Pore-forming toxins induce multiple cellular responses promoting survival

Abstract

SummaryPore-forming toxins (PFTs) are secreted proteins that contribute to the virulence of a great variety of bacterial pathogens. They inflict one of the more disastrous damages a target cell can be exposed to: disruption of plasma membrane integrity. Since this is an ancient form of attack, which bares similarities to mechanical membrane damage, cells have evolved response pathways to these perturbations. Here, it is reported that PFTs trigger very diverse yet specific response pathways. Many are triggered by the decrease in cytoplasmic potassium, which thus emerges as a central regulator. Upon plasma membrane damage, cells activate signalling pathways aimed at restoring plasma membrane integrity and ion homeostasis. Interestingly these pathways do not require protein synthesis. Cells also trigger signalling cascades that allow them to enter a quiescent-like state, where minimal energy is consumed while waiting for plasma membrane damage to be repaired. More specifically, protein synthesis is arrested, cytosolic constituents are recycled by autophagy and energy is stored in lipid droplets.

Oligomerization and Pore Formation by Equinatoxin II Inhibit Endocytosis and Lead to Plasma Membrane Reorganization

“…A possible reason for this failure to repair EqtII-induced membrane injuries could be related to the small size of the pores induced. Similarly to EqtII, ␣-toxin or aerolysin form pores with ϳ2-nm diameter, and cells treated with these toxins had more difficulties or were unable to recover (38). However, the nature of the cell survival mechanisms in response to the attack of PFPs is still poorly understood.…”

Biophysical and biochemical strategies to understand membrane binding and pore formation by sticholysins, pore-forming proteins from a sea anemone

“…Using this methodology, the intracellular kinase proteins activated as a consequence of pore formation by StII have been elucidated . Employing 46 antibodies against 29 different kinases, it was observed that the phosphorylation of MAP kinases p38 and ERK was similar to what has been described for other PFT, such as streptolysin O, pneumolysin O, anthrolysin O, Cry5B, aerolysin and LLO (Ratner et al 2006;Aguilar et al 2009;Porta et al 2011;Gonzalez et al 2011).…”

“…Strikingly, it has been found that membrane recovery upon StII damage takes place in a time scale similar to that upon LLO damage even though these two PFT form pores that differ greatly in size. In addition, for StII, membrane recovery occurs in a completely different time span to that observed for other bacterial PFT also producing small pores (Husmann et al 2009;Gonzalez et al 2011). At sub-lytic concentrations (100 ng/ml) in BHK cells, StII is able to cause a drop of intracellular potassium (<40%) after 20 min of incubation.…”

“…In this sense, the interaction between nucleated cells and bacterial PFT is yet not fully understood. Studies with aerolysin and LLO have shown that sub-lytic doses of these proteins produce a primary effect on the target cells characterized by a decrease in intracellular potassium and a concomitant increase in calcium (Gonzalez et al 2011). These changes in cytoplasmic ionic composition trigger what are known as side effects that result in the activation of various signaling pathways of mitogen-activated protein (MAP) kinases (Huffman et al 2004;Gurcel et al 2006;Bischof et al 2008), which are considered to be essential for survival following toxinmediated membrane disruption.…”

“…Cells (~10 6 cells/ml) can be incubated with different toxin concentrations for periods ranging from 10 min to 24 h. For StI and StII in particular, protein amounts fluctuating in the range of nanomolar and micromolar concentrations have been evaluated. Following the challenge, the supernatant containing the toxin is eliminated and the cellular monolayer washed out with a potassium-free buffer (Gonzalez et al 2011). The rupture of the cellular membrane to quantify intracellular potassium concentration is achieved using a washing buffer containing Triton X-100.…”