Oncogenic ras inhibits anoikis of intestinal epithelial cells by preventing the release of a mitochondrial pro-apoptotic protein Omi/HtrA2 into the cytoplasm

Zaiping Liu, Hongbing Li, Mathieu Derouet, Alexander Berezkin, Takehiko Sasazuki, Senji Shirasawa, Kirill Rosen

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Resistance of cancer cells to anoikis, apoptosis induced by cell detachment from the extracellular matrix, is thought to represent a critical feature of the malignant phenotype. Mechanisms that control anoikis of normal and cancer cells are understood only in part. Previously we found that anoikis of non-malignant intestinal epithelial cells is driven by detachment-induced down-regulation of Bcl-XL, a protein that blocks apoptosis through preventing the release of death-promoting factors from the mitochondria. Mitochondrial proteins the release of which causes anoikis are presently unknown. Similar to what was previously observed by others for keratinocytes and fibroblasts, we show here that anoikis of intestinal epithelial cells does not involve caspase-9, a target of a mitochondrial protein cytochrome c. Furthermore, Smac/Diablo, another mitochondrial pro-apoptotic factor, does not appear to play a role in detachment-dependent apoptosis of these cells either. Instead, anoikis of intestinal epithelial cells is triggered by the release of a mitochondrial protein Omi/HtrA2, an event driven by detachment-induced down-regulation of Bcl-XL. Moreover, we established that oncogenic ras inhibits anoikis by preventing the release of Omi/HtrA2. This effect of ras required ras-induced down-regulation of a pro-apoptotic protein Bak and could be blocked by an inhibitor of phosphoinositide 3-kinase, a target of Ras that was previously implicated by us in the down-regulation of Bak and blockade of anoikis. We conclude that Omi/HtrA2 is an inducer of anoikis and an important regulator of ras-induced transformation.

Original languageEnglish
Pages (from-to)14738-14747
Number of pages10
JournalJournal of Biological Chemistry
Issue number21
Publication statusPublished - May 26 2006
Externally publishedYes


All Science Journal Classification (ASJC) codes

  • Biochemistry

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