SMAD1 and malignant glioma: Furthermore, the protein expression of BMPR-IB and phospho-Smad1/5/8 in all malignant glioma cell lines was lower than the levels in normal astrocytes; intracellular protein expression of BMPR-IB was moderately lower in SF763 cells and drastically lower in other malignant glioma cell lines compared to normal astrocytes (Figure 1B).