Basement membrane invasion by first trimester human trophoblast: requirement for branched complex-type Asn-linked oligosaccharides.

Trophoblast cells of normal first trimester human placenta share with malignant tumor cells the ability for significant cellular proliferation and invasion of basement membranes. Because tumor cell metastasis in vivo and invasion of basement membranes in vitro have recently been shown to require the expression of -GlcNAc beta 1-6 Man alpha 1-6 Man beta 1-branched complex type Asn-linked oligosaccharides in tumor cell surface glycoproteins, we decided to determine if such structures were also necessary for invasion by trophoblast cells. We report here that invasive first trimester trophoblasts express leukoagglutinin-reactive beta 1-6 branched Asn-linked oligosaccharides on their surface. Moreover, basement membrane invasion by trophoblast was significantly inhibited by pretreating the cells with swainsonine, a non-toxic inhibitor of Golgi alpha-mannosidase II which blocks beta 1-6 branching of Asn-linked oligosaccharides. The first trimester trophoblast cells pretreated with swainsonine attached more avidly to the amnion basement membrane and to an extracellular matrix (ECM) preparation compared to control non-treated erophoblast cells. Swainsonine treatment did not inhibit secretion of gelatinase or plasminogen activator activities by trophoblast cells. These results suggest that expression of beta 1-6 branched oligosaccharides in trophoblast cells may be functionally important for the implantation and placentation processes by reducing cell adhesion to ECM and thereby facilitating trophoblast cell invasion.