Calcium signaling is a critical regulator of cell proliferation. Elevated expression of calcium channels and pumps is a characteristic of some cancers, including breast cancer. We show that the plasma membrane calcium channel TRPV6, which is highly selective for Ca 2þ , is overexpressed in some breast cancer cell lines. Silencing of TRPV6 expression in a breast cancer cell line with increased endogenous TRPV6 expression leads to a reduction in basal calcium influx and cellular proliferation associated with a reduction in DNA synthesis. TRPV6 gene amplification was identified as one mechanism of TRPV6 overexpression in a subset of breast cancer cell lines and breast tumor samples. Analysis of two independent microarray expression datasets from breast tumor samples showed that increased TRPV6 expression is a feature of estrogen receptor (ER)-negative breast tumors encompassing the basal-like molecular subtype, as well as HER2-positive tumors. Breast cancer patients with high TRPV6 levels had decreased survival compared with patients with low or intermediate TRPV6 expression. Our findings suggest that inhibitors of TRPV6 may offer a novel therapeutic strategy for the treatment of ER-negative breast cancers. Mol Cancer Ther; 11(10); 2158-68. Ó2012 AACR.

The Ca2+ signal has major roles in cellular processes important in tumorigenesis, including migration, invasion, proliferation, and apoptotic sensitivity. New evidence has revealed that, aside from altered expression and effects on global cytosolic free Ca2+ levels via direct transport of Ca2+, some Ca2+ pumps and channels are able to contribute to tumorigenesis via mechanisms that are independent of their ability to transport Ca2+ or effect global Ca2+ homeostasis in the cytoplasm. Here, we review some of the most recent studies that present evidence of altered Ca2+ channel or pump expression in tumorigenesis and discuss the importance and complexity of localized Ca2+ signaling in events critical for tumor formation.

SPCA1 is a Ca2+ pump located on the membrane of the Golgi apparatus and is involved in controlling calcium levels within the Golgi. We have previously shown that SPCA1 is upregulated in some basal-like breast cancers. Given the role of the Golgi in protein trafficking and processing, we hypothesised that SPCA1 may be involved in regulating the expression of proteins important in cancer. To address this hypothesis we used 2D-DIGE to identify proteins that are altered when SPCA1 is silenced in MDA-MB-231 basal cancer cells. MDA-MB-231 cells were seeded into 6-well plates (75,000 cells/well) and treated with SPCA1 or non-targeting siRNA. Protein was isolated 72 h post siRNA treatment, and SPCA1 silencing was confirmed by immunoblotting. 2D-DIGE and MS/MS were used to identify proteins with differential expression with SPCA1 silencing. Heat shock protein 60 (HSP60) was identified as a protein potentially sensitive to SPCA1 silencing using 2D-DIGE. Immunoblotting and real time RT-PCR showed that SPCA1 silencing reduced HSP60 protein and mRNA expression by 81±2% and 60±7% (n=3, P<0.05), respectively. Given the role of HSP60 in cell death pathways, we also assessed the consequences of SPCA1 silencing on heat shock and staurosporine-induced cell death. SPCA1 silencing had no effect on heat shock-induced cell death but reduced the sensitivity of MDA-MB-231 breast cancer cells to staurosporine. Although further studies are required to fully characterize the functional consequences of HSP60 downregulation upon SPCA1 silencing, this work suggests that SPCA1 is a complex regulator of proteins important in cancer pathways. Citation Format: Jane M. Lee, Diana G. Ross, Gregory R. Monteith, Sarah J. Roberts-Thomson. Inhibition of the secretory pathway calcium ATPase 1 (SPCA1) in MDA-MB-231 breast cancer cells and the effect on protein expression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3301. doi:10.1158/1538-7445.AM2014-3301