NF-kappaB responds to mechanical strains in osteoblast-like cells, and lighter strains create an NF-kappaB response more readily

This study was to examine the early responses of nuclear factor kappa B (NF-kappaB) to mechanical strains in MG-63. MG-63 cells were subjected to cyclic uniaxial compressive or tensile strain, produced by a four-point bending system, at 1000 microstrain or 4000 microstrain for 5 min, 15 min, 30 min and 1h, respectively. Control cells received the same treatment with no mechanical stress loading. Expression of NF-kappaB (p60) was measured by Western blotting. NF-kappaB responded rapidly to mechanical stimuli in MG-63 cells. NF-kappaB was activated by cyclic uniaxial stretch at 1000 microstrain while it was restrained under a compressive strain environment at 1000 microstrain (P<0.001). The effects reversed for tension and compression at 4000 microstrain (P<0.001). Furthermore, strains at 1000 microstrain affected NF-kappaB expression much easier than those at 4000 microstrain. This indicates that there may be different responding mechanisms or mechanotransduction pathways for different mechanical stimuli.     

Quiescence and attenuated DNA damage response promote survival of esophageal cancer stem cells

Accumulating evidence indicates cancer stem cells (CSCs) possess the capability to resist DNA‐damage induced cell death, whereas the mechanism is largely unknown. Here we show that cell cycle status and DNA damage response (DDR) in CSCs probably contribute to their survival in genotoxic insults. In this study, we isolated esophageal cancer stem cells (ECSCs) from esophageal cancer cell line EC9706 by side‐population (SP) phenotype through flow cytometry and found that ECSCs preferentially stay quiescent as compared to the non‐ECSCs and are more resistant to DNA damage agents. Further study revealed that ECSCs express a lower level of EGFR, phosphoralated Stat3, and c‐Myc, yet abnormally upregulated p27. More interestingly, different from non‐ECSCs, when suffering DNA damage agents, ECSCs showed attenuated DDR, as well as declined DNA repair potential. These data indicated ECSCs probably employed an impaired DDR to handle severe genomic insults. Conclusively, we infer that the damage‐resistance ability of ECSCs is likely attributed to their slow‐cycling status and avoidance of apoptosis or senescence triggered by an excessive DDR. J. Cell. Biochem. 113: 3643–3652, 2012. © 2012 Wiley Periodicals, Inc.     

PI-3-kinase/NF-kappaB mediated response of Jurkat T leukemic cells to two different chemotherapeutic drugs, etoposide and TRAIL

Jurkat T leukemic cells respond to Etoposide, antineoplastic agent which targets the DNA unwinding enzyme, Topoisomerase II, and TNF-Related-Apoptosis-Inducing-Ligand (TRAIL), 34 kDa transmembrane protein, which displays minimal or no toxicity on normal cells and tissues, not only disclosing the occurrence of apoptosis but also a kind of resistance. A similar rate of viability upon the exposure to these two drugs up to 24 h has been evidenced, followed by the occurrence of a rescue process against TRAIL, not performed against Etoposide, along with an higher number of dead cells upon Etoposide exposure, in comparison with TRAIL treatment. These preliminary results let us to speculate on the possible involvement of PI-3-kinase in TRAIL resistance disclosed by surviving cells (20%), may be phosphorylating Akt-1 and, in parallel, IkappaB alpha on both serine and tyrosine residues. On the other hand, in Etoposide Jurkat exposed cells Ser 32-36 phosphorylation of IkappaB alpha is not sufficient to overbalance the apoptotic fate of the cells, since Bax increase, IAP decrease, and caspase-3 activation determine the persistence of the apoptotic state along with the occurrence of cell death by necrosis. Thus, the existence of a balance between apoptotic and rescue response in 20% of cells surviving to TRAIL suggests the possibility of pushing it in favor of cell death in order to improve the yield of pharmacological strategies.     

Mechanism of LIGHT/interferon-gamma-induced cell death in HT-29 cells

LIGHT is a member of tumor necrosis factor (TNF) superfamily, and previous studies have indicated that in the presence of interferon-gamma (IFN-gamma), LIGHT through LTbetaR signaling can induce cell death with features unlike classic apoptosis. In present study, we investigated the mechanism of LIGHT/IFN-gamma-induced cell death in HT-29 cells, where the cell death was profoundly induced when sub-toxic concentrations of LIGHT and IFN-gamma were co-treated. LIGHT/IFN-gamma-induced cell death was accompanied by DNA fragmentation and slight LDH release. This effect was not affected by caspase, JNK nor cathepsin B inhibitors, but was partially prevented by p38 mitogen-activated protein kinase (MAPK) and poly (ADP-ribose) polymerase (PARP) inhibitors, and abolished by aurintricarboxylic acid (ATA), which is an inhibitor of endonuclease and STATs signaling of IFN-gamma. Immunobloting reveals that LIGHT/IFN-gamma could induce p38 MAPK activity, Bak and Fas expression, but down-regulate Mcl-1. Besides, LIGHT/IFN-gamma could not activate caspase-3 and -9, but decreased mitochondrial membrane potential. Although LIGHT could not affect IFN-gamma-induced STAT1 phosphorylation and transactivation activity, which was required for the sensitization of cell death, survival NF-kappaB signaling of LIGHT was inhibited by IFN-gamma. These data suggest that co-presence of LIGHT and IFN-gamma can induce an integrated interaction in signaling pathways, which lead to mitochondrial dysfunction and mix-type cell death, not involving caspase activation.