Gene expression profiling identifies FYN as an important molecule in tamoxifen resistance and a predictor of early recurrence in patients treated with endocrine therapy

Abstract

To elucidate the molecular mechanisms of tamoxifen resistance in breast cancer, we performed gene array analyses and identified 366 genes with altered expression in four unique tamoxifen-resistant (TamR) cell lines vs the parental tamoxifen-sensitive MCF-7/S0.5 cell line. Most of these genes were functionally linked to cell proliferation, death and control of gene expression, and include FYN, PRKCA, ITPR1, DPYD, DACH1, LYN, GBP1 and PRLR. Treatment with FYN-specific small interfering RNA or a SRC family kinase inhibitor reduced cell growth of TamR cell lines while exerting no significant effect on MCF-7/S0.5 cells. Moreover, overexpression of FYN in parental tamoxifen-sensitive MCF-7/S0.5 cells resulted in reduced sensitivity to tamoxifen treatment, whereas knockdown of FYN in the FYN-overexpressing MCF-7/S0.5 cells restored sensitivity to tamoxifen, demonstrating growth- and survival-promoting function of FYN in MCF-7 cells. FYN knockdown in TamR cells led to reduced phosphorylation of 14-3-3 and Cdc25A, suggesting that FYN, by activation of important cell cycle-associated proteins, may overcome the anti-proliferative effects of tamoxifen. Evaluation of the subcellular localization of FYN in primary breast tumors from two cohorts of endocrine-treated ER+ breast cancer patients, one with advanced disease (N=47) and the other with early disease (N=76), showed that in the former, plasma membrane-associated FYN expression strongly correlated with longer progression-free survival (P<0.0002). Similarly, in early breast cancer patients, membrane-associated expression of FYN in the primary breast tumor was significantly associated with increased metastasis-free (P<0.04) and overall (P<0.004) survival independent of tumor size, grade or lymph node status. Our results indicate that FYN has an important role in tamoxifen resistance, and its subcellular localization in breast tumor cells may be an important novel biomarker of response to endocrine therapy in breast cancer.

Fibroblast Subtypes Regulate Responsiveness of Luminal Breast Cancer to Estrogen

“…Analysis revealed that MCF-7 cells co-cultured with CD146 neg fibroblasts had increased expression of transcripts from 21 genes identified in the literature as up regulated in tamoxifen resistance (26–32) (STable 2). Conversely, MCF-7 cells co-cultured with CD146 pos fibroblasts had increased expression of 15 genes identified in the literature as down-regulated in tamoxifen resistance (STable 3).…”

Aberrant expression of SETD1A promotes survival and migration of estrogen receptor α‐positive breast cancer cells

“…37 We analyzed the correlation between SETD1A-dependent genes in MCF-7 cells and genes previously reported to have altered expression in Tam-R cells. Our analysis revealed that 12.2% of genes that were aberrantly expressed in Tam-R cells overlapped with SETD1A-dependent genes in MCF-7 cells (Fig.…”

BASP1 interacts with oestrogen receptor α and modifies the tamoxifen response

“…These data demonstrate that BASP1 regulates the expression of genes that are also regulated by ER α . Indeed, this group contains several known ER α target genes including BMPER, FHL1 and INHBB 15, 21, 22 (see Supplementary Table 2). …”

“…Many breast cancers can present tamoxifen resistance and several studies have identified the gene expression changes that accompany this resistance but the underlying reasons are still not clear. 12, 13, 14, 15, 16 …”