Endocytosis

Abstract

Mammalian cells take up extracellular material by a variety of different mechanisms that are collectively termed endocytosis. Endocytic mechanisms serve many important cellular functions including the uptake of extracellular nutrients, regulation of cell-surface receptor expression, maintenance of cell polarity, and antigen presentation. Endocytic pathways are also utilized by viruses, toxins, and symbiotic microorganisms to gain entry into cells. One of the best-characterized endocytic mechanisms is receptor-mediated endocytosis via clathrin-coated pits. This type of endocytosis constitutes the major emphasis of this review, with a brief discussion of other endocytic mechanisms and their comparison with the receptor-mediated pathway. This review describes and evaluates critically current understanding of the mechanisms of entry of plasma membrane components such as the receptor-ligand complexes and membrane lipids as well as the extracellular fluid into cells. The intracellular sorting and trafficking of these molecules upon internalization are also described. The roles of endocytosis in physiological and pathological processes are discussed. These include maintenance of cell polarization, antigen presentation, glucose transport, atherosclerosis, Alzheimer's disease, and the endocytosis of toxins and viruses.

Intracellular trafficking of nonviral vectors

“…56 Receptor binding typically triggers the localized accumulation of clathrin structures on the cytoplasmic surface of the plasma membrane as it begins to invaginate, forming clathrincoated pits (Figure 1). The coat is composed of clathrin heavy and light chains that assemble into three-legged triskelions and associate with adaptor proteins (APs).…”

“…73 In the first pathway, the receptor undergoes rapid recycling from early endosomes to the cell surface, within 10 min after uptake. In the second pathway, the receptor undergoes slow recycling to the cell surface from the recycling compartment, which is an organelle that recycling endosomes enter or exit 56,74 ( Figure 1). In CHO cells, Tf receptors recycle rapidly back from early endosomes to the cell surface with a half time of B10 min.…”

Azithromycin, a Lysosomotropic Antibiotic, Has Distinct Effects on Fluid-Phase and Receptor-Mediated Endocytosis, but Does Not Impair Phagocytosis in J774 Macrophages

“…Endocytosis plays a central role in cell physiology and pathology [1][2][3]. The pathways followed by materials internalized by its three main modes (fluid-phase endocytosis, receptor-mediated endocytosis, and phagocytosis) have been amply delineated and the complexity of the underlying protein machineries and their interaction motives are becoming increasingly unraveled [4].…”

“…When studied, drugs were 1 Present address: Department of Membrane Cell Biology, Faculty of Medical Sciences, University of Groningen, Groningen, The Netherlands. 2 To whom correspondence and reprint requests should be addressed. Fax: ϩ32-2-764.…”

Degradation of yolk platelets in the early amphibian embryo is regulated by fusion with late endosomes

“…The present results show that yolk degradation in newt embryos depends on lysosomal enzymes being carried into yolk platelets via newly synthesized endo- (Tanaka et al 1990;Akasaki et al 1995;Nixon & Cataldo 1995;Mukherjee et al 1997 (Prydz et al 1992 (Bowman et al 1988), and the interference by bafilomycin A1 with acidification in vacuoles disrupts intracellular transport (Van Weert et al 1995). Mastoparan activates GTP-binding regulatory proteins (G proteins;Higashijima et al 1988;Kikkawa et al 1992;Klinker et al 1996), which play important roles in the endocytic pathway (Olkkonen & Stenmark 1997).…”