| HCAR1 | 
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| Identifiers | 
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| Aliases | HCAR1, GPR104, GPR81, HCA1, LACR1, TA-GPCR, TAGPCR, FKSG80, hydroxycarboxylic acid receptor 1 | 
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| External IDs | OMIM: 606923; MGI: 2441671; HomoloGene: 13060; GeneCards: HCAR1; OMA:HCAR1 - orthologs | 
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| | Gene location (Mouse) | 
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 |  |  | Chr. | Chromosome 5 (mouse) | 
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 |  |  | Band | 5|5 F | Start | 124,014,799 bp | 
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 | End | 124,018,083 bp | 
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| | RNA expression pattern | 
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 | Bgee | | Human | Mouse (ortholog) | 
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 | | Top expressed in |  | gonad
 spleen
 minor salivary glands
 body of stomach
 subcutaneous adipose tissue
 stromal cell of endometrium
 right lobe of thyroid gland
 left lobe of thyroid gland
 ganglionic eminence
 human kidney
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 | | Top expressed in |  | brown adipose tissue
 white adipose tissue
 mammary gland
 embryo
 transitional epithelium of urinary bladder
 subcutaneous adipose tissue
 esophagus
 dentate gyrus of hippocampal formation granule cell
 right kidney
 lacrimal gland
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 |  | More reference expression data | 
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 | BioGPS |  | 
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| Wikidata | 
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Hydroxycarboxylic acid receptor 1 (HCA1), formerly known as G protein-coupled receptor 81 (GPR81), is a protein that in humans is encoded by the HCAR1 gene. HCA1, like the other hydroxycarboxylic acid receptors HCA2 and HCA3, is a Gi/o-coupled G protein-coupled receptor (GPCR). The primary endogenous agonist of HCA1 is lactic acid (and its conjugate base, lactate). More recently, 3,5-dihydroxybenzoic acid has been reported to activate HCA1.
Lactate was initially found to activate HCA1 on fat cells and thereby to inhibit these cells lipolysis i.e., break-down of their fats into free fatty acids and glycerol. Subsequent studies have found that in addition to fat cells, HCA1 is expressed on cells in the brain, skeletal muscle, lymphoid tissue, uterus, kidney, liver, and pancreas as well as on immune cells such as macrophages and antigen-presenting cells. In the brain, HCA1 acts to dampen neuron excitation and may also function to promote neurogenesis (the production of neurons from neural stem cells) and angiogenesis (the formation of new blood vessels from pre-existing blood vessels). The functions of HCA1 in non-fat and non-neural tissues have not been fully defined but in many cases appear to involve promoting the survival of cells, including various types of cancer cells.