Heparan Sulfate Proteoglycans Retain Noggin at the Cell Surface

Abstract

Bone morphogenetic proteins (BMPs) are expressed broadly and regulate a diverse array of developmental events in vivo. Essential to many of these functions is the establishment of activity gradients of BMP, which provide positional information that influences cell fates. Secreted polypeptides, such as Noggin, bind BMPs and inhibit their function by preventing interaction with receptors on the cell surface. These BMP antagonists are assumed to be diffusible and therefore potentially important in the establishment of BMP activity gradients in vivo. Nothing is known, however, about the potential interactions between Noggin and components of the cell surface or extracellular matrix that might limit its diffusion. We have found that Noggin binds strongly to heparin in vitro, and to heparan sulfate proteoglycans on the surface of cultured cells. Noggin is detected only on the surface of cells that express heparan sulfate, can be specifically displaced from cells by heparin, and can be directly cross-linked to a cell surface proteoglycan in culture. Heparan sulfate-bound Noggin remains functional and can bind BMP4 at the plasma membrane. A Noggin mutant with a deletion in a putative heparin binding domain has reduced binding to heparin and does not bind to the cell surface but has preserved BMP binding and antagonist functions. Our results imply that interactions between Noggin and heparan sulfate proteoglycans in vivo regulate diffusion and therefore the formation of gradients of BMP activity.

Bone morphogenetic protein-5, -6 and -7 inhibit growth and induce apoptosis in human myeloma cells

“…Noggin is known to bind several BMPs in the extracellular space, among them BMP-4 and -7, thereby inhibiting ligand-receptor interactions. By binding to heparan sulfate proteoglycans, noggin is able to establish a BMP activity gradient reaching across several cell diameters (Paine-Saunders et al, 2002), as heparan sulfate-bound noggin retains its biological activity and can bind BMPs. This is hypothesized to be a major post-translational mechanism to govern BMP activity, at least in the embryo.…”

Bone morphogenetic protein 2 stimulation of tumor growth involves the activation of Smad-1/5

“…This may be because BMP-2 delivered from Affi-Blue agarose beads can readily diffuse into surrounding tissue, delivering biologically active BMP-2 to the tumor. BMP-2 secreted from the cell may not diffuse as far in the subcutaneous tissue, allowing inhibition by natural antagonists (Paine-Saunders et al, 2002). Human tumors rarely metastasize to the skin, suggesting the subcutaneous position is not the best environment for human tumors.…”

“…During development BMP-2/4 form a functional gradient, which can elicit different biological responses (Nellen et al, 1996;Myers et al, 2002;Sutherland et al, 2003). The activity gradient of BMP-2/4 is determined by its concentration, as well as intracellular (Yoshida et al, 2000) and extracellular inhibitors (Paine-Saunders et al, 2002). BMP-2 is secreted from the cell and then becomes attached to the extracellular matrix (Paine-Saunders et al, 2002).…”

“…The activity gradient of BMP-2/4 is determined by its concentration, as well as intracellular (Yoshida et al, 2000) and extracellular inhibitors (Paine-Saunders et al, 2002). BMP-2 is secreted from the cell and then becomes attached to the extracellular matrix (Paine-Saunders et al, 2002). This interaction with the extracellular matrix is essential for BMP-2-mediated responses (Suzawa et al, 1999).…”

Mutational Analysis of Norrin-Frizzled4 Recognition

“…cystine knot BMP2 antagonist Noggin (45)(46)(47)(48). For Wingless and the Drosophila TGF-␤ family member Dpp (Decapentaplegic), heparan sulfate proteoglycans have been shown genetically to control the diffusion of the ligands in vivo (49 -53).…”