Proteolytic exposure of unique matrix immobilized cryptic epitopes and subsequent cellular interactions with these regulatory sites play crucial roles in regulating tumorigenesis. Recent studies demonstrated that the HUIV26 cryptic epitope is specifically exposed within the extracellular matrix of tumors and angiogenic blood vessels (Xu et al. 2001). Moreover, a function blocking monoclonal antibody specifically directed to the HUIV26 cryptic site inhibits angiogenesis, tumor growth and metastasis in vivo (Roth et al. 2006, Hangai et al. 2002, Xu et al. 2001).

Cellular interactions with the HUIV26 cryptic collagen epitope appear to be mediated by αvβ3 (Xu et al. 2001). To gain a more in-depth understanding of the molecular mechanisms by which αvβ3-dependent cellular interactions with the HUIV26 cryptic site regulate melanoma tumor growth, a differential cDNA microarray analysis was carried out. Inhibition of cellular interactions with the HUIV26 cryptic epitope up-regulates several genes including the cyclin dependent kinase inhibitor p21^cip1 as well as the endogenous angiogenesis inhibitor thrombospondin-1. Moreover, inhibiting cellular interactions with the HUIV26 cryptic site also upregulates insulin-like growth factor binding protein-4 (IGFBP-4) expression. Recombinant human IGFBP-4 potently inhibited (>70%) bFGF-induced angiogenesis and melanoma tumor growth in vivo. These finding suggest that IGFBP-4 may represent a novel angiogenesis inhibitor. The regulation of IGBFP-4 expression appears to be partly dependent upon αvβ3 expression as well as in part upon the PI3K/Akt pathway.

Inhibiting cellular interactions with the HUIV26 epitope reduced melanoma cell adhesion, migration and invasion, suggesting that this epitope is at least partially responsible for regulating melanoma cell adhesion, motility and invasion in vitro. To characterize the amino acid sequence comprising the HUIV26 epitope several methods were employed including a phage display library, N-terminal microsequencing and competition ELISAs. The "VGMK" motif present in the α2 chain of collagen IV appears to at least partially comprise the HUIV26 epitope although further experimentation is needed. In conclusion, inhibiting cellular interactions with the HUIV26 epitope inhibits tumor growth in part by the upregulation of genes important in tumor growth/angiogenesis. One of these genes, IGFBP-4, appears to function as a novel anti-angiogenic factor whose expression may be important in the regulation of tumorigenesis.