ROBO1 Expression in Metastasizing Breast and Ovarian Cancer: SLIT2-induced Chemotaxis Requires Heparan Sulfates (Heparin).

Abstract

The members of the slit homolog (SLIT) and roundabout homolog (ROBO) families have emerged as important signaling molecules in tumor metastasis. This study analyzed their role in regulating breast cancer (BC) cell motility and chemotaxis and assessed expression of ROBO1 in brain metastases (BMs) of breast, lung, and colon cancer, and in peritoneal metastases (PMs) of ovarian cancer. The BC cell line MDA-MB231 was subjected to scratch, motility, and chemotaxis assays using heparin and a purified recombinant N-terminal SLIT2 fragment. Protein expression was assessed in primary tumors and metastases by immunohistochemistry. Exposure to SLIT2 induced MDA-MB231 cell motility, but no significant chemotaxis without the presence of heparin. ROBO1 was expressed in 4/5 primary BC and in 18/21 BC-derived BM samples; 7/9 BM primary lung cancer samples also stained positive. In contrast, BMs from colorectal cancer were negative for ROBO1. Primary ovarian cancer and ovarian PM showed ROBO1 expression in 0/6 and in only 2/6 samples, respectively, whereas SLIT2 was observed in 1/6 primary cancer and in 6/6 PMs samples. SLIT2 can induce BC cell motility and chemotaxis, but the latter requires the presence of heparin. BM expression of ROBO1 is a common feature of some, but not all cancer types. SLIT2 expression appears to be a general feature of ovarian cancer-derived PMs.