THE TISSUE INHIBITOR OF METALLOPROTEINASES-3 GENE IN BREAST-CARCINOMA- IDENTIFICATION OF MULTIPLE POLYADENYLATION SITES AND A STROMAL PATTERN OF EXPRESSION

Background: Tissue inhibitor of metalloproteinases-3 (TIMP3) is the th ird member of the TIMP family of proteins, believed to play a signific ant role in controlling extracellular matrix remodeling. Materials and Methods: Differential screening of a human breast carcinoma cDNA libr ary using substracted and PCR-amplified cDNA probes identified a 4.6-k b TIMP3 cDNA, which was used for further cDNA library screenings, Nort hern blot hybridizations, and the synthesis of riboprobes for in situ RNA hybridization analyses. Results: The 4.6-kb full-length TIMP3 cDNA contains 3.7 kb of 3'-untranslated sequence. Additional TIMP3 cDNAs s ubsequently identified were colinear with the original sequence, but r evealed use of four different polyadenylation signals within the 3'-un translated region, which accounted for the 4.6-, 2.7-, 2.5-, and 2.1-k b TIMP3 transcripts noted in this and in previous studies. In situ RNA hybridizations demonstrated that in breast carcinoma the TIMP3 gene w as predominantly expressed by fibroblastic cells within the tumor stro ma adjacent to cancer cells. TIMP3 transcripts were also strongly dete cted in fibroblastic decidual cells of pregnant endometrium. Conclusio ns: Modulating the length of the 3'-untranslated region may represent a mechanism by which TIMP3 gene expression is controlled in tissues. T he strong expression of the TIMP3 gene by fibroblastic cells in breast carcinoma supports the importance of tumor stroma as a source of fact ors influencing human carcinoma growth and progression.