CDKN1B and glioblastoma: Human GBM cells treated with VD3 showed increased expression of the cyclin-dependent kinase inhibitors (CDNK1) CDKN1A (p21), CDKN1B (p27), and p57 and reduced expression of cyclin D1 (Figure 3), and the response was mediated through the vitamin D receptor (VDR), which resulted in cell growth arrest [28].