ID2 and glioblastoma: In agreement with our observation that receptor dependent SMAD1/3/8 are activated in GBM SDCs (Fig 2A), inhibitor of DNA binding 1 (ID1), ID2 and ID3, BMP/retinoic acid inducible neural specific 1 (BRINP1), downstream of BMP signaling, were upregulated in HF2927 SDCs (Fig 7C).