Resveratrol nanoparticles induce apoptosis in oral cancer stem cells by disrupting the interaction between β-catenin and GLI-1 through p53-independent activation of p21

Cancer stem cells (CSCs) are mainly responsible for tumorigenesis, chemoresistance, and cancer recurrence. CSCs growth and progression are regulated by multiple signaling cascades including Wnt/β-catenin and Hh/GLI-1, which acts independently or via crosstalk. Targeting the crosstalk of signaling pathways would be an effective approach to control the CSC population. Both Wnt/β-catenin and Hh/GLI-1 signaling cascades are known to be regulated by p53/p21-dependent mechanism. However, it is interesting to delineate whether p21 can induce apoptosis in a p53-independent manner. Therefore, utilizing various subtypes of oral CSCs (SCC9-PEMT p53^+/+p21^+/+, SCC9-PEMT p53^−/−p21^+/+, SCC9-PEMT p53^+/+p21^−/− and SCC9-PEMT p53^−/−p21^−/−), we have examined the distinct roles of p53 and p21 in Resveratrol nanoparticle (Res-Nano)-mediated apoptosis. It is interesting to see that, besides the p53/p21-mediated mechanism, Res-Nano exposure also significantly induced apoptosis in oral CSCs through a p53-independent activation of p21. Additionally, Res-Nano-induced p21-activation deregulated the β-catenin-GLI-1 complex and consequently reduced the TCF/LEF and GLI-1 reporter activities. In agreement with in vitro data, similar experimental results were obtained in in vivo mice xenograft model.

Schematic representation of Res-Nano deregulating the crosstalk of β-catenin-GLI-1 through activation of p21. (I) Plausible mechanism of β-catenin-GLI-1 interaction before Res-Nano treatment. (1a&1b) Co-localization of Wnt/β-catenin and Hh/GLI-1 pathways proteins along with p21. (2) β-catenin and GLI-1 release from their negative regulators like GSK3β, CK1α, AXIN, APC, and SUFU. (3) Formation of β-catenin-GLI-1 complex. (4) Nuclear localization of β-catenin-GLI-1 complex. (5) β-catenin and GLI-1 bind to their respective promoter binding region. (6) Activation of transcriptional target genes. (7) Cell growth and proliferation. (II) Plausible mechanism of β-catenin-GLI-1 interaction in the regulation of apoptosis after Res-Nano treatment. (1a&1b) Co-localization of Wnt/β-catenin and Hh/GLI-1 pathways proteins along with p21. (2) Res-Nano activates p21. (3) Activated p21 deregulates β-catenin-GLI-1 complex. (4) β-catenin and GLI-1 degraded in cytoplasm. (5) β-catenin and GLI-1 are unable to enter into the nucleus. (6) Downregulation of target genes. (7) Induction of apoptosis.