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Biomedical subjects

M Ramirez

Publications and source records attributed to M Ramirez.

At least 109 records · Page 6Linked to original sources
PubMed1992

Mutations activating the yeast eIF-2 alpha kinase GCN2: isolation of alleles altering the domain related to histidyl-tRNA synthetases.

The protein kinase GCN2 stimulates expression of the yeast transcriptional activator GCN4 at the translational level by phosphorylating the alpha subunit of translation initiation factor 2 (eIF-2 alpha) in amino acid-starved cells. Phosphorylation of eIF-2 alpha reduces its activity, allowing ribosomes to bypass short open reading frames present in the GCN4 mRNA leader and initiate translation at the GCN4 start codon. We describe here 17 dominant GCN2 mutations that lead to derepression of GCN4 expression in the absence of amino acid starvation. Seven of these GCN2c alleles map in the protein kinase moiety, and two in this group alter the presumed ATP-binding domain, suggesting that ATP binding is a regulated aspect of GCN2 function. Six GCN2c alleles map in a region related to histidyl-tRNA synthetases, and two in this group alter a sequence motif conserved among class II aminoacyl-tRNA synthetases that directly interacts with the acceptor stem of tRNA. These results support the idea that GCN2 kinase function is activated under starvation conditions by binding uncharged tRNA to the domain related to histidyl-tRNA synthetase. The remaining GCN2c alleles map at the extreme C terminus, a domain required for ribosome association of the protein. Representative mutations in each domain were shown to depend on the phosphorylation site in eIF-2 alpha for their effects on GCN4 expression and to increase the level of eIF-2 alpha phosphorylation in the absence of amino acid starvation. Synthetic GCN2c double mutations show greater derepression of GCN4 expression than the parental single mutations, and they have a slow-growth phenotype that we attribute to inhibition of general translation initiation. The phenotypes of the GCN2c alleles are dependent on GCN1 and GCN3, indicating that these two positive regulators of GCN4 expression mediate the inhibitory effects on translation initiation associated with activation of the yeast eIF-2 alpha kinase GCN2.

Alleles↗
PubMed1991

Continuous automated monitoring of somatosensory evoked potentials in posttraumatic coma.

Using a microcomputer system, 36 patients were continuously monitored with somatosensory evoked potentials (SSEPs) following closed head injury. The mean duration of monitoring was five days. The patients' GCS scores at the start of monitoring ranged from 3-10. Mortality was 44%. Of 14 patients who had initial absence of SSEP activity after the N20 wave or lost this activity during the period of monitoring, 12 died and two remained vegetative. Eighteen of 22 patients who had preservation or enhancement of this activity had a functional survival (3-month outcomes, p less than 0.001). The best outcomes were observed in the patients with the greatest number of peaks and highest amplitudes in the SSEPs, often in spite of increased intracranial pressure (ICP). The management of three patients was altered as a result of SSEP monitoring. We conclude that continuous monitoring of SSEPs is a useful adjunct in the management of comatose head-injured patients.

Adolescent↗
PubMed1991

Ribosome association of GCN2 protein kinase, a translational activator of the GCN4 gene of Saccharomyces cerevisiae.

The GCN4 gene of the yeast Saccharomyces cerevisiae encodes a transcriptional activator of amino acid biosynthetic genes that is regulated at the translational level according to the availability of amino acids. GCN2 is a protein kinase required for increased translation of GCN4 mRNA in amino acid-starved cells. Centrifugation of cell extracts in sucrose gradients indicated that GCN2 comigrates with ribosomal subunits and polysomes. The fraction of GCN2 cosedimenting with polysomes was reduced under conditions in which polysomes were dissociated, suggesting that GCN2 is physically bound to these structures. When the association of 40S and 60S subunits was prevented by omitting Mg2+ from the gradient, almost all of the GCN2 comigrated with 60S ribosomal subunits, and it remained bound to these particles during gel electrophoresis under nondenaturing conditions. GCN2 could be dissociated from 60S subunits by 0.5 M KCl, suggesting that it is loosely associated with ribosomes rather than being an integral ribosomal protein. Accumulation of GCN2 on free 43S-48S particles and 60S subunits occurred during polysome runoff in vitro and under conditions of reduced growth rate in vivo. These observations, plus the fact that GCN2 shows preferential association with free ribosomal subunits during exponential growth, suggest that GCN2 interacts with ribosomes during the translation initiation cycle. The extreme carboxyl-terminal segment of GCN2 is essential for its interaction with ribosomes. These sequences are also required for the ability of GCN2 to stimulate GCN4 translation in vivo, leading us to propose that ribosome association by GCN2 is important for its access to substrates in the translational machinery or for detecting uncharged tRNA in amino acid-starved cells.

Amino Acid Sequence↗
PubMed1991

Diurnal variation and left-right distribution of pyroglutamyl peptidase I activity in the rat brain and retina.

The thyroliberin and luliberin contents exhibit a diurnal rhythm within the brain and an asymmetrical distribution of both neuropeptides has been demonstrated in the hypothalamus. Since they have been described as substrates of pyroglutamyl peptidase I, this activity was analysed in several rat brain regions and other structures, in order to investigate its putative diurnal variations and changes in relation to the distribution of these neuropeptides and/or other susceptible substrates. Fluorometric activity was assayed in the retina, pituitary gland, superior cervical ganglia, pineal gland, some selected brain regions, and serum of adult male rats at six different time points of a 12:12 h light:dark cycle, using pyroglutamyl-beta-naphthylamide as substrate. A significant circadian rhythm was demonstrated in the retina, the hypothalamus, and the intermediate-posterior pituitary lobe. In addition, a small but significant asymmetrical distribution of this activity, at certain time points, was disclosed: The activity was higher in the left than in the right retina at 10 h of the light period, whereas it was predominant in the right side at 01 h of the dark period. Furthermore, the activity was higher in the left anterior than in the right hypothalamic area at 13 and 01 h. These results could be indicative of a role of this enzymatic activity in the control of the functional status of its endogenous substrates.

Animals↗
PubMed1991

HIV infection in childbearing women.

A blinded survey of HIV infection in childbearing women is being conducted in 43 states and territories. After one year of participation in the survey, 6 of 37,846 women bearing live children in Iowa were found to be infected with HIV.

Adult↗
PubMed1990

Increasing recognition of corticosteroid-induced tumor lysis syndrome in non-Hodgkin's lymphoma.

The acute tumor lysis syndrome has been reported in patients with aggressive non-Hodgkin's lymphoma, acute lymphoblastic leukemia, and rarely in other malignancies in association with the administration of cytotoxic chemotherapy. We report a case of a young man with a large cell lymphoma in whom the acute tumor lysis syndrome developed in association with the administration of corticosteroids. Two similar cases have been reported recently. Clinicians who treat patients with neoplastic diseases should be aware that corticosteroids alone may produce this potentially life threatening complication.

Adult↗
PubMed1990

Identification of positive-acting domains in GCN2 protein kinase required for translational activation of GCN4 expression.

GCN4 is a transcriptional activator of amino acid-biosynthetic genes in the yeast Saccharomyces cerevisiae. GCN2, a translational activator of GCN4 expression, contains a domain homologous to the catalytic subunit of eucaryotic protein kinases. Substitution of a highly conserved lysine residue in the kinase domain abolished GCN2 regulatory function in vivo and its ability to autophosphorylate in vitro, indicating that GCN2 acts as a protein kinase in stimulating GCN4 expression. Elevated GCN2 gene dosage led to derepression of GCN4 under nonstarvation conditions; however, we found that GCN2 mRNA and protein levels did not increase in wild-type cells in response to amino acid starvation. Therefore, it appears that GCN2 protein kinase function is stimulated posttranslationally in amino acid-starved cells. Three dominant-constitutive GCN2 point mutations were isolated that led to derepressed GCN4 expression under nonstarvation conditions. Two of the GCN2(Con) mutations mapped in the kinase domain itself. The third mapped just downstream from a carboxyl-terminal segment homologous to histidyl-tRNA synthetase (HisRS), which we suggested might function to detect uncharged tRNA in amino acid-starved cells and activate the adjacent protein kinase moiety. Deletions and substitutions in the HisRS-related sequences and in the carboxyl-terminal segment in which one of the GCN2(Con) mutation mapped abolished GCN2 positive regulatory function in vivo without lowering autophosphorylation activity in vitro. These results suggest that sequences flanking the GCN2 protein kinase moiety are positive-acting domains required to increase recognition of physiological substrates or lower the requirement for uncharged tRNA to activate kinase activity under conditions of amino acid starvation.

Alleles↗
PubMed1990

A functional vagotomy induced by unilateral forced right nostril breathing decreases intraocular pressure in open and closed angle glaucoma.

There is evidence of the central regulation of intraocular pressure, and it has been suggested that vagal tone might be increased in glaucoma simplex. The nasal cycle, the simultaneous congestion-decongestion response in the nasal cavities, reflects the dynamic lateralisation of the autonomic nervous system. Since this lateralisation presents with sympathetic activity induced by left brain hemisphere stimulation and parasympathetic activity induced by right hemisphere stimulation, it was subsequently demonstrated that forced unilateral nostril breathing induces selective contralateral hemispheric stimulation as measured by relative increases in the electroencephalographic amplitude in the contralateral hemisphere as well as alternating lateralisation of plasma catecholamines. Using this functional vagotomy, we report that left hemispheric stimulation by 20 minutes of forced unilateral right nostril breathing led to a significant bilateral decrease of 4.6 mmHg (25%) in intraocular pressure in 46 patients with open and closed angle glaucoma. However, it significantly increased the IOP in three patients with neovascular, one with juvenile onset, and one with closed angle glaucoma.

Adolescent↗
PubMed1990

Serum and brain aminopeptidase activities in cyclic rats.

Research into the functional role of brain peptides is performed, in part, by studying peptidase enzymes which might be involved in the processing or inactivation of the brain peptides. Aminopeptidase activity has been proposed as a candidate for the regulation of the degradation of these peptides. In this paper, acid (Asp-) and basic (Arg-) aminopeptidase activities were studied in several brain regions and in the serum during the estrous cycle of the rat. Asp-aminopeptidase activity did not significantly change at any point. However, a marked rise was found in Arg-aminopeptidase activity in all the brain areas studied and the serum during the proestrus. It is suggested that this activity plays a role in the hormonal changes that take place during the cycle, possibly in regulating the activity of several neuroactive peptides.

Aminopeptidases↗
PubMed1990

Subcellular distribution of soluble and membrane-bound Leu-, Arg- and Asp-beta-naphthylamide-hydrolysing activities in rat brain.

Subcellular distribution of soluble and membrane-bound Leu-, Arg- and Asp-beta-naphthylamide hydrolysing activities (arylamidase activity) was studied from left and right rat brains, each including hemisphere, cerebellum and brain stem. Both soluble Leu- and Arg-beta-naphthylamide hydrolysing activities showed the highest levels in the synaptosomal fraction. However, the microsomal fraction presented the highest levels when membrane-bound activity was assayed. When we used Asp-beta-naphthylamide as substrate, there were no differences among fractions in the membrane-bound activity, and the highest soluble activity was present at the mitochondrial level. Two different patterns in the subcellular distribution of enzymatic activity were observed: One of them was the result of the use of Leu- or Arg-beta-naphthylamide as substrate and the other when Asp-beta-naphthylamide was employed. No differences between left and right brains in soluble or membrane-bound activities were found.

Aminopeptidases↗
PubMed1988

In vivo amplification and rearrangement of c-myc oncogene in human breast tumors.

We have studied the genomic organization of cellular myc (c-myc) proto-oncogene in 48 human primary breast tumors. Two types of alterations (amplification and rearrangement) were observed in 27 (56%) of the tumors studied. The c-myc proto-oncogene appeared to be amplified 2- to 15-fold in the DNA of 20 tumors (41%). Non-germ line c-myc-related fragments (rearrangements) of variable size were detected in 7 primary breast tumors (6 malignant, 1 benign); 4 of these tumors presented both rearrangement and amplification, and the other 3 presented rearrangement only. The majority of the tumors analyzed were invasive ductal adenocarcinomas; 58% of these showed c-myc locus genetic alterations. Although the c-myc alterations described here do not appear to correlate with the aggressive behavior of primary breast tumors, they seem to be associated with development of breast carcinoma.

Alleles↗
PubMed1988

Aminopeptidase activity is asymmetrically distributed in selected zones of rat brain.

Levels of soluble aminopeptidase (AP), measured as arylamidase activity using L-Leucine-2-Naphthylamide (Leu-2-NA) as substrate, were determined in the soluble fraction of eleven zones of rat brain. Results showed that AP activity is asymmetrically distributed in frontal cortex and hypothalamus with both left sides having significantly higher levels of AP activity, respectively, than the right sides. Simultaneously, the activities of lactate dehydrogenase (LDH) and glutamate-oxalacetate aminotransferase (GOT) were measured in the same cerebral regions; no significant difference was recorded in these activities between either side of the rat brain in any of the zones studied. Provided that aminopeptidases are involved in the degradation of some endogenously released neuropeptides, the results suggest a new mode of expression of cerebral lateralization.

Aminopeptidases↗
PubMed1987

Correlation of continuous-wave Doppler assessment of chronic aortic regurgitation with hemodynamics and angiography.

Fifteen patients with chronic aortic regurgitation (AR) were studied by cardiac catheterization and continuous-wave (CW) Doppler echocardiography. The slope of the AR CW Doppler signal was higher in patients with severe AR (5.7 +/- 2.1 m/s2) than in those with moderate (2.5 +/- 1.3 m/s2) or mild (1.8 +/- 0.7 m/s2) AR (p less than 0.05). The slopes in patients with mild (less than or equal to 18 mm Hg), moderate (19 to 24 mm Hg) and severe (greater than 24 mm Hg) elevation of left ventricular end-diastolic pressure were significantly different (1.9 +/- 0.6, 3.3 +/- 1.2 and 7.1 +/- 0.4 m/s2, respectively, p less than 0.05). Patients with severe AR had shorter pressure half-times than those with mild AR (283 +/- 141 vs 820 +/- 393 ms, p less than 0.05). There was a significant correlation between the slope and left ventricular end-diastolic pressure (r = 0.80, p less than 0.001) and a weaker inverse correlation between pressure half-time and left ventricular end-diastolic pressure (r = -0.59, p less than 0.05). The end-diastolic pressure gradient estimated from CW Doppler using a simplified Bernoulli equation correlated poorly with the catheter measured gradient (r = 0.59, p less than 0.02). The slope of the CW Doppler signal is a better predictor of severity than pressure half-time and is affected by left ventricular end-diastolic pressure in addition to angiographic severity of AR.

Angiocardiography↗
PubMed1987

Expression of only one myelin basic protein allele in mouse is compatible with normal myelination.

Myelin deficiency (mld) is an autosomal recessive mutation in mice characterized by a severe myelin deficit in the central nervous system (CNS). The primary defect in mld is a reduction of the synthesis of the myelin basic protein (MBP) and probably lies in a regulatory element of the MBP gene. In young mld heterozygotes, the MBP mRNA and MBP levels are intermediate. In order to study whether reduced levels of MBP gene expression affect myelination, we determined the levels of MBP mRNA and MBP itself in mld heterozygous and control brains, at different ages during development. Total proteins and MBP were also measured in myelin isolated at 25 and 85 days of age. Myelin proteins were analyzed by SDS-PAGE. In addition, we carried out a morphometric analysis on 25- and 85-day-old optic nerves. Our results indicate that in spite of a roughly 50% reduction of MBP gene expression (compared to controls), the amounts of myelin isolated and the concentration of MBP in myelin were normal in heterozygous brains. Nevertheless, morphometric analyses of optic nerves, which myelinate later than the brainstem, showed thinner myelin sheaths in 25-day-old heterozygotes when compared to controls. This difference disappeared at 85 days of age. These results indicate that normal mice synthesize MBP in excess. The synthesis of this extramyelinic pool of MBP represents a safety factor allowing normal myelination to proceed even when MBP synthesis is severely reduced. In mld heterozygotes, a 30-50% reduction of this rate of synthesis can represent a limiting factor and locally delay myelin deposition without affecting the overall myelin content or myelin composition in heterozygous adult brains.

Aging↗
PubMed1986

Asymmetrical distribution of aminopeptidase activity in the cortex of rat brain.

The levels of soluble aminopeptidase (AP) activity were measured in the right and left frontal (FC), parietotemporal (PTC) and occipital (OC) cortex of male albino rat brains. The results showed more AP activity in the left cortex than in the right. Analyzing these results further, we found that the differences are significant for frontal cortex but not for parietotemporal nor occipital cortex. However, 76% of the rats were left-predominant for AP activity in the 3 cortical areas studied.

Aminopeptidases↗
PubMed1986

Prefrontal cortex excitability in early postnatally malnourished rats.

The effect of early postnatal malnutrition on the responsiveness of the rat prefrontal cortex was studied by determining excitability thresholds and fatigability to direct cortical stimulation. Malnutrition imposed during the period of rapid brain growth caused a significant increase of cortical chronaxie values as well as increased fatigability of direct cortical responses, indicating a detrimental effect on the axodendritic synapses. Since the prefrontal cortex plays an important role in the temporal organization of behavior, a dysfunction of this cortical area could be a causal link between nutritional and behavioral deficits.

Animal Population Groups↗