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Blood, 15 May 2006, Vol. 107, No. 10, pp. 4003-4010. Prepublished online as a Blood First Edition Paper on February 9, 2006; DOI 10.1182/blood-2005-04-1523.
Submitted April 14, 2005
Department of Biochemistry, BioSciences Institute, University College Cork, Cork, Ireland * Corresponding author; email: s.mckenna{at}ucc.ie.
The Bcr-Abl oncoprotein plays a major role in the development and progression of chronic myeloid leukemia (CML). Several studies have suggested that the expression levels of Bcr-Abl are elevated at disease progression to blast crisis and that this plays a significant role in the achievement of drug resistance. We have established cell lines expressing low and high levels of Bcr-Abl to study the molecular mechanisms involved in disease progression and drug resistance. It is now known that the ER can play a major role in the regulation of apoptosis. We therefore investigated whether Bcr-Abl expression modulates ER homeostasis and interferes with ER-mediated apoptotic pathways in order to promote survival. Bcr-Abl expressing cells exhibit a decreased amount of free releasable calcium in the ER as well as a weaker capacitative calcium entry response, relative to parental cells. This effect is independent of Bcl-2 - a known modulator of ER calcium homeostasis. The reduction in ER releasable calcium results in inhibition of the ER-mitochondria coupling process and mitochondrial calcium uptake. This study demonstrates a novel downstream consequence of Bcr-Abl signaling. The ability to negate calcium dependent apoptotic signaling is likely to be a major pro-survival mechanism in Bcr-Abl expressing cells.
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