Mouse
entactin derived from the extracellular matrix of M1536-B3 cells and from insect cells infected with a recombinant virus containing
entactin sequences were shown to promote the attachment of mouse mammary
tumor, human
melanoma, and other cells. The cell attachment was inhibited by
antibodies against mouse
entactin but not by anti-
fibronectin or anti-
laminin antibodies. On a weight basis
entactin was as effective as
laminin in promoting the attachment of mouse mammary
tumor cells. The attachment of cells to
entactin was in part mediated by the
integrin recognition
RGD peptide sequence. This was demonstrated by the cell attachment properties of
peptides derived from
entactin which contained this sequence. Furthermore, the
peptide RGDS could inhibit the attachment of mouse mammary
tumor cells to
entactin to approximately 60% of control. It is suggested that additional cell recognition sequences may be present in
entactin. The direct binding of
calcium ions to
entactin was observed. It is probable that the binding sites reside in
peptide sequences located toward the NH2 terminus region of
entactin. This conclusion was supported by the demonstration that synthetic
peptides, containing potential
calcium binding sequences derived from
entactin, bound
calcium. In addition, a recombinant
peptide containing the amino-terminal 330
amino acids of
entactin also bound
calcium ions. The significance of these properties of
entactin is discussed.