Modified Panax ginseng Extract Inhibits uPAR-Mediated α5β1-Integrin Signaling by Modulating Caveolin-1 to Induce Early Apoptosis in Lung Cancer Cells
Abstract
Urokinase receptor (uPAR) is enhanced in many human cancer cells and is frequently an indicator of poor prognosis. Activation of α5β1-integrin requires caveolin-1 and is regulated by uPAR. However, the underlying molecular mechanism responsible for the interaction between uPAR and α5β1-integrin remains obscure. We found that modified regular Panax ginseng extract (MRGX) had a negative modulating effect on the uPAR/α5β1-integrin interaction, disrupted the uPAR/integrin interaction by modulating caveoline-1, and caused early apoptosis in cancer cells. Additionally, we found that siRNA-mediated caveoline-1 downregulation inhibited uPAR-mediated α5β1-integrin signaling, whereas caveoline-1 up-regulation stimulated the signaling, which suppressed p53 expression, thereby indicating negative crosstalk exists between the integrin α5β1 and the p53 pathways. Thus, these findings identify a novel mechanism whereby the inhibition of α5β1 integrin and the activation of p53 modulate the expression of the anti-apoptotic proteins that are crucially involved in inducing apoptosis in A549 lung cancer cells. Furthermore, MRGX causes changes in the expressions of members of the Bcl-2 family (Bax and Bcl-2) in a pro-apoptotic manner. In addition, MGRX-mediated inhibition of α5β1 integrin attenuates ERK phosphorylation (p-ERK), which up-regulates caspase-8 and Bax. Therefore, ERK may affect mitochondria through a negative regulation of caspase-8 and Bax. Taken together, these findings reveal that MRGX is involved in uPAR-α5β1-integrin signaling by modulating caveolin-1 signaling to induce early apoptosis in A549 lung-cancer cells and strongly indicate that MRGX might be useful as a herbal medicine and may lead to the development of new herbal medicine that would suppress the growth of lung-cancer cells.
