Integrin alpha(5)beta(1), a major
fibronectin receptor, functions in a wide variety of biological phenomena. We have found that alpha 2-8-linked oligosialic
acids with 5 < or = degree of polymerization (DP) < or = 7 occur on
integrin alpha(5) subunit of the human
melanoma cell line G361. The
integrin alpha(5) subunit immunoprecipitated with anti-
integrin alpha(5) antibody reacted with the
monoclonal antibody 12E3, which recognizes oligo/
polysialic acid with DP > or = 5 but not with the polyclonal antibody H.46 recognizing oligo/
polysialic acid with DP > or = 8. The occurrence of oligosialic
acids was further demonstrated by fluorometric C(7)/C(9) analysis on the immunopurified
integrin alpha(5) subunit. Oligosialic
acids were also found in the alpha(5) subunit of several other human cells such as foreskin fibroblast and chronic
erythroleukemia K562 cells. These results suggest the ubiquitous modification with unique oligosialic
acids occurs on the alpha(5) subunit of
integrin alpha(5)beta(1). The adhesion of human
melanoma G361 cells to
fibronectin was mainly mediated by
integrin alpha(5)beta(1). Treatment of cells with
sialidase from Arthrobacter ureafaciens cleaving alpha 2-3-, alpha 2-6-, and alpha 2-8-linked
sialic acids inhibited adhesion to
fibronectin. On the other hand, N-acetylneuraminidase II, which cleaves alpha 2-3 and alpha 2-6 but not alpha 2-8 linkages, showed no inhibitory activity. After the loss of oligosialic
acids,
integrin alpha(5)beta(1) failed to bind to
fibronectin-conjugated
Sepharose, indicating that the oligosialic
acid on the alpha(5) subunit of
integrin alpha(5)beta(1) plays important roles in cell adhesion to
fibronectin.