CLPTM1L induces estrogen receptor ß signaling-mediated radioresistance in non-small cell lung cancer cells.

ABSTRACT

INTRODUCTION: Radioresistance is a major challenge in lung cancer radiotherapy, and new radiosensitizers are urgently needed. Estrogen receptor ß (ERß) is involved in the progression of non-small cell lung cancer (NSCLC), however, the role of ERß in the response to radiotherapy in lung cancer remains elusive. In the present study, we investigated the mechanism underlying ERß-mediated transcriptional activation and radioresistance of NSCLC cells. METHODS: Quantitative real-time PCR, western blot and immunohistochemistry were used to detect the expression of CLPTM1L, ERß and other target genes. The mechanism of CLPTM1L in modulation of radiosensitivity was investigated by chromatin immunoprecipitation assay, luciferase reporter gene assay, immunofluorescence staining, confocal microscopy, coimmunoprecipitation and GST pull-down assays. The functional role of CLPTM1L was detected by function assays in vitro and in vivo. RESULTS: CLPTM1L expression was negatively correlated with the radiosensitivity of NSCLC cell lines, and irradiation upregulated CLPTM1L in radioresistant (A549) but not in radiosensitive (H460) NSCLC cells. Meanwhile, IR induced the translocation of CLPTM1L from the cytoplasm into the nucleus in NSCLC cells. Moreover, CLPTM1L induced radioresistance in NSCLC cells. iTRAQ-based analysis and cDNA microarray identified irradiation-related genes commonly targeted by CLPTM1L and ERß, and CLPTM1L upregulated ERß-induced genes CDC25A, c-Jun, and BCL2. Mechanistically, CLPTM1L coactivated ERß by directly interacting with ERß through the LXXLL NR (nuclear receptor)-binding motif. Functionally, ERß silencing was sufficient to block CLPTM1L-enhanced radioresistance of NSCLC cells in vitro. CLPTM1L shRNA treatment in combination with irradiation significantly inhibited cancer cell growth in NSCLC xenograft tumors in vivo. CONCLUSIONS: The present results indicate that CLPTM1L acts as a critical coactivator of ERß to promote the transcription of its target genes and induce radioresistance of NSCLC cells, suggesting a new target for radiosensitization in NSCLC therapy. Video Abstract.