Investigating the role of IGF-1R in the cellular response to DNA damage

IGF-1R plays an important role in regulating cell proliferation, survival and migration. Its overexpression in a number of cancers has been associated with radio-resistance. Previous studies from our group and others have confirmed that depletion or inhibition of IGF 1R can sensitise cancer cells to ionising radiation. However, the underlying mechanisms remain elusive. Our study aimed to uncover the mechanisms of radio-sensitisation associated with the IGF-1R signalling pathway. This was achieved by investigating changes at the proteome, transcriptome and metabolome levels using siRNA-mediated gene silencing and also IGF-1R mutant isogenic models which we generated from p53 wild-type osteosarcoma U2OS cells using the CRISPR/Cas9 genome editing technique. We confirmed that suppressing the IGF-1R function through either transient or permanent depletion of the protein enhances U2OS sensitivity to γ-irradiation with average dose enhancement ratios of 3.5 and 3 respectively at 5Gy. Double-strand break induction and resolution were not impaired in IGF1R-deficient cells as determined by γH2AX foci tracking and there was no evidence that the activation of the DNA damage response was compromised in the mutant with evidence of ATM, CHK1 and RPA phosphorylation along with p53 accumulation. Moreover, we did not find defects in cell cycle checkpoint integrity which prompted us to evaluate intrinsic properties associated with IGF 1R deficiency that may affect cell survival following exposure to γ-irradiation. Transcriptome and metabolome profiling revealed significant differences in genes and metabolites associated with various cellular pathways, particularly the cellular response to stress, intracellular metabolism and, cell motility and migration. The interplay of molecular changes affecting these cellular processes might account for the radio-sensitisation of IGF 1R deficient cells. Future investigations should attempt to explore this possibility given that previous research on this same topic have hinted at the likelihood that the cellular response to ionising radiation is governed by complex multiple factors.