Midkine and LDL-receptor-related protein 1 contribute to the anchorage-independent cell growth of cancer cells

Abstract

The growth factor midkine (MK) is highly associated with cancer progression. Knockdown of MK expression strikingly suppresses tumor growth in nude mice. Thus, MK is a candidate target for cancer treatment. LDL-receptor-related protein 1 (LRP1) is a receptor for MK. We found that among the four ligand-binding domains of LRP1, the N-terminal half of the second domain (designated as MK-TRAP) had the strongest affinity to MK. MK-TRAP bound to MK, but not to HB-GAM/pleiotrophin, basic fibroblast growth factor or platelet-derived growth factor (PDGF)-BB. Exogenous MK-TRAP inhibited the binding between MK and LRP1. G401 cells that transiently or stably overexpress MK-TRAP showed decreased cell growth in monolayer culture and reduced colony formation in soft agar, which could be rescued by exogenous MK administration. MK-TRAP collected from conditioned medium also inhibited anchorage-independent growth of G401 cells and CMT-93 cells. Anti-MK antibody also inhibited the anchorage-independent growth. CMT-93 cells stably expressing MK-TRAP formed smaller tumors in a xenograft nude mouse model than control cells. Moreover, GST-RAP, a potent inhibitor of LRP1, inhibited the anchorage-independent growth of control G401 cells but not that of MK-TRAP stable transformants. Collectively, these data demonstrate a crucial role of MK-LRP1 signaling in anchorage-independent cell growth.

Premature Ligand-Receptor Interaction during Biosynthesis Limits the Production of Growth Factor Midkine and Its Receptor LDL Receptor-related Protein 1

“…These data were also consistent with our previous finding in experiments using soluble LRP1 fragments: the N-terminal halves of the second and fourth ligand-binding domains in the LRP1 moiety show the highest affinity to MK (27). We further performed Scatchard plot analysis to reveal the affinity between MK and the N-terminal half of the second ligand-binding domain of LRP1 (formerly designated MK-TRAP; Fig.…”

“…1E, the N-terminal half of the second ligand-binding domain of LRP1 (MK-TRAP) has a high affinity for MK. MK-TRAP traps extracellular MK, blocks MK binding to cell surface LRP1, and consequently suppresses MK function (27). We next utilized this fragment to investigate the biological role of the immature ligand-receptor interaction during biosynthesis.…”

16-kDa fragment of pleiotrophin acts on endothelial and breast tumor cells and inhibits tumor development

“…In contrast to the members of the low-density lipoprotein receptorrelated protein family (10) that are considered to be exclusively receptors of MDK (11), members of the proteoglycans including the receptor protein-tyrosine phosphatase (RPTP) have been assigned as the receptors of PTN involved in the migration and adhesion of tumor and endothelial cells (12). It has been shown that PTN binds to the extracellular RPTPh/~domain 6B4 proteoglycan/ phosphacan (13).…”

Expression of midkine and vascular endothelial growth factor in gastric cancer and the association of high levels with poor prognosis and survival

“…Previous studies have shown that MK is highly and frequently expressed in a variety of cancer tissues, demonstrating that MK may be associated with tumorigenesis and tumor growth, invasion and metastasis (14)(15)(16)(17)(18). MK binds to complex membrane protein receptors, including protein tyrosine phosphatase ζ (PTPζ), low-density lipoprotein-related protein (LRP), anaplastic lymphoma kinase and syndecan (19,20). Maeda et al (21) found that chondroitin sulfate proteoglycan binds to the heparin binding site of MK.…”