Epidermal growth factor and ionizing radiation up-regulate the DNA repair genes, XRCC1 and ERCC1 in DU145 and LNCaP prostate carcinoma via MAPK signaling

A Yacoub, Ph.D., P Dent, Ph.D., and M Hagan, MD, Ph.D.

Medical College of Virginia, VCU, Richmond, Virginia United States

Introduction/Purpose: The androgen-independent prostate carcinoma cell line DU145 (p53-/-) expresses high levels of the EGF receptor (EGFR). We have reported that EGFR-dependent signaling in these cells, which confers greater tumorigenicity and resistance to ionizing radiation, is associated with the regulation of DNA repair activity. Here, examining p53+/+ LNCaP cells expressing low levels of the ERK1/2, we have tested the notion that EGF-EGFR signaling activates MAPK to regulate DNA repair. Methods: Expression of XRCC1 and ERCC1 was examined in the androgen independent human prostate cancer cell line DU145 and the androgen dependent cell line LNCaP. Quantitative RT-PCR and Western analyses were performed after irradiation and stimulation (EGF) or inhibition (AG1478, PD98059) of EGFR-ERK signaling. Results: In DU145 cells and LNCaP cells ionizing radiation activated the DNA repair genes XRCC1 and ERCC1 in a MAPK (ERK1/2) dependent fashion. EGF up-regulated the levels of both XRCC1 and ERCC1 repair enzymes. EGF administration markedly increased this up-regulation after exposure to ionizing radiation. The EGFR inhibitor tyrphostin (AG-1478), and the MEK inhibitor PD90859 each attenuated EGF induction of ERCC1 and XRCC1 mRNA and protein levels, indicating that the EGFR-mediated signal pathway and MAPK are involved in the DNA repair responses to radiation damage. The EGF-induced increases in XRCC1 and ERCC1 were prevented by the protein synthesis inhibitor cyclohexamide. Inhibition of ERK1/2 was more effective that EGFR blockade in blocking radiation-induced up-regulation of both proteins. Conclusions: Taken together these data imply a complex control of DNA repair activation, which may be more generally dependent on MAPK signaling than was previously noted. These data provide novel insights into the capacity of the EGFR-ERK signaling to modulate DNA repair in cancer cells.

KEY WORDS: Ionizing radiation, DNA repair, epidermal growth factor receptor (EGFR), mitogen activated protein kinase (MAPK), nucleotide excision repair cross complimenting group enzyme 1 (ERCC1), X-ray cross-complementing group 1 protein (XRCC1).

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Gene Expression, Part 2.