Identification of DJ-1 as a contributor to multidrug resistance in human small-cell lung cancer using proteomic analysis.

Proteomic approaches have been proven to provide an important tool in identifying drug resistance-associated proteins. The aim of this study was to investigate the protein profiling of drug resistance-related proteins in small-cell lung cancer (SCLC) by proteomic analysis. The proteomic profiling was performed by two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) coupled with MALDI-TOF-TOF of SCLC in the multidrug-resistant cell line H69AR and its parental cell line H69. A total of 11 proteins were identified to be >2-fold up-or downregulated between the two cell lines. DJ-1, one of the differently expressed proteins identified by proteomics, was further examined by immunohistochemistry staining in 116 cases of SCLC tissues. Immunohistochemical results demonstrated that DJ-1 was expressed in 51.7% (60/116) of SCLC. DJ-1 expression was correlated significantly with survival time of SCLC patients (P < 0.05), but not with other clinical parameters such as gender, age and clinical stage (P > 0.05). Downregulation of DJ-1 using DJ-1-siRNA in H69AR cells sensitized cancer cells to chemotherapeutic drugs through increasing drug-induced cell apoptosis accompanied with G0-G1 phase arrest. These findings suggest DJ-1 may serve as a potential biomarker for chemoresistance and prognostic factor for patients with SCLC.