Cooperative Regulation of the Induction of the Novel Antibacterial Listericin by Peptidoglycan Recognition Protein LE and the JAK-STAT Pathway

Intracellular bacteria cause serious infectious diseases such as tuberculosis, shigellosis, and listeriosis. The Drosophila peptidoglycan recognition protein (PGRP)-LE functions as an important host pattern recognition receptor against intracellular bacteria such as Listeria monocytogenes. One PGRP-LE-mediated intracellular response against L. monocytogenes infection is the induction of autophagy, a conserved intracellular degradation system. Here, to further elucidate PGRP-LE-mediated intracellular innate immune responses, we performed a strategic microarray analysis and identified the Listericin gene, whose expression is induced in response to L. monocytogenes infection in a PGRP-LE-dependent manner. RNA interference and overexpression experiments demonstrated that Listericin gene induction is cooperatively regulated by PGRP-LE and the JAK-STAT (Janus kinase-signal transducers and activators of transcription) pathway. An in vitro cell culture assay showed that Listericin is secreted as processed forms and suppresses the growth of L. monocytogenes and Gram-negative bacteria. A colony formation unit assay clearly demonstrated that induction of the Listericin gene suppresses not only the growth of L. monocytogenes but also the growth of Gram-negative bacteria in vivo. Based on these findings, we propose that the Listericin gene encodes a novel antibacterial peptide-like protein whose induction is cooperatively regulated by PGRP-LE and the JAK-STAT pathway.