PMID- 12812918
OWN - NLM
STAT- MEDLINE
DCOM- 20031030
LR  - 20211203
IS  - 0193-1849 (Print)
IS  - 0193-1849 (Linking)
VI  - 285
IP  - 4
DP  - 2003 Oct
TI  - Potential role of leucine metabolism in the leucine-signaling pathway involving 
      mTOR.
PG  - E854-63
AB  - Leucine has been shown to stimulate adipose tissue protein synthesis in vivo as 
      well as leptin secretion, protein synthesis, hyper-plastic growth, and tissue 
      morphogenesis in in vitro experiments using freshly isolated adipocytes. 
      Recently, others have proposed that leucine oxidation in the mitochondria may be 
      required to activate the mammalian target of rapamycin (mTOR), the cytosolic 
      Ser/Thr protein kinase that appears to mediate some of these effects. The first 
      irreversible and rate-limiting step in leucine oxidation is catalyzed by the 
      branched-chain alpha-keto acid dehydrogenase (BCKD) complex. The activity of this 
      complex is regulated acutely by phosphorylation of the E1alpha-subunit at Ser293 
      (S293), which inactivates the complex. Because the alpha-keto acid of leucine 
      regulates the activity of BCKD kinase, it has been suggested as a potential 
      target for leucine regulation of mTOR. To study the regulation of BCKD 
      phosphorylation and its potential link to mTOR activation, a 
      phosphopeptide-specific antibody recognizing this site was developed and 
      characterized. Phospho-S293 (pS293) immunoreactivity in liver corresponded 
      closely to diet-induced changes in BCKD activity state. Immunoreactivity was also 
      increased in TREMK-4 cells after the induction of BCKD kinase by a drug-inducible 
      promoter. BCKD S293 phosphorylations in adipose tissue and gastrocnemius (which 
      is mostly inactive in vivo) were similar. This suggests that BCKD complex in 
      epididymal adipose tissue from food-deprived rats is mostly inactive (unable to 
      oxidize leucine), as is the case in muscle. To begin to test the leucine 
      oxidation hypothesis of mTOR activation, the dose-dependent effects of orally 
      administered leucine on acute activation of S6K1 (an mTOR substrate) and BCKD 
      were compared using the pS293 antibodies. Increasing doses of leucine directly 
      correlated with increases in plasma leucine concentration. Phosphorylation of 
      S6K1 (Thr389, the phosphorylation site leading to activation) in adipose tissue 
      was maximal at a dose of leucine that increased plasma leucine approximately 
      threefold. Changes in BCKD phosphorylation state required higher plasma leucine 
      concentrations. The results seem more consistent with a role for BCKD and BCKD 
      kinase in the activation of leucine metabolism/oxidation than in the activation 
      of the leucine signal to mTOR.
FAU - Lynch, Christopher J
AU  - Lynch CJ
AD  - Department of Cellular & Molecular Physiology (MC H166, Rm C4757), Penn State 
      College of Medicine, 500 University Drive, Hershey, PA 17033, USA. clynch@psu.edu
FAU - Halle, Beth
AU  - Halle B
FAU - Fujii, Hisao
AU  - Fujii H
FAU - Vary, Thomas C
AU  - Vary TC
FAU - Wallin, Reidar
AU  - Wallin R
FAU - Damuni, Zahi
AU  - Damuni Z
FAU - Hutson, Susan M
AU  - Hutson SM
LA  - eng
GR  - DK 34738/DK/NIDDK NIH HHS/United States
GR  - DK 53843/DK/NIDDK NIH HHS/United States
GR  - DK 62880/DK/NIDDK NIH HHS/United States
GR  - GM 39277/GM/NIGMS NIH HHS/United States
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PT  - Research Support, U.S. Gov't, Non-P.H.S.
PT  - Research Support, U.S. Gov't, P.H.S.
DEP - 20030617
PL  - United States
TA  - Am J Physiol Endocrinol Metab
JT  - American journal of physiology. Endocrinology and metabolism
JID - 100901226
RN  - EC 2.7.- (Protein Kinases)
RN  - EC 2.7.11.1 (Ribosomal Protein S6 Kinases)
RN  - EC 2.7.11.1 (TOR Serine-Threonine Kinases)
RN  - EC 2.7.11.4 ((3-methyl-2-oxobutanoate dehydrogenase (lipoamide)) kinase)
RN  - GMW67QNF9C (Leucine)
SB  - IM
MH  - Adipose Tissue/*metabolism
MH  - Administration, Oral
MH  - Animals
MH  - Dose-Response Relationship, Drug
MH  - Enzyme Activation
MH  - Leucine/*administration & dosage/*metabolism
MH  - Liver/drug effects/*metabolism
MH  - Male
MH  - Protein Kinases/*metabolism
MH  - Rats
MH  - Rats, Sprague-Dawley
MH  - Ribosomal Protein S6 Kinases/*metabolism
MH  - Signal Transduction/physiology
MH  - TOR Serine-Threonine Kinases
EDAT- 2003/06/19 05:00
MHDA- 2003/10/31 05:00
CRDT- 2003/06/19 05:00
PHST- 2003/06/19 05:00 [pubmed]
PHST- 2003/10/31 05:00 [medline]
PHST- 2003/06/19 05:00 [entrez]
AID - 00153.2003 [pii]
AID - 10.1152/ajpendo.00153.2003 [doi]
PST - ppublish
SO  - Am J Physiol Endocrinol Metab. 2003 Oct;285(4):E854-63. doi: 
      10.1152/ajpendo.00153.2003. Epub 2003 Jun 17.