Biomedical subjects

Nand K Sah

Publications and source records attributed to Nand K Sah.

7 recordsLinked to original sources

PubMed2006

Effect of downregulation of survivin expression on radiosensitivity of human epidermoid carcinoma cells.

PURPOSE: The expression of survivin, a member of the inhibitor-of-apoptosis protein family, is elevated in many types of human cancer. High survivin expression has been associated with poor patient prognosis and tumor resistance to chemotherapy and radiotherapy. The purpose of this study was to compare the radiosensitizing effects of five agents that target survivin on their relative ability to downregulate survivin expression. METHODS AND MATERIALS: The human epidermoid carcinoma cell line A431 was treated with adenoviral-mediated wild-type p53, antisense to survivin, the mitogen-activated protein kinase inhibitor PD98059, the cyclin-dependent kinase inhibitor Purvalanol A, or the histone deacetylase inhibitor trichostatin A. The radiosensitizing effects of these treatments were determined by clonogenic survival curve analysis and their abilities to suppress survivin expression by Western blot analysis. RESULTS: All the strategies were shown to radiosensitize A431 cells. This effect correlated with their abilities to downregulate survivin. CONCLUSION: Expression of survivin appears to confer a radioresistant phenotype that can be overcome using several clinically achievable strategies that target survivin either specifically or nonspecifically.

CDC2 Protein Kinase↗

PubMed2005

Indian herb 'Sanjeevani' (Selaginella bryopteris) can promote growth and protect against heat shock and apoptotic activities of ultra violet and oxidative stress.

Selaginella bryopteris is a lithophyte with remarkable ressurection capabilities. It is full of medicinal properties, hence also known as 'Sanjeevani' (one that infuses life). For lack of credible scientific evidence the plant is not in active use as a medicinal herb. We provide scientific evidence for why S. bryopteris is known as 'Sanjeevani'. The aqueous extract of S. bryopteris possesses growth-promoting activity as well as protective action against stress-induced cell death in a number of experimental cell systems including mammalian cells. Treatment of the cells in culture with 10% aqueous extract enhanced cell growth by about 41% in Sf9 cells and 78% in mammalian cells. Pre-treatment of cells with the Selaginella extract (SE) (1-2.5%) protected against oxidative stress (H2O2) -induced cell death. The killing potential of ultra violet (UV) was also significantly reduced when the cells were pre-treated with SE for 1 h. Thermal radiation suppressed cell growth by about 50%. Pre-treatment of cells with SE for 1 h afforded complete protection against heat-induced growth suppression. SE may possess anti-stress and antioxidant activities that could be responsible for the observed effects. Chemical analysis shows that SE contains hexoses and proteins. Taken together, S. bryopteris extract may help in stress-induced complications including those due to heat shock.

Animals↗

PubMed2003

Baculoviral p35 inhibits oxidant-induced activation of mitochondrial apoptotic pathway.

In this study we report that the baculovirus p35 anti-apoptotic protein prevents cell death by quenching free radicals at a very upstream step in the apoptotic pathway. Mitochondria of activated rat peritoneal macrophages as well as Spodoptera frugiperda (Sf9) insect cells, following treatment with oxidants, H(2)O(2)/UVB irradiation, release cytochrome c followed by activation of caspase-3. Transfection of macrophages/Sf9 cells with a construct carrying the p35 gene under the CMV/HSP promoters resulted in p35 expression and consequent arrest of oxidative stress-induced apoptosis. p35 expression also inhibited cytochrome c release from the mitochondria of oxidant-exposed cells and blocked caspase-3 activation.

Animals↗

PubMed2003

Translation inhibitors sensitize prostate cancer cells to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) by activating c-Jun N-terminal kinase.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in several human tumors both in vitro and in vivo, however, some tumors remain resistant for poorly understood reasons. Using a quantitative DNA fragmentation assay for apoptosis, we have shown that human prostate cancer cells are resistant to a wide range of TRAIL doses up to 500 ng/ml. However, translation inhibitors, such as anisomycin, cycloheximide, emetine, harringtonine, and puromycin, unlike several transcription inhibitors, significantly sensitized PC3-neomycin (PC3-neo) cells to TRAIL-induced apoptosis. These effects were inhibited in PC3 cells engineered to express bcl2 (PC3-bcl2). Translation inhibitors led to activation of c-Jun N-terminal kinase (JNK), which plays a role in this sensitization process because inhibition of JNK activation resulted in protection against TRAIL plus translation inhibitor-induced apoptosis. JNK activation may be required for this process, but it is not sufficient because activation of JNK using an MEKK2 expression vector did not mimic the sensitizing effect of translation inhibitors. Other stress-activated protein kinases, such as ERK and p38, play an insignificant role in determining the apoptotic sensitivity. We conclude that activation of JNK is required for sensitization of PC3 cells to TRAIL-induced apoptosis by translation inhibitors in cells that are otherwise TRAIL-resistant. However, in addition to JNK activation, other aspects of translation inhibition such as the suppressed activity of apoptosis-inhibitory proteins or activation of other signal transduction pathways must also be involved.

Activating Transcription Factor 2↗

PubMed2003

Host-pathogen interactions during apoptosis.

Host pathogen interaction results in a variety of responses, which include phagocytosis of the pathogen, release of cytokines, secretion of toxins, as well as production of reactive oxygen species (ROS). Recent studies have shown that many pathogens exert control on the processes that regulate apoptosis in the host. The induction of apoptosis upon infection results from a complex interaction of parasite proteins with cellular host proteins. Abrogation of host cell apoptosis is often beneficial for the pathogen and results in a successful host invasion. However, in some cases, it has been shown that induction of apoptosis in the infected cells significantly imparts protection to the host from the pathogen. There is a strong correlation between apoptosis and the host protein translation machinery: the pathogen makes all possible efforts to modify this process so as to inhibit cell suicide and ensure that it can survive and, in some cases, establish latent infection. This review discusses the significance of various pathways/steps during virus-mediated modulation of host cell apoptosis.

Animals↗

PubMed2003

Antioxidants prevent UV-induced apoptosis by inhibiting mitochondrial cytochrome c release and caspase activation in Spodoptera frugiperda (Sf9) cells.

Oxidative stress has been shown to be associated with apoptosis (programmed cell death) in a number of cell systems. We earlier reported in vitro cultured Spodoptera frugiperda (Sf9) cells as a model system to study oxidative stress induced apoptosis (J Biosciences 24 (1999) 13) and the inhibition of UV-induced apoptosis by the baculovirus antiapoptotic p35 protein that acts as a sink to sequester reactive oxygen species (Proc Natl Acad Sci USA 96 (1999) 4838). We now show that UV-induced apoptosis in Sf9 cells, is preceded by the release of mitochondrial cytochrome c into the cytosol and consequent activation of Sf-caspase-1. The inhibitory effect of different antioxidants including scavengers of oxygen radicals such as butylated hydroxyanisole (BHA), alpha tocopherol acetate, benzoate and reduced-glutathione (GSH) on ultra violet B (UVB)-induced apoptosis in cultured Sf9 cells was assessed. Both, cytochrome c release as well as Sf-caspase-1 activation was inhibited by pre-treatment with antioxidants such as BHA and alpha tocopherol acetate, suggesting that these antioxidants inhibit apoptosis by acting quite upstream in the apoptosis cascade at the mitochondrial level, as well as downstream at the caspase level.

Animals↗

PubMed2003

Adenovirus-mediated wild-type p53 radiosensitizes human tumor cells by suppressing DNA repair capacity.

Functional inactivation of the p53 gene and robust DNA repair capacity may be among the salient causes of radioresistance in tumor cells. We expressed the wild-type (wt) p53 gene in a p53-mutant human epidermoid carcinoma cell line, A431, using an adenoviral vector [adenovirus-p53 (Ad-p53), INGN 201], examined its radiosensitivity, and correlated p53 status and radiosensitivity with cellular repair functions. Using clonogenic survival assays and the terminal deoxynucleotidyl transferase-mediated nick end labeling assay for apoptosis, we demonstrated that preirradiation treatment with Ad-p53 significantly increased the radiosensitivity of A431 cells over controls. Induction of p53 expression using a construct where p53 expression was under the control of an inducible promoter also significantly increased radiosensitivity of H1299 lung tumor cells, which are otherwise null for p53. These results did not correlate with radiation-induced apoptosis but did correlate with functional impairment of DNA repair and suppressed expression of several repair-related genes, such as Ku70, DNA-dependent protein kinase, ataxia telangiectasia mutated, and X-ray-sensitive complementation group 4. Normal human fibroblast MRC-9 cells showed no impairment in the repair capability due to Ad-p53 despite the suppression of some repair genes. Expression of Ku70, which is known to mediate diverse cellular functions, correlated with the differential effects of p53 on radiosensitivity in the normal and tumor cells.

Adenoviridae↗