Enhanced tenascin-C expression and matrix deposition during Ras/TGF-beta-induced progression of mammary tumor cells.
Overexpression of tenascin-C (TN-C) in breast carcinomas has been associated with a migratory or even invasive tumor cell phenotype. The mechanisms regulating expression and matrix deposition of TN-C in normal and cancerous breast tissues are, however, little understood. Here, we demonstrate that mouse mammary epithelial cells (EpH4) transformed by oncogenic Ha-Ras (EpRas) overexpress TN-C, which accumulates in the cytoplasm. When EpRas cells undergo epithelial-mesenchymal transition (EMT) in response to TGFbeta1, they secrete TN-C into the culture medium. In EpRas cells undergoing TGFbeta1-induced EMT in three-dimensional (3D)-collagen gel cultures, TN-C was deposited into an extracellular matrix (ECM) already containing fibronectin and perlecan. Under less physiological 2D plastic cultures, EpRas cells undergoing EMT failed to deposit TN-C into an (apparently incomplete) ECM. Ras-downstream signaling was dissected by pharmacological inhibitors and effector-specific Ras mutants (V12S35, V12C40), specifically inhibiting or activating ERK/MAPK or PI3K signaling, respectively. We showed that TN-C overexpression required a hyperactive ERK/MAPK-signaling pathway, while elevated PI3K signaling did not enhance TN-C expression. Similarly, tumors induced by cells exhibiting hyperactive ERK/MAPK signaling showed expression of TN-C in the tumor cells themselves, while only endothelial cells expressed TN-C in tumors caused by the V12C40 mutant (incapable of EMT in vivo). Taken together, our data indicate that hyperactive ERK/MAPK signaling causes enhanced expression of TN-C, while its secretion is induced by TGFbeta1 and both signals cooperate in TN-C matrix deposition. Importantly, both signals also cooperate to induce EMT in vitro and tumor progression/metastasis in vivo.
Maschler
Sabine
S
Institute of Molecular Pathology, Dr. Bohrgasse 7, 1030 Vienna, Austria.
Grunert
Stefan
S
Danielopol
Adriana
A
Beug
Hartmut
H
Wirl
Gerhard
G
D000818:Animals; D003470:Culture Media; D005109:Extracellular Matrix / Q000378:metabolism*; D005260:Female; D015674:Mammary Neoplasms, Animal / Q000378:metabolism*; D051379:Mice; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051381:Rats; D019063:Tenascin / Q000096:biosynthesis / Q000235:genetics*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D015854:Up-Regulation / Q000502:physiology; D018631:ras Proteins / Q000378:metabolism*
D003470:Culture Media; D019063:Tenascin; D016212:Transforming Growth Factor beta; D019869:Phosphatidylinositol 3-Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins