Downregulation of praja2 restrains endocytosis and boosts tyrosine kinase receptors in kidney cancer

Clear cell renal cell carcinoma (ccRCC) is the most common kidney cancer in the adult population. Late diagnosis, resistance to therapeutics and recurrence of metastatic lesions account for the highest mortality rate among kidney cancer patients. Identifying novel biomarkers for early cancer detection and elucidating the mechanisms underlying ccRCC will provide clues to treat this aggressive malignant tumor. Here, we report that the ubiquitin ligase praja2 forms a complex with-and ubiquitylates the AP2 adapter complex, contributing to receptor endocytosis and clearance. In human RCC tissues and cells, downregulation of praja2 by oncogenic miRNAs (oncomiRs) and the proteasome markedly impairs endocytosis and clearance of the epidermal growth factor receptor (EGFR), and amplifies downstream mitogenic and proliferative signaling. Restoring praja2 levels in RCC cells downregulates EGFR, rewires cancer cell metabolism and ultimately inhibits tumor cell growth and metastasis. Accordingly, genetic ablation of praja2 in mice upregulates RTKs (i.e. EGFR and VEGFR) and induces epithelial and vascular alterations in the kidney tissue.In summary, our findings identify a regulatory loop between oncomiRs and the ubiquitin proteasome system that finely controls RTKs endocytosis and clearance, positively impacting mitogenic signaling and kidney cancer growth.

Ubiquitylation of BBSome is required for ciliary assembly and signaling

Bardet-Biedl syndrome (BBS) is a ciliopathy characterized by retinal degeneration, obesity, renal abnormalities, postaxial polydactyly, and developmental defects. Genes mutated in BBS encode for components and regulators of the BBSome, an octameric complex that controls the trafficking of cargos and receptors within the primary cilium. Although both structure and function of the BBSome have been extensively studied, the impact of ubiquitin signaling on BBSome is largely unknown. We identify the E3 ubiquitin ligase PJA2 as a novel resident of the ciliary compartment and regulator of the BBSome. Upon GPCR-cAMP stimulation, PJA2 ubiquitylates BBSome subunits. We demonstrate that ubiquitylation of BBS1 at lysine 143 increases the stability of the BBSome and promotes its binding to BBS3, an Arf-like GTPase protein controlling the targeting of the BBSome to the ciliary membrane. Downregulation of PJA2 or expression of a ubiquitylation-defective BBS1 mutant (BBS1^K143R ) affects the trafficking of G-protein-coupled receptors (GPCRs) and Shh-dependent gene transcription. Expression of BBS1^K143R in vivo impairs cilium formation, embryonic development, and photoreceptors' morphogenesis, thus recapitulating the BBS phenotype in the medaka fish model.

Control of Mitochondrial Activity by the Ubiquitin Code in Health and Cancer

Cellular homeostasis is tightly connected to the broad variety of mitochondrial functions. To stay healthy, cells need a constant supply of nutrients, energy production and antioxidants defenses, undergoing programmed death when a serious, irreversible damage occurs. The key element of a functional integration of all these processes is the correct crosstalk between cell signaling and mitochondrial activities. Once this crosstalk is interrupted, the cell is not able to communicate its needs to mitochondria, resulting in oxidative stress and development of pathological conditions. Conversely, dysfunctional mitochondria may affect cell viability, even in the presence of nutrients supply and energy production, indicating the existence of feed-back control mechanisms between mitochondria and other cellular compartments. The ubiquitin proteasome system (UPS) is a multi-step biochemical pathway that, through the conjugation of ubiquitin moieties to specific protein substrates, controls cellular proteostasis and signaling, removing damaged or aged proteins that might otherwise accumulate and affect cell viability. In response to specific needs or changed extracellular microenvironment, the UPS modulates the turnover of mitochondrial proteins, thus influencing the organelle shape, dynamics and function. Alterations of the dynamic and reciprocal regulation between mitochondria and UPS underpin genetic and proliferative disorders. This review focuses on the mitochondrial metabolism and activities supervised by UPS and examines how deregulation of this control mechanism results in proliferative disorders and cancer.

Targeted inhibition of ubiquitin signaling reverses metabolic reprogramming and suppresses glioblastoma growth

Glioblastoma multiforme (GBM) is the most frequent and aggressive form of primary brain tumor in the adult population; its high recurrence rate and resistance to current therapeutics urgently demand a better therapy. Regulation of protein stability by the ubiquitin proteasome system (UPS) represents an important control mechanism of cell growth. UPS deregulation is mechanistically linked to the development and progression of a variety of human cancers, including GBM. Thus, the UPS represents a potentially valuable target for GBM treatment. Using an integrated approach that includes proteomics, transcriptomics and metabolic profiling, we identify praja2, a RING E3 ubiquitin ligase, as the key component of a signaling network that regulates GBM cell growth and metabolism. Praja2 is preferentially expressed in primary GBM lesions expressing the wild-type isocitrate dehydrogenase 1 gene (IDH1). Mechanistically, we found that praja2 ubiquitylates and degrades the kinase suppressor of Ras 2 (KSR2). As a consequence, praja2 restrains the activity of downstream AMP-dependent protein kinase in GBM cells and attenuates the oxidative metabolism. Delivery in the brain of siRNA targeting praja2 by transferrin-targeted self-assembling nanoparticles (SANPs) prevented KSR2 degradation and inhibited GBM growth, reducing the size of the tumor and prolonging the survival rate of treated mice. These data identify praja2 as an essential regulator of cancer cell metabolism, and as a potential therapeutic target to suppress GBM growth.

The E3 ubiquitin ligase praja2  is expressed in glioblastoma (GBM), targets the kinase suppressor of Ras 2 for degradation and attenuates oxidative metabolism. Nanoparticle-mediated delivery of praja2 siRNA to GBM-bearing mice reduces tumour size.

Pathophysiology of Primary Cilia: Signaling and Proteostasis Regulation

Primary cilia are microtubule-based, non-motile sensory organelles present in most types of growth-arrested eukaryotic cells. They are transduction hubs that receive and transmit external signals to the cells in order to control growth, differentiation and development. Mutations of genes involved in the formation, maintenance or disassembly of ciliary structures cause a wide array of developmental genetic disorders, also known as ciliopathies. The primary cilium is formed during G1 in the cell cycle and disassembles at the G2/M transition. Following the completion of the cell division, the cilium reassembles in G1. This cycle is finely regulated at multiple levels. The ubiquitin-proteasome system (UPS) and the autophagy machinery, two main protein degradative systems in cells, play a fundamental role in cilium dynamics. Evidence indicate that UPS, autophagy and signaling pathways may act in synergy to control the ciliary homeostasis. However, the mechanisms involved and the links between these regulatory systems and cilium biogenesis, dynamics and signaling are not well defined yet. Here, we discuss the reciprocal regulation of signaling pathways and proteolytic machineries in the control of the assembly and disassembly of the primary cilium, and the impact of the derangement of these regulatory networks in human ciliopathies.

Identification of human liver cytochrome P450 enzymes involved in the metabolism of SCH 351125, a CCR5 antagonist

The identification and relative contribution of human cytochrome P450 enzyme(s) involved in the metabolism of SCH 351125 were investigated. In human liver microsomes, O-deethylation was the major metabolic pathway, whereas aromatization of a piperidine ring to pyridine and the reduction of the N-oxide moiety were minor routes. Recombinant human CYP3A4 and CYP2C9 both exhibited catalytic activity with respect to the formation of rotameric O-deethylated metabolites (M12, M13), the metabolites resulting from aromatization (M22/M24) and N-oxide reduction (M31). Using the relative activity factor (RAF) approach, the relative contributions of CYP3A4 and CYP2C9 to M13 formation were estimated to be 76 and 24%, respectively. There was a high correlation (r>0.96) between the rate of formation of M12 and M13 and 6 beta-hydroxylation of testosterone catalysed by CYP3A4/5. Ketoconazole (2microM) and CYP3A4/5-specific inhibitory monoclonal antibody inhibited the formation of M12 and M13 from human liver microsomes by approximately 60 and 71%, respectively. The results demonstrate that the in vitro metabolism of SCH 351125 is mediated primarily via CYP3A4 and that CYP2C9 plays a minor role. Clinical study designs should encompass these enzymology data to address any potential drug interactions.

Electron cyclotron resonance ion sources in use for heavy ion cancer therapy

The use of electron cyclotron resonance (ECR) ion sources for producing ion beams for heavy ion cancer therapy has been established for more than ten years. After the Heavy Ion Medical Accelerator (HIMAC) at Chiba, Japan started therapy of patients with carbon ions in 1994 the first carbon ion beam for patient treatment at the accelerator facility of GSI was delivered in 1997. ECR ion sources are the perfect tool for providing the required ion beams with good stability, high reliability, and easy maintenance after long operating periods. Various investigations were performed at GSI with different combinations of working gas and auxiliary gas to define the optimal beam conditions for an extended use of further ion species for the dedicated Heidelberg Ion Beam Therapy (HIT) facility installed at the Radiological University Hospital Heidelberg, Germany. Commercially available compact all permanent magnet ECR ion sources operated at 14.5 GHz were chosen for this facility. Besides for (12)C(4+) these ion sources are used to provide beams of (1)H(3)(1+), (3)He(1+), and (16)O(6+). The final commissioning at the HIT facility could be finished at the end of 2006.

Immunocytochemical characterization of murine Hex, a homeobox-containing protein

A polyclonal antibody against a glutathione S:-transferase fusion protein containing the 76 COOH-terminal amino acids of Hex, a divergent homeobox gene, was raised in rabbits. Western blot and immunofluorescence reveal that Hex is a 35-37-kD soluble protein present both in the nucleus and cytoplasm of transfected and nontransfected cultured cells as well as in whole mouse embryo. Confocal microscopy of whole mount immunostained mouse embryos at E7. 5 and E8.5 demonstrates that Hex is differentially localized in the cytoplasm and nucleus of definitive endoderm, developing blood islands, and hepatic diverticulum. In particular, in the region of the foregut that gives rise to the liver, Hex expression is nuclear in the endodermal cells of the hepatic diverticulum, whereas expression is primarily cytoplasmic in cells lateral to the liver-forming region. This suggests that nuclear localization of Hex is involved in early hepatic specification and that compartmentalization of Hex protein plays an important role in its function during mouse development.

Prinomide tromethamine pharmacokinetics: mutually dependent saturable and competitive protein binding between prinomide and its own metabolite

Prinomide tromethamine, a nonsteroidal antiinflammatory drug, was orally administered at doses of 250, 500, and 1000 mg every 12 hr for 28 days to healthy male volunteers. The pharmacokinetic behavior of prinomide and its primary plasma metabolite displayed nonlinear characteristics, while those of free prinomide and its metabolite were dose proportional. The nonlinear pharmacokinetic behavior of total prinomide and p-hydroxy metabolite was found to be caused by both saturable and mutually dependent competitive Langmuir-type plasma protein binding between prinomide and its p-hydroxy metabolite. The extent of the protein interaction displayed at steady state was due to the extensive accumulation of the p-hydroxy metabolite. While ligand-protein interactions are known for xenobiotic competitors, the characteristic behavior of prinomide is the first known example to be reported for a competitive protein interaction between a xenobiotic and its own in vivo generated metabolite. The findings of this study may have implications regarding the disposition of other extensively bound nonsteroidal antiinflammatory drugs with long-lived metabolites.

Physiological disposition of CGS 16617 in rat, dog, and man

The disposition and metabolism of CGS 16617 (3-[(5-amino-1-carboxy-1S-pentyl)amino],2,3,4,5-tetrahydro-2-oxo-3S-1H-1 - benzazepine-1-acetic acid), and angiotensin l-converting enzyme inhibitor, were investigated in rats, dogs, and man. In rats, a single oral dose of 10 mg/kg 14C-CGS 16617 afforded peak plasma concentrations of drug between 0.5 and 6 hr of dosing. The AUC was on average 9.6% of that after iv administration of the same dose, indicating low oral absorption of the drug. The apparent volumes of distribution, V1 and Vdss, were 0.45 and 2.5 liters/kg, respectively. Disappearance of the drug from plasma after the iv dose was biphasic, with mean half-lives of 0.5 and 13 hr, respectively, for the lambda 1 and lambda 2 phases. After single iv doses (10 mg/kg) to dogs and rats, 14CGS 16617 was almost exclusively eliminated by the renal route, with urinary recoveries of greater than 90% of dose. The same dose administered orally gave urinary recoveries of less than 10% of the dose in rats and about 15% in the dog. The remainder of the dose was eliminated in the feces. Bile duct-cannulated rats excreted less than 3% of an oral 10 mg/kg dose in the bile, in 24 hr. In man (N = 4), a single oral dose of 100 mg 14C-CGS 16617 resulted in peak plasma concentrations of 0.02-0.07 microgram of drug eq/ml between 4 and 6 hr of dosing. The mean terminal half-life was estimated at 81 hr.(ABSTRACT TRUNCATED AT 250 WORDS)