Midkine binds to 37-kDa laminin binding protein precursor, leading to nuclear transport of the complex

Midkine (AM) is a heparin binding multifunctional protein that promotes cel l survival and cell migration. MK was found to bind to 37-kDa laminin bindi ng protein precursor (LBP), a precursor of 67-kDa laminin receptor, with K- d of 1.1 nM between MR and LBP-glutathione-S-transferase fusion protein. Th e binding was inhibited by laminin, anti-LBP, amyloid beta -peptide, and he parin; the latter two are known to bind to MR. In CMT-93 mouse rectal carci noma cells, LBP was mostly located in the cytoplasm as revealed by Immunost aining with anti-LBP antibody. That a portion of LBP or 67-kDa laminin rece ptor was located at the surface of these cells was verified by inhibition o f cell attachment to laminin-coated dishes by anti-LBP antibody. When MK wa s added to culture medium of these cells, a part of LBP migrated to the nuc leus. The movement occurred concomitantly with nuclear transport of biotin- labeled MR. These findings suggested that the binding of AM to LBP caused n uclear translocation. of the molecular complex. (C) 2001 Academic Press.