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Evidence on the operation of ATP‐induced capacitative calcium entry in breast cancer cells and its blockade by 17β‐estradiol

2002; Wiley; Volume: 87; Issue: 3 Linguagem: Inglês

10.1002/jcb.10303

1097-4644

Ana M. Rossi, Gabriela Picotto, Ana Russo de Boland, Ricardo Boland,

Ion Channels and Receptors

Abstract Little is known about the regulation of cytosolic calcium Ca 2+ levels ([Ca 2+ ] i ) in breast cancer cells. We investigated the existence of capacitative calcium entry (CCE) in the tumorigenic cell line MCF‐7 and its responsiveness to ATP. MCF‐7 cells express purinergic receptors as well as estrogen receptors (ER). Depletion of calcium stores with thapsigargin (TG, 500 nM) or ATP (10 μM) in the absence of extracellular Ca 2+ , resulted in a rapid and transient elevation in [Ca 2+ ] i . After recovery of basal levels, Ca 2+ readmission (1.5 mM) to the medium increased Ca 2+ influx (twofold over basal), reflecting pre‐activation of a CCE pathway. Cells pretreated with TG were unable to respond to ATP, thus indicating that the same Ca 2+ store is involved in their response. Moreover, IP 3 ‐dependent ATP‐induced calcium mobilization and CCE were completely blocked using compound U‐73122, an inhibitor of phospholipase C. Compound 2‐APB (75 μM) and Gd 3+ (10 μM), antagonists of the CCE pathway, completely prevented ATP‐stimulated capacitative Ca 2+ entry. CCE in MCF‐7 cells was highly permeable to Mn 2+ and to the Ca 2+ surrogate Sr 2+ . Mn 2+ entry sensitivity to Gd 3+ matched that of the Ca 2+ entry pathway. 17β‐estradiol blocked ATP‐induced CCE, but was without effect on TG‐induced CCE. Besides, the estrogen blockade of the ATP‐induced CCE was completely abolished by preincubation of the cells with an ER monoclonal antibody. ER α immunoreactivity could also be detected in a purified plasma membrane fraction of MCF‐7 cells. These results represent the first evidence on the operation of a ATP‐responsive CCE pathway in MCF‐7 cells and also indicate that 17β‐estradiol interferes with this mechanism by acting at the cell surface level. J. Cell. Biochem. 87: 324–333, 2002. © 2002 Wiley‐Liss, Inc.