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. 2011 Feb 2;108(8):3336–3341. doi: 10.1073/pnas.1012351108

Fig. 5.

Fig. 5.

CHK1 is phosphorylated in response to MYCN activation, and CHK1 inhibition causes apoptosis and replication arrest. (A) Treatment of the neuroblastoma cell lines SKNAS and KELLY with the CHK1 inhibitor SB (500 nM) decreased cellular viability by >50% (average ± SD; P < 0.0001), whereas the control RPE-1 cells are viable. (B) CHK1 inhibition by TCS and SB caused significant apoptosis in KELLY cells by 48 h as determined by annexin/PI staining. (C) Representative cell cycle histogram by PI staining demonstrated that CHK1 inhibited by TCS in neuroblastoma KELLY cells harvested at 48 h after treatment are arrested during replication compared with control (P < 0.0001), whereas there is no S-phase arrest in RPE1 cells. (D) Western blot of CHK1 Ser296, total CHK1, MYCN-ER (as analyzed by an anti-MYCN and an anti-ER antibody, 90 kDa), and actin in RPE1–MYCN-ER or parental RPE1 cells with and without MYCN-ER activation by 4-OHT. (E) There is a significant decrease (P = 0.001) in cellular growth after CHK1 inhibition by PF-00477736 (PF-736) only in RPE1 cells with activated MYCN (RPE1–MYCN-ER treated with 4-OHT).