Abstract
The culture of human submandibular gland (HSG) cells on laminin-1 induces acinar differentiation. We identified a site on laminin involved in acinar differentiation using synthetic peptides derived from the C-terminal G-domain of the laminin alpha1 and alpha2 chains. The alpha1 chain peptide AG73 (RKRLQVQLSIRT) decreases the size of acini formed on laminin-1. Cells cultured with either AG73 or the homologous alpha2 chain peptide MG73 (KNRLTIELEVRT) form structures that appear acinar-like, but the cell nuclei are not polarized to the basal surface and no lumen formation occurs, indicating that additional sites on laminin are required for complete differentiation. The G-domain of laminin-1 contains both integrin and heparin binding sites, and anti-beta1-integrin antibodies disrupt acinar formation. Cell adhesion to the peptides and to E3, an elastase digest fragment of laminin-1 containing AG73, is specific, since other laminin peptides or EDTA do not compete the binding. Heparin and heparan sulfate decrease cell adhesion to AG73 and MG73 but anti-beta1-integrin antibodies have no effect. Treating the cell surface with heparitinase inhibits adhesion to both AG73 and MG73. We isolated cell surface ligands using both peptide affinity chromatography and laminin-1 affinity chromatography. Treating the material bound to the affinity columns with heparitinase and chondroitinase enriches for a core protein identified as syndecan-1 by Western blot analysis, thus identifying a syndecan-1 binding site in the globular domain of laminin-1 and laminin-2. In summary, multiple interactions between laminin and HSG cells contribute to acinar differentiation, involving both beta1-integrins and syndecan-1.
Highlights
The culture of human submandibular gland (HSG) cells on laminin-1 induces acinar differentiation
We have shown that laminin-1 promotes acinar differentiation of the human submandibular gland (HSG)1 cell line, and other components such as transforming growth factor-3 contribute to acinar formation [23]
Our results suggest multiple interactions between laminin-1 and HSG cells occur during acinar formation involving both 1-integrins and syndecan-1
Summary
The culture of human submandibular gland (HSG) cells on laminin-1 induces acinar differentiation. A family of heterotrimeric glycoproteins found in basement membranes, promote cell adhesion, migration, differentiation, proliferation, neurite outgrowth, and tumor growth [1, 2] Such diverse biological functions suggest multiple cellular interactions with the laminin molecule. Testing these peptides for activity with neuronal cell lines identified peptide sequences from corresponding regions of the ␣1 and ␣2 laminin chains with cell type specificity for neurite outgrowth [20] These two active sequences, AG73 (RKRLQVQLSIRT) from laminin-1 and MG73 (KNRLTIELEVRT) from laminin-2, are in the E3 fragment of the G-domain and are highly conserved between murine laminin ␣ chains (Table I). AG73 promotes malignant behavior of melanoma cells in vitro and tumor growth and metastases in
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