Agouti-related protein is posttranslationally cleaved by proprotein convertase 1 to generate agouti-related protein (AGRP)83-132: interaction between AGRP83-132 and melanocortin receptors cannot be influenced by syndecan-3.
Agouti-related protein (AGRP) plays a key role in energy homeostasis. The carboxyl-terminal domain of AGRP acts as an endogenous antagonist of the melanocortin-4 receptor (MC4-R). It has been suggested that the amino-terminal domain of AGRP binds to syndecan-3, thereby modulating the effects of carboxyl-terminal AGRP at the MC4-R. This model assumes that AGRP is secreted as a full-length peptide. In this study we found that AGRP is processed intracellularly after Arg(79)-Glu(80)-Pro(81)-Arg(82). The processing site suggests cleavage by proprotein convertases (PCs). RNA interference and overexpression experiments showed that PC1/3 is primarily responsible for cleavage in vitro, although both PC2 and PC5/6A can also process AGRP. Dual in situ hybridization demonstrated that PC1/3 is expressed in AGRP neurons in the rat hypothalamus. Moreover, hypothalamic extracts from PC1-null mice contained 3.3-fold more unprocessed full-length AGRP, compared with wild-type mice, based on combined HPLC and RIA analysis, demonstrating that PC1/3 plays a role in AGRP cleavage in vivo. We also found that AGRP(83-132) is more potent an antagonist than full-length AGRP, based on cAMP reporter assays, suggesting that posttranslational cleavage is required to potentiate the effect of AGRP at the MC4-R. Because AGRP is cleaved into distinct amino-terminal and carboxyl-terminal peptides, we tested whether amino-terminal peptides modulate food intake. However, intracerebroventricular injection of rat AGRP(25-47) and AGRP(50-80) had no effect on body weight, food intake, or core body temperature. Because AGRP is cleaved before secretion, syndecan-3 must influence food intake independently of the MC4-R.
Creemers
John W M
JW
Department of Human Genetics, University of Leuven and Flanders Interuniversity Institute for Biotechnology, Belgium
Pritchard
Lynn E
LE
Gyte
Amy
A
Le Rouzic
Philippe
P
Meulemans
Sandra
S
Wardlaw
Sharon L
SL
Zhu
Xiaorong
X
Steiner
Donald F
DF
Davies
Nicola
N
Armstrong
Duncan
D
Lawrence
Catherine B
CB
Luckman
Simon M
SM
Schmitz
Catherine A
CA
Davies
Rick A
RA
Brennand
John C
JC
White
Anne
A
D054369:Agouti-Related Protein; D000818:Animals; D004734:Energy Metabolism / Q000187:drug effects; D007031:Hypothalamus / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D008297:Male; D008562:Membrane Glycoproteins / Q000502:physiology*; D010446:Peptide Fragments / Q000378:metabolism*; D036361:Peptide Hormones / Q000494:pharmacology; D045664:Proprotein Convertase 1 / Q000502:physiology*; D011499:Protein Processing, Post-Translational; D011509:Proteoglycans / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044105:Receptor, Melanocortin, Type 4 / Q000502:physiology*; D053670:Syndecan-3
C515197:AGRP protein, rat; D054369:Agouti-Related Protein; D036341:Intercellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D036361:Peptide Hormones; D011509:Proteoglycans; D044105:Receptor, Melanocortin, Type 4; C508303:Sdc3 protein, rat; D053670:Syndecan-3; C411703:agouti-related protein-(83-132); D045664:Proprotein Convertase 1