Abstract 2567: Exploring novel roles of the GPCR Smoothened in AKT signaling and drug resistance

The Smoothened receptor (SMO) belongs to the frizzled-class-G-protein coupled receptor and its activity can be classified in the canonical and the non-canonical pathway. The canonical pathway concludes in the transcriptional activation of the Hedgehog target genes through the GLI family of transcription factors whereas the non-canonical pathway leads to the recruitment and activation of trimeric G proteins. Recently, we have reported two novel roles of SMO with relevance to cell survival and drug resistance in DLBCL. In the first, SMO promotes a shift in the ubiquitination pattern for TNF receptor-associated factor 6 (TRAF6) from degradation inducing K48-ubiquitin branching towards K63-ubiquitination. TRAF6 is a K63-Ub E3 ubiquitin ligase for AKT and K63-ubiquitination of AKT increases membrane recruitment, activation and stability. Evidently, SMO promotes the formation of a scaffold-like protein complex including the de-ubiquitinating enzyme Ubiquitin specific peptidase 8 (USP8) and TRAF6. In its second novel role, SMO influences the vesicular sorting of IGF1R and other receptor tyrosine kinases. Loss of SMO leads to increased IGF1R lysosomal degradation and reduced IGF1R recycling, while overexpression increases IGF1R levels and AKT signaling. These observations indicate SMO receptor biology outside of the established canonical and non-canonical pathway functions. We have set out to use BioID to investigate the SMO interactome that contributes to these novel functionalities using a fusion protein of SMO and the reengineered E. coli biotinyl transferase BirA (Turbo) as bait. Preliminary BioID using SMO-Turbo returned a list of candidates which will require further data filtering approaches, but thus far shows a marked enrichment for proteins involved in vesicular trafficking.

Citation Format: Samantha Manuel, Nitin Agarwal, Daniel Bilbao, Francisco Vega, Ralf Landgraf. Exploring novel roles of the GPCR Smoothened in AKT signaling and drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2567.

Smoothened (SMO) regulates insulin-like growth factor 1 receptor (IGF1R) levels and protein kinase B (AKT) localization and signaling

The oncoprotein Smoothened (SMO), a Frizzled-class-G-protein-coupled receptor, is the central transducer of hedgehog (Hh) signaling. While canonical SMO signaling is best understood in the context of cilia, evidence suggests that SMO has other functions in cancer biology that are unrelated to canonical Hh signaling. Herein, we provided evidence that elevated levels of human SMO show a strong correlation with elevated levels of insulin-like growth factor 1 receptor (IGF1R) and reduced survival in diffuse large B-cell lymphoma (DLBCL). As an integral component of raft microdomains, SMO plays a fundamental role in maintaining the levels of IGF1R in lymphoma and breast cancer cells as well IGF1R-associated activation of protein kinase B (AKT). Silencing of SMO increases lysosomal degradation and favors a localization of IGF1R to late endosomal compartments instead of early endosomal compartments from which much of the receptor would normally recycle. In addition, loss of SMO interferes with the lipid raft localization and retention of the remaining IGF1R and AKT, thereby disrupting the primary signaling context for IGF1R/AKT. This activity of SMO is independent of its canonical signaling and represents a novel and clinically relevant contribution to signaling by the highly oncogenic IGF1R/AKT signaling axis.

Statins enhance the chemosensitivity of R-CHOP in diffuse large B-cell lymphoma

The beneficial effect of statins on the anti-lymphoma activity of the rituximab-based chemotherapy regimen is controversial. Here, we retrospectively reviewed patients with naïve-treated advanced diffuse large B-cell lymphoma (DLBCL) receiving frontline R-CHOP, and for whom data regarding differential statins use was available at the time of initiation of treatment. We observe that patients treated with statins and R-CHOP experienced a significantly higher CR rate as compared to those who received R-CHOP only. We further show that patients receiving medium or high intensity statins and R-CHOP experienced a significantly higher CR as compared to those treated with R-CHOP. Six-year progression free survival was higher for patients who received medium or higher intensity statins as compared to low or no statins. The potential contribution of cholesterol pathway in doxorubicin sensitivity was supported by in vitro/in vivo studies. Our study suggests that targeting cholesterol-using lovastatin could be a therapeutic strategy to enhance responses to R-CHOP in DLBCL patients.

Experimental and numerical analysis of cord–elastomer composites

In this paper, experimental and numerical investigations on cord–elastomer composites are presented. A finite-element model is introduced, which was developed within the framework of an industrial project. The model is able to simulate an elastomer matrix with inserted cords as load bearing elements and to predict the strains and stresses in cord and elastomer sections. The inelastic material behavior of the elastomer matrix and the yarns is described by corresponding material models suitable for large deformation processes. With the help of a specially developed demonstrator bellows, which is similar to an air spring, the simulation results are compared with experiments. For this purpose, the digital image correlation method is used to determine the deformations on the outer surface of the demonstrator bellows and to calculate the strains on and between the cords. The comparison of the results shows that the employed simulation method is very well suited to predict the strains in these cord–elastomer composites.

Media for Dimensional Stabilization of Rubber Compounds during Additive Manufacturing and Vulcanization

The current article proposes a concept for the additive manufacturing of rubber components using extrusion-based 3D printing, in which an additional medium is added to ensure the maintenance of shape within the elastomeric structure during the additive manufacturing process and in the subsequent vulcanization process. Specific requirements for the dimensional stabilization of the media were defined and suitable media were derived. Silicone rubber, molding sand, and plaster were examined in experimental vulcanization tests for their suitability as possible media with regard to shape retention. Selected rubber geometries made of NBR were embedded in these media to undergo the vulcanization process. The results show a significant influence of the media on the heating times. All media were able to ensure that the rubber geometries maintained their shape during vulcanization. Nevertheless, some side effects were found. The silicone rubber did not cure properly around the rubber sample. Therefore, it was difficult to remove it from the rubber after vulcanization. The molding sand caused an increased surface roughness on the rubber. Plaster changed the glossy surfaces at the beginning to a matte one after vulcanization and residuals were difficult to remove. However, all media can serve as stabilization media with specific changes.

Vaccination against cocaine using a modifiable dendrimer nanoparticle platform

Pharmacological therapies for the treatment of cocaine addiction have had disappointing efficacy, and the lack of recent developments in the clinical care of cocaine-addicted patients indicates a need for novel treatment strategies. Recent studies have shown that vaccination against cocaine to elicit production of antibodies that reduce concentrations of free drug in the blood is a promising method to protect against the effects of cocaine and reduce rates of relapse. However, the poorly immunogenic nature of cocaine remains a major hurdle to active immunization. Therefore, we hypothesized that strategies to increase targeted exposure of cocaine to the immune system may produce a more effective vaccine. To specifically direct an immune response against cocaine, in the present study we have conjugated a cocaine analog to a dendrimer-based nanoparticle carrier with MHC II-binding moieties that previously has been shown to activate antigen-presenting cells necessary for antibody production. This strategy produced a rapid, prolonged, and high affinity anti-cocaine antibody response without the need for an adjuvant. Surprisingly, additional evaluation using multiple adjuvant formulations in two strains of inbred mice found adjuvants were either functionally redundant or deleterious in the vaccination against cocaine using this platform. The use of conditioned place preference in rats after administration of this vaccine provided proof of concept for the ability of this vaccine to diminish cocaine reward. Together these data demonstrate the intrinsic efficacy of an immune-targeting dendrimer-based cocaine vaccine, with a vast potential for design of future vaccines against other poorly immunogenic antigens by substitution of the conjugated cargo.

Design of a mediator-free, non-enzymatic electrochemical biosensor for glutamate detection

A mediator-free, non-enzymatic electrochemical biosensor was constructed by covalent immobilization of a genetically engineered periplasmic glutamate binding protein onto gold nanoparticle-modified, screen-printed carbon electrodes (GluBP/AuNP/SPCE) for the purpose of direct measurement of glutamate levels. Glutamate serves as the predominant excitatory neurotransmitter in the central nervous system. As high levels of glutamate are an indicator of many neurologic disorders, there is a need for advancements in glutamate detection technologies. The biosensor was evaluated for glutamate detection by cyclic voltammetry. Binding of glutamate to the immobilized glutamate binding protein results in a conformational change of the latter that alters the microenvironment on the surface of the sensor, which is manifested as a change in signal. Dose-response plots correlating the electrochemical signal to glutamate concentration revealed a detection limit of 0.15 μM with a linear range of 0.1-0.8 μM. Selectivity studies confirmed a strong preferential response of the biosensor for glutamate against common interfering compounds.

Smoothened stabilizes and protects TRAF6 from degradation: A novel non-canonical role of smoothened with implications in lymphoma biology

Tumor necrosis factor receptor-associated factor 6 (TRAF6), an (K63) E3-ligase, plays a role in many biological processes and its activity is relevant in diffuse large B cell lymphoma (DLBCL) biology. Although molecules that trigger TRAF6 activation have been defined, those that stabilize TRAF6 and/or enhance TRAF6 function remain largely unclear. We found that TRAF6 amplifies pAKT signaling in DLBCL. Moreover, TRAF6 activation and stabilization of its ubiquitination profile are facilitated by smoothened (SMO), signal transducer of canonical Hedgehog signaling. Here, we report that SMO is needed to facilitate and maintain TRAF6-dependent elevated pAKT levels, and that the SMO/TRAF6 axis contributes to doxorubicin resistance in DLBCL. Mechanistically, we found that SMO, through its C-terminal tail, stabilizes and protects TRAF6 from degradation, an effect mediated by ubiquitin-specific protease-8. Moreover, this functional link between SMO and TRAF6 is reflected in DLBCL patients where high expression of both molecules correlates with poor prognosis. In summary, our study reveals a novel cell survival mechanism in which SMO stabilizes and protects TRAF6 from degradation. The axis SMO/TRAF6/AKT is highly relevant in the biology of DLBCL and is involved in doxorubicin resistance.

Identification, characterization and application of a new peptide against anterior gradient homolog 2 (AGR2)

The cancer-associated protein Anterior Gradient 2 (AGR2) has been described, predominantly in adenocarcinomas. Increased levels of extracellular AGR2 (eAGR2) have been correlated with poor prognosis in cancer patients, making it a potential biomarker. Additionally, neutralizing AGR2 antibodies showed preclinical effectiveness in murine cancer models suggesting eAGR2 may be a therapeutic target.

We set out to identify a peptide by mRNA display that would serve as a theranostic tool targeting AGR2. This method enables the selection of peptides from a complex (>10¹¹) library and incorporates a protease incubation step that filters the selection for serum stable peptides. We performed six successive rounds of enrichment using a 10-amino acid mRNA display library and identified several AGR2 binding peptides. One of these peptides (H10), demonstrated high affinity binding to AGR2 with a binding constant (K_D) of 6.4 nM. We developed an AGR2 ELISA with the H10 peptide as the capture reagent. Our H10-based ELISA detected eAGR2 from cancer cell spent media with a detection limit of (20-50 ng/ml). Furthermore, we investigated the therapeutic utility of H10 and discovered that it inhibited cell viability at IC₅₀ (9-12 μmoles/L) in cancer cell lines. We also determined that 10 μg/ml of H10 was sufficient to inhibit cancer cell migration in breast and prostate cancer cell lines. A control peptide did not show any appreciable activity in these cells. The H10 peptide showed promise as both a novel diagnostic and a potential therapeutic peptide.

Blood Glucose Measurement by Infrared Spectroscopy

For the development of an implantable artificial endocrine pancreas, a sensor for blood glucose measurement is needed providing a long-term stability. This goal can be achieved by the application of infrared spectroscopy which, unlike electrochemical sensors, responds directly to the glucose molecule.

An investigation under physiological conditions revealed five glucose absorption bands in the near and middle infrared range. These are 1040, 1085, 1109, 1160 and 1365 cm–1. Only the 1040 cm–1 frequency coincides with none of the other infrared-active blood substances like proteins, lipids and urea. Nevertheless, the other absorption bands too, especially the 1109 cm–1 frequency, can be used for blood glucose measurement, if the superimposed absorptions are compensated. Methods for the compensation have been found. Technically feasible embodiments of an infrared glucose sensor are described.

Synthesis and photophysical properties of a fluorescent cyanoquinoline probe for profiling ERBB2 kinase inhibitor response

A fluorescent probe targeting the ERBB2 receptor tyrosine was designed, synthesized and evaluated as reporter of ERBB2 dynamics in overexpressing BT474, i.e. Her2(+), cells. Two cyanoquinazoline (CQ) probes modeled after type-I (CQ1) or active state and type-II (CQ2) or inactive state inhibitors were designed and synthesized with extended π systems that impart binding-induced, turn-on fluorescence. Solution spectroscopy revealed that CQ1 exhibited attractive photophysical properties and displayed turn-on emission in the presence of purified, soluble ERBB2 kinase domain, while CQ2 was found to be non-emissive, likely due to quenching via a photoinduced electron transfer mechanism. Live cell imaging with CQ1 revealed that this probe targeted an intracellular population of ERBB2, which increased following treatment with type-I inhibitors, gefinitib and canertinib, but showed no response to type-II inhibitors. CQ1 thus provides a novel means of imaging the dynamic response of ERBB2(+) cells to kinase inhibitors.

Molecular Mechanism of Protein Kinase Recognition and Sorting by the Hsp90 Kinome-Specific Cochaperone Cdc37

Despite the essential functions of Hsp90, little is known about the mechanism that controls substrate entry into its chaperone cycle. We show that the role of Cdc37 cochaperone reaches beyond that of an adaptor protein and find that it participates in the selective recruitment of only client kinases. Cdc37 recognizes kinase specificity determinants in both clients and nonclients and acts as a general kinase scanning factor. Kinase sorting within the client-to-nonclient continuum relies on the ability of Cdc37 to challenge the conformational stability of clients by locally unfolding them. This metastable conformational state has high affinity for Cdc37 and forms stable complexes through a multidomain cochaperone interface. The interaction with nonclients is not accompanied by conformational changes of the substrate and results in substrate dissociation. Collectively, Cdc37 performs a quality control of protein kinases, where induced conformational instability acts as a "flag" for Hsp90 dependence and stable cochaperone association.

High-Performance Chromatographic Separation of Cerebrosides

High-performance thin-layer chromatography (HPTLC) is a very robust, fast, and inexpensive technique that enables separation of complex mixtures. Here, we describe the analytical separation of glucosylceramide and galactosylceramide by HPTLC. This technique can be used for quantitation purposes but also with small modification for subsequent mass spectrum analyses for structural determination.

Fluorescent Kinase Probes Enabling Identification and Dynamic Imaging of HER2(+) Cells

The human epidermal growth factor receptor, EGFR/ERBB/HER, family of receptor tyrosine kinases is central to many signaling pathways and a validated chemotherapy target in multiple cancers. While EGFR/ERBB-targeted therapies, including monoclonal antibodies, e.g., trastuzumab, and small molecule kinase inhibitors, such as lapatinib, have been developed, rapid identification and classification of cancer cells is key to identifying the best treatment regime. We report ERBB2 (also HER2) targeting kinase probes that exhibit a "turn-on" emission response upon binding. These live cell compatible probes differentiate ERBB2(+) cells from low-level, ERBB2(-) cells by targeting the intracellular ATP-binding pocket of ERBB2 with therapeutic inhibitor-like specificity. Beyond kinase expression levels, probe signal is linked to the phosphotyrosine-correlated activation state of the ERBB2 population. Additionally, the rapid signaling capability of the probes can report changes in activation state in live cells providing a unique type of complementary information to immunohistochemical assays of receptor kinase populations.

ERBB2 Overexpression Establishes ERBB3-Dependent Hypersensitivity of Breast Cancer Cells to Withaferin A

The catalytically deficient ERBB3 strongly synergizes with the receptor tyrosine kinase ERBB2, and elevated levels represent an overall risk factor for unfavorable disease outcomes in breast cancer. Although itself not a target of pan-ERBB kinase inhibitors, it contributes to resistance in ERBB2-targeted treatment regiments. The steroidal lactone Withaferin A (WA) has established broad anticancer properties through several modes of action and was shown to be effective against triple-negative breast cancers at elevated concentrations. We found that ERBB2 overexpression does render cells hypersensitive to WA. Although ERBB2 downregulation is one aspect of WA treatment at high concentrations, it is not causal for the elevated sensitivity at lower dosages. Instead, WA targets the ability of ERBB3 to amplify ERBB2 signaling. ERBB3 receptor levels, constitutive phosphorylation of both ERBB3 and ERBB2, as well as signaling through AKT are eliminated by WA treatment. By targeting ERBB2/ERBB3 as a functional unit, it is also effective in cases in which ERBB2-directed inhibitors, such as lapatinib, alone show reduced potency. Hence, WA or derivatives thereof may present a low toxicity addition to ERBB2-targeting therapeutics, especially in cases in which ERBB3 involvement is driving resistance or reduced overall sensitivity. Mol Cancer Ther; 15(11); 2750-7. ©2016 AACR.

The Small Molecule IMR-1 Inhibits the Notch Transcriptional Activation Complex to Suppress Tumorigenesis

In many cancers, aberrant Notch activity has been demonstrated to play a role in the initiation and maintenance of the neoplastic phenotype and in cancer stem cells, which may allude to its additional involvement in metastasis and resistance to therapy. Therefore, Notch is an exceedingly attractive therapeutic target in cancer, but the full range of potential targets within the pathway has been underexplored. To date, there are no small-molecule inhibitors that directly target the intracellular Notch pathway or the assembly of the transcriptional activation complex. Here, we describe an in vitro assay that quantitatively measures the assembly of the Notch transcriptional complex on DNA. Integrating this approach with computer-aided drug design, we explored potential ligand-binding sites and screened for compounds that could disrupt the assembly of the Notch transcriptional activation complex. We identified a small-molecule inhibitor, termed Inhibitor of Mastermind Recruitment-1 (IMR-1), that disrupted the recruitment of Mastermind-like 1 to the Notch transcriptional activation complex on chromatin, thereby attenuating Notch target gene transcription. Furthermore, IMR-1 inhibited the growth of Notch-dependent cell lines and significantly abrogated the growth of patient-derived tumor xenografts. Taken together, our findings suggest that a novel class of Notch inhibitors targeting the transcriptional activation complex may represent a new paradigm for Notch-based anticancer therapeutics, warranting further preclinical characterization. Cancer Res; 76(12); 3593-603. ©2016 AACR.

Regulation of Receptor for Advanced Glycation End Products (RAGE) Ectodomain Shedding and Its Role in Cell Function

The receptor for advanced glycation end products (RAGE) is a multiligand transmembrane receptor that can undergo proteolysis at the cell surface to release a soluble ectodomain. Here we observed that ectodomain shedding of RAGE is critical for its role in regulating signaling and cellular function. Ectodomain shedding of both human and mouse RAGE was dependent on ADAM10 activity and induced with chemical activators of shedding (ionomycin, phorbol 12-myristate 13-acetate, and 4-aminophenylmercuric acetate) and endogenous stimuli (serum and RAGE ligands). Ectopic expression of the splice variant of RAGE (RAGE splice variant 4), which is resistant to ectodomain shedding, inhibited RAGE ligand dependent cell signaling, actin cytoskeleton reorganization, cell spreading, and cell migration. We found that blockade of RAGE ligand signaling with soluble RAGE or inhibitors of MAPK or PI3K blocked RAGE-dependent cell migration but did not affect RAGE splice variant 4 cell migration. We finally demonstrated that RAGE function is dependent on secretase activity as ADAM10 and γ-secretase inhibitors blocked RAGE ligand-mediated cell migration. Together, our data suggest that proteolysis of RAGE is critical to mediate signaling and cell function and may therefore emerge as a novel therapeutic target for RAGE-dependent disease states.

Binding-induced, turn-on fluorescence of the EGFR/ERBB kinase inhibitor, lapatinib

We report the photophysical properties, binding-induced turn-on emission, and fluorescence imaging of the cellular uptake and distribution of lapatinib, an EGFR/ERBB inhibitor. Lapatinib, a type II, i.e. inactive state, inhibitor that targets the ATP binding pocket of the EGFR family of receptor tyrosine kinases. DFT calculations predict that the 6-furanylquinazoline core of lapatinib should exhibit an excited state with charge transfer character and an S0 to S1 transition energy of 3.4 eV. Absorption confirms an optical transition in the near UV to violet, while fluorescence spectroscopy shows that photoemission is highly sensitive to solvent polarity. The hydrophobicity of lapatinib leads to fluorescent aggregates in solution, however, binding to the lipid-carrier protein, BSA or to the kinase domain of ERBB2, produces spectroscopically distinct photoemission. Confocal fluorescence microscopy imaging of lapatinib uptake in ERBB2-overexpressing MCF7 and BT474 cells reveals pools of intracellular inhibitor with emission profiles consistent with aggregated lapatinib.

Phosphorylated and unphosphorylated serine 13 of CDC37 stabilize distinct interactions between its client and HSP90 binding domains

Folding and maturation of most protein kinases require chaperone assistance. In higher eukaryotes, CDC37 is the predominant cochaperone that facilitates the transfer of kinase clients to HSP90. Kinase recognition is thought to occur through the N-terminal domain, which has, thus far, eluded structure determination. Client processing also requires the phosphorylation of the N-terminal tail at Ser13 by protein kinase CK2 (casein kinase 2). How phosphorylation alters the molecular properties of CDC37 is not understood. We show that the phosphorylation at Ser13 induces a large shift toward a more compact structure, based on ANS fluorescence, while modestly increasing secondary structure. Moreover, this transition requires interactions of the N-terminal domain and the remainder of CDC37. The stabilizing property of the phosphorylation event can be recreated in trans by a (phospho-Ser13) peptide derived from the N-terminal tail. However, the phosphorylation-induced transition is not dependent on the transferred phosphate group but rather the loss of serine-like properties at position 13. The complete absence of the N-terminal tail results in reduced secondary structure and unresponsiveness to subsequent addition of peptides. The N-terminal tail may therefore serve as an intramolecular chaperone that ensures that CDC37 assumes one of two readily interconvertible states in a manner that impacts the interaction of the client binding N-domain and the MC-domains, involved in dimerization and HSP90 binding.

Emission tuning of fluorescent kinase inhibitors: conjugation length and substituent effects

Fluorescent N-phenyl-4-aminoquinazoline probes targeting the ATP-binding pocket of the ERBB family of receptor tyrosine kinases are reported. Extension of the aromatic quinazoline core with fluorophore “arms” through substitution at the 6- position of the quinazoline core with phenyl, styryl, and phenylbutadienyl moieties was predicted by means of TD-DFT calculations to produce probes with tunable photoexcitation energies and excited states possessing charge-transfer character. Optical spectroscopy identified several synthesized probes that are nonemissive in aqueous solutions and exhibit emission enhancements in solvents of low polarity, suggesting good performance as turn-on fluorophores. Ligand-induced ERBB2 phosphorylation assays demonstrate that despite chemical modification to the quinazoline core these probes still function as ERBB2 inhibitors in MCF7 cells. Two probes were found to exhibit ERBB2-induced fluorescence, demonstrating the utility of these probes as turn-on, fluoroescent kinase inhibitors.

Bidirectional rescue of extreme genetic predispositions to anxiety: impact of CRH receptor 1 as epigenetic plasticity gene in the amygdala

The continuum of physiological anxiety up to psychopathology is not merely dependent on genes, but is orchestrated by the interplay of genetic predisposition, gene x environment and epigenetic interactions. Accordingly, inborn anxiety is considered a polygenic, multifactorial trait, likely to be shaped by environmentally driven plasticity at the genomic level. We here took advantage of the extreme genetic predisposition of the selectively bred high (HAB) and low anxiety (LAB) mouse model exhibiting high vs low anxiety-related behavior and tested whether and how beneficial (enriched environment) vs detrimental (chronic mild stress) environmental manipulations are capable of rescuing phenotypes from both ends of the anxiety continuum. We provide evidence that (i) even inborn and seemingly rigid behavioral and neuroendocrine phenotypes can bidirectionally be rescued by appropriate environmental stimuli, (ii) corticotropin-releasing hormone receptor 1 (Crhr1), critically involved in trait anxiety, shows bidirectional alterations in its expression in the basolateral amygdala (BLA) upon environmental stimulation, (iii) these alterations are linked to an increased methylation status of its promoter and, finally, (iv) binding of the transcription factor Yin Yang 1 (YY1) to the Crhr1 promoter contributes to its gene expression in a methylation-sensitive manner. Thus, Crhr1 in the BLA is critically involved as plasticity gene in the bidirectional epigenetic rescue of extremes in trait anxiety.

The growth factor receptor ERBB2 regulates mitochondrial activity on a signaling time scale

Overexpression of the ERBB2 receptor tyrosine kinase and the mitochondrial inner membrane protein UCP2 occurs frequently in aggressive cancers with dysfunctional mitochondria. Overexpressed ERBB2 signals constitutively and elevated UCP2 can uncouple mitochondria and alleviate oxidative stress. However, the physiological contributions of UCP2 and ERBB2 at the low expression levels that are typical of most tissues, as well as the path to oncogenic deregulation, are poorly understood. We now show that ERBB2 directly controls UCP2 levels, both at low physiological levels and oncogenic overexpression. At low levels of receptor and UCP2, ligand stimulation creates a distinct temporal response pattern driven by the opposing forces of translational suppression of the exceptionally short lived UCP2 protein and a time delayed transcriptional up-regulation. The latter becomes dominant through constitutive signaling by overexpressed ERBB2, resulting in high levels of UCP2 that contribute mitochondrial uncoupling. By contrast, ligand stimulation of non-overexpressed ERBB2 transiently removes UCP2 and paradoxically reduces the mitochondrial membrane potential, oxygen consumption, and OXPHOS on a signaling time scale. However, neither the transporter activity nor down-regulation of already low UCP2 levels drive this reduction in mitochondrial activity. Instead, UCP2 is required to establish mitochondria that are capable of responding to ligand. UCP2 knockdown impairs proliferation at high glucose but its absence specifically impairs ligand-induced growth when glucose levels fluctuate. These findings demonstrate the ability of growth factor signaling to control oxidative phosphorylation on a signaling time scale and point toward a non-transporter role for low levels of UCP2 in establishing dynamic response capability.

Dynamic analysis of the epidermal growth factor (EGF) receptor-ErbB2-ErbB3 protein network by luciferase fragment complementation imaging

ErbB3 is a member of the ErbB family of receptor tyrosine kinases. It is unique because it is the only member of the family whose kinase domain is defective. As a result, it is obliged to form heterodimers with other ErbB receptors to signal. In this study, we characterized the interaction of ErbB3 with the EGF receptor and ErbB2 and assessed the effects of Food and Drug Administration-approved therapeutic agents on these interactions. Our findings support the concept that ErbB3 exists in preformed clusters that can be dissociated by NRG-1β and that it interacts with other ErbB receptors in a distinctly hierarchical fashion. Our study also shows that all pairings of the EGF receptor, ErbB2, and ErbB3 form ligand-independent dimers/oligomers. The small-molecule tyrosine kinase inhibitors erlotinib and lapatinib differentially enhance the dimerization of the various ErbB receptor pairings, with the EGFR/ErbB3 heterodimer being particularly sensitive to the effects of erlotinib. The data suggest that the physiological effects of these drugs may involve not only inhibition of tyrosine kinase activity but also a dynamic restructuring of the entire network of receptors.

Oxytocin in Brattleboro rats: increased synthesis is contrasted by blunted intrahypothalamic release from supraoptic nucleus neurones

Adult male Brattleboro rats were used to investigate the impact of the congenital absence of vasopressin on the release pattern of oxytocin (OXT) within the hypothalamic supraoptic nucleus (SON) in response to a 10-min forced swimming session and osmotic stimulation. Both immunohistochemical and in situ hybridisation data suggest that vasopressin-deficient animals have more oxytocin-synthesising neurones in the SON than homozygous wild-type controls. Unexpectedly, both forced swimming and peripheral osmotic stimulation resulted in a blunted release profile of oxytocin within the SON of vasopressin-deficient rats compared to controls. A similar intranuclear OXT response to direct osmotic stimulation of the SON by retrodialysis with hypertonic Ringer's solution in both genotypes confirmed the capability of SON neurones to locally release oxytocin in vasopressin-deficient rats, indicating an altered processing of information originating from multisynaptic inputs rather than a deficit in release capacity. Taken together with data obtained in previous studies, the present findings provide evidence suggesting that autocrine and paracrine signalling of magnocellular neurones differs within the paraventricular nucleus and the SON. Thus, significant alterations in intra-SON oxytocin mRNA levels cannot easily be extrapolated to intranuclear release profiles and the local signal intensity of this neuropeptide after physiological stimulation.

Plasma oxytocin and vasopressin do not predict neuropeptide concentrations in human cerebrospinal fluid

The involvement of the neuropeptides oxytocin (OXT) and vasopressin (AVP) in human socio-emotional behaviours is attracting increasing attention. There is ample evidence for elevated plasma levels upon a wide variety of social and emotional stimuli and scenarios, ranging from romantic love via marital distress up to psychopathology, with cause versus consequence being largely unclear. The present study examined whether plasma levels of both OXT and AVP are reflective of central neuropeptide levels, as assumed to impact upon socio-emotional behaviours. Concomitant plasma and cerebrospinal fluid (CSF) samples were taken from 41 non-neurological and nonpsychiatric patients under basal conditions. Although OXT and AVP levels in the CSF exceeded those in plasma, there was no correlation between both compartments, clearly suggesting that plasma OXT and AVP do not predict central neuropeptide concentrations. Thus, the validity of plasma OXT and AVP as potential biomarkers of human behaviour needs further clarification.