LKB1-MARK2 signalling mediates lipopolysaccharide-induced production of cytokines in mouse macrophages

SARS-CoV-2-derived protein Orf9b enhances MARK2 activity via interaction with the autoinhibitory KA1 domain

Microtubule affinity-regulating kinase 2 (MARK2) is a Ser/Thr protein kinase that regulates cell polarity and immune responses. Here, we report that Orf9b, one of the accessory proteins encoded in the SARS-CoV-2 genome, increases MARK2 activity via interaction with the autoinhibitory KAI domain. We found that co-expression of Orf9b enhances the kinase activity of MARK2 in HEK293 cells. Orf9b does not bind to or enhance the activity of the mutant form of MARK2 lacking the KA1 domain. Orf9b lowers inhibitory phosphorylation of MARK2 at T595 while mutation experiments indicate that this site is dispensable for Orf9b-mediated enhancement of MARK2 activity. Our results suggest that Orf9b enhances MARK2 activity by binding the autoinhibitory KA1 domain, which closely interacts with the kinase domain.

Navigating the Maze of Kinases: CaMK-like Family Protein Kinases and Their Role in Atherosclerosis

Circulating low-density lipoprotein (LDL) levels are a major risk factor for cardiovascular diseases (CVD), and even though current treatment strategies focusing on lowering lipid levels are effective, CVD remains the primary cause of death worldwide. Atherosclerosis is the major cause of CVD and is a chronic inflammatory condition in which various cell types and protein kinases play a crucial role. However, the underlying mechanisms of atherosclerosis are not entirely understood yet. Notably, protein kinases are highly druggable targets and represent, therefore, a novel way to target atherosclerosis. In this review, the potential role of the calcium/calmodulin-dependent protein kinase-like (CaMKL) family and its role in atherosclerosis will be discussed. This family consists of 12 subfamilies, among which are the well-described and conserved liver kinase B1 (LKB1) and 5' adenosine monophosphate-activated protein kinase (AMPK) subfamilies. Interestingly, LKB1 plays a key role and is considered a master kinase within the CaMKL family. It has been shown that LKB1 signaling leads to atheroprotective effects, while, for example, members of the microtubule affinity-regulating kinase (MARK) subfamily have been described to aggravate atherosclerosis development. These observations highlight the importance of studying kinases and their signaling pathways in atherosclerosis, bringing us a step closer to unraveling the underlying mechanisms of atherosclerosis.

LKB1 regulates autophagy through AMPK/TOR signaling pathway to alleviate the damage caused by Vibrio alginolyticus infection

LKB1 (liver kinase B1) is a key upstream kinase of AMPK and plays an important role in various cellular activities. While the function and mechanism of LKB1 have been widely reported in the study of tumor, there are few reports on its role in bacterial infectious diseases, especially in shrimp. In the present study, molecular characterization revealed that LvLKB1 has an open reading frame (ORF) of 1266 bp encoding 421 amino acids with a molecular weight of about 48 KDa, including the kinase region, N-terminal regulatory domain and C-terminal regulatory domain. LvLKB1 in hepatopancreas and hemocytes was significantly upregulated after infection with Vibrio alginolyticus (V. alginolyticus). After silencing LvLKB1 gene in Litopenaeus vannamei (L. vannamei) and artificially infecting V. alginolyticus, the survival rate of L. vannamei was significantly decreased. Subsequently, it was found that the expression of inflammatory factors in hepatopancreas and hemocytes of shrimp was up-regulated, and the expression of lipid oxidation factors was decreased after silencing LKB1, leading to the phenomenon of lipid accumulation in hepatopancreas. In order to explore the mechanism, autophagy levels of shrimp were detected after silencing LKB1, which showed that autophagy levels in hepatopancreas and hemocytes were significantly reduced. Further studies conclusively showed that silencing LvLKB1 inhibited AMPK phosphorylation induced by V. alginolyticus infection, thereby activating TOR pathway and inhibiting autophagy in shrimp. These results indicate that LvLKB1 regulates autophagy through AMPK/TOR signaling pathway to alleviate the damage caused by V. alginolyticus infection.

Myeloid liver kinase B1 contributes to lung inflammation induced by lipoteichoic acid but not by viable Streptococcus pneumoniae

Background

Liver kinase B1 (Lkb1, gene name Stk11) functions as a tumor suppressor in cancer. Myeloid cell Lkb1 potentiates lung inflammation induced by the Gram-negative bacterial cell wall component lipopolysaccharide and in host defense during Gram-negative pneumonia. Here, we sought to investigate the role of myeloid Lkb1 in lung inflammation elicited by the Gram-positive bacterial cell wall component lipoteichoic acid (LTA) and during pneumonia caused by the Gram-positive respiratory pathogen Streptococcus pneumoniae (Spneu).

Methods

Alveolar and bone marrow derived macrophages (AMs, BMDMs) harvested from myeloid-specific Lkb1 deficient (Stk11-ΔM) and littermate control mice were stimulated with LTA or Spneu in vitro. Stk11-ΔM and control mice were challenged via the airways with LTA or infected with Spneu in vivo.

Results

Lkb1 deficient AMs and BMDMs produced less tumor necrosis factor (TNF)α upon activation by LTA or Spneu. During LTA-induced lung inflammation, Stk11-ΔM mice had reduced numbers of AMs in the lungs, as well as diminished cytokine release and neutrophil recruitment into the airways. During pneumonia induced by either encapsulated or non-encapsulated Spneu, Stk11-ΔM and control mice had comparable bacterial loads and inflammatory responses in the lung, with the exception of lower TNFα levels in Stk11-ΔM mice after infection with the non-encapsulated strain.

Conclusion

Myeloid Lkb1 contributes to LTA-induced lung inflammation, but is not important for host defense during pneumococcal pneumonia.

The current landscape of microRNAs (miRNAs) in bacterial pneumonia: opportunities and challenges

MicroRNAs (miRNAs), which were initially discovered in Caenorhabditis elegans, can regulate gene expression by recognizing cognate sequences and interfering with the transcriptional or translational machinery. The application of bioinformatics tools for structural analysis and target prediction has largely driven the investigation of certain miRNAs. Notably, it has been found that certain miRNAs which are widely involved in the inflammatory response and immune regulation are closely associated with the occurrence, development, and outcome of bacterial pneumonia. It has been shown that certain miRNA techniques can be used to identify related targets and explore associated signal transduction pathways. This enhances the understanding of bacterial pneumonia, notably for "refractory" or drug-resistant bacterial pneumonia. Although these miRNA-based methods may provide a basis for the clinical diagnosis and treatment of this disease, they still face various challenges, such as low sensitivity, poor specificity, low silencing efficiency, off-target effects, and toxic reactions. The opportunities and challenges of these methods have been completely reviewed, notably in bacterial pneumonia. With the continuous improvement of the current technology, the miRNA-based methods may surmount the aforementioned limitations, providing promising support for the clinical diagnosis and treatment of "refractory" or drug-resistant bacterial pneumonia.

LKB1 Regulates Vascular Macrophage Functions in Atherosclerosis

Liver kinase B1 (LKB1) is known to shape the regulation of macrophage function by participating in multiple processes including cell metabolism, growth, and polarization. However, whether LKB1 also affects the functional plasticity of macrophages in atherosclerosis has not attracted much attention. Abnormal macrophage function is a pathophysiological hallmark of atherosclerosis, characterized by the formation of foam cells and the maintenance of vascular inflammation. Mounting evidence supports that LKB1 plays a vital role in the regulation of macrophage function in atherosclerosis, including affecting lipid metabolism reprogramming, inflammation, endoplasmic reticulum stress, and autophagy in macrophages. Thus, decreased expression of LKB1 in atherosclerosis aggravates vascular injury by inducing excessive lipid deposition in macrophages and the formation of foam cells. To systematically understand the role and potential mechanism of LKB1 in regulating macrophage functions in atherosclerosis, this review summarizes the relevant data in this regard, hoping to provide new ideas for the prevention and treatment of atherosclerosis.

Vasorin deficiency leads to cardiac hypertrophy by targeting MYL7 in young mice

Vasorin (VASN) is an important transmembrane protein associated with development and disease. However, it is not clear whether the death of mice with VASN deficiency (VASN^-/- ) is related to cardiac dysfunction. The aim of this research was to ascertain whether VASN induces pathological cardiac hypertrophy by targeting myosin light chain 7 (MYL7). VASN^-/- mice were produced by CRISPR/Cas9 technology and inbreeding. PCR amplification, electrophoresis, real-time PCR and Western blotting were used to confirm VASN deficiency. Cardiac hypertrophy was examined by blood tests, histological analysis and real-time PCR, and key downstream factors were identified by RNA sequencing and real-time PCR. Western blotting, immunohistochemistry and electron microscopy analysis were used to confirm the downregulation of MYL7 production and cardiac structural changes. Our results showed that sudden death of VASN^-/- mice occurred 21-28 days after birth. The obvious increases in cardiovascular risk, heart weight and myocardial volume and the upregulation of hypertrophy marker gene expression indicated that cardiac hypertrophy may be the cause of death in young VASN^-/- mice. Transcriptome analysis revealed that VASN deficiency led to MYL7 downregulation, which induced myocardial structure abnormalities and disorders. Our results revealed a pathological phenomenon in which VASN deficiency may lead to cardiac hypertrophy by downregulating MYL7 production. However, more research is necessary to elucidate the underlying mechanism.

LKB1-MARK2 signalling mediates lipopolysaccharide-induced production of cytokines in mouse macrophages

Lipopolysaccharide (LPS) is an endotoxin involved in a number of acute and chronic inflammatory syndromes. Although LPS-induced signalling has been extensively studied, there are still mysteries remaining to be revealed. In the current study, we used high-throughput phosphoproteomics to profile LPS-initiated signalling and aimed to find novel mediators. A total of 448 phosphoproteins with 765 phosphorylation sites were identified, and we further validated that the phosphorylation of MARK2 on T208 was important for the regulation on LPS-induced CXCL15 (human IL-8 homolog), IL-1β, IL-6 and TNF-α release, in which LKB1 had a significant contribution. In summary, induction of cytokines by LPS in mouse macrophage is regulated by LKB1-MARK2 signals. Our study provides new clues for further exploring the underlying mechanisms of LPS-induced diseases, and new therapeutic approaches concerning bacterial infection may be derived from these findings.