title: Isoleucine, leucine, methionine, and threonine effects on mammalian target of rapamycin signaling in mammary tissue.
abstract: Improved representation of postabsorptive N metabolism in lactating dairy cows requires a better understanding of protein synthesis regulation in the mammary glands. This study aimed to determine the quantitative effects of Ile, Leu, Met, and Thr on the phosphorylation state of signaling proteins that regulate protein synthesis. The experiment used a composite design with a central point, 2 axial points per AA, and a complete 2(4) factorial. All of the other AA were provided at the concentrations in Dulbecco's modified Eagle's medium. The experiment was replicated with tissues from 5 lactating cows. Mammary tissue slices (0.12 ± 0.02 g) were incubated for 4h. Total and site-specific phosphorylated mammalian target of rapamycin (mTOR; Ser2448), eukaryotic elongation factor (eEF) 2 (Thr56), ribosomal protein S6 (Ser235/236), and eukaryotic initiation factor 2α (Ser51) were determined by western immunoblotting. Tissue concentrations of the 4 AA studied responded linearly to media supply. Addition of Ile, Leu, Met, or Thr had no effect on eukaryotic initiation factor 2α phosphorylation. Isoleucine and Thr positively affected mTOR phosphorylation. However, the 2 AA had an antagonistic relationship. Similarly, Ile linearly increased ribosomal protein S6 phosphorylation, and Thr inhibited the Ile effect. In addition, eEF2 phosphorylation was linearly decreased by Ile and Leu. Threonine curvilinearly decreased eEF2 phosphorylation, Ile and Leu negatively interacted on eEF2, and Thr tended to inhibit Leu effects on eEF2. This work demonstrated saturable responses and interactions between AA on activation of the mTOR pathway. Incorporation of these concepts into milk protein response models will help to improve milk and milk protein yield predictions and increase postabsorptive N efficiency and reduce N excretion by dairy cows.
authors.affiliation: Department of Dairy Science, Virginia Tech, Blacksburg 24061. Electronic address: sebuy@vt.edu.
authors.forename: S I
authors.initials: SI
authors.lastname: Arriola Apelo
authors.affiliation: Department of Dairy Science, Virginia Tech, Blacksburg 24061.
authors.forename: L M
authors.initials: LM
authors.lastname: Singer
authors.affiliation: Animal Science and Technology College, Shandong Agriculture University, 271018, China.
authors.forename: X Y
authors.initials: XY
authors.lastname: Lin
authors.affiliation: Department of Dairy Science, Virginia Tech, Blacksburg 24061.
authors.forename: M L
authors.initials: ML
authors.lastname: McGilliard
authors.affiliation: Department of Animal Sciences, The Ohio State University, Columbus 43210.
authors.forename: N R
authors.initials: NR
authors.lastname: St-Pierre
authors.affiliation: Department of Dairy Science, Virginia Tech, Blacksburg 24061.
authors.forename: M D
authors.initials: MD
authors.lastname: Hanigan
mesh_terms: D000818:Animals; D002417:Cattle; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D007532:Isoleucine / Q000494:pharmacology*; D007774:Lactation / Q000187:drug effects / Q000502:physiology; D007930:Leucine / Q000494:pharmacology*; D008321:Mammary Glands, Animal / Q000187:drug effects* / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D008892:Milk / Q000378:metabolism; D008894:Milk Proteins / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism; D038601:Ribosomal Protein S6 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D013912:Threonine / Q000494:pharmacology*
chemical_list: D008894:Milk Proteins; D011506:Proteins; D038601:Ribosomal Protein S6; D007532:Isoleucine; D013912:Threonine; D008715:Methionine; D058570:TOR Serine-Threonine Kinases; D007930:Leucine; D020123:Sirolimus
keywords: essential amino acid; mammalian target of rapamycin (mTOR); mammary gland; translation regulation