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The SLIT2 gene encodes a secreted glycoprotein that acts as a ligand for the ROBO transmembrane receptors. Studies suggest that the SLIT2-ROBO1 interaction plays an important role in migration of cells in both the nervous and immune system. SLIT2 also seems to be involved in human cancer development. In several types of cancer loss of heterozygosity (LOH) at the SLIT2 (4p15.2) locus was shown. We have previously demonstrated that the CpG island of the SLIT2 gene is frequently hypermethylated in breast, lung, colorectal and glioma primary tumours. Recently we detected methylation of the SLIT2 promoter region in DCIS (ductal carcinoma in situ) lesions indicating that inactivation of this gene may play a role in early stages of breast cancer. We also found hypermethylation of the SLIT3 promoter region in breast and colorectal tumours albeit to a lesser degree than SLIT2. In addition we have shown that secreted SLIT2 has the ability to induce apoptosis in colorectal tumour cell lines. Colony formation and soft agar assays have also demonstrated that exogenous expression of SLIT2 can significantly suppress growth of breast tumour cell lines. SLIT2 expressing stable clones, generated from a breast tumour cell line that does not normally express this gene, were used for gene target identification. Expression microarray analysis identified 60 genes differentially regulated by SLIT2 that are now being confirmed by quantitative real-time RT-PCR. Among these targets are genes involved in cell cycle, apoptosis, cell adhesion, signalling, protein synthesis and transcription. We have also used siRNA to successfully knock down endogenous SLIT2 in a breast tumour cell line. We will investigate the properties of these cells by analysing their cell cycle profile along with carrying out apoptosis, cell migration and growth suppression assays. Overall there is increasing evidence supporting a role for SLIT2 as a tumour suppressor gene involved in breast cancer development.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]