Shiga Toxins Induce Apoptosis and ER Stress in Human Retinal Pigment Epithelial Cells

Abstract

Shiga toxins (Stxs) produced by Shiga toxin-producing bacteria Shigella dysenteriae serotype 1 and select serotypes of Escherichia coli are the most potent known virulence factors in the pathogenesis of hemorrhagic colitis progressing to potentially fatal systemic complications such as acute renal failure, blindness and neurological abnormalities. Although numerous studies have defined apoptotic responses to Shiga toxin type 1 (Stx1) or Shiga toxin type 2 (Stx2) in a variety of cell types, the potential significance of Stx-induced apoptosis of photoreceptor and pigmented cells of the eye following intoxication is unknown. We explored the use of immortalized human retinal pigment epithelial (RPE) cells as an in vitro model of Stx-induced retinal damage. To the best of our knowledge, this study is the first report that intoxication of RPE cells with Stxs activates both apoptotic cell death signaling and the endoplasmic reticulum (ER) stress response. Using live-cell imaging analysis, fluorescently labeled Stx1 or Stx2 were internalized and routed to the RPE cell endoplasmic reticulum. RPE cells were significantly sensitive to wild type Stxs by 72 h, while the cells survived challenge with enzymatically deficient mutant toxins (Stx1A− or Stx2A−). Upon exposure to purified Stxs, RPE cells showed activation of a caspase-dependent apoptotic program involving a reduction of mitochondrial transmembrane potential (Δψm), increased activation of ER stress sensors IRE1, PERK and ATF6, and overexpression CHOP and DR5. Finally, we demonstrated that treatment of RPE cells with Stxs resulted in the activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38MAPK), suggesting that the ribotoxic stress response may be triggered. Collectively, these data support the involvement of Stx-induced apoptosis in ocular complications of intoxication. The evaluation of apoptotic responses to Stxs by cells isolated from multiple organs may reveal unique functional patterns of the cytotoxic actions of these toxins in the systemic complications that follow ingestion of toxin-producing bacteria.

The C/EBP Homologous Protein (CHOP) Transcription Factor Functions in Endoplasmic Reticulum Stress-Induced Apoptosis and Microbial Infection

“…Shiga toxins produced by Shigella dysenteriae serotype I activate both apoptotic cell death signaling and the ER stress response. Treatment of human retinal pigment epithelial cells (RPE cells) with Stxs results in the activation of JNK and p38MAPK, and up-regulation of CHOP and DR5 expression (123, 132). Collectively, characterization of CHOP functions during microbial infection will help us to understand the pathogenesis of microorganisms and provide a better theoretical basis to control and prevent diseases.…”

Cholix protein domain I functions as a carrier element for efficient apical to basal epithelial transcytosis

“…For example, Shiga toxin disrupts retrograde vesicle trafficking 43 to incite epithelial cell intoxication. 44 Vibrio parahaemolyticus injects a series of virulence factors into enterocytes that alter the polarity properties of these cells as part of their actions to incite seafood-borne gastritis. 45 Our data demonstrate a distinct approach used by an extracellular pathogen to manipulate host cell functions: vesicular trafficking that results in efficient A→B transcytosis of a virulence factor that target cells within the lamina propria whose intoxication could limit immune responses and stabilize infections of nonpandemic V. cholerae in the intestinal lumen.…”

A portable and high-sensitivity optical sensing system for detecting fluorescently labeled enterohaemorrhagic Escherichia coli Shiga toxin 2B-subunit

“…The Stxs produced by Shigella dysenteriae serotype 1 and select serotypes of E. coli are the most potent known virulence factors involved in the pathogenesis of hemorrhagic colitis, which can progress to potentially fatal systemic complications such as acute renal failure [6] and neurological abnormalities [7,8]. Although multiple studies have defined the pathologic host responses to Stx1 and Stx2 in multiple cell types, sensors capable of detecting Stxs in susceptible cells following intoxication have also been recognized as critical tools (reviewed in [9,10]).…”