Chaperone-assisted selective autophagy in healthy and papillomavirus-associated neoplastic urothelium of cattle.

Chaperone-assisted selective autophagy (CASA) is a newly-described selective tension-induced macroautophagy pathway mediated by Bag3 that is believed to be essential for mechanotransduction in skeletal muscle and to be an important regulator of the immune system. We investigated CASA machinery both in healthy and in fifteen papillomavirus-associated neoplastic bovine urothelium. The components of CASA complex, that comprises the molecular chaperones HspA8/Hsc70 and Hsp8B/Hsp22 and the cochaperones Bag3 and STUB1/CHIP, were studied by molecular, microscopic and submicroscopic investigations. CASA complex was found to be constitutively expressed in healthy bovine urothelium; its expression increased in urothelial cancers of cattle, namely thirteen papillary carcinomas and two papillary urothelial neoplasm of low malignant potential (PUNLMPs). We suggest that basal levels of CASA are important in the healthy urothelium which interfaces with the community of urinary microbiota thus representing an important epithelial cell-autonomous mechanism of antibacterial defense. Co-immunoprecipitation studies using an antibody against bovine papillomavirus E5 protein revealed that the oncoprotein co-localized with CASA complex in urothelial cancer cells. This suggests that infection by BPV E5 could influence cell behaviour by interfering with basal autophagy processes although this study did not conclusively show that this interaction increased the expression of CASA proteins. In neoplastic urothelium, CASA could be involved in regulating fundamental cellular processes such adhesion, migration, and proliferation and so might influence the biological behaviour of urothelial tumors in cattle.