CDK6 and glioblastoma: The protein expression of cdk2, cdk4, cdk6, cyclin D1 and cyclin E in BP-treated GBM cells was also measured, and all five proteins were decreased in DBTRG-05MG and DBTRG 8401 cells; similar results for cdk2, cdk4, cdk6, cyclin D1, cyclin E and p21 were detected in RG2 cells after treatment with BP (Fig. 2b).