Host cytoskeleton

Abstract: Salmonella enterica serovars cause severe disease in humans, such as gastroenteritis and typhoid fever. The bacteria are able to invade and replicate within host cells, including epithelial cells and macrophages. Pathogenesis of Salmonella is facilitated by a type III secretion system (T3SS) encoded by genes of Salmonella pathogenicity island 2 (SPI-2). Intracellular replication occurs in a specialized membrane compartment, the Salmonella-containing vacuole (SCV), and depends on translocation of approximately 30 effector proteins via the SPI-2 T3SS into the host endomembrane system and cytoplasm. In this review we discuss the many different functions of these effectors, which range from maintaining the integrity of the SCV and its juxtanuclear location, to interference with the host cytoskeleton and immune signalling.

Abstract: Toxoplasma gondii is an obligate intracellular parasite that infects a wide variety of vertebrate cells including macrophages. We have used a combination of video microscopy and fluorescence localization to examine the entry of Toxoplasma into macrophages and nonphagocytic host cells. Toxoplasma actively invaded host cells without inducing host cell membrane ruffling, actin microfilament reorganization, or tyrosine phosphorylation of host proteins. Invasion occurred rapidly and within 25-40 seconds the parasite penetrated into a tight-fitting vacuole formed by invagination of the plasma membrane. In contrast, during phagocytosis of Toxoplasma, extensive membrane ruffling captured the parasite in a loose-fitting phagosome that formed over a period of 2-4 minutes. Phagocytosis involved both reorganization of the host cytoskeleton and tyrosine phosphorylation of host proteins. In some cases, parasites that were first internalized by phagocytosis, were able to escape from the phagosome by a process analogous to invasion. These studies reveal that active penetration of the host cell by Toxoplasma is fundamentally different from phagocytosis or induced endocytic uptake. The novel ability to penetrate the host cell likely contributes to the capability of Toxoplasma-containing vacuoles to avoid endocytic processing.

Abstract: ▪ Abstract The host cytoskeleton plays important roles in the entry, replication, and egress of viruses. An assortment of viruses hijack cellular motor proteins to move on microtubules toward the cell interior during the entry process; others reverse this transport during egress to move assembling virus particles toward the plasma membrane. Polymerization of actin filaments is sometimes used to propel viruses from cell to cell, while many viruses induce the destruction of select cytoskeletal filaments apparently to effect efficient egress. Indeed, the tactics used by any given virus to achieve its infectious life cycle are certain to involve multiple cytoskeletal interactions. Understanding these interactions, and their orchestration during viral infections, is providing unexpected insights into basic virology, viral pathogenesis, and the biology of the cytoskeleton.