CDKN2A and glioblastoma: Levels of p16, p21, Bax and AIF protein in BP-treated GBM cells were therefore measured, and protein expression levels of all four proteins increased in DBTRG-05MG and DBTRG 8401 cells; similar results for p27, Bax and AIF were detected in RG2 cells after treatment with BP (Figs 2b and c).