Of the four latent
transforming growth factor (
TGF)-beta-
binding proteins (LTBPs), LTBP-2 is different in the respect that it does not bind small latent forms of
TGF-beta. LTBP-2 is therefore likely to have other roles in the extracellular matrix. LTBP-2 contains an RGD putative
integrin recognition site, suggesting a role in cell adhesion. We carried out a study on cell attachment to LTBP-2. Purified recombinant LTBP-2 was used as substratum in cell adhesion and migration studies. We found that, unlike most adherent cell lines, all of the
melanoma cell lines tested adhered to LTBP-2 very efficiently and in a concentration-dependent manner. Bowes
melanoma cells bound most efficiently to LTBP-2 and were used for further characterization. Cell adhesion assays with recombinant LTBP-2 fragments indicated that the adhesive site is located in an N-terminal region of LTBP-2. The attachment of
melanoma cells to LTBP-2 was prevented with
monoclonal antibody against
beta1 integrin in a concentration-dependent manner, suggesting an important role for
beta1 integrin in the process.
Antibodies against
integrin subunits alpha3 and alpha6 decreased
melanoma cell adhesion as well. The beta1 and alpha3
integrins were localized on the cell surface, especially in lamellipodia, as observed by immunofluorescence. In addition to
integrin antagonists, heparin also markedly decreased
melanoma cell adhesion. LTBP-2 also supported Bowes cell migration in modified Boyden chamber assays in a manner similar to the migration on
fibronectin. Current data indicate that LTBP-2 can play a role in
melanoma cell adhesion.