PubMed Health⌕ Search

Biomedical subjects

R Mittal

Publications and source records attributed to R Mittal.

At least 55 records · Page 3Linked to original sources
PubMed1996

Formation of a transition-state analog of the Ras GTPase reaction by Ras-GDP, tetrafluoroaluminate, and GTPase-activating proteins.

Unlike the alpha subunits of heterotrimeric guanosine triphosphate (GTP)-binding proteins, Ras-related GTP-binding proteins have hitherto been considered not to bind or become activated by tetrafluoroaluminate (AIF4-). However, the product of the proto-oncogene ras in its guanosine diphosphate (GDP)-bound form interacted with AIF4 - in the presence of stoichiometric amounts of either of the guanosine triphosphatase (GTPase)-activating proteins (GAPs) p120GAP and neurofibromin. Neither oncogenic Ras nor a GAP mutant without catalytic activity produced such a complex. Together with the finding that the Ras-binding domain of the protein kinase c-Raf, whose binding site on Ras overlaps that of the GAPs, did not induce formation of such a complex, this result suggests that GAP and neurofibromin stabilize the transition state of the GTPase reaction of Ras.

Aluminum Compounds↗
PubMed1996

Uncoupling of GTP binding from target stimulation by a single mutation in the transducin alpha subunit.

Glutamic acid-203 of the alpha subunit of transducin (alphaT) resides within a domain that undergoes a guanosine triphosphate (GTP)-induced conformational change that is essential for effector recognition. Changing the glutamic acid to an alanine in bovine alpha(T) yielded an alpha subunit (alpha(T)E203A) that was fully dependent on rhodopsin for GTP-guanosine diphosphate (GDP) exchange and showed GTP hydrolytic activity similar to that measured for wild-type alpha(T). However, unlike the wild-type protein, the GDP-bound form of alpha(T)E203A was constitutively active toward the effector of transducin, the cyclic guanosine monophosphate phosphodiesterase. Thus, the alpha(T)E203A mutant represents a short-circuited protein switch that no longer requires GTP for the activation of the effector target phosphodiesterase.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1996

Post transplant diabetes mellitus in live related renal allograft recipients: a single centre experience.

The incidence of post-transplant diabetes mellitus (PTDM) was evaluated in 250 patients who underwent live-related renal transplantation at our hospital between 1978 and 1992. Twelve (4.8%) patients developed PTDM requiring drug therapy. PTDM occurred in 4 of 197 (2%) patients on conventional prednisolone-azathioprine immunosuppression as compared to 8 of 53 (15.1%) patients receiving cyclosporine in addition (triple-therapy). Three patients (25%) developed PTDM during or immediately following anti-rejection therapy with intravenous methylprednisolone. Eight patients (66.6%) developed PTDM within six months of transplantation. Majority of our patients (66.6%) could be managed successfully with oral hypoglycemic agents. Two patients (16.6%) showed spontaneous resolution of hyperglycemia within six months of onset of PTDM. Eleven patients (91.6%) were symptomatic for their hyperglycemia with two patients presenting as 'pseudorejection' and one with diabetic ketoacidosis. Females were more predisposed to develop PTDM in our study (10% vs. 4.1%). HLA-B15 and DR 3 were the commonest phenotypes in our PTDM patients. No other known predisposing or triggering factors associated with PTDM were found in our patients. The current study suggests, that addition of cyclosporine to the conventional immunosuppression in live-related renal allograft recipients has contributed to an increased incidence of post-transplant diabetes mellitus. Close and regular blood sugar monitoring is thus recommended in post-transplant patients especially those on triple drug immunosuppression.

Adult↗
PubMed1995

Use of resonance energy transfer to determine the proximity of the guanine nucleotide binding site of transducin relative to a conformationally-sensitive site on the gamma subunit of the cyclic GMP phosphodiesterase.

In this work, we have used resonance energy transfer to determine the relative positions of a reactive cysteine residue on the gamma subunit of the retinal cyclic GMP phosphodiesterase (gamma PDE) and a reactive lysine residue on the alpha subunit of transducin (alpha T). The single cysteine residue on gamma PDE (residue 68) is located at a site that is sensitive to the binding of both the inactive and active forms of alpha T. This is demonstrated by the finding that the addition of an alpha T-GDP complex to a gamma PDE subunit labeled with the environmentally-sensitive probe 2-(4-maleimidoanilino)naphthalene-6-sulfonate (MIANS) results in an enhancement in the MIANS fluorescence. The alpha TGDP-induced fluorescence enhancement is dose-dependent and yields an apparent Kd value of approximately 3 microM. Activation of alpha TGDP by aluminum fluoride, when bound to the MIANS-labeled gamma PDE (M-gamma PDE), then results in a quenching of the MIANS fluorescence. The aluminum fluoride-induced change in M-gamma PDE fluorescence occurs on a time scale identical to that observed for changes in the intrinsic alpha T fluorescence that correspond to activating conformational changes in the alpha T "switch II" region. These results suggest that the induction of the activated state of the alpha T subunit results in a change in conformation close to cysteine 68 in gamma PDE.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1995

Clinical profile and course and outcome of late acute rejection episodes in living-related-donor renal allograft recipients.

We prospectively monitored clinical data and renal function at monthly intervals in 165 patients who had received living-related-donor renal allografts in our institution between January 1981 and December 1991 and had a functioning allograft for 1 year or longer. During a mean follow-up period of 47.2 (range 13-155) months, 32 patients (17.2%) developed late acute rejections, of which 14 (43.7%) were asymptomatic. Amongst the symptomatic late acute rejections, worsening of hypertension was the commonest finding, being present in 11 (61.1%) patients, followed by oliguria in 8 (44.4%) and weight gain in 7 (38.8%) patients. Of these 32 late acute rejections, as many as 28 (87.5%) showed a response to antirejection therapy with high-dose steroids: 5 (15.6%) a complete response and 23 (71.9%) a partial response. The response rate was 100% if it was the first acute rejection (20% complete and 80% partial), 78.6% if it was the second (14.3% complete and 64.3% partial), and no or only a partial response to treatment if it was the third acute rejection episode. On long-term follow-up, patients who had responded to to antirejection treatment had a significantly better graft survival as compared with nonresponding patients: 76 and 27%, respectively. Our observations suggest that routine monitoring of the renal function at frequent intervals is essential for early diagnosis and treatment of acute rejections, even during the late posttransplant period. The chances of a response to antirejection therapy are higher during the first episode of late acute transplant rejection as compared with second or a third late rejection event.

Acute Disease↗
PubMed1994

Aluminum fluoride activation of bovine transducin induces two distinct conformational changes in the alpha subunit.

We have used resonance energy transfer to read out the interactions of the alpha subunit of transducin (alpha T) with the transducin beta gamma subunit complex (beta gamma T) and to compare the rate of aluminum fluoride-induced alpha T activation, as reflected by the enhancement of the alpha T tryptophan fluorescence, with the rate for the dissociation of holotransducin into its component subunits. Specifically, a beta gamma T complex that was labeled with 5-(iodoacetamido)fluorescein (IAF-beta gamma T) served as a donor for resonance energy transfer and an alpha T-GDP species labeled with eosin 5-isothiocyanate (EITC-alpha TGDP) served as the acceptor. The quenching of IAF-beta gamma T fluorescence emission by the addition of the EITC-alpha TGDP species, due to resonance energy transfer between the IAF and EITC moieities, ranged from 10% to 15%. The association of the transducin subunits was rapid (i.e., within the time period of mixing) and dose-dependent, yielding an apparent Kd of approximately 150 nM for the alpha TGDP/beta gamma T interaction. Unexpectedly, we find that the dissociation of IAF-beta gamma T from an aluminum fluoride-activated alpha TGDP/IAF-beta gamma T complex occurs prior to the onset of the intrinsic fluorescence changes in alpha T that accompany activation of this subunit. Thus, there are at least two structural changes in alpha T that result from the occupation of the gamma-phosphate position in the nucleotide binding cleft of alpha T by aluminum fluoride.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Compounds↗
PubMed1994

Role of steroid hormones in potentiating transformation of cervical cells by human papillomaviruses.

Human papillomaviruses (HPVs) are etiologically involved in cervical neoplasia, and epidemiological evidence suggests that steroid hormones can increase the risk of this cancer in HPV-infected women. Steroids can interact with hormone-response elements in the viral long control region, enhancing HPV transcription and resulting in transformation of cervical cells. Subsequent malignant progression may involve virus-induced chromosomal instability, facilitating viral DNA integration and deregulation of gene expression.

Animals↗
PubMed1994

Differential regulation by c-jun and c-fos protooncogenes of hormone response from composite glucocorticoid response element in human papilloma virus type 16 regulatory region.

Glucocorticoid hormones positively regulate human papilloma virus (HPV) type 16 gene expression, and we have previously shown that this regulation is through three glucocorticoid response elements (GREs). The GRE at nucleotide 7640 is a composite GRE (cGRE) containing an overlapping activator protein-1 (AP-1) motif for the c-jun homodimer and c-jun/c-fos heterodimer. This report examined the effects of c-jun and/or c-fos AP-1 protooncogenes and the glucocorticoid hormone dexamethasone on expression of the HPV 16 cGRE in AP-1-deficient P19 embryonal carcinoma cells. The activity of the full-length HPV 16 enhancer was progressively increased with increasing levels of c-jun. The hormone induced an additional response. For the c-jun/c-fos heterodimer, the response to hormone was progressively diminished. Site-specific mutations of the cGRE revealed that the regulation by AP-1 and hormone required both GRE and the AP-1 motif. An enhancer fragment containing the cGRE and excluding the two simple GREs gave similar results. Two disruption mutations of the AP-1 site confirmed the requirement of this site for hormone response. A cGRE oligonucleotide construct substantiated the effect of c-jun for response to hormone. For heterodimer, activity and hormone response were both also progressively increased. The results reveal a unique cross-talk between the distinct AP-1- and hormone-signaling pathways, suggesting the involvement of a complex interaction of c-jun and c-fos and glucocorticoid hormone receptor with the HPV 16 cGRE, resulting in novel control patterns for regulating viral expression.

Animals↗
PubMed1993

Multiple human papillomavirus type 16 glucocorticoid response elements functional for transformation, transient expression, and DNA-protein interactions.

We have previously shown that human papillomavirus type 16 (HPV-16) can efficiently transform primary baby rat kidney cells in the presence of the steroid hormones progesterone and the glucocorticoid dexamethasone. To study this effect of hormone, different combinations of the previously identified glucocorticoid response element (GRE) at nucleotide 7640 of HPV-16 and the other two GREs that we have recently identified, at nucleotides 7385 and 7474, were mutated. The previously described GRE and the other two GREs were shown to be functional for the induction of transformation by dexamethasone. In addition, transient assays in cervical HeLa cells demonstrated the functional importance of the three individual GREs. Assays for in vitro interaction demonstrated the specific binding of a 97-kDa protein, the glucocorticoid receptor, to both recently identified HPV-16 GREs.

Animals↗