GROα is highly expressed in adenocarcinoma of the colon and down-regulates fibulin-1

Purpose: The growth-related oncogene α (GROα) is a secreted interleukin-like molecule that interacts with the CXCR2 G-protein - coupled receptor. We found that the mRNA and protein products of GROα are more highly expressed in neoplastic than normal colon epithelium, and we studied potential mechanisms by which GROα may contribute to tumor initiation or growth. Experimental Design: Cell lines that constitutively overexpress GROα were tested for growth rate, focus formation, and tumor formation in a xenograft model. GROα expression was determined by Affymetrix GeneChip (241 microdissected colon samples), real-time PCR (n = 32), and immunohistochemistry. Primary colon cancer samples were also employed to determine copy number changes and loss of heterozygosity related to the GAOα and fibul-1 genes. Results: In cell cultures, GROα transfection transformed NIH 3T3 cells, whereas inhibition of GROα by inhibitory RNA was associated with apoptosis, decreased growth rate, and marked up-regulation of the matrix protein fibulin-1. Forced expression of GROα was associated with decreased expression of fibulin-1. Expression of GROα mRNA was higher in primary adenocarcinomas (n = 132), adenomas (n = 32), and metastases (n = 52) than in normal colon epithelium (P < 0.001). These results were confirmed by real-time PCR and by immunohistochemistry. Samples of primary and metastatic colon cancer showed underexpression of fibulin-1 when compared with normal samples. There were no consistent changes in gene copy number of GROα or fibulin-1, implying a transcriptional basis for these findings. Conclusion: Elevated expression of GROα is frequent in adenocarcinoma of the colon and is associated with down-regulation of the matrix protein fibulin-1 in experimental models and in clinical samples. GROα overexpression abrogates contact inhibition in cell culture models, whereas inhibition of GROα expression is associated with apoptosis. Importantly, coexpression of fibulin-1 with GROα abrogates key aspects of the transformed phenotype, including tumor formation in a murine xenograft model. Targeting GRO proteins may provide new opportunities for treatment of colon cancer.