טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGoldbraikh Dana
SubjectRole of USP1 in Skeletal Muscle Atrophy
DepartmentDepartment of Biology
Supervisor Professor Shenhav Cohen
Full Thesis textFull thesis text - English Version


Abstract

PI3K-Akt-FoxO-mTOR signaling is the central pathway controlling cell growth and
metabolism in all cells. Activation of this pathway by IGF-I or insulin promotes cell
division, and in non-dividing muscle cells, it promotes growth by stimulating overall
protein synthesis and inhibiting protein degradation. Activation of insulin signaling
requires ubiquitination of Akt prior to its activation by phosphorylation. Here, we found that the deubiquitinating (DUB) enzyme USP1 removes K63-linked polyubiquitin chains on Akt to sustain PI3K-Akt-FoxO signaling low during prolonged starvation. DUB screening platform identified USP1 as a direct DUB for Akt, and USP1 depletion in mouse muscle during fasting increased Akt ubiquitination and phosphorylation at T308,PI3K-Akt-FoxO signaling, and glucose uptake. However, the reduction in Akt phosphorylation at S473 in fasting required another enzyme, the Ser/Thr phosphatase PHLPP1, which bound to USP1 to promote the complete inhibition of Akt. Coimmunoprecipitation experiments followed by mass spectrometry analysis identified Disabled-2 (Dab2) and the tuberous sclerosis complex TSC1/TSC2 as USP1 bound proteins. During starvation, Dab2 was essential for Akt recruitment to the USP1-PHLPP1 complex, Akt deubiquitination, and for inhibition of PI3K-Akt-FoxO signaling. In addition, to maintain its own protein levels high, USP1 limits TSC1 protein levels to sustain mTOR mediated basal protein synthesis rates. The USP1-mediated inhibition of PI3K-Akt signaling probably contributes to insulin resistance in catabolic diseases and perhaps to human cancers seen with USP1 mutations.