HDAC9 and glioblastoma: In the present study, we also found in GBM cells, both CUL4B and HDAC1/3 bounded to the p21 promoter, CUL4B knockdown and HDAC inhibitor treatment promoted p21 transcription, indicating CUL4B negatively regulates p21 transcription by coordinating HDACs to co-occupy the p21 promoter in GBM cells.