Passage
Adeno-associated virus 2 (AAV2) is a nonpathogenic, nonenveloped DNA virus that requires helper viruses such as adenovirus (AV) or herpes simplex virus (HSV) to replicate efficiently. Because it can transduce human cells, including quiescent (nondividing) cells, without causing disease, AAV2 is attractive as a gene therapy vector. In clinical trials, a modified AAV2 virus has successfully treated the retinal disease Leber's congenital amaurosis as well as the blood clotting disorder hemophilia B. AAV2 transduces cells via a multistep process, shown in Figure 1.
Figure 1 Schematic showing the mechanism of transduction by AAV2Studies indicate that unlike AV and HSV, AAV2 inhibits pathways other than the endosomal pathway, such as trafficking to the Golgi, increasing the percentage of invading virus particles that arrive at the nucleus.
Adapted from Xiao PJ, Samulski RJ. Cytoplasmic trafficking, endosomal escape, and perinuclear accumulation of adeno-associated virus type 2 particles are facilitated by microtubule network. J Virol. 2012;86(19) :10462-73.
-AAV2 entry into cells could best be blocked by a drug that inhibits which of the following mechanisms?

Question

Passage
Adeno-associated virus 2 (AAV2) is a nonpathogenic, nonenveloped DNA virus that requires helper viruses such as adenovirus (AV) or herpes simplex virus (HSV) to replicate efficiently. Because it can transduce human cells, including quiescent (nondividing) cells, without causing disease, AAV2 is attractive as a gene therapy vector. In clinical trials, a modified AAV2 virus has successfully treated the retinal disease Leber's congenital amaurosis as well as the blood clotting disorder hemophilia B. AAV2 transduces cells via a multistep process, shown in Figure 1.

Figure 1 Schematic showing the mechanism of transduction by AAV2Studies indicate that unlike AV and HSV, AAV2 inhibits pathways other than the endosomal pathway, such as trafficking to the Golgi, increasing the percentage of invading virus particles that arrive at the nucleus.
Adapted from Xiao PJ, Samulski RJ. Cytoplasmic trafficking, endosomal escape, and perinuclear accumulation of adeno-associated virus type 2 particles are facilitated by microtubule network. J Virol. 2012;86(19) :10462-73.
-AAV2 entry into cells could best be blocked by a drug that inhibits which of the following mechanisms?

Quizplus · Accepted Answer

11ecba2d_0fee_b7a4_a3bf_0b03f667725d_MD0008_00 Cells constantly take up matter from their surrounding environment by endocytosis, in which the surroundings are enveloped by a portion of the cell membrane. That portion subsequently pinches off from the rest of the membrane and becomes a vesicle inside the cell. This vesicle then matures and merges with other membrane-bound compartments to become an endosome. Cells can conduct endocytosis through three major mechanisms: phagocytosis, pinocytosis, and receptor-mediated endocytosis. Figure 1 shows that AAV2 enters cells by receptor-mediated endocytosis, in which an external ligand (ie, AAV2) binds specific receptor proteins on the cell surface. This binding induces the plasma membrane to bud inward toward the cytosol before pinching off as a vesicle that contains both the ligand and its receptor. Therefore, a drug that inhibits this inward budding would likely prevent AAV2 from entering cells. (Choice A) Viruses with a capsid encased in a phospholipid membrane, known as enveloped viruses, can fuse their membranes with the cell membrane. When this occurs, no vesicle is formed and the capsid is released directly into the cytosol. As a nonenveloped virus, AAV2 cannot enter cells by this method; therefore, membrane fusion is not the method of entry shown in Figure 1. (Choice B) Phagocytosis, also called "cell eating," occurs when cells engulf external particles by extending portions of their membrane to reach around the particle rather than by the inward budding of the membrane, shown in Figure 1. (Choice D) Pinocytosis is a nonspecific process (ie, does not require receptor binding) that involves the continuous invagination of the cell membrane to take up extracellular fluid. Because it is a distinct process, inhibiting pinocytosis does not inhibit receptor-mediated endocytosis. Educational objective: Cells take up their surrounding environment via endocytosis, which includes mechanisms of phagocytosis, pinocytosis, and receptor-mediated endocytosis. Many viruses use receptor-mediated endocytosis to enter cells. Enveloped viruses can also enter cells by fusing their membrane with the membrane of the cell.

Passage Adeno-Associated Virus 2 (AAV2) Is a Nonpathogenic, Nonenveloped DNA Virus