Biomedical subjects

S C Kaul

Publications and source records attributed to S C Kaul.

61 records · Page 4Linked to original sources

PubMed1991

Effect of heat shock on growth and division of Stylonychia mytilus.

Stylonychia mytilus cells grown at 23 degrees C exhibit an immediate arrest at G1 and S stages in the cell cycle when subjected to a heat shock of 1 h at 35 degrees C. The duration of arrest was seen to be dependent on the stage at which heat shock was given. It varied from 3 to 7 h and was synchronously accompanied by the delay in the completion of cell cycle. G2 and the early dividing stage D1 were found to be even more sensitive to heat shock than G1 and S phases. Cells divide normally when heat shock was given at the late dividing stage D2. However, the G1 stage of progeny cells was prolonged to 30 h from normal 5.5 h. These observations have been compiled from the cytological studies of normal and heat-shocked Stylonychia mytilus cells at different stages of cell cycle.

Animals↗

PubMed1991

Heat shock induced ultrastructural alterations in Stylonychia mytilus cells.

Fine structural observations on heat shocked cells of S. mytilus reveal that cell organelles undergo structural alterations. Mitochondria show distorted shapes with disorganized cristae and vacuolar spaces. Pulse heat shock results in dilated rough endoplasmic reticulum, abundant polysomes as well as smooth endoplasmic reticulum. Heat shocked cells show membrane bound bodies containing osmiophilic cores. In macronuclei, dense chromatin breaks up into discrete bodies accompanied by the appearance of bundles of fine filaments and clustering of nuclear pores. The most prominent changes are noticed in nucleoli. Within 15 min of heat shock, nucleoli show hypertrophy and fine fibrillar zone which gradually replaces the granular zone by 120 min giving the nucleoli ring shaped configuration. In S phase cells, macronuclei show the arrested replication band in which the diffused zone (the site of DNA replication) is absent.

Animals↗

PubMed1990

Do heat shock proteins provide protection against freezing?

Yeast cells were frozen by plunging directly into liquid nitrogen (LN2) after exposure at 43 degrees C. Both the cells frozen without prior exposure to heat shock and those treated with cycloheximide showed almost 100% loss of viability during freezing and thawing. Heat exposure prior to freezing and thawing significantly increased the cell viability. This increase in cell viability was associated with the induction of heat shock protein synthesis, which was detected by gel electrophoresis. This protein may act by stabilizing the macromolecules and by increasing the hydrophobic interactions.

Cycloheximide↗

PubMedDate not supplied

Protein markers for cellular mortality and immortality.

Fixed mortality of normal somatic cells is a well-established fact though the mechanism underlying this universal phenomenon remains unknown. Use of immortal cells in conjunction with their normal mortal counterparts has delineated the dominant genetic nature of the senescent phenotype over immortalization. Although the involvement of proteins in determining the entry/exit/arrest of cells in the cell cycle is evident from the literature, none of them has been confirmed for its role in senescence-associated irreversible cell cycle exit/arrest. The identification of true mortality markers might be possible by selecting a system of natural and conditional aging achieved by the fusion of mortal and spontaneously immortalized cells of the same origin. We report here a few such protein markers which might serve as useful handles to tease out the molecular events determining mortality/immortality of cultured cells.

Animals↗

PubMedDate not supplied

Expression of endothelin, fibronectin, and mortalin as aging and mortality markers.

Studies on fibronectin, endothelin-1, and mortalin from our laboratory are reviewed here. Fibronectin expression has been analyzed as upregulated during in vitro serial passaging of human fetal lung and neonatal foreskin fibroblasts as well as umbilical vein endothelial cells. In vivo aging of skin fibroblasts, as well as aortic endothelial cells, are also accompanied by upregulation of fibronectin expression. Fibronectin promoter binding proteins from young and old cell nuclear extracts were further explored by gel retardation assay. Preliminary analyses have detected age-related differential binding activities with respect to AP-1, CRES, TFIID, CTF, and AP-2 regions, whereas Sp1 binding proteins remain unaltered. Endothelin-1 expression is also seen as upregulated during in vitro and in vivo aging of endothelial cells. This can contribute to the hypertension commonly observed in elderly patients. Mortalin, a novel member of hsp 70 family of proteins, was initially identified by virtue of its association with a cellular mortal phenotype. Subsequently, normal cells and the ones with an immortal phenotype have been found to have differential subcellular localization of this protein. Antiproliferative activity of this protein in normal cells and the deregulation of expression in transformed cells is observed which suggests the association of mortalin in pathways that determine cellular divisional phenotype.

Aging↗

PubMedDate not supplied

An N-terminal region of mot-2 binds to p53 in vitro.

The mouse mot-2 protein was earlier shown to bind to the tumor suppressor protein, p53. The mot-2 binding site of p53 was mapped to C-terminal amino acid residues 312-352, which includes the cytoplasmic sequestration domain. In the present study, we have found that both mot-1 and mot-2 bind to p53 in vitro. By using His-tagged deletion mutant proteins, the p53-binding domain of mot-2 was mapped to its N-terminal amino acid residues 253-282, which are identical in mot-1 and mot-2 proteins. Some peptides containing the p53-binding region of mot-2 were able to compete with the full-length protein for p53 binding. The data provided rationale for in vitro binding of mot-1 and mot-2 proteins to p53 and supported the conclusion that inability of mot-1 protein to bind p53 in vivo depends on secondary structure or its binding to other cellular factors. Most interestingly, the p53-binding region of mot-2 was common to its MKT-077, a cationic dye that exhibits antitumor activity, binding region. Therefore it is most likely that MKT-077-induced nuclear translocation and restoration of wild-type p53 function in transformed cells takes place by a competitional mechanism.

Amino Acids↗

PubMedDate not supplied

Cold shock response of yeast cells: induction of a 33 kDa protein and protection against freezing injury.

Cold shock (10 degrees C) treatment to Saccharomyces cerevisiae cells normally grown at 30 degrees C resulted in splitting of vacuoles and retarded membrane fluidity as detected by phase contrast microscopy and in vivo nuclear magnetic resonance (NMR) studies, respectively. The treatment was found to impart protection against subsequent freezing as studied by cell viability and colony forming efficiency. We have earlier reported similar protection and retarded membrane fluidity as a result of heat shock treatment to these cells (Obuchi et al., 1990). This suggests that cold shock and heat shock treatments to yeast cells evoke some analogous responses. However, biochemically a new 33 kDa protein (CSP 33) was detected upon cold shock treatment which is distinct from heat shock induced family of proteins (Kaul et al., 1992). We present here the first report of this kind and its practical implications for protection against freezing.

Cold Temperature↗