A Receptor-like Protein-tyrosine Phosphatase PTPζ/RPTPβ Binds a Heparin-binding Growth Factor Midkine

Abstract

Midkine is a 13-kDa heparin-binding growth factor with 45% sequence identity to pleiotrophin. Pleiotrophin has been demonstrated to bind to protein-tyrosine phosphatase (PTP ) with high affinity. In this study, we examined the binding of midkine to PTP by solidphase binding assay. Midkine and pleiotrophin binding to PTP were equally inhibited by soluble pleiotrophin and also by some specific glycosaminoglycans. For both bindings, Scatchard analysis revealed low (3.0 nM) and high (0.58 nM) affinity binding sites. These results suggested that PTP is a common receptor for midkine and pleiotrophin. Midkine is structurally divided into the Nand C-terminal halves, and the latter exhibited full activity for PTP binding and neuronal migration induction. The C-terminal half contains two heparin-binding sites consisting of clusters of basic amino acids, Clusters I and II. A mutation at Arg 78 in Cluster I resulted in loss of the high affinity binding and reduced neuronal migration-inducing activity, while mutations at Lys 83 and Lys 84 in Cluster II showed almost no effect on either activity. Chondroitinase ABC-treated PTP exhibited similar low affinity binding both to the native midkine and midkine mutants at Arg 78 . These results suggested that Arg 78 in midkine plays an essential role in high affinity binding to PTP by interacting with the chondroitin sulfate portion of this receptor.PTP /RPTP␤ 1 is a receptor-like protein-tyrosine phosphatase, which is abundantly expressed in the central nervous system as a chondroitin sulfate proteoglycan (1-4). PTP is composed of an N-terminal carbonic anhydrase-like domain, a fibronectin type III domain, a serine, glycine-rich domain that is thought to be chondroitin sulfate attachment region, a transmembrane segment, and two tyrosine phosphatase domains (1, 2). There are three splice variants of this molecule: (a) the full-length PTP (PTP -A); (b) the short form of PTP , in which most of the serine, glycine-rich region is deleted (PTP -B); and (c) the secreted form (PTP -S), which corresponds to the extracellular region of PTP -A and is also known as 6B4 proteoglycan/phosphacan (3, 5). All these splice variants are expressed as chondroitin sulfate proteoglycans in the brain (6), suggesting that chondroitin sulfate plays an essential role in receptor function.Several proteins such as contactin, tenascin, L1, NCAM, and TAG1 have been reported to bind PTP (7-9). Contactin is thought to be a neuronal receptor of PTP expressed on glial cells (7). Recently, we found that PTP binds with pleiotrophin/ heparin-binding growth-associated molecule (10), in that a chondroitin sulfate portion of PTP constitutes a part of the pleiotrophin binding site and regulates the affinity of PTPpleiotrophin binding (10). We further demonstrated that pleiotrophin-induced neurite outgrowth and neuronal migration were suppressed by chondroitin sulfate, polyclonal antibodies against the extracellular domain of PTP , and sodium vanadate, a protein-tyrosine phosphatase inhibitor. These findings suggested that P...

Correlation of elevated level of blood midkine with poor prognostic factors of human neuroblastomas

“…Statistical analysis is summarised in Table 2. Table 3. kinase, and LDL receptor-related protein (LRP) were recently identified as MK receptors (Maeda et al, 1999;Muramatsu et al, 2000;Stoica et al, 2002). Although it has not been elucidated yet whether or not these receptors form complexes for MK signalling, each protein serves as a receptor transducing intracellular signals for midkine.…”

“…Its expression is induced as early as at the precancerous stages of human colorectal and prostate carcinomas (Konishi et al, 1999;Ye et al, 1999), increases with the stages of human carcinomas, and is significantly linked to the prognosis (O'Brien et al, 1996;Mishima et al, 1997). MK transforms NIH3T3 cells , enhances fibrinolysis (Kojima et al, 1995), and promotes cell growth (Muramatsu and Muramatsu, 1991;Muramatsu et al, 1993;Takei et al, 2001), cell survival (Qi et al, 2000), cell migration (Takada et al, 1997;Maeda et al, 1999;Horiba et al, 2000;Qi et al, 2001), and angiogenesis (Choudhuri et al, 1997). MK antisense oligodeoxyribonucleotide suppresses tumour progression in nude mice (Takei et al, 2001(Takei et al, , 2002.…”

Appican, the Proteoglycan Form of the Amyloid Precursor Protein, Contains Chondroitin Sulfate E in the Repeating Disaccharide Region and 4-O-Sulfated Galactose in the Linkage Region

“…These oversulfated disaccharides are distinct from the more common monosulfated A (GlcUA␤1-3GalNAc(4S)) and C (GlcUA␤1-3GalNAc(6S)) units, which may either show no neurotrophic activity or may act as inhibitors of neurite outgrowth. Furthermore, oversulfated CS variants specifically interact with and regulate the neurotrophic activity of several growth factors including pleiotrophin (35) and midkine (35,36). CS chains containing either D or E disaccharide units are rarely detected in peripheral mammalian tissues but are detectable in brain, albeit at low levels (36 -38).…”

Functional Analysis of the Chondroitin 6-Sulfotransferase Gene in Relation to Lymphocyte Subpopulations, Brain Development, and Oversulfated Chondroitin Sulfates

“…Chondroitin sulfate chains also play critical roles in lymphocyte-endothelial cell interactions (11) and enhancing stimulation of T cell responses (12). Furthermore, chondroitin sulfate proteoglycans bearing chondroitin sulfate D or E bind to a growth factor, midkine (13)(14)(15)(16), and chemokines (17), and have been suggested to participate in signaling or modulation of the activities of these factors. However, the in vivo function of chondroitin sulfate has not been clarified directly.…”