PKCδ-dependent signaling mediates ethambutol-induced toxic effects on human retinal pigment cells

Department of Ophthalmology, Buddhist Tzu Chi General Hospital, Hualien, Taiwan.
Molecular vision (Impact Factor: 1.99). 06/2011; 17:1564-76.
Source: PubMed


Our previous report demonstrated that ethambutol (EMB) might induce cytoplasmic vacuolization and reduce the uptake of photoreceptor rod outer segments (ROS) in retinal pigment epithelium (RPE) cells, which are mediated via a protein kinase C (PKC)-dependent pathway. In the present study, we sought to identify the PKC isozyme(s) involved.
EMB-induced cytoplasmic vacuolization and uptake of ROS were observed under a phase contrast microscope. Western blots were performed to observe the membrane translocation of PKC isozymes and cytoplasmic release of cathepsin D. Quantitative PCR were performed to analyze gene expression of PKCδ. Human RPE cell line RPE50 and ARPE19 cells were pretreated with specific inhibitors or transfected with shRNAs of various PKC isozymes, including PKCα, β, ε, γ, and δ, to examine whether EMB-induced toxic effects were prevented.
In RPE50 cells, gene expression of PKCδ on both mRNA and protein levels was induced by EMB within 30 min to 3 h. EMB-induced cytoplasmic vacuolization in both RPE50 and ARPE19 cells was prevented by pretreating the cells with a specific inhibitor of PKCδ, Rottlerin, or depletion of PKCδ by shRNA. EMB-triggered reduction of ROS uptake was also significantly suppressed by pretreatment with Rottlerin, or depletion of PKCδ by shRNA technology. In contrast, pretreatment of the cells with specific inhibitors of PKCα, β, ε, or γ, or depletion of PKCα or β didn't influence the aforementioned EMB-triggered toxic effects. In addition, in RPE50, EMB induced the release of lysosomal enzyme cathepsin D into cytosol within 30 min to 6 h, which was also prevented by Rottlerin.
EMB-induced vacuole formation, cytoplasmic release of cathepsin D, and reduction of phagocytosis in RPE are intimately correlated and regulated by the PKCδ signal pathway.

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    • "Our previous studies have demonstrated that EMB induces cytosolic vacuoles formation and reduces the phagocytic activity in human RPE-derived cells, including RPE50 and ARPE19 cells (Tsai et al., 2008a). Furthermore, we also found that EMB-induced cytotoxicity and reduced phagocytosis in RPE cells are mediated via the protein kinase C (PKC)δ signaling pathway (Tsai et al., 2011). PKC is a family of serine/threonine kinases that are involved in different neuronal development events, such as proliferation, differentiation, survival and apoptosis (Wooten, 1999). "
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