IRF7 suppresses hematopoietic regeneration under stress via CXCR4

Insight into the role of IRF7 in skin and connective tissue diseases

Interferons (IFNs) are signalling proteins primarily involved in initiating innate immune responses against pathogens and promoting the maturation of immune cells. Interferon Regulatory Factor 7 (IRF7) plays a pivotal role in the IFNs signalling pathway. The activation process of IRF7 is incited by exogenous or abnormal nucleic acids, which is followed by the identification via pattern recognition receptors (PRRs) and the ensuing signalling cascades. Upon activation, IRF7 modulates the expression of both IFNs and inflammatory gene regulation. As a multifunctional transcription factor, IRF7 is mainly expressed in immune cells, yet its presence is also detected in keratinocytes, fibroblasts, and various dermal cell types. In these cells, IRF7 is critical for skin immunity, inflammation, and fibrosis. IRF7 dysregulation may lead to autoimmune and inflammatory skin conditions, including systemic scleroderma (SSc), systemic lupus erythematosus (SLE), Atopic dermatitis (AD) and Psoriasis. This comprehensive review aims to extensively elucidate the role of IRF7 and its signalling pathways in immune cells and keratinocytes, highlighting its significance in skin-related and connective tissue diseases.

Direct TLR2 signaling through mTOR and TBK1 induces C/EBPβ and IRF7-dependent macrophage differentiation in hematopoietic stem and progenitor cells

During an infection, hematopoiesis is altered to increase the output of mature myeloid cells to fight off the pathogen. Despite convincing evidence that hematopoietic stem and progenitor cells (HSPCs) can sense pathogens directly, more mechanistic studies are needed to reveal whether pattern recognition receptor (PRR) signaling initiates myeloid development directly, or indirectly through the production of cytokines by HSPCs that can act in an autocrine/paracrine manner, or by a combination of both direct and indirect mechanisms. In this study, we have used an in vitro model of murine HSPCs to study myeloid differentiation in response to the TLR2 ligand Pam3CSK4 and showed that, besides indirect mechanisms, TLR2 stimulation of HSPCs promotes myelopoiesis directly by initiating a MyD88-dependent signaling. This direct differentiation program involves a combined activation of the transcription factors PU.1, C/EBPβ and IRF7 driven by TBK1 and PI3K/mTOR. Notably, downstream of MyD88, the activated TBK1 kinase can activate mTOR directly and IRF7 induction is mediated by both TBK1 and mTOR. TLR2 signaling also induces NF-κB dependent IL-6 production that may further induce indirect myeloid differentiation. Our results have identified the direct signaling pathways and the transcription factors involved in macrophage development from HSPCs in response to TLR2 engagement, a critical process to trigger a rapid immune response during infection.

Inhibition of BTK and PI3Kδ impairs the development of human JMML stem and progenitor cells

Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasia that lacks effective targeted chemotherapies. Clinically, JMML manifests as monocytic leukocytosis, splenomegaly with consequential thrombocytopenia. Most commonly, patients have gain-of-function (GOF) oncogenic mutations in PTPN11 (SHP2), leading to Erk and Akt hyperactivation. Mechanism(s) involved in co-regulation of Erk and Akt in the context of GOF SHP2 are poorly understood. Here, we show that Bruton's tyrosine kinase (BTK) is hyperphosphorylated in GOF Shp2-bearing cells and utilizes B cell adaptor for PI3K to cooperate with p110δ, the catalytic subunit of PI3K. Dual inhibition of BTK and p110δ reduces the activation of both Erk and Akt. In vivo, individual targeting of BTK or p110δ in a mouse model of human JMML equally reduces monocytosis and splenomegaly; however, the combined treatment results in a more robust inhibition and uniquely rescues anemia and thrombocytopenia. RNA-seq analysis of drug-treated mice showed a profound reduction in the expression of genes associated with leukemic cell migration and inflammation, leading to correction in the infiltration of leukemic cells in the lung, liver, and spleen. Remarkably, in a patient derived xenograft model of JMML, leukemia-initiating stem and progenitor cells were potently inhibited in response to the dual drug treatment.

Loss of IRF7 accelerates acute myeloid leukemia progression and induces VCAM1-VLA-4 mediated intracerebral invasion

Interferon regulatory factor 7 (IRF7) is widely studied in inflammatory models. Its effects on malignant progression have been documented mainly from the perspective of the microenvironment. However, its role in leukemia has not been established. Here we used MLL-AF9-induced acute myeloid leukemia (AML) mouse models with IRF7 knockout or overexpression and xenograft mouse models to explore the intrinsic effects of IRF7 in AML. AML-IRF7^−/− mice exhibited accelerated disease progression with intracerebral invasion of AML cells. AML-IRF7^−/− cells showed increased proliferation and elevated leukemia stem cell (LSC) levels. Overexpression of IRF7 in AML cells decreased cell proliferation and LSC levels. Furthermore, overexpression of transforming growth-interacting factor 1 (TGIF1) rescued the enhanced proliferation and high LSC levels caused by IRF7 deficiency. Moreover, upregulation of vascular cell adhesion molecule 1 (VCAM1), which correlated with high LSC levels, was detected in AML-IRF7^−/− cells. In addition, blocking VCAM1-very late antigen 4 (VLA-4) axis delayed disease progression and attenuated intracerebral invasion of AML cells. Therefore, our findings uncover the intrinsic effects of IRF7 in AML and provide a potential strategy to control central nervous system myeloid leukemia.

Deletion of Wild-type p53 Facilitates Bone Metastatic Function by Blocking the AIP4 Mediated Ligand-Induced Degradation of CXCR4

Background: Management of patients with prostate cancer and bone metastatic disease remains a major clinical challenge. Loss or mutation of p53 has been identified to be involved in the tumor progression and metastasis. Nevertheless, direct evidence of a specific role for wild-type p53 (wt-p53) in bone metastasis and the mechanism by which this function is mediated in prostate cancer remain obscure.

Methods: The expression and protein levels of wt-53, AIP4, and CXCR4 in prostate cancer cells and clinical specimens were assessed by real-time PCR, immunohistochemistry and western blot analysis. The role of wt-p53 in suppressing aggressive and metastatic tumor phenotypes was assessed using in vitro transwell chemotaxis, wound healing, and competitive colocalization assays. Furthermore, whether p53 deletion facilitates prostate cancer bone-metastatic capacity was explored using an in vivo bone-metastatic model. The mechanistic model of wt-p53 in regulating gene expression was further explored by a luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay.

Results: Our findings revealed that wt-p53 suppressed the prostate cancer cell migration rate, chemotaxis and attachment toward the osteoblasts in vitro. The bone-metastatic model showed that deletion of wt-p53 remarkably increased prostate cancer bone-metastatic capacity in vivo. Mechanistically, wt-p53 could induce the ligand-induced degradation of the chemokine receptor CXCR4 by transcriptionally upregulating the expression of ubiquitin ligase AIP4. Treatment with the CXCR4 inhibitor AMD3100 or transduction of the AIP4 plasmid abrogated the pro-bone metastasis effects of TP53 deletion.

Conclusion: Wt-p53 suppresses the metastasis of prostate cancer cells to bones by regulating the CXCR4/CXCL12 activity in the tumor cells/bone marrow microenvironment interactions. Our findings suggest that targeting the wt-p53/AIP4/CXCR4 axis might be a promising therapeutic strategy to manage prostate cancer bone metastasis.