hydroxycarboxylic acid receptor 3 hydroxycarboxylic acid receptor 3 hydroxycarboxylic acid receptor 3 (hca3), also known as niacin receptor 2 (niacr2) and gpr109b, is a protein which in humans is encoded by the hcar3 gene. hca3, like the other hydroxycarboxylic acid receptors hca1 and hca2, is a gi/o-coupled g protein-coupled receptor (gpcr). the primary endogenous agonists of hca3 are 3-hydroxyoctanoic acid and kynurenic acid. hca3 is also a low-affinity biomolecular target for niacin (aka nicotinic acid). hcar3identifiersaliaseshcar3, gpr109b, hca3, hm74, pumag, puma-g, niacin receptor 2, hydroxycarboxylic acid receptor 3external idsomim: 606039 homologene: 130547 genecards: hcar3 gene location (human)chr.chromosome 12 (human)band12q24.31start122,714,756 bpend122,716,811 bprna expression patternbgeehumanmouse (ortholog)top expressed inbloodspleenmonocytebone marrowskin of abdomenappendixbone marrow cellsplacentaupper lobe of left lungsubcutaneous adipose tissuen/amore reference expression databiogpsn/agene ontologymolecular function g protein-coupled receptor activity signal transducer activity cellular component integral component of membrane cell junction plasma membrane integral component of plasma membrane membrane biological process g protein-coupled receptor signaling pathway signal transduction sources:amigo / quickgoorthologsspecieshumanmouseentrez8843n/aensemblensg00000255398n/auniprotp49019n/arefseq (mrna)nm_006018n/arefseq (protein)np_006009n/alocation (ucsc)chr 12: 122.71 – 122.72 mbn/apubmed searchn/awikidataview/edit human