Co-option of Membrane Wounding Enables Virus Penetration into Cells

Abstract

During cell entry, non-enveloped viruses undergo partial uncoating to expose membrane lytic proteins for gaining access to the cytoplasm. We report that adenovirus uses membrane piercing to induce and hijack cellular wound removal processes that facilitate further membrane disruption and infection. Incoming adenovirus stimulates calcium influx and lysosomal exocytosis, a membrane repair mechanism resulting in release of acid sphingomyelinase (ASMase) and degradation of sphingomyelin to ceramide lipids in the plasma membrane. Lysosomal exocytosis is triggered by small plasma membrane lesions induced by the viral membrane lytic protein-VI, which is exposed upon mechanical cues from virus receptors, followed by virus endocytosis into leaky endosomes. Chemical inhibition or RNA interference of ASMase slows virus endocytosis, inhibits virus escape to the cytosol, and reduces infection. Ceramide enhances binding of protein-VI to lipid membranes and protein-VI-induced membrane rupture. Thus, adenovirus uses a positive feedback loop between virus uncoating and lipid signaling for efficient membrane penetration.

Endosomophagy clears disrupted early endosomes but not virus particles during virus entry into cells     

“…The report here also impinges on gene therapy and vaccination protocols, considering the prominent roles of adenoviruses in clinical gene therapy, and as vaccination adjuvants [61]. Follow-up analyses of this observation can be directed to the identification of host and viral targets for ubiquitin ligases and deubiquitinases, host adaptor proteins, or the role of virus-induced sphingolipids in tuning endosomophagy [34]. Notably, sphingolipids have key roles in the regulation of autophagy at the levels of transcription, translation, and morphogenesis of autophagosomes [62].…”

“…Virus penetration into the cytosol occurs from early endosomes in a pHindependent manner [29] [30]. It requires the membrane-lytic viral protein VI [31] [32] [33], lysosomal secretion, the sphingolipid ceramide [34] [35], and gates the pathway for viral DNA genome separation from the capsid and nuclear delivery of the viral genome [36] [37]. Here, we describe a novel observation, the recruitment of Gal3, ubiquitin and the poly-ubiquitin binding protein p62/SQSTM1 to ruptured early endosomes, followed by clearance of disrupted membranes without clearance of virus particles from the in-fected cell.…”

Annexins in Translational Research: HIDDEN Treasures to Be Found

“…The importance of the rapid and effective toxin removal for the host protection has been impressively demonstrated in vivo, as the administration of artificial liposomes that effectively compete with the host cell membranes sequester such toxins and successfully prevent the development of severe sepsis in a murine staphylococcal sepsis model [151]. Another example of a pathogen exploiting the host cell PM repair mechanism is the induction of lysosomal exocytosis during the host cell entry process of adenoviruses [152]. Fusion of lysosomes with the PM is also a means to control the propagation of intracellular bacteria [153].…”

Fluorescence Tracking of Genome Release during Mechanical Unpacking of Single Viruses

“…This facilitates the liberation of a fraction of the viral membrane lytic protein VI, which forms small pores in the plasma membrane. 19 These pores are too small for the virus to penetrate, but they trigger a membrane repair process which eventually leads to the uptake of the virus in endosomes. The membrane lytic function of protein VI is enhanced by an increase of cellular ceramide lipid levels which leads to an early rupture of the endosomal membrane, notably in a pH independent manner.…”

“…The membrane lytic function of protein VI is enhanced by an increase of cellular ceramide lipid levels which leads to an early rupture of the endosomal membrane, notably in a pH independent manner. [19][20][21][22] Upon access to the cytosol, the viral genome remains in a partially disrupted capsid which is transported along microtubules by motor-proteins to the nuclear pore complexes where it docks. [23][24][25][26][27] At the nuclear pore complex, the genome is released by mechanical forces arising from the antagonistic action of kinesin motor-proteins against the holding force of the nuclear pore complex where the virus is attached.…”