Fig. 4.

MYC inhibits and cyclin-dependent kinase 18 (CDK18) promotes homologous recombination (HR) in glioblastoma stem-like cells (GSCs). a Representative flow cytometry plots showing HR in MGG4-DRGFP expressing shRNA-Control (shCon) or shRNA-MYC (shMYC; two independent sequences) and MGG18-DRGFP expressing empty vector (Con) or MYC. GSCs were induced with doxycycline for 6 days before infection with lentivirus with (+) or without (−) I-SceI expression, followed by flow cytometry to measure green fluorescent protein (GFP)-positive cells (right quadrant) at 5 days after infection. b HR efficiency (percentage of GFP⁺) from a and two additional independent experiments. c HR efficiency in MGG4-DRGFP-CDK18 or MGG18-DRGFP-shCDK18 (two independent sequences). Western blot and representative fluorescence-activated cell sorting (FACS) plots shown in Supplementary Fig. 7. d HR efficiency in MGG4- or MGG18-DRGFP with double knockdown or overexpression of MYC and CDK18. Western blot and representative FACS plots shown in Supplementary Fig. 8. e–g Quantification of immunofluorescence staining of γH2AX (e), Rad51 positive foci in RPA positive (f), and BRCA2 (g) foci in GSCs with CDK18 overexpression or knockdown (sh) (shCDK18 #2 in e, g). Cells were treated with olaparib (Ola; 15 μM) or mock for 12 h before staining. Cell with ≥5 foci/cell were counted as positive. Representative images shown in Supplementary Fig. 9. Mean ± SEM, from three independent experiments. *p < 0.05, **p < 0.01 and ***p < 0.001, t test