Transgenic TIMP-1 inhibits simian virus 40 T antigen-induced hepatocarcinogenesis by impairment of hepatocellular proliferation and tumor angiogenesis

Tissue inhibitors of metalloproteinases (TIMP) block proteolytic degradatio n of extracellular matrix and consequently impede tumor invasion and metast asis. In addition, we have previously reported that hepatic TIMP-1 modulati on alters the susceptibility of the liver to oncogene (simian virus 40 T-an tigen; TAg)-induced tumorigenesis in a double-transgenic mouse model. To id entify the cellular processes by which TIMP-1 inhibits hepatocarcinogenesis , we examined the effects of TIMP-1 on four specific events that are import ant during tumorigenesis: hepatocellular proliferation, apoptosis, the stro mal characteristics of the liver, and tumor vascularization. Transgenic mic e with elevated or reduced hepatic TIMP-1 expression were bred independentl y with TAg transgenics. Liver tissue from littermates were analyzed by in s itu hybridization with TIMP-1 cDNA probes; gelatin enzymography; immunohist ochemistry for proliferating cell nuclear antigen, von Willebrand factor, a nd collagen type IV; reticulin histochemistry; and collagens type III and I V, laminin, fibronectin, and CD31 immunoblotting. We demonstrate that TIMP- 1 overexpression significantly inhibited the proliferation of hepatocytes i n TAg mice but did not affect their apoptotic index, the hepatic parenchyma l architecture, or extracellular matrix composition, including collagens ty pe III and IV, laminin, and fibronectin. Moreover, the hepatocellular carci nomas formed in TIMP-1-overexpressing mice had significantly reduced tumor vascularization; conversely, tumor vascularization was significantly increa sed in TIMP-1-reduced livers. These data indicate that TIMP-1 inhibits TAg- induced hepatocarcinogenesis by altering hepatocellular proliferation and t umor vascularization, without any effect on hepatocyte apoptosis and stroma l composition. To our knowledge, this is the first in vivo demonstration th at genetic modulation of TIMP-1 inhibits cellular proliferation and angioge nesis during hepatocarcinogenesis. This potentially extends the use of matr ix metalloproteinase inhibitors in cancer beyond control of invasion and me tastasis.