Identification and pharmacological characterization of prokineticin 2β as a selective ligand for prokineticin receptor 1

Prokineticins 1 and 2 (PK1 and PK2) have been recently identified from humans and other mammals and play multiple functional roles. PK proteins are ligands for two G protein-coupled receptors, PK receptor 1 (PKR1) and PK receptor 2 (PKR2). Here, we report the molecular cloning and pharmacological characterization of an alternatively spliced product of the PK2 gene encoding 21 additional amino acids compared with PK2, designated PK2L (for PK2 long form). PK2L mRNA is broadly expressed, as is PK2. However, PK2L mRNA expression is lower in brain, undetectable in kidney, and much higher in lung and spleen than that of PK2. We expressed PK2L in mammalian cells and characterized the resulting peptide in comparison with PK1 and PK2. Biochemical characterization indicates that secreted PK2L protein is processed into a smaller peptide by proteolytic cleavage. We designate this smaller form of peptide as PK2 beta. Coexpression of furin with PK2L significantly increased the PK2 beta processing efficiency. Functional studies showed that PK1, PK2, and PK2 beta stimulate intracellular Ca2+ responses in PKR1-expressing cells with similar potencies. However, the PK2 beta stimulus of Ca2+ responses in PKR2-expressing cells is at least 10-fold less potent than that of PK1 or PK2. Differences in receptor selectivity combined with differential tissue expression patterns suggest PK2 and PK2 beta might have different functions in vivo. PKRs have been reported to couple to G(q) and G(i) proteins. In this report, we show that PKs not only stimulate Ca2+ mobilization but also induce cAMP accumulation in PKR-expressing cells.