AUTHOR=Ko Hye Jin , Patnaik Bharat Bhusan , Park Ki Beom , Kim Chang Eun , Baliarsingh Snigdha , Jang Ho Am , Lee Yong Seok , Han Yeon Soo , Jo Yong Hun 

TITLE=TmIKKε Is Required to Confer Protection Against Gram-Negative Bacteria, E. coli by the Regulation of Antimicrobial Peptide Production in the Tenebrio molitor Fat Body

JOURNAL=Frontiers in Physiology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.758862

DOI=10.3389/fphys.2021.758862

ISSN=1664-042X

ABSTRACT=<p>The inhibitor of nuclear factor-kappa B (NF-κB) kinase (IKK) is the core regulator of the NF-κB pathway against pathogenic invasion in vertebrates or invertebrates. IKKβ, -ε and -γ have pivotal roles in the Toll and immune deficiency (IMD) pathways. In this study, a homolog of IKKε (<italic>Tm</italic>IKKε) was identified from <italic>Tenebrio molitor</italic> RNA sequence database and functionally characterized for its role in regulating immune signaling pathways in insects. The <italic>TmIKKε</italic> gene is characterized by two exons and one intron comprising an open reading frame (ORF) of 2,196 bp that putatively encodes a polypeptide of 731 amino acid residues. <italic>Tm</italic>IKKε contains a serine/threonine protein kinases catalytic domain. Phylogenetic analysis established the close homology of <italic>Tm</italic>IKKε to <italic>Tribolium castaneum</italic> IKKε (<italic>Tc</italic>IKKε) and its proximity with other IKK-related kinases. The expression of <italic>TmIKKε</italic> mRNA was elevated in the gut, integument, and hemocytes of the last-instar larva and the fat body, Malpighian tubules, and testis of 5-day-old adults. <italic>TmIKKε</italic> expression was significantly induced by <italic>Escherichia coli</italic>, <italic>Staphylococcus aureus</italic>, and <italic>Candida albicans</italic> challenge in whole larvae and tissues, such as hemocytes, gut, and fat body. The knockdown of the <italic>TmIKKε</italic> messenger RNA (mRNA) expression significantly reduced the survival of the larvae against microbial challenges. Further, we investigated the induction patterns of 14 <italic>T. molitor</italic> antimicrobial peptides (AMPs) genes in <italic>TmIKKε</italic> gene-silencing model after microbial challenges. While in hemocytes, the transcriptional regulation of most AMPs was negatively regulated in the gut and fat body tissue of <italic>T. molitor</italic>, AMPs, such as <italic>TmTenecin 1</italic>, <italic>TmTenecin 4</italic>, <italic>TmDefensin</italic>, <italic>TmColeoptericin A</italic>, <italic>TmColeoptericin B</italic>, <italic>TmAttacin 1a</italic>, and <italic>TmAttacin 2</italic>, were positively regulated in <italic>TmIKKε</italic>-silenced individuals after microbial challenge. Collectively, the results implicate <italic>TmIKKε</italic> as an important factor in antimicrobial innate immune responses in <italic>T. molitor</italic>.</p>