Sealing effects of (-)-epigallocatechin gallate on protein kinase C and protein phosphatase 2A

(-)-Epigallocatechin gallate (EGCG) was reported to inhibit protein kinase 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 various concentrations of EGCG dispersed in the liposome. EGCG added to a liposome dispersion existed either in a buffer solution as aggregates or in phospholipid bilayer membranes, and EGCG disturbed membrane structure. The potency of inhibitory effect of EGCG on PKC activation was dependent on the nature of Liposomes, indicating that interaction of EGCG with phospholipid bilayer membrane affects PKC activation. Moreover, EGCG prevented the binding of adenosine 5'-triphosphate and TPA to PKC, resulting in inhibition of PKC activation. On the other hand, the activity of protein phosphatase 2A (PP?A) was suppressed in the presence of liposomes, but was not influenced by EGCG. Moreover, EGCG recovered phosphatase activity of PP2A in a buffer solution, the activity of which was inhibited by okadaic acid. All the results indicated that EGCG possesses sealing effects in terms of PKC and PP2A, by inhibiting interaction of various ligands with proteins. (C) 1997 Elsevier Science B.V.