Phospholipase A2 receptor (PLA2R) mediates various biological responses elicited by group IB secretory phospholipase A2 (sPLA2-IB). The recently cloned group X sPLA2 (sPLA2-X) possesses several structural features characteristic of sPLA2-IB. Here, we detected a specific binding site of sPLA2-X in mouse osteoblastic MC3T3-E1 cells. Cross-linking experiments demonstrated its molecular weight (180 kDa) to be similar to that of PLA2R. In fact, sPLA2-X was found to bind the recombinant PLA2R expressed in COS-7 cells, and its specific binding detected in mouse lung membranes was abolished by the deficiency of PLA2R. These findings demonstrate sPLA2-X to be one of the high-affinity ligands for mouse PLA2R.
