Fig. 4. A defective replication stress response leads to PARPi sensitivity in SF3B1^MUT cells.

a, Western blot of pCHK1 (S317), total CHK1 and CINP expression in MEL202^R625G-DEG cells after non-targeting control (NTC) or CINP siRNA-mediated gene silencing, with 0, 1 or 3 h of 500 nM talazoparib exposure. Images are representative of n = 3 biological replicates. b, Talazoparib dose–response curves showing the SF, relative to DMSO, of MEL202 isogenic cells after NTC or CINP siRNA-mediated gene silencing. Data are mean of three replicates, error bars show ±s.e.m. c, Western blot of pCHK1 (S317) and total CHK1 expression in MEL202^R625G cells expressing control–GFP or CINP–GFP, following 0, 1 and 3 h of 500 nM talazoparib exposure. Images are representative of two biological replicates. d, Talazoparib dose–response curves showing the SF, relative to DMSO, of MEL202 isogenic cells, and MEL202^R625G cells expressing control–GFP or CINP–GFP. Data are mean of n = 3 biological replicates, error bars show ±s.e.m. e,f, Scatterplots showing the number of 53BP1 (e) and γH2AX (f) foci per nucleus in MEL202 isogenic cells after 0, 3 h (500 nM) and 48 h (50 nM) talazoparib exposure. Data are representative of n = 3 biological replicates, error bars show ±s.d. g,h, Representative immunofluorescence images (g) of FANCD2 and MUS81 foci and scatterplot of FANCD2 foci (h) in MEL202 isogenic cells after 48 h DMSO or (50 nM) talazoparib exposure. Scale bar, 100 μm. Data are representative of n = 3 biological replicates, error bars show ±s.d. of individual nuclei assessed. P values are calculated by one-way ANOVA (e, f and h), ****P < 0.0001. NTC, nontargeting control; NS, not significant.

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