Publications by authors named "Nisha E Thomas"

4 Publications

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Reversible action of diaminothiazoles in cancer cells is implicated by the induction of a fast conformational change of tubulin and suppression of microtubule dynamics.

Mol Cancer Ther 2014 Jan 5;13(1):179-89. Epub 2013 Nov 5.

Corresponding Author: Suparna Sengupta, Division of Cancer Research, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram 695014, India.

Diaminothiazoles are novel cytotoxic compounds that have shown efficacy toward different cancer cell lines. They show potent antimitotic and antiangiogenic activity upon binding to the colchicine-binding site of tubulin. However, the mechanism of action of diaminothiazoles at the molecular level is not known. Here, we show a reversible binding to tubulin with a fast conformational change that allows the lead diaminothiazole DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino)thiazole] to cause a reversible mitotic block. DAT1 also suppresses microtubule dynamic instability at much lower concentration than its IC(50) value in cancer cells. Both growth and shortening events were reduced by DAT1 in a concentration-dependent way. Colchicine, the long-studied tubulin-binding drug, has previously failed in the treatment of cancer due to its toxicity, even though it generates a strong apoptotic response. The toxicity is attributable to its slow removal from the cell due to irreversible tubulin binding caused by a slow conformational change. DAT1 binds to tubulin at an optimal pH lower than colchicine. Tubulin conformational studies showed that the binding environments of DAT1 and colchicine are different. Molecular dynamic simulations showed a difference in the number of H-bonding interactions that accounts for the different pH optima. This study gives an insight of the action of compounds targeting tubulin's colchicine-binding site, as many such compounds have entered into clinical trials recently.
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http://dx.doi.org/10.1158/1535-7163.MCT-13-0479DOI Listing
January 2014

Fodrin in centrosomes: implication of a role of fodrin in the transport of gamma-tubulin complex in brain.

PLoS One 2013 1;8(10):e76613. Epub 2013 Oct 1.

Cancer Research Programme III, Rajiv Gandhi Centre for Biotechnology, Thiruvanantha-puram, Kerala, India.

Gamma-tubulin is the major protein involved in the nucleation of microtubules from centrosomes in eukaryotic cells. It is present in both cytoplasm and centrosome. However, before centrosome maturation prior to mitosis, gamma-tubulin concentration increases dramatically in the centrosome, the mechanism of which is not known. Earlier it was reported that cytoplasmic gamma-tubulin complex isolated from goat brain contains non-erythroid spectrin/fodrin. The major role of erythroid spectrin is to help in the membrane organisation and integrity. However, fodrin or non-erythroid spectrin has a distinct pattern of localisation in brain cells and evidently some special functions over its erythroid counterpart. In this study, we show that fodrin and γ-tubulin are present together in both the cytoplasm and centrosomes in all brain cells except differentiated neurons and astrocytes. Immunoprecipitation studies in purified centrosomes from brain tissue and brain cell lines confirm that fodrin and γ-tubulin interact with each other in centrosomes. Fodrin dissociates from centrosome just after the onset of mitosis, when the concentration of γ-tubulin attains a maximum at centrosomes. Further it is observed that the interaction between fodrin and γ-tubulin in the centrosome is dependent on actin as depolymerisation of microfilaments stops fodrin localization. Image analysis revealed that γ-tubulin concentration also decreased drastically in the centrosome under this condition. This indicates towards a role of fodrin as a regulatory transporter of γ-tubulin to the centrosomes for normal progression of mitosis.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0076613PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3788121PMC
April 2014

Cytoplasmic gamma-tubulin complex from brain contains nonerythroid spectrin.

J Cell Biochem 2010 Aug;110(6):1334-41

Cytoskeleton Research Laboratory, Division of Cancer Research, Rajiv Gandhi Centre for Biotechnology, Trivandrum 695014, India.

The newer member of the tubulin superfamily, gamma-tubulin, is known to mediate microtubule nucleation from the centrosome of eukaryotic cells with the aid of some other proteins. The major amount of gamma-tubulin is believed to be located in the centrosome before the onset of mitotic division. However, a considerable amount has been found in the cytoplasm in the form of a complex whose function is not well known. Microtubules are most abundant in brain tissues and brain microtubules have been extensively used in many in vitro studies. Thus, it is relevant to use brain tissue to characterize cytoplasmic gamma-tubulin complex. Here we show that cytoplasmic gamma-tubulin in brain tissues exists as a ring complex as in other tissues. Interestingly, along with the common members of the gamma-TuRC reported from several tissues and species, the purified brain cytoplasmic complex contains some high molecular weight proteins including alpha and beta nonerythroid spectrin which are not found in other tissues. Immunohistochemical studies of brain tissue sections also show the co-localization of gamma-tubulin and spectrin. The possible implications have been discussed.
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http://dx.doi.org/10.1002/jcb.22647DOI Listing
August 2010

4-Amino-5-benzoyl-2-(4-methoxyphenylamino)thiazole (DAT1): a cytotoxic agent towards cancer cells and a probe for tubulin-microtubule system.

Br J Pharmacol 2005 Aug;145(8):1076-83

Department of Biophysical Chemistry, Rajiv Gandhi Centre for Biotechnology, Trivandrum 695014, India.

Microtubule binding drugs are of special interest as they have important roles in the modulation of cellular functions and many of them act as anticancer agents. 4-Amino-5-benzoyl-2-(4-methoxyphenylamino)thiazole (DAT1) was identified as one of the active compounds from a series of diaminoketothiazoles in a cell-based screening assay to discover cytotoxic compounds. DAT1 shows cytotoxicity with GI(50) values ranging from 0.05 to 1 microM in different malignant cell lines with an average value of 0.35 microM. It blocks mitosis in the prometaphase and metaphase stages. In HeLa cells, DAT1 blocks the spindle function by disturbing spindle microtubule and chromosome organization. The drug also inhibits assembly of brain microtubules and binds tubulin specifically at a single site with induction of fluorescence. The dissociation constant of DAT1 binding to tubulin was determined as 2.9+/-1 microM at 24 degrees C. The binding site of DAT1 on tubulin overlaps with that of the conventional colchicine-binding site. DAT1 can thus be considered as a lead compound of a new class of small molecules and this study can be used as a step to develop potent antimitotic agents for the control of cytoskeletal functions and cell proliferation. It would also be an interesting probe for the structure-function studies of tubulin-microtubule system.
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http://dx.doi.org/10.1038/sj.bjp.0706276DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1576226PMC
August 2005
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