
<ArticleTitle>Human MCF10A mammary epithelial cells undergo apoptosis following <prot>actin</prot> depolymerization that is independent of attachment and rescued by <prot>Bcl-2</prot>.</ArticleTitle>
<AbstractText>Many tumor cells are impaired in adhesion-regulated apoptosis, which contributes to their metastatic potential. However, suppression of this apoptotic pathway in untransformed cells is not mediated only by adhesion to the extracellular matrix but also through the resulting ability to spread and adopt a distinct morphology. Since cell spreading is dependent on the integrity of the <prot>actin</prot> microfilament cytoskeleton, we sought to determine if <prot>actin</prot> depolymerization was sufficient to induce apoptosis, even in the presence of continuous attachment. For this study, we used a human mammary epithelial cell line (MCF10A), which is immortalized but remains adhesion dependent for survival. Treatment of MCF10A cells with latrunculin-A (LA), an inhibitor of <prot>actin</prot> polymerization, rapidly led to disruption of the <prot>actin</prot> cytoskeleton and caused cell rounding but preserved attachment. Initiation of apoptosis in LA-treated MCF10A cells was detected by mitochondrial localization of the <prot>Bax</prot> apoptotic protein, which was prevented by overexpression of <prot>Bcl-2</prot>. DNA fragmentation and <prot>poly(ADP-ribose) polymerase</prot> (<prot>PARP</prot>) cleavage in LA-treated MCF10A cells indicated progression to the execution phase of apoptosis. The MDA-MB-453 cell line, which was derived from a metastatic human mammary tumor, was resistant to <prot>PARP</prot> cleavage and loss of viability in response to <prot>actin</prot> depolymerization. Stable overexpression of <prot>Bcl-2</prot> in the untransformed MCF10A cells was able to recapitulate the resistance to apoptosis found in the tumor cell line. We demonstrate that inhibition of <prot>actin</prot> polymerization is sufficient to stimulate apoptosis in attached MCF10A cells, and we present a novel role for <prot>Bcl-2</prot> in cell death induced by direct disruption of the <prot>actin</prot> cytoskeleton.</AbstractText>
