TGF-β stimulates Pyk2 expression as part of an epithelial-mesenchymal transition program required for metastatic outgrowth of breast cancer

• Published in: Oncogene Vol. 32; no. 16; pp. 2005 - 2015
• Main Authors: Wendt, M K, Schiemann, B J, Parvani, J G, Lee, Y-H, Kang, Y, Schiemann, W P
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 18.04.2013
• Subjects: Animals; Biomarkers, Tumor - biosynthesis; Breast cancer; Breast Neoplasms - enzymology; Breast Neoplasms - genetics; Breast Neoplasms - pathology; Cell Line, Tumor; Development and progression; E-cadherin; Epithelial-Mesenchymal Transition - drug effects; Epithelial-Mesenchymal Transition - physiology; Female; Focal adhesion kinase; Focal Adhesion Kinase 2 - biosynthesis; Humans; Invasiveness; Kinases; Lung cancer; Lung Neoplasms - enzymology; Lung Neoplasms - secondary; Mammary Neoplasms, Experimental - enzymology; Mammary Neoplasms, Experimental - genetics; Mammary Neoplasms, Experimental - pathology; Mesenchyme; Metastases; Metastasis; Mice; Mice, Inbred BALB C; Microenvironments; Physiological aspects; Protein kinases; Protein-tyrosine kinase; Signal Transduction - drug effects; Smad4 Protein - metabolism; src-Family Kinases - metabolism; Transforming Growth Factor beta - metabolism; Transforming Growth Factor beta - pharmacology; Transforming growth factor-b; Transforming growth factors; United States
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/onc.2012.230

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.