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Science 334 (6056): 611-612

Copyright © 2011 by the American Association for the Advancement of Science

Growth Signaling from Inside

Hilde Abrahamsen1,2, and Harald Stenmark1,2

All cells have the ability to sense whether nutrients are scarce or abundant so that appropriate anabolic or catabolic programs can be initiated. A key sensor of nutrient status in eukaryotes is target of rapamycin (TOR) (1), an enzyme that phosphorylates a subset of proteins that function in cell growth and metabolism (2). In mammalian cells, TOR associates with accessory proteins to form mammalian TOR complex 1 (mTORC1) (3). Amino acids are potent activators of mTORC1 (4, 5), but it has not been clear how mTORC1 senses amino acids within the cell. On page 678 of this issue, Zoncu et al. (6) describe how sensing amino acids occurs inside the lumen of lysosomes, the main degradative organelles in the cell.

1 Department of Biochemistry, Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, N-0310 Oslo, Norway.
2 Centre for Cancer Biomedicine, University of Oslo, Montebello, N-0310 Oslo, Norway.

E-mail: stenmark{at}

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