Dissecting the role of integrin subunits alpha 2 and beta 3 in rotavirus cell entry by RNA silencing

Rotaviruses Associate with Distinct Types of Extracellular Vesicles

Rotaviruses are the leading cause of viral gastroenteritis among children under five years of age. Rotavirus cell entry has been extensively studied; however, rotavirus cell release is still poorly understood. Specifically, the mechanism by which rotaviruses leave the cell before cell lysis is not known. Previous works have found rotavirus proteins and viral particles associated with extracellular vesicles secreted by cells. These vesicles have been shown to contain markers of exosomes; however, in a recent work they presented characteristics more typical of microparticles, and they were associated with an increase in the infectivity of the virus. In this work, we purified different types of vesicles from rotavirus-infected cells. We analyzed the association of virus with these vesicles and their possible role in promotion of rotavirus infection. We confirmed a non-lytic rotavirus release from the two cell lines tested, and observed a notable stimulation of vesicle secretion following rotavirus infection. A fraction of the secreted viral particles present in the cell supernatant was protected from protease treatment, possibly through its association with membranous vesicles; the more pronounced association of the virus was with fractions corresponding to cell membrane generated microvesicles. Using electron microscopy, we found different size vesicles with particles resembling rotaviruses associated from both- the outside and the inside. The viral particles inside the vesicles were refractory to neutralization with a potent rotavirus neutralizing monoclonal antibody, and were able to infect cells even without trypsin activation. The association of rotavirus particles with extracellular vesicles suggests these might have a role in virus spread.

Assessing the oncolytic potential of rotavirus on mouse myeloma cell line Sp2/0-Ag14

INTRODUCTION

Cancer is the second leading cause of death in the United States, surpassed only by cardiovascular disease. However, cancer has now overtaken cardiovascular disease as the main cause of death in 12 countries in Western Europe. The burden of cancer is posing a major challenge to health care systems worldwide and demanding improvements in methods for cancer prevention, diagnosis, and treatment. Alternative and complementary strategies for orthodox surgery, radiotherapy, and chemotherapy need to be developed.

OBJECTIVE

To determine the oncolytic potential of tumor cell-adapted rotavirus in terms of their ability to infect and lysate murine myeloma Sp2/0-Ag14 cells.

MATERIALS AND METHODS

We inoculated rotaviruses Wt1-5, WWM, TRUYO, ECwt-O, and WTEW in Sp2/0-Ag14 cells and we examined their infectious effects by immunocytochemistry, immunofluorescence, flow cytometry, and DNA fragmentation assays.

RESULTS

Rotavirus infection involved the participation of some heat shock proteins, of protein disulfide isomerase (PDI), and integrin β3. We detected the accumulation of viral antigens within the virus-inoculated cells and in the culture medium in all the rotavirus isolates examined. The rotavirus-induced cell death mechanism in Sp2/0-Ag14 cells involved changes in cell membrane permeability, chromatin condensation, and DNA fragmentation, which were compatible with cytotoxicity and apoptosis.

CONCLUSIONS

The ability of the rotavirus isolates Wt1-5, WWM, TRUYO, ECwt-O, and WTEW to infect and cause cell death of Sp2/0-Ag14 cells through mechanisms that are compatible with virus-induced apoptosis makes them potential candidates as oncolytic agents.

Rhesus rotavirus trafficking during entry into MA104 cells is restricted to the early endosome compartment

Endocytosis has recently been implicated in rotavirus (RV) entry. We examined the role of Rabs, which regulate endosomal trafficking, during RV entry. Several structural proteins of neuraminidase-sensitive and -insensitive RVs colocalized with Rab5, an early endosome marker, but not Rab7, a late endosome marker. Dominant-negative and constitutively active mutants demonstrated that Rab5 but not Rab4 or Rab7 affects rhesus RV (RRV) infectivity. These data suggest that early RRV trafficking is confined to the early endosome compartment and requires Rab5.

Rhesus rotavirus entry into a polarized epithelium is endocytosis dependent and involves sequential VP4 conformational changes

Rotavirus (RV) cell entry is an incompletely understood process, involving VP4 and VP7, the viral proteins composing the outermost layer of the nonenveloped RV triple-layered icosahedral particle (TLP), encasing VP6. VP4 can exist in three conformational states: soluble, cleaved spike, and folded back. In order to better understand the events leading to RV entry, we established a detection system to image input virus by monitoring the rhesus RV (RRV) antigens VP4, VP6, and VP7 at very early times postinfection. We provide evidence that decapsidation occurs directly after cell membrane penetration. We also demonstrate that several VP4 and VP7 conformational changes take place during entry. In particular, we detected, for the first time, the generation of folded-back VP5 in the context of the initiation of infection. Folded-back VP5 appears to be limited to the entry step. We furthermore demonstrate that RRV enters the cell cytoplasm through an endocytosis pathway. The endocytosis hypothesis is supported by the colocalization of RRV antigens with the early endosome markers Rab4 and Rab5. Finally, we provide evidence that the entry process is likely dependent on the endocytic Ca(2+) concentration, as bafilomycin A1 treatment as well as an augmentation of the extracellular calcium reservoir using CaEGTA, which both lead to an elevated intraendosomal calcium concentration, resulted in the accumulation of intact virions in the actin network. Together, these findings suggest that internalization, decapsidation, and cell membrane penetration involve endocytosis, calcium-dependent uncoating, and VP4 conformational changes, including a fold-back.