Cadmium induces endosomal/lysosomal enlargement and blocks autophagy flux in rat hepatocytes by damaging microtubules

Abstract

Acute exposure to cadmium (Cd) causes vacuolar degeneration in buffalo rat liver 3 A (BRL 3 A) cells. The present study aimed to determine the relationship between Cd-induced microtubule damage and intracellular vacuolar degeneration. Western blotting results showed that Cd damaged the microtubule network and downregulated the expression of microtubule-associated proteins—kinesin-1 heavy chain (KIF5B), γ-tubulin, and acetylated α-tubulin in BRL 3 A cells. Immunofluorescence staining revealed that Cd inhibited interactions between α-tubulin and microtubule-associated protein 4 (MAP4) as well as KIF5B. Increasing Cd concentrations decreased the levels of the lipid kinase, PIKfyve, which regulates the activity of endosome-lysosome fission. Immunofluorescence and transmission electron microscopy revealed vacuole-like organelles that were late endosomes and lysosomes. The PIKfyve inhibitor, YM201636, and the microtubule depolymerizer, nocodazole, aggravated Cd-induced endosome-lysosome enlargement. Knocking down the kif5b gene that encodes KIF5B intensified the enlargement of endosome-lysosomes and expression of early endosome antigen 1 (EEA1), Ras-related protein Rab-7a (RAB7), and lysosome-associated membrane glycoprotein 2 (LAMP2). Nocodazole, YM201636, and the knockdown of kif5b blocked autophagic flux. We concluded that Cd-induced damage to the microtubule network is the main reason for endosome-lysosome enlargement and autophagic flux blockage in BRL 3 A cells, and kinesin-1 plays a critical role in this process.