Carboxyl-terminal region conserved among phosphoinositide-kinase-related kinases is indispensable for mTOR function in vivo and in vitro

Background: The mammalian target of rapamycin (mTOR) belongs to the family of phosphoinositide (PI)-kinase-related kinases that includes the ataxia-te langiectasia gene product (ATM). mTOR plays a critical role in controlling translational effectors such as p70 S6 kinase alpha (p70 alpha) and eukaryo tic initiation factor 4E binding protein 1 (4EBP1). Results: We show that the C-terminal region of mTOR, which is highly conser ved among the PI-kinase-related kinases, plays a critical role in the mTOR protein kinase activity. Deletion of the C-terminal residues did not advers ely affect the expression of mTOR, but caused a nearly complete loss of the mTOR protein kinase activity toward both 4EBP1 and p70 alpha in vitro. The se deletions also abolished the ability of a rapamycin-resistant mTOR mutan t to rescue the activity of p70 alpha from inhibition induced by rapamycin in vivo. Furthermore, replacement of Trp2545, a conserved residue in the C- terminal region throughout the PI-kinase-related kinase family, abolished t he function of the mTOR kinase, both in vivo and in vitro. However, substit ution of 32 C-terminal residues of mTOR with those of ATM did not restore t he mTOR function. Conclusions: These findings define an indispensable role for the noncatalyt ic C-terminal region of mTOR and indicate that, although this highly conser ved region may be important throughout the PI-kinase-related kinase family, it is not functionally interchangeable within the family.