Normal epithelial cells require matrix attachment for survival and the ability of tumour cells to survive outside their natural extracellular matrix (ECM) niches is dependent on acquisition of anchorage independence1. While apoptosis is the most rapid mechanism for eliminating cells lacking appropriate ECM attachment2, recent reports suggest that non-apoptotic death processes prevent survival when apoptosis is inhibited in matrix-deprived cells3 , 4. Here we demonstrate that detachment of mammary epithelial cells from ECM causes an ATP deficiency due to loss of glucose transport. Overexpression of ErbB2 rescues the ATP deficiency by restoring glucose uptake through stabilization of EGFR and PI(3)K activation and this rescue is dependent on glucose-stimulated flux through the antioxidant-generating pentose phosphate pathway (PPP). Interestingly, we found that the ATP deficiency could be rescued by antioxidant treatment without rescue of glucose uptake. This rescue was found to be dependent on stimulation of fatty acid oxidation (FAO), which is inhibited by detachment-induced reactive oxygen species (ROS). The significance of these findings was supported by evidence of an elevation in ROS in matrix-deprived cells in the luminal space of mammary acini and that antioxidants facilitate the survival of these cells and enhance anchorageindependent colony formation. These results reveal both the importance of matrix attachment in regulating metabolic activity and an unanticipated mechanism for cell survival in altered matrix environments through antioxidant restoration of ATP generation.Epithelial cells are dependent on interactions with specific extracellular matrix (ECM) components for survival, proliferation, and differentiation functions 5 . Loss of matrix attachment of cultured epithelial cells activates a caspase-mediated apoptotic program known as anoikis2. In glandular cancers, like breast cancer, tumour cells are displaced from their * To whom correspondence should be addressed: Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, Phone: 617-432-3974, Fax: 617-432-3969, joan_brugge@hms.harvard.edu. 4 Present address: Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556 † These authors contributed equally to this work.Supplementary information is linked to the online version of the paper at www.nature.com/nature. A figure summarising the main result of this paper ( Supplementary Fig. 1) is included in the supplementary information.Author Contributions Z.T.S. and J.S.B. were responsible for the overall study design. Z.T.S., A.R.G., H.Y.I., and S.G. conducted experiments. L.S. and Z.J. conducted the experiments measuring native fluorescence of NAD(P)H in 3D cell culture. Z.G.-H. and P.P. designed the fatty acid oxidation studies and Z.T.S. and Z.G.-H. conducted the fatty acid oxidation assays. Z.T.S. and J.S.B. drafted the manuscript and all other authors made revisions. Author InformationReprints and permissions information is available...

Abstract-Silent information regulator (Sir)2, a class III histone deacetylase, mediates lifespan extension in model organisms and prevents apoptosis in mammalian cells. However, beneficial functions of Sir2 remain to be shown in mammals in vivo at the organ level, such as in the heart. We addressed this issue by using transgenic mice with heart-specific overexpression of Sirt1, a mammalian homolog of Sir2. Sirt1 was significantly upregulated (4-to 8-fold) in response to pressure overload and oxidative stress in nontransgenic adult mouse hearts. Low (2.5-fold) to moderate (7.5-fold) overexpression of Sirt1 in transgenic mouse hearts attenuated age-dependent increases in cardiac hypertrophy, apoptosis/fibrosis, cardiac dysfunction, and expression of senescence markers. In contrast, a high level (12.5-fold) of Sirt1 increased apoptosis and hypertrophy and decreased cardiac function, thereby stimulating the development of cardiomyopathy. Moderate overexpression of Sirt1 protected the heart from oxidative stress induced by paraquat, with increased expression of antioxidants, such as catalase, through forkhead box O (FoxO)-dependent mechanisms, whereas high levels of Sirt1 increased oxidative stress in the heart at baseline. Thus, mild to moderate expression of Sirt1 retards aging of the heart, whereas a high dose of Sirt1 induces cardiomyopathy. Furthermore, although high levels of Sirt1 increase oxidative stress, moderate expression of Sirt1 induces resistance to oxidative stress and apoptosis. These results suggest that Sirt1 could retard aging and confer stress resistance to the heart in vivo, but these beneficial effects can be observed only at low to moderate doses (up to 7.5-fold) of Sirt1. (Circ Res. 2007;100:1512-1521.)

Autophagy has been proposed to promote cell death during lumen formation in three-dimensional mammary epithelial acini because numerous autophagic vacuoles are observed in the dying central cells during morphogenesis. Because these central cells die due to extracellular matrix (ECM) deprivation (anoikis), we have directly interrogated how matrix detachment regulates autophagy. Detachment induces autophagy in both nontumorigenic epithelial lines and in primary epithelial cells. RNA interference-mediated depletion of autophagy regulators (ATGs) inhibits detachment-induced autophagy, enhances apoptosis, and reduces clonogenic recovery after anoikis. Remarkably, matrix-detached cells still exhibit autophagy when apoptosis is blocked by Bcl-2 overexpression, and ATG depletion reduces the clonogenic survival of Bcl-2-expressing cells after detachment. Finally, stable reduction of ATG5 or ATG7 in MCF-10A acini enhances luminal apoptosis during morphogenesis and fails to elicit long-term luminal filling, even when combined with apoptotic inhibition mediated by Bcl-2 overexpression. Thus, autophagy promotes epithelial cell survival during anoikis, including detached cells harboring antiapoptotic lesions.

Summary The PI3K/mTOR-pathway is the most commonly dysregulated pathway in epithelial cancers and represents an important target for cancer therapeutics. Here we show that dual inhibition of PI3K/mTOR in ovarian cancer-spheroids leads to death of inner matrix-deprived cells, whereas matrix-attached cells are resistant. This matrix-associated resistance is mediated by drug-induced upregulation of cellular survival programs that involve both FOXO-regulated transcription and cap-independent translation. Inhibition of any one of several upregulated proteins, including Bcl-2, EGFR, or IGF1R, abrogates resistance to PI3K/mTOR inhibition. These results demonstrate that acute adaptive responses to PI3K/mTOR inhibition in matrix-attached cells resemble well-conserved stress responses to nutrient and growth factor deprivation. Bypass of this resistance mechanism through rational design of drug combinations could significantly enhance PI3K-targeted drug efficacy.

Ephrin signaling through Eph receptor tyrosine kinases can promote attraction or repulsion of axonal growth cones during development. However, the mechanisms that determine whether Eph signaling promotes attraction or repulsion are not known. We show here that the Rho family GEF Vav2 plays a key role in this process. We find that, during axon guidance, ephrin binding to Ephs triggers Vav-dependent endocytosis of the ligand-receptor complex, thus converting an initially adhesive interaction into a repulsive event. In the absence of Vav proteins, ephrin-Eph endocytosis is blocked, leading to defects in growth cone collapse in vitro and significant defects in the ipsilateral retinogeniculate projections in vivo. These findings suggest an important role for Vav family GEFs as regulators of ligand-receptor endocytosis and determinants of repulsive signaling during axon guidance.