Impact of transient stress and stress enzymes on development

Stress enzymes triggered by transient stress mediate reprioritization of developmental and homeostatic events to flexibly accomplish the next essential developmental event. This review analyzes recent studies on stress and stress enzyme function during early mammalian development and describes the diverse consequences that result from measurement, analysis of function, and management of stress and stress enzymes during development.     

Cyclooxygenase 2 inhibits SAPK activation in neuronal apoptosis

Cyclooxygenase 2 (COX-2) expressed in cultured neuronal PC12 cells under inducible promoter protects cells from trophic withdrawal apoptosis. Stimulation of SAPK is thought to play a significant role in initiation of PC12 cell death. We have therefore examined whether COX-2 expression inhibits trophic withdrawal-mediated activation of SAPK. SAPK activity increased during the first 6h after NGF removal in mock-transfected PC12 cells. COX-2 expression attenuated the increase of SAPK, as detected by Western blot analysis with phosphorylation state specific anti-SAPK antibodies and by SAPK activity assays. We propose that COX-2 attenuated SAPK activation by preventing activation of nNOS, which occurs, as we have shown before, via COX-2-mediated expression of dynein light chain (DLC). Activation of SAPK in neuronal cell death was attenuated by DLC expression. These observations support a role for NO production and SAPK activation in the neuronal death mechanisms.     

Defective stress kinase and Bak activation in response to ionizing radiation but not cisplatin in a non-small cell lung carcinoma cell line

We have here examined ionizing radiation (IR)-induced apoptotic signaling in one IR-sensitive small cell lung carcinoma (SCLC) and one resistant non-small cell lung carcinoma (NSCLC) cell line, both harboring mutant p53. In the sensitive SCLC cell line, IR induced conformational modulation of Bak and Bax, mitochondrial depolarization, and nuclear fragmentation. These events were not observed in the IR-resistant NSCLC cell line. However, in the same cells, cisplatin, a DNA-damaging drug, induced Bak and Bax modulation, mitochondrial depolarization, and nuclear fragmentation. Pre-mitochondrial signaling events were examined in order to further characterize the differing IR response. In the SCLC cell line, IR-induced apoptotic signaling was found to involve a MEKK1-related pathway and activation of the stress-activated kinases JNK and p38. In comparison, the NSCLC cell line had higher basal levels of activity of JNK and p38, and IR treatment did not further activate these kinases. However, NSCLC cells were sensitive to Bak modulation and apoptosis induced by a kinase-active mutant of MEKK1. Together, the results delineate a mechanism of IR resistance in NSCLC cells and indicate that IR and cisplatin induce Bak modulation and apoptosis via different pathways.     

The role of erythropoietin and its receptor in growth,survival and therapeutic response of human tumor cells: From clinic to bench — a critical review

Recombinant human erythropoietin (rhEPO) has been used clinically to alleviate cancer- and chemotherapy-related anemia. However, recent clinical trials have reported that rhEPO also may adversely impact disease progression and survival. The expression of functional EPO receptors (EPOR) has been demonstrated in many human cancer cells where, at least in vitro, rhEPO can stimulate cell growth and survival and may induce resistance to selected therapies.     

NEMO-binding domain peptide promotes osteoblast differentiation impaired by tumor necrosis factor alpha

Osteogenesis associated with persistent inflammation or infection exists in a broad range of conditions including rheumatoid arthritis and traumatic bone fracture. The poor outcomes of these conditions will benefit from more effective treatments. Here we investigated the molecular mechanisms and tested NEMO-binding domain peptide as a new approach of circumventing TNF-α inhibition of osteoblast differentiation. Our results showed: TNF-α markedly decreased BMP-2-induced alkaline phosphatase activity in the multipotent myoblast C2C12 cells in a dose dependent manner; stepwise experiments demonstrated that BMP-2-induced Smad1 activity was abrogated by addition of exogenous TNF-α or overexpression of NF-κB, and it was significantly elevated by overexpression of IκBα, an inhibitor of NF-κB; Western blotting showed that TNF-α markedly decreased the amount of phospho-Smad1 in BMP-2-activated C2C12 cells, but it did not alter Smad1 mRNA abundance as measured by real-time PCR; addition of a functional cell-permeable NEMO-binding domain (NBD) peptide antagonized NF-κB activity and ameliorated TNF-α inhibition of osteoblast differentiation. Taken together, our study reveals for the first time that NF-κB activation inhibits osteoblast differentiation by attenuating Smad1 activity and application of NBD peptide ameliorates this inhibitory effect. This could lead to new therapeutic drugs that circumvent the inflammatory inhibition of osteogenesis for treatment of traumatic open fractures with infection, rheumatoid arthritis and other bone loss disorders.     

Oxidative stress resistance through blocking Hsp60 translocation followed by SAPK/JNK inhibition in aged human diploid fibroblasts

The stress‐activated protein kinase/c‐Jun N‐terminal kinase (SAPK/JNK) pathway is a well‐known senescence‐related stress activated protein kinase. Multiple environmental stresses induce programmed cell death, such as apoptosis. Normal human diploid fibroblast (HDF) cells have a limited life span in vitro, halting proliferation after a fixed number of cell divisions. Aged passage HDF showed resistance to oxidative stress involving heat shock proteins (Hsp60) through a mechanism involving the translocation of Hsp60 from the mitochondria to the cytosol. The present study showed that the translocation of Hsp60 from the mitochondria to the cytosol followed by high levels of p‐SAPK/JNK activation as a result of oxidative stress was observed in the young cells only. The inhibition of SAPK/JNK activation by SP600125 under oxidative stress almost completely blocked the translocation of Hsp60 in both young and aged cells. This suggests that aged HDF cells are resistant to oxidative stress by blocking the translocation of Hsp60 from the mitochondria to the cytosol followed by SAPK/JNK inhibition. Overall, the mechanism of resistance by oxidative stress in aged cells is induced by blocked of the translocation of Hsp60 followed by SAPK/JNK inactivation. Copyright © 2008 John Wiley & Sons, Ltd.     

Synergistic activation of JNK/SAPK induced by TNF-alpha and IFN-gamma: apoptosis of pancreatic beta-cells via the p53 and ROS pathway

IFN-γ and TNF-α are major proinflammatory cytokines implicated in islet β-cell destruction, which results in type-1 diabetes; however, the underlying mechanism is not clear. Using pancreatic β-cell line MIN6N8 cells, co-treatment with TNF-α and IFN-γ, but neither cytokine alone, synergistically induced apoptosis, correlated with the activation of the JNK/SAPK, which resulted in the production of reactive oxidative species (ROS) and loss of mitochondrial transmembrane potential (ΔΨm). Additionally, cells transfected with wild-type JNK1 became more susceptible to apoptosis induced by TNF-α/IFN-γ through ROS production and loss of Δψm, while cascading apoptotic events were prevented in dominant-negative JNK1-transfected or JNK inhibitor SP600125-treated cells. As the antioxidant, N-acetyl-cysteine, failed to completely suppress apoptosis induced by TNF-α/IFN-γ, an additional pathway was considered to be involved. The level of p53 was significantly increased through synergistic activation of JNK by TNF-α/IFN-γ. Furthermore, the synergistic effect of TNF-α/IFN-γ on apoptosis and ROS production was further potentiated by the overexpression of wild-type p53, but not with mutant p53. This synergistic activation of JNK/SAPK by TNF-α/IFN-γ was also induced in insulin-expressing pancreatic islet cells, and increased ROS production and p53 level, which was significantly inhibited by SP600125. Collectively, these data demonstrate that TNF-α/IFN-γ synergistically activates JNK/SAPK, playing an important role in promoting apoptosis of pancreatic β-cell via activation of p53 pathway together with ROS.     

MCP-1/CCL2 protects cardiac myocytes from hypoxia-induced apoptosis by a G(alphai)-independent pathway

Chemokines, in addition to their chemotactic properties, act upon resident cells within a tissue and mediate other cellular functions. In a previous study, we demonstrated that CCL2 protects cultured mouse neonatal cardiac myocytes from hypoxia-induced cell death. Leukocyte chemotaxis has been shown to contribute to ischemic injury. While the chemoattractant properties of CCL2 have been established, the protective effects of this chemokine suggest a novel role for CCL2 in myocardial ischemia/reperfusion injury. The present study examined the cellular signaling pathways that promote this protection. Treatment of cardiac myocyte cultures with CCL2 protected them from hypoxia-induced apoptosis. This protection was not mediated through the activation of G(alphai) signaling that mediates monocyte chemotaxis. Inhibition of the ERK1/2 signaling pathway abrogated CCL2 protection. Caspase 3 activation and JNK/SAPK phosphorylation were decreased in hypoxic myocytes co-treated with CCL2 as compared to hypoxia only-treated cultures. Expression of the Bcl-2 family proteins, Bcl-xL and Bag-1, was increased in CCL2-treated myocytes subjected to hypoxia. There was also downregulation of Bax protein levels as a result of CCL2 co-treatment. These data suggest that CCL2 cytoprotection and chemotaxis may occur through distinct signaling mechanisms.     

Distinct roles of the ERK pathway in modulating apoptosis of Ras-transformed and non-transformed cells induced by anticancer agent FR901228

Ectopic expression of oncogenic H-Ras in cells results in increases of cell susceptibility to the anticancer agent FR901228. Investigating the roles of Ras-induced pathways in FR901228-induced apoptosis, we have found that the phosphatidylinositol 3-kinase pathway plays an anti-apoptotic role, whereas the stress-activated protein kinase p38 pathway plays a pro-apoptotic role in FR901228-induced apoptosis. Interestingly, the extracellular signal-regulated kinase (ERK) pathway plays an anti-apoptotic role in non-transformed cells; however, it plays a pro-apoptotic role in Ras-transformed cells in response to FR901228 treatment. An essential role of the ERK pathway in regulating caspase-3 contents may contribute to its pro-apoptotic role in Ras-transformed cells.