The Human Lysyl-tRNA Synthetase Secreted by Shiga Toxins Triggers Proinflammatory Response to the Toxin-sensitive Cells

Abstract

Shiga toxin producing Escherichia coli (STEC) strains are foodborne pathogens that cause fatal systemic complications such as hemolytic uremic syndrome and central nervous system (CNS). In patients infected with STEC, inflammatory responses are involved in reducing or exacerbating disease severity upon infections with the pathogen and require the participation of cytokine/chemokine in concert of leukocytes on Stxs-induced intestinal, renal, and CNS vascular lesions. To date, although numerous studies have been reported defining the proinflammatory response to Shiga toxin type 1 (Stx1) or Shiga toxin type 2 (Stx2) in in vivo and in vitro, no coherent mechanism has been proposed to explain the dynamic immune regulation involving cytokines or unknown mediators of inflammation during intoxication. A complex of aminoacyl-tRNA synthetases, known as Multi-aminoacyl-tRNA synthetase complex (MSC), is only founded in higher organisms such as yeast, zebra-fish, mouse, and human. In human, MSC is composed of eight aminoacyl-tRNA synthetases and three axillary proteins. It is well known that each aminoacyl-tRNA synthetases has noncanonical functions such as immune response, tumorigenesis, angiogenesis, and inflammatory response. Classical role of human lysyl-tRNA synthetase (KRS) within MSC is to support translational regulation. Otherwise, KRS also has been known that cytosolic KRS can regulate transcriptional activity of transcription factor MITF and USF2. Furthermore, the form of secreted KRS engages in secondary cellular function triggering inflammatory response. However, the function of KRS against infection of human pathogenic bacteria was poorly understood. This study identified the release of KRS to the extracellular space from the Stx1 or Stx2-treated human cervical cancer cells (HeLa) or macrophage-like THP-1 cells (D-THP-1). As I predicted, incubations of the D-THP-1 cells with enzymatic deficient Stxs were not capable of secreting KRS into the media. Furthermore, neither Stx1 nor Stx2 induced transcription of KRS mRNA and nucleus translocation. Unlike KRS, aminoacyl-tRNA synthetase complex-interacting multifunctional protein 2 (AIMP2), known as cytosolic binding partner of KRS, remained in cytosol without extracellular secretion when it is exposed to Stx2. Furthermore, addition of the exogenous KRS or co-treatment of KRS with Stxs activated secretion of inflammatory cytokines including IL-1β or TNF-α and chemokines including IL-8 or MIP1α in autocrine and paracrine manner. To support the pathogenesis mechanisms of Stxs associated with KRS, mouse model following the administration with Stx2 LD50 (10 ng/kg) demonstrated that the survival rate from the intoxicated KRS-hetero knockdown mice was significantly higher than that of the wild-type mice. In conclusion, this study implicated that KRS may be a key player to mediate proinflammatory signal transductions in susceptible host infected with STEC.