The Role of Dragon (Repulsive Guidance Molecule-B, RGM-B) in Human Breast Cancer.

Abstract

Abstract Introduction: Repulsive guidance molecules (RGMs) are involved in embryonic development and iron homeostasis. RGM-A mediates repulsive axonal guidance and neural tube closure, and RGM-C is mutated in juvenile hemochromatosis. RGM-B, also known as Dragon, is a myelin-derived inhibitor of axon growth in the central nervous system. The RGM family was also identified as co-receptors of bone morphogenetic proteins (BMPs), a group of proteins that are involved in development of bones, the differentiation and progression of cancer. However, the role of RGMs played in breast cancer remains unclear. In the present study, we examined the pattern of expression of the RGM family in human breast cancer cells and investigated the impact of Dragon (RGM-B) on BMP-induced cell function in breast cancer cells.Material and Methods: Conventional RT-PCR was performed to screen the expression of RGMs in human breast cancer samples and a range of breast cancer cell lines. Dragon/RGM-B ribozyme transgenes were generated and in order to knock down the Dragon transcript. Subsequently, MDA-231RGMB-Knock-down variants were created by way of the transgenes. A series of cell function assays were employed to investigate any biological effects upon RGM-B knockdown on the breast cancer cells as well as cell's response to recombinant BMP proteins.Results: RGM-A and RGM-C transcripts were barely detectable in breast cancer cell lines (MDA-MB-231 and MCF-7) and tissues. However RGM-B transcripts were expressed in both cell lines. Using anti-RGM-B transgenes, MDA-231RGMB-Knock-down variant cell lines, in which RGM-B transcripts were knocked down, were created. Compared with wild type and control transfection, MDA-231RGMB-Knock-down variants displayed a significant increase in both the adhesiveness and cells growth (p < 0.05, vs the respective controls, for adheresion and for cell growth). Interestingly, RGM-B knockdown did not have any significant effects on the invasiveness of the cells. Finally, wild type breast cancer cells and the RGMB knock down variant cell lines showed a similar response to the treatment with rhBMP-11, indicating that RGM-B is less critical in BMP-11 mediated cell functions.Conclusion: The present study is the first to examine the role of RGM-B in breast cancer and has demonstrated that knock-down of RGMB could enhance breast cancer cells' ability to grow and attach, indicating that RGM-B may act as an inhibitor in breast cancer. This property is unique to RGMB, as this ability is not associated with any other member in the RGM family. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6158.