Date of Award

Spring 2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Committee Director

Stephen Beebe

Committee Member

Karl Schoenbach

Committee Member

Peter Blackmore

Committee Member

John Semmes

Abstract

Apoptosis, programmed cell death, is a highly regulated and complex pathway essential for embryonic development, immune-system function and maintenance of tissue homeostasis where cells induce their own cell death. Cells undergoing apoptosis exhibit a distinctive phenotype characterized by maintenance of membrane integrity, cell shrinkage, phosphatidylserine (PS) externalization at the plasma membrane, caspase protease activation, DNA fragmentation, release of cytochrome c from the mitochondrion, and membrane blebbing. An important regulatory protein in the apoptotic pathway is p53. The p53 protein functions to modulate the cell cycle by arresting cells in the G1 and G 2 phases to repair DNA damage, and/or to induce apoptosis. Another important cell cycle phase is S-phase, when the cell synthesizes DNA. Apoptosis has been extensively studied when induced by natural ligands, irradiation (IR), ultraviolet (UV) light, and chemical stimuli. Recently, apoptosis has been studied using a new technology that targets intracellular structures entitled nanosecond pulsed electric fields (nsPEF). NsPEF are high intensity power, low energy, very short pulses (nanosecond) that can provide a new biological tool for modulating intracellular structures and functions. In several cell types nsPEFs have been shown to induce apoptosis determined by maintenance of the plasma membrane integrity, PS externalization, caspase activation, DNA fragmentation, cytochrome c release, cell shrinkage, and ultimately cell death. The overall objective of this dissertation is to investigate the effects of nsPEF exposure under a range of sub-lethal and lethal conditions and ultimately to reach an apoptotic threshold for colon carcinoma cells using HM 16p53+/+ and HCT116p53-/- cells. There are three specific aims in this dissertation, (1) determine the effect of nsPEF exposures on colon carcinoma cells in respect to apoptosis, p53 and proliferation at conditions that induce apoptosis in Jurkat and HL60 cells, (2) determine the response of HCT116p53+/+ cells to nsPEFs during DNA synthesis in respect to apoptosis and proliferation at conditions that induce apoptosis in Jurkat and HL60 cells; and (3) determine conditions of nsPEFs that induce approximately fifty percent cell death in colon carcinoma cells and analyze effects of these pulses in respect to apoptosis, p53 and proliferation. These aims will be determined by analyzing apoptotic markers, proliferative markers, and morphological markers. Results of this dissertation show that (1) HCT116 cells have a higher tolerance for nsPEF exposure as compared to HL60 and Jurkat cells and p53 effects are more readily observed under sub-lethal conditions, (2) in order to induce apoptosis in HCT116 cells the number of nsPEF exposures must be increased, (3) S-phase provides a protective effect while being exposed to nsPEF, and (4) apoptosis is induced in these cells through the mitochondrial pathway in both p53 and Bax-dependent and -independent mechanisms.

DOI

10.25777/6sjm-eg98

ISBN

9780542580055

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