The Coxsackievirus 2B Protein Suppresses Apoptotic Host Cell Responses by Manipulating Intracellular Ca2+ Homeostasis

Abstract

. In our studies of the physiological importance of the 2B-induced alterations in Ca 2؉ signaling, we found that the expression of 2B suppressed caspase activation and apoptotic cell death induced by various stimuli, including actinomycin D and cycloheximide. Mutants of 2B that were defective in reducing the Ca 2؉ content of the stores failed to suppress apoptosis. These data implicate a functional role of the perturbation of intracellular Ca 2؉ compartmentalization in the enteroviral strategy to suppress intrinsic apoptotic host cell responses. The putative down-regulation of an endoplasmic reticulum-dependent apoptotic pathway is discussed.

Viroporins: structure, function and potential as antiviral targets

“…2B fused to maltose-binding protein forms tetramers with a pore radius of *6 Å (Agirre et al, 2002), consistent with modelling studies that predict tetrameric pores of 5-7 Å radius with a lumen lined by a stretch of three Lys followed by a Ser (Patargias et al, 2009). 2B multimerization has been observed in mammalian cells (de Jong et al, 2002(de Jong et al, , 2004van Kuppeveld et al, 2002) and the protein readily permeabilizes vesicles in vitro (Agirre et al, 2008;Sánchez-Martínez et al, 2008). 2B expression gives rise to elevated cytosolic Ca 2+ , which alters vesicle trafficking, induces apoptosis and directly lyses cells as protein levels accumulate, reminiscent of a membrane-active toxin (Campanella et al, 2004;de Jong et al, 2003de Jong et al, , 2004de Jong et al, , 2006Sandoval & Carrasco, 1997;van Kuppeveld et al, 1997).…”

“…2B multimerization has been observed in mammalian cells (de Jong et al, 2002(de Jong et al, , 2004van Kuppeveld et al, 2002) and the protein readily permeabilizes vesicles in vitro (Agirre et al, 2008;Sánchez-Martínez et al, 2008). 2B expression gives rise to elevated cytosolic Ca 2+ , which alters vesicle trafficking, induces apoptosis and directly lyses cells as protein levels accumulate, reminiscent of a membrane-active toxin (Campanella et al, 2004;de Jong et al, 2003de Jong et al, , 2004de Jong et al, , 2006Sandoval & Carrasco, 1997;van Kuppeveld et al, 1997). Localization to the Golgi is essential for these functions as the ERlocalized hepatovirus 2B protein does not affect cytosolic Ca 2+ levels.…”

“…Perhaps the most striking example is that of the rotavirus NSp4 protein, which causes the release of Ca 2+ ions from intracellular stores during infection to promote the formation of viroplasms and expedite virus release (Browne et al, 2000;Dong et al, 1997;Hyser et al, 2010Hyser et al, , 2013Newton et al, 1997;Tian et al, 1996), but which is also secreted via a Golgiindependent, microtubule-driven mechanism and acts directly as an enterotoxin when applied to the enteric tract, inducing diarrhoeal symptoms synonymous with rotaviral disease (Einerhand, 1998;Halaihel et al, 2000;Horie et al, 1999;Morris et al, 1999;Tafazoli et al, 2001). Picornavirus 2B channel activity also increases cytosolic Ca 2+ by releasing it from the Golgi and mitochondria, which is thought to specifically increase viral internal ribosome entry site (IRES)-mediated translation at early times during infection and drive membrane instability to expedite the release of viral progeny at late times (Campanella et al, 2004;de Jong et al, 2003de Jong et al, , 2006Sandoval & Carrasco, 1997;van Kuppeveld et al, 1997van Kuppeveld et al, , 2002. 2B expression also alters cellular trafficking, evidenced by effects on the passage of vesicular stomatitis virus G glycoprotein to the cell surface (Doedens & Kirkegaard, 1995).…”

Bcl-2 and Ca2+ homeostasis in the endoplasmic reticulum

“…The antiapoptotic Coxsackie viral protein 2B was shown to reduce ER Ca 2 þ levels. 65 On the contrary the proapoptotic protein of HBx augments the cytosolic Ca 2 þ signals evoked by InsP 3 -linked agonists. However, this is not due to ER Ca 2 þ overload, as the steady-state [Ca 2 þ ] er levels are identical to those of mock-transfected cells.…”

Mitochondria and the central nervous system: searching for a pathophysiological basis of psychiatric disorders

“…Following the initiation of necrosis, mitochondria are overloaded with Ca 2+ , the electrochemical proton gradient collapses, and necrotic cell death is induced. 61 Thus, it seems that alteration of this cellular response (for example, by a tumor or viral proteins) 51,54,62,63 plays a role in the pathogenesis of human disorders. Prolonged permeability transition pore opening leads to a complete collapse of the membrane potential and Ca 2+ release, which results in the complete loss of mitochondrial function and necrotic cell death.…”