Inhibition of urokinase-type plasminogen activator receptor induces apoptosis in melanoma cells by activation of p53

Abstract

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.

uPAR and cathepsin B-mediated compartmentalization of JNK regulates the migration of glioma-initiating cells

“…Radiotherapy is a key treatment modality for treating patients with intracranial tumors, but its efficacy is limited by radioresistance and by the promotion of malignant behavior of the cancer cells (Kang et al, 2012; Kil et al, 2012). In our present study, radiation treatment increased the migration of the glioma cells as well as the expression of uPAR and cathepsin B. Elevated levels of uPAR and cathepsin B have been strongly correlated with tumor invasiveness (Besch et al, 2007; Levicar et al, 2003; Rao, 2003; Sevenich et al, 2011), indicating that the cells treated with radiation were adapting towards an aggressive invasive phenotype.…”

Plasminogen activator urokinase expression reveals TRAIL responsiveness and supports fractional survival of cancer cells

“…Indeed, alterations in levels of Bcl-2 family members have been previously reported upon uPAR knockdown in cancer cells. 38, 45 In that regard, increased levels of proapoptotic Bim and Bak were observed, indicating that uPA knockdown changes the expression pattern of Bcl-2 family members to a proapoptotic setting (Figure 3f). Therefore, we investigated whether a cross-talk between the extrinsic and intrinsic apoptotic pathways was required for the sensitization effect observed upon uPA knockdown.…”

“…Indeed, uPA and its membrane-bound receptor urokinase plasminogen activator receptor (uPAR) have been primarily documented as promoting the proliferation and survival of cancer cells; 38, 39, 40 however, other reports propose that uPA/uPAR may support cell death. 41, 42, 43 Notably, the previously analyzed cancer cell lines and stepwise transformed cells with high expression of PLAU mRNA show fractional killing (Figures 1b, d and 2d and Supplementary Figure 1).…”

Proapoptotic signaling induced by RIG-I and MDA-5 results in type I interferon–independent apoptosis in human melanoma cells

“…Noxa and Puma, the two BH3-only proteins most strongly induced by pppRNA, were originally isolated as target genes upregulated by the tumor suppressor p53. The tumor suppressor p53 is rarely mutated in melanoma, in contrast to many other malignancies, and serves as an important regulator of apoptosis (21,22). However, expression studies revealed no increase in p53 on the mRNA (data not shown) and protein levels ( Figure 6A) upon treatment with pppRNA or poly(I:C).…”