LL-37 Inhibits EV71 Infection by Upregulating STAC via the EGFR-ERK Signaling Pathway

LL-37, a 37-amino acid human-derived antimicrobial peptide, was shown in our earlier clinical study to shorten the negative conversion time of the Omicron BA.5.1.3 variant of SARS-CoV-2. In this work, we investigated the broad mechanism of LL-37 by examining its inhibitory effect on non-enveloped virus Enterovirus 71 (EV71). LL-37 treatment dose-dependently reduced EV71 viral RNA abundance, suppressed virus-encoded protein expression, and decreased infectious titers, acting predominantly at a post-entry stage of the viral life cycle. Transcriptomic analysis revealed that the SH3 and cysteine-rich domain protein (Stac) was uniquely upregulated by LL-37 irrespective of EV71 infection. Short hairpin RNA (shRNA)-mediated Stac silencing significantly enhanced EV71 infection, while Stac overexpression markedly reduced it. Furthermore, we found that LL-37 activates the EGFR-ERK signaling pathway, leading to time-dependent upregulation of Stac expression. These findings uncover a novel host-directed mechanism by which LL-37 combats EV71 infection and suggests a potential therapeutic use of LL-37 against non-enveloped viral disease.