In this study, we investigated the signaling pathways involved in bradykinin (BK)-induced NF-κB activation and cyclooxygenase-2 (COX-2) expression in human airway epithelial cells (A549). BK caused concentration- and time-dependent increase in COX-2 expression, which was attenuated by a selective B2 BK receptor antagonist (HOE140), a Ras inhibitor (manumycin A), a Raf-1 inhibitor (GW 5074), a MEK inhibitor (PD 098059), an NF-κB inhibitor (pyrrolidine dithiocarbate), and an IκB protease inhibitor (l-1-tosylamido-2-phenylethyl chloromethyl ketone). The B1 BK receptor antagonist (Lys-(Leu8)des-Arg9-BK) had no effect on COX-2 induction by BK. BK-induced increase in COX-2-luciferase activity was inhibited by cells transfected with the κB site deletion of COX-2 construct. BK-induced Ras activation was inhibited by manumycin A. Raf-1 phosphorylation at Ser338 by BK was inhibited by manumycin A and GW 5074. BK-induced ERK activation was inhibited by HOE140, manumycin A, GW 5074, and PD 098059. Stimulation of cells with BK activated IκB kinase αβ (IKKαβ), IκBα phosphorylation, IκBα degradation, p65 and p50 translocation from the cytosol to the nucleus, the formation of an NF-κB-specific DNA-protein complex, and κB-luciferase activity. BK-mediated increase in IKKαβ activity and formation of the NF-κB-specific DNA-protein complex were inhibited by HOE140, a Ras dominant-negative mutant (RasN17), manumycin A, GW 5074, and PD 098059. Our results demonstrated for the first time that BK, acting through B2 BK receptor, induces activation of the Ras/Raf-1/ERK pathway, which in turn initiates IKKαβ and NF-κB activation, and ultimately induces COX-2 expression in human airway epithelial cell line (A549).

A pathological hallmark of Alzheimer's disease is accumulation of amyloid-␤ peptide (A␤) in senile plaques. A␤ has also been implicated in vascular degeneration in cerebral amyloid angiopathy because of its cytotoxic effects on non-neuronal cells, including cerebral endothelial cells (CECs). We explore the role of apoptosis signal-regulating kinase 1 (ASK1) in A␤-induced death in primary cultures of murine CECs. A␤ induced ASK1 dephosphorylation, which could be prevented by selective inhibition of protein phosphatase 2A (PP2A) but not PP2B. ASK1 dephosphorylation resulted in its dissociation from 14-3-3. ASK1, released from 14-3-3 inhibition, activated p38 mitogen-activated protein kinase (p38MAPK), leading to p53 phosphorylation. p53, a proapoptotic transcription factor, in turn transactivated the expression of Bax, a proapoptotic protein. Transfection with various dominant-negative mutants (DNs), including ASK1 DN and p38MAPK DN, suppressed A␤-induced p38MAPK activation, p53 phosphorylation, and Bax upregulation and partially prevented CEC death. Bax knockdown using a bax small interfering RNA strategy also reduced Bax expression and subsequent CEC death. These results suggest that A␤ activates the ASK1-p38MAPK-p53-Bax cascade to cause CEC death in a PP2A-dependent manner.

LIGHT (homologous to lymphotoxins, shows inducible expression, and competes with herpes simplex virus glycoprotein D for herpesvirus entry mediator, a receptor expressed by T lymphocytes) is a member of the tumor necrosis factor superfamily that can interact with lymphotoxin-␤ receptor (LT␤R), herpes virus entry mediator, and decoy receptor (DcR3). In our previous study, we showed that LIGHT is able to induce cell death via the non-death domain containing receptor LT␤R to activate both caspase-dependent and caspase-independent pathway. In this study, a LIGHT mutein, LIGHT-R228E, was shown to exhibit similar binding specificity as wild type LIGHT to LT␤R, but lose the ability to interact with herpes virus entry mediator. By using both LIGHT-R228E and agonistic anti-LT␤R monoclonal antibody, we found that signaling triggered by LT␤R alone is sufficient to activate both caspase-dependent and caspase-independent pathways. Cross-linking of LT␤R is able to recruit TRAF3 and TRAF5 to activate ASK1, whereas its activity is inhibited by free radical scavenger carboxyfullerenes. The activation of ASK1 is independent of caspase-3 activation, and kinase-inactive ASK1-KE mutant can inhibit LT␤R-mediated cell death. This suggests that ASK1 is one of the factors involved in the caspase-independent pathway of LT␤R-induced cell death.

No abstract

LIGHT is a member of the tumor necrosis factor superfamily and is the ligand for LT-␤R, HVEM, and decoy receptor 3. LIGHT has a cytotoxic effect, which is further enhanced by the presence of interferon-␥ (