G-protein coupled receptor for Big LEN, a 16-amino acid neuropeptide produced from the precursor protein, proSAAS (encoded by PCSK1N) (PubMed:24043826, PubMed:28425495). Acts through a G(i)-alpha-mediated pathway in response to Big LEN (PubMed:24043826). Big LEN-GPR171 system plays an important role in regulating feeding and metabolism (PubMed:24043826). Also plays a role in modulating fear and anxiety-like behaviors in the basolateral amygdala (PubMed:28425495). Big LEN-GPR171 modulates the mu-type opioid receptor signaling and antinociception (PubMed:31308196). Acts as a negative regulator T cell function (PubMed:34615877). Colocalized with GPR83 in the paraventricular nucleus. Highly expressed in hypothalamus, including the arcuate nucleus, paraventricular nucleus and dorsomedial hypothalamus (PubMed:24043826). Expressed in periaqueductal gray (at protein level), found primarily in GABAergic neurons and to a lesser extent in glutamatergic neurons (PubMed:31308196). Expressed in T cells and natural killer cells (PubMed:34615877). Induced upon antigen stimulation. Deficient mice exhibit stronger antitumor immunity. Belongs to the G-protein coupled receptor 1 family.