Insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1) has potential tumour-suppressive activity in human lung cancer.

The expression of insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1) is decreased in various tumours, but the role of IGFBP-rP1 in lung cancer is not yet clear. In this study, IGFBP-rP1 expression in lung cancer cell lines was evaluated and reduced expression of IGFBP-rP1 was found. In tissue microarrays containing 138 primary tumours and 20 normal lung tissues analysed by immunohistochemistry, 58 tumours (42%) exhibited no expression of IGFBP-rP1, while all 20 normal lung tissues showed high expression. In squamous cell lung cancer, low expression of IGFBP-rP1 was significantly linked to high-grade tumours. Treatment with 5-aza-2'-deoxycytidine restored the expression of IGFBP-rP1 in three of four lung cancer cell lines. Sequencing of PCR products of sodium bisulphite-treated genomic DNA from the three lung cancer cell lines revealed a heterogeneous methylation pattern in the region of exon 1 and intron 1. Stable transfection of IGFBP-rP1 full-length cDNA into the H2170 lung cancer cell line led to increased expression of IGFBP-rP1 protein. IGFBP-rP1-positive transfectants exhibited remarkably reduced colony-forming ability in soft agar, suppression of tumour growth rate in nude mice, and increased apoptotic cell number as well as activated caspase-3 expression level. The data suggest that IGFBP-rP1 is a tumour suppressor inactivated by DNA methylation in human lung cancer.