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Biomedical subjects

S K Gupta

Publications and source records attributed to S K Gupta.

At least 19 recordsLinked to original sources
PubMed1992

Myristoylation of the G alpha i2 polypeptide, a G protein alpha subunit, is required for its signaling and transformation functions.

GTPase-inhibiting mutations of the alpha subunit (alpha i2) of the G protein, Gi2, result in constitutive activation of alpha i2 signal transduction functions. GTPase-inhibited alpha i2 mutant polypeptides, referred to as gip2 oncoproteins, have glutamine-205 mutated to leucine (alpha i2Q205L). Expression of the alpha i2Q205L polypeptide inhibits adenylyl cyclase stimulation, constitutively activates p42 mitogen-activated protein kinase, and transforms Rat 1a fibroblasts. The alpha i2 polypeptides are N-terminal-myristoylated, but the function of myristoylation is unclear in alpha i2 signal transduction. We have tested the requirement for myristoylation on the ability of the alpha i2Q205L mutant polypeptide to constitutively regulate signal pathways and cell transformation. When expressed in Rat 1a cells, the nonmyristoylated alpha i2Q205L polypeptide is membrane associated but is unable to regulate adenylyl cyclase or p42 mitogen-activated protein kinase and does not induce cellular transformation. We conclude that myristoylation is absolutely necessary for alpha i2Q205L signal transduction and regulation of effector enzymes in the cell.

Adenylate Cyclase Toxin↗
PubMed1992

Mitogen-activated protein kinase activation resulting from selective oncogene expression in NIH 3T3 and rat 1a cells.

Mitogen-activated protein kinases (MAPKs) are serine/threonine kinases that are rapidly activated in response to a variety of growth factors in many cell types. MAPKs are activated by phosphorylation of both tyrosine and threonine residues. They are proposed to be key integrators of growth factor receptor transduction systems involving conversion of tyrosine kinase signals to serine/threonine kinase activation. We have studied the influence of specific oncogenes on the regulation of MAPK activity in NIH 3T3 and Rat 1a fibroblasts. In NIH 3T3 cells, ras or raf oncogene expression, but not gip2 oncogene expression, induces a significant constitutive MAPK activation. In contrast, in Rat 1a cells, gip2, but not ras or raf oncogene expression, induces a strong constitutive MAPK activation. The findings indicate that, in a cell type-selective manner, different oncoproteins are capable of causing the constitutive activation of MAPK. However, the magnitude of oncogene-induced MAPK activation is not directly correlated with cellular transformation in either cell type. It appears that expression of only a subset of transforming oncogenes in a specific cell type is able to alter the regulation of the MAPK activation pathway. Thus, the network of cytoplasmic serine/threonine kinases will be differentially regulated when the same oncogene is expressed in different cell types.

3T3 Cells↗
PubMed1992

MAP kinase is constitutively activated in gip2 and src transformed rat 1a fibroblasts.

Rat 1a fibroblasts transformed by the Gi2 oncogene, gip2, exhibit a constitutively elevated mitogen-activated protein (MAP) kinase activity that correlates with enhanced tyrosine phosphorylation of the p42 MAP kinase polypeptide. The MAP kinase activity in gip2 transformed cells is 50-60% of the pertussis toxin-sensitive, thrombin-stimulated activity observed in wild-type Rat 1a cells. A similar activation of MAP kinase is observed in src but not ras or raf transformed Rat 1a cells, indicating that the persistent MAP kinase activity results from the action of the specific oncoprotein and is not the consequence of cellular transformation. The enhanced transactivation function of c-Jun characteristic of the transformed phenotype, measured using a collagenase promoter-CAT reporter gene, is observed in gip2, src, ras, and raf transformed Rat 1a cells. The regulatory networks controlled by the four transforming oncogenes therefore alter the activity of specific transcription factors, but only gip2 and src constitutively activate MAP kinase. The findings demonstrate that the catalytic activity of growth factor-regulated cytoplasmic kinases are selectively and stably activated as a consequence of specific oncogene expression.

Animals↗
PubMed1992

Preparation and biological properties of native and recombinant ciliary neurotrophic factor.

CNTF (ciliary neurotrophic factor), purified from rabbit sciatic nerves by a relatively simple procedure, is bioactive in tissue culture at low picomolar concentration and appears as a doublet on polyacrylamide gel electrophoresis (PAGE). In these nerves, CNTF accounts for more than one-half of the survival-promoting activity on ciliary neurons. The concentration of CNTF in rabbit sciatic nerves is estimated to be 5 nmol/kg, more than 1000 times higher than would seem to be required to support neurons if the neurotrophic factor were homogeneously distributed. With recombinant DNA technology, rat CNTF has been synthesized in Escherichia coli, purified without denaturating agents, and found to be bioactive at a slightly lower concentration than CNTF extracted from rabbit sciatic nerves. After radioiodination, CNTF retains biological activity but is not specifically internalized and retrogradely transported in motor and sensory axons. In peripheral nerves, ciliary neurotrophic factor differs biologically from nerve growth factor (NGF) by its much higher tissue concentration and apparent lack of internalization by peripheral nerve axons.

Amino Acid Sequence↗
PubMed1992

Management of juxtarenal aortic occlusions: technique for suprarenal clamp placement.

Atherosclerotic occlusion of the entire infrarenal abdominal aorta can produce gangrene, rest pain or claudication and can progress to involve the renal artery origins. Features of the operative technique for treating these juxtarenal aortic occlusions include self-retaining retraction, mobilization of the left renal vein with division of all non-renal branches, exposure of the suprarenal aorta and renal arteries by division between clamps of the surrounding paraaortic fibroareolar tissue and fat, sharp division of crural attachments to the aorta, control of the two renal arteries with doubled vessel loops and then direct vertical clamping of the suprarenal aorta. Through an arteriotomy below the renal arteries, 2-4 cm of pararenal aorta are cleared of thrombus and atherosclerotic debris under direct vision. After transfer of the suprarenal clamp to an infrarenal position, conventional aortobifemoral bypass is then performed. In a series of 18 patients with juxtarenal aortic occlusion managed by this technique, suprarenal clamp time ranged from 4 to 25 minutes (mean, 13 minutes). There was no morbidity from renal failure or emboli and no mortality. This technique allows for deliberate, careful disobliteration of the pararenal and infrarenal aorta and minimizes the risk of renal embolization.

Aorta, Abdominal↗
PubMed1992

Modeling the pharmacokinetics and pharmacodynamics of dexamethasone in depressed patients.

Changes in time course effected by cortisol suppression and the relationship of these changes to the plasma dexamethasone concentration of suppressor and non-suppressor patients are described in this report on a combined pharmacokinetic-pharmacodynamic model. Thirteen depressed patients (8 suppressors and 5 non-suppressors) received an intravenous dose (1.5 mg) of dexamethasone. The drug-induced effect changes are found to lag behind, in time, the plasma drug level changes. To accurately relate the temporal relationship of effect changes to plasma dexamethasone levels, a pharmacodynamic model (sigmoid-Emax) was combined with a pharmacokinetic model that incorporated an effect compartment. The magnitude of the time-lag was quantified by the half-time of equilibration between concentrations in the hypothetical effect compartment and the plasma dexamethasone levels (t1/2keo). The t1/2keo of the nonsuppressing group was about 50% of that of the suppressing group, indicating that for a given plasma level the onset and termination of effect for the nonsuppressing group is about two times more rapid than for the suppressing group. Moreover, the model can estimate the effect-site concentration that causes one-half of the maximal predicted effect (EC50), a measure of an individual's sensitivity to dexamethasone. The receptor sensitivity (as determined from the EC50 ratio) of the suppressing group was about twice that of the nonsuppressing group.

Depression↗
PubMed1992

Effects of chronic treatment of haloperidol and clozapine on levels of G-protein subunits in rat striatum.

Chronic administration of typical neuroleptic drugs, such as haloperidol, causes the supersensitivity of brain dopamine D2 receptor in striatum and limbic regions, while the atypical neuroleptic clozapine does not. In order to understand the mechanism of their action at a molecular level, studies were carried out to assess the effects of chronic treatment of these drugs on the levels of G-proteins in the rat striatum using the Western blot method. Results of the present study demonstrate that the treatment with haloperidol or clozapine, respectively, down-regulate or up-regulate the levels of G proteins. Quantitative immunoblotting, using site-directed specific antisera, demonstrated that chronic treatment with haloperidol down-regulates Gi alpha, Gs alpha, and beta subunits while chronic treatment with clozapine upregulates Gi alpha, Gs alpha, and beta subunits. Neither of these drugs has any effect on the levels of Go alpha.

Amino Acid Sequence↗
PubMed1992

System functionality and physicochemical model of fentanyl transdermal system.

Fentanyl is an opioid traditionally administered by infusion or injection and more recently in a rate-controlled transdermal dosage form. This system is a four-layer laminate on a protective liner. A backing layer seals and protects the drug reservoir, the source for continuous delivery of fentanyl. A membrane controls the release rate of fentanyl from the system. An adhesive layer attaches the system to skin and releases an initial loading dose of fentanyl. The rate of fentanyl delivery through skin is determined by the system and the skin at the application site. The release rate from the system is approximated by Fick's first law of diffusion and is controlled by the rate-controlling membrane. A complete simulation model that combines both in vitro release data and the pharmacokinetic model has been developed and used to show the influence of various physiologic and system variables on serum fentanyl concentrations.

Administration, Cutaneous↗
PubMed1992

Rapid antibody capture assay for detection of group-A streptococci using monoclonal antibody and colloidal gold-monospecific polyvalent antibody conjugate.

A rapid one step, sensitive and specific antibody capture assay for detection of group-A streptococci from the throat swabs of children is described. Monoclonal antibody either MA-106 or MA-107 specific for group-A streptococci polysaccharide (APS) was used as the capture antibody on nitrocellulose paper and rabbit monospecific polyvalent antibody conjugated with colloidal gold to detect the presence of antigen. The lower detection limit of this assay is 15.6ng APS/ml. The assay is specific for APS and failed to recognize polysaccharides obtained from group-B,-C,-G streptococci as well as Staphylococcus aureus. Antigen extracted from throat swabs of children who were positive for beta-hemolytic plaques (other than group-A streptococci) as seen on blood agar culture gave negative readings, thereby confirming the specificity of the assay for APS.

Adolescent↗
PubMed1992

Analysis of the fibroblast transformation potential of GTPase-deficient gip2 oncogenes.

Expression of GTPase-deficient Gi2 alpha subunit (alpha i2) mutant polypeptides and overexpression of the wild-type alpha i2 polypeptide in Rat 1a, Swiss 3T3, and NIH 3T3 fibroblasts altered normal growth regulation and induced a loss of contact inhibition. In Rat 1a cells (but not in NIH 3T3 or Swiss 3T3 cells), expression of the GTPase-deficient alpha i2 mutant polypeptides allowed colony formation in soft agar, which correlated with a loss in anchorage dependence and a decreased serum requirement. The altered growth regulatory properties of Rat 1a cells induced by expression of alpha i2 mutant polypeptides was not significantly inhibited by cotransfection with a dominant negative Ha-ras mutant polypeptide (Asn-17rasH), indicating that the activated Gi2 membrane signal transduction protein is uniquely capable of altering the regulation of Rat 1a cell growth by a predominantly c-ras-independent mechanism. The results show that GTPase-deficient alpha i2 mutant polypeptides have the properties of an oncogene that can induce the phenotypic characteristics of transformation in Rat 1a cells but that only a subset of these changes is observed with NIH 3T3 and Swiss 3T3 cells.

3T3 Cells↗
PubMed1992

Failure of accentuated vertical body movements to induce cardiac-locomotor coupling.

Cardiac-locomotor coupling (CLC) has been reported during a variety of rhythmic human activities. One reason postulated for such coupling is that axial movements of the viscera during some activities (the "visceral piston") may enhance expulsion of blood from the heart; if so, accentuated vertical movements of the body should provide a powerful stimulus to coupling. To test this hypothesis, we studied 20 subjects hopping and 20 others skipping rope for greater than or equal to 10 min while electrocardiographic and force-platform signals were recorded, from which we derived the subjects' exercise and heart rates. The incidence and intensity of apparent coupling in the test subjects were compared with those of cross-over controls, where the heart rate of each subject was related to the hopping or skipping rate of a matched subject. Ratios consistent with coupling were seen in 10 (50%) hopping subjects under test conditions and in 13 (65%) under control conditions; among skipping subjects, the incidences were 11 (55%) and 10 (50%). In neither group of subjects was the difference in the incidences or the intensities of apparent CLC statistically significant. Our failure to detect CLC while our subjects were hopping or skipping suggests that the visceral piston is unimportant to the CLC phenomenon.

Adult↗
PubMed1992

Macrodystrophia lipomatosa: radiographic observations.

23 cases of macrodystrophia lipomatosa (MDL) are reported showing a wide spectrum of radiographic findings. Typical findings were hypertrophy of all the mesodermal tissues of the affected digits with dramatic overgrowth of fat. Phalanges were enlarged both in length and transverse diameter, but the trabecular pattern was maintained. In one patient, the phalanges and metatarsals were elongated but thinned. In another case, all the phalanges and metatarsals of the great toe were small. The little toe was also involved in two cases. Articular surfaces were slanting. There was a high incidence of palmar and plantar involvement. In a few cases the forearm and leg were also involved. Other uncommon features observed were early maturation of epiphyseal centres of ossification of phalanges and metatarsals, syndactyly, polydactyly, brachydactyly and symphalangism. Angiography was uncharacteristic.

Adolescent↗