Growth factor receptors: structure, mechanism, and drug discovery

Epidermal growth factor receptors unveiled: a comprehensive survey on mutations, clinical insights of global inhibitors, and emergence of heterocyclic derivatives as EGFR inhibitors

Mutations that overexpress the epidermal growth factor receptor (EGFR) are linked to cancers like breast (15-20%), head and neck (10-15%), colorectal (5-8%), and non-small cell lung cancer (10-50%), especially in East Asian populations. EGFR activation stimulates 'RAS/RAF/MEK/ERK, PI3K/Akt, and MAPK' pathways, which enhance cell division, survival, angiogenesis, and tumour growth while inhibiting apoptosis and metastasis. Secondary mutations (e.g. 'T790M', 'C797S'), off-target effects, and resistance due to alternate pathway activation reduce the efficacy of currently available EGFR inhibitors. To address these issues, 'novel heterocyclic inhibitors with structural versatility were developed to improve selectivity and binding affinity for mutant EGFR forms'. These new EGFR reduce side effects, enhance pharmacokinetics, and enhance therapeutic efficacy at low concentrations. This review focuses on 'EGFR mutations in various cancers' detailing the biochemical effects, clinical profiles, and binding interactions of globally approved EGFR inhibitors. Furthermore, it focuses into recent progress in nano-formulations and the development of heterocyclic derivatives that can successfully 'target mutant EGFRs' through varied synthesis methods. These inhibitors have the potential to have better binding affinities, selectivity's, and less side-effect. Further research required to refine the structures and develop nanoformulations of EGFR-targeted therapeutics in order to improve therapeutic efficiency and, provide more effective cancer treatments.

CSK-mediated signalling by integrins in cancer

Cancer progression and metastasis are processes heavily controlled by the integrin receptor family. Integrins are cell adhesion molecules that constitute the central components of mechanosensing complexes called focal adhesions, which connect the extracellular environment with the cell interior. Focal adhesions act as key players in cancer progression by regulating biological processes, such as cell migration, invasion, proliferation, and survival. Src family kinases (SFKs) can interplay with integrins and their downstream effectors. SFKs also integrate extracellular cues sensed by integrins and growth factor receptors (GFR), transducing them to coordinate metastasis and cell survival in cancer. The non-receptor tyrosine kinase CSK is a well-known SFK member that suppresses SFK activity by phosphorylating its specific negative regulatory loop (C-terminal Y⁵²⁷ residue). Consequently, CSK may play a pivotal role in tumour progression and suppression by inhibiting SFK oncogenic effects in several cancer types. Remarkably, CSK can localise near focal adhesions when SFKs are activated and even interact with focal adhesion components, such as phosphorylated FAK and Paxillin, among others, suggesting that CSK may regulate focal adhesion dynamics and structure. Even though SFK oncogenic signalling has been extensively described before, the specific role of CSK and its crosstalk with integrins in cancer progression, for example, in mechanosensing, remain veiled. Here, we review how CSK, by regulating SFKs, can regulate integrin signalling, and focus on recent discoveries of mechanotransduction. We additionally examine the cross talk of integrins and GFR as well as the membrane availability of these receptors in cancer. We also explore new pharmaceutical approaches to these signalling pathways and analyse them as future therapeutic targets.

Insulin-Like Growth Factor-1-Loaded Polymeric Poly(Lactic-Co-Glycolic) Acid Microspheres Improved Erectile Function in a Rat Model of Bilateral Cavernous Nerve Injury

BACKGROUND

Previous studies have documented improvement in erectile function after bilateral cavernous nerve injury (BCNI) in rats with the use of pioglitazone. Our group determined this improvement to be mediated by the insulin-like growth factor-1 (IGF-1) pathway.

AIM

To eliminate the systemic effects of pioglitazone and evaluate the local delivery of IGF-1 by polymeric microspheres after BCNI in the rat.

METHODS

Male Sprague-Dawley rats aged 10-12 weeks were assigned at random to 3 groups: sham operation with phosphate buffered saline (PBS)-loaded microspheres (sham group), crush injury with PBS-loaded microspheres (crush group), and crush injury with IGF-1-loaded microspheres (IGF-1 group). Poly(lactic-co-glycolic) acid microspheres were injected underneath the major pelvic ganglion (MPG). IGF-1 was released at approximately 30 ng/mL/day per MPG per rat.

OUTCOMES

Functional results were demonstrated by maximal intracavernosal pressure (ICP) normalized to mean arterial pressure (MAP). Protein-level analysis data of IGF-1 receptor (IGF-1R), extracellular signal-regulated kinase (ERK)-1/2, and neuronal nitric oxide synthase (nNOS) were obtained using Western blot analysis and immunohistochemistry for both the cavernosal tissue and the MPG and cavernous nerve (CN).

RESULTS

At 2 weeks after nerve injury, animals treated with IGF-1 demonstrated improved erectile functional recovery (ICP/MAP) at all voltages compared with BCNI (2.5V, P = .001; 5V, P < .001; 7.5V, P < .001). Western blot results revealed that up-regulation of the IGF-1R and ERK-1/2 in both the nervous and erectile tissue was associated with improved erectile function recovery. There were no significant between-group differences in nNOS protein levels in cavernosal tissue, but there was an up-regulation of nNOS in the MPG and CN. Immunohistochemistry confirmed these trends.

CLINICAL TRANSLATION

Local up-regulation of the IGF-1R in the neurovascular bed at the time of nerve injury may help men preserve erectile function after pelvic surgery, such as radical prostatectomy, eliminating the need for systemic therapy.

STRENGTHS & LIMITATIONS

This study demonstrates that local drug delivery to the MPG and CN can affect the CN tissue downstream, but did not investigate the potential effects of up-regulation of the growth factor receptors on prostate cancer tissue.

CONCLUSION

Stimulating the IGF-1R at the level of the CN has the potential to mitigate erectile dysfunction in men after radical prostatectomy, but further research is needed to evaluate the safety of this growth factor in the setting of prostate cancer. Haney NM, Talwar S, Akula PK, et al. Insulin-Like Growth Factor-1-Loaded Polymeric Poly(Lactic-Co-Glycolic) Acid Microspheres Improved Erectile Function in a Rat Model of Bilateral Cavernous Nerve Injury. J Sex Med 2019;16:383-393.

Norgestrel, a Progesterone Analogue, Promotes Significant Long-Term Neuroprotection of Cone Photoreceptors in a Mouse Model of Retinal Disease

Purpose

Retinitis pigmentosa (RP) refers to a group of inherited blinding retinal diseases, whereby the death of mutated rod photoreceptors is followed closely by the death of cone photoreceptors. Cone cell death can be hugely debilitating as color/daytime vision becomes impaired. Thus, treatments that are effective against cone cell death are urgently needed. Our research has been working toward development of a neuroprotective treatment for RP. We have previously demonstrated significant neuroprotective properties of norgestrel, a progesterone analogue, in the mouse retina. The current study further investigates the potential of norgestrel as a treatment for RP, with a focus on long-term preservation of cone photoreceptors.

Methods

Using the well-established rd10 mouse model of RP, we administered a norgestrel-supplemented diet at postnatal day (P)30, following widespread loss of rod photoreceptors and at the outset of cone degeneration. We subsequently assessed cone cell morphology and retinal function at P50, P60, and P80, using immunohistochemistry, electroretinograph recordings, and optomotor testing.

Results

While cone cell degeneration was widespread in the untreated rd10 retina, we observed profound preservation of cone photoreceptor morphology in the norgestrel-treated mice for at least 50 days, out to P80. This was demonstrated by up to 28-fold more cone arrestin-positive photoreceptors. This protection transpired to functional preservation at all ages.

Conclusions

This work presents norgestrel as an incredibly promising long-term neuroprotective compound for the treatment of RP. Crucially, norgestrel could be used in the mid-late stages of the disease to protect remaining cone cells and help preserve color/daytime vision.

Structure optimisation to improve the delivery efficiency and cell selectivity of a tumour-targeting cell-penetrating peptide

Cell-penetrating peptide (CPP) is used for the delivery of biomacromolecules across the cell membrane and is limited in cancer therapy due to the lack of cell selectivity. Epidermal growth factor receptor (EGFR) has been widely used in clinical targeted therapy for tumours. Here, we reported a novel tumour targeting cell-penetrating peptide (TCPP), EHB (ELBD-C6H) with 20-fold and 3000-fold greater transmembrane ability and tumour cell selectivity than our previously reported S3-HBD and classic CPP TAT, respectively. In this new TCPP, a specific alpha helix structure was inserted into a repeated amino acid (AA) sequence formed by tandem multiple selected key AA residues of vaccinia growth factor (VGF), and this sequence was then fused to a tailored heparin binding domain sequence (C6H) derived from heparin-binding epidermal growth factor-like growth factor to intensify its targeting delivery ability. EHB could carry anticancer proteins such as MAP30 (Momordica Antiviral Protein 30 kDa) into EGFR-overexpressing cancer cell and inhibit cell growth, but it had a greatly reduced interaction with normal cells. These results indicated that EHB, as a novel efficient TCPP for the selective delivery of drug molecules into cancer cells, would help to improve the efficacy and safety of anti-tumour drugs.

Functional expression of full-length TrkA in the prokaryotic host Magnetospirillum magneticum AMB-1 by using a magnetosome display system

Tropomyosin receptor kinase A (TrkA), a receptor tyrosine kinase, is known to be associated with various diseases. Thus, TrkA has become a major drug-screening target for these diseases. Despite the fact that the production of recombinant proteins by prokaryotic hosts has advantages, such as fast growth and ease of genetic engineering, the efficient production of functional receptor tyrosine kinase by prokaryotic hosts remains a major experimental challenge. Here, we report the functional expression of full-length TrkA on magnetosomes in Magnetospirillum magneticum AMB-1 by using a magnetosome display system. TrkAwas fused with the magnetosome-localized protein Mms13 and expressed on magnetosome surfaces. Recombinant TrkA showed both nerve growth factor (NGF)-binding and autophosphorylation activities. TrkA expressed on magnetosomes has the potential to be used, not only for further functional analysis of TrkA, but also for ligand screening.

Tea Catechin Suppresses Adipocyte Differentiation Accompanied by Down-regulation of PPARγ2 and C/EBPα in 3T3-L1 Cells

Obesity is a serious health problem, and its prevention is promoted through life style including diet and exercise. In this study, we investigated the suppressive effects of tea catechin on the differentiation of 3T3-L1 preadipocytes to adipocytes. (-)-Catechin 3-gallate (CG), (-)-epigallocatechin (EGC), (-)-epicatechin 3-gallate, and (-)-epigallocatechin 3-gallate at 5 muM suppressed intracellular lipid accumulation. The suppressive effects of CG and EGC were stronger than the others, and CG and EGC also suppressed the activity of glycerol-3-phosphate dehydrogenase as a differentiation marker. These catechins inhibited the expression of peroxisome proliferator-activated receptor (PPAR) gamma2 and CCAAT/enhancer-binding protein (C/EBP) alpha, both of which act as key transcription factors at an early stage of differentiation, followed by the expression of glucose transporter (GLUT) 4 at a later stage. In addition, the catechins did not affect the phosphorylation status of the insulin signal pathway. Thus, catechin suppressed adipocyte differentiation accompanied by the down-regulation of PPARgamma2, C/EBPalpha, and GLUT4. These results suggest that tea catechin prevents obesity through the suppression of adipocyte differentiation.

Sorafenib: targeting multiple tyrosine kinases in cancer

Sorafenib (BAY 43-9006, Nexavar®) is an oral multiple tyrosine kinase inhibitor. Main targets are receptor tyrosine kinase pathways frequently deregulated in cancer such as the Raf-Ras pathway, vascular endothelial growth factor (VEGF) pathway, and FMS-like tyrosine kinase 3 (FLT3). Sorafenib was approved by the FDA in fast track for advanced renal cell cancer and hepatocellular cancer and shows good clinical activity in thyroid cancer. Multiple clinical trials are undertaken to further investigate the role of sorafenib alone or in combination for the treatment of various tumor entities.

The lysin motif receptor-like kinase (LysM-RLK) CERK1 is a major chitin-binding protein in Arabidopsis thaliana and subject to chitin-induced phosphorylation

Plants detect potential pathogens by sensing microbe-associated molecular patterns via pattern recognition receptors. In the dicot model plant Arabidopsis, the lysin motif (LysM)-containing chitin elicitor receptor kinase 1 (CERK1) has been shown to be essential for perception of the fungal cell wall component chitin and for resistance to fungal pathogens. Recent in vitro studies with CERK1 protein expressed heterologously in yeast suggested direct chitin binding activity. Here we show in an affinity purification approach that CERK1 is a major chitin-binding protein of Arabidopsis cells, along with several known and putative chitinases. The ectodomain of CERK1 harbors three distinct LysM domains with potential ligand binding capacity. We demonstrate that the CERK1 ectodomain binds chitin and partially deacetylated chitosan directly without any requirement for interacting proteins and that all three LysM domains are necessary for chitin binding. Ligand-induced phosphorylation events are a general feature of animal and plant signal transduction pathways. Our studies show that chitin, chitin oligomers, and chitosan rapidly induce in vivo phosphorylation of CERK1 at multiple residues in the juxtamembrane and kinase domain. Functional analyses with a kinase dead variant provide evidence that kinase activity of CERK1 is required for its chitin-dependent in vivo phosphorylation, as well as for early defense responses and downstream signaling. Collectively, our data suggest that in Arabidopsis, CERK1 is a major chitin, chitosan, and chito-oligomer binding component and that chitin signaling depends on CERK1 post-translational modification and kinase activity.

A monovalent agonist of TrkA tyrosine kinase receptors can be converted into a bivalent antagonist

BACKGROUND

Receptor tyrosine kinases (RTK) act through dimerization. Previously it was thought that only bivalent ligands could be agonistic, whereas monovalent ligands should be antagonistic. This notion changed after the demonstration that monovalent ligands can be agonistic, including our report of a small molecule monovalent ligand "D3" that is a partial agonist of the NGF receptor TrkA. A bivalent "D3-linker-D3" was expected to increase agonism.

METHODS

Dimeric analogs were synthesized and tested in binding, biochemical, and biological assays.

RESULTS

One analog, 1-ss, binds TrkA with higher affinity than D3 and induces or stabilizes receptor dimers. However, 1-ss exhibited antagonistic activity, through two mechanisms. One mechanism is that 1-ss blocks NGF binding, unlike D3 which is non-competitive. Inhibition of NGF binding may be due to the linker of 1-ss filling the inter-receptor space that NGF traverses before docking. In a second mechanism, 1-ss acts as a pure antagonist, inhibiting NGF-independent TrkA activity in cells over-expressing receptors. Inhibition is likely due to 1-ss "freezing" the TrkA dimer in the inactive state.

CONCLUSIONS

Dimerization of an RTK can result in antagonism, through two independent mechanisms.

GENERAL SIGNIFICANCE

we report a small molecule monovalent agonist being converted to a bivalent antagonist.

Clinical significance of EGFR, Her-2 and EGF in oral squamous cell carcinoma: a case control study

Background

The erbB receptors and their ligands are involved in the pathogenesis and progression of oral squamous cell carcinoma (OSCC). Although EGFR and Her-2 are frequently overexpressed in OSCC, few studies evaluated these proteins in saliva and their association with the tumor, which may represent potential usefulness in a clinical setting.

Methods

The levels of EGFR, Her-2, and EGF were evaluated in saliva of 46 patients with OSCC before and after the surgical removal of the lesion, as well as in matched healthy controls. The relationship of salivary levels and EGFR and Her-2 immunoexpression in tumor samples with clinicopathological features was analyzed.

Results

EGFR and Her-2 salivary levels did not show difference between to pre-surgery and control groups, however, both demonstrated an increase after surgical removal of the tumor. No association was detectable among receptor salivary levels, tissue expression and clinicopathological features. EGF levels in pre-surgery group were significantly lower when compared to the control group.

Conclusions

EGFR and Her-2 were not considered to be valuable salivary tumor markers in OSCC, however, lower levels of EGF in saliva may suggest a higher susceptibility for OSCC development.

Sorafenib

Sorafenib (BAY 43-9006, Nexavar) is a novel oral kinase inhibitor that targets multiple tyrosine kinases in vivo and in vitro. Main targets are receptor tyrosine kinase pathways frequently deregulated in cancer such as the raf-ras pathway, vascular endothelial growth factor (VEGF) pathway, and FMS-like tyrosine kinase 3 (FLT3). Sorafenib was approved by the FDA in fast track for advanced renal cell cancer and hepatocellular cancer and shows good clinical activity in thyroid cancer. Multiple clinical trials are undertaken to further investigate the role of sorafenib alone or in combination for the treatment of various tumor entities.

A peptidomimetic of NT-3 acts as a TrkC antagonist

Neurotrophins are a family of growth factors that regulate the peripheral and central nervous system. We designed and tested a mini-library of small molecules peptidomimetics based on beta-turns of the neurotrophin growth factor polypeptides NT-3, which is the natural ligand for TrkC receptors. Biological studies identified a peptidomimetic 2Cl that exhibited selective antagonism of TrkC. 2Cl reduces TrkC activation and signaling promoted by NT-3, and selectively blocks ligand-dependent cell survival. 2Cl also blocks ligand-independent TrkC activation and signals that take place when the receptor is over-expressed. This work adds to our understanding of how the neurotrophins function through Trk receptors, and demonstrates that peptidomimetics can be designed to selectively disturb neurotrophin-receptor interactions, and receptor activation.

Cholinergic system during the progression of Alzheimer's disease: therapeutic implications

Alzheimer's disease (AD) is characterized by a progressive phenotypic downregulation of markers within cholinergic basal forebrain (CBF) neurons, frank CBF cell loss and reduced cortical choline acetyltransferase activity associated with cognitive decline. Delaying CBF neurodegeneration or minimizing its consequences is the mechanism of action for most currently available drug treatments for cognitive dysfunction in AD. Growing evidence suggests that imbalances in the expression of NGF, its precursor proNGF and the high (TrkA) and low (p75(NTR)) affinity NGF receptors are crucial factors underlying CBF dysfunction in AD. Drugs that maintain a homeostatic balance between TrkA and p75(NTR) may slow the onset of AD. A NGF gene therapy trial reduced cognitive decline and stimulated cholinergic fiber growth in humans with mild AD. Drugs treating the multiple pathologies and clinical symptoms in AD (e.g., M1 cholinoceptor and/or galaninergic drugs) should be considered for a more comprehensive treatment approach for cholinergic dysfunction.

Somatostatin receptors 1 and 5 heterodimerize with epidermal growth factor receptor: agonist-dependent modulation of the downstream MAPK signalling pathway in breast cancer cells

The role of somatostatin (SST) and epidermal growth factor (EGF) in breast cancer is undisputed; however, the molecular mechanisms underlying their antiproliferative or proliferative effects are not well understood. We initially confirmed that breast tumour tissues express all five somatostatin receptors (SSTR1-5) and four epidermal growth factor receptors (ErbB1-4). Subsequently, to gain insight into the function of SSTRs and ErbBs in oestrogen receptor (ER)-positive (MCF-7) or ERalpha-negative (MDA-MB-231) breast cancer cells, we defined SSTR1, SSTR5 and ErbB1 mRNA and protein expression in these two tumour cell lines. Consistent with previous studies showing SSTR1/SSTR5 heterodimerization and having seen cell-specific and ligand-selective alterations in receptor expression, we next elucidated whether SSTR1 and SSTR5 functionally interact with ErbB1 using pbFRET analysis. We subsequently determined the effects of SST and EGF either alone, or in combination, on selected downstream signalling molecules such as erk1/2, p38 and JNK. Here, we showed that both SST and EGF influenced erk1/2 phosphorylation and that SST modulated the effects of EGF in a cell-specific manner. We also demonstrated agonist-, time and cell-dependent regulation of p38 phosphorylation. We further investigated modulation of Grb2, SOS, Shc, SH-PTP1 and SH-PTP2. ErbB1 adaptor proteins known to play a role in MAPK activation, Shc, Grb2 and SOS, changed in an agonist- and cell-specific manner whereas, SH-PTP1 and SH-PTP2, adaptor proteins reported to interact with SSTRs, translocated from the cytosol to membrane in a cell-specific manner following SST and/or EGF treatment. Although several previous studies have shown crosstalk between RTKs and GPCRs, there are no reports describing SSTR (GPCR) modulation of ErbBs (RTK) in breast cancer. To the best of our knowledge, this is the first report describing crosstalk/interactions between SSTRs and ErbBs.

Inhibition of autophosphorylation of epidermal growth factor receptor by a small peptide not employing an ATP-competitive mechanism

Previously we found that short peptides surrounding major autophosphorylation sites of EGFR (VPEY(1068)INQ, DY(1148)QQD, and ENAEY(1173)LR) suppress phosphorylation of purified EGFR to 30-50% at 4000 microM. In an attempt to improve potencies of the peptides, we modified the sequences by substituting various amino acids for tyrosine or by substituting Gln and Asn for Glu and Asp, respectively. Among the modified peptides, Asp/Asn- and Glu/Gln-substitution in DYQQD (NYQQN) and ENAEYLR (QNAQYLR), respectively, improved inhibitory potencies. The inhibitory potency of NYQQN was not affected by the concentration of ATP, while that of QNAQYLR was affected. Docking simulations showed different mechanisms of inhibition for the peptides: inhibition by binding to the ATP-binding site (QNAQYLR) and inhibition by binding to a region surrounded by alphaC, the activation loop, and the catalytic loop and interfering with the catalytic reaction (NYQQN). The inhibitory potency of NYQQN for insulin receptor drastically decreased, whereas QNAQYLR inhibited autophosphorylation of insulin receptor as well as EGFR. In conclusion, NYQQN is not an ATP-competitive inhibitor and the binding site of this peptide appears to be novel as a tyrosine kinase inhibitor. NYQQN could be a promising seed for the development of anti-cancer drugs having specificity for EGFR.

Evaluation of an 111In-radiolabeled peptide as a targeting and imaging agent for ErbB-2 receptor expressing breast carcinomas

PURPOSE

The cellular targeting and tumor imaging properties of a novel ErbB-2-avid peptide, discovered from bacteriophage display, were evaluated in human breast carcinoma cells and in breast carcinoma-xenografted mice.

EXPERIMENTAL DESIGN

The affinity of the ErbB-2 targeting peptide KCCYSL and its alanine substituted counterparts for the extracellular domain (ECD) of purified recombinant ErbB-2 (ErbB-2-ECD) was assessed by fluorescence titration. Binding of the KCCYSL peptide to breast and prostate carcinoma cells was analyzed by confocal microscopy. A DOTA(GSG)-KCCYSL peptide conjugate was radiolabeled with 111In, and stability, target binding, and internalization were analyzed in vitro. In vivo biodistribution and single-photon emission computed tomography imaging studies were done with the radiolabeled peptide in MDA-MB-435 human breast tumor-bearing severe combined immunodeficient mice.

RESULTS

KCCYSL peptide exhibited high affinity (295 +/- 56 nmol/L) to ErbB-2-ECD. Substitution of alanine for lysine, tryptophan, and cysteine reduced the peptide affinity approximately 1- to 2.4-fold, whereas replacing leucine completely abolished binding. Both biotin-KCCYSL and 111In-DOTA(GSG)-KCCYSL were capable of binding ErbB-2-expressing human breast carcinoma cells in vitro. Approximately 11% of the total bound radioactivity was internalized in the carcinoma cells. Competitive binding studies indicated that the radiolabeled peptide exhibited an IC(50) value of 42.5 +/- 2.76 nmol/L for the breast carcinoma cells. 111In-DOTA(GSG)-KCCYSL was stable in serum and exhibited rapid tumor uptake (2.12 +/- 0.32 %ID/g) at 15 min postinjection and extended retention coupled with rapid whole body disappearance, as observed by biodistribution and single-photon emission computed tomography imaging studies, respectively.

CONCLUSIONS

The DOTA(GSG)-KCCYSL peptide has the potential to be used as a tumor-imaging agent and a vehicle for specific delivery of radionuclide or cytotoxic agents for tumors overexpressing ErbB-2.

Structure, evolution, and biology of the MUC4 mucin

Mucins are high-molecular-weight glycoproteins and are implicated in diverse biological functions. MUC4, a member of transmembrane mucin family, is expressed in airway epithelial cells and body fluids like saliva, tear film, ear fluid, and breast milk. In addition to its normal expression, an aberrant expression of MUC4 has been reported in a variety of carcinomas. Among various potential domains of MUC4, epidermal growth factor (EGF) -like domains are hypothesized to interact with and activate the ErbB2 receptors, suggesting an intramembrane-growth factor function for MUC4. The heavily glycosylated tandem repeat domain provides the structural rigidity to the extended extracellular region. MUC4, by virtue of its extended structure, serves as a barrier for some cell-cell and cell-extracellular matrix interactions and as a potential reservoir for certain growth factors. An intricate relationship between MUC4 and growth factor signaling is also reflected in the transcriptional regulation of MUC4. The MUC4 promoter has binding sites for different transcription factors, which are responsible for the regulation of its expression in different tissues. The interferon-gamma, retinoic acid, and transforming growth factor-beta signaling pathways regulate MUC4 expression in a partially interdependent manner. Taken together, all of these features of MUC4 strongly support its role as a potential candidate for diagnostic and therapeutic applications in cancer and other diseases.

The nerve growth factor and its receptors in airway inflammatory diseases

The nerve growth factor (NGF) belongs to the neurotrophin family and induces its effects through activation of 2 distinct receptor types: the tropomyosin-related kinase A (TrkA) receptor, carrying an intrinsic tyrosine kinase activity in its intracellular domain, and the receptor p75 for neurotrophins (p75NTR), belonging to the death receptor family. Through activation of its TrkA receptor, NGF activates signalling pathways, including phospholipase Cgamma (PLCgamma), phosphatidyl-inositol 3-kinase (PI3K), the small G protein Ras, and mitogen-activated protein kinases (MAPK). Through its p75NTR receptor, NGF activates proapoptotic signalling pathways including the MAPK c-Jun N-terminal kinase (JNK), ceramides, and the small G protein Rac, but also activates pathways promoting cell survival through the transcription factor nuclear factor-kappaB (NF-kappaB). NGF was first described by Rita Levi-Montalcini and collaborators as an important factor involved in nerve differentiation and survival. Another role for NGF has since been established in inflammation, in particular of the airways, with increased NGF levels in chronic inflammatory diseases. In this review, we will first describe NGF structure and synthesis and NGF receptors and their signalling pathways. We will then provide information about NGF in the airways, describing its expression and regulation, as well as pointing out its potential role in inflammation, hyperresponsiveness, and remodelling process observed in airway inflammatory diseases, in particular in asthma.

Construction of a mutated pro-nerve growth factor resistant to degradation and suitable for biophysical and cellular utilization

Precursor of nerve growth factor (proNGF) has been found to be proapoptotic in several cell types and mediates its effects by binding to p75 neurotrophin receptor (p75NTR) and sortilin. The proNGF molecule is processed by proteases at three dibasic sites found in the pro domain to form mature NGF (termed herein as sites 1, 2, and 3 from the proNGF N terminus). Of these processing sites, site 3, adjacent to the N terminus of mature NGF, was thought to be the major site responsible for processing of proNGF to mature NGF. We found that mutating this major processing site (site 3) resulted in a form of proNGF that was only partially stable. On introducing additional mutations in the pro domain at the other two dibasic sites, we found the stability of proNGF to increase significantly. Here we describe the construction, expression, and purification of this more stable proNGF molecule. The two consecutive basic residues at each of the three sites were mutated to neutral alanine residues. Expression was performed in stably transfected Sf21 insect cells. Purification involved strong cation-exchange chromatography and N60 immunoaffinity column chromatography. The construct with all three sites mutated (termed proNGF123) gave all proNGF with no mature NGF and was not cleaved by three proconvertases (furin, PACE-4, and PC-2) known to proteolyze proneurotrophins in vivo. This stable proNGF molecule demonstrated proapoptotic activity on rat pheocytochroma PC12 cells, PC12nnr cells, C6 glioblastoma cells, and RN22 schwannoma cells.

Association with HSP90 Inhibits Cbl-Mediated Down-regulation of Mutant Epidermal Growth Factor Receptors

Activating mutations in the epidermal growth factor receptor (EGFR), localized in the activation loop within the kinase domain, have been discovered in non-small cell lung cancers (NSCLC). Most of these mutants are exquisitely sensitive to EGFR tyrosine kinase inhibitors, suggesting that they generate receptor dependence in the cancers that express them. 32D cells stably expressing EGFR-L861Q and EGFR-L858R but not wild-type EGFR exhibited ligand-independent receptor phosphorylation and viability. Ligand-induced receptor down-regulation (LIRD) was impaired in mutant-expressing cells. The EGFR mutants were constitutively associated with the E3 ubiquitin ligase Cbl but did not associate with the adaptor protein CIN85 on the addition of ligand. Inhibition of HSP90 activity with geldanamycin restored Cbl function as indicated by receptor ubiquitination and LIRD. These results suggest that EGFR mutants form defective endocytic complexes. In addition, HSP90 plays a role in maintaining the functional conformation of EGFR mutants and protecting activated receptors from LIRD.

Mechanism of action of potato carboxypeptidase inhibitor (PCI) as an EGF blocker

The epidermal growth factor receptor (EGFR) signal transduction pathway plays a prominent role in the development of carcinomas, and is an interesting target for antitumoral therapy. We have previously described how potato carboxypeptidase inhibitor (PCI), a 39-amino acid protease inhibitor with a T-Knot motif, binds to EGFR receptor and inhibits the activation of receptor protein tyrosine kinase. In this paper it is shown that PCI interferes with EGFR activation through inhibition of receptor dimerization and receptor transphosphorylation induced by epidermal growth factor (EGF) and by transforming growth factor alpha (TGF-alpha). Moreover, PCI blocks the formation and activation of ErbB1/ErbB-2 heterodimers that have a prominent role in carcinoma development. As a result of these effects, PCI interferes in the EGFR signal transduction pathway by reversing the effects of EGF on the growth of two tumoral cell lines, A431 and MDA-MB-453, and promotes EGFR down-regulation. These results show that PCI acts as an EGF/TGF-alpha antagonist, which suggests its therapeutic potential in the treatment of carcinomas.

Methyl scanning: total synthesis of demethylasterriquinone B1 and derivatives for identification of sites of interaction with and isolation of its receptor(s)

The principle of methyl scanning is proposed for determination of the sites of interaction between biologically active small molecules and their macromolecular target(s). It involves the systematic preparation of a family of methylated derivatives of a compound and their biological testing. As a functional assay, the method can identify the regions of a molecule that are important (and unimportant) for biological activity against even unknown targets, and thus provides an excellent complement to structural biology. Methyl scanning was applied to demethylasterriquinone B1, a small-molecule mimetic of insulin. A new, optimal total synthesis of this natural product was developed that enables the family of methyl scan derivatives to be concisely prepared for evaluation in a cellular assay. The results of this experiment were used to design a biotin-demethylasterriquinone conjugate for use as an affinity reagent. This compound was prepared in tens of milligram quantities in a four-step synthesis.

Discordant changes in cortical TrkC mRNA and protein during the human lifespan

Neurotrophin-3 (NT-3) exerts its trophic effects in brain via tyrosine kinase receptor C (trkC) signaling. TrkC splice variants produce receptors with (full-length) and without (truncated) a tyrosine kinase domain. The relative abundance of trkC isoforms and the anatomical localization of trkC in the human prefrontal cortex (PFC) in relationship to development and maturation are currently unknown. We have examined the temporo-spatial expression of trkC protein and mRNA during the development of the human PFC. We have found two major isoforms, a full-length (150 kDa) and a truncated (50 kDa) form of the trkC protein in the human PFC. We report that the full-length form is expressed at low levels throughout development while the truncated form is expressed at moderate levels early in development and increases to reach mature levels by adolescence. In contrast, trkC mRNA levels are uniformly expressed throughout most of postnatal life, but decline in ageing. TrkC protein and mRNA are expressed in both pyramidal and non-pyramidal neurons; additionally, trkC protein is detected in glia and neuropil. Our results suggest that truncated trkC is prevalent in the human PFC and that neurons and glia may be responsive to NT-3 in the PFC throughout life.

Epidermal growth factor-like motifs 1 and 2 of Plasmodium vivax merozoite surface protein 1 are critical domains in erythrocyte invasion

Plasmodium vivax merozoite surface protein 1 (PvMSP1) is believed to be important in erythrocyte invasion. However, the detailed mechanism of PvMSP1-mediated invasion has been unclear. We demonstrate that the C-terminal 19 kDa domain (PvMSP119) of PvMSP1, the 42-kDa fragment of PvMSP1 is further cleaved to a 33 kDa N-terminal polypeptide and a 19 kDa C-terminal fragment in a secondary processing step, is a critical domain in the binding between parasite ligand and erythrocyte receptor. Also, its cytoadherence was successfully blocked by naturally acquired immunity, was partially sensitive to neuraminidase and trypsin. When expressed separately epidermal growth factor (EGF)-like motifs 1 and 2, subunits of the PvMSP119, mediated 64% and 66% of the erythrocyte-binding activity, respectively, relative to their expression together as a single intact ligand domain. These results suggest that the EGF-like motifs 1 and 2 of PvMSP119 function as a core-binding portion in the attachment of PvMSP1 to erythrocytes.

Specific Residues in Plasmatocyte-spreading Peptide Are Required for Receptor Binding and Functional Antagonism of Insect Immune Cells

Plasmatocyte-spreading peptide (PSP) is a 23-amino acid cytokine that activates a class of insect immune cells called plasmatocytes. PSP consists of two regions: an unstructured N terminus (1-6) and a highly structured core (7-23). Prior studies identified specific residues in both the structured and unstructured regions required for biological activity. Most important for function were Arg13, Phe3, Cys7, Cys19, and the N-terminal amine of Glu1. Here we have built on these results by conducting cell binding and functional antagonism studies. Alanine replacement of Met12 (M12A) resulted in a peptide with biological activity indistinguishable from PSP. Competitive binding experiments using unlabeled and 125I-M12A generated an IC50 of 0.71 nm and indicated that unlabeled M12A, at concentrations > or =100 nm, completely blocked binding of label to hemocytes. We then tested the ability of other peptide mutants to displace 125I-M12A at a concentration of 100 nm. In the structured core, we found that Cys7 and Cys19 were essential for cell binding and functional antagonism, but these effects were likely because of the importance of these residues for maintaining the tertiary structure of PSP. Arg13, in contrast, was also essential for binding and activity but is not required for maintenance of structure. In the unstructured N-terminal region, deletion of the phenyl group from Phe3 yielded a peptide that reduced binding of 125I-M12A 326-fold. This and all other mutants of Phe3 we bioassayed were unable to antagonize PSP. Deletion of Glu1 in contrast had almost no effect on binding and was a strong functional antagonist. Experiments using a photoaffinity analog indicated that PSP binds to a single 190-kDa protein.

Effect of insulin-like growth factor-1 and insulin-like growth factor binding protein-3 complex in cavernous nerve cryoablation

The purpose of this work was to study the effect of insulin-like growth factor 1 (IGF-1) and its binding protein (IGFBP-3) on the recovery of erectile function in a rat model for neurogenic impotence. In all, 28 male Sprague-Dawley rats were divided into four groups: seven underwent a sham operation; seven underwent bilateral cavernous nerve freezing (control group); seven underwent bilateral cavernous nerve freezing followed by intraperitoneal injection of IGF-1; and seven underwent bilateral cavernous nerve freezing followed by intraperitoneal injection of IGFBP-3. Erectile response was assessed by cavernous nerve electrostimulation at 3 months, and samples of penile tissue were evaluated histochemically for nitric oxide synthase (NOS)-containing fibers. In the sham and IGF-1 group, there were significantly higher maximal intracavernous pressures compared to the IGFBP-3 complex and the control group. Correspondingly in the cavernosum, there were significantly more NOS-containing nerve fibers in the sham and IGF-1 groups. In conclusion, administration of IGF-1 can facilitate the regeneration of NOS-containing nerve fibers in penile tissue and enhance the recovery of erectile function after bilateral cavernous nerve cryoablation. The reverse effect was noted with the IGFBP-3 complex injection.

Signaling effects of demethylasterriquinone B1, a selective insulin receptor modulator

A possible breakthrough in the treatment of diabetes was made with the discovery that a fungal natural product, demethylasterriquinone B1 (DAQ B1), is an orally active, small-molecule mimic of insulin. Subsequent work has shown that the glucose-lowering effects of DAQ B1 are not accompanied by enhanced vascular proliferation, which is a side effect of chronic insulin administration that can lead to arteriosclerosis. Our recent short and modular total synthesis of DAQ B1 could be readily modified to create congeners and afforded ample supplies of the natural product, which permitted intracellular signal transduction of DAQ B1 to be examined. The activities of DAQ B1 and over a dozen related structures were studied for insulin receptor (IR) and insulin receptor substrate-1 phosphorylation. Examination of the effect of DAQ B1 on kinases downstream of the IR in insulin signal transduction showed selective activation of Akt kinase (a metabolic effect) but not of extracellular-regulated kinase (a proliferative effect). The influence of DAQ B1 on gene expression (determined by a microarray study) was also divergent from that of insulin, which activates both proliferative and metabolic pathways. The action of DAQ B1 as a selective insulin receptor modulator can be accounted for by its ability to selectively activate one kinase among the many emanating from insulin receptor autophosphorylation and its reduced effects on gene expression.

Molecular dynamics simulations of the NGF-TrkA domain 5 complex and comparison with biological data

The nerve growth factor (NGF) is an important pharmacological target for Alzheimer's and other neurodegenerative diseases. Its action derives partly from its binding to the tyrosine kinase A receptor (TrkA). Here we study energetics and dynamics of the NGF-TrkA complex by carrying out multinanosecond molecular dynamics simulations, accompanied by electrostatic calculations based on the Poisson-Boltzmann equation. Our calculations, which are based on the x-ray structure of the complex, suggest that some of the mutations affecting dramatically the affinity of the complex involve residues that form highly favorable, direct or water-mediated hydrogen bond interactions at the ligand-receptor interface and, in some cases, that also critically participate to the large-scale motions of the complex. Furthermore, our calculations offer a rationale for the small effect on binding affinity observed upon specific mutations involving large changes in electrostatics (i.e., the charged-to-neutral mutations). Finally, these calculations, used along with the mutagenesis data, provide a basis for designing new peptides that mimic NGF in TrkA binding function.

The role of receptor tyrosine kinase inhibition in treating gastrointestinal malignancy

Tyrosine kinase receptors are proteins that transduce the signal from many growth factor and cytokine ligands to produce intracellular responses. As such they can activate multiple signalling cascade pathways and influence cell division, migration and survival. Many show upregulation in certain malignancies, including those of the gastrointestinal tract, and are thought to play key roles in carcinogenesis. This makes them attractive targets for drug therapy and in recent years many inhibitors have been developed. This review discusses the current situation regarding the development of inhibitors with particular reference to the erbB family, the insulin-like growth factor receptor, the Met receptor, the receptor for vascular endothelial growth factor and the Kit receptor. The evidence will be related back to cancers of the gut lumen. Clinical effectiveness in this area seems to lie in using a combinatorial approach that inhibits multiple key signalling points, and the reasons for this will be discussed.

Neurotrophins in cultured cells from periodontal tissues

We review the basic functions of neurotrophins and their receptors and discuss the expression and functions of neurotrophins and their specific receptors based on recent data using cultured cells from human periodontal tissues. Neurotrophins, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) play crucial roles in the differentiation and survival of neural cells. Neurotrophins activate 2 different receptor classes: the tropomyosin-related kinase (Trk) family of receptor tyrosine kinases (TrkA, TrkB, and TrkC) and the p75 receptor, a member of the tumor necrosis factor receptor superfamily. Neurotrophins regulate both cell death and cell survival through activations of Trk receptors and/or p75 neurotrophin receptor. It has been reported that neurotrophins are also produced from non-neuronal cells, such as leukocytes, osteoblasts, or fibroblasts, and act in many other ways on non-neuronal cells. Neurotrophin expression during bone fracture healing is especially interesting, and neurotrophins are now implicated in hard tissue regeneration. It is well known that neurotrophins and their receptors are expressed in tooth development. Recent studies have found that neurotrophins and Trk receptors are expressed in mouse osteoblastic cell lines. Human periodontal ligament cells, human gingival fibroblasts, and human gingival keratinocytes expressed mRNA for NGF and TrkA. The secretion of bioactive NGF peptides from human periodontal ligament cells and human gingival keratinocytes was confirmed by bioassay using PC12 cells (rat adrenal pheochromocytoma cells). The expression of NGF and TrkA.mRNA was regulated by interleukin (IL)-1beta. NGF increased DNA synthesis and expressions of mRNA for bone-related proteins, alkaline phosphatase, and osteopontin in human periodontal ligament cells. Neurotrophins and Trk receptors expressed in human periodontal tissue may contribute to regeneration as well as innervation of periodontal tissue through local autocrine and paracrine pathways. Recent data suggest that some functions of neurotrophins and Trk receptors relate to periodontal disease and periodontal tissue regeneration. However, in vivo studies will be required to clarify the roles of neurotrophins and their receptors, including p75, in periodontal disease and periodontal tissue regeneration.

Seeing the light: preassembly and ligand-induced changes of the interferon gamma receptor complex in cells

Our experiments were designed to test the hypothesis that the cell surface interferon gamma receptor chains are preassembled rather than associated by ligand and to assess the molecular changes on ligand binding. To accomplish this, we used fluorescence resonance energy transfer, a powerful spectroscopic technique that has been used to determine molecular interactions and distances between the donor and acceptor. However, current commercial instruments do not provide sufficient sensitivity or the full spectra to provide decisive results of interactions between proteins labeled with blue and green fluorescent proteins in living cells. In our experiments, we used the blue fluorescent protein and green fluorescent protein pair, attached a monochrometer and charge-coupled device camera to a modified confocal microscope, reduced background fluorescence with the use of two-photon excitation, and focused on regions of single cells to provide clear spectra of fluorescence resonance energy transfer. In contrast to the prevailing view, the results demonstrate that the receptor chains are preassociated and that the intracellular domains move apart on binding the ligand interferon gamma. Application of this technology should lead to new rapid methods for high throughput screening and delineation of the interactome of cells.

Identification and characterization of peptides that bind human ErbB-2 selected from a bacteriophage display library

The ErbB-2 receptor, a member of the tyrosine kinase type 1 family of receptors, has been implicated in many human malignancies. The overexpression of ErbB-2 in cancer cells as well as its extracellular accessibility makes it an attractive target for the development of tumor-specific agents. In this study, random peptide bacteriophage display technology was employed to identify peptides that bound the extracellular domain of human ErbB-2. The peptide KCCYSL, most frequently occurring in the affinity-selected phage population, was chemically synthesized and characterized for its binding activities to ErbB-2. The synthetic peptide exhibited high specificity for ErbB-2 and an equilibrium dissociation constant of 30 microM. Peptide binding to ErbB-2 positive human breast and prostate carcinoma cells was visualized in direct cell binding assays. In conclusion, the peptide KCCYSL has the potential to be developed into a cancer imaging or therapeutic agent targeting malignant cells overexpressing the ErbB-2 receptor.

A specific binding site for a fragment of the B-loop of epidermal growth factor and related peptides

Fragments of the B-loop of the epidermal growth factor family of peptides are reported to have mitogenic and angiogenic properties but appear to fail to compete with radioiodinated EGF in receptor binding. In this study, 11 analogs of a fragment of the B-loop of EGF-related peptides from several species were synthesized to study binding to A431 human epidermoid carcinoma using both 125I-EGF and [3'4'-3H-Tyr(22,29), Abu(20,31)]EGF(20-31)-NH(2). Specific binding sites were found for the human fragment and 8 analogs at a density five times higher than that of the EGF receptors. Analogs did not compete with 125I-EGF for binding to the EGF receptor. The novel binding site may mediate the biological effects of the fragments. The primary rather than secondary structure of the fragments appears to determine affinity.

Specificity in Trk receptor:neurotrophin interactions: the crystal structure of TrkB-d5 in complex with neurotrophin-4/5

BACKGROUND

The binding of neurotrophin ligands to their respective Trk cellular receptors initiates intracellular signals essential for the growth and survival of neurons. The site of neurotrophin binding has been located to the fifth extracellular domain of the Trk receptor, with this region regulating both the affinity and specificity of Trk receptor:neurotrophin interaction. Neurotrophin function has been implicated in a number of neurological disorders, including Alzheimer's disease and Parkinson's disease.

RESULTS

We have determined the 2.7 A crystal structure of neurotrophin-4/5 bound to the neurotrophin binding domain of its high-affinity receptor TrkB (TrkB-d5). As previously seen in the interaction of nerve growth factor with TrkA, neurotrophin-4/5 forms a crosslink between two spatially distant receptor molecules. The contacts formed in the TrkB-d5:neurotrophin-4/5 complex can be divided into a conserved area similar to a region observed in the TrkA-d5:NGF complex and a second site-unique in each ligand-receptor pair-formed primarily by the ordering of the neurotrophin N terminus.

CONCLUSIONS

Together, the structures of the TrkB-d5:NT-4/5 and TrkA-d5:NGF complexes confirm a consistent pattern of recognition in Trk receptor:neurotrophin complex formation. In both cases, the N terminus of the neurotrophin becomes ordered only on complex formation. This ordering appears to be directed largely by the receptor surface, with the resulting complementary surfaces providing the main determinant of receptor specificity. These features provide an explanation both for the limited crossreactivity observed between the range of neurotrophins and Trk receptors and for the high-affinity binding associated with respective ligand-receptor pairs.

Discovery of a series of nonpeptide small molecules that inhibit the binding of insulin-like growth factor (IGF) to IGF-binding proteins

Insulin-like growth factors (IGF-I and II) play an important role in metabolic and mitogenic activities through stimulation of the IGF-I receptor on the cell surface. Although the concentration of IGF in blood and cerebrospinal fluid is quite high (>100 nM), this large pool of IGF is biologically inactive because of its association with six distinct binding proteins, which form high-affinity complexes with IGF. Thus, inhibitors of IGF-binding proteins (IGFBPs), especially IGFBP-3, could potentially alter the distribution between the "free" and "bound" forms of IGF and thereby elevate biologically active IGF-I to exert a beneficial effect on those patients with diseases that respond to the application of exogenous IGF-I. Whereas IGF-I peptide variants, which bind to IGFBPs but not the IGF-I receptor, have been shown to be potent IGF/IGFBP inhibitors, small molecule nonpeptide IGF/IGFBP inhibitors have the potential advantages of oral bioavailability and flexible dosing regimen. Here we report the discovery of several isoquinoline analogues, exemplified by 1 and 2, which bind IGFBP-3 as well as other IGFBPs at low nanomolar concentrations. More importantly, both compounds were shown to be able to release biologically active IGF-I from the IGF-I/IGFBP-3 complex. These results point to the feasibility of developing orally active therapeutics to treat IGF-responsive diseases by optimization of the lead molecules 1 and 2.

Capacitation dependent activation of tyrosine phosphorylation generates two sperm head plasma membrane proteins with high primary binding affinity for the zona pellucida

The recognition and binding of sperm cells to the zona pellucida (the extracellular matrix of the oocyte) are essential for fertilization and are believed to be species specific. Freshly ejaculated sperm cells do not bind to the zona pellucida. Physiologically this interaction is initiated after sperm activation in the female genital tract (capacitation) via a yet unknown mechanism, resulting in the binding of a receptor in the apical sperm plasma membrane to the zona pellucida. In order to mimic this biochemically, we isolated zona pellucida fragments from gilt ovaries to prepare an affinity column with the intact zona pellucida structure and loaded this column with solubilized apical plasma membranes of boar sperm cells before and after in vitro capacitation. With this technique we demonstrated that two plasma membrane proteins of capacitated boar sperm cells showed high affinity for zona pellucida fragments. Further analysis showed that these proteins were tyrosine phosphorylated. Plasma membrane proteins from freshly ejaculated sperm cells did not exhibit any zona pellucida binding proteins, likely because these proteins were not tyrosine phosphorylated.

Alanine-scanning mutagenesis of plasmatocyte spreading peptide identifies critical residues for biological activity

Plasmatocyte spreading peptide (PSP) is a 23-amino acid cytokine that induces a class of insect immune cells called plasmatocytes to spread on foreign surfaces. The structure of PSP consists of a disordered N terminus (residues 1-6) and a well-defined core (residues 7-23) stabilized by a disulfide bridge between Cys(7) and Cys(19), hydrophobic interactions, and a short beta-hairpin. Structural comparisons also indicate that the core region of PSP adopts an epidermal growth factor (EGF)-like fold very similar to the C-terminal subdomain of EGF-like module 5 of thrombomodulin. To identify residues important for plasmatocyte spreading activity, we bioassayed PSP mutants in which amino acids were either replaced with alanine or deleted. Within the well-defined core of PSP, alanine replacement of Cys(7) and Cys(19) (C7.19A) eliminated all activity. Alanine replacement of Arg(13) reduced activity approximately 1000-fold in comparison to wild-type PSP, whereas replacement of the other charged residues (Asp(16), Arg(18), Lys(20)) surrounding Cys(19) diminished activity to a lesser degree. The point mutants Y11A, T14A, T22A, and F23A had activity identical or only slightly reduced to that of wild-type PSP. The mutant PSP-(7-23) lacked the entire unstructured domain of PSP and was found to have no plasmatocyte spreading activity. Surprisingly, E1A and N2A had higher activity than wild-type PSP, but F3A had almost no activity. We thus concluded that the lack of activity for PSP-(7-23) was largely due to the critical importance of Phe(3). To determine whether reductions in activity correlated with alterations in tertiary structure, we compared the C7.19A, R13A, R18A, and F3A mutants to wild-type PSP by NMR spectroscopy. As expected, the simultaneous replacement of Cys(7) and Cys(19) profoundly affected tertiary structure, but the R13A, R18A, and F3A mutants did not differ from wild-type PSP. Collectively, these results indicate that residues in both the unstructured and structured domains of PSP are required for plasmatocyte-spreading activity.

Hippocampal tyrosine kinase A receptors are restricted primarily to presynaptic vesicle clusters

Adult septohippocampal cholinergic neurons are dependent on trophic support for normal functioning and survival; these effects are largely mediated by the tyrosine kinase A receptor (TrkA), which binds its ligand, nerve growth factor (NGF), with high affinity. To determine the subcellular localization of TrkA within septohippocampal terminal fields, two rabbit polyclonal antisera to the extracellular domain of TrkA were localized immunocytochemically in rat dentate gyrus by light and electron microscopy. By light microscopy, TrkA immunoreactivity was found mostly in fine, varicose fibers primarily in the hilus and, to a lesser extent, in the granule cell and molecular layers. By electron microscopy, the central and infragranular regions of the hilus contained the highest densities of TrkA-immunoreactive profiles. Most TrkA-labeled profiles were axons (31% of 3,473), axon terminals (20%), and glia (38%); fewer were dendrites (6%), dendritic spines (5%), and granule cell and interneuron somata (<1%). TrkA immunolabeling in axons and axon terminals was discrete, often concentrated in patches of small synaptic vesicles that were adjacent to somatic and dendritic profiles. TrkA-labeled terminals formed both asymmetric and symmetric synapses, primarily with dendritic shafts and spines. TrkA-immunoreactive glial profiles frequently apposed terminals contacting dendritic spines. The findings that presynaptic profiles contain TrkA immunolabeling in sites of vesicle accumulation suggest that NGF binding to TrkA may influence transmitter release. The presence of TrkA immunoreactivity in somata, dendrites, and glia further suggests that cells within the dentate gyrus may take up NGF.

Design of GFB-111, a platelet-derived growth factor binding molecule with antiangiogenic and anticancer activity against human tumors in mice

We have designed a molecule, GFB-111, that binds to platelet-derived growth factor (PDGF), prevents it from binding to its receptor tyrosine kinase, and blocks PDGF-induced receptor autophosphorylation, activation of Erk1 and Erk2 kinases, and DNA synthesis. GFB-111 is highly potent (IC50 = 250 nM) and selective for PDGF over EGF, IGF-1, aFGF, bFGF, and HRGbeta (IC50 values > 100 microM), but inhibits VEGF-induced Flk-1 tyrosine phosphorylation and Erk1/Erk2 activation with an IC50 of 10 microM. GFB-111 treatment of nude mice bearing human tumors resulted in significant inhibition of tumor growth and angiogenesis. The results demonstrate the feasibility of designing novel growth factor-binding molecules with potent anticancer and antiangiogenic activity.

Nerve growth factor (NGF) loop 4 dimeric mimetics activate ERK and AKT and promote NGF-like neurotrophic effects

Previous work indicating that nerve growth factor (NGF) protein loops 2 and 4 interact with TrkA receptors raise the possibility that small molecule mimetics corresponding to TrkA-interacting domains that have NGF agonist activity can be developed. We applied our previously developed strategy of dimeric peptidomimetics to address the hypothesis that loop 4 small molecule dimeric mimetics would activate TrkA-related signal transduction and mimic NGF neurotrophic effects in a structure-specific manner. A loop 4 cyclized peptide dimer demonstrated NGF-like neurotrophic activity, whereas peptides with scrambled sequence, added or substituted residues, or cyclized in monomeric form were inactive. Activity was blocked by the TrkA inhibitors K252a and AG879 but not by NGF p75 receptor blocking antibody. Dimeric, but not monomeric, peptides partially blocked NGF activity. This profile was consistent with that of a NGF partial agonist. ERK and AKT phosphorylation was stimulated only by biologically active peptides and was blocked by K252a. The ERK inhibitor U0126 blocked the neurite- but not the survival-promoting activity of both NGF and active peptide. These studies support the proof of concept that small molecule NGF loop 4 mimetics can activate NGF signaling pathways and can mimic death-preventing and neurite-promoting effects of NGF. This finding will guide the rational design of NGF single-domain mimetics and contribute to elucidating NGF signal transduction mechanisms.

Design and solution structure of functional peptide mimetics of nerve growth factor

The C-D loop in nerve growth factor (NGF) is involved in binding to the NGF receptor, TrkA. It is flexible and adopts several different types conformations in different NGF crystal forms. We have previously shown that a small cyclic peptide derived from the C-D loop of NGF binds to the TrkA receptor by mimicking the structure of this loop. To understand structure-function relationships in NGF C-D loop mimetics, we have produced a series of peptides predicted to form different types of beta-turns. The peptides were tested for their ability to promote cell survival in serum-free medium and to induce TrkA tyrosine phosphorylation. NMR structural studies were used to determined the backbone conformation and the spatial orientation of side chains involved in binding to the TrkA receptor. Peptides that form type I or type gammaL-alphaR beta-turns were the most active. The variety of active loop conformations suggests that the mimetics (and NGF) accommodate the binding site on TrkA by an 'induced fit' mechanism. In agreement with this hypothesis, NMR relaxation measurements detected both fast and slow motion in the peptides. We also characterized a retro-inverso peptide derived from the NGF C-D loop. This D-amino acid cyclic peptide did not adopt a conformation homologous to the NGF C-D loop and was inactive. This may be representative of difficulties in producing structural and functional mimetics by retro-inverso schemes.

Glial cells as targets and producers of neurotrophins

Glial cells fulfill important tasks within the neural network of the central and peripheral nervous systems. The synthesis and secretion of various polypeptidic factors (cytokines) and a number of receptors, with which glial cells are equipped, allow them to communicate with their environment. Evidence has accumulated during recent years that neurotrophins play an important role not only for neurons but also for glial cells. This brief update of some morphological, immunocytochemical, and biochemical characteristics of glial cell lineages conveys our present knowledge about glial cells as targets and producers of neurotrophins under normal and pathological conditions. The chapter discusses the presence of neurotrophin receptors on glial cells, glial cells as producers of neurotrophins, signaling pathways downstream Trk and p75NTR, and the significance of neurotrophins and their receptors for glial cells during development, in cell death and survival, and in neurological disorders.

Plasmatocyte spreading peptide (PSP1) and growth blocking peptide (GBP) are multifunctional homologs

Recently, we identified Plasmatocyte spreading peptide (PSP1) from the moth Pseudoplusia includens and reported that it mediates adhesion of hemocytes to foreign surfaces. PSP1 is structurally very similar to three classes of peptides identified earlier from other species of Lepidoptera: growth blocking peptide (GBP) originally identified in Pseudaletia separata, and a series of related peptides from other species designated as paralytic (PP) or cardioactive (CAP) peptides. In this study, we conducted parallel experiments in P. includens and P. separata to determine whether PSP1 and GBP have distinct or multiple biological activities. Both peptides affected the adhesive state of hemocytes from each moth very similarly. PSP1 and GBP exhibited significant growth blocking and paralytic activity in P. separata. Both peptides also had growth blocking activity in P. includens although larvae had to be injected with higher doses of each peptide to reduce weight gain than was observed for P. separata. However, GBP and PSP1 had little paralytic activity in P. includens. Collectively, our results indicate that GBP and PSP1 are multifunctional, but that some interspecific variation also exists in their growth blocking and paralytic activities. We suggest that all PSP1, GBP, PP and CAP family members are homologs that likely have multiple biological activities. Based upon the unique consensus sequence of their N termini, we propose that these molecules be henceforth referred to as members of the "ENF" peptide family.