Pro-survival AKT and ERK signaling from EGFR and mutant EGFRvIII enhances DNA double-strand break repair in human glioma cells

Abstract

The epidermal growth factor receptor (EGFR) is frequently dysregulated in malignant glioma that leads to increased resistance to cancer therapy. Upregulation of wild type or expression of mutant EGFR is associated with tumor radioresistance and poor clinical outcome. EGFR variant III (EGFRvIII) is the most common EGFR mutation in malignant glioma. Radioresistance is thought to be, at least in part, the result of a strong cytoprotective response fueled by signaling via AKT and ERK that is heightened by radiation in the clinical dose range. Several groups including ours have shown that this response may modulate DNA repair. Herein, we show that expression of EGFRvIII promoted γ-H2AX foci resolution, a surrogate for double-strand break (DSB) repair, and thus enhanced DNA repair. Conversely, small molecule inhibitors targeting EGFR, MEK, and the expression of dominant-negative EGFR (EGFR-CD533) significantly reduced the resolution of γ-H2AX foci. When homologous recombination repair (HRR) and non-homologous end joining (NHEJ) were specifically examined, we found that EGFRvIII stimulated and CD533 compromised HRR and NHEJ, respectively. Furthermore, NHEJ was blocked by inhibitors of AKT and ERK signaling pathways. Moreover, expression of EGFRvIII and CD533 increased and reduced, respectively, the formation of phospho-DNA-PKcs and -ATM repair foci, and RAD51 foci and expression levels, indicating that DSB repair is regulated at multiple levels. Altogether, signaling from EGFR and EGFRvIII promotes both HRR and NHEJ that is likely a contributing factor towards the radioresistance of malignant gliomas.

Involvement of the insulin-like growth factor binding proteins in the cancer cell response to DNA damage

“…Both cytoplasmic signaling pathways appear to be involved in NHEJ and HR repair, potentially contributing to radioresistance (Golding et al 2009). Akt has a role in phosphorylation of DNA-PKcs at the Ser2056 and Thr2609 clusters (Toulany et al 2008) and, reciprocally, Akt can be activated by DNA-PKcs, providing a pro-survival feedback (Bozulic et al 2008).…”

Role of epidermal growth factor receptor in DNA damage repair

“…DNA-PK-mediated phosphorylation of Akt-1 Ser473 is a key step in activation of Akt-1, and results in a 10-fold enhancement of kinase activity. The cross talk between ATM and DNA-PKcs is probably a central axis in the response of cells to IR-induced DNA damage [1, [18][19][20].…”

“…It is well-accepted that HR is most active in late S-phase and G2. It is plausible, therefore, that these apparently disparate changes in HR can be reconciled by considering the cell cycle phase in which they have occurred [18,24,25].…”

Epidermal Growth Factor Receptor-Related DNA Repair and Radiation-Resistance Regulatory Mechanisms: A Mini-Review

“…However, the EGFR signaling pathway, which can modulate cell growth and death, is frequently misregulated in malignant tumors. The up-regulation of the wild-type EGFR or the expression of its mutants is associated with tumor radioresistance and poor clinical outcomes (Golding et al, 2009). Overexpression of EGFR promotes unregulated growth, inhibits apoptosis, and likely contributes to clinical radiation resistance (Tanaka et al, 2008).…”

“…Overexpression of EGFR promotes unregulated growth, inhibits apoptosis, and likely contributes to clinical radiation resistance (Tanaka et al, 2008). Radioresistance is thought to be, at least in part, the result of a strong cytoprotective response (Golding et al, 2009). However, the precise mechanism for the resistance to radiation associated with EGFR signaling and DNA repair is still unclear, and further research should be conducted.…”