Biomedical subjects
Sunita Gupta
Publications and source records attributed to Sunita Gupta.
Fixed drug eruption caused by ornidazole.
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Inducible, reversible, and stable RNA interference in mammalian cells.
RNA interference is a powerful genetic approach for efficiently silencing target genes. The existing method of gene suppression by the constitutive expression of short hairpin RNAs (shRNAs) allows analysis of the consequences of stably silencing genes but limits the analysis of genes essential for cell survival, cell cycle regulation, and cell development. We have developed an inducible U6 promoter for synthesis of shRNAs in both human and murine cells. Cells containing stably integrated shRNA expression constructs demonstrate stringent dosage- and time-dependent kinetics of induction with undetectable background expression in the absence of the inducer ecdysone. Inducible suppression of human p53 in glioblastoma cells shows striking morphological changes and defects in cell cycle arrest caused by DNA damage, as expected. Remarkably, the inducibility is reversible after withdrawal of the inducer, as observed by reappearance of the protein and a restoration of the original cell phenotype. Inducible and reversible regulation of RNA interference has broad applications in the areas of mammalian genetics and molecular therapeutics.
The tumor suppressor interferon regulatory factor 1 interferes with SP1 activation to repress the human CDK2 promoter.
Cell growth control by interferons (IFNs) involves up-regulation of the tumor suppressor interferon regulatory factor 1 (IRF1). To exert its anti-proliferative effects, this factor must ultimately control transcription of several key genes that regulate cell cycle progression. Here we show that the G1/S phase-related cyclin-dependent kinase 2 (CDK2) gene is a novel proliferation-related downstream target of IRF1. We find that IRF1, but not IRF2, IRF3, or IRF7, selectively represses CDK2 gene transcription in a dose- and time-dependent manner. We delineate the IRF1-responsive repressor element between nt -68 to -31 of the CDK2 promoter. For comparison, the tumor suppressor p53 represses CDK2 promoter activity independently of IRF1 through sequences upstream of nt -68, and the CDP/cut/Cux1 homeodomain protein represses transcription down-stream of -31. Thus, IRF1 repression represents one of three distinct mechanisms to attenuate CDK2 levels. The -68/-31 segment lacks a canonical IRF responsive element but contains a single SP1 binding site. Mutation of this element abrogates SP1-dependent enhancement of CDK2 promoter activity as expected but also abolishes IRF1-mediated repression. Forced elevation of SP1 levels increases endogenous CDK2 levels, whereas IRF1 reduces both endogenous SP1 and CDK2 protein levels. Hence, IRF1 represses CDK2 gene expression by interfering with SP1-dependent transcriptional activation. Our findings establish a causal series of events that functionally connect the anti-proliferative effects of interferons with the IRF1-dependent suppression of the CDK2 gene, which encodes a key regulator of the G1/S phase transition.
Topological modelling of analgesia.
Analgesic activity (log IC) of a large series of 97 analgesics was modelled topologically using a series of distance-based topological indices. The results show that analgesic activity (log IC) exhibit inter familial correlation and these can only be modelled by splitting 97 analgesics into five different categories. The regression analyses of the data show that the Wiener (W)-, Branching (B)- and first-order connectivity (chi)- indices are the better topological indices for modelling the activity (log IC), and that W index gave the excellent results.
Tumor suppressor pRB functions as a co-repressor of the CCAAT displacement protein (CDP/cut) to regulate cell cycle controlled histone H4 transcription.
The CCAAT displacement protein (CDP-cut/CUTL1/cux) performs a key proliferation-related function as the DNA binding subunit of the cell cycle controlled HiNF-D complex. HiNF-D interacts with all five classes (H1, H2A, H2B, H3, and H4) of the cell-cycle dependent histone genes, which are transcriptionally and coordinately activated at the G(1)/S phase transition independent of E2F. The tumor suppressor pRB/p105 is an intrinsic component of the HiNF-D complex. However, the molecular interactions that enable CDP and pRB to form a complex and thus convey cell growth regulatory information onto histone gene promoters must be further defined. Using transient transfections, we show that CDP represses the H4 gene promoter and that pRB functions with CDP as a co-repressor. Direct physical interaction between CDP and pRB was observed in glutathione-S-transferase (GST) pull-down assays. Furthermore, interactions between these proteins were established by yeast and mammalian two-hybrid experiments and co-immunoprecipitation assays. Confocal microscopy shows that subsets of each protein are co-localized in situ. Using a series of pRB mutants, we find that the CDP/pRB interaction, similar to the E2F/pRB interaction, utilizes the A/B large pocket (LP) of pRB. Thus, several converging lines of evidence indicate that complexes between CDP and pRB repress cell cycle regulated histone gene promoters.
Maxillary odontogenic myxoma: a diagnostic pitfall on aspiration cytology.
A painless, slow-growing cheek swelling in a young male clinically considered a salivary gland mass was aspirated. Cytology smears were hypocellular. The striking feature was abundant myxoid material with a few monomorphic oval cells, interpreted as myxoid variant of pleomorphic adenoma. Subsequent CT scan was suggestive of a malignant tumor but biopsy confirmed it as myxoma. Myxoma of the jaw is a rare benign tumor that has a tendency for bone destruction, invasion into surrounding structures, and a relatively high recurrence rate. Maxillary myxoma is less frequent but behaves more aggressively than in the mandible, as it spreads through the maxillary sinus. Cytologically, it should be differentiated from other tumors showing predominant myxoid change. Awareness of potential diagnostic pitfalls and careful evaluation of clinical and radiological data is necessary to narrow the differential diagnosis.
Oral fixed drug eruption due to fluconazole.
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