Brain dopamine and obesity

BACKGROUND

The cerebral mechanisms underlying the behaviours that lead to pathological overeating and obesity are poorly understood. Dopamine, a neurotransmitter that modulates rewarding properties of food, is likely to be involved. To test the hypothesis that obese individuals have abnormalities in brain dopamine activity we measured the availability of dopamine D2 receptors in brain.

METHODS

Brain dopamine D2 receptor availability was measured with positron emission tomography (PET) and [C-11]raclopride (a radioligand for the dopamine D2 receptor). Bmax/Kd (ratio of the distribution volumes in striatum to that in cerebellum minus 1) was used as a measure of dopamine D2 receptor availability. Brain glucose metabolism was also assessed with 2-deoxy-2[18F]fluoro-D-glucose (FDG).

FINDINGS

Striatal dopamine D2 receptor availability was significantly lower in the ten obese individuals (2.47 [SD 0.36]) than in controls (2.99 [0.41]; p < or = 0.0075). In the obese individuals body mass index (BMI) correlated negatively with the measures of D2 receptors (r=0.84; p < or = 0.002); the individuals with the lowest D2 values had the largest BMI. By contrast, neither whole brain nor striatal metabolism differed between obese individuals and controls, indicating that striatal reductions in D2 receptors were not due to a systematic reduction in radiotracer delivery.

INTERPRETATION

The availability of dopamine D2 receptor was decreased in obese individuals in proportion to their BMI. Dopamine modulates motivation and reward circuits and hence dopamine deficiency in obese individuals may perpetuate pathological eating as a means to compensate for decreased activation of these circuits. Strategies aimed at improving dopamine function may be beneficial in the treatment of obese individuals.

A calcineurin-dependent transcriptional pathway controls skeletal muscle fiber type

Slow- and fast-twitch myofibers of adult skeletal muscles express unique sets of muscle-specific genes, and these distinctive programs of gene expression are controlled by variations in motor neuron activity. It is well established that, as a consequence of more frequent neural stimulation, slow fibers maintain higher levels of intracellular free calcium than fast fibers, but the mechanisms by which calcium may function as a messenger linking nerve activity to changes in gene expression in skeletal muscle have been unknown. Here, fiber-type-specific gene expression in skeletal muscles is shown to be controlled by a signaling pathway that involves calcineurin, a cyclosporin-sensitive, calcium-regulated serine/threonine phosphatase. Activation of calcineurin in skeletal myocytes selectively up-regulates slow-fiber-specific gene promoters. Conversely, inhibition of calcineurin activity by administration of cyclosporin A to intact animals promotes slow-to-fast fiber transformation. Transcriptional activation of slow-fiber-specific transcription appears to be mediated by a combinatorial mechanism involving proteins of the NFAT and MEF2 families. These results identify a molecular mechanism by which different patterns of motor nerve activity promote selective changes in gene expression to establish the specialized characteristics of slow and fast myofibers.

Arginine methylation of STAT1 modulates IFNalpha/beta-induced transcription

Transcriptional induction by interferons requires the tyrosine and serine phosphorylation of STAT transcription factors. The N-terminal region is highly homologous among the STAT proteins and surrounds a completely conserved arginine residue. Here we demonstrate arginine methylation of STAT1 by the protein arginine methyl-transferase PRMT1 as a novel requirement for IFNalpha/beta-induced transcription. Methyl-thioadenosine, a methyl-transferase inhibitor that accumulates in many transformed cells, inhibits STAT1-mediated IFN responses. This inhibition arises from impaired STAT1-DNA binding due to an increased association of the STAT inhibitor PIAS1 with phosphorylated STAT1 dimers in the absence of arginine methylation. Thus, arginine methylation of STAT1 is an additional posttranslational modification regulating transcription factor function, and alteration of arginine methylation might be responsible for the lack of interferon responsiveness observed in many malignancies.

Low-field electron emission from undoped nanostructured diamond

Strong and sustained electron emission at low electric fields was observed in undoped, nanostructured diamond. Electron emission of 10 milliamperes per square centimeter was observed at applied fields of 3 to 5 volts per micrometer. These are the lowest fields ever reported for any field-emitting material at technologically useful current densities. The emitter consists of a layer of nanometer-size diamond particulates, which is heat-treated in a hydrogen plasma. These emission characteristics are attributed to the particles' high defect density and the low electron affinity of the diamond surface. Such emitters are technologically useful, because they can be easily and economically fabricated on large substrates.

Circulating microRNAs in breast cancer and healthy subjects

Background

It has been demonstrated that extracellular mRNA can be detected in the circulation. Our hypothesis was that circulating miRNAs are also present and differentially expressed in the serum of breast cancer patients compared to controls.

Findings

We measured miRNA in the serum of samples with and without the addition of miRNA prior to analysis. To test our RNA extraction efficiency, we spiked-in serial dilutions of single-strand C elegens miR-39 (cel-miR-39) and human miR-145 (has-miR-145) into goat serum and a 10 year old human serum specimen. We next analyzed miR-16, -145, and -155 in archived serum specimens from 21 participants, 13 of whom did and 8 of whom did not have breast cancer. We were able to detect the miRNAs from all the serum samples to which the miRNAs had been added. We were also able to detect endogenous miR-16, -145, and -155 in all serum samples. While the expression of all three miRNAs was similar in samples from healthy women compared to those with breast cancer, women with progesterone receptor (PR, p = 0.016) positive tumors had higher miR-155 expression than tumors that were negative for these receptors.

Conclusion

1) RNA species can be detected in archived serum; 2) miR-155 may be differentially expressed in the serum of women with hormone sensitive compared to women with hormone insensitive breast cancer. Screening serum for miRNAs that predict the presence of breast cancer is feasible, and may be useful for breast cancer detection.

Differential display using one-base anchored oligo-dT primers

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PRAK, a novel protein kinase regulated by the p38 MAP kinase

We have identified and cloned a novel serine/ threonine kinase, p38-regulated/activated protein kinase (PRAK). PRAK is a 471 amino acid protein with 20-30% sequence identity to the known MAP kinase-regulated protein kinases RSK1/2/3, MNK1/2 and MAPKAP-K2/3. PRAK was found to be expressed in all human tissues and cell lines examined. In HeLa cells, PRAK was activated in response to cellular stress and proinflammatory cytokines. PRAK activity was regulated by p38alpha and p38beta both in vitro and in vivo and Thr182 was shown to be the regulatory phosphorylation site. Activated PRAK in turn phosphorylated small heat shock protein 27 (HSP27) at the physiologically relevant sites. An in-gel kinase assay demonstrated that PRAK is a major stress-activated kinase that can phosphorylate small heat shock protein, suggesting a potential role for PRAK in mediating stress-induced HSP27 phosphorylation in vivo.

The biphasic poroviscoelastic behavior of articular cartilage: role of the surface zone in governing the compressive behavior

Surface fibrillation of articular cartilage is an early sign of degenerative changes in the development of osteoarthritis. To assess the influence of the surface zone on the viscoelastic properties of cartilage under compressive loading, we prepared osteochondral plugs from skeletally mature steers, with and without the surface zone of articular cartilage, for study in the confined compression creep experiment. The relative contributions of two viscoelastic mechanisms, i.e. a flow-independent mechanism [Hayes and Bodine, J. Biomechanics 11, 407-419 (1978)], and a flow-dependent mechanism [Mow et al. J. biomech. Engng 102, 73-84 (1980)], to the compressive creep response of these two types of specimens were determined using the biphasic poroviscoelastic theory proposed by Mak. [J. Biomechanics 20, 703-714 (1986)]. From the experimental results and the biphasic poroviscoelastic theory, we found that frictional drag associated with interstitial fluid flow and fluid pressurization are the dominant mechanisms of load support in the intact specimens, i.e. the flow-dependent mechanisms alone were sufficient to describe normal articular cartilage compressive creep behavior. For specimens with the surface removed, we found an increased creep rate which was derived from an increased tissue permeability, as well as significant changes in the flow-independent parameters of the viscoelastic solid matrix. permeability, as well as significant changes in the flow-independent parameters of the viscoelastic solid matrix. From these tissue properties and the biphasic poroviscoelastic theory, we determined that the flow-dependent mechanisms of load support, i.e. frictional drag and fluid pressurization, were greatly diminished in cartilage without the articular surface. Calculations based upon these material parameters show that for specimens with the surface zone removed, the cartilage solid matrix became more highly loaded during the early stages of creep. This suggests that an important function of the articular surface is to provide for a low fluid permeability, and thereby serve to restrict fluid exudation and increase interstitial fluid pressurization. Thus, it is likely that with increasing severity of damage to the articular surface, load support in cartilage under compression shifts from the flow-dependent modes of fluid drag and pressurization to increased solid matrix stress. This suggests that it is important to maintain the integrity of the articular surface in preserving normal compressive behavior of the tissue and normal load carriage in the joint.

Viscoelastic shear properties of articular cartilage and the effects of glycosidase treatments

The objectives of this study were to determine the viscoelastic shear properties of articular cartilage and to investigate the effects of the alteration of proteoglycan structure on these shear properties. Glycosidase treatments (chondroitinase ABC and Streptomyces hyaluronidase) were used to alter the proteoglycan structure and content of the tissue. The dynamic viscoelastic shear properties of control and treated tissues were measured and statistically compared. Specifically, cylindrical bovine cartilage specimens were subjected to oscillatory shear deformation of small amplitude (gamma degrees = 0.001 radian) over a physiological range of frequencies (0.01-20 Hz) and at various compressive strains (5, 9, 12, and 16%). The dynamic complex shear modulus was calculated from the measurements. The experimental results show that the solid matrix of normal articular cartilage exhibits intrinsic viscoelastic properties in shear over the range of frequencies tested. These viscoelastic shear properties were found to be dependent on compressive strains. Our data also provide significant insights into the structure-function relationships for articular cartilage. Significant correlations were found between the material properties (the magnitude of dynamic shear modulus, the phase shift angle, and the equilibrium compressive modulus), and the biochemical compositions of the cartilage (collagen, proteoglycan, and water contents). The shear modulus was greatly reduced when the proteoglycans were degraded by either chondroitinase ABC or Streptomyces hyaluronidase. The results suggest that the ability of collagen to resist tension elastically provides the stiffness of the cartilage matrix in shear and its elastic energy storage capability. Proteoglycans enmeshed in the collagen matrix inflate the collagen network and induce a tensile prestress in the collagen fibrils. This interaction of the collagen and proteoglycan within the cartilage matrix provides the complex mechanism that allows the tissue to resist shear deformation.

Homologues of neisserial heme oxygenase in gram-negative bacteria: degradation of heme by the product of the pigA gene of Pseudomonas aeruginosa

The oxidative cleavage of heme to release iron is a mechanism by which some bacterial pathogens can utilize heme as an iron source. The pigA gene of Pseudomonas aeruginosa is shown to encode a heme oxygenase protein, which was identified in the genome sequence by its significant homology (37%) with HemO of Neisseria meningitidis. When the gene encoding the neisserial heme oxygenase, hemO, was replaced with pigA, we demonstrated that pigA could functionally replace hemO and allow for heme utilization by neisseriae. Furthermore, when pigA was disrupted by cassette mutagenesis in P. aeruginosa, heme utilization was defective in iron-poor media supplemented with heme. This defect could be restored both by the addition of exogenous FeSO4, indicating that the mutant did not have a defect in iron metabolism, and by in trans complementation with pigA from a plasmid with an inducible promoter. The PigA protein was purified by ion-exchange chromotography. The UV-visible spectrum of PigA reconstituted with heme showed characteristics previously reported for other bacterial and mammalian heme oxygenases. The heme-PigA complex could be converted to ferric biliverdin in the presence of ascorbate, demonstrating the need for an exogenous reductant. Acidification and high-performance liquid chromatography analysis of the ascorbate reduction products identified a major product of biliverdin IX-beta. This differs from the previously characterized heme oxygenases in which biliverdin IX-alpha is the typical product. We conclude that PigA is a heme oxygenase and may represent a class of these enzymes with novel regiospecificity.

Insulin prevents cardiomyocytes from oxidative stress-induced apoptosis through activation of PI3 kinase/Akt

BACKGROUND

Loss of cardiomyocytes by apoptosis is proposed to cause heart failure. Reactive oxygen species induce apoptosis in many types of cells including cardiomyocytes. Because insulin has been reported to have protective effects, we examined whether insulin prevents cardiomyocytes from oxidative stress-induced apoptotic death.

METHODS AND RESULTS

Cultured cardiomyocytes of neonatal rats were stimulated by hydrogen peroxide (H(2)O(2)). Apoptosis was evaluated by means of the TUNEL method and DNA laddering. Incubation with 100 micromol/L H(2)O(2) for 24 hours increased the number of TUNEL-positive cardiac myocytes (control, approximately 4% versus H(2)O(2), approximately 23%). Pretreatment with 10(-)(6) mol/L insulin significantly decreased the number of H(2)O(2)-induced TUNEL-positive cardiac myocytes (approximately 12%) and DNA fragmentation induced by H(2)O(2). Pretreatment with a specific phosphatidylinositol 3 kinase (PI3K) inhibitor, wortmannin, and overexpression of dominant negative mutant of PI3K abolished the cytoprotective effect of insulin. Insulin strongly activated both PI3K and the putative downstream effector AKT: Moreover, a proapoptotic protein, BAD:, was significantly phosphorylated and inactivated by insulin through PI3K.

CONCLUSIONS

These results suggest that insulin protects cardiomyocytes from oxidative stress-induced apoptosis through the PI3K pathway.

Identification of the low density lipoprotein receptor-binding site in apolipoprotein B100 and the modulation of its binding activity by the carboxyl terminus in familial defective apo-B100

Familial defective apolipoprotein B100 (FDB) is caused by a mutation of apo-B100 (R3500Q) that disrupts the receptor binding of low density lipoproteins (LDL), which leads to hypercholesterolemia and premature atherosclerosis. In this study, mutant forms of human apo-B were expressed in transgenic mice, and the resulting human recombinant LDL were purified and tested for their receptor-binding activity. Site-directed mutagenesis and other evidence indicated that Site B (amino acids 3,359-3,369) binds to the LDL receptor and that arginine-3,500 is not directly involved in receptor binding. The carboxyl-terminal 20% of apo-B100 is necessary for the R3500Q mutation to disrupt receptor binding, since removal of the carboxyl terminus in FDB LDL results in normal receptor-binding activity. Similarly, removal of the carboxyl terminus of apo-B100 on receptor-inactive VLDL dramatically increases apo-B-mediated receptor-binding activity. We propose that the carboxyl terminus normally functions to inhibit the interaction of apo-B100 VLDL with the LDL receptor, but after the conversion of triglyceride-rich VLDL to smaller cholesterol-rich LDL, arginine-3,500 interacts with the carboxyl terminus, permitting normal interaction between LDL and its receptor. Moreover, the loss of arginine at this site destabilizes this interaction, resulting in receptor-binding defective LDL.

The virulence factor AvrXa7 of Xanthomonas oryzae pv. oryzae is a type III secretion pathway-dependent nuclear-localized double-stranded DNA-binding protein

AvrXa7 is a member of the avrBs3 avirulence gene family, which encodes proteins targeted to plant cells by a type III secretion apparatus. AvrXa7, the product of avrXa7, is also a virulence factor in strain PXO86 of Xanthomonas oryzae pv. oryzae. Avirulence and virulence specificities are associated with the central repeat domain, which, in avrXa7, consists of 25.5 direct repeat units. Mutations in three C-terminal nuclear localization signal motifs eliminated avirulence and virulence activities in rice and severely reduced nuclear localization in a yeast assay system. Both pathogenicity functions and nuclear localization were restored on the addition of the sequence for the nuclear localization signal motif from SV40 T-antigen. The loss of avirulence activity because of mutations in the acidic transcriptional activation domain was restored by addition of the activation domain from the herpes simplex viral protein VP16. The activation domain was also required for virulence activity. However, the VP16 domain could not substitute for the endogenous domain in virulence assays. In gel shift assays, AvrXa7 bound double-stranded DNA with a preference for dA/dT rich sequences. The results indicate that products of the avrBs3-related genes are virulence factors targeted to host cell nuclei and have the potential to interact with the host DNA and transcriptional machinery as part of their mode of action. The results also suggest that the host defensive recognition mechanisms are targeted to the virulence factor site of action.

Rat pregnane X receptor: molecular cloning, tissue distribution, and xenobiotic regulation

An orphan nuclear receptor, termed the pregnane X receptor (PXR), has recently been cloned from mouse and human and defines a novel steroid signaling pathway (Cell 92, 73-82, 1998; Proc. Natl. Acad. Sci. USA 95, 12208-122313, 1998). Transient cotransfection experiments demonstrate that the PXR responds to structurally dissimilar compounds and confers the induction of cytochrome P4503A (CYP3A), a subfamily of enzymes that involve the metabolism of two-thirds of drugs and other xenobiotics. In this report, we describe the molecular cloning, tissue distribution, and xenobiotic regulation of a rat PXR designated rPXR-1. rPXR-1 exhibits a 95% sequence identity with the mouse PXR, but only 79% identity with the human PXR, providing the molecular basis that rats and mice have a similar CYP3A induction profile but differ from humans. rPXR-1 gene was expressed abundantly in liver, intestine, and, to a lesser extent, kidney, lung, and stomach. The tissue distribution and the relative abundance of rPXR-1 mRNA among these tissues resemble those of CYP3A, suggesting that PXR is important not only for induction but also for constitutive expression of these enzymes. Xenobiotics known to induce liver microsomal enzymes showed differential effects on the rPXR-1 expression as determined by Northern blot analysis. Dexamethasone, for example, increased the accumulation of rPXR-1 mRNA, whereas troleandomycin slightly suppressed it. Compounds that increase PXR expression (inducers) and compounds that interact with PXR (ligands) likely have synergistic effects on CYP3A induction, which provides a novel molecular explanation for drug-drug interactions.

Trans-resveratrol alters mammary promoter hypermethylation in women at increased risk for breast cancer

Trans-resveratrol, present in high concentration in the skin of red grapes and red wine, has a dose-dependent antiproliferative effect in vitro, prevents the formation of mammary tumors, and has been touted as a chemopreventive agent. Based upon in vitro studies demonstrating that trans-resveratrol downregulates the expression of 1) DNA methyltransferases and 2) the cancer promoting prostaglandin (PG)E(2), we determined if trans-resveratrol had a dose-related effect on DNA methylation and prostaglandin expression in humans. Thirty-nine adult women at increased breast cancer risk were randomized in double-blind fashion to placebo, 5 or 50 mg trans-resveratrol twice daily for 12 wk. Methylation assessment of 4 cancer-related genes (p16, RASSF-1α, APC, CCND2) was performed on mammary ductoscopy specimens. The predominant resveratrol species in serum was the glucuronide metabolite. Total trans-resveratrol and glucuronide metabolite serum levels increased after consuming both trans-resveratrol doses (P < .001 for both). RASSF-1α methylation decreased with increasing levels of serum trans-resveratrol (P = .047). The change in RASSF-1α methylation was directly related to the change in PGE(2) (P = .045). This work provides novel insights into the effects of trans-resveratrol on the breast of women at increased breast cancer risk, including a decrease in methylation of the tumor suppressor gene RASSF-1α. Because of the limited sample size, our findings should be validated in a larger study.

Degradation of heme in gram-negative bacteria: the product of the hemO gene of Neisseriae is a heme oxygenase

A full-length heme oxygenase gene from the gram-negative pathogen Neisseria meningitidis was cloned and expressed in Escherichia coli. Expression of the enzyme yielded soluble catalytically active protein and caused accumulation of biliverdin within the E. coli cells. The purified HemO forms a 1:1 complex with heme and has a heme protein spectrum similar to that previously reported for the purified heme oxygenase (HmuO) from the gram-positive pathogen Corynebacterium diphtheriae and for eukaryotic heme oxygenases. The overall sequence identity between HemO and these heme oxygenases is, however, low. In the presence of ascorbate or the human NADPH cytochrome P450 reductase system, the heme-HemO complex is converted to ferric-biliverdin IXalpha and carbon monoxide as the final products. Homologs of the hemO gene were identified and characterized in six commensal Neisseria isolates, Neisseria lactamica, Neisseria subflava, Neisseria flava, Neisseria polysacchareae, Neisseria kochii, and Neisseria cinerea. All HemO orthologs shared between 95 and 98% identity in amino acid sequences with functionally important residues being completely conserved. This is the first heme oxygenase identified in a gram-negative pathogen. The identification of HemO as a heme oxygenase provides further evidence that oxidative cleavage of the heme is the mechanism by which some bacteria acquire iron for further use.

Circulating FGF-21 levels in normal subjects and in newly diagnose patients with Type 2 diabetes mellitus

Fibroplast growth factor (FGF-21) is a recently discovered metabolic regulator. Its pathophysiologic role in humans remains unknown. In this study, we have investigated whether or not plasma FGF-21 level was different in patients with type 2 diabetes mellitus (T2DM) and non-diabetic controls. We also assessed associations between plasma FGF-21 body composition and several metabolic parameters. Fasting FGF-21 levels were significantly increased in patients with T2DM compared with controls (1.82+/-0.65 VS. 1.53+/-0.60 microg/L, P<0.05). In T2DM patients, fasting plasma FGF-21 correlate negatively with fasting blood glucose ( R= -0.31, P<0.05). Multiple regression analysis showed that FBG, plasma insulin and HOMA (IS) were independent influencing plasma FGF-21 levels. The present work suggests a potential role for FGF-21 in the pathogenesis of insulin resistance and T2DM.

The alpha 6 beta 1 and alpha 6 beta 4 integrins in human prostate cancer progression

Prostatic secretions are formed by glands composed of basal and luminal cells and surrounded by a basal lamina. The normal basal cells express several integrins (extracellular matrix receptors) including alpha 2, 3, 4, 5, 6, v, beta 1 and beta 4. These integrin units are polarized at the base of the cells adjacent to the basal lamina. The integrin alpha 6 beta 4 is associated with hemidesmosomal-like structures. The natural history of prostate cancer involves the presence of prostatic intraepithelial neoplasia (PIN) lesions (considered precursor lesions), carcinoma in situ and invasive carcinoma. Hemidesmosomal proteins and the alpha 3 beta 1 and alpha 6 beta 1 integrins (laminin receptors) are retained in the early PIN lesions. Expression of the integrins alpha 2, alpha 4, alpha 5, alpha v and beta 4 is lost in carcinoma. The alpha 3 beta 1 and alpha 6 beta 1 integrins remain associated with invasive carcinoma, the latter being predominant. Integrin expression in carcinoma is diffuse in the plasma membrane and not restricted to the basal aspects of the cell. The alpha 6 beta 1 integrin is fully functional as judged by an ability to adhere to laminin and contains the wild type alpha 6A cytoplasmic signaling domain. The alpha 6 beta 1 integrin is a leading candidate for conferring the invasive phenotype in prostatic carcinoma. Tumor cells with high expression of alpha 6 integrin are more invasive when tested in a SCID mouse model system. Following intraperitoneal injection, the human tumor cells invade the mouse diaphragm and move through the muscle on the surface of the laminin coated muscle cells. Our current working hypothesis is that the production of alpha 6 beta 1 and laminin in human tumor cells contributes to the invasive phenotype. Invasion could occur on the surfaces of laminin coated structures such as the nerves, blood vessels or muscle and account for the known patterns of human prostate tumor progression. Blockage of the expression or function of alpha 6 beta 1 or laminin or preventing the loss of beta 4 would be essential steps in confining the carcinoma to the prostate gland where conventional treatment has already proven effective.

Compressive mechanical properties of the human anulus fibrosus and their relationship to biochemical composition

To enhance understanding of the biomechanical role of the intervertebral disc, the compressive properties and biochemical composition of nondegenerate samples of anulus fibrosus were determined as a function of radial position, region, and level. Because of the large swelling propensity of this tissue, a method was developed to test excised specimens while maintaining their in situ geometry and hydration. Using an analysis based on linear biphasic theory, the compressive modulus, hydraulic permeability, and isometric swelling pressure of the anulus fibrosus were determined and correlated with the tissue composition. The findings indicate that the anulus fibrosus is inhomogeneous, with regional and radial variations in both material properties and biochemical composition. The results of this study suggest that both structural and compositional factors may determine the mechanical behavior.

Rho family small G proteins play critical roles in mechanical stress-induced hypertrophic responses in cardiac myocytes

-Mechanical stress induces a variety of hypertrophic responses, such as activation of protein kinases, reprogramming of gene expression, and an increase in protein synthesis. In the present study, to elucidate how mechanical stress induces such events, we examined the role of Rho family small GTP-binding proteins (G proteins) in mechanical stress-induced cardiac hypertrophy. Treatment of neonatal rat cardiomyocytes with the C3 exoenzyme, which abrogates Rho functions, suppressed stretch-induced activation of extracellular signal-regulated protein kinases (ERKs). Overexpression of the Rho GDP dissociation inhibitor (Rho-GDI), dominant-negative mutants of RhoA (DNRhoA), or DNRac1 significantly inhibited stretch-induced activation of transfected ERK2. Overexpression of constitutively active mutants of RhoA slightly activated ERK2 in cardiac myocytes. Overexpression of C-terminal Src kinase, which inhibits functions of the Src family of tyrosine kinases, or overexpression of DNRas had no effect on stretch-induced activation of transfected ERK2. The promoter activity of skeletal alpha-actin and c-fos genes was increased by stretch, and these increases were completely inhibited by either cotransfection of Rho-GDI or pretreatment with C3 exoenzyme. Mechanical stretch increased phenylalanine incorporation into cardiac myocytes by approximately 1.5-fold compared with control, and this increase was also significantly suppressed by pretreatment with C3 exoenzyme. Overexpression of Rho-GDI or DNRhoA did not affect angiotensin II-induced activation of ERK. ERKs were activated by culture media conditioned by stretch of cardiomyocytes without any treatment, but not of cardiomyocytes with pretreatment by C3 exoenzyme. These results suggest that the Rho family of small G proteins plays critical roles in mechanical stress-induced hypertrophic responses.

Identification of two novel hrp-associated genes in the hrp gene cluster of Xanthomonas oryzae pv. oryzae

We have cloned a hrp gene cluster from Xanthomonas oryzae pv. oryzae. Bacteria with mutations in the hrp region have reduced growth in rice leaves and lose the ability to elicit a hypersensitive response (HR) on the appropriate resistant cultivars of rice and the nonhost plant tomato. A 12,165-bp portion of nucleotide sequence from the presumed left end and extending through the hrpB operon was determined. The region was most similar to hrp genes from Xanthomonas campestris pv. vesicatoria and Ralstonia solanacearum. Two new hrp-associated loci, named hpa1 and hpa2, were located beyond the hrpA operon. The hpa1 gene encoded a 13-kDa glycine-rich protein with a composition similar to those of harpins and PopA. The product of hpa2 was similar to lysozyme-like proteins. Perfect PIP boxes were present in the hrpB and hpa1 operons, while a variant PIP box was located upstream of hpa2. A strain with a deletion encompassing hpa1 and hpa2 had reduced pathogenicity and elicited a weak HR on nonhost and resistant host plants. Experiments using single mutations in hpa1 and hpa2 indicated that the loss of hpa1 was the principal cause of the reduced pathogenicity of the deletion strain. A 1,519-bp insertion element was located immediately downstream of hpa2. Hybridization with hpa2 indicated that the gene was present in all of the strains of Xanthomonas examined. Hybridization experiments with hpa1 and IS1114 indicated that these sequences were detectable in all strains of X. oryzae pv. oryzae and some other Xanthomonas species.