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M V Kumar

Publications and source records attributed to M V Kumar.

At least 37 records · Page 2Linked to original sources
PubMed1994

The mouse androgen receptor gene contains a second functional promoter which is regulated by dihydrotestosterone.

The androgen receptor (AR) is a developmental and tissue-specific transcription factor which is activated by binding testosterone or dihydrotestosterone. Several different methods of transcriptional regulation of the AR have been shown, including regulation by androgens, follicle-stimulating hormone, epidermal growth factor, and the cAMP pathway. In order to further characterize the transcriptional regulation of the AR, portions of the mouse androgen receptor (mAR) promoter were cloned into the promoterless pBLCAT3 vector and assayed for chloramphenicol acetyltransferase activity. The results indicate that in addition to the previously characterized promoter (+1) there is a second distinct promoter located 3' to the first promoter. Amplification of the 5'-end of the AR gene indicates that RNA originating from the second promoter is initiated from 162 and 170 bases downstream from the 5'-most previously characterized site. Northern blot analysis indicated that RNA initiated from the two promoters is differentially expressed in several cell lines and multiple tissues. Androgen ablation by castration showed that both promoters are controlled by androgens in the kidney. Sequence analysis revealed that the second promoter does not contain a TATA or CAAT box. Further characterization of this promoter may provide important insights into the transcriptional regulation of the androgen receptor since previous studies have often included only the first promoter.

Animals↗
PubMed1994

Identification and characterization of a suppressor element in the 5'-flanking region of the mouse androgen receptor gene.

Androgens play an important role in the development and maintenance of male reproductive organs through the androgen receptor (AR). In order to study the mechanism of regulation of AR at the molecular level, a 1571 bp fragment in the 5'-flanking region of the mouse androgen receptor (mAR) gene was isolated and sequenced. Transfection of 5'-deletion constructs cloned into vectors containing the chloramphenicol acetyl transferase (CAT) gene indicated the presence of a promoter in the sequence -146 to +131. These experiments also suggested the presence of a suppressor element. Further characterization indicated that the suppressor is present between -486 to -351. It is functional in the context of the natural AR promoter and the heterologous thymidine kinase promoter. Transfection of a -546/ + 131 construct in which the putative suppressor element (-421 to -448) had been deleted caused increased basal CAT activity suggesting that the suppressor is limited to this 28 bp element in the 5'-flanking region of the mouse AR gene.

Animals↗
PubMed1994

Molecular mechanisms of androgen action.

Androgens directly regulate a vast number of physiological events. These direct androgen effects are mediated by a nuclear receptor that exhibits four major functions or activities: steroid binding, DNA binding, transactivation, and nuclear localization. The SBD consists of a hydrophobic pocket of amino acids that exhibits high-affinity, androgen-specific binding. Based on studies of mutant AR, it appears that a number of different amino acids contribute to the steroid binding characteristics of the AR. The DNA binding domain confers sequence-specific binding to structures called androgen-responsive elements. The specificity of steroid binding and DNA binding provides a crucial basis for androgen-specific regulation of target genes. The nuclear localization signal shares homology with known nuclear localization signals and, coupled with the presence of androgens, is responsible for localizing the AR to the nucleus. The transactivation functions reside mostly in the NH2 terminus but the responsible domains are as yet poorly defined. Though the different domains can act as independent moieties, one domain can clearly alter the behavior of another domain. For instance, the SBD appears to inhibit the transactivating functions until steroid is bound and the amino terminus prevents DNA binding activity until steroid is bound. The relative ease of introducing mutations with polymerase chain reaction technology will facilitate further delineation of critical amino acids and domains responsible for the various activities of the AR. The recent cloning and characterization of AR promoters revealed that the AR genes are driven by a TATA-less promoter characteristics of housekeeping genes. Analysis of transcription rates, mRNA levels, and protein levels indicates that androgens and pkA and pkC pathways modulate expression of AR mRNA and protein. This indicates that the same signal pathways that interact to regulate androgen target genes also regulate the levels of AR in the target tissues. Surprisingly few androgen-regulated genes have been well characterized for the mechanisms by which androgen regulates the gene. The C(3), Slp, probasin, PSA, and hKLK2 genes have provided examples where androgens regulate transcription. Posttranscriptional regulation by androgens has been demonstrated for the SVP1, 2, 3, and 4 and AR genes. The mechanisms underlying posttranscriptional regulation are poorly defined but substantial progress has been made in defining the critical elements that mediate transcriptional effects of androgens. Transcriptional effects are mediated through binding of androgen-AR complexes to specific DNA sequences called AREs. Simple AREs such as those found in C(3) and kallikrein genes tend to be permissive in that GR and PR can also act through the same element.(ABSTRACT TRUNCATED AT 400 WORDS)

Androgens↗
PubMed1994

Cerebrovascular disease in children.

Stroke although rare in children, is an important cause of morbidity in the paediatric age group. Over a period of 8 years, 43 children (17 boys and 26 girls) in the age groups of 1-16 years (mean 8.02 yrs) presented with stroke which constituted 10% of all strokes in the young and 0.7% of all paediatric admissions. The chief clinical features were hemiplegia (86%), convulsions (27%), fever (23%), dysphasia (23%), headache (11%) and altered level of consciousness (11%). Routine laboratory tests were non-contributory. Cranial computerized tomography (CCT) on 21 patients was abnormal in 95% and was useful in revealing the extent of infarction. Infarction was confined to middle cerebral artery territory, often involving basal ganglionic structures and was associated with focal or diffuse atrophy. Angiograms were abnormal in 78% of the patients (18/23) and were complimentary to the CCT. Etiological factors identified were: Moya-moya disease 6, arteritis 5, fibromuscular dysplasia 2, scorpion sting 2, and venous sinus thrombosis and small vessel occlusion one each. Though 23% of the patients had fever at onset, no obvious evidence of systemic or CNS infection was noticed. Stroke in children continues to pose a diagnostic challenge.

Adolescent↗
PubMed1994

The mouse androgen receptor is suppressed by the 5'-untranslated region of the gene.

The androgen receptor (AR) mediates the biological functions of androgens and is essential for normal growth and differentiation of urogenital organs as well as initiation and maintenance of spermatogenesis. Withdrawal of androgens by castration or other methods has been shown to cause a marked, although often temporary, regression of many prostate cancers. In order to gain a better understanding of the transcriptional regulation of the AR, a series of truncation mutants derived from the 5'-region of the mouse AR (mAR) were inserted into the promoter-less plasmid pBLCAT3 and transiently expressed in the mouse alpha T3-1 and GT1-7 cell lines. The results of these experiments indicate the presence of a negative regulatory element in the 5'-untranslated region of the gene, which is able to reduce chloramphenicol acetyltransferase (CAT) activity by 77-89%. We have named this element the mAR suppressor (mARS). DNase-I protection assays of the 5'-untranslated region disclosed a protected domain. Gel mobility assays using the mARS revealed the presence of three protein-DNA complexes that could specifically bind to this protected domain. Insertion of the mARS into the thymidine kinase promoter containing pBLCAT2 vector resulted in a 2- to 10-fold decrease in CAT activity, but only if the insert was 3' to the start of transcription initiation. Finally, point mutations within the mARS were able to increase transcription of the AR promoter by 2.3-fold. The results of these experiments indicate that the mAR 5'-untranslated region contains a suppressor element.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Bilateral scrotal urinary extravasation in a transplant recipient mimicking acute filariasis.

Urinary leak following renal transplantation is less common nowadays with better techniques. Bilateral scrotal extravasation following urinary leak is extremely rare. A history of filariasis in an endemic zone could mask and delay the diagnosis. One such case is described wherein ureteroneocystostomy was revised and the patient could be successfully managed following urinary leak.

Acute Disease↗
PubMed1994

The androgen receptor in the testicular feminized (Tfm) mouse may be a product of internal translation initiation.

Androgen insensitivity in the testicular feminized (Tfm) mouse is caused by frame-shift mutation in the androgen receptor (AR) mRNA, which results in a stop codon in the amino terminus. Despite this mutation, a smaller sized protein corresponding to the DNA- and steroid-binding domain of the AR can be synthesized from the cloned Tfm AR cDNA by in vitro translation. The Tfm AR construct was demonstrated to express a protein capable of binding androgen with an affinity similar to the cloned wild-type AR. Although the Tfm AR product failed to transactivate mouse mammary tumor virus-long terminal repeat (MMTV-LTR) promoter when low concentrations (100 ng) of Tfm AR vector were cotransfected, higher concentrations (5000 ng) resulted in a residual amount of transactivation, suggesting lower level transactivating capabilities. By cotransfecting the Tfm AR expression vector with the wild-type receptor, it was demonstrated that the product of the Tfm AR gene is capable of inhibiting the transactivation activity of the wild-type receptor. These data suggest that although the Tfm AR mRNA fails to produce a full-length AR because of the frame-shift mutation, a smaller protein capable of binding both steroid and DNA can be produced by translation from an internal initiation codon. This product could account for the low levels of androgen-binding activity detected previously in the Tfm mouse.

Androgen-Insensitivity Syndrome↗
PubMed1993

Left ventricular diastolic function in end-stage renal disease and the impact of hemodialysis.

Twenty-one patients (17 men and 4 women, aged 20 to 40 years) with end-stage renal disease (creatinine clearance persistently < 5 ml/min for > 3 months) were evaluated for left ventricular (LV) diastolic function by Doppler echocardiography before and after hemodialysis. Fifteen patients were on maintenance hemodialysis (group A) and 6 were studied before and after their first hemodialysis (group B). The following indexes of LV diastolic function were studied: (1) isovolumic relaxation time; and (2) Doppler indexes from mitral inflow signal--peak early velocity, peak late velocity (atrial), deceleration of early filling phase, and deceleration time of early filling phase. LV systolic function in groups A and B (LV ejection fraction 68 +/- 6 and 77 +/- 5%, fractional shortening 0.39 +/- 0.06 and 0.46 +/- 0.05%) was normal and did not change after hemodialysis. Group A had a prolonged isovolumic relaxation time of 80 +/- 22 ms, which decreased to 57 +/- 14 ms (p < 0.005). Deceleration time decreased from 248 +/- 58 to 184 +/- 38 ms (p < 0.00005) and the deceleration slope increased from 4.3 +/- 1.8 to 5.1 +/- 1.6 m/s2 (p < 0.005) after hemodialysis. In group B, isovolumic relaxation time decreased from 87 +/- 21 to 73 +/- 15 ms (p < 0.05), deceleration time decreased from 256 +/- 43 to 185 +/- 34 ms (p < 0.05), and deceleration slope increased from 3.5 +/- 0.8 to 4.2 +/- 1.1 m/s2 (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

The scapular fasciocutaneous flap: a new flap for reconstruction of the posterior neck.

The axial, myocutaneous and free flaps have made immediate reconstruction of head and neck defects possible. Notwithstanding this remarkable progress, defects of the posterior neck leave the reconstructive surgeon with very little choice. The scapular fasciocutaneous flap is easy to harvest, reliable and versatile, with functional and cosmetic results comparable to free flaps. We describe the anatomy and the technique of this new donor site, along with a case report.

Adult↗
PubMed1993

Variability of cardiovascular and plasma noradrenaline responses to sustained isometric contraction in normal human subjects.

1. Eight healthy adult males underwent three sustained isometric contractions at 30% of maximal voluntary contraction for 3 min, within a 9 day period. 2. The study focuses on the inter-individual and day-to-day intra-individual variability of cardiovascular and plasma noradrenaline responses to sustained isometric contraction. 3. The results of this study indicate that inter-individual variability is generally greater than intra-individual variability. Diastolic blood pressure was the most sensitive as well as the least variable cardiovascular parameter measured. 4. The variability of plasma noradrenaline levels in both the basal and the stimulated state was high. The present study suggests that it is preferable to determine the 'true' noradrenaline peak after the release of handgrip, as this is associated with a lower variability than the plasma noradrenaline peak taken at the time of the release of handgrip.

Adult↗
PubMed1993

Regulation of the 5'-flanking region of the mouse androgen receptor gene by cAMP and androgen.

Both androgens and cAMP-mediated hormones are known to regulate expression of the androgen receptor (AR) gene. In order to determine whether these effects occur at the transcriptional level, transfection studies were conducted with a 1.5-kilobase fragment of the 5'-flanking region of the mouse AR gene coupled to a chloramphenicol acetyltransferase (CAT) reporter gene. We demonstrated that the cAMP pathway regulates expression of the mouse AR (mAR) 5'-CAT construct in mouse pituitary (alpha T3-1), rat pituitary (GC), and quail fibroblast (QT6) cell lines. Deletional analysis indicated that several areas of this clone, including a region containing a putative cAMP response element (CRE), are involved in mediating cAMP regulation of the AR gene. Oligonucleotides containing a putative CRE, linked to the thymidine kinase promoter of pBLCAT2, conferred increased forskolin induction of CAT activity. Furthermore, overexpression of a CRE binding protein up-regulated expression of the mAR 5'-CAT constructs. Bandshift data demonstrated that the putative CRE forms specific, competable complexes with nuclear proteins from alpha T3-1 and QT6 cells. Additional experiments indicated that AR can modulate both basal and forskolin-induced CAT activity in an androgen-dependent fashion. These data provide evidence that the 5'-flanking region of the mAR gene contains sequences which mediate the effects of both cAMP and androgens.

1-Methyl-3-isobutylxanthine↗
PubMed1992

Value and limitations of Doppler echocardiographic determination of mitral valve area in Lutembacher syndrome.

OBJECTIVES: Our objective was to compare the Doppler pressure half-time, Doppler continuity equation and two-dimensional echocardiographic planimetric methods of estimating mitral valve area in Lutembacher syndrome. BACKGROUND: Fluid dynamics theory predicts that mitral pressure half-time varies inversely with mitral valve area and directly with net chamber compliance and the peak early diastolic transmitral gradient in pure mitral stenosis. The effects of an atrial shunt on these interrelations have not been investigated. METHODS: Correlation and agreement between mitral valve area estimates obtained by the three methods and that obtained by cardiac catheterization was ascertained in 11 patients with Lutembacher syndrome. RESULTS: Valve areas determined by planimetry and the continuity equation method correlated and agreed well with catheterization measurements (r = 0.83 and 0.81, respectively). The pressure half-time method consistently overestimated mitral valve area; the extent of overestimation was greater in patients with larger atrial shunts. The hemodynamic pressure half-time was independent of the mitral valve area, chamber compliance and the peak transmitral gradient. It was dependent on the magnitude of the atrial shunt, although the correlation obtained was only fair (r = 0.61). CONCLUSIONS: These findings suggest that the Doppler pressure half-time method is an inaccurate measure of mitral valve area whenever an atrial shunt coexists with mitral stenosis. Planimetry and the Doppler continuity equation methods yield accurate estimates of mitral valve area in Lutembacher syndrome.

Adolescent↗
PubMed1992

Effect of chronic consumption of methylparathion on rat brain regional acetylcholinesterase activity and on levels of biogenic amines.

Wistar rat pups (female) were exposed to methylparathion (MPTH) by gastric intubation in single doses, or in a chronic regimen of different durations. A single dose of 1 mg MPTH/kg body weight in 15-day-old pups caused a significant decrease of acetylcholinesterase (AChE) activity in cerebellum (CE), motor cortex (MC) and brain stem (BS). The effect began to appear in about 20 min after administration, the peak effect was attained in 120 min and later on this waned off completely by 24 h. The effect was similar in young (15 days) and in adult (70 days) rats. A single dose of 0.2 mg MPTH/kg in 15 day old pups caused a reduction of AChE activity only in the BS, while a 0.1 mg MPTH/kg single dose given to 15-day-old pups caused no effect even in seven regions of the brain examined. Effect of low dose chronic administration of MPTH on AChE activity was also studied in CE, MC, BS, hippocampus (HI), striatum-accumbens (SA), spinal cord (SC) and also in the hypothalamus (HY). Administration of 0.1 mg MPTH/kg from second day to 15 days of age caused significant reduction of AChE activity in only 2 of the 7 brain regions studied. Administration of double the dose (0.2 mg MPTH/kg) and for a longer duration (2nd day to 150 days of age), caused a depression in all the brain regions studied. In all these regions, the levels of NA, DA and 5HT did practically not change. The results suggest that chronic consumption of MPTH leads to a moderate decrease of AChE activity in several brain regions.

Acetylcholinesterase↗
PubMed1992

EEG spectral power reduction and learning disability in rats exposed to lead through postnatal developing age.

The present study was carried out to assess electrophysiological and behavioral changes in Wistar rats caused by consuming a daily dose of lead acetate (400 micrograms lead/g body weight/day, given by gastric intubation, from second day of birth to 60 days of age. At 60 days of age, the lead treated rats showed in both wakeful and slow wave sleep stages, a statistically significant reduction in the delta, theta, alpha and beta band EEG spectral power in motor cortex (MC) and hippocampus (HI) with the exception of the delta and beta bands power of MC in wakeful state (WA). Lead administration was discontinued after that age for allowing rehabilitation for 40 days. Then, operant behavioral assessment was done. Results revealed that the lead treated animals took significantly more time and sessions than control normal animals in attaining criterion of learning. Hence exposure to lead in early age could result in a learning disability persisting even after discontinuation of exposure.

Animals↗
PubMed1991

A frame-shift mutation in the androgen receptor gene causes complete androgen insensitivity in the testicular-feminized mouse.

The testicular feminized (Tfm) mouse lacks completely androgen responsiveness; and therefore, is unique for studying the role of androgenic steroids in different biological processes. In order to understand the molecular basis of this mutation, 2.8 kilobases of cDNA encoding the Tfm mouse androgen receptor (AR) were amplified with a polymerase chain reaction (PCR) technique. No large deletion in the coding region of the Tfm mouse AR was detected. However, sequence analysis revealed a single base deletion in the coding region of the Tfm AR mRNA. This mutation, which is located in the amino-terminus domain of the receptor, is predicted to cause a frame-shift in translation resulting in a premature termination of AR synthesis at amino acid 412. In vitro translation studies of the recombinant wild type and Tfm AR's demonstrated that the Tfm AR cDNA failed to produce a full-length receptor. Furthermore, the Tfm AR was demonstrated to lack transcriptional activation capability by cotransfection experiments using the Tfm AR with a reporter plasmid of mouse mammary tumor virus long terminal repeat linked to the chloramphenicol acetyltransferase gene. These studies provide evidence of the molecular defect which causes androgen insensitivity in the Tfm mouse.

Amino Acid Sequence↗
PubMed1991

Variability in cardiovascular and plasma norepinephrine responses to head-up tilt in healthy human subjects.

Eight healthy, young adult males underwent three separate, 10-min 70 degrees head-up tilts (HUT) over a period of nine days, in order to assess the intra- and inter-individual variability of cardiovascular and plasma norepinephrine (NE) responses to the manoeuvre. Cardiovascular parameters and plasma NE were measured in the basal state and at 2-min intervals during the HUT. The results indicate that: (1) the intra-individual variability is a smaller component of the total variability of both cardiovascular and plasma NE responses to HUT; (2) the variability in cardiovascular parameters is smaller than that in plasma NE levels, both basal and in response to postural stress; (3) there does not appear to be any difference in variability when expressed either as the maximal or the mean response to HUT; and (4) there does not appear to be an increase in the variability of the measured parameters over the duration of the HUT.

Adult↗