The expression of metalloproteinases, such as type IV collagenase/gelatinase, enables tumor cells to degrade type IV collagen present in the basement membrane and correlates with metastatic potential of several tumor types. We found that increased levels of rat serum type IV collagenolytic activity are associated with increased 13762NF mammary adenocarcinoma metastases in lungs and lymph nodes of syngeneic rats. To investigate serum metalloproteinases responsible for type IV collagenolysis, we performed zymography and Western blot analysis of rat sera. A Mr 92,000 progelatinase (progelatinase B, Mr 92,000 type IV procollagenase, MMP-9) was detected on zymograms of rat sera within 16 days after intramammary fat pad inoculation of highly metastatic MTLn3 cells. The activated serum Mr 92,000 progelatinase degraded sodium dodecyl sulfate-denatured type I and IV collagens but was not active on casein, albumin, hemoglobin, and immunoglobulin. Sera from rats with fat pad tumors and lung metastases formed from highly metastatic clones possessed greater than 7 times higher levels of serum Mr 92,000 progelatinase than control sera or sera from rats bearing similar size fat-pad tumors of low or nonmetastatic clones. The results were confirmed by Western blot analysis of rat sera using rabbit anti-human Mr 92,000 progelatinase antibodies. Similar results were obtained from the analysis of rat plasma samples. The serum and plasma Mr 92,000 progelatinase levels correlated with the extent of metastases in the lung and lymph nodes. The results indicate that high levels of serum and plasma Mr 92,000 progelatinase are associated with the presence of disseminated metastatic adenocarcinoma cells and suggest that this enzyme may facilitate the invasion of bloodborne tumor cells through vascular basement membranes.

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This work was supported in part by National Cancer Institute RO1-CA41524 [M. N.], R35-CA44352(OIG) (G. L. N.), National Foundation for Cancer Research (G. L. N.), the Jake Gittlen Memorial Golf Tournament (D. R. W.), and the Ministry of Education, Science and Culture, Japan (M. N., T. T).

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