ABSTRACT
Prodigiosin is a bacterial tripyrrole pigment with potent cytotoxicity against diverse human cancer cell lines. Endoplasmic reticulum (ER) stress is initiated by accumulation of unfolded or misfolded proteins in the ER lumen and may induce cell death when irremediable. In this study, the role of ER stress in prodigiosin-induced cytotoxicity was elucidated for the first time. Comparable to the ER stress inducer thapsigargin, prodigiosin up-regulated signature ER stress markers GRP78 and CHOP in addition to activating the IRE1, PERK and ATF6 branches of the unfolded protein response (UPR) in multiple human breast carcinoma cell lines, confirming prodigiosin as an ER stress inducer. Prodigiosin transcriptionally up-regulated CHOP, as evidenced by its promoting effect on the CHOP promoter activity. Of note, knockdown of CHOP effectively lowered prodigiosin's capacity to evoke PARP cleavage, reduce cell viability and suppress colony formation, highlighting an essential role of CHOP in prodigiosin-induced cytotoxic ER stress response. In addition, prodigiosin down-regulated BCL2 in a CHOP-dependent manner. Importantly, restoration of BCL2 expression blocked prodigiosin-induced PARP cleavage and greatly enhanced the survival of prodigiosin-treated cells, suggesting that CHOP-dependent BCL2 suppression mediates prodigiosin-elicited cell death. Moreover, pharmacological inhibition of JNK by SP600125 or dominant-negative blockade of PERK-mediated eIF2α phosphorylation impaired prodigiosin-induced CHOP up-regulation and PARP cleavage. Collectively, these results identified ER stress-mediated cell death as a mode-of-action of prodigiosin's tumoricidal effect. Mechanistically, prodigiosin engages the IRE1-JNK and PERK-eIF2α branches of the UPR signaling to up-regulate CHOP, which in turn mediates BCL2 suppression to induce cell death.
Subject(s)
Antineoplastic Agents/pharmacology , Breast Neoplasms/drug therapy , Breast Neoplasms/pathology , Endoplasmic Reticulum Stress/drug effects , Prodigiosin/pharmacology , Activating Transcription Factor 6/genetics , Activating Transcription Factor 6/metabolism , Breast Neoplasms/genetics , Breast Neoplasms/metabolism , Cell Death/drug effects , Cell Line, Tumor , Endoplasmic Reticulum Chaperone BiP , Endoplasmic Reticulum Stress/physiology , Endoribonucleases/genetics , Endoribonucleases/metabolism , Female , Gene Expression Regulation, Neoplastic/drug effects , Heat-Shock Proteins/genetics , Heat-Shock Proteins/metabolism , Humans , Immunoblotting , MCF-7 Cells , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , RNA/chemistry , RNA/genetics , Reverse Transcriptase Polymerase Chain Reaction , Transcription Factor CHOP/genetics , Transcription Factor CHOP/metabolism , Unfolded Protein Response , Up-Regulation/drug effects , eIF-2 Kinase/genetics , eIF-2 Kinase/metabolismABSTRACT
This study aimed to explore the mechanisms by which prodigiosin protects against hypoxia-induced oxidative/nitrosative brain injury induced by middle cerebral artery occlusion/reperfusion (MCAo/r) injury in mice. Hypoxia in vitro was modeled using oxygen-glucose deprivation (OGD) followed by reoxygenation of BV-2 microglial cells. Our results showed that treatment of mice that have undergone MCAo/r injury with prodigiosin (10 and 100µg/kg, i.v.) at 1h after hypoxia ameliorated MCAo/r-induced oxidative/nitrosative stress, brain infarction, and neurological deficits in the mice, and enhanced their survival rate. MCAo/r induced a remarkable production in the mouse brains of reactive oxygen species (ROS) and a significant increase in protein nitrosylation; this primarily resulted from enhanced expression of NADPH oxidase 2 (gp91(phox)), inducible nitric oxide synthase (iNOS), and the infiltration of CD11b leukocytes due to breakdown of blood-brain barrier (BBB) by activation of nuclear factor-kappa B (NF-κB). All these changes were significantly diminished by prodigiosin. In BV-2 cells, OGD induced ROS and nitric oxide production by up-regulating gp91(phox) and iNOS via activation of the NF-κB pathway, and these changes were suppressed by prodigiosin. In conclusion, our results indicate that prodigiosin reduces gp91(phox) and iNOS expression possibly by impairing NF-κB activation. This compromises the activation of microglial and/or inflammatory cells, which then, in turn, mediates prodigiosin's protective effect in the MCAo/r mice.
Subject(s)
Hypoxia-Ischemia, Brain/prevention & control , Membrane Glycoproteins/antagonists & inhibitors , NADPH Oxidases/antagonists & inhibitors , Neuroprotective Agents/therapeutic use , Nitric Oxide Synthase Type II/biosynthesis , Prodigiosin/therapeutic use , Animals , Blotting, Western , Dose-Response Relationship, Drug , Male , Membrane Glycoproteins/biosynthesis , Mice , Mice, Inbred ICR , NADPH Oxidase 2 , NADPH Oxidases/biosynthesis , Neuroprotective Agents/pharmacology , Nitric Oxide/metabolism , Nitric Oxide Synthase Type II/antagonists & inhibitors , Nitrosation/drug effects , Oxidative Stress/drug effects , Prodigiosin/pharmacology , Reactive Oxygen Species/metabolism , Tyrosine/analogs & derivatives , Tyrosine/biosynthesisABSTRACT
Prodigiosin is a bacterial metabolite with potent anticancer activity, which is attributed to its proapoptotic effect selectively active in malignant cells. Still, the molecular mechanisms whereby prodigiosin induces apoptosis remain largely unknown. In particular, the role of survivin, a vital inhibitor of apoptosis, in prodigiosin-induced apoptosis has never been addressed before and hence was the primary goal of this study. Our results showed that prodigiosin dose-dependently induced down-regulation of survivin in multiple breast carcinoma cell lines, including MCF-7, T-47D and MDA-MB-231. This down-regulation is mainly regulated at the level of transcription, as prodigiosin reduced the levels of both survivin mRNA and survivin promoter activity but failed to rescue survivin expression when proteasome-mediated degradation is abolished. Importantly, overexpression of survivin rendered cells more resistant to prodigiosin, indicating an essential role of survivin down-regulation in prodigiosin-induced apoptosis. In addition, we found that prodigiosin synergistically enhanced cell death induced by paclitaxel, a chemotherapy drug known to up-regulate survivin that in turn confers its own resistance. This paclitaxel sensitization effect of prodigiosin is ascribed to the lowering of survivin expression, because prodigiosin was shown to counteract survivin induction by paclitaxel and, notably, the sensitization effect was severely abrogated in cells that overexpress survivin. Taken together, our results argue that down-regulation of survivin is an integral component mediating prodigiosin-induced apoptosis in human breast cancer cells, and further suggest the potential of prodigiosin to sensitize anticancer drugs, including paclitaxel, in the treatment of breast cancer.
