REDUCTION OF CRIPTO-1 EXPRESSION BY A HAMMERHEAD-SHAPED RNA MOLECULE RESULTS FROM INHIBITION OF TRANSLATION RATHER THAN MESSENGER-RNA CLEAVAGE

Cripto-1 (CR-1) is a transforming growth factor which has been associa ted with breast, colon, and pancreatic cancer. Overexpression of CR-1 in non-tumorigenic mouse mammary epithelial cells and fibroblasts resu lts in an increase in anchorage-dependent and -independent growth in v itro. Reduction of CR-1 expression in human colon carcinoma or embryon al teratoma cells results in a decrease in growth in vitro. In an effo rt to better define the role of CR-1 in breast cancer, we have develop ed an underexpression vector for CR-1 to reduce CR-1 levels in a tumor igenic mouse mammary epithelial cell line (-SA). This vector specifica lly targets the expression of the murine homolog of CR-1 in murine can cer lines and utilizes a hammerhead ribozyme-like structure directed t oward the extreme 5' end of the Cripto-1 mRNA. We dramatically reduced expression of CR-1 through the expression of this RNA. This is the fi rst use of a ribozyme-like molecule to alter Cripto-1 expression. This ribozyme-shaped molecule appears to act principally through a block i n translation. A possible mechanism for this block is described, and i ts implications for modifying expression of other bioactive proteins a re discussed. (C) 1998 Academic Press.