Inhibition of EGFR/ErbB does not protect against C. difficile toxin B

Clostridioides difficile is a common cause of diarrhea and mortality, especially in immunosuppressed and hospitalized patients. C. difficile is a toxin-mediated disease, but the host cell receptors for C. difficile toxin B (TcdB) have only recently been revealed. Emerging data suggest TcdB interacts with receptor tyrosine kinases during infection. In particular, TcdB can elicit Epidermal Growth Factor Receptor (EGFR) transactivation in human colonic epithelial cells. The mechanisms for this function are not well understood, and the involvement of other receptors in the EGFR family of Erythroblastic Leukemia Viral Oncogene Homolog (ErbB) receptors remains unclear. Furthermore, in an siRNA-knockdown screen for protective genes involved with TcdB toxin pathogenesis, we show ErbB2 and ErbB3 loss resulted in increased cell viability. We hypothesize TcdB induces the transactivation of EGFR and/or ErbB receptors as a component of its cell-killing mechanism. Here, we show in vivo intrarectal instillation of TcdB in mice leads to phosphorylation of ErbB2 and ErbB3. However, immunohistochemical staining for phosphorylated ErbB2 and ErbB3 indicated no discernible difference between control and TcdB-treated mice for epithelial phospho-ErbB2 and phospho-ErbB3. Human colon cancer cell lines (HT29, Caco-2) exposed to TcdB were not protected by pre-treatment with lapatinib, an EGFR/ErbB2 inhibitor. Similarly, lapatinib pre-treatment failed to protect normal human colonoids from TcdB-induced cell death. Neutralizing antibodies against mouse EGFR failed to protect mice from TcdB intrarectal instillation as measured by edema, inflammatory infiltration, and epithelial injury. Our findings suggest TcdB-induced colonocyte cell death does not require EGFR/ErbB receptor tyrosine kinase activation.