Challenging the roles of CD44 and lipolysis stimulated lipoprotein receptor in conveying Clostridium perfringens iota toxin cytotoxicity in breast cancer.

Katerina D Fagan-Solis,Jodie M Fleming,Bradley G Stiles,Michel R Popoff,M Cristina Rangel,Denise K Reaves

doi:10.1186/1476-4598-13-163

Katerina D Fagan-Solis, Jodie M Fleming + Show 4 more

Open Access

https://doi.org/10.1186/1476-4598-13-163

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Abstract

BackgroundTranslational exploration of bacterial toxins has come to the forefront of research given their potential as a chemotherapeutic tool. Studies in select tissues have demonstrated that Clostridium perfringens iota toxin binds to CD44 and lipolysis stimulated lipoprotein receptor (LSR) cell-surface proteins. We recently demonstrated that LSR expression correlates with estrogen receptor positive breast cancers and that LSR signaling directs aggressive, tumor-initiating cell behaviors. Herein, we identify the mechanisms of iota toxin cytotoxicity in a tissue-specific, breast cancer model with the ultimate goal of laying the foundation for using iota toxin as a targeted breast cancer therapy.MethodsIn vitro model systems were used to determine the cytotoxic effect of iota toxin on breast cancer intrinsic subtypes. The use of overexpression and knockdown technologies confirmed the roles of LSR and CD44 in regulating iota toxin endocytosis and induction of cell death. Lastly, cytotoxicity assays were used to demonstrate the effect of iota toxin on a validated set of tamoxifen resistant breast cancer cell lines.ResultsTreatment of 14 breast cancer cell lines revealed that LSR+/CD44- lines were highly sensitive, LSR+/CD44+ lines were slightly sensitive, and LSR-/CD44+ lines were resistant to iota cytotoxicity. Reduction in LSR expression resulted in a significant decrease in toxin sensitivity; however, overexpression of CD44 conveyed toxin resistance. CD44 overexpression was correlated with decreased toxin-stimulated lysosome formation and decreased cytosolic levels of iota toxin. These findings indicated that expression of CD44 drives iota toxin resistance through inhibition of endocytosis in breast cancer cells, a role not previously defined for CD44. Moreover, tamoxifen-resistant breast cancer cells exhibited robust expression of LSR and were highly sensitive to iota-induced cytotoxicity.ConclusionsCollectively, these data are the first to show that iota toxin has the potential to be an effective, targeted therapy for breast cancer.

Highlights

Translational exploration of bacterial toxins has come to the forefront of research given their potential as a chemotherapeutic tool
Lipolysis stimulated lipoprotein receptor (LSR) was detectable in the majority of luminal and basal-like subtypes, while the claudin-low lines had little to no expression of LSR (Figure 1A,B)
Reintroduction of CD44 resulted in a significant decrease in detectable Ib when compared to the control or LSRoverexpressing cells. This indicates that expression of CD44 in breast cancer cells confers iota toxin resistance by inhibiting endocytosis, a role not previously defined for CD44

Summary

Introduction

Translational exploration of bacterial toxins has come to the forefront of research given their potential as a chemotherapeutic tool. We recently demonstrated that LSR expression correlates with estrogen receptor positive breast cancers and that LSR signaling directs aggressive, tumor-initiating cell behaviors. The claudinlow subtype is characterized by low gene expression of junction and adhesion proteins that include claudins 3, 4 and 7, as well as E-cadherin [3]. While these tumors initially respond to chemotherapy, there is a high risk of recurrence and disease progression, leading to poor patient survival [9,10,11]

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