Endosomes and lysosomes are involved in early steps of Tl(III)-mediated apoptosis in rat pheochromocytoma (PC12) cells

• Published in: Archives of toxicology 2012-11, Vol.86 (11), p.1667-1680
• Main Authors: Hanzel, Cecilia E., Almeira Gubiani, María F., Verstraeten, Sandra V.
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Apoptosis - drug effects; Apoptosis - physiology; BH3 Interacting Domain Death Agonist Protein - metabolism; Biomedical and Life Sciences; Biomedicine; Caspase 3 - metabolism; Cathepsin B - antagonists & inhibitors; Cathepsin B - metabolism; Cathepsin D - antagonists & inhibitors; Cathepsin D - metabolism; Cell Compartmentation - drug effects; Cellular biology; Endosomes - drug effects; Endosomes - metabolism; Environmental Health; Enzymes; Inorganic Compounds; Lysosomal Membrane Proteins - metabolism; Lysosomes - drug effects; Lysosomes - metabolism; Occupational Medicine/Industrial Medicine; PC12 Cells - drug effects; Pepstatins - pharmacology; Pharmacology/Toxicology; Rats; Rodents; Thallium - pharmacology; Thallium - toxicity; Toxicity
• ISSN: 0340-5761; 1432-0738
• DOI: 10.1007/s00204-012-0878-3

The mechanisms that mediate thallium (Tl) toxicity are still not completely understood. The exposure of rat pheochromocytoma (PC12) cells to Tl(I) or Tl(III) activates both mitochondrial (Tl(I) and Tl(III)) and extrinsic (Tl(III)) pathways of apoptosis. In this work we evaluated the hypothesis that the effects of Tl(III) may be mediated by the damage to lysosomes, where it might be incorporated following the route of iron uptake. PC12 cells exposed for 3 h to 100 μM Tl(III) presented marked endosomal acidification, effect that was absent when cells were incubated in a serum-free medium and that was fully recovered when the latter was supplemented with transferrin. After 6 h of incubation the colocalization of cathepsins D and B with the lysosomal marker Lamp-1 was decreased together with an increase in the total activity of the enzymes. A permanent damage to lysosomes after 18 h of exposure was evidenced from the impairment of acridine orange uptake. Cathepsin D caused the cleavage of pro-apoptotic protein BID that is involved in the activation of the intrinsic pathway of apoptosis. Supporting that, BID cleavage and the activation of caspase 3 by Tl(III) were fully prevented when cells were preincubated with cathepsin D inhibitor (pepstatin A) and only partially prevented when cathepsin B inhibitor (E64d) was used. None of these inhibitors affected BID cleavage or caspase 3 activation in Tl(I)-treated cells. Together, experimental results support the role of Tl(III) uptake by the acidic cell compartments and their involvement in the early steps of Tl(III)-mediated PC12 cells apoptosis.