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Abstract
Zinc plays a critical role in many biological processes. However, it is toxic at high concentrations and its homeostasis is strictly regulated by metal-responsive transcription factor 1 (MTF-1) together with many other proteins to protect cells against metal toxicity and oxidative stresses. In this paper, we used high-resolution two-dimensional gel electrophoresis (2DE) to profile global changes of the whole soluble proteome in human lung adenocarcinoma (A549) cells in response to exogenous zinc treatment for 24 h. Eighteen differentially expressed proteins were identified by MALDI TOF/TOF and MASCOT search. In addition, we used Western blotting and RT-PCR to examine the time-dependent changes in expression of proteins regulated by MTF-1 in response to Zn treatment, including the metal binding protein MT-1, the zinc efflux protein ZnT-1, and the zinc influx regulator ZIP-1. The results indicated that variations in their mRNA and protein levels were consistent with their functions in maintaining the homeostasis of zinc. However, the accumulation of ZIP-1 transcripts was down-regulated while the protein level was up-regulated during the same time period. This may be due to the complex regulatory mechanism of ZIP-1, which is involved in multiple signaling pathways. Maximal changes in protein abundance were observed at 10 h following Zn treatment, but only slight changes in protein or mRNA levels were observed at 24 h, which was the time-point frequently used for 2DE analyses. Therefore, further study of the time-dependent Zn-response of A549 cells would help to understand the dynamic nature of the cellular response to Zn stress. Our findings provide the basis for further study into zinc-regulated cellular signaling pathways.
Highlights
Cells respond to a variety of extracellular stimuli such as metal stress, growth factors and hormones through the activities of a number of biological processes including metabolism, transcription, development, and differentiation [1,2,3]
Increases in ZnSO4 concentration led to reduced viability of A549 cells and the viability of A549 cells was lower than 3% after treatment with 300 mM ZnSO4 for 24 h or 48 h
This work has provided an overview of the proteome profiles of A549 cells in response to exogenous zinc ion stress in vivo
Summary
Cells respond to a variety of extracellular stimuli such as metal stress, growth factors and hormones through the activities of a number of biological processes including metabolism, transcription, development, and differentiation [1,2,3]. The proper functioning of these pathways is disrupted by the deficiency or excess of essential metals or by the presence of other nonessential metals [4], [5]. The second most abundant and essential transition metal in human tissues, plays a critical role in regulating vital cellular components such as enzymes and the translation machinery. Zinc is efficiently uptaken from the environment, transported, and stored to maintain intracellular zinc homeostasis. Intracellular zinc ion concentrations are strictly regulated by zinc channels and zincbinding proteins to maintain cellular zinc-dependent functions [6], [7]. Over 300 enzymes and other proteins have been identified that require zinc for their proper functioning [8], [9]. Zn-binding and Zn-responsive proteins have been extensively identified and assayed by two-dimensional gel electrophoresis (2DE) and mass spectrometry (MS) [10,11,12,13]
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