Entry of Adenovirus into Cells
With the advent of the electron microscope, it became possible to study the entry of adenoviruses into eukaryotic cells. Time course experiments of adenovirus uptake into the cells indicated a pathway of adenovirus entry which is similar to that followed by other ligands which enter the cells by receptor-mediated endocytosis. Images taken at different time intervals showed adenoviruses bound to cell surface at initial time points. Soon thereafter, adenoviruses are detected in clathrin coated pits, and in endocytic vesicles termed endosomes. Adenoviruses escape from the endosomes into the cytosol, then traverse towards the nucleus using the microtubule system. The journey of adenovirus from the cell surface to the nucleus is completed in about 30 minutes, indicating a rapid rate of adenoviral uptake. While the binding of adenovirus to the cell surface is independent of temperatures in the range of 4-37°C, the internalization of the adenovirus into the cells is temperature dependent, and is optimum at 37°C. Known inhibitors of ATP-dependent transport processes also abolish adenovirus uptake into cells, suggesting that the entry of the adenovirus into cells is an active process. The following are the key steps involved in adenovirus entry into the cells.