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Mutations in ubiquitin ligase Parkin are associated with Parkinson’s disease and defective mitophagy. Conceptually, Parkin-dependent mitophagy is classified into two phases; 1. Parkin recruits to and ubiquitinates mitochondrial proteins, 2. Formation of autophagosome membrane, sequestering mitochondria for degradation. Recently, endosomal machineries were reported to contribute to the later stage for membrane assembly. We report a role for endosomes in the events upstream of phase 1. We demonstrate that an endosomal ubiquitin ligase CARP2 associates with damaged mitochondria, and this association precedes that of Parkin. CARP2 interacts with Parkin, and stable recruitment of Parkin to damaged mitochondria was substantially reduced in CARP2 KO cells. Our study unravels a novel role of endosomes in modulating upstream pathways of Parkin-dependent mitophagy initiation.

Chemo-resistance remains the main hurdle to cancer therapy, challenging the improvement of clinical outcomes in cancer patients. Therefore, exploratory studies to address chemo-resistance through various approaches are highly rewarding. Nanomedicine is a promising recent advancement in this direction. Comprehensive studies to understand the precise molecular interactions of nanomaterials is necessary to validate their specific “nano induced” effects. Here, we illustrate in detail the specific biological interactions of vanadium pentoxide nanoparticles (VnNp) on triple-negative breast cancer cells and provide initial insights towards its potential in breast cancer management at the cellular level. VnNp shows a time-dependent anti-oxidant and pro-oxidant property in vitro. These nanoparticles specifically accumulate in the lysosomes and mitochondria, modulate various cellular processes including impaired lysosomal function, mitochondrial damage, and induce autophagy. At more extended periods, VnNp influences cell cycle arrest and inhibits cell migration potentiating the onset of apoptosis. Preliminary in vivo studies, on exposing healthy Swiss albino mice to VnNp demonstrated normal blood parameters, organ distribution, and tissue redox balance which further indicated the absence of any adverse organ toxicity. Hence, we foresee tumor-targeting VnNp as a potential drug molecule for future cancer management.

Lysosomal exocytosis and resealing of damaged plasma membrane play critical roles in physiological and pathological processes, including, restoration of cellular homeostasis and tumor invasion. However, to-date, only a few regulatory molecules of these biological processes have been identified. Moreover, no mutations in any of the known regulators of lysosomal exocytosis in primary tumors of patients have been characterized. Here we demonstrate that RNF167, a lysosomal associated ubiquitin ligase, negatively regulates lysosomal exocytosis by inducing perinuclear clustering of lysosomes. Importantly, we also characterized a set of novel natural mutations in RNF167, which are commonly found in diverse tumor types. We found that RNF167-K97N mutant, unlike the wild-type, localizes in the cytoplasm and does not promote perinuclear lysosomal clustering and that cells expressing RNF167-K97N exhibit dispersed lysosomes, increased exocytosis, and enhanced plasma membrane repair. Interestingly, these functional features of RNF167-K97N were shared with a naturally occurring short version of RNF167, i.e. isoform b. In brief, the results presented here reveal a novel role of RNF167 as well as its natural variants, RNF167-K97N and RNF167-b as an upstream regulator of lysosomal exocytosis and plasma membrane resealing which might play an important role in organelle dynamics or tumor progression or both.