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Expression of USP2a and study of its interaction with clathrin in human oral squamous carcinoma and prostate cancer cells

Author(s):
Michelle Agostini
Total Authors: 1
Document type: Doctoral Thesis
Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Odontologia de Piracicaba
Defense date:
Examining board members:
Fabio Daumas Nunes; Karina Gotardello Zecchin; Pablo Agustin Vargas; Ricardo Della Coletta
Advisor: Edgard Graner
Abstract

The ubiquitin (Ub)-proteasome pathway controls cellular protein turnover by degrading targeted intracellular proteins tagged with poly-Ub chains. Ubiquitination is a reversible process and the deubiquitinating enzymes (DUBs) are proteases that specifically cleave off Ub from Ub-protein conjugates. They can act in a preproteasomal level removing the poly-Ub tag from specific substrates and preventing and modulating their degradation. The DUBs USP2a and USP2b were recently identified in the prostate of men and rats. USP2a is androgen-regulated, overexpressed in prostate cancer, and interacts with and stabilizes fatty acid synthase (FAS) and the protein murine double minute (Mdm2). FAS is overexpressed in several human malignancies, including oral squamous cell carcinoma, and is correlated with a poor prognosis for some tumors. Mdm2 is an Ub-protein ligase responsible for its own ubiquitination and ubiquitination of p53, that is degraded by the proteasome. When overexpressed in nontransformed cells USP2a exhibits oncogenic behavior both in vitro and in vivo and prevents apoptosis induced by chemotherapeutic agents. Considering that USP2a stabilizes FAS and Mdm2 and then protects tumoral cells from apoptosis, the purpose of the present study was to investigate the USP2a expression and its biological role in human oral squamous carcinoma cells. mRNAs for USP2a were detected in the four studied cell lines, mainly in SCC-4 and -15. The USP2a protein levels were similar in all cell lines, being slightly higher in SCC-9 and -25. By using immunofluorescence we showed that USP2a is located in the cytoplasm of SCC-9 cells and eventually concentrated around the nuclei. No significant differences were found in the proliferative rates of USP2a overexpressing SCC-9 cells, however, cells overexpressing mutant USP2a had lower proliferative potential. In contrast with LNCaP cells, USP2a silencing by siRNA slightly induced apoptosis. The treatment with different concentrations of EGF was able to modulate the USP2a expression in SCC-9 cells and change the amount of ubiquitinated forms of FAS. We also show in the present study experiments performed in the laboratory of Dr. Massimo Loda at the Dana-Farber Cancer Institute, in which the possible interaction between USP2a and clathrin was analyzed. Clathrin is involved in the internalization and endocytosis of proteins located in at the plasma membrane. Here we show that USP2a and clathrin heavy chain colocalize in the cytoplasm of AR-iPrEC and SCC-9 cells and that clathrin protein expression is regulated by androgens in LNCaP cells. We found higher amounts of clathrin in cells that stably express USP2a than in the controls. USP2a was found at the plasma membrane in LNCaP cells and after EGF stimulation a granular positivity for USP2a was observed in the cytoplasm. These results suggest that USP2a may have a role in the clathrin mediated endocytosis (AU)