MOLECULAR-CLONING OF 5 MESSENGER-RNAS DIFFERENTIALLY EXPRESSED IN PRENEOPLASTIC OR NEOPLASTIC JB6 MOUSE EPIDERMAL-CELLS - ONE IS HOMOLOGOUSTO HUMAN TISSUE INHIBITOR OF METALLOPROTEINASES-3

To better understand the molecular mechanism of multistage carcinogene sis, we have attempted to identify putative oncogenes and/or tumor sup pressor genes involved in preneoplastic-to-neoplastic progression of m ouse epidermal JB6 variants. The JB6 variants consist of P- (promotion resistant), P+ (promotion sensitive), and Tx [transformed; both apopt osis-sensitive (A(5)) and apoptosis-resistant (A(r))] cells, represent ing progression from early to late stages of carcinogenesis. By using the newly developed differential mRNA display technique, we have isola ted five clones from these JB6 variants. The isolated clones were uniq uely expressed either in P-/P+ cells or in Tx (A(s)/A(r)) cells or sho wed highly differential expression among the variants. The expression pattern shown by differential mRNA display was confirmed by Northern b lot analysis. DNA sequencing followed by computer search against Genba nk and EMBL DNA databases indicates that three clones are novel and tw o have high homology with recorded genes. One of the clones (Cl.14), w hich detects expression in preneoplastic not neoplastic JB6 cells, was used as a probe for complementary DNA library screening. The correspo nding gene, named sun for specifically unexpressed in neoplastic JB6 c ells, was isolated and sequenced. The longest open reading frame of th e sun clone predicts a peptide showing 96% amino acid sequence identit y to the recorded sequence of human tissue inhibitor of metalloprotein ases-3, one of a family of genes implicated in tumorigenesis and tumor invasion. This is the first report, to our knowledge, of the simultan eous display of mRNAs of four phenotypically distinct cell variants an d of the isolation of five clones which may be associated with specifi c stages of tumor promotion and/or progression and apoptosis.