Chelerythrine inhibits the sarco/endoplasmic reticulum Ca2+-ATPase and results in cell Ca2+ imbalance

The isoquinoline alkaloid chelerythrine is described as an inhibitor of SERCA. The ATPase inhibition presented two non-competitive components, K-i1 = 1, 2 mu M and K-i2 = 26 mu M. Conversely, chelerythrine presented a dual effect on the p-nitrophenylphosphatase (pNPPase) of SERCA. Ca2+-dependent pNPPase was activated up to similar to 5 mu M chelerythrine with inhibition thereafter. Ca2+-independent pNPPase was solely inhibited. The phospholylation of SERCA with ATP reached half-inhibition with 10 mu M chelerythrine and did not parallel the decrease of ATPase activity. In contrast, chelerythrine up to 50 mu M increased the phosphorylation by P-i. Cross-linking of SERCA with glutaraldehyde was counteracted by high concentrations of chelerythrine. The controlled tryptic digestion of SERCA shows that the low-affinity binding of chelerythrine evoked an E-2-like pattern. Our data indicate a non-competitive inhibition of ATP hydrolysis that favors buildup of the E-2-conformers of the enzyme. Chelerythrine as low as 0.5-1.5 mu M resulted in an increase of intracellular Ca2+ on cultured PBMC cells. The inhibition of SERCA and the loss of cell Ca2+ homeostasis could in part be responsible for some described cytotoxic effects of the alkaloid. Thus, the choice of chelerythrine as a PKC-inhibitor should consider its potential cytotoxicity due to the alkaloid's effects on SERCA. (C) 2015 Elsevier Inc. All rights reserved.