Tissue inhibitor of metalloproteinases-1 (TIMP-1) RNA is expressed at elevated levels in malignant non-Hodgkin's lymphomas

Secreted metalloproteinases (MPs) and their specific inhibitors (TIMPs, tissue inhibitors of MPs) are important mediators of extracellular matrix metabolism. Previous studies have linked either excessive MP release or reduced TIMP-1 production to the invasive and metastatic phenotypes of cancer cells. In the present study we investigated the relationship between the expression of TIMP-1 and the clinical behavior of 28 non-Hodgkin's lymphomas. Northern blot analysis showed that levels of TIMP-1 mRNAs correlated directly with clinical aggressiveness: tumors in the high-grade category contained the highest levels of TIMP-1 transcripts approaching those found in maximally growth factor-stimulated fibroblasts in vitro. In situ hybridization localized the TIMP-1 expression to stromal cells of endothelial and fibroblastic origin. In contrast, transcripts hybridizing with metalloproteinase gene probes (interstitial collagenase and 72-Kd type IV collagenase) were expressed at very low levels in malignant lymphomas and their expression was not coordinately regulated with that of TIMP-1. The majority of tumors expressed either interstitial collagenase or 72-Kd type IV collagenase, and only a small number expressed both. Interstitial collagenase transcripts were only detected in high-grade tumors. The relative levels of TIMP-1 expression did not correlate with the degree of fibrosis of the tumors. Our data suggest the importance of tumor-stromal interactions in non-Hodgkin's lymphomas, and moreover, our results indicate a possible relationship between high-level, localized expression of TIMP-1 and the malignant phenotype of high-grade advanced-stage lymphomas.