Functional effects of transforming growth factor beta on adhesive properties of porcine trophectoderm

In pigs, expression and amounts of biologically active TGFbetas at the conceptus-maternal interface increase significantly as conceptuses elongate and begin the implantation process. Before their activation, secreted TGFbetas are noncovalently associated with their respective, isoform-specific latency-associated peptides (LAPs), which contain the Arg-Gly-Asp (RGD) amino acid sequence that serves as a ligand for numerous integrins. Objectives of this study were to determine whether TGFbeta1 increases production of fibronectin by porcine trophectoderm, whether porcine trophectoderm adheres specifically to fibronectin and LAP, and whether functional interactions between porcine trophectoderm and the two TGFbeta-associated proteins, fibronectin and LAP, are integrin mediated. Porcine trophectoderm cells (pTr2) were cultured in presence of TGFbeta1, LAP, or pan-neutralizing anti-TGFbeta antibody; TGFbeta specifically increased (P < 0.05) fibronectin mRNA levels, as determined by Northern and slot blot analyses. Immunofluorescence microscopy demonstrated a TGFbeta-induced increase in fibronectin in pTr2 cells. In dispersed cell adhesion assays, adhesion of pTr2 cells to fibronectin was inhibited by an RGD-containing peptide (P < 0.05) and pTr2 cells attached to recombinant LAP but not to an LAP mutant, which contained an RGE sequence rather than the RGD site (P < 0.05). Fibronectin- and LAP-coated microbeads induced integrin activation at apical surfaces of both trophectoderm and uterine luminal epithelial cells, as indicated by aggregation and transmembrane accumulation of talin detected with immunofluorescence microscopy. Cell surface biotinylation and immunoprecipitation revealed integrin subunits alphav and beta1 on apical membranes of pTr2 cells. These results suggest multiple effects of TGFbeta at the porcine conceptus-maternal interface, including integrin-mediated conceptus-maternal communication through LAP.