Prohibitin 2 (PHB2), an inner mitochondrial membrane (IMM) protein, has recently been identified as a novel receptor involved in parkin-mediated mitophagy. In the field of veterinary medicine, the role of PHB2 in parkin-mediated mitophagy was described, for the first time, in urothelial cells of cattle, naturally infected with bovine papillomavirus (BPV). The BPV2 and BPV13 E5 oncoprotein, responsible for abortive infections in urothelial cells, was detected by RT-PCR. Severe ultrastructural abnormalities of the inner mitochondrial membrane were detected using transmission electron microscopy. PHB2 formed a functional complex with PHB1. PHB2 was significantly overexpressed in mitochondrial fractions from urothelial mucosa samples taken from cattle harbouring BPV infection. PHB2 overexpression could be attributed to mitochondrial dysfunction, as its expression levels in the cytosolic, microsomal, and nuclear fractions were seen to be unmodified. Immunoprecipitation studies revealed the interaction between PHB2 and phosphorylated forms of both PINK1 and parkin. Furthermore, PHB2 interacted with LC3-II, a marker of autophagosomal membranes and autophagy receptors, such as p62 and optineurin. PHB2 was shown to interact with transcription factor EB (TFEB), which is activated following parkin-mediated mitophagy, and embryonic stem cell-expressed Ras (ERAS), a constitutive protein coded by ERas. Western blot analysis revealed a significant overexpression of unphosphorylated TFEB in mitochondrial and nuclear fractions from urothelial mucosa samples from cattle suffering from BPV infection. Finally, PHB2 interacted with ERAS, believed to be involved in mitophagosome maturation. Taken together, the molecular and ultrastructural findings of this study suggested that BPV infection is responsible for parkin-dependent mitophagy, in the pathway of which PHB2 plays a crucial role.
Keywords: Bovine papillomavirus; ERAS; optic atrophy 1 (OPA1); parkin-dependent mitophagy; prohibitin-2 (PHB2); transcription factor EB (TFEB).