SEALING EFFECTS OF (-)-EPIGALLOCATECHIN GALLATE ON PROTEIN-KINASE-C AND PROTEIN PHOSPHATASE-2A

(-)-Epigallocatechin gallate (EGCG) was reported to inhibit protein ki nase C (PKC) activation by 12-O-tetradecanoylphorbol-13-acetate (TPA), and inhibit interaction of tumor promoter with its receptors, named ' a sealing effect'. In order to clarify the sealing effect of EGCG, we prepared Liposomes and examined inhibition of PKC activation by variou s concentrations of EGCG dispersed in the liposome. EGCG added to a li posome dispersion existed either in a buffer solution as aggregates or in phospholipid bilayer membranes, and EGCG disturbed membrane struct ure. The potency of inhibitory effect of EGCG on PKC activation was de pendent on the nature of Liposomes, indicating that interaction of EGC G with phospholipid bilayer membrane affects PKC activation. Moreover, EGCG prevented the binding of adenosine 5'-triphosphate and TPA to PK C, resulting in inhibition of PKC activation. On the other hand, the a ctivity of protein phosphatase 2A (PP?A) was suppressed in the presenc e of liposomes, but was not influenced by EGCG. Moreover, EGCG recover ed phosphatase activity of PP2A in a buffer solution, the activity of which was inhibited by okadaic acid. All the results indicated that EG CG possesses sealing effects in terms of PKC and PP2A, by inhibiting i nteraction of various ligands with proteins. (C) 1997 Elsevier Science B.V.