Phosphorylation of laminin-1 by protein kinase C

Several extracellular proteins have been reported to be phosphorylated, Pre vious studies of our laboratory indicated that laminin-l can be phosphoryla ted by protein kinase A (PKA), Moreover, it has been reported that protein kinase C (PKC), although known to be intracellular, can phosphorylate extra cellular proteins in the case of cellular damage and/or platelet activation . In the present study we examined the possibility of laminin-l serving as a substrate of PKC, Amino acid analysis revealed that laminin-l is phosphor ylated by this enzyme on serine residues. Self assembly, heparin binding, a nd cell attachment on the phosphorylated molecule were then studied. Phosph orylated laminin-l showed an increased and more rapid self assembly than th e non-phosphorylated molecule. Heparin binding and cell attachment experime nts indicated enhanced heparin and cell binding capacity of the phosphoryla ted molecule in comparison to the non- phosphorylated control. These result s indicate that laminin-l carl be phosphorylated by protein kinase C. Furth ermore, phosphorylation by protein kinase C seems to alter several properti es of the molecule, though, the in vivo significance of this phenomenon rem ains to be studied.