Abstract
Pleckstrin homology-like domain, family A, member 1 (PHLDA1) has been reported to be expressed in many mammalian tissues and cells. However, the functions and exact mechanisms of PHLDA1 remain unclear. In this study, we found that PHLDA1 expression was significantly altered in macrophages after exposure to lipopolysaccharide (LPS) in vitro, suggesting that PHLDA1 may be involved in the regulation of TLR4 signaling pathway activated by LPS. PHLDA1 attenuated the production of LPS-stimulated proinflammatory cytokines (TNF-α, IL-6, and IL-1β). Further research showed that the phosphorylation levels of some important signal molecules in TLR4/MyD88-mediated MAPK and NF-κB signaling pathways were reduced by PHLDA1, which in turn impaired the transcription factors NF-κB and AP1 nuclear translocation and their responsive element activities. Furthermore, we found that PHLDA1 repressed LPS-induced proinflammatory cytokine production via binding to Tollip which restrained TLR4 signaling pathway. A mouse model of endotoxemia was established to confirm the above similar results. In brief, our findings demonstrate that PHLDA1 is a negative regulator of LPS-induced proinflammatory cytokine production by Tollip, suggesting that PHLDA1 plays an anti-inflammatory role through inhibiting the TLR4/MyD88 signaling pathway with the help of Tollip. PHLDA1 may be a novel therapeutic target in treating endotoxemia.
Highlights
Pleckstrin homology-like domain, family A, member 1 (PHLDA1), which is called T-cell deathassociated gene 51 (TDAG51), was first found to induce apoptosis through cross-linking T-cell receptor (TCR) signaling pathway to Fas expression [1]
The results showed that different concentrations of LPS increased significantly PHLDA1 expression in RAW264.7 cells, but two higher concentrations (1 and 10 mg/ml) of LPS did not increase further the expression level of PHLDA1 after PHLDA1 expression reached the peak level with 0.1 mg/ml of LPS treatment for 12 h (Figure 1A)
To explore the kinetics of the regulation of PHLDA1 expression in RAW264.7 cells induced by LPS, we tested PHLDA1 expression in RAW264.7 cells treated with LPS for different time periods with Western blot
Summary
Pleckstrin homology-like domain, family A, member 1 (PHLDA1), which is called T-cell deathassociated gene 51 (TDAG51), was first found to induce apoptosis through cross-linking T-cell receptor (TCR) signaling pathway to Fas expression [1]. Numerous studies have confirmed PHLDA1 expression at the protein and mRNA levels in many mammalian tissues, including the brain, endocrine tissues, and proximal digestive tract. PHLDA1 was found to express in many types of cancer, such as brain, liver, bladder, and lung cancer [2, 4, 5]. Studies have suggested that PHLDA1 is involved in many biological processes, such as cell proliferation, cell differentiation, cell death, cancer metastasis, epithelial– mesenchymal transition, and cancer stem cell properties [6,7,8,9]. PHLDA1 has gotten increasing attention over the past 20 years, its role in endotoxemia remains to be elucidated
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