Proteomic characterization of the E3 ubiquitin-ligase Hakaibiological insights and new therapeutic strategies

Abstract

Carcinoma is the most common type of cancer and arises from epithelial cells. Transition from adenoma to carcinoma is associated with the loss of E-cadherin and, in consequence, the disruption of cell−cell contacts. E-cadherin is a tumor suppressor which is down-regulated during epithelial-to-mesenchymal transition (EMT), and its loss is a predictor of poor prognosis during tumor progression. Hakai is an E3 ubiquitin-ligase that mediates E-cadherin ubiquitination, endocytosis and consequent degradation. Although E-cadherin is the most established substrate for Hakai activity, other regulated molecular targets for Hakai may be involved in cancer cell plasticity during tumor progression. In this work we employed an iTRAQ approach to explore novel molecular pathways involved in Hakai-driven EMT. Our results show that Hakai may have an important influence on cytoskeleton-related proteins, extracellular exosome-associated proteins, RNA-related proteins and proteins involved in metabolism. Among Hakai-down-regulated proteins, we describe Annexin A2 as a new possible susbtrate for Hakai. Moreover, we also report an interaction between Hakai and the heat shock protein 90 (Hsp90) chaperone complex. Besides, our results reveal that the pharmacological inhibition of Hsp90 with geldanamycin results in the degradation of Hakai in a lysosome-dependent manner. Based on that, we propose Hakai as a new client protein of Hsp90 chaperone highlighting a new mechanism by which Hsp90 inhibitors may influence Hakai-mediated EMT process and cancer treatment.