BACKGROUND Triple negative breast cancer (TNBC) accounts for 16% of breast cancers and represents an aggressive subtype that lacks targeted therapeutic options. In this study, mass spectrometry (MS)-based tyrosine phosphorylation profiling identified aberrant FGFR3 activation in a subset of TNBC cell lines. This kinase was therefore evaluated as a potential therapeutic target. METHODS MS-based tyrosine phosphorylation profiling was undertaken across a panel of 24 TNBC cell lines. Immunoprecipitation and Western blot were used to further characterize FGFR3 phosphorylation. Indirect immunofluorescence and confocal microscopy were used to determine FGFR3 localization. The selective FGFR1-3 inhibitor, PD173074 and siRNA knockdowns were used to characterize the functional role of FGFR3 in vitro. The TCGA and Metabric breast cancer datasets were interrogated to identify FGFR3 alterations and how they relate to breast cancer subtype and overall patient survival. RESULTS High FGFR3 expression and phosphorylation were detected in SUM185PE cells, which harbor a FGFR3-TACC3 gene fusion. Low FGFR3 phosphorylation was detected in CAL51, MFM-223 and MDA-MB-231 cells. In SUM185PE cells, the FGFR3-TACC3 fusion protein contributed the majority of phosphorylated FGFR3, and largely localized to the cytoplasm and plasma membrane, with staining at the mitotic spindle in a small subset of cells. Knockdown of the FGFR3-TACC3 fusion and wildtype FGFR3 in SUM185PE cells decreased FRS2, AKT and ERK phosphorylation, and induced cell death. Knockdown of wildtype FGFR3 resulted in only a trend for decreased proliferation. PD173074 significantly decreased FRS2, AKT and ERK activation, and reduced SUM185PE cell proliferation. Cyclin A and pRb were also decreased in the presence of PD173074, while cleaved PARP was increased, indicating cell cycle arrest in G1 phase and apoptosis. Knockdown of FGFR3 in CAL51, MFM-223 and MDA-MB-231 cells had no significant effect on cell proliferation. Interrogation of public datasets revealed that increased FGFR3 expression in breast cancer was significantly associated with reduced overall survival, and that potentially oncogenic FGFR3 alterations (eg mutation and amplification) occur in the TNBC/basal, luminal A and luminal B subtypes, but are rare. CONCLUSIONS These results indicate that targeting FGFR3 may represent a therapeutic option for TNBC, but only for patients with oncogenic FGFR3 alterations, such as the FGFR3-TACC3 fusion. Video abstract.

中文翻译：

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FGFR3信号传导和三阴性乳腺癌的功能。

背景技术三阴性乳腺癌（TNBC）占乳腺癌的16％，并且是缺乏靶向治疗选择的侵略性亚型。在这项研究中，基于质谱（MS）的酪氨酸磷酸化图谱鉴定了TNBC细胞系子集中异常的FGFR3激活。因此，将该激酶评估为潜在的治疗靶标。方法在24个TNBC细胞系中进行基于MS的酪氨酸磷酸化分析。免疫沉淀和蛋白质印迹用于进一步表征FGFR3磷酸化。间接免疫荧光和共聚焦显微镜用于确定FGFR3的定位。选择性FGFR1-3抑制剂PD173074和siRNA敲低被用来表征FGFR3的体外功能。询问了TCGA和Metabric乳腺癌数据集，以确定FGFR3改变及其与乳腺癌亚型和总体患者生存率的关系。结果在带有FGFR3-TACC3基因融合体的SUM185PE细胞中检测到了高FGFR3表达和磷酸化。在CAL51，MFM-223和MDA-MB-231细胞中检测到低的FGFR3磷酸化。在SUM185PE细胞中，FGFR3-TACC3融合蛋白贡献了大部分磷酸化的FGFR3，并主要定位于细胞质和质膜，在一小部分细胞中在有丝分裂纺锤体上染色。在SUM185PE细胞中敲低FGFR3-TACC3融合蛋白和野生型FGFR3可降低FRS2，AKT和ERK磷酸化，并诱导细胞死亡。抑制野生型FGFR3仅导致增殖减少的趋势。PD173074显着降低FRS2，AKT和ERK激活，并减少SUM185PE细胞增殖。在PD173074的存在下，细胞周期蛋白A和pRb也降低，而裂解的PARP增加，表明细胞周期停滞在G1期和细胞凋亡。敲低CAL51，MFM-223和MDA-MB-231细胞中的FGFR3对细胞增殖没有显着影响。对公共数据集的询问显示，乳腺癌中FGFR3表达的增加与总体存活率降低显着相关，并且潜在的致癌性FGFR3改变（例如突变和扩增）发生在TNBC /基础，管腔A和管腔B亚型中，但很少见。结论这些结果表明，靶向FGFR3可能代表TNBC的治疗选择，但仅适用于具有致癌性FGFR3改变（例如FGFR3-TACC3融合）的患者。录像摘要。