Figure 2 A. HEK293 cells treated for 24 h with 100 μM H2O2. Basal and phospho-active forms of ATM and CHK2 were assessed by Western blot. Phospho:basal level ratios of ATM and CHK2 immunoreactive bands are normalized to Vinculin, selected as loading control, and expressed as arbitrary units. Values shown represent the means ± SD of n ≥ 4 independent experiments. *, p<0.05; **, p<0.01.  B. HEK293 cells were treated for 24 h with 100 μM H2O2 in the presence or absence of the ATM inhibitor KU55933 (KU). Basal and phospho-active forms of ATM, CHK2, and GSNOR were assessed by Western blot. Vinculin and GAPDH were used as loading controls. Phospho:basal level ratios of ATM and CHK2 (normalized to Vinculin), along with densitometry of GSNOR immunoreactive bands (normalized to GAPDH) are expressed as arbitrary units. Values shown represent the means ± SD of n = 3 independent experiments. *, p<0.05.  C. HEK293 cells were treated for 24 h with 100 μM H2O2 in the presence or absence of the CHK2 inhibitor AZD7762 (AZD). Basal and phospho-active forms of CHK2, together with GSNOR were assesses by Western blot. Phospho:basal level ratios of CHK2 and densitometry of GSNOR immunoreactive bands are normalized to GAPDH, selected as loading control, and expressed as arbitrary units. Values shown represent the means ± SD of n = 3 independent experiments. *, p<0.05; **, p<0.01; n.s., not significant.  D. HEK293 cells were transfected with a pool of siRNA against ATM (siATM) or with control siRNA (siScr) for 18 h and treated for additional 24 h with 100 μM H2O2. Basal and phospho-active forms of ATM, together with GSNOR were assessed by Western blot. Vinculin and GAPDH were used as loading controls. Densitometry of GSNOR immunoreactive bands is normalized to GAPDH and expressed as arbitrary units. Values shown represent the means ± SD of n = 3 independent experiments. *, p<0.05; **, p<0.01.  E. HEK293 cells were transfected with a pool of siRNA against CHK2 (siCHK2) or with control siRNA (siScr) for 18 h and treated for additional 24 h with 100 μM H2O2. Basal and phospho-active forms of CHK2, together with GSNOR were assessed by Western blot. GAPDH was used as loading control. Densitometry of GSNOR immunoreactive bands is normalized to GAPDH and expressed as arbitrary units. Values shown represent the means ± SD of n = 3 independent experiments. *, p<0.05.  F. HEK293 cells were treated for 24 h with 100 μM H2O2 in the presence or absence of the ATM inhibitor KU55933 (KU). Lysates were subjected to biotin-switch assay, and S-nitrosylated proteins (PSNOs) revealed by incubation with horseradish peroxidase (HRP)-conjugated streptavidin. Results obtained in the absence of ascorbate (- ASC) are shown as negative controls. Densitometry of each lane intensity is normalized to LDH, selected as loading control, and expressed as arbitrary units. Values shown represent the means ± SD of n = 3 independent experiments. *, p<0.05; **, p<0.01.  G. RT-qPCR analyses of GSNOR mRNA in input and heavy polysome fraction pooled together in H2O2 treated samples in the absence or in the presence of the ATM inhibitor KU55933 (KU). H3A mRNA expression level was used as housekeeping gene control. Results are the means ± SEM of n = 3 independent experiments run in duplicate and shown as %, normalized by H3A. *, p<0.05.  H. HEK293 cells were treated for 8 or 24 h with 100 μM H2O2 or, alternatively, for 2 h with 2 mM hydroxyurea (HU), selected as positive control of CHK1 phosphorylation at Ser317. Phospho-CHK1Ser317 was assessed by Western blot; densitometry normalized to Vinculin, selected as loading control, and expressed as arbitrary units (with HU arbitrarily set to 1). Values shown represent the means ± SD of n = 3 independent experiments. n.s., not significant.  I. HEK293 cells were transfected with a pool of siRNA against CHK1 (siCHK1) or with control siRNA (siScr) for 18 h and treated for additional 24 h with 100 μM H2O2. CHK1 and GSNOR were assessed by Western blot analysis of. Densitometry of GSNOR immunoreactive bands is normalized to Vinculin, selected as loading control, and expressed as arbitrary units. Values shown represent the means ± SD of n = 3 independent experiments. *, p<0.05.