Effect Of Exogenous Zinc On Cells Growth And The Related Cellular Signaling Pathways

As we all know, heavy metals can damage the nervous system, liver and bones, even the function of many vital enzymes in humans. The main targets by which metals induce carcinogenesis are regulatory or signaling proteins, which are able to participate in the process of cell growth, apoptosis, cycle control, DNA repair, and differentiation. For example, metal-induced apoptosis may be significantly associated with mitochondrial-mediated signaling pathway. In addition, given that many metal are carcinogens or suspected carcinogens, the potential carcinogenic effects may affect the expression of cell cycle regulatory proteins and the function to achieve, especially they may affect the cell cycle checkpoint proteins. As a vital metal ion in cellular processes, zinc is the second in abundance transition metal element in humans. There exists a complex regulation system of the total cellular zinc and its distribution, which is the necessary foundation for signal transduction functions of zinc in cells. Zinc can protect cells from apoptosis which induced by a variety of factors. In some mammalian cell lines, however, when the extracellular concentration of zinc exceeded the cellular zinc homeostasis to regulate and control, zinc will induce programmed cell death. In addition, zinc is proven to be one of the structural elements of the enzymes involved in DNA synthesis, transcription and synthesis of aminoacyl-tRNA and ribosomes functions, which proved its functions in cell proliferation.In this thesis, we used zinc sulfate as exogenous stimuli for the first time to study the content and cellular distribution of zinc, cell cycle, apoptosis and proliferation of human lung adenocarcinoma cells (A549) treated with various concentration of zinc. As a new zinc ion fluorescent probe which could penetrate the cell membrane, NBD-TPEA was used to observe intracellular zinc content and distribution. The results showed that, within a specific zinc concentration range, there exists a regulatory mechanism in the cells which can maintain intracellular zinc at a certain level, resulting in less changes of cell cycle, apoptosis and proliferation. Then we examined the changes on cell cycle, proliferation and apoptosis of human breast cancer cell lines (MDAMB231), human embryonic kidney epithelial cell line (293T) and human hepatoma cell line (HepG2) with the higher concentration range of zinc sulfate. It was found that when exogenous zinc concentration exceeded the scope of its regulatory capacity, cell cycle, apoptosis, proliferation, and intracellular zinc content will produce corresponding changes, and the responses to the same stimulus conditions in various cell lines are different. Finally, zinc sulfate, zinc gluconate and bacitracin zinc were used respectively as inorganic, organic and biological zinc species for investigating the cell cycle, proliferation and apoptosis of MDAMB231. Accordding to the changes on the cell cycle, apoptosis and other physiological and biochemical indexes of MDAMB231cells, the Western Blot method examined the expression levels of MTF-1, p21, cyclin A, cyclin B1, cyclin D1and caspase-8and caspase-9. Cyclin B1, cyclin D1were up-regualted, which is in accordance with cell cycle arrest in G1and G2/M phases of MDAMB231. Meanwhile, high concentrations of zinc induced apoptosis of MDAMB231mainly via the mitochondrial pathway as the observation of caspase-9cleavage.