The Regulation of Mtorc2 Kinase Activity and Complex Integrity

<p>Growth factor signaling promotes anabolic processes via activation of the</p> <p>PI3K-Akt kinase cascade. Deregulation of the growth factor-dependent PI3K-Akt</p> <p>pathway was implicated in tumorigenesis. Akt is an essential serine/threonine</p> <p>protein kinase that controls multiple physiological functions such as cell growth,</p> <p>proliferation, and survival to maintain cellular homeostasis. Recently, the</p> <p>mammalian Target of Rapamycin Complex 2 (mTORC2) was identified as the</p> <p>main Akt Ser-473 kinase, and Ser-473 phosphorylation is required for Akt</p> <p>hyperactivation. However, the detailed mechanism of mTORC2 regulation in</p> <p>response to growth factor stimulation or cellular stresses is not well understood.</p> <p>In the first project, we studied the regulation of the mTORC2-Akt signaling</p> <p>under ER stress. We identified the inactivation of mTORC2 by glycogen synthase</p> <p>kinase-3β (GSK-3β). Under ER stress, the essential mTORC2 component, rictor,</p> <p>is phosphorylated by GSK-3β at Ser-1235. This phosphorylation event results in</p> <p>the inhibition of mTORC2 kinase activity by interrupting Akt binding to mTORC2.</p> <p>Blocking rictor Ser-1235 phosphorylation can attenuate the negative impacts of</p> <p>GSK-3β on mTORC2/Akt signaling and tumor growth. Thus, our work</p> <p>demonstrated that GSK-3β-mediated rictor Ser-1235 phosphorylation in response</p> <p>to ER stress interferes with Akt signaling by inhibiting mTORC2 kinase activity.</p> <p>In the second project, I investigated the regulation of the mTORC2 integrity.</p> <p>We found that basal mTOR kinase activity depends on ATP level, which is tightly</p> <p>regulated by cell metabolism. The ATP-sensitive mTOR kinase is required for</p> <p>SIN1 protein phosphorylation and stabilization. SIN1 is an indispensable subunit of</p> <p>mTORC2 and is required for the complex assembly and mTORC2 kinase activity.</p> <p>Our findings reveal that mTOR-mediated phosphorylation of SIN1 is critical for</p> <p>maintaining complex integrity by preventing SIN1 from lysosomal degradation.</p> <p>In sum, our findings verify two distinct mTORC2 regulatory mechanisms via</p> <p>its components rictor and SIN1. First, GSK-3β-mediated rictor Ser-1235</p> <p>phosphorylation results in mTORC2 inactivation by interfering its substrate binding</p> <p>ability. Second, mTOR-mediated Ser-260 phosphorylation of SIN1 preserves its</p> <p>complex integrity. Thus, these two projects provide novel insights into the</p> <p>regulation of mTORC2.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation (PhD)

Year dc:date.available

2012

Author dc:creator

• Chen, Chien-Hung

Contributors dc:contributor

• Dos Sarbassov
• Xin Lin
• Mong-Hong Lee

• cell signaling
• mTORC2
• Akt
• GSK-3 beta
• ER stress
• complex integrity
• Medicine and Health Sciences

Repository record dc:identifier

https://digitalcommons.library.tmc.edu/utgsbs_dissertations/280

OAI identifier oai:identifier

oai:digitalcommons.library.tmc.edu:utgsbs_dissertations-1296