Curcumin is known to exert its anticancer effect either by scavenging or by generating reactive oxygen species (ROS). In this study, we report that curcumin-mediated rapid generation of ROS induces apoptosis by modulating different cell survival and cell death pathways in HuT-78 cells. Curcumin induces the activation of caspase-8, -2, and -9, alteration of mitochondrial membrane potential, release of cytochrome c, and activation of caspase-3 and concomitant PARP cleavage, but the addition of caspase inhibitors only partially blocked the curcumin-mediated apoptosis. Curcumin also downregulates the expression of antiapoptotic proteins c-FLIP, Bcl-xL, cellular inhibitor of apoptosis protein, and X-linked IAP in a ROS-dependent manner. Curcumin disrupts the integrity of IKK and beclin-1 by degrading Hsp90. Degradation of IKK leads to the inhibition of constitutive NF-kB. Degradation of beclin-1 by curcumin leads to the accumulation of autophagy-specific marker, microtubule-associated protein-I light chain 3 (LC3), LC3-I. Our findings indicate that HuT-78 cells are vulnerable to oxidative stress induced by curcumin and as a result eventually undergo cell death. Mol Cancer Ther; 11(9); 1873-83. Ó2012 AACR.

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Methicillin Resistant Staphylococcus aureus (MRSA) cause pneumonia and empyema thoraces. TLR9 activation provides protection against bacterial infections and Heme oxygenase-1 (HO-1) is known to enhance host innate immunity against bacterial infections. However, it is still unclear whether HO-1 regulates TLR-9 expression in the pleura and modulates the host innate defenses during MRSA empyema. In order to determine if HO-1 regulates host innate immune functions via modulating TLR expression, in MRSA empyema, HO-1+/+ and HO-1-/- mouse pleural mesothelial cells (PMCs) were infected with MRSA (1:10, MOI) in the presence or absence of Cobalt Protoporphyrin (CoPP) and Zinc Protoporphyrin (ZnPP) or CORM-2 (a Carbon monoxide donor) and the expression of mTLR9 and mBD14 was assessed by RT-PCR. In vivo, HO-1+/+ and HO-1-/- mice were inoculated with MRSA (5x106 CFU) intra-pleurally and host bacterial load was measured by CFU, and TLR9 expression in the pleura was determined by histochemical-immunostaining. We noticed MRSA inducing differential expression of TLR9 in HO-1+/+ and HO-1 -/- PMCs. In MRSA infected HO-1+/+ PMCs, TLR1, TLR4, and TLR9 expression was several fold higher than MRSA infected HO-1-/- PMCs. Particularly TLR9 expression was very low in MRSA infected HO-1-/- PMCs both in vivo and in vitro. Bacterial clearance was significantly higher in HO-1+/+ PMCs than compared to HO-1-/- PMCs in vitro, and blocking TLR9 activation diminished MRSA clearance significantly. In addition, HO-1-/- mice were unable to clear the MRSA bacterial load in vivo. MRSA induced TLR9 and mBD14 expression was significantly high in HO-1+/+ PMCs and it was dependent on HO-1 activity. Our findings suggest that HO-1 by modulating TLR9 expression in PMCs promotes pleural innate immunity in MRSA empyema.