Cytoplasmic Domain Interactions of Syndecan-1 and Syndecan-4 with α6β4 Integrin Mediate Human Epidermal Growth Factor Receptor (HER1 and HER2)-dependent Motility and Survival

Abstract

Background: The ␣6␤4 integrin assembles via an unknown mechanism with receptor tyrosine kinases. Results: HER2-dependent activation of ␣6␤4 depends on capture of the ␤4 cytoplasmic domain by syndecan-1, whereas HER1 (EGFR) relies on syndecan-4. Conclusion: Cell invasion and survival mediated by the ␣6␤4 integrin depend on its assembly with kinase-specific syndecans. Significance: These novel interactions may provide targets for new therapeutics to combat carcinogenesis.

Syndecan-1 and Syndecan-4 Capture Epidermal Growth Factor Receptor Family Members and the α3β1 Integrin Via Binding Sites in Their Ectodomains

“…MCF10A human breast epithelial cells were cultured in DMEM F12 50/50, 15 mM Hepes, 5% horse serum, 10 g/ml insulin, 0.5 g/ml hydrocortisone, and 0.02 g/ml EGF (2).…”

“…Cells were cultured an additional 15 h in DMEM (serum-free) in the presence or absence of GSTfusion proteins or peptide inhibitors and containing either LPA (3 M), mAb 3E1 (10 g/ml), and goat anti-mouse IgG (30 g/ml) to cluster ␣6␤4 integrin and mimic matrix-stimulated chemokinesis, or EGF (10 ng/ml) to stimulate EGF chemokinesis as described previously (2). Note that short sequences of S4ED appear to become masked by GST in the fusion proteins.…”

“…We have shown recently that another feature of the integrin cytoplasmic signaling domain is its ability to engage syndecans, a family of cell surface heparan-sulfate proteoglycans that serve as matrix receptors (2,3). This discovery implicated syndecans as central organizers of the ␣6␤4 integrin/growth factor receptor complexes.…”

“…All four syndecan family members have been shown by yeast-two hybrid analysis to engage the cytoplasmic domain of the ␤4 integrin (3). Recent work (2) has shown that syndecan-1 (Sdc1) engages arginine 1733 (Arg-1733) near the distal tip of the ␤4 integrin cytoplasmic domain. When the syndecan and integrin are engaged, HER2 is captured by the Sdc1-coupled complex and undergoes autophosphorylation when the complex is clustered to sites of matrix engagement.…”

“…Syndecan-4 (Sdc4) is implicated in a similar mechanism (2). It also binds the distal tip of the ␤4 integrin cytoplasmic domain, requiring glutamate 1729 (Glu-1729) in the integrin.…”