EGFR- and EGFR VIII–Mediated Regulation of Urokinase Promotes Astrocytic Tumor Invasion Via the C-SRC/MEK/AP-1 Signaling Pathways
PubMed Central® ID
One of the major pathophysiological features of malignant astrocy-tomas is their ability to diffusely infiltrate the surrounding brain tissue. Although it is known that the epidermal growth factor receptor (EGFR) is amplified or overexpressed in primary glioblastomas and that malignant gliomas express higher levels of urokinase-type plasminogen activator (uPA) than normal brain tissue, little is known about the possible interaction between the activation of EGFR or EGFR VIII and uPA and its role in promoting astrocytic tumor invasion. In this study, we characterized the signal transduction pathway by which EGF regulates uPA expression and promotes astrocytoma invasion. Our data showed that the treatment of glioblastoma cell lines with EGF upregulates the expression and activity of uPA in a time-dependent manner. Similarly, the expression of the EGFR VIII mutant receptor also induced high uPA expression levels. The increase in uPA protein by EGF or EGFR VIII was abrogated by the MEK inhibitor UO 126, the tyrosine kinase inhibitor AG 1478, the small interfering RNA (siRNA) targeting c-Src, and the c-Src inhibitor PP2. Also, EGF-increased uPA promoter activity was abrogated by mutations in the AP-1 sites. Furthermore, treatment with UO 126 attenuated the promoter activity, while the phosphatidylinositol 3-kinase inhibitor LY294002 did not affect the EGF-induced increase in promoter activity. Treatment with EGF increased the extent of in vitro invasion as determined by the Boyden chamber assay, and invasion was attenuated by UO 126, siRNA, and short hairpin RNA (shRNA) directed against uPA. In addition, uPA knockdown cells formed fewer colonies on soft agar than wild-type cells and formed smaller, well-circumscribed tumors than parent U1242 cells in a xeno-graft glioblastoma multiforme mouse model. In summary, we conclude that EGF requires EGFR kinase activity, mitogen-activated protein kinase, and AP-1-dependent pathways to induce uPA expression and to promote glioblastoma invasion.
Epidermal growth factor receptor (EGFR), brain tissue, tumors, urokinase
Amos, Samson; Redpath, Gerard T.; Carpenter, Joan E.; diPierro, Charles G.; Parsons, Sarah J.; Huang, Shaung; Habib, Amyn; Cavenee, Webster; and Hussaini, Isa M., "EGFR- and EGFR VIII–Mediated Regulation of Urokinase Promotes Astrocytic Tumor Invasion Via the C-SRC/MEK/AP-1 Signaling Pathways" (2008). Pharmaceutical Sciences Faculty Publications. 167.