Figure 5. Effects of the folate-independent salvage path-way of nucleotide biosynthesis on metformin-induced activation of ATM. Immunofluorescence for phospho-ATMSer1981 in MDA-MB-231 cells either untreated or treated with 1 mmol/L metformin (MET) in the absence or presence of thymidine plus hypoxanthine for 48 h. Images were captured in different channels for phospho-ATMSer1981 (green) and Hoechst 33258 (blue) with a 20x objective.