Interaction of the Human Prostacyclin Receptor and the NHERF4 Family member Intestinal and Kidney Enriched PDZ Protein (IKEPP)

Prostacyclin and its I Prostanoid receptor, the IP, play central roles in haemostasis and in re-endothelialization in response to vascular injury. Herein, Intestinal and Kidney Enriched PDZ Protein (IKEPP) was identified as an interactant of the human (h) IP mediated through binding of PDZ domain 1 (PDZD1) and, to a lesser extent, PDZD2 of IKEPP to a carboxyl-terminal Class I ‘PDZ ligand’ within the hIP. While the interaction is constitutive, agonist-activation of the hIP leads to cAMP-dependent protein kinase (PK) A and PKC- phosphorylation of IKEPP, coinciding with its increased interaction with the hIP. Ectopic expression of IKEPP increases functional expression of the hIP, enhancing its ligand binding and agonist-induced cAMP generation. Originally thought to be restricted to renal and gastrointestinal tissues, herein, IKEPP was also found to be expressed in vascular endothelial cells where it co-localizes and complexes with the hIP. Furthermore, siRNA-disruption of IKEPP expression impaired hIP-induced endothelial cell migration and in vitro angiogenesis, revealing the functional importance of the IKEPP:IP interaction within the vascular endothelium. Identification of IKEPP as a functional interactant of the IP reveals novel mechanistic insights into the role of these proteins within the vasculature and, potentially, in other systems where they are co-expressed.