CDK4 and breast cancer: As described above, MAP9 silencing induced the G1 arrest of BC cells, so we detected the expression of G1/S phase-related cell cycle-genes, including cyclin D1, cyclin E1, cyclin-dependent kinase 2 (CDK2), CDK4, CDK6, CDK inhibitor 2B (CDKN2B; also named p15), CDKN1A (also named p21), CDKN1C (also named p57), cell division cycle 25 A (CDC25A; also named p16), retinoblastoma transcriptional corepressor 1 (Rb1), and E2F transcription factor (E2F1) in BC cells with or without MAP9 silencing.