Regulation of Polyamine Analogue-Induced Apoptosis in Human Breast Cancer Cells

Sammanfattning: Apoptosis is a defined process for cells to commit suicide through a set of biochemical and morphological cell changes. Activated apoptotic signals converge on the mitochondria, leading to permeabilization of mitochondrial membranes and release of different apoptosis regulatory proteins into the cytosol. With my studies I wanted to investigate the importance of polyamines in the regulation of apoptosis. The homeostasis of polyamines is highly regulated since polyamines are essential for cell proliferation and cell death. A common feature of polyamine analogue treatment is inhibition of cell proliferation, but sometimes cells also die through apoptosis. When several different breast cancer cell lines were treated with polyamine analogues, mitochondrial activity increased indicating a cellular stress response. The stress response may be caused by polyamine analogue-induced polyamine depletion and/or by the presence of high concentration of a polyamine analogue that does not function as a natural polyamine. Polyamine analogue treatment of L56Br-C1 breast cancer cells resulted in a number of responses culminating in mitochondrial apoptotic cell death, as confirmed by the release of a number of apoptosis-related proteins from the mitochondria. Another response to analogue treatment was the activation of the polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase (SSAT). Using several different methods we have shown that there is an association of SSAT with the mitochondria implicating that SSAT and polyamine depletion are part of the apoptotic process induced by polyamine analogue treatment. To investigate the role of the antiapoptotic protein Bcl-2 in polyamine analogue-induced apoptosis, a vector carrying the gene for Bcl-2 was introduced into the genome of L56Br-C1 cells. The degree of cell death, polyamine reduction, and SSAT activity decreased in Bcl-2 overexpressing cells compared to control cells. In conclusion, polyamine analogue treatment clearly affects the mitochondria and can induce apoptosis as a response, something which can be prevented by Bcl-2 overexpression.