Transcriptional analysis of the mts1 gene with specific reference to 5' flanking sequences

The mts1 gene is specifically expressed in certain metastatic tumors but not in their nonmetastatic counterparts. It is also expressed in several normal cell and tissue types that exhibit the ability to be motile. The gene was cloned from both mouse and human sources and the 5' flanking regions were sequenced. The sequencing data revealed a 135-base-pair region of high homology between the mouse and human mts1 gene. This homology was observed in the vicinity of the TATA box. The 5' region of the mts1 gene was also observed to have a high degree of homology to some known promoter and enhancer sequences. To determine the role this region plays in regulating the transcription of mts1, promoter analysis was performed. Sixteen constructs were prepared in which the chloramphenicol acetyltransferase gene was fused to different regions of the mouse mts1 promoter. These constructs were analyzed in transient transfection assays in two related cell lines derived from mouse mammary adenosarcomas: CSML-0, a nonmetastatic cell line with low levels of mts1 expression, and CSML-100, a metastatic cell line with high levels of mts1 expression. Results of our transient transfection assays in conjunction with results obtained from in vitro and in vivo footprinting of the promoter region show no evidence of cis-acting control elements important for the transcriptional regulation of mts1 in these cell lines. A few nucleotides upstream of the TATA box are sufficient for maximal levels of mts1 transcription. Because no cis-acting control elements were found, restriction of mts1 transcription in CSML-0 cells must exist on some other level. mts1 was found to be hypermethylated in CSML-0 cells but not in CSML-100 cells. The possible role of methylation in progression of the nonmetastatic CSML-0 adenosarcoma cell line toward the metastatic CSML-100 adenosarcoma cell line is discussed.