Cdk4 Regulates Glioblastoma Cell Invasion and Stemness and Is Target of a Notch Inhibitor Plus Resveratrol Combined Treatment

Glioblastoma multiforme (GBM) is one of the most aggressive types of cancer characterized by poor patient outcomes. To date, it is believed that the major cause of its recurrence and chemoresistance is represented by the enrichment of GBM stem cells (GSCs) sustained by the abnormal activation of a number of signaling pathways. In this study, we found that in GBM cells, treatment with low toxicity doses of the & gamma;-secretase inhibitor RO4929097 (GSI), blocking the Notch pathway activity, in combination with resveratrol (RSV) was able to reverse the basal mesenchymal phenotype to an epithelial-like phenotype, affecting invasion and stemness interplay. The mechanism was dependent on cyclin D1 and cyclin-dependent kinase (CDK4), leading to a reduction of paxillin (Pxn) phosphorylation. Consequently, we discovered the reduced interaction of Pxn with vinculin (Vcl), which, during cell migration, transmits the intracellular forces to the extracellular matrix. The exogenous expression of a constitutively active Cdk4 mutant prevented the RSV + GSI inhibitory effects in GBM cell motility/invasion and augmented the expression of stemness-specific markers, as well as the neurosphere sizes/forming abilities in untreated cells. In conclusion, we propose that Cdk4 is an important regulator of GBM stem-like phenotypes and invasive capacity, highlighting how the combined treatment of Notch inhibitors and RSV could be prospectively implemented in the novel therapeutic strategies to target Cdk4 for these aggressive brain tumors.

Automated summary

Glioblastoma multiforme (GBM) is an aggressive cancer type with poor outcomes, and enrichment of GBM stem cells (GSCs) is believed to be the cause of its recurrence and chemoresistance. In this study, low-dose treatment of γ-secretase inhibitor RO4929097 (GSI) and resveratrol (RSV) reversed the mesenchymal phenotype of GBM cells to an epithelial-like phenotype, affecting invasion and stemness. The mechanism involves cyclin D1, cyclin-dependent kinase (CDK4), and paxillin (Pxn) phosphorylation, leading to reduced Pxn interaction with vinculin (Vcl) and altered cell migration. The study suggests that targeting Cdk4 with Notch inhibitors and RSV could be a potential therapeutic strategy for aggressive brain tumors.