Invasion of Melanoma in Double Knockout Mice Lacking Tenascin‐X and Tenascin‐C

The roles of extracellular matrix glycoproteins belonging to the tenascin family in the regulation of tumor cell proliferation, invasion, and metastasis are not known. To address this issue, we generated tenascin‐X (TNX) and tenascin‐C (TNC) double knockout mice and compared findings in these mice with those in single knockout (TNX+/+TNC‐/‐ and TNX‐/‐TNC+/+) mice. We investigated the proliferation and invasion of B16‐BL6 melanoma cells after these cells had been injected into the footpads of mice in each group. The primary tumor size and invasion to the ankle adjacent to the primary tumor site were examined at 35 days after injection of the melanoma cells. The primary tumor size in TNX‐/‐TNC+/+ mice was significantly larger than that in wild‐type mice, but those of TNX+/+TNC‐/‐ and double knockout mice were comparable to that in the wild‐type mice. On the other hand, invasion to the ankle was obviously promoted in TNX‐ I ‐ TNC+/+ and double knockout mice compared with that in the wild‐type mice, but invasion to the ankle in TNX+/+TNC‐/‐ mice was only slightly promoted. Gelatin zymography confirmed increased matrix metalloproteinase (MMP)‐9 activity in the dorsal skin of TNX‐/‐TNC+/+, TNX+/+TNC‐/‐ and double knockout mice. However, the amounts of MMP‐9 mRNA in the dorsal skins of all mice were almost the same, indicating that the increased activity of MMP‐9 in the single and double knockout mice is regulated at the MMP‐9 processing level. These results indicate that MMP‐9 is activated in all TN‐deficient mice, but that TNX exerts a greater effect on tumor invasion than does TNC.