adult-onset ultra-rare neurological disease caused by iron accumulation as a result of ceruloplasmin mutations. Intraperitoneally administered ceruloplasmin, purified from an unused plasma fractionation intermediate, was able to prevent neurological, hepatic and hematological phenotypes in ceruloplasmin-deficient mice. These data demonstrate the feasibility of transforming industrial waste plasma fraction into a raw material for manufacturing of new candidate proteins for replacement therapies, optimizing plasma use and reducing waste generation.

ZHX2 promotes HIF1α oncogenic signaling in triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is an aggressive and highly lethal disease, which warrants the critical need to identify new therapeutic targets. We show that Zinc Fingers and Homeoboxes 2 (ZHX2) is amplified or overexpressed in TNBC cell lines and patients. Functionally, depletion of ZHX2 inhibited TNBC cell growth and invasion in vitro, orthotopic tumor growth, and spontaneous lung metastasis in vivo. Mechanistically, ZHX2 bound with hypoxia-inducible factor (HIF) family members and positively regulated HIF1α activity in TNBC. Integrated ChIP-seq and gene expression profiling demonstrated that ZHX2 co-occupied with HIF1α on transcriptionally active promoters marked by H3K4me3 and H3K27ac, thereby promoting gene expression. Among the identified ZHX2 and HIF1α coregulated genes, overexpression of AP2B1, COX20, KDM3A, or PTGES3L could partially rescue TNBC cell growth defect by ZHX2 depletion, suggested that these downstream targets contribute to the oncogenic role of ZHX2 in an accumulative fashion. Furthermore, multiple residues (R491, R581, and R674) on ZHX2 are important in regulating its phenotype, which correspond with their roles on controlling ZHX2 transcriptional activity in TNBC cells. These studies establish that ZHX2 activates oncogenic HIF1α signaling, therefore serving as a potential therapeutic target for TNBC.

Adenylosuccinate lyase hydroxylation contributes to triple negative breast cancer via the activation of cMYC.

Hydroxylation is a post-translational modification affecting protein stability, activity or interactome. We identified adenylosuccinate lyase (ADSL) as a novel hydroxylation substrate in triple negative breast cancer. Hydroxylation affects ADSL enzymatic activity and, therefore, adenosine levels. Adenosine, in turn, favors the translation of cMYC, triggering its oncogenic downstream cascade.

Identification of BBOX1 as a Therapeutic Target in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is an aggressive and highly lethal disease. Because of its heterogeneity and lack of hormone receptors or HER2 expression, targeted therapy is limited. Here, by performing a functional siRNA screening for 2-OG-dependent enzymes, we identified gamma-butyrobetaine hydroxylase 1 (BBOX1) as an essential gene for TNBC tumorigenesis. BBOX1 depletion inhibits TNBC cell growth while not affecting normal breast cells. Mechanistically, BBOX1 binds with the calcium channel inositol-1,4,5-trisphosphate receptor type 3 (IP3R3) in an enzymatic-dependent manner and prevents its ubiquitination and proteasomal degradation. BBOX1 depletion suppresses IP3R3-mediated endoplasmic reticulum calcium release, therefore impairing calcium-dependent energy-generating processes including mitochondrial respiration and mTORC1-mediated glycolysis, which leads to apoptosis and impaired cell-cycle progression in TNBC cells. Therapeutically, genetic depletion or pharmacologic inhibition of BBOX1 inhibits TNBC tumor growth in vitro and in vivo. Our study highlights the importance of targeting the previously uncharacterized BBOX1-IP3R3-calcium oncogenic signaling axis in TNBC. SIGNIFICANCE: We provide evidence from unbiased screens that BBOX1 is a potential therapeutic target in TNBC and that genetic knockdown or pharmacologic inhibition of BBOX1 leads to decreased TNBC cell fitness. This study lays the foundation for developing effective BBOX1 inhibitors for treatment of this lethal disease.This article is highlighted in the In This Issue feature, p. 1611.

Prolyl hydroxylase substrate adenylosuccinate lyase is an oncogenic driver in triple negative breast cancer.

Protein hydroxylation affects protein stability, activity, and interactome, therefore contributing to various diseases including cancers. However, the transiency of the hydroxylation reaction hinders the identification of hydroxylase substrates. By developing an enzyme-substrate trapping strategy coupled with TAP-TAG or orthogonal GST- purification followed by mass spectrometry, we identify adenylosuccinate lyase (ADSL) as an EglN2 hydroxylase substrate in triple negative breast cancer (TNBC). ADSL expression is higher in TNBC than other breast cancer subtypes or normal breast tissues. ADSL knockout impairs TNBC cell proliferation and invasiveness in vitro and in vivo. An integrated transcriptomics and metabolomics analysis reveals that ADSL activates the oncogenic cMYC pathway by regulating cMYC protein level via a mechanism requiring ADSL proline 24 hydroxylation. Hydroxylation-proficient ADSL, by affecting adenosine levels, represses the expression of the long non-coding RNA MIR22HG, thus upregulating cMYC protein level. Our findings highlight the role of ADSL hydroxylation in controlling cMYC and TNBC tumorigenesis.

Novel RNA-Affinity Proteogenomics Dissects Tumor Heterogeneity for Revealing Personalized Markers in Precision Prognosis of Cancer.

To discriminate the patient subpopulations with different clinical outcomes within each breast cancer (BC) subtype, we introduce a robust, clinical-practical, activity-based proteogenomic method that identifies, in their oncogenically active states, candidate biomarker genes bearing patient-specific transcriptomic/genomic alterations of prognostic value. First, we used the intronic splicing enhancer (ISE) probes to sort ISE-interacting trans-acting protein factors (trans-interactome) directly from a tumor tissue for subsequent mass spectrometry characterization. In the retrospective, proteogenomic analysis of patient datasets, we identified those ISE trans-factor-encoding genes showing interaction-correlated expression patterns (iCEPs) as new BC-subtypic genes. Further, patient-specific co-alterations in mRNA expression of select iCEP genes distinguished high-risk patient subsets/subpopulations from other patients within a single BC subtype. Function analysis further validated a tumor-phenotypic trans-interactome contained the drivers of oncogenic splicing switches, representing the predominant tumor cells in a tissue, from which novel personalized biomarkers were clinically characterized/validated for precise prognostic prediction and subsequent individualized alignment of optimal therapy.

Sirtuin 1 regulates pulmonary artery smooth muscle cell proliferation: role in pulmonary arterial hypertension.

OBJECTIVE: Energy metabolism shift from oxidative phosphorylation toward glycolysis in pulmonary artery smooth muscle cells (PASMCs) is suggested to be involved in their hyperproliferation in pulmonary arterial hypertension (PAH). Here, we studied the role of the deacetylase sirtuin1 (SIRT1) in energy metabolism regulation in PASMCs via various pathways including activation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), master regulator of mitochondrial biogenesis. APPROACH AND RESULTS: Contents of PGC-1α and its downstream targets as well as markers of mitochondrial mass (voltage-dependent anion channel and citrate synthase) were diminished in human PAH PASMCs. These cells and platelet-derived growth factor-stimulated rat PASMCs demonstrated a shift in cellular acetylated/deacetylated state, as evidenced by the increase of the acetylated forms of SIRT1 targets: histone H1 and Forkhead box protein O1. Rat and human PASMC proliferation was potentiated by SIRT1 pharmacological inhibition or specific downregulation via short-interfering RNA. Moreover, after chronic hypoxia exposure, SIRT1 inducible knock out mice displayed a more intense vascular remodeling compared with their control littermates, which was associated with an increase in right ventricle pressure and hypertrophy. SIRT1 activator Stac-3 decreased the acetylation of histone H1 and Forkhead box protein O1 and strongly inhibited rat and human PASMC proliferation without affecting cell mortality. This effect was associated with the activation of mitochondrial biogenesis evidenced by higher expression of mitochondrial markers and downstream targets of PGC-1α. CONCLUSION: Altered acetylation/deacetylation balance as the result of SIRT1 inactivation is involved in the pathogenesis of PAH, and this enzyme could be a promising therapeutic target for PAH treatment.

VHL substrate transcription factor ZHX2 as an oncogenic driver in clear cell renal cell carcinoma.

Inactivation of the von Hippel-Lindau (VHL) E3 ubiquitin ligase protein is a hallmark of clear cell renal cell carcinoma (ccRCC). Identifying how pathways affected by VHL loss contribute to ccRCC remains challenging. We used a genome-wide in vitro expression strategy to identify proteins that bind VHL when hydroxylated. Zinc fingers and homeoboxes 2 (ZHX2) was found as a VHL target, and its hydroxylation allowed VHL to regulate its protein stability. Tumor cells from ccRCC patients with VHL loss-of-function mutations usually had increased abundance and nuclear localization of ZHX2. Functionally, depletion of ZHX2 inhibited VHL-deficient ccRCC cell growth in vitro and in vivo. Mechanistically, integrated chromatin immunoprecipitation sequencing and microarray analysis showed that ZHX2 promoted nuclear factor κB activation. These studies reveal ZHX2 as a potential therapeutic target for ccRCC.

EglN2 contributes to triple negative breast tumorigenesis by functioning as a substrate for the FBW7 tumor suppressor.

EglN2 contributes to ERα-positive breast tumorigenesis by acting as an estrogen-inducible gene. However, the detailed molecular mechanism(s) underlying the post-transcriptional regulation of EglN2 and its potential role in Triple Negative Breast Cancer (TNBC) remains largely unclear. By using C3Tag transgenic mice and tumor-derived C3Tag cell line, here we report that EglN2 contributes to TNBC tumor progression and genetic knockout of EglN2 improves C3Tag mice survival from tumor progression. Mechanistically, we further show that FBW7, an E3 ligase complex component that is frequently downregulated in TNBC, negatively regulates EglN2 protein stability. As such, depletion of FBW7 in breast cell lines leads to upregulation of EglN2 and other canonical FBW7 substrates. Conversely, FBW7 overexpression leads to EglN2 downregulation in a GSK3ß-dependent manner. Furthermore, we identified some potential serine or threonine residues on the C-terminal of EglN2 that may mediate its binding and potential regulation by FBW7. Together, our study reveals that EglN2 might act as an FBW7 ubiquitin ligase substrate contributing to TNBC.