Oncogene：TGF-β上调Pyk2表达促进乳腺癌转移

上皮-间质转化（epithelial mesenchymal transitions，EMT）是指上皮细胞在形态学上发生向成纤维细胞或间充质细胞表型的转变并获得迁移的能力。EMT是胚胎发育中的一个基本过程，它使在特殊部位产生的上皮细胞从上皮组织分离并迁移到其他位置，是正常发育、伤口愈合以及恶性上皮肿瘤发生的基础。

上皮间质转化（EMT）对促进乳腺癌侵袭、全身性的散播是必不可少的，乳腺癌细胞发生上皮间质转化后可以引起乳腺癌细胞微转移，EMT过程部分依赖于粘着斑激酶（FAK）发挥作用。

研究人员证实Pyk2的表达存在以下几点：（一）人乳腺癌复发患者中水平上调；（二）该蛋白的表达可以预测人源MDA-MB-231乳腺癌癌细胞的转移性生长，但不与肿瘤细胞的侵袭能力相关；（三）与原发肿瘤组织细胞相比，体外培养转移性病灶乳腺癌细胞中高表达。

进一步的研究表明，转移性人源和小鼠来源的乳腺癌细胞在EMT过程中，接受转化生长因子-β（TGF-β）刺激情况下会高表达Pyk2。基因水平或是药物水平抑制PYK2表明，这种蛋白酪氨酸激酶的活性对于乳腺癌细胞接受TGF-β后侵袭能力上调、小鼠原位乳腺肿瘤的形成是非常重要的。

与之形成鲜明对比的，PYK2的缺失会阻止三维培养过程中TGF-β刺激的乳腺癌细胞生长，而在体内研究中PYK2的缺失会抑制乳腺癌细胞转移至老鼠肺部。Pyk2表达与E-钙粘素的表达呈负相关，PYK2表达水平的增高稳定整合素β1的表达，而整合素β1的表达对启动转移性乳腺癌细胞的生长至关重要。

因此，该研究阐明了PYK2在EMT过程中以及TGF-β刺激的肿瘤转移中起关键调控作用，该蛋白的表达会促进新生转移灶肿瘤细胞的生长。

doi:10.1038/onc.2012.230
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TGF-β stimulates Pyk2 expression as part of an epithelial-mesenchymal transition program required for metastatic outgrowth of breast cancer

M K Wendt1, B J Schiemann1, J G Parvani1, Y-H Lee1, Y Kang2 and W P Schiemann1

Epithelial-mesenchymal transition (EMT) programs are essential in promoting breast cancer invasion, systemic dissemination and in arousing proliferative programs in breast cancer micrometastases, a reaction that is partially dependent on focal adhesion kinase (FAK). Many functions of FAK are shared by its homolog, protein tyrosine kinase 2 (Pyk2), raising the question as to whether Pyk2 also participates in driving the metastatic outgrowth of disseminated breast cancer cells. In addressing this question, we observed Pyk2 expression to be (i) significantly upregulated in recurrent human breast cancers; (ii) differentially expressed across clonal isolates of human MDA-MB-231 breast cancer cells in a manner predictive for metastatic outgrowth, but not for invasiveness; and (iii) dramatically elevated in ex vivo cultures of breast cancer cells isolated from metastatic lesions as compared with cells that produced the primary tumor. We further show that metastatic human and murine breast cancer cells robustly upregulate their expression of Pyk2 during EMT programs stimulated by transforming growth factor-β (TGF-β). Genetic and pharmacological inhibition of Pyk2 demonstrated that the activity of this protein tyrosine kinase was dispensable for the ability of breast cancer cells to undergo invasion in response to TGF-β, and to form orthotopic mammary tumors in mice. In stark contrast, Pyk2-deficiency prevented TGF-β from stimulating the growth of breast cancer cells in 3D-organotypic cultures that recapitulated pulmonary microenvironments, as well as inhibited the metastatic outgrowth of disseminated breast cancer cells in the lungs of mice. Mechanistically, Pyk2 expression was inversely related to that of E-cadherin, such that elevated Pyk2 levels stabilized β1 integrin expression necessary to initiate the metastatic outgrowth of breast cancer cells. Thus, we have delineated novel functions for Pyk2 in mediating distinct elements of the EMT program and metastatic cascade regulated by TGF-β, particularly the initiation of secondary tumor outgrowth by disseminated cells.