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FUNCTION G-protein coupled receptor for endogenous cannabinoids (eCBs), including N-arachidonoylethanolamide (also called anandamide or AEA) and 2-arachidonoylglycerol (2-AG), as well as phytocannabinoids, such as delta(9)-tetrahydrocannabinol (THC) (PubMed:15620723, PubMed:27768894, PubMed:27851727, PubMed:35637350). Mediates many cannabinoid-induced effects, acting, among others, on food intake, memory loss, gastrointestinal motility, catalepsy, ambulatory activity, anxiety, chronic pain. Signaling typically involves reduction in cyclic AMP (PubMed:1718258, PubMed:21895628, PubMed:27768894). In the hypothalamus, may have a dual effect on mitochondrial respiration depending upon the agonist dose and possibly upon the cell type. Increases respiration at low doses, while decreases respiration at high doses. At high doses, CNR1 signal transduction involves G-protein alpha-i protein activation and subsequent inhibition of mitochondrial soluble adenylate cyclase, decrease in cyclic AMP concentration, inhibition of protein kinase A (PKA)-dependent phosphorylation of specific subunits of the mitochondrial electron transport system, including NDUFS2. In the hypothalamus, inhibits leptin-induced reactive oxygen species (ROS) formation and mediates cannabinoid-induced increase in SREBF1 and FASN gene expression. In response to cannabinoids, drives the release of orexigenic beta-endorphin, but not that of melanocyte-stimulating hormone alpha/alpha-MSH, from hypothalamic POMC neurons, hence promoting food intake. In the hippocampus, regulates cellular respiration and energy production in response to cannabinoids. Involved in cannabinoid-dependent depolarization-induced suppression of inhibition (DSI), a process in which depolarization of CA1 postsynaptic pyramidal neurons mobilizes eCBs, which retrogradely activate presynaptic CB1 receptors, transiently decreasing GABAergic inhibitory neurotransmission. Also reduces excitatory synaptic transmission (By similarity). In superior cervical ganglions and cerebral vascular smooth muscle cells, inhibits voltage-gated Ca(2+) channels in a constitutive, as well as agonist-dependent manner (PubMed:17895407). In cerebral vascular smooth muscle cells, cannabinoid-induced inhibition of voltage-gated Ca(2+) channels leads to vasodilation and decreased vascular tone (By similarity). Induces leptin production in adipocytes and reduces LRP2-mediated leptin clearance in the kidney, hence participating in hyperleptinemia. In adipose tissue, CNR1 signaling leads to increased expression of SREBF1, ACACA and FASN genes (By similarity). In the liver, activation by endocannabinoids leads to increased de novo lipogenesis and reduced fatty acid catabolism, associated with increased expression of SREBF1/SREBP-1, GCK, ACACA, ACACB and FASN genes. May also affect de novo cholesterol synthesis and HDL-cholesteryl ether uptake. Peripherally modulates energy metabolism (By similarity). In high carbohydrate diet-induced obesity, may decrease the expression of mitochondrial dihydrolipoyl dehydrogenase/DLD in striated muscles, as well as that of selected glucose/ pyruvate metabolic enzymes, hence affecting energy expenditure through mitochondrial metabolism (By similarity). In response to cannabinoid anandamide, elicits a pro-inflammatory response in macrophages, which involves NLRP3 inflammasome activation and IL1B and IL18 secretion (By similarity). In macrophages infiltrating pancreatic islets, this process may participate in the progression of type-2 diabetes and associated loss of pancreatic beta-cells (PubMed:23955712).FUNCTION Binds both 2-arachidonoylglycerol (2-AG) and anandamide.FUNCTION Only binds 2-arachidonoylglycerol (2-AG) with high affinity. Contrary to its effect on isoform 1, 2-AG behaves as an inverse agonist on isoform 2 in assays measuring GTP binding to membranes.FUNCTION Only binds 2-arachidonoylglycerol (2-AG) with high affinity. Contrary to its effect on isoform 1, 2-AG behaves as an inverse agonist on isoform 3 in assays measuring GTP binding to membranes.ACTIVITY REGULATION Hemopressin, a peptide derived from hemoglobin subunit alpha (HBA1 and/or HBA2), acts as an antagonist peptide: hemopressin-binding efficiently blocks cannabinoid receptor CNR1 and subsequent signaling.SUBUNIT Interacts (via C-terminus) with CNRIP1; this interaction attenuates constitutive, but not agonist-dependent, inhibition of voltage-gated Ca(2+) channels in neurons (PubMed:17895407). Associates with G protein alpha subunits, including G(i) alpha-1/GNAI1, G(i) alpha-2/GNAI2, G(i) alpha-3/GNAI3 and G(o)-alpha/GNAO1; palmitoylation is important for interaction with GNAI3 and GNAO1 (PubMed:12237474).INTERACTION Unexpectedly, in the mitochondria, the C-terminus is located in the mitochondrial intermembrane space, a compartment topologically considered as extracellular. In canonical seven-transmembrane G-protein coupled receptors, the C-terminus is cytosolic (By similarity). Found on presynaptic axon terminals in some GABAergic neurons in the somatosensory cortex (By similarity).ALTERNATIVE PRODUCTS Widely expressed, with highest levels in fetal and adult brain. Expression levels of isoform 2 and isoform 3 are much lower than those of isoform 1.INDUCTION Up-regulated by endocannabinoid anandamide.PTM Palmitoylation at Cys-415 is important for recruitment at plasma membrane and lipid rafts and association with G protein alpha subunits.DISEASE The protein represented in this entry may be involved in disease pathogenesis. May contribute to the development of diet-induced obesity and several obesity-associated features, such as dyslipidemia and liver steatosis, regulating peripheral lipogenesis, energy expenditure and feeding behavior. CNR1 inverse agonists have been shown to reduce body weight and improve metabolic abnormalities in obese subjects, although adverse neuropsychiatric effects, including anxiety, irritability, and depressed mood, halted their therapeutic development (PubMed:18177726). In obese mice, peripherally restricted CNR1 inverse agonists have been shown to normalize metabolic abnormalities, including insulin resistance and fatty liver, and to reverse leptin resistance.DISEASE Dysfunction of the endogenous cannabinoid system including CNR1 has been implicated in the pathogenesis of a number of central nervous system disorders, including Huntington disease, Parkinson disease, and Alzheimer disease (PubMed:32549916). In post-mortem brains from Huntington disease patients, a progressive CNR1 loss has been observed in the caudate nucleus, putamen, and substantia nigra pars reticulata, and altered expression and abnormal endocannabinoid levels precede motor symptoms in a disease mouse model (PubMed:10828533, PubMed:19524019, PubMed:8255419). In Parkinson disease, low CNR1 expression in mid-superior frontal gyrus and mid-cingulate cortex has been associated with poor mind, poor executive functioning and poor episode memory, while patients with more severe visuospatial dysfunction showed decreased receptor availability in the precuneus, mid-cingulate, supplementary motor cortex, inferior orbitofrontal gyrus and thalamus (PubMed:31342135). In an animal model for Alzheimer disease, CNR1 heterozygous deletion has been associated with decreased levels of postsynaptic density protein 95 (DLG4/PSD95) and accelerated memory impairment, suggesting synaptic dysfunction and a crucial role for CNR1 in the progression of disease symptoms (PubMed:10828533, PubMed:19524019, PubMed:30096288, PubMed:31342135, PubMed:8255419).MISCELLANEOUS High-fat diet also increases the hepatic levels of CNR1 ligand anandamide, but not that of 2-arachidonoylglycerol.MISCELLANEOUS Dubious isoform. A putative downstream initiation AUG is used to produce isoform 2 (PubMed:1718258). The use of the first AUG (same as isoform 1) gives a truncated protein of 36 AA.SIMILARITY Belongs to the G-protein coupled receptor 1 family.
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