Department of Medical Microbiology, Immunology and Cell Biology, Southern Illinois University School of Medicine and Simmons Cancer Institute, Springfield, IL 62794-9677, USA.
Cell Calcium. 2011 Feb;49(2):79-88. doi: 10.1016/j.ceca.2011.01.003. Epub 2011 Feb 5.
Both BRCA1 and CaSR have been shown to suppress the expression of survivin and promote sensitivity to paclitaxel in human breast cancer cells. In this study we determined the functional linkage, if any, between BRCA1 and CaSR. We found that mutant cells (harboring mutant BRCA1 with loss of BRCA1 expression) had a significant reduction in the expression of CaSR with a concurrent up-regulated expression of survivin and were resistant to paclitaxel by comparison to wild type cells (harboring wild type BRCA1 and expressing BRCA1). Knocking down the expression of BRCA1 in wild type cells resulted in a reduction in CaSR expression with a concurrent up-regulated expression of survivin and reduction in sensitivity to paclitaxel. Re-expression of BRCA1 in BRCA1 knocked-down wild type cells restored CaSR expression with a concurrent down-regulated expression of survivin and restoration of sensitivity to paclitaxel. Corollary, ectopic expression of BRCA1 in mutant cells induced CaSR expression, suppressed the expression of survivin and restored sensitivity to paclitaxel. These results suggest that BRCA1 action is linked to that of CaSR. In a final series of experiments, we show that ectopic expression of CaSR in either the BRCA1 knocked-down wild type or mutant cells suppressed the expression of survivin and promoted sensitivity to paclitaxel. Thus, CaSR can rescue BRCA1 defective cells from the deleterious effects of loss of BRCA1 function. CaSR expression, however, had no effect on the expression of BRCA1. BRCA1 could stimulate the transcriptional activities of the CaSR gene and shRNA targeting CaSR circumvented the action of BRCA1. We conclude, and report for the first time, that BRCA1 regulates the expression of CaSR and that it functions through CaSR in suppressing the expression of survivin and promoting sensitivity to paclitaxel.
BRCA1 和 CaSR 都被证明可以抑制人乳腺癌细胞中 survivin 的表达并增加紫杉醇的敏感性。在本研究中，我们确定了 BRCA1 和 CaSR 之间是否存在功能联系。我们发现，突变细胞（携带丧失 BRCA1 表达的突变 BRCA1）CaSR 的表达显著降低，同时 survivin 的表达上调，并与野生型细胞（携带野生型 BRCA1 并表达 BRCA1）相比对紫杉醇产生耐药性。在野生型细胞中敲低 BRCA1 的表达导致 CaSR 表达减少，同时 survivin 的表达上调，对紫杉醇的敏感性降低。在 BRCA1 敲低的野生型细胞中重新表达 BRCA1 恢复了 CaSR 的表达，同时 survivin 的表达下调，对紫杉醇的敏感性恢复。推论，BRCA1 在突变细胞中的异位表达诱导了 CaSR 的表达，抑制了 survivin 的表达，并恢复了对紫杉醇的敏感性。这些结果表明 BRCA1 的作用与 CaSR 的作用相关。在最后的一系列实验中，我们表明 CaSR 的异位表达无论是在 BRCA1 敲低的野生型还是突变细胞中都抑制了 survivin 的表达并增加了对紫杉醇的敏感性。因此，CaSR 可以使 BRCA1 功能缺失的细胞免受 BRCA1 功能丧失的有害影响。然而，CaSR 的表达对 BRCA1 的表达没有影响。BRCA1 可以刺激 CaSR 基因的转录活性，并且针对 CaSR 的 shRNA 避开了 BRCA1 的作用。我们的结论是，并且首次报告，BRCA1 调节 CaSR 的表达，并且通过 CaSR 抑制 survivin 的表达并增加紫杉醇的敏感性。
