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Immunodetection of DNA Repair Endonuclease ERCC1-XPF in Human Tissue

¹ Department of Human Genetics, University of Pittsburgh School of Public Health; ² University of Pittsburgh Cancer Institute, Hillman Cancer Center; Departments of ³ Pharmacology and Chemical Biology and ⁴ Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine; ⁵ Department of Pathology, University of Pittsburgh Medical Center Shadyside, Pittsburgh, Pennsylvania

Requests for reprints: Laura J. Niedernhofer, University of Pittsburgh Cancer Institute, Hillman Cancer Center, 5117 Centre Avenue, 2.6, Pittsburgh, PA 15213-1863. Phone: 412-623-7763; Fax: 412-623-7761; E-mail: niedernhoferl{at}upmc.edu.

Key Words: biomarker • interstrand crosslink • platinum

The high incidence of resistance to DNA-damaging chemotherapeutic drugs and severe side effects of chemotherapy have led to a search for biomarkers able to predict which patients are most likely to respond to therapy. ERCC1-XPF nuclease is required for nucleotide excision repair of helix-distorting DNA damage and the repair of DNA interstrand crosslinks. Thus, it is essential for several pathways of repair of DNA damage by cisplatin and related drugs, which are widely used in the treatment of non–small cell lung carcinoma and other late-stage tumors. Consequently, there is tremendous interest in measuring ERCC1-XPF expression in tumor samples. Many immunohistochemistry studies have been done, but the antibodies for ERCC1-XPF were not rigorously tested for antigen specificity. Herein, we survey a battery of antibodies raised against human ERCC1 or XPF for their specificity using ERCC1-XPF–deficient cells as a negative control. Antibodies were tested for the following applications: immunoblotting, immunoprecipitation from cell extracts, immunofluorescence detection in fixed cells, colocalization of ERCC1-XPF with UV radiation–induced DNA damage in fixed cells, and immunohistochemistry in paraffin-embedded samples. Although several commercially available antibodies are suitable for immunodetection of ERCC1-XPF in some applications, only a select subset is appropriate for detection of this repair complex in fixed specimens. The most commonly used antibody, 8F1, is not suitable for immunodetection in tissue. The results with validated antibodies reveal marked differences in ERCC1-XPF protein levels between samples and cell types. [Cancer Res 2009;69(17):6831–8]