Antibodies specific for gp40 inhibit cell-cell adhesion by cross-linking the protein on the surface of Dictyostelium purpureum

Characterization and Endocytic Internalization of Epith-2 Cell Surface Glycoprotein during the Epithelial-to-Mesenchymal Transition in Sea Urchin Embryos

The epithelial cells of the sea urchin Hemicentrotus pulcherrimus embryo express an Epith-2, uncharacterized glycoprotein, on the lateral surface. Here, we describe internalization of Epith-2 during mesenchyme formation through the epithelial-to-mesenchymal transition (EMT). Epith-2 was first expressed on the entire egg surface soon after fertilization and on the blastomeres until the 4-cell stage, but was localized to the lateral surface of epithelial cells at and after the 16-cell stage throughout the later developmental period. However, primary mesenchyme cells (PMC) and secondary mesenchyme cells (SMC) that ingress by EMT lost Epith-2 from their cell surface by endocytosis during dissociation from the epithelium, which was associated with the appearance of cytoplasmic Epith-2 dots. The cytoplasmic Epith-2 retained a similar relative molecular mass to that of the cell surface immediately after ingression through the early period of the spreading to single cells. Then, Epith-2 was completely lost from the cytoplasm. Tyrosine residues of Epith-2 were phosphorylated. The endocytic retraction of Epith-2 was inhibited by herbimycin A (HA), a protein tyrosine kinase (PTK) inhibitor, and suramin, a growth factor receptor (GFR) inhibitor, suggesting the involvement of the GFR/PTK (GP) signaling pathway. These two GP inhibitors also inhibited PMC and SMC spreading to individual cells after ingression, but the dissociation of PMC and SMC from the epithelium was not inhibited. In suramin-treated embryos, dissociated mesenchyme cells migrated partially by retaining their epithelial morphology. In HA-treated embryos, no mesenchyme cells migrated. Thus, the EMT occurs in relation to internalization of Epith-2 from presumptive PMC and SMC.

Keratinocytes store the antimicrobial peptide cathelicidin in lamellar bodies

Innate immune defense against microbial pathogens occurs by physical barriers, by recruitment of cells such as neutrophils, NK cells, and macrophages, and by secretion of molecules with antimicrobial activity. Such molecules are produced by various epithelia including skin. The importance of antimicrobial peptides has been shown in cathelicidin-deficient mice, which have increased susceptibility to skin infection by Streptococcus. Although keratinocytes increase cathelicidin expression upon injury, their role relative to neutrophil cathelicidin and their sites of peptide storage and activation have not been elucidated. Herein, it is reported that cathelicidin predominantly resides in granules of the superficial epidermis and partially localizes in lamellar bodies as determined by immunogold electron microscopy and immunoblot of lamellar bodies isolated from mice. In cultured keratinocytes, cathelicidin displays a granular distribution and partially localizes within the Golgi apparatus. Cathelicidin processing can be observed by western blot analysis in keratinocyte extracts but not in conditioned media. Further, fluorescent bacteria colocalize with cathelicidin in granules both intracellularly and at the cell surface. These observations illustrate the immune defense potential of keratinocytes acting directly through storage and processing of antimicrobial peptides.