Both group IB and group IIA secreted phospholipases A2 are natural ligands of the mouse 180-kDa M-type receptor.

Snake venom and mammalian secreted phospholipases A2 (sPLA2s) have been associated with toxic (neurotoxicity, myotoxicity, etc.), pathological (inflammation, cancer, etc.), and physiological (proliferation, contraction, secretion, etc.) processes. Specific membrane receptors (M and N types) for sPLA2s have been initially identified with snake venom sPLA2s as ligands, and the M-type 180-kDa receptor was cloned from different animal species. This paper addresses the problem of the endogenous ligands of the M-type receptor. Recombinant group IB and group IIA sPLA2s from human and mouse species have been prepared and analyzed for their binding properties to M-type receptors from different animal species. Both mouse group IB and group IIA sPLA2s are high affinity ligands (in the 1-10 nM range) for the mouse M-type receptor. These two sPLA2s are expressed in the mouse tissues where the M-type receptor is also expressed, making it likely that both types of sPLA2s are physiological ligands of the mouse M-type receptor. This conclusion does not hold for human group IB and IIA sPLA2s and the cloned human M-type receptor. The two mouse sPLA2s have relatively high affinities for the mouse M-type receptor, but they can have much lower affinities for receptors from other animal species, indicating that species specificity exists for sPLA2 binding to M-type receptors. Caution should thus be exerted in avoiding mixing sPLA2s, cells, or tissues from different animal species in studies of the biological roles of mammalian sPLA2s associated with an action through their membrane receptors.