Inositol 1,4,5-trisphosphate-induced Ca2+ signalling is involved in estradiol-induced breast cancer epithelial cell growth

Our results show that the IP3 receptor (IP3R) inhibitors caffeine, 2-APB and xestospongin C (XeC) inhibited the growth of MCF-7 stimulated by 5% foetal calf serum or 10 nM E2. Furthermore, Ca2+ imaging experiments showed that serum and E2 were able to trigger, in a Ca2+-free medium, an elevation of internal Ca2+ in a 2-APB and XeC-sensitive manner. Moreover, the phospholipase C (PLC) inhibitor U-73122 was able to prevent intracellular Ca2+ elevation in response to serum, whereas the inactive analogue U-73343 was ineffective. Western-blotting experiments revealed that the 3 types of IP3Rs are expressed in MCF-7 cells and that a 48 hours treatment with 10 nM E2 elevated IP3R3 protein expression level in an ICI-182,780 (a specific estrogen receptor antagonist)-dependent manner. Furthermore, IP3R3 silencing by the use of specific small interfering RNA was responsible for a drastic modification of the temporal feature of IICS, independently of a modification of the sensitivity of the Ca2+ release process and acted to counteract the proliferative effect of 10 nM E2.Altogether, our results are in favour of a role of IICS in MCF-7 cell growth, and we hypothesize that the regulation of IP3R3 expression by E2 is involved in this effect.Ca2+ is a ubiquitous messenger that has been shown to be responsible for controlling numerous cellular processes including muscle contraction, exocytosis, gene expression, cell growth and cell death [1-3]. Numerous studies have shown that Ca2+ is involved in the control of cellular growth through its interaction with a plethora of intracellular proteins and cellular transduction pathways. The Ca2+-dependent processes are often involved in highly important cellular responses that are strikingly exemplified by their role in life-and-death decisions. Consequently, Ca2+ needs to be used in an appropriate manner to determine cell fate; if this balancing act is compromised, pathology may ensue [4]. In the case of malignant cells, the importance of Ca