Oxidant-mediated activation of cytosolic phospholipase a(2) in pulmonary endothelium: role of protein kinase C alpha and a pertussis toxin-sensitive protein

Live-cell imaging approaches for the investigation of xenobiotic-induced oxidant stress

BACKGROUND

Oxidant stress is arguably a universal feature in toxicology. Research studies on the role of oxidant stress induced by xenobiotic exposures have typically relied on the identification of damaged biomolecules using a variety of conventional biochemical and molecular techniques. However, there is increasing evidence that low-level exposure to a variety of toxicants dysregulates cellular physiology by interfering with redox-dependent processes.

SCOPE OF REVIEW

The study of events involved in redox toxicology requires methodology capable of detecting transient modifications at relatively low signal strength. This article reviews the advantages of live-cell imaging for redox toxicology studies.

MAJOR CONCLUSIONS

Toxicological studies with xenobiotics of supra-physiological reactivity require careful consideration when using fluorogenic sensors in order to avoid potential artifacts and false negatives. Fortunately, experiments conducted for the purpose of validating the use of these sensors in toxicological applications often yield unexpected insights into the mechanisms through which xenobiotic exposure induces oxidant stress.

GENERAL SIGNIFICANCE

Live-cell imaging using a new generation of small molecule and genetically encoded fluorophores with excellent sensitivity and specificity affords unprecedented spatiotemporal resolution that is optimal for redox toxicology studies. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

Role of PKCα-p38 MAPK-Giα axis in peroxynitrite-mediated inhibition of β-adrenergic response in pulmonary artery smooth muscle cells

In the context of cross-talk between transmembrane signaling pathways, we studied the loci within the β-adrenergic receptor/G protein/adenyl cyclase system at which PKC exerts regulatory effects of peroxynitrite (ONOO(-)) on isoproterenol stimulated adenyl cyclase activity in pulmonary artery smooth muscle cells. Treatment of the cells with ONOO(-) stimulated PKC-α activity and that subsequently increased p(38)MAPK phosphorylation. Pretreatment with Go6976 (PKC-α inhibitor) and SB203580 (p(38)MAPK inhibitor) eliminated ONOO(-) caused inhibition on isoproterenol stimulated adenyl cyclase activity. Pretreatment with Go6976, but not SB203580, prevented ONOO(-) induced increase in PKC-α activity. Studies using genetic inhibitors of PKC-α (PKC-α siRNA) and p(38)MAPK (p(38)MAPK siRNA) also corroborated the findings obtained with their pharmacological inhibitors in eliminating the attenuation of ONOO(-) effect on isoproterenol stimulated adenyl cyclase activity. This inhibitory effect of ONOO(-) was found to be eliminated upon pretreatment of the cells with pertussis toxin thereby pointing to a G(i) dependent mechanism. This hypothesis was reinforced by G(i)α phosphorylation as well as by the observation of the loss of the ability of Gpp(NH)p (a measure of G(i) mediated response) to stimulate adenyl cyclase activity upon ONOO(-) treatment to the cells. We suggest the existence of a pertussis toxin sensitive G protein (G(i))-mediated mechanism in isoproterenol stimulated adenyl cyclase activity, which is regulated by PKCα-p(38)MAPK axis dependent phosphorylation of its α-subunit (G(i)α) in the pulmonary artery smooth muscle cells.