Ira Pastan

Adenovirus Entry into Cells: Some New Observations on an Old Problem

With the advent of electron microscopy, it became possible to investigate the pathway of viral entry into cells. Viruses were visualized bound to the cell surface prior to entry and within cells after entry. Some investigators interpreted their findings to indicate that a virus such as adenovirus entered the cell in a vacuole or vesicle whose formation was induced by the presence of the virus at the cell surface. Other investigators concluded that viruses directly crossed the plasma membrane without being transported in a vesicle.

Receptor-Mediated Endocytosis: General Considerations and Morphological Approaches

Cells carefully regulate their internal environment by controlling which molecules are allowed to enter and which are not. Proteins and other large molecules enter cells mainly via receptor-mediated endocytosis. After these molecules enter a cell, they proceed from one membrane-limited compartment to another. Each of the major intracellular membrane compartments has a specific function. In this chapter we will describe the organelles (or compartments) that the cell uses to carry out receptor-mediated endocytosis and describe some of the new methods that have been used to carry out these studies. In our own laboratory we have focused on the ligand α 2-macroglobulin (α 2M) and the route by which fibroblastic cells take it up, but we have also applied these methods to the study of a few other ligands including epidermal growth factor (EGF), low-density lipoprotein (LDL) and some viruses. Some aspects of this process have been recently reviewed (Pastan and Willingham, 1981).