The increase in mucin exocytosis and the upregulation of MUC genes encoding for membrane-bound mucins induced by the thiol-activated exotoxin listeriolysin O is a host cell defence response that inhibits the cell-entry of Listeria monocytogenes.

In vivo Listeria monocytogenes infection results in the massive release of mucus by goblet cells into the lumen of the intestine. We have previously reported that apical infection by L. monocytogenes is followed by listeriolysin O (LLO)-dependent stimulation of mucus exocytosis, and the upregulation of the MUC genes. Here, we report that L. monocytogenes EGD wild-type bacteria enter cultured human polarized, mucin-secreting, HT29-MTX cells apically by an InlA-dependent mechanism. The LLO-induced increase in mucin secretion together with an increase in transcription of the MCU4 and MUC12 genes encoding for membrane-bound mucins, results in the inhibition of the cell-entry of L. monocytogenes into mucin-secreting, HT29-MTX cells. Moreover, we report that sialic acid residues in mucins are crucial for the inhibition of L. monocytogenes internalization. Based on these findings, we suggest that the LLO-induced mucin exocytosis and upregulation of the MUC genes encoding for membrane-bound mucins constitute a host cell defence response that inhibits the cell-entry of L. monocytogenes.