Tetratricopeptide repeat (TPR) motifs of p67(phox) participate in interaction with the small GTPase Rac and activation of the phagocyte NADPH oxidase

The small GTPase Rac functions as a molecular switch in several important cellular events including cytoskeletal reorganization and activation of the phagocyte NADPH oxidase, the latter of which leads to production of superoxide, a precursor of microbicidal oxidants. During formation of the active oxidase complex at the membrane, the GTP-bound Rac appears to interact with the N-terminal region of p67(phox), another indispensable activator that translocates from the cytosol upon phagocyte stimulation. Here we show that the p67(phox) N terminus lacks the CRIB motif, a well known Rac target, but contains four tetratricopeptide repeat (TPR) motifs with highly alpha-helical structure. Disruption of any of the N-terminal three TPRs, but the last one, results in defective interaction with Rac, while all the four are required for the NADPH oxidase activation. We also find that Arg-102 in the third repeat is likely involved in binding to Rac via an ionic interaction, and that replacement of this residue with Glu completely abrogates the capability of activating the oxidase both in vivo and in vitro. Thus the TPR motifs of p67(phox) are packed to function as a Rac target, thereby playing a crucial role in the active oxidase complex formation.

A new water-soluble camptothecin derivative, DX-8951f, exhibits potent antitumor activity against human tumors in vitro and in vivo

CPT-11, a semisynthetic derivative of camptothecin, exhibited strong antitumor activity against lymphoma, lung cancer, colorectal cancer, gastric cancer, ovarian cancer, and cervical cancer. CPT-11 is a pro-drug that is converted to an active metabolite, SN-38, in vivo by enzymes such as carboxylesterase. We synthesized a water-soluble and non-pro-drug analog of camptothecin, DX-8951f. It showed both high in vitro potency against a series of 32 malignant cell lines and significant topoisomerase I inhibition. The anti-proliferative activity of DX-8951f, as indicated by the mean GI50 value, was about 6 and 28 times greater than that of SN-38 or SK&F 10486-A (Topotecan), respectively. These three derivatives of camptothecin showed similar patterns of differential response among 32 cell lines, that is, their spectra of in vitro cytotoxicity were almost the same. The antitumor activity of three doses of DX-8951f administered i.v. at 4-day intervals against human gastric adenocarcinoma SC-6 xenografts was greater than that of CPT-11 or SK&F 10486-A. Moreover, it overcame P-glycoprotein-mediated multi-drug resistance. These data suggest that DX-8951f has a high antitumor activity and is a potential therapeutic agent.

Structure of the N-terminal SH3 domain of GRB2 complexed with a peptide from the guanine nucleotide releasing factor Sos

Src-homology 3 (SH3) domains mediate signal transduction by binding to proline-rich motifs in target proteins. We have determined the high-resolution NMR structure of the complex between the amino-terminal SH3 domain of GRB2 and a ten amino acid peptide derived from the guanine nucleotide releasing factor Sos. The NMR data show that the peptide adopts the conformation of a left-handed polyproline type II helix and interacts with three major sites on the SH3 domain. The orientation of the bound peptide is opposite to that of proline-rich peptides bound to the SH3 domains of Abl, Fyn and p85.

An improved double-tuned and isotope-filtered pulse scheme based on a pulsed field gradient and a wide-band inversion shaped pulse

We have developed an improved isotope-filtered pulse scheme in combination with a double-tuned filter, a hyperbolic secant inversion pulse, and a z-filter with a pulsed field gradient. These filtering pulse schemes have been incorporated into several one-, two-, and three-dimensional experiments, which were applied to the (13)C/(15)N uniformly labeled N-terminal SH3 domain of Grb2 complexed with the unlabeled Sos-derived peptide. The proton resonances of the Sos-derived peptide were unambiguously assigned using isotope-filtered DQF-COSY, TOCSY and NOESY spectra. Furthermore, in the isotope-filtered, isotope-edited 3D NOESY spectrum, intermolecular NOEs between the labeled protein and the unlabeled peptide could be identified. Through these applications, we demonstrate the high filtering efficiency of the presented pulse scheme.

Synthesis and structure-activity relationships of novel 2',2'-difluoro analogues of docetaxel

To investigate the role of the 2'-hydroxy group at the C-13 side chain of docetaxel in the antitumor activity, we prepared several 2',2'-difluoro derivatives of docetaxel and evaluated their cytotoxicity against mouse leukemia and human tumor cell lines and their microtubule disassembly-inhibitory activity. These analogues were prepared by esterification of protected 10-deacetylbaccatin III (21) with appropriate alpha, alpha-difluorinated carboxylic acids (Charts 1 and 2). Among these 2',2'-difluorodocetaxel derivatives, 2',2'-difluorodocetaxel (23b) was approximately 3-10 times as active as 2'-fluorodocetaxel (29a) in terms of cytotoxicity. In addition, the 3'-(2-furyl) (23h) and 3'-(2-pyrrolyl) (23p) analogues showed activity comparable or superior to that of docetaxel (2).

Difluorinated Danishefsky's diene: a versatile C(4) building block for the fluorinated six-membered rings

[reaction: see text] A Mg(0)/Me(3)SiCl system was found to be effective for the preparation of difluoro Danishefsky's dienes 2, which involves selective C-F bond cleavage of trifluoromethyl ketones 3. Subsequent hetero Diels-Alder reactions of 2 with aldehydes and imines gave a variety of fluorinated six-membered heterocycles.

Solution structure and ligand-binding site of the carboxy-terminal SH3 domain of GRB2

BACKGROUND

Growth factor receptor-bound protein 2 (GRB2) is an adaptor protein with three Src homology (SH) domains in the order SH3-SH2-SH3. Both SH3 domains of GRB2 are necessary for interaction with the protein Son of sevenless (Sos), which acts as a Ras activator. Thus, GRB2 mediates signal transduction from growth factor receptors to Ras and is thought to be a key molecule in signal transduction.

RESULTS

The three-dimensional structure of the carboxy-terminal SH3 domain of GRB2 (GRB2 C-SH3) was determined by NMR spectroscopy. The SH3 structure consists of six beta-strands arranged in two beta-sheets that are packed together perpendicularly with two additional beta-strands forming the third beta-sheet. GRB2 C-SH3 is very similar to SH3 domains from other proteins. The binding site of the ligand peptide (VPP-PVPPRRR) derived from the Sos protein was mapped on the GRB2 C-SH3 domain indirectly using 1H and 15N chemical shift changes, and directly using several intermolecular nuclear Overhauser effects.

CONCLUSIONS

Despite the structural similarity among the known SH3 domains, the sequence alignment and the secondary structure assignments differ. We therefore propose a standard description of the SH3 structures to facilitate comparison of individual SH3 domains, based on their three-dimensional structures. The binding site of the ligand peptide on GRB2 C-SH3 is in good agreement with those found in other SH3 domains.

Solution structure of the SH2 domain of Grb2 complexed with the Shc-derived phosphotyrosine-containing peptide

The solution structure of growth factor receptor-bound protein 2 (Grb2) SH2 complexed with a Shc-derived phosphotyrosine (pTyr)-containing peptide was determined by nuclear magnetic resonance (NMR) spectroscopy. The pTyr binding site of Grb2 SH2 was similar to those of other SH2 domains. In contrast, the amino acid residues C-terminal to pTyr did not form an extended structure because of steric hindrance caused by a bulky side-chain of Trp121 (EF1). As a result, the peptide formed a turn-structure on the surface of Grb2 SH2. The asparagine residue at the pTyr+2 position of the Shc-peptide interacted with the main-chain carbonyl groups of Lys109 and Leu120. The present solution structure was similar to the crystal structure reported for Grb2 SH2 complexed with a BCR-Abl-derived phosphotyrosine-containing peptide. Finally, the structure of Grb2 SH2 domain was compared with those of the complexes of Src and phospholipase C-gamma1 with their cognate peptides, showing that the specific conformation of the peptide was required for binding to the SH2 domains.

Possible reduced penetrance of expansion of 44 to 47 CAG/CAA repeats in the TATA-binding protein gene in spinocerebellar ataxia type 17

BACKGROUND

Spinocerebellar ataxia type 17 (SCA17) is an autosomal dominant cerebellar ataxia caused by expansion of CAG/CAA trinucleotide repeats in the TATA-binding protein (TBP) gene. Because the number of triplets in patients with SCA17 in previous studies ranged from 43 to 63, the normal number of trinucleotide units has been considered to be 42 or less. However, some healthy subjects in SCA17 pedigrees carry alleles with the same number of expanded repeats as patients with SCA17.

OBJECTIVE

To investigate the minimum number of CAG/CAA repeats in the TBP gene that causes SCA17.

DESIGN

We amplified the region of the TBP gene containing the CAG/CAA repeat by means of polymerase chain reaction and performed fragment and sequence analyses.

PATIENTS

The subjects included 734 patients with SCA (480 patients with sporadic SCA and 254 patients with familial SCA) without CAG repeat expansions at the SCA1, SCA2, Machado-Joseph disease, SCA6, SCA7, or dentatorubral-pallidolluysian atrophy loci, with 162 healthy subjects, 216 patients with Parkinson disease, and 195 with Alzheimer disease as control subjects.

RESULTS

Eight patients with SCA possessed an allele with more than 43 CAG/CAA repeats. Among the non-SCA groups, alleles with 43 to 45 repeats were seen in 3 healthy subjects and 2 with Parkinson disease. In 1 SCA pedigree, a patient with possible SCA17 and her healthy sister had alleles with 45 repeats. A 34-year-old man carrying alleles with 47 and 44 repeats (47/44) had developed progressive cerebellar ataxia and myoclonus at 25 years of age, and he exhibited dementia and pyramidal signs. He was the only affected person in his pedigree, although his father and mother carried alleles with mildly expanded repeats (44/36 and 47/36, respectively). In another pedigree, 1 patient carried a 43-repeat allele, whereas another patient had 2 normal alleles, indicating that the 43-repeat allele may not be pathologic in this family.

CONCLUSIONS

We estimate that 44 CAG/CAA repeats is the minimum number required to cause SCA17. However, the existence of unaffected subjects with mildly expanded triplets suggests that the TBP gene mutation may not penetrate fully. Homozygosity of alleles with mildly expanded triplet repeats in the TBP gene might contribute to the pathologic phenotype.

Influence of tooth-loss and concomitant masticatory alterations on cholinergic neurons in rats: immunohistochemical and biochemical studies

The influence of tooth loss on the viability of cholinergic neurons was examined in rats. At 25th postnatal week, rats were divided into the three groups; a control group fed a solid diet, a soft diet group fed a powder diet and a molar crown-less group in which all molar crowns were removed and the powder diet was given. At 15 and 35 weeks post-treatment, the number of choline acetyltransferase (ChAT)-positive neurons in the nucleus of the diagonal band/medial septal nucleus (NDB/MS) was significantly smaller in the molar crown-less group than in the control group (P < 0.01). This was not the case in the pedunculopontine tegmental nucleus or (PPT) or in the trigeminal motor nucleus. Biochemical assay showed no statistically significant differences in choline concentrations in the hippocampus between the control and the molar crown-less group both at 15 and at 35 weeks post-treatment. Nevertheless, acetylcholine (ACh) concentration in the hippocampus of the molar crown-less group was significantly lower than that of the control group at 15 weeks post-treatment (P < 0.05). Taken together, a decrease of oral sensory information may have caused a reduction in the number of ChAT-positive neurons selectively in NDB/MS, which in turn caused a decline of ACh concentrations in the hippocampus.

Solution structure of human insulin-like growth factor II; recognition sites for receptors and binding proteins

The three-dimensional structure of human insulin-like growth factor II was determined at high resolution in aqueous solution by NMR and simulated annealing based calculations. The structure is quite similar to those of insulin and insulin-like growth factor I, which consists of an alpha-helix followed by a turn and a strand in the B-region and two antiparallel alpha-helices in the A-region. However, the regions of Ala1-Glu6, Pro31-Arg40 and Thr62-Glu67 are not well-defined for lack of distance constraints, possibly due to motional flexibility. Based on the resultant structure and the results of structure-activity relationships, we propose the interaction sites of insulin-like growth factor II with the type 2 insulin-like growth factor receptor and the insulin-like growth factor binding proteins. These sites partially overlap with each other at the opposite side of the putative binding surface to the insulin receptor and the type 1 insulin-like growth factor receptor. We also discuss the interaction modes of insulin-like growth factor II with the insulin receptor and the type 1 insulin-like growth factor receptor.

Synthesis and antitumor activity of ring A- and F-modified hexacyclic camptothecin analogues

Nineteen ring A- and F-modified hexacyclic analogues of camptothecin were synthesized by Friedländer condensation of appropriately substituted bicyclic amino ketones with tricyclic ketone and were evaluated for cytotoxicity and topoisomerase I inhibitory activity. Seventeen of the compounds showed cytotoxic effects comparable or superior to those of 7-ethyl-10-hydroxycamptothecin (SN-38) against mouse leukemia P388 and human tumor cell lines HOC-21 and QG-56. Introduction of a compact and inductively electron-withdrawing substituent such as a hydroxy, methoxy, chloro, or fluoro group into position 5 of ring A of the hexacyclic compound remarkably increased the antitumor activity. The potency of topoisomerase I inhibition of these compounds showed good correlation with their cytotoxicity. Among them, the 4-methyl-5-fluoro hexacyclic compound was the most potent of all and was 10 times as active as SN-38 in in vitro antitumor activity.

Lack of an association between cystatin C gene polymorphisms in Japanese patients with Alzheimer's disease

Associations between polymorphisms of the cystatin C gene (CST3) at 5' flanking region and exon 1 in Caucasian patients with late onset AD and exon 1 in a US study of late onset AD have been reported. Clinically diagnosed Japanese patients with AD and Japanese normal control subjects were assessed for the presence of polymorphisms of CST3. The authors could not confirm the previously reported association between CST3 polymorphisms and AD in Japan. Age had no effect on the CST3 genotype.

Kinetic analysis on the substrate specificity of 3-isopropylmalate dehydrogenase

Substrate specificity of 3-isopropylmalate dehydrogenase is analyzed using a series of synthetic (2R,3S)-3-alkylmalates. Each analog with hydrogen, methyl, ethyl, isopropyl, isobutyl, tert-butyl, and isoamyl group on C-3 functions as a substrate, implying a broad substrate specificity of the enzyme toward alkylmalates. The incremental binding energy of the isopropyl group of 3-isopropylmalate to the enzyme is estimated to be 3.55 kcal/mol, the rather small value supporting the broad specificity. Although the enzyme shows a broad specificity toward the alkylmalates, it does not show activity with isocitrate which has a negatively charged carboxymethyl group instead of the alkyl groups.

Dinucleotide repeat polymorphisms in the neprilysin gene are not associated with sporadic Alzheimer's disease

In the pathological process of Alzheimer's disease (AD), deposition of amyloid beta-peptide (A beta) in the brain parenchyma plays an important role. Neprilysin (NEP), a neutral endopeptidase, degrades A beta, and it is postulated that decreased NEP activity may contribute to the development of AD by promoting the accumulation of A beta. The human NEP gene possesses four dinucleotide repeat polymorphisms, and it is possible that these polymorphisms regulate the NEP expression levels and influence the pathological cascade of AD. Therefore, we investigated the association of these polymorphisms with AD. We performed genotyping of each polymorphism in 201 Japanese sporadic AD patients and 208 Japanese controls. There were no significant differences between the AD and control groups in allele frequencies of each polymorphism. We conclude that these polymorphisms in the NEP gene do not contribute to genetic risk factors for sporadic AD.

Antitumor agents. V. Synthesis and antileukemic activity of E-ring-modified (RS)-camptothecin analogues

Several E-ring-modified analogues of (RS)-camptothecin were synthesized by total synthesis via Friedländer condensation and evaluated for cytotoxicity and antitumor activity against P388 mouse leukemia cells. Among them, (RS)-20-deoxyamino-7-ethyl-10-methoxycamptothecin (25c) was found to be more active than (RS)-camptothecin (1) in the in vivo assay.

Conformation of an Shc-derived phosphotyrosine-containing peptide complexed with the Grb2 SH2 domain

We have determined the structure of an Shc-derived phosphotyrosine-containing peptide complexed with Grb2 SH2 based on intra- and intermolecular NOE correlations observed by a series of isotope-filtered NMR experiments using a PFG z-filter. In contrast to an extended conformation of phosphotyrosine-containing peptides bound to Src, Syp and PLC gamma SH2s, the Shc-derived peptide formed a turn at the +1 and +2 positions next to the phosphotyrosine residue. Trp121, located at the EF1 site of Grb2 SH2, blocked the peptide binding in an extended conformation. The present study confirms that each phosphotyrosine-containing peptide binds to the cognate SH2 with a specific conformation, which gives the structural basis for the binding specificity between SH2s and target proteins.

A homozygous mutation of VWA3B causes cerebellar ataxia with intellectual disability

BACKGROUND

Hereditary cerebellar ataxia constitutes a heterogeneous group of neurodegenerative disorders, occasionally accompanied by other neurological features. Genetic defects remain to be elucidated in approximately 40% of hereditary cerebellar ataxia cases in Japan. We attempted to identify the gene responsible for autosomal recessive cerebellar ataxia with intellectual disability.

METHODS

The present study involved three patients in a consanguineous Japanese family. Neurological examination and gene analyses were performed in all family members. We performed genome-wide linkage analysis including single nucleotide polymorphism arrays, copy-number variation analysis and whole exome sequencing. To clarify the functional alteration resulting from the identified mutation, we performed cell viability assay of cultured cells expressing mutant protein.

RESULTS

One homozygous region shared among the three patients on chromosomes 2p16.1-2q12.3 was identified. Using whole exome sequencing, six homozygous variants in genes in the region were detected. Only one variant, VWA3B c.A1865C, results in a change of a highly conserved amino acid (p.K622T) and was not present in control samples. VWA3B encodes a von Willebrand Factor A Domain-Containing Protein 3B with ubiquitous expression, including the cerebellum. The viability of cultured cells expressing the specific K622T mutation was proved to decrease through the activation of apoptotic pathway.

CONCLUSIONS

Mutated VWA3B was found to be likely associated with cerebellar degeneration with intellectual disability. Although a rare cause of cerebellar degeneration, these findings indicate a critical role for VWA3B in the apoptosis pathway in neuronal tissues.

Orally active docetaxel analogue: synthesis of 10-deoxy-10-C-morpholinoethyl docetaxel analogues

To improve cytotoxicity of 10-deoxy-10-C-morpholinoethyl docetaxel analogues against various tumor cell lines including resistant cells expressing P-glycoprotein (P-gp), we modified the 7-hydroxyl group to hydrophobic groups (methoxy, deoxy, 6,7-olefin, alpha-F, 7-beta-8-beta-methano, fluoromethoxy). Among these analogues, the 7-methoxy analogue showed the strongest cytotoxicity. This analogue showed potent activity against B16 melanoma BL6 in vivo by oral administration.

Synthesis and antileukemic activity of (+-)-20-deoxyaminocamptothecin analogues

The camptothecin analogues (+-)-7-ethyl-10-methoxy-20-deoxyaminocamptothecin (2) and (+-)-7-ethyl-10-hydroxy-20-deoxyaminocamptothecin.HCl (3) were synthesized from indolizine compound 4 via Friedländer condensation to construct a pentacyclic ring system, and were tested in a P388 mouse antileukemia assay. Compounds 2 and 3 were more active and less toxic than (+)-camptothecin (1), and therefore had higher therapeutic ratios.

Correlation between blood pressure and plasma insulin in acromegaly

OBJECTIVES

The aims of this study were to determine the possible role of hyperinsulinaemia in the increase in blood pressure in acromegalic patients.

DESIGN

After an overnight fast, blood samples were obtained at 0. 30, 60, 120 and 180 min after 75 g glucose ingestion, and plasma growth hormone (GH) and plasma insulin (IRI) were measured by radioimmunoassay. The blood pressure was measured at 10.00 hours for 3 days in a supine position.

SUBJECTS

Nineteen (nine women and 10 men) untreated acromegalic patients, aged 25-69 years.

RESULTS

There were no significant correlations between mean blood pressure (MBP; diastolic+one-third pulse pressure) and basal GH, sum of plasma GH at 0, 30, 60, 120 and 180 min or basal IRI. However, significant correlation was observed between MBP and IRI at 120 min (r = 0.57, P < 0.02) or sum of plasma IRI at 0, 30, 60, 120 and 180 min) (r = 0.58, P < 0.02).

CONCLUSIONS

We conclude that hyperinsulinaemia may be involved in an increase in blood pressure in active acromegalics.