Focal adhesion kinase negatively regulates Lck function downstream of the T cell antigen receptor

Combination of FAK inhibitor and cytokine-induced killer cell therapy: An alternative therapeutic strategy for patients with triple-negative breast cancer

Triple-negative breast cancer (TNBC) is characterized by the loss of expression of several biomarkers, which limits treatment strategies for the disease. In recent years, immunotherapy has shown promising results in the treatment of various tumors. Emerging evidence demonstrated that TNBC is an immune-activated cancer, suggesting that immunotherapy could be a feasible treatment option for TNBC. Cytokine-induced killer (CIK) cell therapy is considered as a potential treatment for cancer treatment. However, it is still not approved as a standard treatment in the clinical setting. Our previous study demonstrated that focal adhesion kinase (FAK) plays important role in regulating the sensitivity of TNBC cells to CIK cells. In this study, we further verify the role of FAK in regulating the immune response in vivo. Our in vitro study indicated that knockdown of FAK in TNBC cells or treat with the FAK inhibitor followed by co-culture with CIK cells induced more cell death than CIK cells treatment only. RNA-seq analysis indicated that suppression of FAK could affect several immune-related gene expressions in TNBC cells that affects the immune response in the tumor microenvironment of TNBC cells. The combination of FAK inhibitor and CIK cells significantly suppressed tumor growth than the treatment of FAK inhibitor or CIK cells alone in vivo. Our findings provide new insights into the cytotoxic effect of CIK cell therapy in TNBC treatment and indicate that the combination of CIK cell therapy with FAK inhibitors may be an alternative therapeutic strategy for patients with TNBC.

Focal Adhesion-Related Signatures Predict the Treatment Efficacy of Chemotherapy and Prognosis in Patients with Gastric Cancer

Background

The current tumor-node-metastasis (TNM) staging system is insufficient for predicting the efficacy of chemotherapy in patients with gastric cancer (GC). This study aimed to analyze the association between the focal adhesion pathway and therapeutic efficacy of chemotherapy in patients with GC.

Methods

RNA sequencing was performed on 33 clinical samples from patients who responded or did not respond to treatment prior to neoadjuvant chemotherapy. The validation sets containing 696 GC patients with RNA data from three cohorts (PKUCH, TCGA, and GSE14210) were analyzed. A series of machine learning and bioinformatics approaches was combined to build a focal adhesion-related signature model to predict the treatment efficacy and prognosis of patients with GC.

Results

Among the various signaling pathways associated with cancer, focal adhesion was identified as a risk factor related to the treatment efficacy of chemotherapy and prognosis in patients with GC. The focal adhesion-related gene model (FAscore) discriminated patients with a high FAscore who are insensitive to neoadjuvant chemotherapy in our training cohort, and the predicted value was further verified in the GSE14210 cohort. Survival analysis also demonstrated that patients with high FAscores had a relatively shorter survival compared to those with low FAscores. In addition, we found that the levels of tumor mutation burden (TMB) and microsatellite instability (MSI) increased with an increase in FAscore, and the tumor microenvironment (TME) also shifted to a pro-tumor immune microenvironment.

Conclusion

The FAscore model can be used to predict the treatment efficacy of chemotherapy and select appropriate treatment strategies for patients with GC.

A randomized phase 2 trial of idiotype vaccination and adoptive autologous T-cell transfer in patients with multiple myeloma

We hypothesized that combining adoptively transferred autologous T cells with a cancer vaccine strategy would enhance therapeutic efficacy by adding antimyeloma idiotype (Id)-keyhole limpet hemocyanin (KLH) vaccine to vaccine-specific costimulated T cells. In this randomized phase 2 trial, patients received either control (KLH only) or Id-KLH vaccine, autologous transplantation, vaccine-specific costimulated T cells expanded ex vivo, and 2 booster doses of assigned vaccine. In 36 patients (KLH, n = 20; Id-KLH, n = 16), no dose-limiting toxicity was seen. At last evaluation, 6 (30%) and 8 patients (50%) had achieved complete remission in KLH-only and Id-KLH arms, respectively (P = .22), and no difference in 3-year progression-free survival was observed (59% and 56%, respectively; P = .32). In a 594 Nanostring nCounter gene panel analyzed for immune reconstitution (IR), compared with patients receiving KLH only, there was a greater change in IR genes in T cells in those receiving Id-KLH relative to baseline. Specifically, upregulation of genes associated with activation, effector function induction, and memory CD8+ T-cell generation after Id-KLH but not after KLH control vaccination was observed. Similarly, in responding patients across both arms, upregulation of genes associated with T-cell activation was seen. At baseline, all patients had greater expression of CD8+ T-cell exhaustion markers. These changes were associated with functional Id-specific immune responses in a subset of patients receiving Id-KLH. In conclusion, in this combination immunotherapy approach, we observed significantly more robust IR in CD4+ and CD8+ T cells in the Id-KLH arm, supporting further investigation of vaccine and adoptive immunotherapy strategies. This trial was registered at www.clinicaltrials.gov as #NCT01426828.

T cell receptor (TCR) signaling in health and disease

Interaction of the T cell receptor (TCR) with an MHC-antigenic peptide complex results in changes at the molecular and cellular levels in T cells. The outside environmental cues are translated into various signal transduction pathways within the cell, which mediate the activation of various genes with the help of specific transcription factors. These signaling networks propagate with the help of various effector enzymes, such as kinases, phosphatases, and phospholipases. Integration of these disparate signal transduction pathways is done with the help of adaptor proteins that are non-enzymatic in function and that serve as a scaffold for various protein-protein interactions. This process aids in connecting the proximal to distal signaling pathways, thereby contributing to the full activation of T cells. This review provides a comprehensive snapshot of the various molecules involved in regulating T cell receptor signaling, covering both enzymes and adaptors, and will discuss their role in human disease.

Fueling influenza and the immune response: Implications for metabolic reprogramming during influenza infection and immunometabolism

Recent studies support the notion that glycolysis and oxidative phosphorylation are rheostats in immune cells whose bioenergetics have functional outputs in terms of their biology. Specific intrinsic and extrinsic molecular factors function as molecular potentiometers to adjust and control glycolytic to respiratory power output. In many cases, these potentiometers are used by influenza viruses and immune cells to support pathogenesis and the host immune response, respectively. Influenza virus infects the respiratory tract, providing a specific environmental niche, while immune cells encounter variable nutrient concentrations as they migrate in response to infection. Immune cell subsets have distinct metabolic programs that adjust to meet energetic and biosynthetic requirements to support effector functions, differentiation, and longevity in their ever-changing microenvironments. This review details how influenza coopts the host cell for metabolic reprogramming and describes the overlap of these regulatory controls in immune cells whose function and fate are dictated by metabolism. These details are contextualized with emerging evidence of the consequences of influenza-induced changes in metabolic homeostasis on disease progression.

Targeting FAK in anticancer combination therapies

Focal adhesion kinase (FAK) is both a non-receptor tyrosine kinase and an adaptor protein that primarily regulates adhesion signalling and cell migration, but FAK can also promote cell survival in response to stress. FAK is commonly overexpressed in cancer and is considered a high-value druggable target, with multiple FAK inhibitors currently in development. Evidence suggests that in the clinical setting, FAK targeting will be most effective in combination with other agents so as to reverse failure of chemotherapies or targeted therapies and enhance efficacy of immune-based treatments of solid tumours. Here, we discuss the recent preclinical evidence that implicates FAK in anticancer therapeutic resistance, leading to the view that FAK inhibitors will have their greatest utility as combination therapies in selected patient populations.

Pretreatment with LCK inhibitors chemosensitizes cisplatin-resistant endometrioid ovarian tumors

Background

Ovarian cancer is the most fatal gynecologic malignancy in the United States. While chemotherapy is effective in the vast majority of ovarian cancer patients, recurrence and resistance to standard systemic therapy is nearly inevitable. We discovered that activation of the non-receptor tyrosine kinase Lymphocyte Cell-Specific Protein-Tyrosine Kinase (LCK) promoted cisplatin resistance. Here, we hypothesized that treating high grade, platinum resistant endometrioid cancer cells with an LCK inhibitor (LCKi) followed by co-treatment with cisplatin would lead to increased cisplatin efficacy. Our objective was to assess clinical outcomes associated with increased LCK expression, test our hypothesis of utilizing LCKi as pre-treatment followed by co-treatment with cisplatin in platinum resistant ovarian cancer in vitro, and evaluate our findings in vivo to assess LCKi applicability as a therapeutic agent.

Results

Kaplan-Meier (KM) plotter data indicated LCK expression is associated with significantly worse median progression-free survival (HR 3.19, p = 0.02), and a trend toward decreased overall survival in endometrioid ovarian tumors with elevated LCK expression (HR 2.45, p = 0.41). In vitro, cisplatin resistant ovarian endometrioid cells treated first with LCKi followed by combination LCKi-cisplatin treatment showed decreased cell viability and increased apoptosis. Immunoblot studies revealed LCKi led to increased expression of phosphorylated H2A histone family X (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\gamma$$\end{document}γ-H2AX), a marker for DNA damage. In vivo results demonstrate treatment with LCKi followed by LCKi-cisplatin led to significantly slowed tumor growth.

Conclusions

We identified a strategy to therapeutically target cisplatin resistant endometrioid ovarian cancer leading to chemosensitization to platinum chemotherapy via treatment with LCKi followed by co-treatment with LCKi-cisplatin.

ZINC40099027 Promotes Gastric Mucosal Repair in Ongoing Aspirin-Associated Gastric Injury by Activating Focal Adhesion Kinase

Nonsteroidal anti-inflammatory drugs cause gastric ulcers and gastritis. No drug that treats GI injury directly stimulates mucosal healing. ZINC40099027 (ZN27) activates focal adhesion kinase (FAK) and heals acute indomethacin-induced small bowel injury. We investigated the efficacy of ZN27 in rat and human gastric epithelial cells and ongoing aspirin-associated gastric injury. ZN27 (10 nM) stimulated FAK activation and wound closure in rat and human gastric cell lines. C57BL/6J mice were treated with 300 mg/kg/day aspirin for five days to induce ongoing gastric injury. One day after the initial injury, mice received 900 µg/kg/6 h ZN27, 10 mg/kg/day omeprazole, or 900 µg/kg/6 h ZN27 plus 10 mg/kg/day omeprazole. Like omeprazole, ZN27 reduced gastric injury vs. vehicle controls. ZN27-treated mice displayed better gastric architecture, with thicker mucosa and less hyperemia, inflammation, and submucosal edema, and lost less weight than vehicle controls. Gastric pH, serum creatinine, serum alanine aminotransferase (ALT), and renal and hepatic histology were unaffected by ZN27. Blinded scoring of pFAK-Y-397 immunoreactivity at the edge of ZN27-treated lesions demonstrated increased FAK activation, compared to vehicle-treated lesions, confirming target activation in vivo. These results suggest that ZN27 ameliorates ongoing aspirin-associated gastric mucosal injury by a pathway involving FAK activation. ZN27-derivatives may be useful to promote gastric mucosal repair.

Advantages of targeting the tumor immune microenvironment over blocking immune checkpoint in cancer immunotherapy

Despite great success in cancer immunotherapy, immune checkpoint-targeting drugs are not the most popular weapon in the armory of cancer therapy. Accumulating evidence suggests that the tumor immune microenvironment plays a critical role in anti-cancer immunity, which may result in immune checkpoint blockade therapy being ineffective, in addition to other novel immunotherapies in cancer patients. In the present review, we discuss the deficiencies of current cancer immunotherapies. More importantly, we highlight the critical role of tumor immune microenvironment regulators in tumor immune surveillance, immunological evasion, and the potential for their further translation into clinical practice. Based on their general targetability in clinical therapy, we believe that tumor immune microenvironment regulators are promising cancer immunotherapeutic targets. Targeting the tumor immune microenvironment, alone or in combination with immune checkpoint-targeting drugs, might benefit cancer patients in the future.

The Adhesome Network: Key Components Shaping the Tumour Stroma

Beyond the conventional perception of solid tumours as mere masses of cancer cells, advanced cancer research focuses on the complex contributions of tumour-associated host cells that are known as "tumour microenvironment" (TME). It has been long appreciated that the tumour stroma, composed mainly of blood vessels, cancer-associated fibroblasts and immune cells, together with the extracellular matrix (ECM), define the tumour architecture and influence cancer cell properties. Besides soluble cues, that mediate the crosstalk between tumour and stroma cells, cell adhesion to ECM arises as a crucial determinant in cancer progression. In this review, we discuss how adhesome, the intracellular protein network formed at cell adhesions, regulate the TME and control malignancy. The role of adhesome extends beyond the physical attachment of cells to ECM and the regulation of cytoskeletal remodelling and acts as a signalling and mechanosensing hub, orchestrating cellular responses that shape the tumour milieu.

The role of competing mechanisms on Lck regulation

Lck is a Src-related protein tyrosine kinase that associates with CD4 and CD8 molecules and is essential to T cell development and T cell activation. Regulatory mechanisms of Lck are diverse and controversy exists regarding the importance of each mechanism. The balance of phosphorylation at the inhibitory and activating Tyr residues is maintained by a balance between CD45 and Csk and is dependent upon intact intracellular trafficking machinery. Current evidence shows that lipid-binding changes depending on Lck conformation and that phosphorylation-induced conformational changes in Lck modulate its kinase activity potentially through regulation of Lck clustering at the plasma membrane. Downstream regulators such as ZAP-70 mediate negative feedback that is dependent on Tyr¹⁹² phosphorylation. This review examines the diverse regulation of Lck in detail, highlighting the role of each mechanism on maintaining an appropriate amount of Lck in each conformational state, thus allowing for an efficient, appropriate, and controlled amount of T cell activation following TCR stimulation.

Transforming growth factor β (TGF-β) receptor signaling regulates kinase networks and phosphatidylinositol metabolism during T-cell activation

The cytokine content in tissue microenvironments shapes the functional capacity of a T cell. This capacity depends on the integration of extracellular signaling through multiple receptors, including the T-cell receptor (TCR), co-receptors, and cytokine receptors. Transforming growth factor β (TGF-β) signals through its cognate receptor, TGFβR, to SMAD family member proteins and contributes to the generation of a transcriptional program that promotes regulatory T-cell differentiation. In addition to transcription, here we identified specific signaling networks that are regulated by TGFβR. Using an array of biochemical approaches, including immunoblotting, kinase assays, immunoprecipitation, and flow cytometry, we found that TGFβR signaling promotes the formation of a SMAD3/4-protein kinase A (PKA) complex that activates C-terminal Src kinase (CSK) and thereby down-regulates kinases involved in proximal TCR activation. Additionally, TGFβR signaling potentiated CSK phosphorylation of the P85 subunit in the P85-P110 phosphoinositide 3-kinase (PI3K) heterodimer, which reduced PI3K activity and down-regulated the activation of proteins that require phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) for their activation. Moreover, TGFβR-mediated disruption of the P85-P110 interaction enabled P85 binding to a lipid phosphatase, phosphatase and tensin homolog (PTEN), aiding in the maintenance of PTEN abundance and thereby promoting elevated PtdIns(4,5)P2 levels in response to TGFβR signaling. Taken together, these results highlight that TGF-β influences the trajectory of early T-cell activation by altering PI3K activity and PtdIns levels.

Beyond the Cell Surface: Targeting Intracellular Negative Regulators to Enhance T cell Anti-Tumor Activity

It is well established that extracellular proteins that negatively regulate T cell function, such as Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4) and Programmed Cell Death protein 1 (PD-1), can be effectively targeted to enhance cancer immunotherapies and Chimeric Antigen Receptor T cells (CAR-T cells). Intracellular proteins that inhibit T cell receptor (TCR) signal transduction, though less well studied, are also potentially useful therapeutic targets to enhance T cell activity against tumor. Four major classes of enzymes that attenuate TCR signaling include E3 ubiquitin kinases such as the Casitas B-lineage lymphoma proteins (Cbl-b and c-Cbl), and Itchy (Itch), inhibitory tyrosine phosphatases, such as Src homology region 2 domain-containing phosphatases (SHP-1 and SHP-2), inhibitory protein kinases, such as C-terminal Src kinase (Csk), and inhibitory lipid kinases such as Src homology 2 (SH2) domain-containing inositol polyphosphate 5-phosphatase (SHIP) and Diacylglycerol kinases (DGKs). This review describes the mechanism of action of eighteen intracellular inhibitory regulatory proteins in T cells within these four classes, and assesses their potential value as clinical targets to enhance the anti-tumor activity of endogenous T cells and CAR-T cells.

Targeting the proviral host kinase, FAK, limits influenza a virus pathogenesis and NFkB-regulated pro-inflammatory responses

Influenza A virus (IAV) infections result in ∼500,000 global deaths annually. Host kinases link multiple signaling pathways at various stages of infection and are attractive therapeutic target. Focal adhesion kinase (FAK), a non-receptor tyrosine kinase, regulates several cellular processes including NFkB and antiviral responses. We investigated how FAK kinase activity regulates IAV pathogenesis. Using a severe infection model, we infected IAV-susceptible DBA/2 J mice with a lethal dose of H1N1 IAV. We observed reduced viral load and pro-inflammatory cytokines, delayed mortality, and increased survival in FAK inhibitor (Y15) treated mice. In vitro IAV-induced NFkB-promoter activity was reduced by Y15 or a dominant negative kinase-dead FAK mutant (FAK-KD) independently of the viral immune modulator, NS1. Finally, we observed reduced IAV-induced nuclear localization of NFkB in FAK-KD expressing cells. Our data suggest a novel mechanism where IAV hijacks FAK to promote viral replication and limit its ability to contribute to innate immune responses.

Influenza Virus Infections and Cellular Kinases

Influenza A viruses (IAVs) are a major cause of respiratory illness and are responsible for yearly epidemics associated with more than 500,000 annual deaths globally. Novel IAVs may cause pandemic outbreaks and zoonotic infections with, for example, highly pathogenic avian influenza virus (HPAIV) of the H5N1 and H7N9 subtypes, which pose a threat to public health. Treatment options are limited and emergence of strains resistant to antiviral drugs jeopardize this even further. Like all viruses, IAVs depend on host factors for every step of the virus replication cycle. Host kinases link multiple signaling pathways in respond to a myriad of stimuli, including viral infections. Their regulation of multiple response networks has justified actively targeting cellular kinases for anti-cancer therapies and immune modulators for decades. There is a growing volume of research highlighting the significant role of cellular kinases in regulating IAV infections. Their functional role is illustrated by the required phosphorylation of several IAV proteins necessary for replication and/or evasion/suppression of the innate immune response. Identified in the majority of host factor screens, functional studies further support the important role of kinases and their potential as host restriction factors. PKC, ERK, PI3K and FAK, to name a few, are kinases that regulate viral entry and replication. Additionally, kinases such as IKK, JNK and p38 MAPK are essential in mediating viral sensor signaling cascades that regulate expression of antiviral chemokines and cytokines. The feasibility of targeting kinases is steadily moving from bench to clinic and already-approved cancer drugs could potentially be repurposed for treatments of severe IAV infections. In this review, we will focus on the contribution of cellular kinases to IAV infections and their value as potential therapeutic targets.

T cells transduce T-cell receptor signal strength by generating different phosphatidylinositols

T-cell receptor (TCR) signaling strength is a dominant factor regulating T-cell differentiation, thymic development, and cytokine signaling. The molecular mechanisms by which TCR signal strength is transduced to downstream signaling networks remains ill-defined. Using computational modeling, biochemical assays, and imaging flow cytometry, we found here that TCR signal strength differentially generates phosphatidylinositol species. Weak TCR signals generated elevated phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and reduced phosphatidylinositol (3,4,5)-trisphosphate (PIP3) levels, whereas strong TCR signals reduced PI(4,5)P2 and elevated PIP3 levels. A proteomics screen revealed that focal adhesion kinase bound PI(4,5)P2, biochemical assays disclosed that focal adhesion kinase is preferentially activated by weak TCR signals and is required for optimal Treg induction, and further biochemical experiments revealed how TCR signaling strength regulates AKT activation. Low PIP3 levels generated by weak TCR signals were sufficient to activate phosphoinositide-dependent kinase-1 to phosphorylate AKT on Thr-308 but insufficient to activate mTOR complex 2 (mTORC2), whereas elevated PIP3 levels generated by a strong TCR signal were required to activate mTORC2 to phosphorylate Ser-473 on AKT. Our results provide support for a model that links TCR signaling to mTORC2 activation via phosphoinositide 3-kinase signaling. Together, the findings in this work establish that T cells measure TCR signal strength by generating different levels of phosphatidylinositol species that engage alternate signaling networks to control cell fate decisions.

Src-family kinases negatively regulate NFAT signaling in resting human T cells

T cell signaling is required for activation of both natural and therapeutic T cells including chimeric antigen receptor (CAR) T cells. Identification of novel factors and pathways regulating T cell signaling may aid in development of effective T cell therapies. In resting human T cells, the majority of Src-family of tyrosine kinases (SFKs) are inactive due to phosphorylation of a conserved carboxy-terminal tyrosine residue. Recently, a pool of enzymatically active SFKs has been identified in resting T cells; however, the significance of these is incompletely understood. Here, we characterized the role of active SFKs in resting human T cells. Pharmacologic inhibition of active SFKs enhanced distal TCR signaling as measured by IL-2 release and CD25 surface expression following TCR-independent activation. Mechanistically, inhibition of the active pool of SFKs induced nuclear translocation of NFAT1, and enhanced NFAT1-dependent signaling in resting T cells. The negative regulation of NFAT1 signaling was in part mediated by the Src-kinase Lck as human T cells lacking Lck had increased levels of nuclear NFAT1 and demonstrated enhanced NFAT1-dependent gene expression. Inhibition of active SFKs in resting primary human T cells also increased nuclear NFAT1 and enhanced NFAT1-dependent signaling. Finally, the calcineurin inhibitor FK506 and Cyclosporin A reversed the effect of SFKs inhibition on NFAT1. Together, these data identified a novel role of SFKs in preventing aberrant NFAT1 activation in resting T cells, and suggest that maintaining this pool of active SFKs in therapeutic T cells may increase the efficacy of T cell therapies.

TRAF3 enhances TCR signaling by regulating the inhibitors Csk and PTPN22

The adaptor protein TNF receptor associated factor (TRAF) 3 is required for effective TCR signaling and normal T cell effector functions, and associates with the CD3/CD28 complex upon activation. To determine how TRAF3 promotes proximal TCR signaling, we studied TRAF3-deficient mouse and human T cells, which showed a marked reduction in activating phosphorylation of the TCR-associated kinase Lck. The impact of TRAF3 on this very early signaling event led to the hypothesis that TRAF3 restrains one or both of two known inhibitors of Lck, C-terminal Src kinase (Csk) and protein tyrosine phosphatase N22 (PTPN22). TRAF3 associated with Csk, promoting the dissociation of Csk from the plasma membrane. TRAF3 also associated with and regulated the TCR/CD28 induced localization of PTPN22. Loss of TRAF3 resulted in increased amounts of both Csk and PTPN22 in T cell membrane fractions and decreased association of PTPN22 with Csk. These findings identify a new role for T cell TRAF3 in promoting T cell activation, by regulating localization and functions of early TCR signaling inhibitors.

Obstacles Posed by the Tumor Microenvironment to T cell Activity: A Case for Synergistic Therapies

T cell dysfunction in solid tumors results from multiple mechanisms. Altered signaling pathways in tumor cells help produce a suppressive tumor microenvironment enriched for inhibitory cells, posing a major obstacle for cancer immunity. Metabolic constraints to cell function and survival shape tumor progression and immune cell function. In the face of persistent antigen, chronic T cell receptor signaling drives T lymphocytes to a functionally exhausted state. Here we discuss how the tumor and its microenvironment influences T cell trafficking and function with a focus on melanoma, and pancreatic and ovarian cancer, and discuss how scientific advances may help overcome these hurdles.

Glycerol Monolaurate (GML) inhibits human T cell signaling and function by disrupting lipid dynamics

Glycerol Monolaurate (GML) is a naturally occurring fatty acid widely utilized in food, cosmetics, and homeopathic supplements. GML is a potent antimicrobial agent that targets a range of bacteria, fungi, and enveloped viruses but select findings suggest that GML also has immunomodulatory functions. In this study, we have mechanistically examined if GML affects the signaling and functional output of human primary T cells. We found that GML potently altered order and disorder dynamics in the plasma membrane that resulted in reduced formation of LAT, PLC-γ, and AKT microclusters. Altered membrane events induced selective inhibition of TCR-induced phosphorylation of regulatory P85 subunit of PI3K and AKT as well as abrogated calcium influx. Ultimately, GML treatment potently reduced TCR-induced production of IL-2, IFN-γ, TNF-α, and IL-10. Our data reveal that the widely used anti-microbial agent GML also alters the lipid dynamics of human T cells, leading to their defective signaling and function.

Novel role for p56/Lck in regulation of endothelial cell survival and angiogenesis

Previous studies have demonstrated that cleaved high-molecular-weight kininogen (HKa) induces endothelial apoptosis and inhibits angiogenesis and have suggested that this occurs through inhibition of Src family kinases. This study assessed the role of tyrosine-protein kinase Lck (p56/Lck) in this pathway. We analyzed early events leading to apoptosis of human endothelial cells exposed to HKa. The role of p56/Lck was investigated using short interfering (si) RNA knockdown and lentivirus expression in assays of endothelial tube formation, sprouting of neovessels from murine aorta, and angiogenesis in Matrigel plugs. HKa stimulated expression and phosphorylation of p56/Lck. siRNA knockdown of p56/Lck promoted endothelial proliferation and blocked HKa-induced apoptosis and activation of p53, Bax, and Bak. Lentivirus expression of p56/Lck in endothelial cells induced apoptosis and blocked tube formation. Expression of p56/Lck in murine aortic rings blocked sprouting angiogenesis. Lentivirus expressing p56/Lck blocked angiogenesis in Matrigel plugs, while p56/Lck short hairpin RNA inhibited the antiangiogenic effect of HKa. Scrambled siRNAs and empty lentiviral vectors were used in all experiments. Apoptosis of proliferating endothelial cells and inhibition of angiogenesis by HKa requires p56/Lck. This suggests a novel role for p56/Lck in regulation of endothelial cell survival and angiogenesis.-Betapudi, V., Shukla, M., Alluri, R., Merkulov, S., McCrae, K. R. Novel role for p56/Lck in regulation of endothelial cell survival and angiogenesis.

Targeting focal adhesion kinase renders pancreatic cancers responsive to checkpoint immunotherapy

Single-agent immunotherapy has achieved limited clinical benefit to date in patients suffering from pancreatic ductal adenocarcinoma (PDAC). This may be due to the presence of a uniquely immunosuppressive tumor microenvironment (TME). Critical obstacles to immunotherapy in PDAC tumors include a high number of tumor-associated immunosuppressive cells and a uniquely desmoplastic stroma that acts as a barrier to T-cell infiltration. We have identified hyperactivated focal adhesion kinase (FAK) activity in neoplastic PDAC cells as a significant regulator of the fibrotic and immunosuppressive TME. We found that FAK activity was elevated in human PDAC tissues and correlates with high levels of fibrosis and poor CD8⁺ cytotoxic T-cell infiltration. Single-agent FAK inhibition using the selective FAK inhibitor VS-4718 significantly limited tumor progression, resulting in a doubling of survival in the p48-Cre/LSL-Kras^G12D/p53^Flox/+ (KPC) mouse model of human PDAC. This delay in tumor progression was associated with dramatically reduced tumor fibrosis, and decreased numbers of tumor-infiltrating immunosuppressive cells. We also found that FAK inhibition rendered the previously unresponsive KPC mouse model responsive to T cell immunotherapy and PD-1 antagonists. These data suggest that FAK inhibition increases immune surveillance by overcoming the fibrotic and immunosuppressive PDAC TME and renders tumors responsive to immunotherapy.

Exposure of Human CD4 T Cells to IL-12 Results in Enhanced TCR-Induced Cytokine Production, Altered TCR Signaling, and Increased Oxidative Metabolism

Human CD4 T cells are constantly exposed to IL-12 during infections and certain autoimmune disorders. The current paradigm is that IL-12 promotes the differentiation of naïve CD4 T cells into Th1 cells, but recent studies suggest IL-12 may play a more complex role in T cell biology. We examined if exposure to IL-12 alters human CD4 T cell responses to subsequent TCR stimulation. We found that IL-12 pretreatment increased TCR-induced IFN-γ, TNF-α, IL-13, IL-4 and IL-10 production. This suggests that prior exposure to IL-12 potentiates the TCR-induced release of a range of cytokines. We observed that IL-12 mediated its effects through both transcriptional and post-transcriptional mechanisms. IL-12 pretreatment increased the phosphorylation of AKT, p38 and LCK following TCR stimulation without altering other TCR signaling molecules, potentially mediating the increase in transcription of cytokines. In addition, the IL-12-mediated enhancement of cytokines that are not transcriptionally regulated was partially driven by increased oxidative metabolism. Our data uncover a novel function of IL-12 in human CD4 T cells; specifically, it enhances the release of a range of cytokines potentially by altering TCR signaling pathways and by enhancing oxidative metabolism.

Evaluation of Intracellular Signaling Downstream Chimeric Antigen Receptors

CD19-targeting CAR T cells have shown potency in clinical trials targeting B cell leukemia. Although mainly second generation (2G) CARs carrying CD28 or 4-1BB have been investigated in patients, preclinical studies suggest that third generation (3G) CARs with both CD28 and 4-1BB have enhanced capacity. However, little is known about the intracellular signaling pathways downstream of CARs. In the present work, we have analyzed the signaling capacity post antigen stimulation in both 2G and 3G CARs. 3G CAR T cells expanded better than 2G CAR T cells upon repeated stimulation with IL-2 and autologous B cells. An antigen-driven accumulation of CAR+ cells was evident post antigen stimulation. The cytotoxicity of both 2G and 3G CAR T cells was maintained by repeated stimulation. The phosphorylation status of intracellular signaling proteins post antigen stimulation showed that 3G CAR T cells had a higher activation status than 2G. Several proteins involved in signaling downstream the TCR were activated, as were proteins involved in the cell cycle, cell adhesion and exocytosis. In conclusion, 3G CAR T cells had a higher degree of intracellular signaling activity than 2G CARs which may explain the increased proliferative capacity seen in 3G CAR T cells. The study also indicates that there may be other signaling pathways to consider when designing or evaluating new generations of CARs.

Regions outside of conserved PxxPxR motifs drive the high affinity interaction of GRB2 with SH3 domain ligands

SH3 domains are evolutionarily conserved protein interaction domains that control nearly all cellular processes in eukaryotes. The current model is that most SH3 domains bind discreet PxxPxR motifs with weak affinity and relatively low selectivity. However, the interactions of full-length SH3 domain-containing proteins with ligands are highly specific and have much stronger affinity. This suggests that regions outside of PxxPxR motifs drive these interactions. In this study, we observed that PxxPxR motifs were required for the binding of the adaptor protein GRB2 to short peptides from its ligand SOS1. Surprisingly, PxxPxR motifs from the proline rich region of SOS1 or CBL were neither necessary nor sufficient for the in vitro or in vivo interaction with full-length GRB2. Together, our findings show that regions outside of the consensus PxxPxR sites drive the high affinity association of GRB2 with SH3 domain ligands, suggesting that the binding mechanism for this and other SH3 domain interactions may be more complex than originally thought.

GRB2 Nucleates T Cell Receptor-Mediated LAT Clusters That Control PLC-γ1 Activation and Cytokine Production

GRB2 is a ubiquitously expressed adaptor protein required for signaling downstream of multiple receptors. To address the role of GRB2 in receptor-mediated signaling, the expression of GRB2 was suppressed in human CD4+ T cells and its role downstream of the T cell receptor (TCR) was examined. Interestingly, GRB2 deficient T cells had enhanced signaling from complexes containing the TCR. However, GRB2 deficient T cells had substantially reduced production of IL-2 and IFN-γ. This defect was attributed to diminished formation of linker for activation of T cells (LAT) signaling clusters, which resulted in reduced MAP kinase activation, calcium flux, and PLC-γ1 recruitment to LAT signaling clusters. Add back of wild-type GRB2, but not a novel N-terminal SH3 domain mutant, rescued LAT microcluster formation, calcium mobilization, and cytokine release, providing the first direct evidence that GRB2, and its ability to bind to SH3 domain ligands, is required for establishing LAT microclusters. Our data demonstrate that the ability of GRB2 to facilitate protein clusters is equally important in regulating TCR-mediated functions as its capacity to recruit effector proteins. This highlights that GRB2 regulates signaling downstream of adaptors and receptors by both recruiting effector proteins and regulating the formation of signaling complexes.

Functions of the FAK family kinases in T cells: beyond actin cytoskeletal rearrangement

T cells control the focus and extent of adaptive immunity in infectious and pathological diseases. The activation of T cells occurs when the T cell antigen receptor (TCR) and costimulatory and/or adhesion receptors are engaged by their ligands. This process drives signaling that promotes cytoskeletal rearrangement and transcription factor activation, both of which regulate the quality and magnitude of the T cell response. However, it is not fully understood how different receptor-induced signals combine to alter T cell activation. The related non-receptor tyrosine kinases focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2) are phosphorylated downstream of the TCR and several costimulatory and adhesion receptors. FAK family proteins integrate receptor-mediated signals that influence actin cytoskeletal rearrangement and effector T cell responses. In this review, we summarize the receptor-specific roles that FAK and Pyk2 control to influence T cell development and activation.

GADS is required for TCR-mediated calcium influx and cytokine release, but not cellular adhesion, in human T cells

GRB2 related adaptor protein downstream of Shc (GADS) is a member of the GRB2 family of adaptors and is critical for TCR-induced signaling. The current model is that GADS recruits SLP-76 to the LAT complex, which facilitates the phosphorylation of SLP-76, the activation of PLC-γ1, T cell adhesion and cytokine production. However, this model is largely based on studies of disruption of the GADS/SLP-76 interaction and murine T cell differentiation in GADS deficient mice. The role of GADS in mediating TCR-induced signals in human CD4+ T cells has not been thoroughly investigated. In this study, we have suppressed the expression of GADS in human CD4+ HuT78 T cells. GADS deficient HuT78 T cells displayed similar levels of TCR-induced SLP-76 and PLC-γ1 phosphorylation but exhibited substantial decrease in TCR-induced IL-2 and IFN-γ release. The defect in cytokine production occurred because of impaired calcium mobilization due to reduced recruitment of SLP-76 and PLC-γ1 to the LAT complex. Surprisingly, both GADS deficient HuT78 and GADS deficient primary murine CD8+ T cells had similar TCR-induced adhesion when compared to control T cells. Overall, our results show that GADS is required for calcium influx and cytokine production, but not cellular adhesion, in human CD4+ T cells, suggesting that the current model for T cell regulation by GADS is incomplete.

TCR-mediated functions are enhanced in activated peripheral blood T cells isolated from leucocyte reduction systems

Buffy coats are the most common method for the acquisition of activated primary human T cells for research or clinical applications, but recently leukocyte reduction system (LRS) cones have emerged as a viable source for these cells. In this study, we determined if activated human T cells derived from buffy coats or LRS cones had different functionality. No changes in the expression of surface receptors were observed except for a significant increase in CD44 expression on T cells isolated from LRS cones. LRS cone-derived T cells trended towards higher receptor-mediated cytokine production and had significantly increased donor-to-donor variability in IFN-γ production. TCR-induced ERK1/ERK2 and AKT phosphorylation was also increased in T cells isolated from LRS cones. In conclusion, LRS cones are an excellent source of T cells for clinical and research applications, but these cells have subtle functional differences from T cells isolated using standard buffy coats.

Proline-rich tyrosine kinase 2 controls PI3-kinase activation downstream of the T cell antigen receptor in human T cells

TCR-induced signaling controls T cell activation that drives adaptive immunity against infections, but it can also induce dysfunctional T cell responses that promote pathologic disease. The PI3K pathway regulates many downstream effector responses after TCR stimulation. However, the molecular mechanisms that induce PI3K function downstream of the TCR are not fully understood. We have previously shown that Pyk2 is activated downstream of the TCR in a PI3K-independent manner. Although Pyk2 controls adhesion, proliferation, and cytokine production in T cells, the mechanisms by which it controls these processes are not known. In this study, we generated Pyk2-deficient human T cells to elucidate further the role that this kinase plays in TCR-induced effector functions and signaling. We observed that Pyk2 localized with the p85 regulatory subunit of PI3K at the LAT complex and that PI3K-dependent signaling was impaired in Pyk2-deficient T cells. Likewise, functions downstream of PI3K, including IFN-γ production and proliferation, were also suppressed in human T cells deficient in Pyk2. Collectively, these data demonstrate that Pyk2 is a critical regulator of PI3K function downstream of the TCR.

Cellular signaling in the aging immune system

Causes for immunosenescence and inflamm-aging have to be established. Efficient function of the immune system requires homeostatic regulation from receptor recognition of antigenic challenge to cell responses and adaptation to its changing environment. It is reasonable to assume that one of the most important molecular causes of immunosenescence is alteration in the regulation of signaling pathways. Indeed, alterations in feed-forward and negative feedback (inhibitory) signaling have been highlighted in all cells involved in the immune response including short-lived (neutrophils) and long-lived (T lymphocytes) cells. These dysregulations tip the balance in favor of altered (less efficient) function of the immune system. In this review, we summarize our knowledge on signal transduction changes in the aging immune system and propose a unifying mechanism as one of the causes of immunosenescence. Modulation of these pathways with aging represents a major challenge to restore the immune response to functional levels.

New insights into FAK function and regulation during spermatogenesis

Germ cell transport across the seminiferous epithelium during the epithelial cycle is crucial to spermatogenesis, although molecular mechanism(s) that regulate these events remain unknown. Studies have shown that spatiotemporal expression of crucial regulatory proteins during the epithelial cycle represents an efficient and physiologically important mechanism to regulate spermatogenesis without involving de novo synthesis of proteins and/or expression of genes. Herein, we critically review the role of focal adhesion kinase (FAK) in coordinating the transport of spermatids and preleptotene spermatocytes across the epithelium and the BTB, respectively, along the apical ectoplasmic specialization (ES) - blood-testis barrier - basement membrane (BM) functional axis during spermatogenesis. In the testis, p-FAK-Tyr³⁸⁷ and p-FAK-Tyr⁴⁰⁷ are spatiotemporally expressed during the epithelial cycle at the actin-rich anchoring junction known as ES, regulating cell adhesion at the Sertoli-spermatid (apical ES) and Sertoli cell-cell (basal ES) interface. Phosphorylated forms of FAK exert their effects by regulating the homeostasis of F-actin at the ES, mediated via their effects on actin polymerization so that microfilaments are efficiently re-organized, such as from their "bundled" to "de-bundled/branched" configuration and vice versa during the epithelial cycle to facilitate the transport of: (i) spermatids across the epithelium, and (ii) preleptotene spermatocytes across the BTB. In summary, p-FAK-Tyr⁴⁰⁷ and p-FAK-Tyr³⁸⁷ are important regulators of spermatogenesis which serve as molecular switches that turn "on" and "off" adhesion function at the apical ES and the basal ES/BTB, mediated via their spatiotemporal expression during the epithelial cycle. A hypothetical model depicting the role of these two molecular switches is also proposed.