Poster Presentation 25th Lorne Cancer Conference 2013

DIFFERENTIAL EFFECTS OF STORE OPERATED CALCIUM ENTRY PROTEINS ON THE CALCIUM-MEDIATED TRANSCRIPTION FACTORS NFκB AND NFAT IN MDA-MB-231 BREAST CANCER CELLS (#260)

Nicole A Luk 1 , Sarah J Roberts-Thomson 1 , Greg R Monteith 1
  1. University of Queensland, Brisbane, QLD, Australia

Store operated calcium entry (SOCE) is associated with cell functions such as proliferation, migration and gene transcription. SOCE involves ORAI proteins located on the plasma membrane that form calcium channels. These channels are activated by STIM proteins when calcium levels in the sarcoplasmic/endoplasmic reticulum are depleted. Aberrant expression of calcium channels is a feature of some cancers. An increase in expression or activity of specific calcium channels in a cancer cell could modulate pathways important in carcinogenesis including proliferation and apoptosis via calcium-dependent transcription factors such as NFκB and NFAT. Activation of NFκB can contribute to malignant transformation and tumour progression, and provides mechanisms by which tumour cells escape immune surveillance and resist cancer therapies. The tumorigenic basal-like breast cancer cell line MDA-MB-231 has constitutively active NFκB and altered expression of ORAI proteins compared to cell lines derived from normal epithelial cells. Overexpression and increased transcriptional activity of NFAT isoforms is detected in multiple tumour tissue types and cancer cell lines and is associated with induction of genes implicated in invasion, differentiation and survival of tumour cells. We investigated the hypothesis that SOCE regulating proteins affect NFκB/NFAT signalling in MDA-MB-231 breast cancer cells. Immunocytochemistry was used to measure NFκB/NFAT translocation to the nucleus. Silencing of specific SOCE regulating proteins had differential effects on NFκB translocation. The greatest effect was seen with ORAI1 silencing, which reduced PMA activated NFκB translocation by 57.46% ± 4.92 (P < 0.0001). We also observed differences in NFκB signalling, dependent on the NFκB activator (TNFα or PMA) and ORAI isoform knockdown. Thapsigargin induced NFAT translocation was significantly decreased (91.61% ± 2.03 P < 0.0001) by siORAI2 knockdown. These studies provide mechanistic insight into how aberrant expression of specific calcium channels may alter cancer relevant processes through modulation of calcium-dependent transcription factors.