(D) Rapamycin sensitivity of LARP1 phosphorylation sites in cells. (C) In vitro kinase activity of mTORC1 towards peptides containing indicated LARP1 sites was analyzed as in (A). The sequences of all indicated phosphorylation sites are available in Fig. Results are displayed as the relative kinase activity of mTORC1 for each peptide and the rapamycin sensitivity of each site is indicated. (B) In vitro kinase activity of mTORC1 toward indicated peptide substrates. Phosphorylation levels of the specified peptides were quantified by densitometry. (A) In vitro kinase activity of mTORC1 toward a set of short synthetic peptides, each containing an established mTORC1 phosphorylation site, was analyzed by autoradiography (representative example shown). Our results reveal a mechanism through which mTORC1 effectors can respond differentially to the same signals. Thus, the intrinsic capacity of a phosphorylation site to serve as an mTORC1 substrate, a property we call substrate quality, is a major determinant of its sensitivity to modulators of the pathway. Slight modifications of the sites were sufficient to alter mTORC1 activity toward them in vitro and to cause concomitant changes within cells in their sensitivity to rapamycin and starvation. We find that the in vitro kinase activity of mTORC1 toward peptides encompassing established phosphorylation sites varies widely and correlates strongly with the resistance of the sites to rapamycin, as well as to nutrient and growth factor starvation within cells. A persistent mystery is why the phosphorylation of many bona fide mTORC1 substrates is resistant to rapamycin. The mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) protein kinase promotes growth and is the target of rapamycin, a clinically useful drug that also prolongs life span in model organisms.
0 Comments
Leave a Reply. |