Suppression of Injuries Caused by a Lytic RNA Virus (Mengovirus) and Their Uncoupling from Viral Reproduction by Mutual Cell/Virus Disarmament

Abstract

Viruses often elicit cell injury (cytopathic effect [CPE]), a major cause of viral diseases. CPE is usually considered to be a prerequisite for and/or consequence of efficient viral growth. Recently, we proposed that viral CPE may largely be due to host defensive and viral antidefensive activities. This study aimed to check the validity of this proposal by using as a model HeLa cells infected with mengovirus (MV). As we showed previously, infection of these cells with wild-type MV resulted in necrosis, whereas a mutant with incapacitated antidefensive (“security”) viral leader (L) protein induced apoptosis. Here, we showed that several major morphological and biochemical signs of CPE (e.g., alterations in cellular and nuclear shape, plasma membrane, cytoskeleton, chromatin, and metabolic activity) in cells infected with L − mutants in the presence of an apoptosis inhibitor were strongly suppressed or delayed for long after completion of viral reproduction. These facts demonstrate that the efficient reproduction of a lytic virus may not directly require development of at least some pathological alterations normally accompanying infection. They also imply that L protein is involved in the control of many apparently unrelated functions. The results also suggest that the virus-activated program with competing necrotic and apoptotic branches is host encoded, with the choice between apoptosis and necrosis depending on a variety of intrinsic and extrinsic conditions. Implementation of this defensive suicidal program could be uncoupled from the viral reproduction. The possibility of such uncoupling has significant implications for the pathogenesis and treatment of viral diseases.

Cytopathic effects: virus-modulated manifestations of innate immunity?

“…Suppression of both apoptosis and necrosis in the MVinfected HeLa cells by an antiapoptotic drug [4] suggests the model shown in Figure 2c. Upon wt MV infection, the two branches of the death program are activated but the apoptotic subroutine is suppressed by newly synthesized L protein, thereby channeling the cells to necrosis.…”

“…Infection with wild type (wt) virus terminated in necrosis, whereas MV mutants with inactivated L induced apoptosis [3]. However, in Lmutant-infected cells, a chemical inhibitor of apoptosis prevented not only apoptosis but also suppressed manifestations of major signs of necrotic CPE or delayed them until well after the completion of the viral reproduction [4]. The yield and time course of the reproduction of Lmutants were unaffected by this inhibitor.…”

“…We have recently proposed that not only apoptosis but also virus-triggered necrosis may represent manifestations of host-encoded death programs, bona fide members of the innate immunity system [4]. A strong argument for this hypothesis is provided by a striking multifunctionality of the small (67 amino acids) nonenzymatic cardiovirus L protein.…”

“…A strong argument for this hypothesis is provided by a striking multifunctionality of the small (67 amino acids) nonenzymatic cardiovirus L protein. If apoptosis of infected HeLa cells was pharmacologically suppressed, diverse signs of necrotic CPE such as permeabilization of the plasma membrane, rearrangements of microtubule and microfilament networks, changes in the cellular and nuclear shapes, condensation of chromatin, and loss of the general metabolic activity all depend on L functionality [4]. This protein also impairs cellular interferon system [32], formation of stress granules [33], and, as mentioned above, nucleocytoplasmic traffic [25].…”

Coxsackievirus B3 Replication and Pathogenesis

“…The cytopathic effect appears as morphological changes coupled with cell rounding, release of cells from the culture surface and altered membrane permeability, leading to lysis of host cells, mainly through apoptosis, necrosis or both. One observation that has emerged from a recent study suggests that the virus-activated cell death induced by both necrotic and apoptotic limbs [72]. Inhibition of host cell transcription, and translation, along with loss of cellular homeostasis due to direct viral protease cleavage of structural proteins such as dystrophin likely contributes to the cellular structure disruption, and cell death of infected cells [19,20].…”