EPIGALLOCATECHIN-3-GALLATE ELICITS Ca2+ SPIKE IN MCF-7 BREAST CANCER CELLS: ESSENTIAL ROLE OF Cav3.2 CHANNELS

We used MCF-7 human breast cancer cells that endogenously express Cav3.1 and Cav3.2 T-type Ca2+ channels toward a mechanistic study on the effect of EGCG on [Ca2+](i). Confocal Ca2+ imaging showed that EGCG induces a [Ca2+](i) spike which is due to extracellular Ca2+ entry and is sensitive to catalase and to low-specificity (mibefradil) and high-specificity (Z944) T-type Ca(2+)channel blockers. siRNA knockdown of T-type Ca2+ channels indicated the involvement of Cav3.2 but not Cav3.1. Application of EGCG to HEK cells expressing either Cav3.2 or Cav3.1 induced enhancement of Cav3.2 and inhibition of Cav3.1 channel activity. Measurements of K+ currents in MCF-7 cells showed a reversible, catalase-sensitive inhibitory effect of EGCG, while siRNA for the Kv1.1 K+ channel induced a reduction of the EGCG [Ca2+](i) spike. siRNA for Cav3.2 reduced EGCG cytotoxicity to MCF-7 cells, as measured by calcein viability assay. Together, data suggest that EGCG promotes the activation of Cav3.2 channels through K+ current inhibition leading to membrane depolarization, and in addition increases Cav3.2 currents. Cav3.2 channels are in part responsible for EGCG inhibition of MCF-7 viability, suggesting that deregulation of [Ca2+](i) by EGCG may be relevant in breast cancer treatment. (C) 2014 Elsevier Ltd. All rights reserved.