Proteasomes play important roles in a variety of cellular processes such as cell cycle progression, signal transduction and immune responses. Proteasome activity is important in maintaining rapid turnover of short-lived proteins, as well as preventing accumulation of misfolded or damaged proteins. Alteration in ubiquitin-proteasome function may be detrimental to its crucial role in maintaining cellular homeostasis. Here, we have found that treatment of pyrrolidine dithiocarbamate (PDTC), a zinc ionophore, resulted in the accumulation of several proteasome substrates including p53 and p21 in HeLa cells. The PDTC effect was due to an extended half-life of these proteins through the mobilization of zinc. PDTC and/or zinc also increased fluorescence intensity of UbG76V-GFP fusion protein that is degraded rapidly by the ubiquitin-proteasome system. Treatment of cells with zinc induced formation of ubiquitinated inclusions in the centrosome, a histological marker of proteasome inhibition. Western blotting showed zinc-induced increase in laddering bands of polyubiquitin-conjugated proteins. In vitro study, zinc inhibited the ubiquitin-independent proteasomal degradations of p21 and α-synuclein. These results suggest that zinc may modulate cell functions through its action on the turnover of proteins that are susceptible to proteasome-dependent proteolysis.
Bibliographical noteFunding Information:
We thank for Dr. Masucci, Karolinska Institute, Stockholm, Sweden, for providing us the Ub G76V -GFP plasmid. We are grateful to Dr. J. Kim, Department of Microbiology, Yonsei University College of Medicine, Seoul, Korea, for providing the α-synuclein protein. This study was supported by a grant of Korea Health 21 R&D Project, Ministry of Health & Welfare, Republic of Korea (00-PJ1-PG1-CH13-0005).
All Science Journal Classification (ASJC) codes
- Cell Biology