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N,N,N,̕N-̕tetrakis (2-pyridylmethyl) ethylenediamine-induced depletion of the labile intracellular pool of zinc suppressed the growth of human breast cancer cells Wu, Bella Wen

Abstract

Zinc is critically involved in many physiological processes including growth. Increasing evidence has revealed the importance of the labile intracellular pool of zinc (LIPZ) in zinc-mediated growth regulation, especially apoptosis, or programmed cell death. However, the mechanisms whereby zinc regulates apoptosis are largely unknown. Zinc has been shown to be associated with several key apoptotic regulatory factors i.e. p53 and members of the Bcl-2 family. We hypothesized that deprivation of LIPZ would reduce cell survival and promote cell death in human breast cancer cells. The overall objectives were to investigate the effects of LIPZ depletion on the growth of human breast cancer cells and to explore the possible mechanisms involved. Three human breast cancer cell lines (MCF-7, MDA-MB-231 and T47D) and a fibrocystic breast cell line (MCF-10), were treated with various concentrations of the intracellular zinc chelator (NNN'N'-tetrakis(2-pyridylmethyl) ethylenediamine; TPEN). After various incubation durations, total cellular zinc concentration and the LIPZ size were quantitated. Cell growth was assessed using cell number counts, cell viability and profiles of cell survival and cell death (necrosis and apoptosis). The expression profile of p53, gadd45, bcl-2 and bax were determined using reverse transcription-polymerase chain reaction (RT-PCR). TPEN induced a dose-dependent reduction in the LIPZ size, but had no effect on the total cellular zinc concentration. TPENinduced depletion of LLPZ led to decreased cell viability and survival, and increased necrosis and apoptosis, indicating that an adequate size of LIPZ was critical to the growth of breast cancer and fibrocystic breast cells. The depletion of LIPZ was also associated with alterations in p53, gadd45, Bcl-2 and Bax mRNA levels in two of the breast cancer cell lines (MDAMB- 231 and T47D) investigated. Overall, this study demonstrated that LIPZ was important to breast cancer cell growth. The TPEN-induced depletion LIPZ was cell line-specific, and was independent of total cellular zinc content. The reduced LIPZ size was associated with reduced growth of human breast cancer cells through increased cell death in a cell linespecific manner. The elevated levels of apoptotic cell death were associated with altered mRNA level of apoptotic regulatory genes.

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