Characterization of secretory type IIA phospholipase A(2) (sPLA(2)-IIA) asa glycyrrhizin (GL)-binding protein and the GL-Induced inhibition of the CK-II-mediated stimulation of sPLA(2)-IIA activity in vitro

By means of heparin-affinity and glycyrrhizin (GL)-affinity column chromato graphies (HPLC), a GL-binding phospholipase A(2) (gbPLA(2)) was selectively purified from the synovial fluids of patients with rheumatoid arthritis. T his purified gbPLA(2) was identified as a secretory type ITA PLA, (sPLA(2)- IIA) since it was crossreacted with anti-sPLA(2)-IIA serum. The activity of purified sPLA(2)IIA was inhibited by glycyrrhetinic acid (GA) and a GA der ivative (oGA) in a dose-dependent manner, but it was more sensitive to GA t han GL. Furthermore, it was found that (i) purified sPLA(2)-IIA is phosphor ylated by casein kinase II (CK-II) in vitro; (ii) this phosphorylation indu ces in a significant stimulation of PLA(2) activity; and (iii) oGA at one-t enth the concentration of GL inhibits the CK-II-mediated stimulation of sPL A(2)-IIA activity. These results show that (i) sPLA(2)-IIA is a GL-binding protein; and (ii) CK-II mediates stimulation of its PLA, activity in vitro.