Resistance to cisplatin-induced cell death conferred by the activity of organic anion transporting polypeptides (OATP) in human melanoma cells.

Expression of organic anion transporting polypeptides (OATP) transporters can be modified with potential incidence in cancers, yet they have not been considered in melanoma. Here, we demonstrate transcriptional and protein expression of OATP members in human melanoma cell lines with sodium-independent organic anion uptake activity. Importantly, uptake of different organic anions over 24 h led to a common resistance signal to apoptotic cell death, induced further by cisplatin in 24 h. The mechanism is not dependent on the transport of cisplatin by the OATP, as it is not an OATP substrate. The resistance signal was modulated by PKC, disclosing it as signal mediator. This study suggests that OATP, which can be constantly activated by endobiotics, may contribute to melanoma chemotherapeutic resistance, thereby justifying the development of OATP targeting strategies.

Anti-apoptotic pro-survival effect of clotrimazole in a normothermic ischemia reperfusion injury animal model.

BACKGROUND: Increasing evidence suggests that apoptosis plays a critical role in ischemia reperfusion (IR)-mediated liver injury. Clotrimazole (CTZ) is a potent antimycotic drug that also has a free radical scavenger activity. This study investigated the possible anti-apoptotic, pro-survival role of CTZ in hepatic IR injury in rats. METHODS: Male Sprague-Dawley rats were divided into three groups: sham, control, and CTZ-treated (n = 10 each). Control and CTZ-treated animals were subjected to 60 min of normothermic ischemia of the left lateral lobe of the liver followed by 6 h of reperfusion. Animals were then sacrificed, the liver excised, and blood samples collected. RESULTS: CTZ induced a significant increase in expression of anti-apoptotic Bcl-xL protein. Serum levels of aspartate transaminase and alanine transaminase were significantly lower in CTZ-treated animals than in controls. Histopathologically, tissue damage in the form of apoptosis was significantly lower in CTZ-treated animals than in controls. Expression of the activated form of caspase-3 and the cleaved form of its substrate, poly-ADP-ribose polymerase, decreased significantly in the CTZ-treated group compared with controls. CTZ increased the expression of phospho-p 44/42 ERK1/2 and decreased the phosphorylated form of JNK, without affecting p38 MAPK. CONCLUSION: CTZ protects the liver against IR apoptosis in rats through overexpression of the anti-apoptotic protein Bcl-xL. Other pro-survival pathways such as phospho-p 44/42 ERK1/2 kinase are also activated while JNK is down-regulated.

Oxidative stress and apoptotic events during thermal stress in the symbiotic sea anemone, Anemonia viridis.

Symbiosis between cnidarian and photosynthetic protists is widely distributed over temperate and tropical seas. These symbioses can periodically breakdown, a phenomenon known as cnidarian bleaching. This event can be irreversible for some associations subjected to acute and/or prolonged environmental disturbances, and leads to the death of the animal host. During bleaching, oxidative stress has been described previously as acting at molecular level and apoptosis is suggested to be one of the mechanisms involved. We focused our study on the role of apoptosis in bleaching via oxidative stress in the association between the sea anemone Anemonia viridis and the dinoflagellates Symbiodinium species. Characterization of caspase-like enzymes were conducted at the biochemical and molecular level to confirm the presence of a caspase-dependent apoptotic phenomenon in the cnidarian host. We provide evidence of oxidative stress followed by induction of caspase-like activity in animal host cells after an elevated temperature stress, suggesting the concomitant action of these components in bleaching.

Regulation of Bcl-2 and Bcl-xL anti-apoptotic protein expression by nuclear receptor PXR in primary cultures of human and rat hepatocytes.

The pregnane X receptor (PXR) plays a major role in the protection of the body by regulating the genes involved in the metabolism and elimination of potentially toxic xeno- and endobiotics. We previously described that PXR activator dexamethasone protects hepatocytes from spontaneous apoptosis. We hypothesise a PXR-dependent co-regulation process between detoxication and programmed cell death. Using primary cultured human and rat hepatocytes, we investigated to determine if PXR is implicated in the regulation of Bcl-2 and Bcl-xL, two crucial apoptosis inhibitors. In the present study we demonstrated that the treatment of primary cultured hepatocytes with PXR agonists increased hepatocyte viability and protects them from staurosporine-induced apoptosis. The anti-apoptotic capacity of PXR activation was correlated with Bcl-2 and Bcl-xL induction at both the transcriptional and protein levels in man and rats, respectively. The inhibition of PXR expression by antisense oligonucleotide abolished PXR activators Bcl-xL induction. Accordingly, PXR overexpression in HepG2 cells led to bcl-2 induction upon clotrimazole treatment and protects cells against Fas-induced apoptosis. Our results demonstrate that PXR expression is required for Bcl-2 and Bcl-xL up-regulation upon PXR activators treatment in human and rat hepatocytes. They also suggest that PXR may protect the liver against chemicals by simultaneously regulating detoxication and the apoptotic pathway.