Interaction of Syndecan and α6β4 Integrin Cytoplasmic Domains

Abstract

The ␣6␤4 integrin is a laminin 332 (LN332) receptor central to the formation of hemidesmosomes in epithelial layers. However, the integrin becomes phosphorylated by keratinocytes responding to epidermal growth factor in skin wounds or by squamous cell carcinomas that overexpress/hyperactivate the tyrosine kinase ErbB2, epidermal growth factor receptor, or c-Met. We show here that the ␤4-dependent signaling in A431 human squamous carcinoma cells is dependent on the syndecan family of matrix receptors. Yeast two-hybrid analysis identifies an interaction within the distal third (amino acids 1473-1752) of the ␤4 cytoplasmic domain and the conserved C2 region of the syndecan cytoplasmic domain. Via its C2 region, Sdc1 forms a complex with the ␣6␤4 integrin along with the receptor tyrosine kinase ErbB2 and the cytoplasmic kinase Fyn in A431 cells. Engagement of LN332 or clustering of the ␣6␤4 integrin with integrin-specific antibodies causes phosphorylation of ErbB2, Fyn, and the ␤4 subunit as well as activation of phosphatidylinositol 3-kinase and Akt and their assimilation into this complex. This leads to phosphatidylinositol 3-kinase-dependent cell spreading and Akt-dependent protection from apoptosis. This is disrupted by RNA interference silencing of Sdc1 but can be rescued by mouse Sdc1 or Sdc4 but not by syndecan mutants lacking their C-terminal C2 region. This disruption does not prevent the phosphorylation of ErbB2 or Fyn but blocks the Fynmediated phosphorylation of the ␤4 tail. We propose that syndecans engage the distal region of the ␤4 cytoplasmic domain and bring it to the plasma membrane, where it can be acted upon by Src family kinases.The ␣6␤4 integrin is a laminin 332 (LN332, 2 also known as LN5 or kalinin) receptor that forms hemidesmosomes in epithelial cells (reviewed in Refs. 1-4). It engages LN332 linked to collagen VII anchoring fibrils in the extracellular matrix (5) and simultaneously engages cytoplasmic proteins (e.g. plectin and BP230) and the transmembrane protein BP180 via the long (ϳ1,000-amino acid) cytoplasmic domain of the ␤4 integrin subunit. These cytoplasmic interactions involve two pairs of fibronectin type III (FNIII) repeats in the ␤4 tail and the connecting segment joining these pairs. This couples the integrin to the intermediate filament cytoskeleton and provides a stable anchorage that resists frictional forces on the epithelium.In contrast to this stabilizing role of the ␣6␤4 integrin, phosphorylation of the ␤4 cytoplasmic domain causes hemidesmosome disassembly and activation of ␣6␤4 signaling. Skin wounding causes relocalization of the integrin to lamellipodia of invading keratinocytes in response to EGF or macrophagestimulating factor (6). In tumor cells, overexpression of the integrin or overexpression and/or hyperactivation of the receptor tyrosine kinase c-Met (hepatocyte growth factor receptor), ErbB1 (EGFR), or ErbB2 causes phosphorylation of the integrin and promotes the proliferation, survival, and invasion of the tumor cells (7-9). The sites targeted by these kin...

Heparanase-induced shedding of syndecan-1/CD138 in myeloma and endothelial cells activates VEGFR2 and an invasive phenotype: prevention by novel synstatins

“…Based on our prior work, 24, 25, 26, 42 we hypothesized that it organizes integrins and receptor tyrosine kinases into a signaling complex. To test this, we treated HPSE high cells with kinase inhibitors in an attempt to block the mechanism, discovering that the VEGFR2 inhibitors vandetanib or VEGFR2 kinase inhibitor II (data not shown) inhibit HPSE high cell spreading (Figure 4a).…”

Use of an in vivo animal model for assessing the role of integrin α6β4 and Syndecan-1 in early steps in papillomavirus infection

“…It has been proposed that a non-HSPG receptor is essential for HPV infection (Kines et al, 2009; Surviladze et al, 2012). That there are interactions between integrin α 6 β 4 and syndecan-1 and others HSPGs (Wang et al, 2010) raises the possibility that integrin α 6 β 4 may act independently or in conjunction with other cellular proteins in facilitating HPV infection in vivo . We applied our mouse model to access the role of integrin α 6 β 4 in HPV infection in vivo by testing whether the efficiency of reporter gene transduction by HPV PVs is diminished significantly in mice deficient for integrin α 6 β 4 .…”

“…The loss of the activity of cyclophilins (CyP), especially Cyclophilin B (CyPB) which colocalizes with syndecan-1, blocks HPV16/18 infection in cells (Bienkowska-Haba et al, 2009). An interesting finding indicates that integrin α 6 β 4 interacts and colocalizes with syndecan-1 (Wang et al, 2010). These findings complicate the interpretation of a role of integrin α 6 β 4 and/or HSPGs in HPV infection process.…”

Inhibition of HER2-integrin signaling by Cucurbitacin B leads to in vitro and in vivo breast tumor growth suppression

“…al. demonstrated augmentation of ITGA6B4 by HER2 [28, 30]. Furthermore, a study supports the physical interaction of HER2 with ITGA6, ITGB1 and ITGB4, which can be augmented by TGFβ [16].…”