Journal Article

Glucagon-like peptide-1 receptor activation stimulates PKA-mediated phosphorylation of Raptor and this contributes to the weight loss effect of liraglutide

Ellis, Blair J, Ceddia, Ryan P, Le, Thao DV, Raghavan, Ritika, Ayala, Julio E, Besing, Gai-Linn K, Collins, Sheila, Liu, Dianxin

2023

Overview

The canonical target of the glucagon-like peptide-1 receptor (GLP-1R), Protein Kinase A (PKA), has been shown to stimulate mechanistic Target of Rapamycin Complex 1 (mTORC1) by phosphorylating the mTOR-regulating protein Raptor at Ser 791 following β-adrenergic stimulation. The objective of these studies is to test whether GLP-1R agonists similarly stimulate mTORC1 via PKA phosphorylation of Raptor at Ser 791 and whether this contributes to the weight loss effect of the therapeutic GLP-1R agonist liraglutide. We measured phosphorylation of the mTORC1 signaling target ribosomal protein S6 in Chinese Hamster Ovary cells expressing GLP-1R (CHO-Glp1r) treated with liraglutide in combination with PKA inhibitors. We also assessed liraglutide-mediated phosphorylation of the PKA substrate RRXS*/T* motif in CHO-Glp1r cells expressing Myc-tagged wild-type (WT) Raptor or a PKA-resistant (Ser 791 Ala) Raptor mutant. Finally, we measured the body weight response to liraglutide in WT mice and mice with a targeted knock-in of PKA-resistant Ser 791 Ala Raptor. Liraglutide increased phosphorylation of S6 and the PKA motif in WT Raptor in a PKA-dependent manner but failed to stimulate phosphorylation of the PKA motif in Ser 791 Ala Raptor in CHO-Glp1r cells. Lean Ser 791 Ala Raptor knock-in mice were resistant to liraglutide-induced weight loss but not setmelanotide-induced (melanocortin-4 receptor-dependent) weight loss. Diet-induced obese Ser 791 Ala Raptor knock-in mice were not resistant to liraglutide-induced weight loss; however, there was weight-dependent variation such that there was a tendency for obese Ser 791 Ala Raptor knock-in mice of lower relative body weight to be resistant to liraglutide-induced weight loss compared to weight-matched controls. Together, these findings suggest that PKA-mediated phosphorylation of Raptor at Ser 791 contributes to liraglutide-induced weight loss.

• Publisher: eLife Science Publications, Ltd,eLife Sciences Publications Ltd
• Subject: Agonists / Animals / Antidiabetics / Birds of prey / Body weight / Body weight loss / CHO Cells / Cricetinae / Cricetulus / Cyclic AMP-Dependent Protein Kinases - metabolism / Glucagon / Glucagon-like peptide 1 / Glucagon-Like Peptide-1 Receptor - metabolism / Health aspects / Insulin / Kinases / Liraglutide / Liraglutide - pharmacology / mechanistic target of rapamycin / Mechanistic Target of Rapamycin Complex 1 - metabolism / Melanocortin / Mice / Myc protein / Obesity - drug therapy / Peptides / Phosphorylation / Protein kinase A / Proteins / Rapamycin / raptor / Receptor mechanisms / Regulatory-Associated Protein of mTOR - metabolism / Ribosomal protein S6 / TOR protein / Weight Loss