Lay summary
We have found that overexpression of podoplanin leads to enhanced cell adhesion and migration, and that siRNA-mediated knockdown of podoplanin gene expression in lymphatic endothelial cells inhibited these functions. We have also produced a novel potential inhibitor of podoplanin's function in cancer progression: We have expressed a recombinant fusion protein containing the extracellular podoplanin domain in several glycosylation-deficient CHO cell lines. We found that soluble podoplanin-Fc inhibits lymphatic endothelial cell migration and tube formation, and that a glycosylation-deficient variant was more potent than the wildtype protein. This new inhibitor also inhibits lymphangiogenesis in vivo. We have performed additional transcriptional profiling studies in endothelial cells after podoplanin knockdown or overexpression, and in a tetracyclin-inducible podoplanin overexpression system in MCF7 breast cancer cells. Thus, we have identified several novel podoplanin target genes. Moreover, we found that podoplanin overexpression in tumor cells promoted lymphangiogenesis in vivo. Using protein arrays, we have identified a previously unknown extracellular binding partner of podoplanin that mediates its interaction with integrin alpha6, with potentially important implications for lymphangiogenesis and cancer progression.