Adiponectin stimulates glucose utilization and fatty-acid oxidation by activating AMP-activated protein kinase

Adiponectin (Ad) is a hormone secreted by adipocytes that regulates energy homeostasis and glucose and lipid metabolism. However, the signaling pathways that mediate the metabolic effects of Ad remain poorly identified. Here we show that phosphorylation and activation of the 5'-AMP-activated protein kinase (AMPK) are stimulated with globular and full-length Ad in skeletal muscle and only with full-length Ad in the liver. In parallel with its activation of AMPK, Ad stimulates phosphorylation of acetyl coenzyme A carboxylase (ACC), fatty-acid oxidation, glucose uptake and lactate production in myocytes, phosphorylation of ACC and reduction of molecules involved in gluconeogenesis in the liver, and reduction of glucose levels in vivo. Blocking AMPK activation by dominant-negative mutant inhibits each of these effects, indicating that stimulation of glucose utilization and fatty-acid oxidation by Ad occurs through activation of AMPK. Our data may provide a novel paradigm that an adipocyte-derived antidiabetic hormone, Ad, activates AMPK, thereby directly regulating glucose metabolism and insulin sensitivity in vitro and in vivo.

Crystal structure of human serum albumin at 2.5 A resolution

A new triclinic crystal form of human serum albumin (HSA), derived either from pool plasma (pHSA) or from a Pichia pastoris expression system (rHSA), was obtained from polyethylene glycol 4000 solution. Three-dimensional structures of pHSA and rHSA were determined at 2.5 A resolution from the new triclinic crystal form by molecular replacement, using atomic coordinates derived from a multiple isomorphous replacement work with a known tetragonal crystal form. The structures of pHSA and rHSA are virtually identical, with an r.m. s. deviation of 0.24 A for all Calpha atoms. The two HSA molecules involved in the asymmetric unit are related by a strict local twofold symmetry such that the Calpha atoms of the two molecules can be superimposed with an r.m.s. deviation of 0.28 A in pHSA. Cys34 is the only cysteine with a free sulfhydryl group which does not participate in a disulfide linkage with any external ligand. Domains II and III both have a pocket formed mostly of hydrophobic and positively charged residues and in which a very wide range of compounds may be accommodated. Three tentative binding sites for long-chain fatty acids, each with different surroundings, are located at the surface of each domain.

Primary structure of Electrophorus electricus sodium channel deduced from cDNA sequence

Cloning and sequence analysis of cDNA for the Electrophorus electricus electroplax sodium channel indicate that this protein, consisting of 1,820 amino acid residues, exhibits four repeated homology units, which are presumably oriented in a pseudosymmetric fashion across the membrane. Each homology unit contains a unique segment with clustered positively charged residues, which may be involved in the gating structure, possibly in conjunction with negatively charged residues clustered elsewhere.

Structural parts involved in activation and inactivation of the sodium channel

Structure-function relationships of the sodium channel expressed in Xenopus oocytes have been investigated by the combined use of site-directed mutagenesis and patch-clamp recording. This study provides evidence that the positive charges in segment S4 are involved in the voltage-sensing mechanism for activation of the channel and that the region between repeats III and IV is important for its inactivation.

A ras-related gene with transformation suppressor activity

A 1.8 kb cDNA clone, Krev-1, with revertant-inducing activity on Kirsten sarcoma virus-transformed NIH/3T3 cells, has been isolated from a human fibroblast cDNA expression library. In Krev-1 transfectants, there is a correlation between the levels of specific mRNA and the degrees of suppression of the transformed phenotype. The cDNA encodes a protein of 21,000 daltons that unexpectedly shares around 50% amino acid identities with ras proteins. The Krev-1 homologs are found in mouse, rat, and chicken DNA, and their transcripts are ubiquitously expressed in many rat organs. Thus, the Krev-1 gene seems to play an important role(s) in a wide variety of tissues, and may be involved in the negative growth regulation of certain cell types.

In vitro guidance of retinal ganglion cell axons by RAGS, a 25 kDa tectal protein related to ligands for Eph receptor tyrosine kinases

The results of previous in vitro experiments indicate that a glycosylphosphatidylinositol (GPI)-anchored protein may play an important role in the guidance of temporal retinal axons during the formation of the topographically ordered retinotectal projection. We have purified and cloned a GPI-anchored, 25 kDa glycoprotein that is a good candidate for a molecule involved in this process. During the time of innervation by retinal ganglion cells, this protein is gradedly expressed in the posterior part of the developing tectum. In two different in vitro assay systems, the recombinant protein induces growth cone collapse and repulsion of retinal ganglion cell axons. These phenomena are observed for axons of temporal as well as nasal origin, indicating that an additional activity may be necessary to confer the nasotemporal specificity observed in previous assays. We named the protein RAGS (for repulsive axon guidance signal). The sequence of RAGS shows significant homology to recently identified ligands for receptor tyrosine kinases of the Eph subfamily.

Molecular distinction between fetal and adult forms of muscle acetylcholine receptor

Distinct classes of acetylcholine receptor channels are formed when Xenopus oocytes are injected with combinations of the bovine alpha-, beta-, gamma- and delta- or the alpha-, beta-, gamma- and epsilon-subunit-specific messenger RNAs. The conductance and gating properties of the two classes of channels, in conjunction with the developmental changes in the muscular contents of the mRNAs, suggest that replacement of the gamma-subunit by the epsilon-subunit is responsible for the functional alteration of the receptor during muscle development.

Cloning and sequence analysis of cDNA for bovine adrenal preproenkephalin

The nucleotide sequence of cloned cDNA for preproenkephalin from bovine adrenal medulla indicates that the precursor protein contains four copies of Met-enkephalin and one copy each of Leu-enkephalin, Met-enkephalin-Arg6-Phe7 and Met-enkephalin-Arg6-Gly7-Leu8, a previously undetected opioid peptide. The enkephalin and extended enkephalin sequences are each bounded by paired basic amino acid residues. Preproenkephalin may represent a multi-hormone precursor, like the corticotropin-beta-lipotropin precursor.

Existence of distinct sodium channel messenger RNAs in rat brain

The sodium channel is a voltage-gated ionic channel essential for the generation of action potentials. It has been reported that the sodium channels purified from the electric organ of Electrophorus electricus (electric eel) and from chick cardiac muscle consist of a single polypeptide of relative molecular mass (Mr) approximately 260,000 (260K), whereas those purified from rat brain and skeletal muscle contain, in addition to the large polypeptide, two or three smaller polypeptides of Mr 37-45K. Recently, we have elucidated the primary structure of the Electrophorus sodium channel by cloning and sequencing the DNA complementary to its messenger RNA. Despite the apparent homogeneity of the purified sodium channel preparations, several types of tetrodotoxin (or saxitoxin) binding sites or sodium currents have been observed in many excitable membranes. The occurrence of distinguishable populations of sodium channels may be attributable to different states of the same channel protein or to distinct channel proteins. We have now isolated complementary DNA clones derived from two distinct rat brain mRNAs encoding sodium channel large polypeptides and present here the complete amino-acid sequences of the two polypeptides (designated sodium channels I and II), as deduced from the cDNA sequences. A partial DNA sequence complementary to a third homologous mRNA from rat brain has also been cloned.

Cloning and sequence analysis of cDNA for porcine beta-neo-endorphin/dynorphin precursor

The primary structure of a precursor protein that contains beta-neo-endorphin, dynorphin and a third leucine-enkephalin sequence with a carboxyl extension has been deduced from the nucleotide sequence of cloned DNA complementary to the porcine hypothalamic mRNA encoding it. The three peptides are each bounded by Lys-Arg. This precursor protein, like adrenal preproenkephalin and the corticotropin/beta-lipotropin precursor, comprises multiple repetitive units and a cysteine-containing amino-terminal sequence preceded by a signal peptide.

Structural homology of Torpedo californica acetylcholine receptor subunits

The nicotinic acetylcholine receptor (AChR) from the electroplax of the ray Torpedo californica is composed of five subunits present in a molar stoichiometry of alpha 2 beta gamma delta (refs 1-3) and contains both the binding site for the neurotransmitter and the cation gating unit (reviewed in refs 4-6). We have recently elucidated the complete primary structures of the alpha-, beta- and delta-subunit precursors of the T. californica AChR by cloning and sequencing cDNAs for these polypeptides. Here, we report the whole primary structure of the gamma-subunit precursor of the AChR deduced from the nucleotide sequence of the cloned cDNA. Comparison of the amino acid sequences of the four subunits reveals marked homology among them. The close resemblance among the hydrophilicity profiles and predicted secondary structures of all the subunits suggests that these polypeptides are oriented in a pseudosymmetric fashion across the membrane. Each subunit contains four putative transmembrane segments that may be involved in the ionic channel. The transmembrane topology of the subunit molecules has also been inferred.

Primary structure of alpha-subunit precursor of Torpedo californica acetylcholine receptor deduced from cDNA sequence

DNA sequences complementary to the Torpedo californica electroplax mRNA coding for the alpha-subunit precursor of the acetylcholine receptor were cloned. The nucleotide sequence of the cloned cDNA indicates that the precursor consists of 461 amino acids including a prepeptide of 24 amino acids. Possible sites for acetylcholine binding and antigenic determinants on the alpha-subunit molecule are discussed.

The membrane-anchored MMP inhibitor RECK is a key regulator of extracellular matrix integrity and angiogenesis

Matrix metalloproteinases (MMPs) are essential for proper extracellular matrix remodeling. We previously found that a membrane-anchored glycoprotein, RECK, negatively regulates MMP-9 and inhibits tumor invasion and metastasis. Here we show that RECK regulates two other MMPs, MMP-2 and MT1-MMP, known to be involved in cancer progression, that mice lacking a functional RECK gene die around E10.5 with defects in collagen fibrils, the basal lamina, and vascular development, and that this phenotype is partially suppressed by MMP-2 null mutation. Also, vascular sprouting is dramatically suppressed in tumors derived from RECK-expressing fibrosarcoma cells grown in nude mice. These results support a role for RECK in the regulation of MMP-2 in vivo and implicate RECK downregulation in tumor angiogenesis.

Induction of apoptosis by the mouse Nedd2 gene, which encodes a protein similar to the product of the Caenorhabditis elegans cell death gene ced-3 and the mammalian IL-1 beta-converting enzyme

By subtraction cloning we previously identified a set of mouse genes (named Nedd1 through Nedd10) with developmentally down-regulated expression in brain. We now show that one such gene, Nedd2, encodes a protein similar to the mammalian interleukin-1 beta-converting enzyme (ICE) and the product of the Caenorhabditis elegans cell death gene ced-3 (CED-3). Both ICE and CED-3 are known to encode putative cysteine proteases and induce apoptosis when overexpressed in cultured cells. Overexpression of Nedd2 in cultured fibroblast and neuroblastoma cells also resulted in cell death by apoptosis, which was suppressed by the expression of the human bcl-2 gene, indicating that Nedd2 is functionally similar to the ced-3 gene in C. elegans. We also show that during embryonic development, Nedd2 is highly expressed in several types of mouse tissue undergoing high rates of programmed cell death such as central nervous system and kidney. Our data suggest that Nedd2 is an important component of the mammalian programmed cell death machinery.

In vivo stimulation of bone formation by transforming growth factor-beta

The effect of transforming growth factor-beta (TGF beta) on bone in vivo was examined. Twelve daily injections of 1 microgram TGF beta directly onto the periostea of parietal bones of neonatal rats stimulated the formation of periosteal woven bone. The thickness of the treated parietal bones increased at least 2-fold in a dose-dependent manner. This TGF beta effect was localized at the sites of injection, and no change was observed in contralateral parietal bones and tibiae. The body weight in these growing rats was not affected by TGF beta 1. TGF beta 2 had effects similar to those of TGF beta 1 on the parietal bones in vivo. These results reveal for the first time that TGF beta stimulates bone formation in vivo and indicate its anabolic role in local bone metabolism.

Identification of a set of genes with developmentally down-regulated expression in the mouse brain

Using a subtraction cloning approach, we have isolated a set of cDNA clones from mouse neural precursor cells whose respective mRNA levels are down-regulated during the development of mouse brain. Single stranded DNA prepared from neuronal precursor cell cDNA library in lambda Zap vector was subtracted with poly (A)+ RNA prepared from postnatal and adult mouse brain to obtain several clones which show developmental down-regulation of expression. Their patterns of expression indicate that these genes may play important roles during the embryonic development and differentiation of central nervous system.

Sarcoma viruses carrying ras oncogenes induce differentiation-associated properties in a neuronal cell line

The growth-promoting and/or differentiation-blocking activities of Kirsten (Ki-MSV) or Harvey murine sarcoma virus (Ha-MSV) on various types of cells in vitro are well documented. Here we report an unexpected effect of these viruses on a rat phaeochromocytoma cell line, PC12. PC12 cells, which multiply indefinitely in growth medium, are known to respond to nerve growth factor (NGF) by cessation of cell division and expression of several properties resembling those of differentiated sympathetic neurones. We have found that Ki- and Ha-MSV mimic some, if not all, of the activities of NGF in PC12 cells, and there is evidence that the viral oncogenes, v-Ki-ras and v-Ha-ras, are responsible for this phenomenon. This system may be of value for studying the mechanism of action of the v-ras genes as well as the regulatory mechanism of growth and differentiation in neuronal cells.

Expression of functional sodium channels from cloned cDNA

The voltage-gated sodium channel is a transmembrane protein essential for the generation of action potentials in excitable cells. It has been reported that sodium channels purified from the electric organ of the electric eel, Electrophorus electricus, and from chick cardiac muscle consist of a single polypeptide of relative molecular mass (Mr) approximately 260,000, whereas those purified from rat brain and from rat and rabbit skeletal muscle contain, in addition to the large polypeptide, one or two smaller polypeptides of Mr 33,000-43,000. The primary structures of the Electrophorus sodium channel and two distinct sodium channel large polypeptides (designated as sodium channels I and II) from rat brain have been elucidated by cloning and sequencing the complementary DNAs. The purified sodium channel preparations from Electrophorus electroplax and from mammalian muscle and brain, when reconstituted into lipid vesicles or planar lipid bilayers, exhibit some functional activities. The successful reconstitution with the Electrophorus preparation would imply that the large polypeptide alone is sufficient to form functional sodium channels. However, studies with the rat brain preparation suggest that the smaller polypeptide of Mr 36,000 is also required for the integrity of the saxitoxin (STX) or tetrodotoxin (TTX) binding site of the sodium channel. Here we report that the messenger RNAs generated by transcription of the cloned cDNAs encoding the rat brain sodium channel large polypeptides, when injected into Xenopus oocytes, can direct the formation of functional sodium channels.

SOX9 enhances aggrecan gene promoter/enhancer activity and is up-regulated by retinoic acid in a cartilage-derived cell line, TC6

SOX9 is a transcription factor that plays a key role in chondrogenesis. Aggrecan is one of the major structural components in cartilage; however, the molecular mechanism of aggrecan gene regulation has not yet been fully elucidated. TC6 is a clonal chondrocytic cell line derived from articular cartilage. The purpose of this study was to examine whether SOX9 modulates aggrecan gene expression and to further identify molecules that regulate Sox9 expression in TC6 cells. SOX9 overexpression in TC6 cells enhanced by approximately 3-fold the transcriptional activity of the AgCAT-8 construct containing 8-kilobase (kb) promoter/first exon/first intron fragments of the aggrecan gene. SOX9 enhancement of aggrecan promoter activity was lost when we deleted a 4.5-kb fragment from the 3'-end of the 8-kb fragment corresponding to the region including the first intron. In TC6 cells, SOX9 enhanced the transcriptional activity of a reporter construct containing the Sry/Sox consensus sequence >10-fold. SOX9 enhancement of aggrecan gene promoter activity and SOX9 transactivation through the Sry/Sox consensus sequence were not observed in osteoblastic osteosarcoma cells (ROS17/2.8), indicating the dependence on the cellular background. Northern blot analysis indicated that TC6 cells constitutively express Sox9 mRNA at relatively low levels. To examine regulation of Sox9 gene expression, we investigated the effects of calciotropic hormones and cytokines. Among these, retinoic acid (RA) specifically enhanced Sox9 mRNA expression in TC6 cells. The basal levels of Sox9 expression and its enhancement by RA were observed similarly at both permissive (33 degrees C) and nonpermissive (39 degrees C) temperatures. Furthermore, RA treatment enhanced the transcriptional activity of a reporter construct containing the Sry/Sox consensus sequence in TC6 cells. Moreover, RA treatment also enhanced the transcriptional activity of another reporter construct containing the enhancer region of the type II procollagen gene in TC6 cells. These observations indicate that SOX9 enhances aggrecan promoter activity and that its expression is up-regulated by RA in TC6 cells.

Angiographic findings of Takayasu arteritis: new classification

Having proposed a new classification on angiographic findings of patients with Takayasu arteritis, we evaluated the angiographic findings of 80 Japanese patients and 102 Indian patients according to this classification. Japanese patients showed a higher frequency of involvement of the ascending aorta, aortic arch and its branches than did the Indians (P < 0.01). On the other hand, the frequency of involvement of the abdominal aorta and/or renal arteries was higher in Indian patients (P < 0.01). Type III cases of the new classification which involves the thoracic descending aorta, abdominal aorta and/or renal arteries were observed in 3% of the Indian patients, but not at all in the Japanese. In conclusion, in Japanese patients, vascular lesions tend to occur primarily in the ascending aorta, aortic arch and/or its branches and extend into the abdominal aorta. On the other hand, in Indian patients, the tendency is primarily in the abdominal aorta including renal arteries and extending into the thoracic aorta.

Cloning and sequence analysis of calf cDNA and human genomic DNA encoding alpha-subunit precursor of muscle acetylcholine receptor

The nicotinic acetylcholine receptor (AChR) from fish electric organ is well characterized and is known to consist of five subunits present in a molar stoichiometry of alpha 2 beta gamma delta (reviewed in refs 1-3). The mammalian skeletal muscle AChR is thought to have a similar subunit structure. We have recently elucidated the primary structures of the alpha-, beta-, gamma- and delta-subunit precursors of the Torpedo californica AChR by cloning and sequencing cDNAs for these polypeptides; cDNA sequences for the gamma-subunit precursor of the T. californica AChR and the alpha-subunit precursor of the Torpedo marmorata AChR have also been reported by other groups. The four subunits exhibit conspicuous sequence homology and are similar in hydrophilicity profile and predicted secondary structure, thus being most probably oriented in a pseudosymmetric fashion across the membrane. The transmembrane topology of the subunit molecules and the locations of functionally important regions, such as the acetylcholine binding site and the trans-membrane segments which may be involved in the ionic channel, have been proposed. We have now cloned cDNA for the alpha-subunit precursor of the calf skeletal muscle AChR and a human genomic DNA segment containing the corresponding gene. Nucleotide sequence analysis of the cloned DNAs has revealed the primary structures of the calf and human AChR alpha-subunit precursors, which exhibit marked sequence homology with their Torpedo counterpart. The protein-coding sequence of the human AChR alpha-subunit precursor gene is divided by eight introns into nine exons, which seem to correspond to different structural and functional domains of the subunit precursor molecule.

Diphtheria toxin receptor-mediated conditional and targeted cell ablation in transgenic mice

Specific cell ablation is a useful method for analyzing the in vivo function of cells. We have developed a simple and sensitive method for conditional cell ablation in transgenic mice, called "toxin receptor-mediated cell knockout." We expressed the diphtheria toxin (DT) receptor in transgenic mice using a hepatocyte-specific promoter and found that injection of DT caused fulminant hepatitis. Three independently established transgenic lines demonstrated a good correlation between the sensitivity of hepatocytes to DT and the expression level of the DT receptors. Moreover, the degree of hepatocyte damage was easily controlled over a wide range of doses of injected DT without any obvious abnormalities in other cells or tissues. This system is useful for generating mouse models of disease and for studying the recovery or regeneration of tissues from cell damage or loss. As DT is a potent inhibitor of protein synthesis in both growing and non-growing cells, the method is applicable to a wide range of cells and tissues in mice or in other DT-insensitive animals.

Regulation of matrix metalloproteinase-9 and inhibition of tumor invasion by the membrane-anchored glycoprotein RECK

A human fibroblast cDNA expression library was screened for cDNA clones giving rise to flat colonies when transfected into v-Ki-ras-transformed NIH 3T3 cells. One such gene, RECK, encodes a membrane-anchored glycoprotein of about 110 kDa with multiple epidermal growth factor-like repeats and serine-protease inhibitor-like domains. While RECK mRNA is expressed in various human tissues and untransformed cells, it is undetectable in tumor-derived cell lines and oncogenically transformed cells. Restored expression of RECK in malignant cells resulted in suppression of invasive activity with concomitant decrease in the secretion of matrix metalloproteinase-9 (MMP-9), a key enzyme involved in tumor invasion and metastasis. Moreover, purified RECK protein was found to bind to, and inhibit the proteolytic activity of, MMP-9. Thus, RECK may link oncogenic signals to tumor invasion and metastasis.