phalloidine and Fibrosarcoma

Laminin 5/laminin 332 (LN332) is an adhesion substrate for epithelial cells. After secretion of LN332, a regulated cleavage occurs at the carboxy-terminus of its alpha3 subunit, which releases a tandem of two globular modules named LG4/5. We show that the presence of the LG4/5 domain in precursor LN332 decreases its integrin-mediated cell adhesion properties in comparison with mature LN332. Whereas cell adhesion to the recombinant LG4/5 fragment relies solely on the heparan sulfate proteoglycan (HSPG) receptor syndecan-1, we reveal that both syndecan-1 and the alpha3beta1 integrin bind to precursor LN332. We further demonstrate that syndecan-1 mediated cell adhesion to the LG4/5 fragment and pre-LN332 allows the formation of fascin-containing protrusions, depending on the GTPases Rac and Cdc42 activation. Reducing syndecan-1 expression in normal keratinocytes prevents cell protrusions on pre-LN332 with subsequent failure of the peripheral localization of the alpha3beta1 integrin. We finally show that cell migration on pre-LN332 requires syndecan-1. Therefore, the LG4/5 domain in precursor LN332 appears to trigger intracellular signaling events, which participate in keratinocyte motility.

Topics: cdc42 GTP-Binding Protein; Cell Adhesion; Cell Adhesion Molecules; Cell Movement; Cells, Cultured; Enzyme Activation; Fibrosarcoma; Fluorescein-5-isothiocyanate; Fluorescent Dyes; Humans; Integrin alpha3beta1; Kalinin; Keratinocytes; Male; Melanoma; Microscopy, Video; Phalloidine; Plasmids; Protein Structure, Tertiary; rac GTP-Binding Proteins; Recombinant Proteins; Rhodamines; Skin; Syndecan-1; Transfection