Induction of G alpha i2-specific antisense RNA in vivo inhibits neonatal growth.

Guanosine triphosphate-binding regulatory proteins (G proteins) are key elements in transmembrane signaling and have been implicated as regulators of more complex biological processes such as differentiation and development. The G protein G alpha i2 is capable of mediating the inhibitory control of adenylylcyclase and regulates stem cell differentiation to primitive endoderm. Here an antisense RNA to G alpha i2 was expressed in a hybrid RNA construct whose expression was both tissue-specific and induced at birth. Transgenic mice in which the antisense construct was expressed displayed a lack of normal development in targeted organs that correlated with the absence of G alpha i2. The loss of G alpha i2 expression in adipose tissue of the transgenic mice was correlated with a rise in basal levels of adenosine 3',5'-monophosphate (cAMP) and the loss of receptor-mediated inhibition of adenylylcyclase. These data expand our understanding of G protein function in vivo and demonstrate the necessity for G alpha i2 in the development of liver and fat.

The role of protein synthesis in the decay of phosphoenolpyruvate carboxykinase messenger RNA.

The role of protein synthesis in the control of phosphoenolpyruvate carboxykinase (PEPCK; 4.1.1.32) mRNA turnover was studied in FTO-2B rat hepatoma cells. A previous study demonstrated that incubation of these cells with cAMP prolongs the half-life of the otherwise short-lived PEPCK mRNA. The decay rate of PEPCK mRNA was also slowed in cells incubated with cycloheximide, but not in cells incubated with other translation inhibitors, such as puromycin or pactamycin, even though protein synthesis was inhibited 85-95% by these agents. No correlation was noted between the rate of L-[3H]valine incorporation into cellular proteins and PEPCK mRNA half-life, suggesting that protein synthesis per se is not required for breakdown of the mRNA. Exposure of cells to the translation initiation inhibitor pactamycin together with cycloheximide abolished the "slowing" effect of cycloheximide, and PEPCK mRNA decayed at the same rate as in cells incubated in the presence of pactamycin alone. In contrast, pactamycin did not reverse the effect of cAMP, and the mRNA decayed at the same slow rate in cells incubated in the presence of either (Bu)2cAMP alone or (Bu)2cAMP together with pactamycin. Since pactamycin promotes polysomes dissociation, these results suggest that cAMP enhances the stability of a polysome-free PEPCK mRNA. Furthermore, these results strongly indicate that neither the rapid decay of PEPCK mRNA nor the cAMP-mediated stabilization of the mRNA requires on-going protein synthesis.

Androgen induction of urokinase gene expression in LNCaP cells is dependent on their interaction with the extracellular matrix.

Urokinase-type plasminogen activator (uPA) plays a central role in tissue remodeling and cell invasion. In the present study, we examined the expression of uPA in the prostate cancer cell lines LNCaP, DU-145 and PC-3. In contrast to DU-145 and PC-3, the androgen-responsive cell line LNCaP does not express uPA. However, seeding LNCaP cells on fibronectin-coated plates stimulated a low level of uPA expression which was further induced upon exposure of the cells to dihydrotestosterone (DHT). Concomitant with the expression of uPA, an androgen-regulated expression of uPA receptor (uPAR) was induced. These results suggest that the interaction of LNCaP cells with the extracellular matrix plays a dominant role in the androgen control of uPA and uPAR gene expression.

Internal carotid artery hypoplasia presenting as anterior ischemic optic neuropathy.

PURPOSE: To describe the occurrence of anterior ischemic optic neuropathy in a young woman with internal carotid artery hypoplasia. METHODS: Case report with clinical and radiologic observations. RESULTS: A 38-year-old woman suffered from a sudden, painless loss of vision in her right eye. The diagnosis of anterior ischemic optic neuropathy was based on the clinical course and appearance of the fundus. Doppler evaluation of the carotid arteries, computed tomography (CT) scan, magnetic resonance imaging (MRI), and CT angiogram all demonstrated internal carotid artery hypoplasia on the same side. CONCLUSION: Although carotid artery disease (mainly atherosclerosis) is not a common predisposing factor for anterior ischemic optic neuropathy, our patient had an ipsilateral coexisting internal carotid artery hypoplasia and anterior ischemic optic neuropathy. We believe that the carotid artery anomaly might have contributed to the development of anterior ischemic optic neuropathy in this patient.

[Retinal injury induced by laser pointers].

Laser pointers originally designed for use during presentations are ubiquitous and are even sold as toys (such as pens or on key chains) in drug stores. Though reported as safe, the laser pointers still carry the risk of potential damage to the eye. We report a 16-year-old boy with bilateral retinal injury caused by 20-30 seconds of exposure to a laser pointing-device. Immediately thereafter, vision was blurred bilaterally and he noted a central red scotoma in each eye. Symptoms resolved spontaneously within 2 days but the retinal scars remained all during the 10 months of follow-up. It is clear from our report and 3 other publications that retinal damage can develop from misusing laser pointers. Laser hazards and safety should be stressed for the general public. We recommend that laser-pointers should not be available as toys to children and teenagers.

[Causes of blindness in Israel].

Of the world population, 38 million are blind and another 110 million are visually impaired. Even in the developed countries there are 3.5 million who are blind. This study of blindness in Israel is based on the National Blind Registry. At the end of 1998, 15,937 were registered as blind, 0.3% of the total population; 776 (5%) of them were 18 years old or younger; 6,426 (40%) 18-65 years old; and 8,735 (55%) 65 years or older. The leading causes of blindness in Israel are glaucoma (2,074, 13%), macular degeneration (1,954, 12%) and diabetes mellitus (1,680, 11%). Since glaucoma and diabetes, and to a lesser extent glaucoma, respond to treatment, blindness could have been avoided in most cases. National screening programs for early diagnosis and treatment of these diseases would reduce prevalence of the newly blind.

The degradation of phosphoenopyruvate carboxykinase (GTP) mRNA is regulated by cyclic AMP but not by dexamethasone.

The relationship between the control by cAMP of phosphoenolpyruvate carboxykinase (GTP) mRNA synthesis and breakdown was examined. The half-life of phosphoenolpyruvate carboxykinase mRNA was estimated from its decay rate in cells exposed to insulin (a specific inhibitor of phosphoenolpyruvate carboxy-kinase gene transcription) in the presence or absence of 8-chlorophenylthio-cyclic AMP after high levels of the mRNA had been induced by the cyclic nucleotide. The mRNA decayed with a half-life of 300-350 min in cells treated with 8-chlorophenylthio-cyclic AMP and insulin whereas the T1/2 was 30-40 min in cells exposed to insulin alone. Similar results were obtained when 5,6-dichloro-1-beta-ribofuranosyl-benzimidazole, a general inhibitor of mRNA synthesis, was used. The mRNA decayed at comparable rates in cells treated with insulin or 5,6-dichloro-1-beta-ribofuranosyl-benzimidazole or in cells exposed to insulin-free medium after withdrawal of the inducer of gene transcription. These results suggest that insulin does not modulate phosphoenolpyruvate carboxykinase mRNA breakdown. 8-Chlorophenylthio-cyclic AMP reversed the rapid decay of the mRNA in cells preexposed to insulin for 1 h even when over 60% of the mRNA had been degraded. In contrast to cAMP, no alterations in the rate of phosphoenolpyruvate carboxykinase mRNA decay were noted in cells exposed to the synthetic glucocorticoid dexamethasone. The half-life of phosphoenolpyruvate carboxy-kinase mRNA, expressed from a hybrid gene driven by the non-cAMP regulated promoter of the mouse metallothionein-I gene, was also increased in cells treated with 8-chlorophenylthio-cyclic AMP. These results suggest that the control by cAMP of phosphoenolpyruvate carboxykinase mRNA breakdown is accomplished by a rapid mechanism which is independent of the induction of gene transcription.

Relationship of the pool of intracellular valine to protein synthesis and degradation in cultured cells.

To explore the role of the pool of intracellular free valine in the processes of protein synthesis and protein degradation, cultured hepatoma (HTC) cells were incubated in media containing varying concentrations of L-valine, under conditions of constant rates of protein synthesis and protein breakdown, and at steady state levels of intracellular valine specific radioactivities. Two types of experiments were compared: in the first (designated "incorporation experiment"), unlabeled cells were exposed to [3H]valine for a short period of time. In the second (termed "reincorporation experiment"), cells were prelabled with [3H]valine and then incubated for a brief period with media containing different concentrations of unlabeled valine; reincorporation of [3H]valine was calculated by the difference between the release of [3H]valine from labeled cellular proteins at low valine concentrations, and the maximal rate of the release at high valine concentrations. In both types of experiments, the rates of [3H]valine incorporation or reincorporation were compared with the respective specific radioactivities of free intracellular valine. In the incorporation experiment, the rates of [3H]valine incorporation into protein calculated by the intracellular specific radioactivities were not constant, but showed an upward deviation at low valine concentrations. This is in agreement with the results of Mortimore, G.E., Woodside, K.H., and Henry, J.E. ((1972) J. Biol. Chem. 247, 2776-2784) in the perfused rat liver. By contrast, in the reincorporation experiment, the calculated rates of [3H]valine reincorporation based on intracellular specific radioactivities were constant throughout the range of valine concentrations. The constant value of calculated valine reincorporation was lower by 30 to 50% than the calculated rate of valine incorporation at high valine concentrations. The following model is proposed to explain these results. There is one common pool of free intracellular valine, but there are two sites where valyl-tRNA can be formed. The first is an internal site that utilizes valine from the intracellular pool, and the second is an external (possibly membranous) system that converts extracellular valine directly to valyl-tRNA. Valine originating from protein degradation flows into the intracellular pool, from which it can be reutilized by the internal system. According to these assumptions, in the incorporation experiment and at low valine concentrations, the specific activity of valyl-tRNA is higher than that of the intracellular pool of free valine, due to the contribution of the external system. On the other hand, in the reincorporation experiment the specific activity of extracellular valine is negligible in comparison with that of the intracellular pool. Therefore, in this case the specific activity of valyl-tRNA is proportional to that of the intracellular pool, with a constant dilution by unlabeled valine of extracellular origin...

A cAMP-regulated RNA-binding protein that interacts with phosphoenolpyruvate carboxykinase (GTP) mRNA.

Cyclic-AMP stabilizes phosphoenolpyruvate carboxykinase (GTP) (PEPCK) mRNA against degradation. To investigate the mechanism of this effect, RNA mobility shift assays were used to determine the interaction of cellular proteins with specific domains from the mRNA. We report here the identification of a protein with an affinity for sequences of PEPCK mRNA with a predicted stem-loop structure. RNA-protein complex formation was significantly reduced if the double-stranded RNA probe was preheated to 90 degrees C. The RNA-binding protein did not bind to the hairpin structure of poly(rI)-poly (rC), indicating some degree of sequence specificity and that the RNA-binding protein is not the interferon-induced double-stranded RNA-activated protein kinase. The binding activity was contained in the cytosolic fraction (100,000 x g) of rat hepatoma FTO-2B cells and was significantly enhanced by high concentrations of KCl. Chromatography on an anion exchanger separated the binding activity from a factor which, upon reconstitution, inhibited the interaction with the RNA probe. Incubation of cells with cAMP resulted in a 3-4-fold decrease in the activity of the RNA-binding protein. An inhibition in complex formation was observed with extracts as early as 60 min after exposure of cells to cAMP. Liver extracts from rats starved for 72 h also had reduced binding activity compared to extracts from fed animals. Cellular extracts treated with alkaline phosphatase exhibited an elevated level of complex formation. An analysis by SDS-polyacrylamide gel electrophoresis of the RNA-protein complex after ultraviolet light cross-linking demonstrated that the RNA-binding protein had a molecular mass of approximately 100 kDa. On the basis of these results, we suggest that liver cells contain a protein whose interaction with PEPCK mRNA is regulated by cAMP-dependent phosphorylation and which may be responsible for the cAMP-mediated control of PEPCK mRNA half-life.

Cyclic AMP stabilizes the mRNA for phosphoenolpyruvate carboxykinase (GTP) against degradation.

It is now well established that cAMP induces the transcription rate of the gene for phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) and that this induction is dependent on a nucleotide domain located within the promoter-regulatory region of the gene (Short, J. M., Wynshaw-Boris, A., Short, H. P., and Hanson, R. W. (1986) J. Biol. Chem. 261, 9721-9726). We report here that cAMP also stabilizes phosphoenolpyruvate carboxykinase mRNA against degradation. Using two independent experimental approaches, we show that the half-life of the mRNA for phosphoenolpyruvate carboxykinase is extended when FTO-2B rat hepatoma cells are exposed to dibutyryl cyclic AMP (Bt2cAMP). In the first experiment, the rate of decay of phosphoenolpyruvate carboxykinase mRNA was determined in cells incubated in the presence of insulin, which has been shown to block the transcription rate of the gene for the enzyme. Under these conditions, the half-life of phosphoenolpyruvate carboxykinase mRNA was 30 min. However, in cells incubated in the presence of Bt2cAMP, the mRNA decayed with a half-life of 150 min. In the other experiment, mRNA stability was measured under steady state conditions, utilizing a "pulse-chase" approach. The apparent half-life of phosphoenolpyruvate carboxykinase mRNA increased from 40 min to over 250 min in Bt2cAMP-treated cells. No significant change in the stability of total cellular RNA was noted. Other experiments have shown that the transcription rate of the gene for phosphoenolpyruvate carboxykinase peaks within the first 20 min after exposing the cells to Bt2cAMP and then levels off, while the abundance of the mRNA reaches a maximum at about 90 min and remains at this level thereafter. Thus, the long term effect of cAMP on the expression of the gene coding for phosphoenolpyruvate carboxykinase occurs at least in part, through an alteration in the degradation rate of the mRNA for this enzyme.

Comparison of fiber optical and video monitor stimulators in normals and multiple sclerosis patients.

A comparison of VEP findings using a fiber optical stimulator with three color combinations (black/red, black/green and red/green) and a conventional video monitor stimulator in black/white was performed in 3 groups of subjects: a group with definite lesions in the visual pathway, a group with suspected lesions and a control group. No significant correlations of P100 latency were found in the normative group, probably because of the small range of their values. All correlations were significant in the two patient groups, except for the red/green stimuli in the definite group. In general, the red/green combination was inferior to other color combinations in eliciting VEPs. The patient groups with definite, as well as suspected, lesions indicated no benefit from the color stimuli, as compared with black/white. The major advantage of the fiber optical stimulator is its simplicity, the lack of stimulus artifacts and the accessibility to the patient's bed side, thanks to its small size. Stimulators with higher illuminance and improved pattern element shape should narrow the still unacceptable normative variability of the wave forms recorded.

The mitochondrial and cytosolic forms of avian phosphoenolpyruvate carboxykinase (GTP) are encoded by different messenger RNAs.

Previous work from our laboratory (Watford, M., Hod, Y., Chiao, Y. B., Utter M. F., and Hanson R. W. (1981) J. Biol. Chem. 256, 10023-10027) indicated that in the chicken, hepatic phosphoenolpyruvate carboxykinase is in the mitochondria, whereas kidney contains both a mitochondrial and cytosolic form of the enzyme. In the present study the two forms of phosphoenolpyruvate carboxykinase were purified and shown to be distinct proteins which differ in size, charge, and immunochemical properties. Using a cell-free protein synthesis system, we demonstrate that the cytosolic isozyme is encoded only by kidney mRNA and that its translation form has similar properties to that of the mature protein. On the other hand, the mitochondrial enzyme is encoded by liver and kidney mRNA and synthesized as a protein about 2000 daltons larger than the mature form. The putative precursor of the mitochondrial phosphoenolpyruvate carboxykinase is processed to a mature size by isolated, respiring mitochondria. We further show that the mRNA species for the cytosolic and mitochondrial forms are separable and are about 3 and 4 kilobases, respectively. It is concluded that the two forms of phosphoenolpyruvate carboxykinase of the chicken are encoded by distinct mRNA species.

Gi alpha 2 mediates the inhibitory regulation of adenylylcyclase in vivo: analysis in transgenic mice with Gi alpha 2 suppressed by inducible antisense RNA.

The role of the GTP-binding regulatory protein (G-protein) Gi alpha 2 in vivo was explored using transgenic mice in which the alpha-subunit of Gi alpha 2 was suppressed by antisense RNA. Rat hepatoma FTO-2B cells provide an ideal test system for constructs employing the expression vector pPCK-AS, designed to express antisense RNA at birth under the control of the phosphoenolpyruvate carboxykinase (PEPCK) promoter. Cells transfected with the expression vector containing a sequence antisense to Gi alpha 2 (pPCK-ASGi alpha 2) displayed expression of RNA antisense to Gi alpha 2 that, like transcription of the PEPCK gene, was inducible by cyclic AMP. Expression of RNA antisense to Gi alpha 2 and suppression of the expression of Gi alpha 2, but not Gsa and Gi alpha 3, was observed in the transfected FTO-2B cells. BDF1 mice carrying the transgene displayed suppression of Gi alpha 2 in liver and fat, two targets for tissue-specific expression of the PEPCK gene. The loss of Gi alpha 2 in white adipocytes of transgenic mice resulted in 3.1-fold elevation of basal cyclic AMP accumulation. Cyclic AMP accumulation in response to stimulation by epinephrine (10 microM) was normal in adipocytes of transgenic mice, demonstrating no alteration in the stimulatory adenylylcyclase capacity in the Gi alpha 2-deficient cells. The inhibitory adenylylcyclase pathway, in sharp contrast, was severely blunted in response to challenge by the inhibitory A1-purinergic agonist, (-)R-N6-phenylisopropyladenosine. These studies illuminate a critical role of Gi alpha 2 in the inhibitory adenylylcyclase signaling pathway in vivo.

The gene encoding the cytosolic form of phosphoenolpyruvate carboxykinase (GTP) from the chicken.

The gene for cytosolic phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) from the chicken was isolated from a recombinant library containing the chicken genome in phage lambda Charon 4A. The isolated clone, lambda PCK1cc, contains the complete gene for the enzyme as well as both 5' and 3' flanking sequences. The gene is approximately 8 kilobases in length divided into 8 exons, as demonstrated by restriction endonuclease mapping and DNA-RNA heteroduplex analysis. Southern blotting of chicken chromosomal DNA digested with various restriction enzymes shows a pattern predicted from the restriction map of lambda PCK1cc. The phosphoenolpyruvate carboxykinase gene is present as a single copy in the haploid chicken genome. The 5' region of the gene was defined by S1 nuclease mapping and by sequencing. Two mRNA species with discrete 5' ends were observed using S1 nuclease mapping. The ratio between the amounts of these multiple forms of mRNA is the same in chicken kidney and liver and is not affected by induction of the enzyme mRNA by cAMP. Examination of sequence homologies with the gene for rat cytosolic phosphoenolpyruvate carboxykinase indicates a putative control region contained in flanking sequences at the 5' end of the gene.

Induction by cAMP of the mRNA encoding the cytosolic form of phosphoenolpyruvate carboxykinase (GTP) from the chicken. Identification and characterization of a cDNA clone for the enzyme.

Previous work from our laboratory (Hod, Y., Utter, M. F., and Hanson, R. W. (1982) J. Biol. Chem. 257, 13787-13794) has demonstrated that chicken kidney contains both mitochondrial and cytosolic forms of phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) and that the two forms are distinct proteins. Using poly(A+) RNA from chicken kidney, a double-stranded cDNA library was constructed. DNA clones containing sequences complementary to the mRNA for the cytosolic form of phosphoenolpyruvate carboxykinase were initially identified by colony hybridization with 32P-labeled cDNA transcribed from an RNA fraction enriched for the enzyme mRNA. The identity of plasmids containing phosphoenolpyruvate carboxykinase cDNA was confirmed by hybrid-selected translation. Mature mRNA for cytosolic phosphoenolpyruvate carboxykinase of the chicken is 2.8 kilobases in length, similar to that previously noted for mRNA coding for the same enzyme in the rat. The cDNA for the chicken enzyme hybridizes with several restriction fragments of the corresponding cDNA for the rat cytosolic phosphoenolpyruvate carboxykinase, indicating conservation of nucleotide sequences during evolution. Wide spread conservation of sequence homology is also demonstrated by the hybridization of the cDNA for the rat phosphoenolpyruvate carboxykinase with a 2.8-kilobase RNA from the livers of a variety of vertebrates including amphibian, avian, and primate species. Specific mRNA coding for the cytosolic form of phosphoenolpyruvate carboxykinase was present in chicken kidney but absent from the liver, even in animals starved for 48 h. However, the administration of cAMP to normal fed chickens caused a rapid induction of phosphoenolpyruvate carboxykinase mRNA. These findings suggest that the gene for the cytosolic enzyme in chicken liver can be expressed if the proper hormonal stimuli are present.

Hormonal control of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene expression in rat hepatoma cells.

The hormonal control of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene expression was studied in the rat hepatoma cells, FTO-2B. In contrast to another hepatoma cell line (HTC), the enzyme in FTO-2B cells displays both kinase and bisphosphatase activities. As in rat liver, the mRNA in FTO-2B cells is 2.2-kilobases in length. However, the 5' region of the mRNA differs from the mRNA in the liver in that it contains sequences unique to 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase mRNA from skeletal muscle. These results suggest that the mRNA in FTO-2B cells may represent an additional alternative splicing product of the 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene. Exposure of FTO-2B cells to media containing either insulin (10(-7) M) or dexamethasone (10(-6) M) induced about a 10-fold increase in the level of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase mRNA within 6-10 h of hormone treatment. The concentrations of insulin or dexamethasone giving half-maximal stimulation were 10(-9) M and 2 x 10(-8) M, respectively, and dibutyryl cyclic AMP (5 x 10(-7) M) completely prevented the increase in enzyme mRNA induced by these hormones. Exposure of cells to glucose-free medium abolished the insulin-mediated enhancement in 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase mRNA, but not that induced by dexamethasone. No alteration in the degradation rate of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase mRNA was noted when cells were treated with insulin. Run-on transcription assays with isolated nuclei showed an increase in the relative transcription rate of the gene in cells treated with either insulin or dexamethasone. The time course of transcription activation preceded the increase in the level of the mRNA, indicating that the main mechanism for the induction of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase expression by insulin and dexamethasone is mediated by stimulation of gene transcription.

ATP citrate-lyase and glycogen synthase kinase-3 beta in 3T3-L1 cells during differentiation into adipocytes.

ATP citrate-lyase (CL), acetyl-CoA carboxylase (ACC) and glycogen synthase kinase-3 beta (GSK-3 beta) levels were measured in cytosol from 3T3-L1 cells during differentiation from fibroblasts into fat-cells. Protein levels were estimated from immunoblots using specific antisera. Cytosol from confluent cells contain significant amounts of GSK-3 beta, which fell during differentiation of these cells into adipocytes. CL from confluent cells was found to be mostly in the form of a single protein band of apparent mass 110 kDa. Levels of CL and ACC increased during cell differentiation into adipocytes. During the first 3 days of differentiation, CL migration changed, and it was expressed as a complex of protein bands of apparent mass 110 kDa, 113 kDa and 115 kDa. At later stages of differentiation, when these cells had assumed the phenotype of fat-cells, they expressed CL mainly as protein bands of 110 and 113 kDa. When samples containing these bands were treated with alkaline phosphatase, the 113 kDa protein band collapsed into the 110 kDa species. This suggests that the slower-migrating species of CL is a higher-order phosphorylation state of the same protein. Furthermore, when purified CL, mostly expressed as the 110 kDa species, was phosphorylated with cyclic AMP-dependent protein kinase alone or together with GSK-3 and resolved by SDS/PAGE, the phosphorylated CL now migrated more slowly as the 113 kDa and 115 kDa forms. CL phosphorylation was hormone-regulated, since, in samples from fat-cells that had the complex two-band pattern, when cultured in medium without serum or hormones, CL migration reverted to a single band of 110 kDa, similar to confluent cells. Treatment of these 'down-regulated' cells with insulin rapidly induced substantial amounts of the 113 kDa species, with a concomitant decrease in the 110 kDa species.