The roles of receptor tyrosine kinases in DNA damage response (DDR) are still largely unknown. In this study, we examined the possible involvement of insulin-like growth factor I receptor (IGF-IR) and epidermal growth factor receptor (EGFR) in the DNA damage response (DDR) following irradiation.
HeLa cells expressing the fluorescence ubiquitination-based cell cycle indicator (Fucci) probes (HeLa-Fucci cells) were used in this study. Kinetics of the Fucci fluorescence were detected by FACS and time-lapse imaging. NVP-AEW541, Tyrphostin AG1478, LY294002, PD98059, NU7026 were used as specific inhibitors for IGF-IR, EGFR, PI3-K, MEK, and DNA-PKcs, respectively. Phosphorylation of ERK1/2 and Akt was detected by western blotting. Double strand breaks (DSBs) were detected by immunofluorescence staining for 53BP1. Cells were irradiated using an RX-650 Cabinet X-radiator system (Faxitron).
To investigate the possible involvement of EGFR and IGF-IR in G2 arrest, FACS analysis and time-lapse imaging of Fucci fluorescence were performed using specific inhibitors. Results showed that inhibition of IGF-IR, but not that of EGFR, prolonged G2 arrest, which was irrespective of cell cycle phases at irradiation, i.e., red (G1 phase) or green (S/G2 phases) phase in the Fucci system. Similarly, only inhibition of IGF-IR decreased the DSB repair activity. Hereafter, further analysis was focused on IGF-IR-associated events. We next attempted to identify the responsible IGF-IR-downstream signaling pathways. Irradiation phosphorylated both Akt and ERK; however, inhibition of IGF-IR abrogated activation of only Akt. Moreover, inhibition of PI3-K/Akt, but not that of MEK/ERK, prolonged G2 arrest, which mimicked that of IGF-IR. Inhibition of DNA-PKcs, a major factor of non-homologous end joining (NHEJ), also prolonged G2 arrest.
We conclude that irradiation is likely to preferentially activate the IGF-IR/PI3-K/Akt signaling pathway in HeLa-Fucci cells, which may enhance DSB repair, eventually contributing to reduction of G2 arrest in the DDR following irradiation.
Clinical trial indentification
Legal entity responsible for the study
Tokyo Medical and Dental University
Tokyo Medical and Dental University, MEXT Japan
All authors have declared no conflicts of interest.