Abstract
In order to verify whether tenascinโC (TNโC) is involved in angiogenesis as an extracellular signal molecule during tumorigenesis, cancerous cell transplantation experiments and coculture experiments were carried out, focusing on the regulation of vascular endothelial growth factor (VEGF). The A375 human melanoma cells introduced the GFP gene (A375โGFP), implanted subcutaneously into BALB/cA nude (WT) and TNโC knockout BALB/cA nude (TNKO) congenic mice. Furthermore, coculture experiments between A375โGFP and embryonic mesenchyme, which was prepared from both genotypes, were carried out to investigate the molecular mechanism in the cellโcell interactions. Both the content of TNโC and that of VEGF in the tumor and the conditioned medium were analyzed by the sandwich ELISA method. Seven days after transplantation of the A375โGFP, capillary nets became far more abundant in the tumors grown in WT mice than those in TNKO mice. Interestingly, VEGF and TNโC expressions showed antithetical expression patterns between the tumors in WT mice and those in TNKO mice. This peculiar phenomenon seems to be caused by a time lag prior to the onset of the mesenchymal regulation for the TNโC expression of A375โGFP. The coculture experiments revealed that WT mesenchyme had a much stronger effect than TNKO mesenchyme on both TNโC and VEGF expression. However, the defects of TNKO mesenchyme were restored in all cases by additional TNโC. These results clearly indicated that the expressions of both TNโC and VEGF depend on the surrounding mesenchyme, and that the function of mesenchyme is regulated by its own mesenchymal TNโC. In conclusion, the present data suggest that the matrix microenvironment organized by the host mesenchyme is very important for angiogenesis in tumor development. ยฉ 2003 WileyโLiss, Inc.