Abstract
Gpr171 is an orphan G-protein-coupled receptor putatively related to the P2Y family of purinergic receptors (P2YRs) for extracellular nucleotides, a group of mediators previously shown to regulate hematopoietic progenitor cells. No information is currently available on the ligand responsible for Gpr171 activation and its biological role remains unknown. We reconstructed Gpr171 phylogenesis in mice and confirmed that Gpr171 is evolutionally related to members of a P2Y gene-cluster localized on mouse chromosome 3. As a first step toward unveiling a role for Gpr171, we investigated its expression profile in murine hematopoietic cells. As opposed to other P2YRs, we found that Gpr171 expression is down-regulated in monocytes and granulocytes, suggesting a negative role in myeloid lineage specification. To test Gpr171 functional role, we next enforced Gpr171 expression in a myeloblastic cell line (32D cells) and in primary Sca-1(+) hematopoietic progenitors, and observed a decreased expression of myeloid markers upon induction of Gpr171, as well as an increased generation of colonies in vitro. Conversely, Gpr171 silencing induced opposite results, diminishing the expression of myeloid markers and the clonogenic potential of 32D cells. In vivo, mice transplanted with hematopoietic progenitor cells overexpressing Gpr171 displayed a significant reduction in the percentage of Mac-1(+)Gr-1(-) cells. As a preliminary step in the investigation of Gpr171 role in murine hematopoiesis, our findings indicate that the orphan receptor Gpr171 negatively regulates myeloid differentiation. Together with phylogenic analyses, our data suggest that Gpr171 may have followed a separate evolutionary pathway as compared to other P2YRs belonging to the same gene cluster.