Inhibition of urokinase-type plasminogen activator receptor induces apoptosis in melanoma cells by activation of p53.
The urokinase-type plasminogen activator receptor (uPAR) is involved in several biological processes, including proteolysis, adhesion, migration and inflammation. Increased expression of uPAR is associated with metastasis in several tumor types. We studied the biological role of uPAR in melanoma and found that inhibition of uPAR via RNA interference induced massive death in three different metastatic cell lines. Annexin-V staining and caspase activation analysis revealed induction of the mitochondrial apoptotic pathway. The expression of members of the Bcl-2 family (Bax, Bcl-2, Bak and Bcl-x(L)) was changed in a pro-apoptotic manner. uPAR inhibition induced the expression of the tumor suppressor p53 and of its downstream target gene p21. Inhibition of p53 rescued cells from apoptosis indicating that p53 was critical for apoptosis induction. Apoptosis was observed in melanoma cells carrying activating BRAF mutations and occurred in the presence of extracellular signal-regulated kinase (ERK) phosphorylation. uPAR can activate focal adhesion kinase (FAK), which is implicated in adhesion-dependent tumor cell survival. However, inhibition of FAK did not induce apoptosis. Our data suggest a new function of uPAR acting as a survival factor for melanoma by downregulating p53. Inhibition of uPAR induces a pro-apoptotic signalling pathway via p53 that is independent of ERK or FAK signalling. These findings may offer new treatment strategies for metastatic melanoma.
Besch
R
R
Department of Dermatology and Allergology, Ludwig-Maximilian University, Munich, Germany. robert.besch@med.uni-muenchen.de
Berking
C
C
Kammerbauer
C
C
Degitz
K
K
D017209:Apoptosis; D014408:Biomarkers, Tumor / Q000378:metabolism; D049109:Cell Proliferation; D002470:Cell Survival; D015536:Down-Regulation / Q000235:genetics; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism; D006801:Humans; D008545:Melanoma / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors* / Q000235:genetics; D055293:Receptors, Urokinase Plasminogen Activator; D015398:Signal Transduction; D012878:Skin Neoplasms / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D014568:Urokinase-Type Plasminogen Activator / Q000502:physiology*
D014408:Biomarkers, Tumor; C524898:PLAUR protein, human; D034741:RNA, Small Interfering; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D016159:Tumor Suppressor Protein p53; D051416:Focal Adhesion Protein-Tyrosine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D014568:Urokinase-Type Plasminogen Activator