Specific Structural Features of Heparan Sulfate Proteoglycans Potentiate Neuregulin-1 Signaling

Abstract

Neuregulins are a family of growth and differentiation factors that act through activation of cell-surface erbB receptor tyrosine kinases and have essential functions both during development and on the growth of cancer cells. One alternatively spliced neuregulin-1 form has a distinct heparin-binding immunoglobulin-like domain that enables it to adhere to heparan sulfate proteoglycans at key locations during development and substantially potentiates its activity. We examined the structural specificity needed for neuregulin-1-heparin interactions using a gel mobility shift assay together with an assay that measures the ability of specific oligosaccharides to block erbB receptor phosphorylation in L6 muscle cells. Whereas the N-sulfate group of heparin was most important, the 2-O-sulfate and 6-O-sulfate groups also contributed to neuregulin-1 binding in these two assays. Optimal binding to neuregulin-1 required eight or more heparin disaccharides; however, as few as two disaccharides were still able to bind neuregulin-1 to a lesser extent. The physiological importance of this specificity was shown both by chemical and siRNA treatment of cultured muscle cells. Pretreatment of muscle cells with chlorate that blocks all sulfation or with an siRNA that selectively blocks N-sulfation significantly reduced erbB receptor activation by neuregulin-1 but had no effect on the activity of neuregulin-1 that lacks the heparin-binding domain. These results suggest that the regulation of glycosaminoglycan sulfation is an important biological mechanism that can modulate both the localization and potentiation of neuregulin-1 signaling.

New Negative Feedback Regulators of Egfr Signaling inDrosophila

“…The NRGs share structural similarity with Vn because both types of growth factors have an Ig domain in addition to the EGF domain . The Ig domain in NRG is required for binding to heparin, and sulfate groups including 6-O-sulfate groups play a role in the interaction (Li and Loeb 2001;Pankonin et al 2005). The addition of a Drosophila EGF ligand to the collection of known ligands regulated by Sulf1 highlights the broad role HSPGs play in signaling pathways.…”

“…Some vertebrate EGF ligands are known to bind HSPGs, including some neuregulins (NRGs) and heparin-binding EGF (Pankonin et al 2005;Mahtouk et al 2006;Iwamoto et al 2010). The NRGs share structural similarity with Vn because both types of growth factors have an Ig domain in addition to the EGF domain .…”

The Tanapoxvirus 15L Protein Is a Virus-Encoded Neuregulin That Promotes Viral Replication in Human Endothelial Cells

“…Figure 2 demonstrates a partial alignment of three proteins (TPV-15L, hNRG1, and EGF) indicating the regions of the highest homology. Heparin binding variants of NRG1 are known to exist, where the domain responsible for heparin binding resides on an Ig-like domain near the N terminus of the EGF-like domain (7,9,35,36). This type of heparin binding motif is clearly absent from the amino acid sequence of TPV-15L.…”

“…Evidence for this notion was derived from the chicken embryo development model, where agrin (an HSPG) and NRG1 form localized complexes that synergistically concentrate to the basal lamina of the NMJ, potentiating a signal that upregulates expression of acetylcholine receptor genes (7,8). Later studies have also suggested that NRGs target specific HSPGs, preferentially choosing N-sulfate over 2-O-and 6-O-sulfate groups (9).…”

<a name="home"></a>Specific structural features of syndecans and heparan sulfate chains are needed for cell signaling

“…Inhibition of sulfation through the use of chlorate or selective blockade of N-sulfation with a siRNA directed against the enzyme that promotes Nsulfation resulted in decreased NRG-1-induced erbB receptor activation. This specificity provides a means by which tissues can localize and potentiate NRG-1 signaling through modifications in glycosaminoglycan composition (52).…”