Identification of the von Hippel-lindau tumor-suppressor protein as part of an active E3 ubiquitin ligase complex

The Role of the PAX Genes in Renal Cell Carcinoma

Renal cell carcinoma (RCC) is a significant oncological challenge due to its heterogeneous nature and limited treatment options. The PAX developmental gene family encodes nine highly conserved transcription factors that play crucial roles in embryonic development and organogenesis, which have been implicated in the occurrence and development of RCC. This review explores the molecular landscape of RCC, with a specific focus on the role of the PAX gene family in RCC tumorigenesis and disease progression. Of the various RCC subtypes, clear cell renal cell carcinoma (ccRCC) is the most prevalent, characterized by the loss of the von Hippel-Lindau (VHL) tumor suppressor gene. Here, we review the published literature on the expression patterns and functional implications of PAX genes, particularly PAX2 and PAX8, in the three most common RCC subtypes, including ccRCC, papillary RCC (PRCC), and chromophobe RCC (ChRCC). Further, we review the interactions and potential biological mechanisms involving PAX genes and VHL loss in driving the pathogenesis of RCC, including the key signaling pathways mediated by VHL in ccRCC and associated mechanisms implicating PAX. Lastly, concurrent with our update regarding PAX gene research in RCC, we review and comment on the targeting of PAX towards the development of novel RCC therapies.

Targeting hypoxia-inducible factors: therapeutic opportunities and challenges

Hypoxia-inducible factors (HIFs) are highly conserved transcription factors that are crucial for adaptation of metazoans to limited oxygen availability. Recently, HIF activation and inhibition have emerged as therapeutic targets in various human diseases. Pharmacologically desirable effects of HIF activation include erythropoiesis stimulation, cellular metabolism optimization during hypoxia and adaptive responses during ischaemia and inflammation. By contrast, HIF inhibition has been explored as a therapy for various cancers, retinal neovascularization and pulmonary hypertension. This Review discusses the biochemical mechanisms that control HIF stabilization and the molecular strategies that can be exploited pharmacologically to activate or inhibit HIFs. In addition, we examine medical conditions that benefit from targeting HIFs, the potential side effects of HIF activation or inhibition and future challenges in this field.

Progress of stimulus responsive nanosystems for targeting treatment of bacterial infectious diseases

In recent decades, due to insufficient concentration at the lesion site, low bioavailability and increasingly serious resistance, antibiotics have become less and less dominant in the treatment of bacterial infectious diseases. It promotes the development of efficient drug delivery systems, and is expected to achieve high absorption, targeted drug release and satisfactory therapy effects. A variety of endogenous stimulation-responsive nanosystems have been constructed by using special infection microenvironments (pH, enzymes, temperature, etc.). In this review, we firstly provide an extensive review of the current research progress in antibiotic treatment dilemmas and drug delivery systems. Then, the mechanism of microenvironment characteristics of bacterial infected lesions was elucidated to provide a strong theoretical basis for bacteria-targeting nanosystems design. In particular, the discussion focuses on the design principles of single-stimulus and dual-stimulus responsive nanosystems, as well as the use of endogenous stimulus-responsive nanosystems to deliver antimicrobial agents to target locations for combating bacterial infectious diseases. Finally, the challenges and prospects of endogenous stimulus-responsive nanosystems were summarized.

[The development of innovative therapeutic drugs targeting hypoxia responses]

The 2019 Nobel Prize in Physiology or Medicine was awarded to Dr. William G. Kaelin Jr, Dr. Peter J. Ratcliffe, and Dr. Gregg L. Semenza for their elucidation of new physiological mechanisms "How cells sense and adapt to oxygen availability". Moreover, two different drugs, HIF-PH inhibitors and HIF-2 inhibitors were also developed based on the discovery. Interestingly, those three doctors have different backgrounds as a medical oncologist, a nephrologist, and a pediatrician, respectively. They have started the research based on their own unique perspectives and eventually merged as "the elucidation of the response mechanism of living organisms to hypoxic environments". In this review, we will explain how the translational research that has begun to solve unmet clinical needs successfully contributed to the development of innovative therapeutic drugs.

von-Hippel Lindau and Hypoxia-Inducible Factor at the Center of Renal Cell Carcinoma Biology

The most common form of kidney cancer is clear cell renal cell carcinoma (ccRCC). Biallelic VHL tumor suppressor gene inactivation is the usual initiating event in both hereditary (VHL Disease) and sporadic ccRCCs. The VHL protein, pVHL, earmarks the alpha subunits of the HIF transcription factor for destruction in an oxygen-dependent manner. Deregulation of HIF2 drives ccRCC pathogenesis. Drugs inhibiting the HIF2-responsive growth factor VEGF are now mainstays of ccRCC treatment. A first-in-class allosteric HIF2 inhibitor was recently approved for treating VHL Disease-associated neoplasms and appears active against sporadic ccRCC in early clinical trials.

On the Roles of the Nuclear Non-Coding RNA-Dependent Membrane-Less Organelles in the Cellular Stress Response

At the beginning of the 21st century, it became obvious that radical changes had taken place in the concept of living matter and, in particular, in the concept of the organization of intracellular space. The accumulated data testify to the essential importance of phase transitions of biopolymers (first of all, intrinsically disordered proteins and RNA) in the spatiotemporal organization of the intracellular space. Of particular interest is the stress-induced reorganization of the intracellular space. Examples of organelles formed in response to stress are nuclear A-bodies and nuclear stress bodies. The formation of these organelles is based on liquid-liquid phase separation (LLPS) of intrinsically disordered proteins (IDPs) and non-coding RNA. Despite their overlapping composition and similar mechanism of formation, these organelles have different functional activities and physical properties. In this review, we will focus our attention on these membrane-less organelles (MLOs) and describe their functions, structure, and mechanism of formation.

Role of SOCS and VHL Proteins in Neuronal Differentiation and Development

The basic helix-loop-helix factors play a central role in neuronal differentiation and nervous system development, which involve the Notch and signal transducer and activator of transcription (STAT)/small mother against decapentaplegic signaling pathways. Neural stem cells differentiate into three nervous system lineages, and the suppressor of cytokine signaling (SOCS) and von Hippel-Lindau (VHL) proteins are involved in this neuronal differentiation. The SOCS and VHL proteins both contain homologous structures comprising the BC-box motif. SOCSs recruit Elongin C, Elongin B, Cullin5(Cul5), and Rbx2, whereas VHL recruits Elongin C, Elongin B, Cul2, and Rbx1. SOCSs form SBC-Cul5/E3 complexes, and VHL forms a VBC-Cul2/E3 complex. These complexes degrade the target protein and suppress its downstream transduction pathway by acting as E3 ligases via the ubiquitin-proteasome system. The Janus kinase (JAK) is the main target protein of the E3 ligase SBC-Cul5, whereas hypoxia-inducible factor is the primary target protein of the E3 ligase VBC-Cul2; nonetheless, VBC-Cul2 also targets the JAK. SOCSs not only act on the ubiquitin-proteasome system but also act directly on JAKs to suppress the Janus kinase-signal transduction and activator of transcription (JAK-STAT) pathway. Both SOCS and VHL are expressed in the nervous system, predominantly in brain neurons in the embryonic stage. Both SOCS and VHL induce neuronal differentiation. SOCS is involved in differentiation into neurons, whereas VHL is involved in differentiation into neurons and oligodendrocytes; both proteins promote neurite outgrowth. It has also been suggested that the inactivation of these proteins may lead to the development of nervous system malignancies and that these proteins may function as tumor suppressors. The mechanism of action of SOCS and VHL involved in neuronal differentiation and nervous system development is thought to be mediated through the inhibition of downstream signaling pathways, JAK-STAT, and hypoxia-inducible factor-vascular endothelial growth factor pathways. In addition, because SOCS and VHL promote nerve regeneration, they are expected to be applied in neuronal regenerative medicine for traumatic brain injury and stroke.

Two Single Nucleotide Polymorphisms in the Von Hippel-Lindau Tumor Suppressor Gene in Patients with Clear Cell Renal Cell Carcinoma

The most common subtype of renal cell carcinoma (RCC) is clear cell type (ccRCC), which accounts for approximately 75% of cases. von Hippel-Lindau (VHL) gene has been shown to be affected in more than half of ccRCC cases. Two single nucleotide polymorphisms (SNPs) located in VHL gene, rs779805 and rs1642742, are reported to be involved in the occurrence of ccRCC. The aim of this study was to assess their associations with clinicopathologic and immunohistochemical parameters, as well as risk and survival of ccRCC. The study population consisted of 129 patients. No significant differences in genotype or allele frequencies of VHL gene polymorphisms were observed between ccRCC cases and control population, and we have found that our results do not indicate a significant relationship of these SNPs with respect to ccRCC susceptibility. Additionally, we did not observe a significant association of these two SNPs with ccRCC survival. However, our results conclude that rs1642742 and rs779805 in the VHL gene are associated with increased tumor size, which is the most important prognostic indicator of renal cancer. Moreover, our analysis showed that patients with genotype AA of rs1642742 have a trend towards higher likelihood of developing ccRCC within their lifetime, while allele G of rs779805 can have a preventive effect against the development of renal cancer in stage 1. Therefore, these SNPs in VHL may be useful as genetic tumor markers for the molecular diagnostics for ccRCC patients.

VHL tumor suppressor as a novel potential candidate biomarker in papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is the most common type of endocrine cancer, with an increasing incidence worldwide. The treatment of PTC is currently the subject of clinical controversy, making it critically important to identify molecular markers that would help improve the risk stratification of PTC patients and optimize the therapeutic approach. The VHL tumor suppressor gene has been implicated in tumorigenesis of various types of carcinoma and linked with their aggressive biological behavior. The role of VHL in the origin and development of PTC has only recently begun to be revealed. In this narrative review we attempt to summarize the existing knowledge that implicates VHL in PTC pathogenesis and to outline its potential significance as a candidate molecular biomarker for the grouping of PTC patients into high and low risk groups.

The Clinical and Molecular Features in the VHL Renal Cancers; Close or Distant Relatives with Sporadic Clear Cell Renal Cell Carcinoma?

Von Hippel-Lindau (VHL) disease is an autosomal dominant inherited cancer syndrome caused by germline mutations in the VHL tumor suppressor gene, characterized by the susceptibility to a wide array of benign and malign neoplasms, including clear-cell renal cell carcinoma. Moreover, VHL somatic inactivation is a crucial molecular event also in sporadic ccRCCs tumorigenesis. While systemic biomarkers in the VHL syndrome do not currently play a role in clinical practice, a new promising class of predictive biomarkers, microRNAs, has been increasingly studied. Lots of pan-genomic studies have deeply investigated the possible biological role of microRNAs in the development and progression of sporadic ccRCC; however, few studies have investigated the miRNA profile in VHL patients. Our review summarize all the new insights related to clinical and molecular features in VHL renal cancers, with a particular focus on the overlap with sporadic ccRCC.

Design and optimization of oestrogen receptor PROTACs based on 4-hydroxytamoxifen

In the last four decades, treatment of oestrogen receptor positive (ER+) breast cancer (BCa), has focused on targeting the estrogenic receptor signaling pathway. This signaling function is pivotal to sustain cell proliferation. Tamoxifen, a competitive inhibitor of oestrogen, has played a major role in therapeutics. However, primary and acquired resistance to hormone blockade occurs in a large subset of these cancers, and new approaches are urgently needed. Aromatase inhibitors and receptor degraders were approved and alternatively used. Yet, resistance appears in the metastatic setting. Here we report the design and synthesis of a series of proteolysis targeting chimeras (PROTACs) that induce the degradation of estrogen receptor alpha in breast cancer MCF-7 (ER+) cells at nanomolar concentration. Using a warhead based on 4-hydroxytamoxifen, bifunctional degraders recruiting either cereblon or the Von Hippel Lindau E3 ligases were synthesized. Our efforts resulted in the discovery of TVHL-1, a potent ERα degrader (DC₅₀: 4.5 nM) that we envisage as a useful tool for biological study and a platform for potential therapeutics.

Presentation, imaging, patterns of care, growth, and outcome in sporadic and von Hippel-Lindau-associated central nervous system hemangioblastomas

OBJECT

Hemangioblastoma is a relatively rare neoplasm occurring mostly in the cerebellum that may arise sporadically or in the context of von Hippel-Lindau (VHL) syndrome. Presentation, imaging, natural history, surgical patterns of care, and outcomes are incompletely defined for this uncommon lesion. We reviewed our large institutional series to help clarify these issues.

METHODS

Retrospective analysis of consecutive, neurosurgically managed CNS hemangioblastomas at Mayo Clinic, 1988-2018.

RESULTS

Two hundred and eighty five hemangioblastomas were treated in 184 unique patients (115 sporadic, 69 VHL). Compared to sporadic patients, VHL patients were younger (36.7 vs 51.7 years; p < 0.0001), were treated while asymptomatic more commonly (47.3 vs 4.2%; p < 0.0001), had smaller lesions (6.6 vs 13.9 mL; p < 0.0001), and harbored lesions with associated cysts less frequently (51.0 vs 75.0%; p = 0.0002). Macrocystic tumor architecture was associated with larger lesion size and greater symptom severity. Solid lesions later formed cysts at a median 130 months. Growth in both total volume and solid component accelerated after cyst formation (10.6 and 6.0 times median rate prior to cyst emergence). VHL patients died at a younger age (47.9 vs 74.5, p = 0.0017) and were more likely to die of direct disease sequelae. Though treatment-free survival time was significantly longer in sporadic cases, a substantial fraction (> 40%) developed tumor recurrence/progression requiring additional treatment.

CONCLUSIONS

Hemangioblastoma presentation varies with etiology and clinical course is more complicated in VHL cases. Nodular lesions often develop cysts over time which is associated with accelerated tumor growth. Sporadic cases have a previously unappreciated but substantial risk of late recurrence/progression requiring treatment.

Generation of a live attenuated influenza A vaccine by proteolysis targeting

The usefulness of live attenuated virus vaccines has been limited by suboptimal immunogenicity, safety concerns or cumbersome manufacturing processes and techniques. Here we describe the generation of a live attenuated influenza A virus vaccine using proteolysis-targeting chimeric (PROTAC) technology to degrade viral proteins via the endogenous ubiquitin-proteasome system of host cells. We engineered the genome of influenza A viruses in stable cell lines engineered for virus production to introduce a conditionally removable proteasome-targeting domain, generating fully infective PROTAC viruses that were live attenuated by the host protein degradation machinery upon infection. In mouse and ferret models, PROTAC viruses were highly attenuated and able to elicit robust and broad humoral, mucosal and cellular immunity against homologous and heterologous virus challenges. PROTAC-mediated attenuation of viruses may be broadly applicable for generating live attenuated vaccines.

Inhibition of HIF-1α Attenuates Silica-Induced Pulmonary Fibrosis

Background: Excessive accumulation of extracellular matrix is a key feature of pulmonary fibrosis (PF), and myofibroblasts are the main producers of extracellular matrix. Fibroblasts are the major source of myofibroblasts, but the mechanisms of transdifferentiation are unclear. Methods: In vitro, transforming growth factor-β1 was used to induce NIH-3T3 cell transdifferentiation. DMOG was used to increase hypoxia-inducible factor-1α subunit (HIF-1α) expression. KC7F2 and siRNA decreased HIF-1α expression. In vivo, silica particles were used to induce PF in C57BL/6N mice, and KC7F2 was used to reduce HIF-1α expression in C57BL/6N mice. Western blot was used to detect the expression of collagen type 1 alpha 1(COL1A1), α-smooth muscle actin (α-SMA), SMAD family member (SAMD) 3, Phospho-SMAD3 (PSMAD3), and HIF-1α. PCR was used to detect the expression of COL1A1, α-SMA, and HIF-1α. Immunohistochemistry was used to detect the expression of COL1A1 and HIF-1α. Results: In vitro, compared to the control group, COL1A1, α-SMA, PSMAD3, and HIF-1α expression were elevated in the DMOG group, and COL1A1, α-SMA, PSMAD3, and HIF-1α expression were decreased in the KC7F2 group and siRNA group. Compared to the DMOG group, COL1A1, α-SMA, and PSMAD3 expression were decreased in the DMOG + SIS3 group. In vivo, compared to the saline group, COL1A1, α-SMA, PSMAD3, and HIF-1α expression were increased in the pulmonary tissue of C57BL/6N mice in the silica group. Compared to the silica group, COL1A1, α-SMA, PSMAD3, and HIF-1α expression and the degree of PF were decreased in the silica + KC7F2 group. Conclusion: Inhibition of HIF-1α reduced α-SMA, decreased COL1A1 expression, and attenuated the degree of PF in C57BL/6N mice. Therefore, HIF-1α may be a new target for the treatment of silica-induced PF.

Human Protein-l-isoaspartate O-Methyltransferase Domain-Containing Protein 1 (PCMTD1) Associates with Cullin-RING Ligase Proteins

The spontaneous l-isoaspartate protein modification has been observed to negatively affect protein function. However, this modification can be reversed in many proteins in reactions initiated by the protein-l-isoaspartyl (d-aspartyl) O-methyltransferase (PCMT1). It has been hypothesized that an additional mechanism exists in which l-isoaspartate-damaged proteins are recognized and proteolytically degraded. Herein, we describe the protein-l-isoaspartate O-methyltransferase domain-containing protein 1 (PCMTD1) as a putative E3 ubiquitin ligase substrate adaptor protein. The N-terminal domain of PCMTD1 contains l-isoaspartate and S-adenosylmethionine (AdoMet) binding motifs similar to those in PCMT1. This protein also has a C-terminal domain containing suppressor of cytokine signaling (SOCS) box ubiquitin ligase recruitment motifs found in substrate receptor proteins of the Cullin-RING E3 ubiquitin ligases. We demonstrate specific PCMTD1 binding to the canonical methyltransferase cofactor S-adenosylmethionine (AdoMet). Strikingly, while PCMTD1 is able to bind AdoMet, it does not demonstrate any l-isoaspartyl methyltransferase activity under the conditions tested here. However, this protein is able to associate with the Cullin-RING proteins Elongins B and C and Cul5 in vitro and in human cells. The previously uncharacterized PCMTD1 protein may therefore provide an alternate maintenance pathway for modified proteins in mammalian cells by acting as an E3 ubiquitin ligase adaptor protein.

Atypical Ubiquitination and Parkinson's Disease

Ubiquitination (the covalent attachment of ubiquitin molecules to target proteins) is one of the main post-translational modifications of proteins. Historically, the type of polyubiquitination, which involves K48 lysine residues of the monomeric ubiquitin, was the first studied type of ubiquitination. It usually targets proteins for their subsequent proteasomal degradation. All the other types of ubiquitination, including monoubiquitination; multi-monoubiquitination; and polyubiquitination involving lysine residues K6, K11, K27, K29, K33, and K63 and N-terminal methionine, were defined as atypical ubiquitination (AU). Good evidence now exists that AUs, participating in the regulation of various cellular processes, are crucial for the development of Parkinson's disease (PD). These AUs target various proteins involved in PD pathogenesis. The K6-, K27-, K29-, and K33-linked polyubiquitination of alpha-synuclein, the main component of Lewy bodies, and DJ-1 (another PD-associated protein) is involved in the formation of insoluble aggregates. Multifunctional protein kinase LRRK2 essential for PD is subjected to K63- and K27-linked ubiquitination. Mitophagy mediated by the ubiquitin ligase parkin is accompanied by K63-linked autoubiquitination of parkin itself and monoubiquitination and polyubiquitination of mitochondrial proteins with the formation of both classical K48-linked ubiquitin chains and atypical K6-, K11-, K27-, and K63-linked polyubiquitin chains. The ubiquitin-specific proteases USP30, USP33, USP8, and USP15, removing predominantly K6-, K11-, and K63-linked ubiquitin conjugates, antagonize parkin-mediated mitophagy.

The evolutionarily conserved arginyltransferase 1 mediates a pVHL-independent oxygen-sensing pathway in mammalian cells

The response to oxygen availability is a fundamental process concerning metabolism and survival/death in all mitochondria-containing eukaryotes. However, the known oxygen-sensing mechanism in mammalian cells depends on pVHL, which is only found among metazoans but not in other species. Here, we present an alternative oxygen-sensing pathway regulated by ATE1, an enzyme ubiquitously conserved in eukaryotes that influences protein degradation by posttranslational arginylation. We report that ATE1 centrally controls the hypoxic response and glycolysis in mammalian cells by preferentially arginylating HIF1α that is hydroxylated by PHD in the presence of oxygen. Furthermore, the degradation of arginylated HIF1α is independent of pVHL E3 ubiquitin ligase but dependent on the UBR family proteins. Bioinformatic analysis of human tumor data reveals that the ATE1/UBR and pVHL pathways jointly regulate oxygen sensing in a transcription-independent manner with different tissue specificities. Phylogenetic analysis suggests that eukaryotic ATE1 likely evolved during mitochondrial domestication, much earlier than pVHL.

PBLD inhibits angiogenesis via impeding VEGF/VEGFR2-mediated microenvironmental cross-talk between HCC cells and endothelial cells

Sustained anti-angiogenesis therapy increases the level of tumor hypoxia, leading to increased expression of HIF-1a, thereby contributing to the resistance to anti-angiogenesis therapy in hepatocellular carcinoma (HCC). Here, we report that phenazine biosynthesis-like domain-containing protein (PBLD) inhibits hypoxia-induced angiogenesis via ERK/HIF-1a/VEGF axis in HCC cells. Bioinformatic analysis of the TCGA database and clinical samples validation also identify a negative correlation between PBLD and angiogenesis-related genes expression including HIF-1a. Apart from the downregulation of HIF-1a/VEGF expression in HCC cells, PBLD also blocks VEGF receptor 2 (VEGFR2) on endothelial cells via HCC-derived exosomal miR-940. PBLD also activates TCF4 transcriptional promotion effects on miR-940 by directly interacting with it. Together, PBLD exerts an inhibitory effect on angiogenesis not only via blocking the VEGFR2 expression in endothelial cells, but also through downregulating HIF-1a-induced VEGF expression and secretion in HCC cells. These explorations may provide a theoretical basis for exploring new targets and strategies to overcome resistance to anti-angiogenesis therapy.

Homeostatic Regulation of Glucocorticoid Receptor Activity by Hypoxia-Inducible Factor 1: From Physiology to Clinic

Glucocorticoids (GCs) represent a well-known class of lipophilic steroid hormones biosynthesised, with a circadian rhythm, by the adrenal glands in humans and by the inter-renal tissue in teleost fish (e.g., zebrafish). GCs play a key role in the regulation of numerous physiological processes, including inflammation, glucose, lipid, protein metabolism and stress response. This is achieved through binding to their cognate receptor, GR, which functions as a ligand-activated transcription factor. Due to their potent anti-inflammatory and immune-suppressive action, synthetic GCs are broadly used for treating pathological disorders that are very often linked to hypoxia (e.g., rheumatoid arthritis, inflammatory, allergic, infectious, and autoimmune diseases, among others) as well as to prevent graft rejections and against immune system malignancies. However, due to the presence of adverse effects and GC resistance their therapeutic benefits are limited in patients chronically treated with steroids. For this reason, understanding how to fine-tune GR activity is crucial in the search for novel therapeutic strategies aimed at reducing GC-related side effects and effectively restoring homeostasis. Recent research has uncovered novel mechanisms that inhibit GR function, thereby causing glucocorticoid resistance, and has produced some surprising new findings. In this review we analyse these mechanisms and focus on the crosstalk between GR and HIF signalling. Indeed, its comprehension may provide new routes to develop novel therapeutic targets for effectively treating immune and inflammatory response and to simultaneously facilitate the development of innovative GCs with a better benefits-risk ratio.

Retinal Diseases Regulated by Hypoxia-Basic and Clinical Perspectives: A Comprehensive Review

In recent years, the number of patients with age-related macular degeneration (AMD) is increasing worldwide along with increased life expectancy. Currently, the standard treatment for wet-AMD is intravitreal injection of anti-vascular endothelial growth factor (VEGF) drugs. The upstream of VEGF is hypoxia-inducible factor (HIF), a master regulator of hypoxia-responsive genes responsive to acute and chronic hypoxia. HIF activation induces various pathological pro-angiogenic gene expressions including VEGF under retinal hypoxia, ultimately leading to the development of ocular ischemic neovascular diseases. In this regard, HIF is considered as a promising therapeutic target in ocular ischemic diseases. In clinical ophthalmology, abnormal hypofluorescent areas have been detected in the late-phase of indocyanine green angiography, which are thought to be lipid deposits at the level of Bruch’s membrane to choriocapillaris in vitreoretinal diseases. These deposits may interfere with the oxygen and nutrients that should be supplied to the retinal pigment epithelium, and that HIF/VEGF is highly suspected to be expressed in the hypoxic retinal pigment epithelium, leading to neovascularization. In this review, we comprehensively summarize pathophysiology of AMD-related ocular diseases with the HIF/VEGF pathway from basic and clinic researches with recent findings.

The ubiquitin ligase HOIL-1L regulates immune responses by interacting with linear ubiquitin chains

The Linear Ubiquitin Chain Assembly Complex (LUBAC), composed of HOIP, HOIL-1L, and SHARPIN, promotes tumor necrosis factor (TNF)-dependent NF-κB signaling in diverse cell types. HOIL-1L contains an Npl4 Zinc Finger (NZF) domain that specifically recognizes linear ubiquitin chains, but its physiological role in vivo has remained unclear. Here, we demonstrate that the HOIL-1L NZF domain has important regulatory functions in inflammation and immune responses in mice. We generated knockin mice (Hoil-1l^{T201A;R208A/T201A;R208A}) expressing a HOIL-1L NZF mutant and observed attenuated responses to TNF- and LPS-induced shock, including prolonged survival, stabilized body temperature, reduced cytokine production, and liver damage markers. Cells derived from Hoil-1l^{T201A;R208A/T201A;R208A} mice show reduced TNF-dependent NF-κB activation and incomplete recruitment of HOIL-1L into TNF Receptor (TNFR) Complex I. We further show that HOIL-1L NZF cooperates with SHARPIN to prevent TNFR-dependent skin inflammation. Collectively, our data suggest that linear ubiquitin-chain binding by HOIL-1L regulates immune responses and inflammation in vivo.

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An RBR-type E3 ligase HOIL-1L decodes linear ubiquitin chains via the NZF domain

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HOIL-1L NZF is essential for proper responses to LPS and TNF-induced shock in mice

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Intact HOIL-1L NZF is required for activating the TNF-induced NF-kB pathway

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HOIL-1L NZF cooperates with SHARPIN to control inflammation in mice

Hydroxylation of the Acetyltransferase NAA10 Trp38 Is Not an Enzyme-Switch in Human Cells

NAA10 is a major N-terminal acetyltransferase (NAT) that catalyzes the cotranslational N-terminal (Nt-) acetylation of 40% of the human proteome. Several reports of lysine acetyltransferase (KAT) activity by NAA10 exist, but others have not been able to find any NAA10-derived KAT activity, the latter of which is supported by structural studies. The KAT activity of NAA10 towards hypoxia-inducible factor 1α (HIF-1α) was recently found to depend on the hydroxylation at Trp38 of NAA10 by factor inhibiting HIF-1α (FIH). In contrast, we could not detect hydroxylation of Trp38 of NAA10 in several human cell lines and found no evidence that NAA10 interacts with or is regulated by FIH. Our data suggest that NAA10 Trp38 hydroxylation is not a switch in human cells and that it alters its catalytic activity from a NAT to a KAT.

Aberrant activation of m6A demethylase FTO renders HIF2αlow/- clear cell renal cell carcinoma sensitive to BRD9 inhibitors

[Figure: see text].

An efficient strategy for digging protein-protein interactions for rational drug design - A case study with HIF-1α/VHL

The ubiquitination of the hypoxia-inducible factor-1α (HIF-1α) is mediated by interacting with the von Hippel-Lindau protein (VHL), and is associated with cancer, chronic anemia, and ischemia. VHL, an E3 ligase, has been reported to degrade HIF-1 for decades, however, there are few successful inhibitors currently. Poor understanding of the binding pocket and a lack of in-depth exploration of the interactions between two proteins are the main reasons. Hence, we developed an effective strategy to identify and design new inhibitors for protein-protein interaction targets. The hydroxyproline (Hyp564) of HIF-1α contributed the key interaction between HIF-1α and VHL. In this study, detailed information of the binding pocket were explored by alanine scanning, site-directed mutagenesis and molecular dynamics simulations. Interestingly, we found the interaction(s) between Y565 and H110 played a key role in the binding of VHL/HIF-1α. Based on the interactions, 8 derivates of VH032, 16a-h, were synthesized by introducing various groups bounded to H110. Further assay on protein and cellular level exhibited that 16a-h accessed higher binding affinity to VHL and markable or modest improvement in stabilization of HIF-1α or HIF-1α-OH in HeLa cells. Our work provides a new orientation for the modification or design of VHL/HIF-1α protein-protein interaction inhibitors.

VHL suppresses RAPTOR and inhibits mTORC1 signaling in clear cell renal cell carcinoma

Inactivation of the tumor suppressor von Hippel-Lindau (VHL) gene is a key event in hereditary and sporadic clear cell renal cell carcinomas (ccRCC). The mechanistic target of rapamycin (mTOR) signaling pathway is a fundamental regulator of cell growth and proliferation, and hyperactivation of mTOR signaling is a common finding in VHL-dependent ccRCC. Deregulation of mTOR signaling correlates with tumor progression and poor outcome in patients with ccRCC. Here, we report that the regulatory-associated protein of mTOR (RAPTOR) is strikingly repressed by VHL. VHL interacts with RAPTOR and increases RAPTOR degradation by ubiquitination, thereby inhibiting mTORC1 signaling. Consistent with hyperactivation of mTORC1 signaling in VHL-deficient ccRCC, we observed that loss of vhl-1 function in C. elegans increased mTORC1 activity, supporting an evolutionary conserved mechanism. Our work reveals important new mechanistic insight into deregulation of mTORC1 signaling in ccRCC and links VHL directly to the control of RAPTOR/mTORC1. This may represent a novel mechanism whereby loss of VHL affects organ integrity and tumor behavior.

Up-down regulation of HIF-1α in cancer progression

Hypoxia induicible factor-1 alpha (HIF-1α) is a key transcription factor in cancer progression and target therapy in cancer. HIF-1α acts differently depending on presence or absence of Oxygen. In an oxygen-immersed environment, HIF-1α completely deactivated and destroyed by the ubiquitin proteasome pathway (UPP). In contrast, in the oxygen-free environment, it escapes destruction and enters to the nucleus of cells then upregulates many genes involved in cancer progression. Overexpressed HIF-1α and downstream genes support cancer progression through various mechanisms including angiogenesis, proliferation and survival of cells, metabolism reprogramming, invasion and metastasis, cancer stem cell maintenance, induction of genetic instability, and treatment resistance. HIF-1α can be provoked by signaling pathways unrelated to hypoxia during cancer progression. Therefore, cancer development and progression can be modulated by targeting HIF-1α and its downstream signaling molecules. In this regard, HIF-1α inhibitors which are categorized into the agents that regulate HIF-1α in gene, mRNA and protein levels used as an efficient way in cancer treatment. Also, HIF-1α expression can be negatively affected by the agents suppressing the activation of mTOR, PI3k/Akt and MAPK pathways.

PRDX2 promotes the proliferation of colorectal cancer cells by increasing the ubiquitinated degradation of p53

Colorectal cancer is the most common gastrointestinal cancer and causes severe damage to human health. PRDX2 is a member of the peroxiredoxin family reported to have a high level of expression in colorectal cancer. However, the mechanisms by which PRDX2 promotes the proliferation of colorectal cancer are still unclear. Here, the results indicated that PRDX2 expression was upregulated in colorectal cancer and closely correlated with poor prognosis. Functionally, PRDX2 promoted the proliferation of colorectal cancer cells. Mechanistically, PRDX2 could bind RPL4, reducing the interaction between RPL4 and MDM2. These findings demonstrate that the oncogenic property of PRDX2 may be attributed to its regulation of the RPL4-MDM2-p53 pathway, leading to p53 ubiquitinated degradation.

Hepatocyte growth factor regulates HIF-1α-induced nucleus pulposus cell proliferation through MAPK-, PI3K/Akt-, and STAT3-mediated signaling

Intervertebral discs are important for maintaining mobility and offer support to the body trunk. If these discs lose their biomechanical features, lower back pain can occur. We previously reported that hepatocyte growth factor (HGF) promotes cell proliferation and suppresses apoptosis, inflammation, and matrix degradation in nucleus pulposus (NP) cells. In the present study, we investigated the molecular mechanisms of how HGF promotes the proliferation of NP cells in hypoxic conditions. Hypoxic stimulation promoted modest cell proliferation, which was further upregulated by HGF. Expression of hypoxia-inducible factor (HIF-1α) protein, which contributes to the maintenance of homeostasis in NP cells, was also upregulated in hypoxia-treated cell groups; HGF further increased HIF-1α expression in NP cells. Additionally, knockdown of HIF-1α expression significantly reduced the proliferation of NP cells. An MAPK inhibitor inhibited the expression of HIF-1α and pERK, as well as cell proliferation in a dose-dependent manner. Similarly, inhibiting the PI3K/Akt and STAT3 pathways also decreased the expression of HIF-1α and cell proliferation. These results show that under hypoxic conditions, HGF promotes NP cell proliferation via HIF-1α-, MAPK-, PI3K/Akt-, and STAT3-mediated signaling which is involved in this pathway. The control of these signaling pathways may be a target for potential therapeutic strategies for the treatment of disc degeneration in hypoxic conditions.

HIF-α Prolyl Hydroxylase Inhibitors and Their Implications for Biomedicine: A Comprehensive Review

Oxygen is essential for the maintenance of the body. Living organisms have evolved systems to secure an oxygen environment to be proper. Hypoxia-inducible factor (HIF) plays an essential role in this process; it is a transcription factor that mediates erythropoietin (EPO) induction at the transcriptional level under hypoxic environment. After successful cDNA cloning in 1995, a line of studies were conducted for elucidating the molecular mechanism of HIF activation in response to hypoxia. In 2001, cDNA cloning of dioxygenases acting on prolines and asparagine residues, which play essential roles in this process, was reported. HIF-prolyl hydroxylases (PHs) are molecules that constitute the core molecular mechanism of detecting a decrease in the partial pressure of oxygen, or hypoxia, in the cells; they can be called oxygen sensors. In this review, I discuss the process of molecular cloning of HIF and HIF-PH, which explains hypoxia-induced EPO expression; the development of HIF-PH inhibitors that artificially or exogenously activate HIF by inhibiting HIF-PH; and the significance and implications of medical intervention using HIF-PH inhibitors.

Site-specific ubiquitination of the E3 ligase HOIP regulates apoptosis and immune signaling

HOIP, the catalytic component of the linear ubiquitin chain assembly complex (LUBAC), is a critical regulator of inflammation. However, how HOIP itself is regulated to control inflammatory responses is unclear. Here, we discover that site-specific ubiquitination of K784 within human HOIP promotes tumor necrosis factor (TNF)-induced inflammatory signaling. A HOIP K784R mutant is catalytically active but shows reduced induction of an NF-κB reporter relative to wild-type HOIP. HOIP K784 is evolutionarily conserved, equivalent to HOIP K778 in mice. We generated Hoip^K778R/K778R knock-in mice, which show no overt developmental phenotypes; however, in response to TNF, Hoip^K778R/K778R mouse embryonic fibroblasts display mildly suppressed NF-κB activation and increased apoptotic markers. On the other hand, HOIP K778R enhances the TNF-induced formation of TNFR complex II and an interaction between TNFR complex II and LUBAC. Loss of the LUBAC component SHARPIN leads to embryonic lethality in Hoip^K778R/K778R mice, which is rescued by knockout of TNFR1. We propose that site-specific ubiquitination of HOIP regulates a LUBAC-dependent switch between survival and apoptosis in TNF signaling.

Algorithmic assessment of missense mutation severity in the Von-Hippel Lindau protein

Von Hippel-Lindau disease (VHL) is an autosomal dominant rare disease that causes the formation of angiogenic tumors. When functional, pVHL acts as an E3 ubiquitin ligase that negatively regulates hypoxia inducible factor (HIF). Genetic mutations that perturb the structure of pVHL result in dysregulation of HIF, causing a wide array of tumor pathologies including retinal angioma, pheochromocytoma, central nervous system hemangioblastoma, and clear cell renal carcinoma. These VHL-related cancers occur throughout the lifetime of the patient, requiring frequent intervention procedures, such as surgery, to remove the tumors. Although VHL is classified as a rare disease (1 in 39,000 to 1 in 91,000 affected) there is a large heterogeneity in genetic mutations listed for observed pathologies. Understanding how these specific mutations correlate with the myriad of observed pathologies for VHL could provide clinicians insight into the potential severity and onset of disease. Using a select set of 285 ClinVar mutations in VHL, we developed a multiparametric scoring algorithm to evaluate the overall clinical severity of missense mutations in pVHL. The mutations were assessed according to eight weighted parameters as a comprehensive evaluation of protein misfolding and malfunction. Higher mutation scores were strongly associated with pathogenicity. Our approach establishes a novel in silico method by which VHL-specific mutations can be assessed for their severity and effect on the biophysical functions of the VHL protein.

The prefoldin complex stabilizes the von Hippel-Lindau protein against aggregation and degradation

Loss of von Hippel-Lindau protein pVHL function promotes VHL diseases, including sporadic and inherited clear cell Renal Cell Carcinoma (ccRCC). Mechanisms controlling pVHL function and regulation, including folding and stability, remain elusive. Here, we have identified the conserved cochaperone prefoldin complex in a screen for pVHL interactors. The prefoldin complex delivers non-native proteins to the chaperonin T-complex-protein-1-ring (TRiC) or Cytosolic Chaperonin containing TCP-1 (CCT) to assist folding of newly synthesized polypeptides. The pVHL-prefoldin interaction was confirmed in human cells and prefoldin knock-down reduced pVHL expression levels. Furthermore, when pVHL was expressed in Schizosaccharomyces pombe, all prefoldin mutants promoted its aggregation. We mapped the interaction of prefoldin with pVHL at the exon2-exon3 junction encoded region. Low levels of the PFDN3 prefoldin subunit were associated with poor survival in ccRCC patients harboring VHL mutations. Our results link the prefoldin complex with pVHL folding and this may impact VHL diseases progression.

Hypoxia-inducible factors not only regulate but also are myeloid-cell treatment targets

Hypoxia describes limited oxygen availability at the cellular level. Myeloid cells are exposed to hypoxia at various bodily sites and even contribute to hypoxia by consuming large amounts of oxygen during respiratory burst. Hypoxia-inducible factors (HIFs) are ubiquitously expressed heterodimeric transcription factors, composed of an oxygen-dependent α and a constitutive β subunit. The stability of HIF-1α and HIF-2α is regulated by oxygen-sensing prolyl-hydroxylases (PHD). HIF-1α and HIF-2α modify the innate immune response and are context dependent. We provide a historic perspective of HIF discovery, discuss the molecular components of the HIF pathway, and how HIF-dependent mechanisms modify myeloid cell functions. HIFs enable myeloid-cell adaptation to hypoxia by up-regulating anaerobic glycolysis. In addition to effects on metabolism, HIFs control chemotaxis, phagocytosis, degranulation, oxidative burst, and apoptosis. HIF-1α enables efficient infection defense by myeloid cells. HIF-2α delays inflammation resolution and decreases antitumor effects by promoting tumor-associated myeloid-cell hibernation. PHDs not only control HIF degradation, but also regulate the crosstalk between innate and adaptive immune cells thereby suppressing autoimmunity. HIF-modifying pharmacologic compounds are entering clinical practice. Current indications include renal anemia and certain cancers. Beneficial and adverse effects on myeloid cells should be considered and could possibly lead to drug repurposing for inflammatory disorders.

VBP1 modulates Wnt/β-catenin signaling by mediating the stability of the transcription factors TCF/LEFs

The Wnt/β-catenin pathway is one of the major pathways that regulates embryonic development, adult homeostasis, and stem cell self-renewal. In this pathway, transcription factors T-cell factor and lymphoid enhancer factor (TCF/LEF) serve as a key switch to repress or activate Wnt target gene transcription by recruiting repressor molecules or interacting with the β-catenin effector, respectively. It has become evident that the protein stability of the TCF/LEF family members may play a critical role in controlling the activity of the Wnt/β-catenin signaling pathway. However, factors that regulate the stability of TCF/LEFs remain largely unknown. Here, we report that pVHL binding protein 1 (VBP1) regulates the Wnt/β-catenin signaling pathway by controlling the stability of TCF/LEFs. Surprisingly, we found that either overexpression or knockdown of VBP1 decreased Wnt/β-catenin signaling activity in both cultured cells and zebrafish embryos. Mechanistically, VBP1 directly binds to all four TCF/LEF family members and von Hippel-Lindau tumor-suppressor protein (pVHL). Either overexpression or knockdown of VBP1 increases the association between TCF/LEFs and pVHL and then decreases the protein levels of TCF/LEFs via proteasomal degradation. Together, our results provide mechanistic insights into the roles of VBP1 in controlling TCF/LEFs protein stability and regulating Wnt/β-catenin signaling pathway activity.

Discovery of linear ubiquitination, a crucial regulator for immune signaling and cell death

Ubiquitination is a reversible post-translational modification that regulates function of conjugated proteins by decorating with ubiquitin chains-polymer of ubiquitin-in most cases. The discovery of linear ubiquitin chains and the linear ubiquitin chain assembly complex (LUBAC) ubiquitin ligase complex can be considered as paradigm shift in the ubiquitin research because the linear ubiquitin chain is generated via the N-terminal Met of ubiquitin, although the other ubiquitin chains are generated via one of seven Lys residues in ubiquitin. Moreover, ubiquitination is distributed throughout eukaryotic kingdoms; however, no linear ubiquitination could be found in lower eukaryotes including yeasts. Although the involvement of ubiquitination in proteolysis is well-documented, linear ubiquitination plays crucial roles in immune signaling and cell death regulation. Moreover, dysregulation of LUBAC-mediated linear ubiquitination underlies various human diseases including autoinflammation and cancer. Here, I introduce how linear ubiquitination was discovered and outline a brief history of linear ubiquitination research.

The pVHL neglected functions, a tale of hypoxia-dependent and -independent regulations in cancer

The von Hippel–Lindau protein (pVHL) is a tumour suppressor mainly known for its role as master regulator of hypoxia-inducible factor (HIF) activity. Functional inactivation of pVHL is causative of the von Hippel–Lindau disease, an inherited predisposition to develop different cancers. Due to its impact on human health, pVHL has been widely studied in the last few decades. However, investigations mostly focus on its role in degrading HIFs, whereas alternative pVHL protein–protein interactions and functions are insistently surfacing in the literature. In this review, we analyse these almost neglected functions by dissecting specific conditions in which pVHL is proposed to have differential roles in promoting cancer. We reviewed its role in regulating phosphorylation as a number of works suggest pVHL to act as an inhibitor by either degrading or promoting downregulation of specific kinases. Further, we summarize hypoxia-dependent and -independent pVHL interactions with multiple protein partners and discuss their implications in tumorigenesis.

Melatonin: an endogenous miraculous indolamine, fights against cancer progression

PURPOSE

Melatonin is an amphipathic indolamine molecule ubiquitously present in all organisms ranging from cyanobacteria to humans. The pineal gland is the site of melatonin synthesis and secretion under the influence of the retinohypothalamic tract. Some extrapineal tissues (skin, lens, gastrointestinal tract, testis, ovary, lymphocytes, and astrocytes) also enable to produce melatonin. Physiologically, melatonin regulates various functions like circadian rhythm, sleep-wake cycle, gonadal activity, redox homeostasis, neuroprotection, immune-modulation, and anticancer effects in the body. Inappropriate melatonin secretion advances the aging process, tumorigenesis, visceral adiposity, etc. METHODS: For the preparation of this review, I had reviewed the literature on the multidimensional activities of melatonin from the NCBI website database PubMed, Springer Nature, Science Direct (Elsevier), Wiley Online ResearchGate, and Google Scholar databases to search relevant articles. Specifically, I focused on the roles and mechanisms of action of melatonin in cancer prevention.

RESULTS

The actions of melatonin are primarily mediated by G-protein coupled MT1 and MT2 receptors; however, several intracellular protein and nuclear receptors can modulate the activity. Normal levels of the melatonin protect the cells from adverse effects including carcinogenesis. Therapeutically, melatonin has chronomedicinal value; it also shows a remarkable anticancer property. The oncostatic action of melatonin is multidimensional, associated with the advancement of apoptosis, the arrest of the cell cycle, inhibition of metastasis, and antioxidant activity.

CONCLUSION

The present review has emphasized the mechanism of the anti-neoplastic activity of melatonin that increases the possibilities of the new approaches in cancer therapy.

Significance of PI3K signalling pathway in clear cell renal cell carcinoma in relation to VHL and HIF status

Renal cell carcinoma (RCC) includes diverse tumour types characterised by various genetic abnormalities. The genetic changes, like mutations, deletions and epigenetic alterations, play a crucial role in the modification of signalling networks, tumour pathogenesis and prognosis. The most prevalent RCC type, clear cell RCC (ccRCC), is asymptomatic in the early stages and has a poorer prognosis compared with the papillary and the chromophobe types RCCs. Generally, ccRCC is refractory to chemotherapy and radiation therapy. Loss of von Hippel-Lindau (VHL) gene and upregulation of hypoxia-inducible factors (HIF), the signature of most sporadic ccRCC, promote multiple growth factors. Hence, VHL/HIF and a variety of pathways, including phosphatase and TEnsin homolog on chromosome 10/phosphatidylinositol-3-kinase (PI3K)/AKT, are closely connected and contribute to the ontogeny of ccRCC. In the recent decade, multiple targeting agents have been developed based on blocking major signalling pathways directly or indirectly involved in ccRCC tumour progression, metastasis, angiogenesis and survival. However, most of these drugs have limitations; either metastatic ccRCC develops resistance to these agents, or despite blocking receptors, tumour cells use alternate signalling pathways. This review compiles the state of knowledge about the PI3K/AKT signalling pathway confined to ccRCC and its cross-talks with VHL/HIF pathway.

Mitochondria in the Pulmonary Vasculature in Health and Disease: Oxygen-Sensing, Metabolism, and Dynamics

In lung vascular cells, mitochondria serve a canonical metabolic role, governing energy homeostasis. In addition, mitochondria exist in dynamic networks, which serve noncanonical functions, including regulation of redox signaling, cell cycle, apoptosis, and mitochondrial quality control. Mitochondria in pulmonary artery smooth muscle cells (PASMC) are oxygen sensors and initiate hypoxic pulmonary vasoconstriction. Acquired dysfunction of mitochondrial metabolism and dynamics contribute to a cancer-like phenotype in pulmonary arterial hypertension (PAH). Acquired mitochondrial abnormalities, such as increased pyruvate dehydrogenase kinase (PDK) and pyruvate kinase muscle isoform 2 (PKM2) expression, which increase uncoupled glycolysis (the Warburg phenomenon), are implicated in PAH. Warburg metabolism sustains energy homeostasis by the inhibition of oxidative metabolism that reduces mitochondrial apoptosis, allowing unchecked cell accumulation. Warburg metabolism is initiated by the induction of a pseudohypoxic state, in which DNA methyltransferase (DNMT)-mediated changes in redox signaling cause normoxic activation of HIF-1α and increase PDK expression. Furthermore, mitochondrial division is coordinated with nuclear division through a process called mitotic fission. Increased mitotic fission in PAH, driven by increased fission and reduced fusion favors rapid cell cycle progression and apoptosis resistance. Downregulation of the mitochondrial calcium uniporter complex (MCUC) occurs in PAH and is one potential unifying mechanism linking Warburg metabolism and mitochondrial fission. Mitochondrial metabolic and dynamic disorders combine to promote the hyperproliferative, apoptosis-resistant, phenotype in PAH PASMC, endothelial cells, and fibroblasts. Understanding the molecular mechanism regulating mitochondrial metabolism and dynamics has permitted identification of new biomarkers, nuclear and CT imaging modalities, and new therapeutic targets for PAH. © 2020 American Physiological Society. Compr Physiol 10:713-765, 2020.

Bone marrow-derived humoral factors suppress oxidative phosphorylation, upregulate TSG-6, and improve therapeutic effects on liver injury of mesenchymal stem cells

Mesenchymal stem cells, which have the potential to be used in regenerative medicine, require improvements in quality for patient use. To maintain stemness of cultured bone marrow-derived mesenchymal stem cells, we focused on the bone marrow microenvironment, generated a conditioned medium of whole bone marrow cells (BMC-CM), and assessed its effects on bone marrow-derived mesenchymal stem cells. BMC-CM suppressed morphological deterioration and proliferative decline in cultured bone marrow-derived mesenchymal stem cells, suppressed mitochondrial oxidative phosphorylation activity, a stemness indicator, and upregulated suppressors of oxidative phosphorylation such as hypoxia-inducible factor-1 alpha, Sirtuin 3, 4, and 5. Furthermore, BMC-CM upregulated TNF-stimulated gene 6 and ameliorated the therapeutic effects of cells on liver injury in carbon tetrachloride-administered rats. Since the elimination of 20-220-nm particles attenuated the effects of BMC-CM, we further analyzed exosomal microRNAs produced by whole bone marrow cells. Among the 49 microRNAs observed to be upregulated during the preparation of BMC-CM, several were identified that were associated with suppression of oxidative phosphorylation, upregulation of TNF-stimulated gene 6, and the pathogenesis of liver diseases. Thus, bone marrow-derived humoral factors including exosomal microRNAs may help to improve the therapeutic quality of bone marrow-derived mesenchymal stem cells for liver regenerative therapy.

Von Hippel-Lindau tumor suppressor (VHL) stimulates TOR signaling by interacting with phosphoinositide 3-kinase (PI3K)

Cell growth is positively controlled by the phosphoinositide 3-kinase (PI3K)-target of rapamycin (TOR) signaling pathway under conditions of abundant growth factors and nutrients. To discover additional mechanisms that regulate cell growth, here we performed RNAi-based mosaic analyses in the Drosophila fat body, the primary metabolic organ in the fly. Unexpectedly, the knockdown of the Drosophila von Hippel-Lindau (VHL) gene markedly decreased cell size and body size. These cell growth phenotypes induced by VHL loss of function were recovered by activation of TOR signaling in Drosophila Consistent with the genetic interactions between VHL and the signaling components of PI3K-TOR pathway in Drosophila, we observed that VHL loss of function in mammalian cells causes decreased phosphorylation of ribosomal protein S6 kinase and Akt, which represent the main activities of this pathway. We further demonstrate that VHL activates TOR signaling by directly interacting with the p110 catalytic subunit of PI3K. On the basis of the evolutionarily conserved regulation of PI3K-TOR signaling by VHL observed here, we propose that VHL plays an important role in the regulation and maintenance of proper cell growth in metazoans.

pVHL-mediated regulation of the anti-angiogenic protein thrombospondin-1 decreases migration of Clear Cell Renal Carcinoma Cell Lines

Thrombospondin-1 (TSP-1) is a multifunctional matrix protein with antitumor activities due in part to its ability to inhibit angiogenesis, which in turn contributes to determine the fate of many tumours. Previous studies have shown that TSP-1 expression supports normal kidney angiostasis, and decreased TSP-1 levels contribute to the angiogenic phenotype of renal cell carcinomas (RCC). The loss of the von Hippel-Lindau tumour suppressor gene (VHL) in these tumours favours stabilization of the Hypoxia Inducible Factors (HIF), which in turn contribute to adapt tumour cells to hostile environments promoting tumour progression. However, HIF-independent regulation of certain genes might also be involved. We have previously shown that TSP-1 is regulated in hypoxia in clear cell RCC (ccRCC) in a HIF-independent manner; however, the effect of VHL protein (pVHL) on TSP-1 expression has not been evaluated. Our results proved that pVHL loss or mutation in its alpha or beta domain significantly decreased TSP-1 levels in ccRCC in a HIF-independent manner. Furthermore, this regulation proved to be important for ccRCC cells behaviour showing that decreased TSP-1 levels rendered ccRCC cells more migratory. This data substantiates a unique regulation pattern for TSP-1 in a pVHL-dependent manner, which may be relevant in the aggressiveness of ccRCC.

The RNA-binding protein QKI suppresses tumorigenesis of clear cell renal cell carcinoma by regulating the expression of HIF-1α

Backgrounds: A number of genetic and biological phenomena imply that tumorigenesis of clear cell renal cell carcinoma (ccRCC) is highly correlated with hypoxia-induced factor-1a (HIF-1α). Recently, research focusing on the post-transcriptional regulation of HIF-1α has provided a new perspective for ccRCC therapy. In this study, we observed the expression pattern of the RNA-binding protein QKI, which could regulate HIF expression in ccRCC both in vitro and in vivo.

Methods: Tissue microarraywas subjected to immunohistochemistry and tumour cell lines and nude mice were used for in vitro and in vivo assays. QKI overexpression or knockdown was assessed in renal cancer cells.

Results: The overexpression of QKI inhibited the proliferation of the 786-0 and caki-1 cells, blocked the cells' entry into the S phase, and promoted apoptosis. In ectopic-implantation nude mice model, QKI depletion significantly increased tumor sizes and initiation rates. Tissue microarrays showed that the expression of QKI genes, and especially QKI-6, was significantly decreased in tumor tissues compared with these in normal kidney tissues. Moreover, decreased QKI expression was closely correlated with high tumor grade, poor differentiation, and poor survival.

Conclusions: QKI may be useful as a novel, independent diagnostic and biological marker for ccRCC.

AR ubiquitination induced by the curcumin analog suppresses growth of temozolomide-resistant glioblastoma through disrupting GPX4-Mediated redox homeostasis

Drug resistance is the main obstacle in the improvement of chemotherapeutic efficacy in glioblastoma. Previously, we showed that dehydroepiandrosterone (DHEA), one kind of androgen/neurosteroid, potentiates glioblastoma to acquire resistance through attenuating DNA damage. Androgen receptor (AR) activated by DHEA or other types of androgen was reported to promote drug resistance in prostate cancer. However, in DHEA-enriched microenvironment, the role of AR in acquiring resistance of glioblastoma remains unknown. In this study, we found that AR expression is significantly correlated with poor prognosis, and AR obviously induced the resistance to temozolomide (TMZ) treatment. Herein, we observed that ALZ003, a curcumin analog, induces FBXL2-mediated AR ubiquitination, leading to degradation. Importantly, ALZ003 significantly inhibited the survival of TMZ-sensitive and -resistant glioblastoma in vitro and in vivo. The accumulation of reactive oxygen species (ROS), lipid peroxidation and suppression of glutathione peroxidase (GPX) 4, which are characteristics of ferroptosis, were observed in glioblastoma cell after treatment of ALZ003. Furthermore, overexpression of AR prevented ferroptosis in the presence of GPX4. To evaluate the therapeutic effect in vivo, we transplanted TMZ-sensitive or -resistant U87MG cells into mouse brain followed by intravenous administration with ALZ003. In addition to inhibiting the growth of glioblastoma, ALZ003 significantly extended the survival period of transplanted mice, and significantly decreased AR expression in the tumor area. Taken together, AR potentiates TMZ resistance for glioblastoma, and ALZ003-mediated AR ubiquitination might open a new insight into therapeutic strategy for TMZ resistant glioblastoma.

von Hippel-Lindau Disease: an Update

Purpose of Review

In this review, we discuss the key molecular and clinical developments in VHL disease that have the potential to impact on the natural history of the disease and improve patient outcomes.

Recent Findings

Identifiable mutations in VHL underlie most cases of VHL and define clear genotype-phenotype correlations. Detailed clinical and molecular characterisation has allowed the implementation of lifelong screening programmes that have improved clinical outcomes. Functional characterisation of the VHL protein complex has revealed its role in oxygen sensing and the mechanisms of tumourigenesis that are now being exploited to develop novel therapies for VHL and renal cancer.

Summary

The molecular and cellular landscape of VHL-associated tumours is revealing new opportunities to modify the natural history of the disease and develop therapies. Drugs are now entering clinical trials and combined with improved clinical and molecular diagnosis, and lifelong surveillance programmes, further progress towards reducing the morbidity and mortality associated with VHL disease is anticipated.

Interactions between TGF-β type I receptor and hypoxia-inducible factor-α mediates a synergistic crosstalk leading to poor prognosis for patients with clear cell renal cell carcinoma

To investigate the significance of expression of HIF-1α, HIF-2α, and SNAIL1 proteins; and TGF-β signaling pathway proteins in ccRCC, their relation with clinicopathological parameters and patient's survival were examined. We also investigated potential crosstalk between HIF-α and TGF-β signaling pathway, including the TGF-β type 1 receptor (ALK5-FL) and the intracellular domain of ALK5 (ALK5-ICD). Tissue samples from 154 ccRCC patients and comparable adjacent kidney cortex samples from 38 patients were analyzed for HIF-1α/2α, TGF-β signaling components, and SNAIL1 proteins by immunoblot. Protein expression of HIF-1α and HIF-2α were significantly higher, while SNAIL1 had similar expression levels in ccRCC compared with the kidney cortex. HIF-2α associated with poor cancer-specific survival, while HIF-1α and SNAIL1 did not associate with survival. Moreover, HIF-2α positively correlated with ALK5-ICD, pSMAD2/3, and PAI-1; HIF-1α positively correlated with pSMAD2/3; SNAIL1 positively correlated with ALK5-FL, ALK5-ICD, pSMAD2/3, PAI-1, and HIF-2α. Intriguingly, in vitro experiments performed under normoxic conditions revealed that ALK5 interacts with HIF-1α and HIF-2α, and promotes their expression and the expression of their target genes GLUT1 and CA9, in a VHL dependent manner. We found that ALK5 induces expression of HIF-1α and HIF-2α, through its kinase activity. Under hypoxic conditions, HIF-α proteins correlated with the activated TGF-β signaling pathway. In conclusion, we reveal that ALK5 plays a pivotal role in synergistic crosstalk between TGF-β signaling and hypoxia pathway, and that the interaction between ALK5 and HIF-α contributes to tumor progression.

HIF-1α as a central mediator of cellular resistance to intracellular pathogens

Hypoxia-inducible transcription factor-1α (HIF-1α) was originally identified as a master regulator of cellular responses to hypoxia. More recently, HIF-1α has emerged as a critical regulator of immune cell function that couples shifts in cellular metabolism to cell type-specific transcriptional outputs. Activation of macrophages with inflammatory stimuli leads to induction of the metabolic program aerobic glycolysis and to HIF-1α stabilization, which reinforce one another in a positive feedback loop that helps drive macrophage activation. This activation of aerobic glycolysis and HIF-1α is important both for production of inflammatory cytokines, such as IL-1β, and for cell intrinsic control of infection. Here, we review the importance of HIF-1α for control of bacterial, fungal, and protozoan intracellular pathogens, highlighting recent findings that reveal mechanisms by which HIF-1α is activated during infection and how HIF-1α coordinates antimicrobial responses of macrophages.

The Role of Ubiquitination in Regulating Embryonic Stem Cell Maintenance and Cancer Development

Ubiquitination regulates nearly every aspect of cellular events in eukaryotes. It modifies intracellular proteins with 76-amino acid polypeptide ubiquitin (Ub) and destines them for proteolysis or activity alteration. Ubiquitination is generally achieved by a tri-enzyme machinery involving ubiquitin activating enzymes (E1), ubiquitin conjugating enzymes (E2) and ubiquitin ligases (E3). E1 activates Ub and transfers it to the active cysteine site of E2 via a transesterification reaction. E3 coordinates with E2 to mediate isopeptide bond formation between Ub and substrate protein. The E1-E2-E3 cascade can create diverse types of Ub modifications, hence effecting distinct outcomes on the substrate proteins. Dysregulation of ubiquitination results in severe consequences and human diseases. There include cancers, developmental defects and immune disorders. In this review, we provide an overview of the ubiquitination machinery and discuss the recent progresses in the ubiquitination-mediated regulation of embryonic stem cell maintenance and cancer biology.

Rapid and Reversible Knockdown of Endogenously Tagged Endosomal Proteins via an Optimized HaloPROTAC Degrader

Inducing post-translational protein knockdown is an important approach to probe biology and validate drug targets. An efficient strategy to achieve this involves expression of a protein of interest fused to an exogenous tag, allowing tag-directed chemical degraders to mediate protein ubiquitylation and proteasomal degradation. Here, we combine improved HaloPROTAC degrader probes with CRISPR/Cas9 genome editing technology to trigger rapid degradation of endogenous target proteins. Our optimized probe, HaloPROTAC-E, a chloroalkane conjugate of high-affinity VHL binder VH298, induced reversible degradation of two endosomally localized proteins, SGK3 and VPS34, with a DC₅₀ of 3–10 nM. HaloPROTAC-E induced rapid (∼50% degradation after 30 min) and complete (D_max of ∼95% at 48 h) depletion of Halo-tagged SGK3, blocking downstream phosphorylation of the SGK3 substrate NDRG1. HaloPROTAC-E more potently induced greater steady state degradation of Halo tagged endogenous VPS34 than the previously reported HaloPROTAC3 compound. Quantitative global proteomics revealed that HaloPROTAC-E is remarkably selective inducing only degradation of the Halo tagged endogenous VPS34 complex (VPS34, VPS15, Beclin1, and ATG14) and no other proteins were significantly degraded. This study exemplifies the combination of HaloPROTACs with CRISPR/Cas9 endogenous protein tagging as a useful method to induce rapid and reversible degradation of endogenous proteins to interrogate their function.