Conditional PDK1 Ablation Promotes Epidermal and T-Cell-Mediated Dysfunctions Leading to Inflammatory Skin Disease

The effect of PDK1 in maintaining immune cell development and function

3-phosphoinositide-dependent protein kinase 1 (PDK1) exhibits a substantial influence on immune cell development by establishing a vital connection between PI3K and downstream mTOR signaling cascades. However, it remains unclear whether PDK1 signaling affects the homeostasis and functionality of immune cells. To explore the impact of PDK1 on different immune cells within immune organs, transgenic mouse strains with lymphocyte-specific PDK1 knockout (PDK1fl/fl CD2-Cre) were generated. Unlike wild-type (WT) mice, lymphocyte-specific PDK1 knockout (KO) mice exhibited thymic atrophy, elevated percentages of CD8+ T cells and neutrophils, and reduced proportions of γδ T cells, B cells, and NK cells in the spleen. Functional analysis revealed elevated release of IFN-γ and IL-17A by T cells in PDK1 KO mice, contrasting with diminished levels observed in γδ T cells and Treg cells. Furthermore, the activation, cytotoxicity, and migratory potential of γδ T cells in PDK1 KO mice are heightened, indicating a potential association with the regulation of the mTOR signaling pathway. To conclude, the findings of this research demonstrated that specific knockout of PDK1 in lymphocytes hindered T cell development in the thymus and exhibited a substantial influence on immune cell homeostasis in the spleen and lymph nodes.

Precise genome-editing in human diseases: mechanisms, strategies and applications

Precise genome-editing platforms are versatile tools for generating specific, site-directed DNA insertions, deletions, and substitutions. The continuous enhancement of these tools has led to a revolution in the life sciences, which promises to deliver novel therapies for genetic disease. Precise genome-editing can be traced back to the 1950s with the discovery of DNA's double-helix and, after 70 years of development, has evolved from crude in vitro applications to a wide range of sophisticated capabilities, including in vivo applications. Nonetheless, precise genome-editing faces constraints such as modest efficiency, delivery challenges, and off-target effects. In this review, we explore precise genome-editing, with a focus on introduction of the landmark events in its history, various platforms, delivery systems, and applications. First, we discuss the landmark events in the history of precise genome-editing. Second, we describe the current state of precise genome-editing strategies and explain how these techniques offer unprecedented precision and versatility for modifying the human genome. Third, we introduce the current delivery systems used to deploy precise genome-editing components through DNA, RNA, and RNPs. Finally, we summarize the current applications of precise genome-editing in labeling endogenous genes, screening genetic variants, molecular recording, generating disease models, and gene therapy, including ex vivo therapy and in vivo therapy, and discuss potential future advances.

Master kinase PDK1 in tumorigenesis

3-phosphoinositide-dependent protein kinase 1 (PDK1) is considered as master kinase regulating AGC kinase family members such as AKT, SGK, PLK, S6K and RSK. Although autophosphorylation regulates PDK1 activity, accumulating evidence suggests that PDK1 is manipulated by many other mechanisms, including S6K-mediated phosphorylation, and the E3 ligase SPOP-mediated ubiquitination and degradation. Dysregulation of these upstream regulators or downstream signals involves in cancer development, as PDK1 regulating cell growth, metastasis, invasion, apoptosis and survival time. Meanwhile, overexpression of PDK1 is also exposed in a plethora of cancers, whereas inhibition of PDK1 reduces cell size and inhibits tumor growth and progression. More importantly, PDK1 also modulates the tumor microenvironments and markedly influences tumor immunotherapies. In summary, we comprehensively summarize the downstream signals, upstream regulators, mouse models, inhibitors, tumor microenvironment and clinical treatments for PDK1, and highlight PDK1 as a potential cancer therapeutic target.

T cell specific deletion of IRF4 with Ox40-Cre impairs effector and memory T cell responses in heart transplantation

BACKGROUND

IRF4 is the pioneer factor for effector T cell maturation. Here we investigated the function of IRF4 in maintaining OX40-related T cell responses following alloantigen activation in a mouse heart transplantation model.

METHODS

Irf4^flox/flox mice were bred with Ox40^cre/+ mice to generate Irf4^flox/floxOx40^cre/+ mice. Wild type C57BL/6, Irf4^flox/floxOx40^cre/+ mice were transplanted with BALB/c heart allografts, with or without BALB/c skin-sensitization. CD4⁺ TEa T cells co-transfer experiments and flow cytometric analysis were conducted to investigate the amount of CD4⁺ T cells and the percentage of the T effector subset.

RESULTS

Irf4^flox/floxOx40^cre/+ and Irf4^flox/floxOx40^cre/+ TEa mice were constructed successfully. IRF4 ablation in activated OX40-mediated alloantigen specific CD4⁺ TEa T cells reduced effector T cell differentiation (CD44^hiCD62L^lo, Ki67, IFN-γ), which caused long-term allograft survival (> 100 d) in the chronic rejection model. In the donor skin-sensitized heart transplantation model, the formation and function of alloantigen-specific memory CD4⁺ TEa cells were also impaired in Irf4^flox/floxOx40^cre/+ mice. Additionally, deletion of IRF4 after T cell activation in Irf4^flox/floxOx40^cre/+ mice reduced T cell reactivation in vitro.

CONCLUSIONS

IRF4 ablation after OX40-related T cell activation could reduce effector and memory T cell formation and inhibit their function in response to alloantigen stimulation. These findings could have significant implications in targeting activated T cells to induce transplant tolerance.

Ox40-Cre-mediated deletion of BRD4 reveals an unexpected phenotype of hair follicle stem cells in alopecia

BRD4 is a bromodomain extraterminal domain family member and functions primarily as a chromatin reader regulating genes involved in cell-fate decisions. Here, we bred Brd4fl/fl Ox40-Cre mice in which Brd4 was conditionally deleted in OX40-expressing cells to examine the role of BRD4 in regulating immune responses. We found that the Brd4fl/fl Ox40-Cre mice developed profound alopecia and dermatitis, while other organs and tissues were not affected. Surprisingly, lineage-tracing experiments using the Rosa26fl/fl-Yfp mice identified a subset of hair follicle stem cells (HFSCs) that constitutively express OX40, and deletion of Brd4 specifically in such HFSCs resulted in cell death and a complete loss of skin hair growth. We also found that death of HFSCs triggered massive activation of the intradermal γδ T cells, which induced epidermal hyperplasia and dermatitis by producing the inflammatory cytokine IL-17. Interestingly, deletion of Brd4 in Foxp3+ Tregs, which also constitutively express OX40, compromised their suppressive functions, and this, in turn, contributed to the enhanced activation of γδ T cells, as well as the severity of dermatitis and hair follicle destruction. Thus, our data demonstrate an unexpected role of BRD4 in regulating skin follicle stem cells and skin inflammation.

The kinase PDK1 is critical for promoting T follicular helper cell differentiation

The kinase PDK1 is a crucial regulator for immune cell development by connecting PI3K to downstream AKT signaling. However, the roles of PDK1 in CD4⁺ T cell differentiation, especially in T follicular helper (Tfh) cell, remain obscure. Here we reported PDK1 intrinsically promotes the Tfh cell differentiation and germinal center responses upon acute infection by using conditional knockout mice. PDK1 deficiency in T cells caused severe defects in both early differentiation and late maintenance of Tfh cells. The expression of key Tfh regulators was remarkably downregulated in PDK1-deficient Tfh cells, including Tcf7, Bcl6, Icos, and Cxcr5. Mechanistically, ablation of PDK1 led to impaired phosphorylation of AKT and defective activation of mTORC1, resulting in substantially reduced expression of Hif1α and p-STAT3. Meanwhile, decreased p-AKT also suppresses mTORC2-associated GSK3β activity in PDK1-deficient Tfh cells. These integrated effects contributed to the dramatical reduced expression of TCF1 and ultimately impaired the Tfh cell differentiation.

MiR-613 suppressed the laryngeal squamous cell carcinoma progression through regulating PDK1

MicroRNAs (miRNAs) are aberrantly expressed in several tumors and play important role in tumorigenesis. However, little is known about the role of miR-613 in laryngeal squamous cell carcinoma (LSCC). We determined the expression of miR-613 in a panel of 30 LSCC specimens. Compared with the adjacent normal samples, 20 cases of LSCC tissues exhibited decreased expression of miR-613. The average expression of miR-613 in LSCC tissues was lower than in normal samples. Moreover, we demonstrated that exogenous expression of miR-613 suppressed LSCC cell proliferation, invasion, and blocked G1/S phase transition. We identified that 3-phosphoinositide-dependent protein kinase-1 (PDK1) was a direct target gene of miR-613 in LSCC cell. Overexpression of miR-613 suppressed PDK1 expression in LSCC cell. Furthermore, we demonstrated that PDK1 was upregulated in LSCC tissues. MiR-613 expression was inversely correlated with the expression of PDK1 in LSCC tissues. Moreover, we showed that PDK1 was involved in the miR-613-mediated cancer suppression of LSCC cell. These results suggested that miR-613 played as a tumor suppressor gene in LSCC partly by inhibiting PDK1 expression.

Phosphoinositide 3-Kinase-Dependent Signalling Pathways in Cutaneous Squamous Cell Carcinomas

Cutaneous squamous cell carcinoma (cSCC) derives from keratinocytes in the epidermis and accounts for 15–20% of all cutaneous malignancies. Although it is usually curable by surgery, 5% of these tumours metastasise leading to poor prognosis mostly because of a lack of therapies and validated biomarkers. As the incidence rate is rising worldwide it has become increasingly important to better understand the mechanisms involved in cSCC development and progression in order to develop therapeutic strategies. Here we discuss some of the evidence indicating that activation of phosphoinositide 3-kinases (PI3Ks)-dependent signalling pathways (in particular the PI3Ks targets Akt and mTOR) has a key role in cSCC. We further discuss available data suggesting that inhibition of these pathways can be beneficial to counteract the disease. With the growing number of different inhibitors currently available, it would be important to further investigate the specific contribution of distinct components of the PI3Ks/Akt/mTOR pathways in order to identify the most promising molecular targets and the best strategy to inhibit cSCC.

Serine/Threonine Kinase 3-Phosphoinositide-Dependent Protein Kinase-1 (PDK1) as a Key Regulator of Cell Migration and Cancer Dissemination

Dissecting the cellular signaling that governs the motility of eukaryotic cells is one of the fundamental tasks of modern cell biology, not only because of the large number of physiological processes in which cell migration is crucial, but even more so because of the pathological ones, in particular tumor invasion and metastasis. Cell migration requires the coordination of at least four major processes: polarization of intracellular signaling, regulation of the actin cytoskeleton and membrane extension, focal adhesion and integrin signaling and contractile forces generation and rear retraction. Among the molecular components involved in the regulation of locomotion, the phosphatidylinositol-3-kinase (PI3K) pathway has been shown to exert fundamental role. A pivotal node of such pathway is represented by the serine/threonine kinase 3-phosphoinositide-dependent protein kinase-1 (PDPK1 or PDK1). PDK1, and the majority of its substrates, belong to the AGC family of kinases (related to cAMP-dependent protein kinase 1, cyclic Guanosine monophosphate-dependent protein kinase and protein kinase C), and control a plethora of cellular processes, downstream either to PI3K or to other pathways, such as RAS GTPase-MAPK (mitogen-activated protein kinase). Interestingly, PDK1 has been demonstrated to be crucial for the regulation of each step of cell migration, by activating several proteins such as protein kinase B/Akt (PKB/Akt), myotonic dystrophy-related CDC42-binding kinases alpha (MRCKα), Rho associated coiled-coil containing protein kinase 1 (ROCK1), phospholipase C gamma 1 (PLCγ1) and β3 integrin. Moreover, PDK1 regulates cancer cell invasion as well, thus representing a possible target to prevent cancer metastasis in human patients. The aim of this review is to summarize the various mechanisms by which PDK1 controls the cell migration process, from cell polarization to actin cytoskeleton and focal adhesion regulation, and finally, to discuss the evidence supporting a role for PDK1 in cancer cell invasion and dissemination.

Coenzyme Q10 Suppresses TNF-α-Induced Inflammatory Reaction In Vitro and Attenuates Severity of Dermatitis in Mice

Anti-oxidant coenzyme Q10 (Co-Q10) is commonly used in clinic. Recently, Co-Q10 was reported to antagonize TNF-α-induced inflammation and play a protective role in various inflammatory conditions. However, its role in dermatitis is unknown. Herein, RAW264.7 macrophage cell line was cultured with stimulation of TNF-α, and administration of Co-Q10 alleviated TNF-α-mediated inflammatory reaction in vitro. Furthermore, oxazolone-induced dermatitis mice model was established, and treatment of Co-Q10 markedly attenuated dermatitis phenotype in this mice model. Moreover, the protective role of Co-Q10 in vitro and in dermatitis was probably due to its repression on NF-κB signaling. Collectively, Co-Q10 may represent a potential molecular target for prevention and treatment of inflammatory skin diseases.

Cre Recombinase and Other Tyrosine Recombinases

Tyrosine-type site-specific recombinases (T-SSRs) have opened new avenues for the predictable modification of genomes as they enable precise genome editing in heterologous hosts. These enzymes are ubiquitous in eubacteria, prevalent in archaea and temperate phages, present in certain yeast strains, but barely found in higher eukaryotes. As tools they find increasing use for the generation and systematic modification of genomes in a plethora of organisms. If applied in host organisms, they enable precise DNA cleavage and ligation without the gain or loss of nucleotides. Criteria directing the choice of the most appropriate T-SSR system for genetic engineering include that, whenever possible, the recombinase should act independent of cofactors and that the target sequences should be long enough to be unique in a given genome. This review is focused on recent advancements in our mechanistic understanding of simple T-SSRs and their application in developmental and synthetic biology, as well as in biomedical research.