Oligonucleosomal DNA Fragmentation in MCF-7 Cells Undergoing Palmitate-Induced Apoptosis

D. V. Semenov^*, P. A. Aronov, E. V. Kuligina, M. O. Potapenko, and V. A. Richter

Novosibirsk Institute of Bioorganic Chemistry, Siberian Division of the Russian Academy of Sciences, pr. Lavrentieva 8, Novosibirsk 630090, Russia; fax: 7 (383-2) 33-36-77; E-mail: semenov@niboch.nsc.ru

^* To whom correspondence should be addressed.

Received December 26, 2002; Revision received April 24, 2003

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Oligonucleosomal fragmentation of nuclear DNA is the late-stage apoptosis hallmark. In apoptotic mammalian cells the fragmentation is catalyzed by DFF40/CAD DNase primarily activated by caspase 3 through the site-specific proteolytic cleavage of DFF45/ICAD. A deletion in the casp3 gene of human breast adenocarcinoma MCF-7 results in lack of procaspase 3 in these cells. The absence of caspase 3 in MCF-7 leads to disability to activate oligonucleosomal DNA fragmentation in TNF-alpha induced cell death. In this study, sodium palmitate was used as an apoptotic stimulus for MCF-7. It has been shown that palmitate but not TNF-alpha induces both apoptotic changes in nuclei and oligonucleosomal DNA fragmentation in casp3-mutated MCF-7. Activation and accumulation of 40-50 kD DFF40-like DNases in nuclei of palmitate-treated apoptotic MCF-7 were detected by SDS-DNA-PAGE assay. Microsomal fraction of apoptotic MCF-7 does not contain any detectable DNases, but activates 40-50 kD nucleases when incubated with human placental chromatin. Furthermore, microsomes of apoptotic MCF-7 induce oligonucleosomal fragmentation of chromatin in a cell-free system. Both the activation of DNases and chromatin fragmentation are suppressed in the presence of the caspase 3/7 inhibitor Ac-DEVD-CHO. Microsome-associated caspase 7 is suggested to play an essential role in the induction of oligonucleosomal DNA fragmentation in casp3-deficient MCF-7 cells.

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KEY WORDS: MCF-7, apoptosis, DNA fragmentation, caspase 3, caspase 7, caspase activated DNase

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