Identification and characterization of the murine ortholog (brms1) of breast-cancer metastasis suppressor 1 (BRMS1)

We have cloned a novel metastasis-suppressor gene (BRMSI) by differential display, comparing metastatic human breast carcinoma cell line MDA-MB-435 to its metastasis-suppressed human chromosome I I microcell hybrid. Screening of a murine cDNA library led to the identification of a 1.4 kb cDNA with a sequence revealing 85% homology to human BRMSI within the open reading frame. The predicted protein sequence for the murine ortholog is 95% identical, suggesting that it is strongly conserved across these 2 species. The cloned cDNA was used to screen a murine strain SV129 BAC library to obtain brmsI genomic DNA. Three BAC clones [226(14), 226(H4) and 239(N7)] were confirmed to encode the entire brmsI gene. Detailed analysis of BAC clone 226(14) shows that the gene spans 8.5 kb and, like the human gene, is organized into 10 exons and 9 introns. While the exons share a high degree of homology, there are greater differences when comparing intron structures between the human and murine genes. The 5' upstream region shares about 64% homology with its human counterpart, retaining several of the many putative regulatory elements. Like the human genomic BRMSI, the murine ortholog of the iGnT gene is found upstream of brmsI and the murine ortholog of the RINI gene is found downstream of brmsI. brmsI was then tested for suppression of metastasis of mouse mammary carcinoma cell line 66cl4 in syngeneic BALB/c mice. Transfection with brmsI did not inhibit 66cl4 primary tumor formation but significantly suppressed its metastatic capability. This suggests that the murine ortholog functions similarly to BRMSI. (C) 2002 Wiley-Liss, Inc.