The mammalian target of rapamycin complex 1 (mTORC1) integrates amino acid (AA) availability to support protein synthesis and cell growth. Taste receptor type 1 member (T1R) is a G protein-coupled receptor that functions as a direct sensor of extracellular AA availability to regulate mTORC1 through Ca2+ stimulation and extracellular signal–regulated kinases 1 and 2 (ERK1/2) activation. However, the roles of specific AAs in T1R1/T1R3-regulated mTORC1 are poorly defined. In this study, T1R1 and T1R3 subunits were expressed in C2C12 myotubes, and l-AA sensing was accomplished by T1R1/T1R3 to activate mTORC1. In response to l-AAs, such as serine (Ser), arginine (Arg), threonine (Thr), alanine (Ala), methionine (Met), glutamine (Gln), and glycine (Gly), Met induced mTORC1 activation and promoted protein synthesis. Met also regulated mTORC1 via T1R1/T1R3-PLCβ-Ca2+-ERK1/2 signal transduction. Results revealed a new role for Met-regulated mTORC1 via an AA receptor. Further studies should be performed to determine the role of T1R1/T1R3 in mediating extracellular AA to regulate mTOR signaling and to reveal its mechanism.

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The polyunsaturated fatty acids (PUFAs) receptor GPR120 exerts a significant impact on systemic nutrient homeostasis in human and rodents. However, the porcine GPR120 (pGPR120) has not been well characterized. In the current study, we found that pGPR120 had 3 spliced variants. Transcript 1 encoded 362-amino acids (aa) wild type pGPR120-WT, which shared 88% homology with human short form GPR120. Transcript 1 was the mainly expressed transcript of pGPR120. It was expressed predominantly in ileum, jejunum, duodenum, spleen, and adipose. Transcript 3 (coding 320-aa isoform) was detected in spleen, while the transcript 2 (coding 310-aa isoform) was only slightly expressed in spleen. A selective agonist for human GPR120 (TUG-891) and PUFAs activated SRE-luc and NFAT-luc reporter in HEK293T cells transfected with construct for pGPR120-WT but not pGPR120-V2. However, 320-aa isoform was not a dominant negative isoform. The extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation levels in cells transfected with construct for pGPR120-WT were well activated by PUFAs, especially n-3 PUFA. These results showed that although pGPR120 had 3 transcripts, transcript 1 which encoded pGPR120-WT was the mainly expressed transcript. TUG-891 and PUFAs, especially n-3 PUFA, well activated pGPR120-WT. The current study contributed to dissecting the molecular regulation mechanisms of n-3 PUFA in pigs.