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

• Published in: Archives of biochemistry and biophysics Vol. 570; pp. 58 - 65
• Main Authors: Vieira, Saulo Martins, de Oliveira, Vanessa Honorato, Valente, Raphael do Carmo, Moreira, Otacílio da Cruz, Fontes, Carlos Frederico Leite, Mignaco, Julio Alberto
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 15-03-2015
• Subjects: ATPase; Calcium; Chelerythrine; Cytotoxicity; PBMC; SERCA; Cytotoxicity; Calcium; SERCA; PBMC; ATPase; Chelerythrine
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/j.abb.2015.02.019

•The sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) is inhibited by chelerythrine.•The inhibition is noncompetitive with ATP and shows high and low affinity sites.•The high affinity component has a Ki near to that described for PKC inhibition.•The E2 conformer of SERCA is favored by chelerythrine binding.•PBMC calcium levels increased after 30min when exposed to 1μM chelerythrine.
The isoquinoline alkaloid chelerythrine is described as an inhibitor of SERCA. The ATPase inhibition presented two non-competitive components, Ki1=1, 2μM and Ki2=26μM. Conversely, chelerythrine presented a dual effect on the p-nitrophenylphosphatase (pNPPase) of SERCA. Ca2+-dependent pNPPase was activated up to ∼5μM chelerythrine with inhibition thereafter. Ca2+-independent pNPPase was solely inhibited. The phosphorylation of SERCA with ATP reached half-inhibition with 10μM chelerythrine and did not parallel the decrease of ATPase activity. In contrast, chelerythrine up to 50μM increased the phosphorylation by Pi. 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 E2-like pattern. Our data indicate a non-competitive inhibition of ATP hydrolysis that favors buildup of the E2-conformers of the enzyme. Chelerythrine as low as 0.5–1.5μM 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.