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 third member of the TIMP family of proteins, believed to play a significant role in controlling extracellular matrix remodeling. Materials and Methods: Differential screening of a human breast carcinoma cDNA library using substracted and PCR-amplified cDNA probes identified a 4.6-kb TIMP3 cDNA, which was used for further cDNA library screenings, Northern 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 subsequently identified were colinear with the original sequence, but revealed use of four different polyadenylation signals within the 3'-untranslated region, which accounted for the 4.6-, 2.7-, 2.5-, and 2.1-kb TIMP3 transcripts noted in this and in previous studies. In situ RNA hybridizations demonstrated that in breast carcinoma the TIMP3 gene was predominantly expressed by fibroblastic cells within the tumor stroma adjacent to cancer cells. TIMP3 transcripts were also strongly detected in fibroblastic decidual cells of pregnant endometrium. Conclusions: Modulating the length of the 3'-untranslated region may represent a mechanism by which TIMP3 gene expression is controlled in tissues. The strong expression of the TIMP3 gene by fibroblastic cells in breast carcinoma supports the importance of tumor stroma as a source of factors influencing human carcinoma growth and progression.