In situ detection of matrix metalloproteinase-2 (MMP2) and the metalloproteinase inhibitor TIMP2 transcripts in human primary hepatocellular carcinoma and in liver metastasis.

BACKGROUND/AIMS: Metalloproteinase (MMP)-2 and the metalloproteinase inhibitor TIMP2, play a critical role in tumor invasion. We have investigated the cellular sources of MMP2 and TIMP2 in primary and secondary human liver cancers.

METHODS

Using in situ hybridization and zymography, we analyzed surgical biopsies from matching pairs of tumoral and non-tumoral liver from six hepatocellular carcinomas and seven liver metastases and from four liver donors. The cellular sources of MMP2 and TIMP2 were further characterized using an anti-alpha-smooth muscle actin antibody on contiguous sections.

RESULTS

In hepatocellular carcinoma and liver metastases, in situ hybridization showed that MMP2 and TIMP2 mRNA were expressed by anti-alpha-smooth muscle actin-positive cells at the invasive front. Slender fibroblasts embedded in a denser matrix were MMP2(+)/TIMP2(+)/anti-alpha-smooth muscle actin(+). Intratumor microvessels showed a strong labeling for MMP2 but weak for TIMP2 mRNA. In contrast, the endothelial lining of the central veins was MMP2(+)/TIMP2(+) in non-tumoral areas with signs of blood-flow obstruction. In control livers, MMP2 and TIMP2 mRNA distribution was restricted to fibroblasts and endothelial cells within portal tracts and scattered sinusoidal cells. Direct zymography of samples comprising the invasive front revealed variable amounts of both proMMP2 and its active form in hepatocellular carcinoma, whereas strong bands corresponding to both active and latent forms of MMP2 were detected in liver metastases.

CONCLUSIONS

The striking density of MMP2(+)/TIMP2(+)/anti-alphaSM(+) stellate-shaped cells in the perisinusoidal space adjacent to liver tumors suggests that hepatic stellate cells, upon differentiation to myofibroblasts, may contribute to the dissemination of liver metastases through the sinusoidal network.