Isolation of Gene Associated with High Metastatic Potential in Rat Mammary Adenocarcinomas

This report describes our isolation of pGM21, a novel gene showing enhanced expression in rat mammary adenocarcinoma cell lines with high metastatic potential. We constructed a library of 25,000 complementary DNA (cDNA) clones enriched for genes associated with metastasis. To build this library, we hybridized messenger RNA (mRNA) from a poorly metastatic rat mammary adenocarcinoma cell line (DMBA8) with cDNA from the highly metastatic variant line (DMBA8 ascites). One-fifth of the library was screened by differential cDNA hybridization. After three rounds of screening, we had isolated 14 cDNA clones that showed higher mRNA expression in the more metastatic cells. When we used Northern blot screening of these cDNA clones against several related rat mammary adenocarcinoma cell lines and a line that was independently derived, one of the clones showed levels of expression consistently correlating with high metastatic potential. Southern blot analysis indicated that no gene rearrangement or amplification accounted for this change. Partial sequencing of this isolated clone revealed a 45-nucleotide segment homologous to mRNA from human elongation factor 1 subunit alpha, which is involved in protein synthesis. Our results demonstrate that overexpression of the gene corresponding to pGM21 may be important in the development of metastasis.