BRCA1 modulates malignant cell behavior, the expression of survivin and chemosensitivity in human breast cancer cells

Abstract

BRCA1 is a multifunctional tumor-suppressive protein. Many functional aspects of BRCA1 are not fully understood. We used a shRNA approach to probe the function of BRCA1 in human breast cancer cells. Knocking down BRCA1 expression by shRNA in the wild-type BRCA1 human breast cancer MCF-7 and MDA-MB-231 cells resulted in an increase in cell proliferation, anchorage-independent growth, cell migration, invasion and a loss of p21/Waf1 and p27 Kip1 expression. In BRCA1 knocked-down cells, the expression of survivin was significantly up regulated with a concurrent decrease in cellular sensitivity to paclitaxel. We also found that cells harboring endogenous mutant or defective BRCA1 (MDA-MB-436 and HCC1937) were highly proliferative and expressed a relatively low level of p21/Waf1 and p27 Kip1 by comparison to wild-type BRCA1 cells. Cells harboring mutated BRCA1 also expressed a high level of survivin and were relatively resistant to paclitaxel by comparison to wild-type cells. Increase resistance to paclitaxel was due to an increase in the expression of survivin in both the BRCA1 knocked-down and mutant BRCA1 cells because knocking down survivin expression by siRNA restored sensitivity to paclitaxel. We conclude that BRCA1 down-modulates the malignant behavior of breast cancer cells, promotes the expression of p21/Waf1, p27 Kip1 and inhibits the expression of survivin. Moreover, loss of BRCA1 expression or function leads to an increase in survivin expression and a reduction in chemosensitivity to paclitaxel. ' UICCKey words: BRCA1; p21/Waf1; p27Kip1; survivin; chemosensitivity Hereditary breast cancer can be caused by germline mutations in 1 of the 2 tumor suppressor genes, BRCA1 and BRCA2 resulting in a loss of gene function. 1,2 Women carrying 1 mutated BRCA1 allele are at increased risk of developing breast cancer but tumor initiation requires a loss of the wild-type allele indicating that BRCA1 is a tumor suppressor gene. 3,4 Hereditary breast cancers account for 5-10% of all breast cancers. 5-8 Breast cancer cumulative risk to age 50 years and 70 years in mutation carriers are 49% and 71%, respectively, for BRCA1. 9 BRCA1 expression is also frequently reduced in sporadic cancer. 10-13 BRCA1 encodes an 1863 amino acid (220 kDa) protein that is targeted to the nucleus by 2 nuclear localization sequences, which interact with the nuclear transport signal receptor. 14-17 BRCA1 protein is multifunctional and interacts with other proteins in the nucleus in transcriptional regulation of gene expression, DNA repair and in the maintenance of genomic stability. 1,18 Thus, loss of BRCA1 function may lead to accumulation of chromosomal damage, abnormalities in growth control and tumorigenesis. 19 BRCA1 is regarded as an important central component in regulating multiple biological pathways. 18,20 The function of BRCA1 intersects with the cyclin-dependent kinase inhibitor p27 Kip1 , cyclin D1, the extracellular matrix [21][22][23] and with the estrogen and progesterone pathways in hormonal driven tumor development and progres...

A Genetic Polymorphism (rs17251221) in the Calcium-Sensing Receptor is Associated with Breast Cancer Susceptibility and Prognosis

“…It has been reported that extracellular Ca 2+ can down-regulate cell proliferation, invasion and anchorage-independent growth in cancer [25,26]. Recent studies showed that BRCA1 expression could increase the sensitivity of breast cancers to paclitaxel by regulating CaSR [27,28,29]. We investigated the rs17251221 SNP because it is one genetic variation of CaSR.…”

A novel crosstalk between BRCA1 and poly (ADP-ribose) polymerase 1 in breast cancer

“…A substantial body of evidence indicates that loss of function of the tumor suppressor gene BRCA1 plays an important role in promoting cancer cell proliferation and survival. 25,26 Consistent with this, BRCA1 is a metabolic switch for NAD, 7 and NAD-dependent signaling pathways are widely involved in cell proliferation and metabolism; 27 and recent studies have suggested a possible role for PARP1-dependent Snail in regulating cell proliferation. 28 Therefore, effects of BRCA1 on cell proliferation, which may Figure 3.…”

Delocalization of γ-tubulin due to increased solubility in human breast cancer cell lines

“…Cell lines were categorized for metastatic potential based on previous studies that determined invasion 27-29 or used genetic profiling matched to patient prognosis. 25, 26, 28-31 MCF-10A were classified as no metastatic potential. BT-20, SKBR3, MCF-7, and BT-474 were classified as low metastatic potential.…”