Matalkah Fatimah, Martin Elisha, Zhao Hua, Agazie Yehenew M
Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA.
The Marry Babb Randolph Cancer Center, School of Medicine, West Virginia University, Morgantown, WV 26506, USA.
Breast Cancer Res. 2016 Jan 4;18(1):2. doi: 10.1186/s13058-015-0659-z.
Dysregulated receptor tyrosine kinase (RTK) signaling is a common occurrence in basal-like and triple-negative breast cancer (BTBC). As a result, RTK-targeting therapies have been initiated but proved difficult, mainly owing to the multiplicity of dysregulated RTKs. Hence, targeting master regulators of RTK signaling might alleviate this obstacle. Before that, however, defining the mechanism of such molecules is required. In this report, we show that the Src homology phosphotyrosyl phosphatase 2 (SHP2) is a master regulator of RTK expression and signaling in BTBC.
Xenograft tumor growth studies were used to determine the effect of SHP2 inhibition on tumorigenesis and/or metastasis. Cell proliferation rate, anchorage-independent growth, mammosphere formation, and ALDEFLUOR assays were used to compare the relative functional importance of SHP2 and the epidermal growth factor receptor (EGFR) in BTBC cells. Immunohistochemistry and immunofluorescence analyses were used to determine the state of SHP2 and EGFR coexpression in BTBC. Analysis of mitogenic and cell survival signaling was performed to show SHP2's role in signaling by multiple RTKs.
Inhibition of SHP2 in BTBC cells suppresses their tumorigenic and metastatic properties. Because EGFR is the most commonly dysregulated RTK in BTBC, we first tested the effect of SHP2 inhibition on EGFR signaling and found that SHP2 is important not only for mediation of the Ras/extracellular signal-regulated kinase and the phosphatidyl inositol 3-kinase/Akt signaling pathways but also for the expression of the receptor itself. The existence of a tight association between SHP2 and EGFR expression in tumors and cell lines further suggested the importance of SHP2 in EGFR expression. Comparison of relative biological significance showed the superiority of SHP2 inhibition over that of EGFR, suggesting the existence of additional RTKs regulated by SHP2. Indeed, we found that the expression as well as the signaling efficiency of c-Met and fibroblast growth factor receptor 1, two other RTKs known to be dysregulated in BTBC, are SHP2-dependent. To our knowledge, this is the first demonstration of SHP2 acting both upstream and downstream of RTKs to promote signaling.
SHP2 upregulates the expression and signaling of multiple RTKs to promote BTBC. These findings provide a mechanistic explanation for the superiority of SHP2 inhibition in BTBC.
受体酪氨酸激酶（RTK）信号失调在基底样和三阴性乳腺癌（BTBC）中很常见。因此，针对RTK的治疗已经开展，但结果证明颇具难度，主要原因是失调的RTK种类繁多。因此，靶向RTK信号的主要调节因子可能会缓解这一障碍。然而在此之前，需要明确此类分子的作用机制。在本报告中，我们表明Src同源磷酸酪氨酸磷酸酶2（SHP2）是BTBC中RTK表达和信号传导的主要调节因子。
采用异种移植肿瘤生长研究来确定抑制SHP2对肿瘤发生和/或转移的影响。使用细胞增殖率、非锚定依赖性生长、乳腺球形成和ALDEFLUOR检测来比较SHP2和表皮生长因子受体（EGFR）在BTBC细胞中的相对功能重要性。采用免疫组织化学和免疫荧光分析来确定BTBC中SHP2和EGFR共表达的状态。进行促有丝分裂和细胞存活信号分析以显示SHP2在多种RTK信号传导中的作用。
抑制BTBC细胞中的SHP2可抑制其致瘤和转移特性。由于EGFR是BTBC中最常失调的RTK，我们首先测试了抑制SHP2对EGFR信号传导的影响，发现SHP2不仅对Ras/细胞外信号调节激酶和磷脂酰肌醇3激酶/Akt信号通路的介导很重要，而且对受体本身的表达也很重要。肿瘤和细胞系中SHP2与EGFR表达之间紧密关联的存在进一步表明SHP2在EGFR表达中的重要性。相对生物学意义的比较显示抑制SHP2优于抑制EGFR，这表明存在由SHP2调节的其他RTK。事实上，我们发现另外两种已知在BTBC中失调的RTK，即c-Met和成纤维细胞生长因子受体1的表达以及信号传导效率均依赖于SHP2。据我们所知，这是首次证明SHP2在RTK的上游和下游均发挥作用以促进信号传导。
SHP2上调多种RTK的表达和信号传导以促进BTBC。这些发现为BTBC中抑制SHP2的优势提供了机制解释。
