Protein Bridge Stabilizes Growth Regulatory Pathway

Researchers studying the molecular clues that stimulate cell growth have identified a protein called GâL, which stabilizes the interactions of other proteins comprising the mTOR regulatory pathway.

A protein called mTOR (mammalian target of rapamycin) and a protein called raptor (regulatory associated protein of mTOR) are components of a signaling pathway that regulates mammalian cell growth in response to nutrients and growth factors. Knowledge of the link between mTOR and cell growth had emerged from work done on the effects of the powerful immunosuppresant rapamycin. Those studies showed that rapamycin blocked the activity of mTOR, while additional research revealed that raptor cooperated with the mTOR protein to directly regulate cell size in response to nutrient levels.

In the current study, reported in the April 2003 issue of Molecular Cell, investigators at the Whitehead Institute for Biomedical Research (Cambridge, MA, USA) described a third protein, GâL, which acts as a bridge to stabilize the interaction between the mTOR protein and raptor. The proper balance and activity of theses proteins determine whether the cell will grow in response to nutrient clues.

"As we learn more about mTOR at the cellular level, we can begin to understand its function in the regulation of growth throughout the body,” explained senior author Dr. David Sabatini, a researcher at the Whitehead Institute. "This complex has opened up a window onto how nutrient signaling is involved in different mammalian processes and provide a new way to investigate the role nutrients and metabolism play in disease. In some cases, a cell becomes insensitive to nutrient signaling and growth goes out of control. This suggests that the role of nutrients and signaling has been underestimated in the study of cancer.”