Non-receptor Tyrosine Kinase Src Research Articles

Artocarpus tonkinensis Extract Inhibits LPS-Triggered Inflammation Markers and Suppresses RANKL-Induced Osteoclastogenesis in RAW264.7

Artocarpus tonkinensis (At) leaf decoction, a traditional remedy prepared in North Vietnam by the Hmong ethnic group, is a tea extract rich in bioactive compounds that may have therapeutic effects in arthritis and backache. Indeed, it has been demonstrated that At is able to inhibit Th17 lymphocytes development and to protect mice in an experimental model of collagen-induced arthritis. By resorting to macrophage in vitro models of inflammation and osteoclastogenesis, we showed that At extract significantly reduced nitric oxide synthase 2 (NOS2) activity and IL-6 production by RAW 264.7 murine cells. Moreover, At demonstrated an anti-osteoclastogenic effect, as revealed by complete inhibition of TRAP-positive osteoclast formation and decreased expression of key osteoclast-related genes. This At activity likely relies on the inhibition of RANK downstream signaling pathway, as the activation of non-receptor tyrosine kinase Src is reduced upon RANKL-At exposure. Protective effect of At against bone loss was also enlightened in vivo by collagen-induced arthritis (CIA) experiment demonstrating that, although paw edema was only weakly opposed by drinking At decoction, bone and cartilage were well preserved in CIA+At mice and joint tissue expressed decreased levels of osteoclast marker genes respect to CIA control group. Maesopsin 4-O-β-D-glucoside (i.e., TAT-2, one of the main decoction bioactive components) was capable to contrast NOS2 activity, IL-6 expression and osteoclast formation, too, albeit to a lesser extent when compared to At decoction. Overall, this study enlightens another At cell target, macrophages, beside Th17 lymphocytes, and suggests that the anti-arthritic beneficial effects of At decoction largely derives from its ability to counteract not only inflammation, but also osteoclastogenesis.

Scaffold dependent role of the inositol 5′-phosphatase SHIP2, in regulation of oxidative stress induced apoptosis

Cell apoptosis is an important process that occurs during development or in response to stress stimuli such as oxidative stress. The serine-threonine kinase Akt enhances survival and suppress apoptosis. SHIP2 is known as a negative regulator of Akt. In addition to its lipid 5′-phosphatase activity, SHIP2 interacts and signals as a scaffolding complex with several proteins. Several findings have pointed out a possible role of SHIP2 in apoptosis regulation. However, the molecular mechanisms behind remain unknown. Using embryonic fibroblast lacking the lipid 5′-phosphatase domain as a genetic model system and human liver cancer cells treated with SHIP2 inhibitor (AS1949490), as a pharmacological model system. We provide the first evidence that SHIP2 regulates apoptosis independently of its 5′-phosphates activity. Indeed, absence of the 5′-phosphatase domain of SHIP2 did not prevent H2O2-induced apoptosis in fibroblasts. Whereas chemical inactivation or RNAi knockdown of SHIP2 blocked H2O2-induced apoptosis in HepG2 cells. We found that suppression of apoptosis upon SHIP2 inhibition is PI3K/Akt independent but rather MAP kinase dependent. In addition, we found that AS1949490 altered both 5′-phosphatase and scaffolding function of SHIP2. Indeed, AS1949490 mediated SHIP2 inhibition promotes protein complex formation of SHIP2 together with non-receptor tyrosine kinase SRC and ABL which in turn enhances PI3K/Akt and MAP kinase pathways activation. Dual inhibition of SRC/ABL blocked activation of both pathways upon SHIP2 inhibition and H2O2 treatment. Altogether, these findings indicate that SHIP2 protein play a determinant role in H2O2-induced apoptosis.

Effects of the amide alkaloid piperyline on apoptosis, autophagy, and differentiation of pre-osteoblasts

BackgroundAmide alkaloidsare typical constituents in plants of the Piperaceae family. Most of the pharmacological properties of Piper nigrum L. are attributed to the major amide alkaloid, piperine. Piperyline (PIPE) is a further amide alkaloid that has been isolated from P. nigrum. Hypothesis/PurposeThis study was performed to examine the biological effects of PIPE on pre-osteoblasts and elucidate the underlying mechanisms. Study DesignWe investigated the effects of PIPE in MC3T3E-1 cells, which are widely used for studying osteoblast behavior in in vitro cell systems. MethodsWe evaluated cell viability based on the MTT assay, apoptosis by TUNEL staining, adhesion and migration by cell adhesion and migration assays, and osteoblast differentiation by alkaline phosphatase activity and staining. Western blot and immunocytochemical analyses were used to investigate cell signaling pathways. ResultsWe found that at concentrations ranging from 1 to 30 μM, PIPE inhibited cell growth and induced apoptosis in pre-osteoblasts, which was accompanied by the upregulation of apoptotic proteins but downregulation of anti-apoptotic proteins. In contrast, PIPE had no appreciable effect on the autophagy pathway. Nevertheless, PIPE reduced cell adhesion and migration via the inactivation of non-receptor tyrosine kinase (Src)/focal adhesion kinase (FAK) and mitogen-activated protein kinases, and also promoted the downregulation of matrix metalloproteinase 2 and 9 levels. Furthermore, at concentrations of 10 and 30 μM, PIPE suppressed osteoblast differentiation, as indicated by reductions in alkaline phosphatase staining and activity. In addition, PIPE reduced the protein levels of phospho-Smad1/5/8 and runt-related transcription factor 2, and the mRNA levels of osteopontin, alkaline phosphatase, and osteocalcin. ConclusionThe findings of this study indicate that PIPE has biological effects associated with cell adhesion, migration, proliferation, and osteoblast differentiation, and suggest a potential role for this alkaloid in the treatment of bone diseases.

Mechanisms of the Regulation and Dysregulation of Glucagon Secretion.

Glucagon, a hormone secreted by pancreatic alpha cells, contributes to the maintenance of normal blood glucose concentration by inducing hepatic glucose production in response to declining blood glucose. However, glucagon hypersecretion contributes to the pathogenesis of type 2 diabetes. Moreover, diabetes is associated with relative glucagon undersecretion at low blood glucose and oversecretion at normal and high blood glucose. The mechanisms of such alpha cell dysfunctions are not well understood. This article reviews the genesis of alpha cell dysfunctions during the pathogenesis of type 2 diabetes and after the onset of type 1 and type 2 diabetes. It unravels a signaling pathway that contributes to glucose- or hydrogen peroxide-induced glucagon secretion, whose overstimulation contributes to glucagon dysregulation, partly through oxidative stress and reduced ATP synthesis. The signaling pathway involves phosphatidylinositol-3-kinase, protein kinase B, protein kinase C delta, non-receptor tyrosine kinase Src, and phospholipase C gamma-1. This knowledge will be useful in the design of new antidiabetic agents or regimens.

Targeting SRC Family Kinases in Mesothelioma: Time to Upgrade.

Malignant mesothelioma (MM) is a deadly tumor mainly caused by exposure to asbestos. Unfortunately, no current treatment is able to change significantly the natural history of the disease, which has a poor prognosis in the majority of patients. The non-receptor tyrosine kinase SRC and other SRC family kinase (SFK) members are frequently hyperactivated in many cancer types, including MM. Several works have indeed suggested that SFKs underlie MM cell proliferation, survival, motility, and invasion, overall affecting multiple oncogenic pathways. Consistently, SFK inhibitors effectively counteracted MM cancerous features at the preclinical level. Dasatinib, a multi-kinase inhibitor targeting SFKs, was also assessed in clinical trials either as second-line treatment for patients with unresectable MM or, more recently, as a neoadjuvant agent in patients with resectable MM. Here, we provide an overview of the molecular mechanisms implicating SFKs in MM progression and discuss possible strategies for a more successful clinical application of SFK inhibitors. Our aim is to stimulate discussion and further consideration of these agents in better designed preclinical and clinical studies to make the most of another class of powerful antitumoral drugs, which too often are lost in translation when applied to MM.

Abstract A08: A new driver pathway in ovarian cancer stem cells

Abstract Ovarian cancer stem cells (OCSC) are believed to fuel tumor metastasis, recurrence, and chemoresistance. Therefore, understanding the molecular players involved in OCSC function represents an urgent need towards the design of innovative and more efficacious treatments of this neoplasm. Our molecular profiling of primary OCSC isolated from high-grade serous ovarian cancer patients revealed a series of novel genes and pathways specifically associated with this cell subpopulation. Among these, we initially focused on CD73, a cell-surface 5’-ectonucleotidase that catalyzes the production of extracellular adenosine. Our data revealed the new role of CD73 as a driver of OC stemness and a potential target for OCSC-eradicating treatments. More recently, we investigated the functional role in OCSC of the immunoglobulin-like cell adhesion molecule L1 (L1CAM), a transmembrane protein that we have previously implicated in OC malignancy (Zecchini et al., 2008). Loss- and gain-of-function studies were performed by manipulating the expression of L1CAM in OC cells. These experiments revealed the causal role of L1CAM not only in stemness-related properties such as anoikis resistance, clonogenic proliferation under low-attachment conditions and self-renewal, but also in OCSC-driven tumor initiation. Mechanistically, L1CAM appeared to act through the induction, activation, and nuclear translocation of STAT3, all events that occurred predominantly in the OCSC compartment rather than in the bulk tumor cell population. Indeed, the inhibition of STAT3 activity abolished L1-induced OC stemness. Of note, L1-dependent activation of STAT3 was not mediated by the canonical JAK pathway, but rather by the nonreceptor tyrosine kinase SRC. Accordingly, SRC inhibition prevented the induction of stemness-related features by L1CAM. Finally, to identify the molecular mechanisms that link L1CAM with SRC, we built on our previous findings that the L1CAM-related molecule NCAM activates FGFR1 signaling. This enabled us to find a crosstalk between L1CAM and FGFR1 which, in turn, accounts for the stimulation of SRC-mediated activation of STAT3 and, ultimately, OCSC function. Finally, we provide evidence that the inactivation of L1CAM enhances the sensitivity of OCSC to chemotherapeutics, implicating L1CAM as a potential target to overcome chemoresistance. In conclusion, our results uncovered a novel L1/FGFR1/SRC/STAT3 pathway that acts as a driver in OC stemness, shedding light on the pathophysiology of OCSC and opening new therapeutic perspectives for the eradication of such a devastating disease.

SRC Kinase in Glioblastoma News from an Old Acquaintance.

Glioblastoma multiforme (GBM) is one of the most recalcitrant brain tumors characterized by a tumor microenvironment (TME) that strongly supports GBM growth, aggressiveness, invasiveness, and resistance to therapy. Importantly, a common feature of GBM is the aberrant activation of receptor tyrosine kinases (RTKs) and of their downstream signaling cascade, including the non-receptor tyrosine kinase SRC. SRC is a central downstream intermediate of many RTKs, which triggers the phosphorylation of many substrates, therefore, promoting the regulation of a wide range of different pathways involved in cell survival, adhesion, proliferation, motility, and angiogenesis. In addition to the aforementioned pathways, SRC constitutive activity promotes and sustains inflammation and metabolic reprogramming concurring with TME development, therefore, actively sustaining tumor growth. Here, we aim to provide an updated picture of the molecular pathways that link SRC to these events in GBM. In addition, SRC targeting strategies are discussed in order to highlight strengths and weaknesses of SRC inhibitors in GBM management, focusing our attention on their potentialities in combination with conventional therapeutic approaches (i.e., temozolomide) to ameliorate therapy effectiveness.

Temperature sensitivities of metazoan and pre-metazoan Src kinases

Homologous enzymes from different species display functional characteristics that correlate with the physiological and environmental temperatures encountered by the organisms. In this study, we have investigated the temperature sensitivity of the nonreceptor tyrosine kinase Src. We compared the temperature dependencies of c-Src and two Src kinases from single-celled eukaryotes, the choanoflagellate Monosiga brevicollis and the filasterean Capsaspora owczarzaki. Metazoan c-Src exhibits temperature sensitivity, with high activity at 30 °C and 37 °C. This sensitivity is driven by changes in substrate binding as well as maximal velocity, and it is dependent on the amino acid sequence surrounding tyrosine in the substrate. When tested with a peptide that displays temperature-dependent phosphorylation by c-Src, the enzymatic rates for the unicellular Src kinases show much less variation over the temperatures tested. The data demonstrate that unicellular Src kinases are temperature compensated relative to metazoan c-Src, consistent with an evolutionary adaptation to their environments.

TASK channels: channelopathies, trafficking, and receptor-mediated inhibition

TWIK-related acid-sensitive K+ (TASK) channels contribute to the resting membrane potential in various kinds of cells, such as brain neurons, smooth muscle cells, and endocrine cells. Loss-of-function mutations at multiple sites in the KCNK3 gene encoding for TASK1 channels are one of the causes of pulmonary arterial hypertension in humans, whereas a mutation at only one site is reported for TASK3 channels, resulting in a syndrome of mental retardation, hypotonia, and facial dysmorphism. TASK channels are subject to regulation by G protein-coupled receptors (GPCRs). Two mechanisms have been proposed for the GPCR-mediated inhibition of TASK channels: a change in gating and channel endocytosis. The most feasible mechanism for altered gating is diacylglycerol binding to a site in the C-terminus, which is shared by TASK1 and TASK3. The inhibition of channel function by endocytosis requires the presence of a tyrosine residue subjected to phosphorylation by the non-receptor tyrosine kinase Src and a dileucine motif in the C-terminus of TASK1. Therefore, homomeric TASK1 and heteromeric TASK1-TASK3 channels, but not homomeric TASK3, are internalized by GPCR stimulation. Tyrosine phosphorylation by Src is expected to result in a conformational change in the C-terminus, allowing for AP-2, an adaptor protein for clathrin, to bind to the dileucine motif. It is likely that a raft membrane domain is a platform where TASK1 is located and the signaling molecules protein kinase C, Pyk2, and Src are recruited in sequence in response to GPCR stimulation.

Modulation of EPS8 functions by phosphorylation

Objectives Epidermal growth factor receptor pathway substrate 8 (EPS8) is a scaffolding protein involved in regulating cell proliferation, actin dynamics, and receptor trafficking in human cells. EPS8 expression is increased in a range of human cancers, including head and neck squamous cell carcinoma (HNSCC). Previous studies have indicated that overexpression of EPS8 enhances mitogenesis and migration of tumor cells and is sufficient to convert nontumorigenic cells to a tumorigenic phenotype. The nonreceptor tyrosine kinase Src is reported to phosphorylate EPS8 at 4 tyrosine residues, although the impact of this on EPS8 function is unknown. The purpose of this study was to investigate the role of tyrosine phosphorylation of EPS8 at Src target sites in modulating biochemical functions, cell growth, and motility in HNSCC. Study Design Expression plasmids encoding EPS8 with amino acid substitutions to phenylalanine (F) at the 4 putative Src phosphorylation sites (Y485 F, Y525 F, Y602 F, Y774 F), and all 4 combined (4 F), were prepared by site-directed mutagenesis. To evaluate the effect of unphosphorylated EPS8 on downstream signals and biologic behavior, plasmids were transduced into a model cell line expressing a normal endogenous level of EPS8. Additionally, cells were treated with dasatinib, a Src inhibitor, to block phosphorylation of Src substrates. Expression of downstream targets was evaluated by Western blotting. Wound closure and proliferation assays were used to investigate the impact of these mutations on cell motility and growth. Results FOXM1, AURKA, and AURKB levels were decreased in cells expressing the nonphosphorylatable 4 F and Y602 F EPS8 mutants, whereas cells harboring the Y485 F, Y525 F, and Y774 F EPS8 mutants showed no differences in the expression of these proteins compared with controls. Moreover, dasatinib treatment resulted in a significant decrease in the expression of EPS8 downstream targets. In addition, both Y602 F and 4 F mutants elicited a significant reduction in tumor cell proliferation and migration. Conclusions The nonphosphorylatable Y602 F-EPS8 and 4 F-EPS8 mutants decreased the expression of EPS8 downstream targets, as well as reducing tumor cell growth and motility, implying a crucial role for phosphorylation of EPS8, principally at Y602, in mediating protumorigenic signal transduction.

Second-generation Src/Abl inhibitor bosutinib effectively induces apoptosis in human esophageal squamous cell carcinoma (ESCC) cells via inhibiting Src/Abl signaling.

Esophageal cancer is a prevalent type of cancer worldwide and is ranked sixth among cancer-associated mortalities. Aberrant activation of the non-receptor tyrosine kinase Src and c-Abl contribute to the progression of ESCC. Thus, targeting these kinases to treat ESCC is a promising strategy. In this paper, we report that the potent dual Src/Abl inhibitor bosutinib exerts anti-tumor effects on ESCC. Bosutinib inhibits ESCC cell proliferation in a dose-dependent manner. Furthermore, bosutinib suppresses the colony formation ability of ESCC cells. Mechanistically, bosutinib effectively inhibits c-Abl and Src and its downstream signaling pathways, PI3K/AKT/mTOR and JAK/STAT3. In addition, bosutinib enhances the cytotoxic effects of doxorubicin on ESCC cells. In summary, our results reveal that Src and Abl are potential therapeutic targets in ESCC and that the novel Src/Abl inhibitor bosutinib alone or in combination with other chemotherapeutic agents may be a viable option for treating ESCC patients.

Muscarinic receptor stimulation induces TASK1 channel endocytosis through a PKC-Pyk2-Src pathway in PC12 cells

Muscarinic receptor stimulation or protein kinase C (PKC) activation in rat adrenal medullary and PC12 cells rapidly induces tyrosine phosphorylation of TWIK-related-acid-sensitive K+ 1 (TASK1) channels with the subsequent clathrin-dependent endocytosis. Our previous study suggested that the muscarinic signal is transmitted to the non-receptor tyrosine kinase Src through PKC and Pyk2. Although PKC activation is known to stimulate Pyk2 in certain types of cells, its molecular mechanism remains unclear. In this study, proximity ligation assay (PLA) and other molecular biological approaches were used to elucidate the details of this muscarinic signaling in PC12 cells. When green fluorescent protein (GFP)-TASK1 was expressed, the majority of GFP-TASK1 was located at the cell periphery. However, the simultaneous expression of GFP-TASK1 and PKCα, but not PKCδ, led to GFP-TASK1 internalization. Muscarinic receptor stimulation resulted in transient co-localization of Pyk2 and Src at the cell periphery, and expression of kinase dead (KD) Pyk2 and Src, but not Pyk2 and KD Src, resulted in GFP-TASK1 internalization. PLA analysis revealed that in response to muscarine, PKCαactivates Pyk2 through phosphorylating its serine residues. These results indicate that muscarinic receptor stimulation induces TASK1 channel endocytosis sequentially through PKCα, Pyk2, and Src, and PKCα activates Pyk2 through phosphorylation.

Randomized phase-II evaluation of letrozole plus dasatinib in hormone receptor positive metastatic breast cancer patients

The non-receptor tyrosine kinase Src activation plays a role in the malignant progression of breast cancer, including development of endocrine therapy resistance and survival of bone metastases. This study investigated whether adding Src kinase inhibitor dasatinib to aromatase inhibitor (AI) therapy improved outcomes in estrogen receptor (ER)-positive, HER2-negative metastatic breast cancer (MBC). Postmenopausal patients with ER-positive, HER2-negative MBC (0–1 prior chemotherapies and no prior AI for MBC) were eligible for this non-comparative, parallel group, phase-II study. Patients were randomized to letrozole (2.5 mg/day PO) alone or with dasatinib (100 mg/day PO). Patients with disease progression on letrozole alone could crossover to dasatinib plus continued letrozole. The primary endpoint was clinical-benefit-rate (CBR; complete response + partial response + stable disease ≥6 months). A total of 120 patients were randomized. The CBR of 71% (95% CI 58–83%) was observed with letrozole + dasatinib versus the projected CBR of the combination of 56%. The CBR of 66% (95% CI 52–77%) with letrozole alone also exceeded the projected CBR of 39% with letrozole alone. The CBR was 23% in the crossover arm of letrozole plus dasatinib in patients progressing on letrozole alone. Median progression-free survival with the combination was 20.1 months and 9.9 months with letrozole alone. Letrozole plus dasatinib was well tolerated, although 26% of patients required dasatinib dose reductions. In this non-comparative phase-II trial, the CBR of 71% and the median PFS of 20.1 months with letrozole + dasatinib are encouraging and suggest that dasatinib may inhibit the emergence of acquired resistance to AI therapy.

An exploratory randomized-controlled trial of the efficacy of the Src-kinase inhibitor saracatinib as a novel analgesic for cancer-induced bone pain

Pain is a major symptom of bone metastases from advanced cancer and represents a clinical challenge to treat effectively. Basic neurobiology in preclinical animal models implicates enhanced sensory processing in the central nervous system, acting through N-methyl-D-aspartate (NMDA) glutamate receptors, as an important mechanism underpinning persistent pain. The non-receptor tyrosine kinase Src is thought to act as a hub for regulating NMDA receptor activity and the orally available Src inhibitor saracatinib has shown promise as a potential analgesic in recent animal studies. Here we tested the efficacy of saracatinib as a novel analgesic in an exploratory phase II randomized controlled trial on cancer patients with painful bone metastases. Twelve patients completed the study, with 6 receiving saracatinib 125 mg/day for 28 days and 6 receiving placebo. Pharmacokinetic measurements confirmed appropriate plasma levels of drug in the saracatinib-treated group and Src inhibition was achieved clinically by a significant reduction in the bone resorption biomarker serum cross-linked C-terminal telopeptide of type I collagen. Differences between the saracatinib and placebo groups self-reported pain scores, measured using the short form of the Brief Pain Inventory, were not clinically significant after 4 weeks of treatment. There was also no change in consumption of maintenance analgesia in the saracatinib-treated group and no improvement in Quality-of-Life scores. The data were insufficient to demonstrate saracatinib has efficacy as analgesic, although it may have a role as an anti-bone resorptive agent.

Src-mediated crosstalk between FXR and YAP protects against renal fibrosis.

Renal fibrosis is the common pathway of chronic kidney disease progression. The nuclear receptor farnesoid X receptor [FXR, NR1H4 (nuclear receptor subfamily 1 group member 4)], a multifunctional transcription factor, plays a pivotal role in protecting against fibrosis. However, the mechanisms underlying these antifibrotic actions of FXR in kidney disease are largely unknown. Here, we show that agonist GW4064-mediated FXR activation inhibits the activity of the nonreceptor tyrosine kinase Src (proto-oncogene tyrosine-protein kinase), which is critical for regulation of yes-associated protein (YAP) phosphorylation and nuclear localization in renal fibrosis. Activation of FXR suppressed renal fibrosis and Tyr416-Src phosphorylation in TGF-β-treated human renal proximal tubule epithelial (HK2) cells. Moreover, GW4064 treatment in HK2 cells increased Ser127 phosphorylation, cytosolic accumulation of YAP, and interaction of the hippo core kinases (Ste20-like kinase 1, large tumor suppressor kinase 1, and salvador homolog 1). Inhibition of Src using PP2 (Src kinase inhibitor) prevented renal fibrosis and increased Ser127 phosphorylation and cytosolic accumulation of YAP. The expression of fibrosis markers, inflammatory genes, and YAP target genes was increased in the kidneys of FXR knockout mice compared with those of wild-type mice. In addition, GW4064 or WAY-362450 (turofexorate isopropyl) treatment protected against unilateral ureteral obstruction-induced renal fibrosis. Collectively, our data support the novel conclusion that Src-mediated crosstalk between FXR and YAP protects against renal fibrosis, making this pathway a possible therapeutic target for chronic kidney disease.-Kim, D.-H., Choi, H.-I., Park, J. S., Kim, C. S., Bae, E. H., Ma, S. K., Kim, S. W. Src-mediated crosstalk between FXR and YAP protects against renal fibrosis.

SNX10 (sorting nexin 10) inhibits colorectal cancer initiation and progression by controlling autophagic degradation of SRC

ABSTRACTThe non-receptor tyrosine kinase SRC is a key mediator of cellular protumorigenic signals. SRC is aberrantly over-expressed and activated in more than 80% of colorectal cancer (CRC) patients, therefore regulation of its stability and activity is essential. Here, we report a significant down regulation of SNX10 (sorting nexin 10) in human CRC tissues, which is closely related to tumor differentiation, TNM stage, lymph node metastasis and survival period. SNX10 deficiency in normal and neoplastic colorectal epithelial cells promotes initiation and progression of CRC in mice. SNX10 controls SRC levels by mediating autophagosome-lysosome fusion and SRC recruitment for autophagic degradation. These mechanisms ensure proper controlling of the activities of SRC-STAT3 and SRC-CTNNB1 signaling pathways by up-regulating SNX10 expression under stress conditions. These findings suggest that SNX10 acts as a tumor suppressor in CRC and it could be a potential therapeutic target for future development.Abbreviations: ACTB: actin beta; ATG5: autophagy related 5; ATG12: autophagy related 12; CQ: chloroquine; CRC: colorectal cancer; CTNNB1: catenin beta 1; EBSS: Earle’s balanced salt solution; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LAMP2: lysosomal associated membrane protein 2; MAP1LC3: microtubule associated protein 1 light chain 3; MKI67: marker of proliferation Ki-67; mRNA: messenger RNA; PX: phox homology; RT-qPCR: real time quantitative polymerase chain reaction; siRNA: small interfering RNA; SNX10: sorting nexin 10; SQSTM1: sequestosome 1; SRC: SRC proto-oncogene, non-receptor tyrosine kinase; STAT3: signal transducer and activator of transcription 3; WT: wild type.

The Involvement of Src in Airway Inflammation Induced by Repeated Exposure to Lipopolysaccharide in Mice

Corticosteroid insensitive airway inflammation is one of major barrier to effective managements of chronic airway diseases, such as chronic obstructive pulmonary disease (COPD) and severe asthma. The role of nonreceptor tyrosine kinase Src is important in airway inflammation in mice models of atopic asthma and COPD. Thus, in this study, we determined the effects of Src inhibitor, dasatinib, on airway inflammation induced by repeated intranasal exposure to lipopolysaccharide (LPS). Male mice (A/J strain, 5 weeks old) were intranasally exposed to LPS twice daily for 3 d, and dasatinib was intranasally treated 2 h prior to each LPS exposure. A day after the last stimulation, lungs and bronchoalveolar lavage fluid (BALF) were collected. Dasatinib attenuated the accumulation of inflammatory cells in lungs, and the increase in the numbers of inflammatory cells and the accumulation of cytokines/chemokines in BALF in a dose dependent manner. Therefore, this study suggested that targeting the Src can provide a new therapeutic approach for corticosteroid insensitive pulmonary diseases.

Phosphorylation of hepatic farnesoid X receptor by FGF19 signaling–activated Src maintains cholesterol levels and protects from atherosclerosis

The bile acid (BA) nuclear receptor, farnesoid X receptor (FXR/NR1H4), maintains metabolic homeostasis by transcriptional control of numerous genes, including an intestinal hormone, fibroblast growth factor-19 (FGF19; FGF15 in mice). Besides activation by BAs, the gene-regulatory function of FXR is also modulated by hormone or nutrient signaling-induced post-translational modifications. Recently, phosphorylation at Tyr-67 by the FGF15/19 signaling-activated nonreceptor tyrosine kinase Src was shown to be important for FXR function in BA homeostasis. Here, we examined the role of this FXR phosphorylation in cholesterol regulation. In both hepatic FXR-knockout and FXR-knockdown mice, reconstitution of FXR expression up-regulated cholesterol transport genes for its biliary excretion, including scavenger receptor class B member 1 (Scarb1) and ABC subfamily G member 8 (Abcg5/8), decreased hepatic and plasma cholesterol levels, and increased biliary and fecal cholesterol levels. Of note, these sterol-lowering effects were blunted by substitution of Phe for Tyr-67 in FXR. Moreover, consistent with Src's role in phosphorylating FXR, Src knockdown impaired cholesterol regulation in mice. In hypercholesterolemic apolipoprotein E-deficient mice, expression of FXR, but not Y67F-FXR, ameliorated atherosclerosis, whereas Src down-regulation exacerbated it. Feeding or treatment with an FXR agonist induced Abcg5/8 and Scarb1 expression in WT, but not FGF15-knockout, mice. Furthermore, FGF19 treatment increased occupancy of FXR at Abcg5/8 and Scarb1, expression of these genes, and cholesterol efflux from hepatocytes. These FGF19-mediated effects were blunted by the Y67F-FXR substitution or Src down-regulation or inhibition. We conclude that phosphorylation of hepatic FXR by FGF15/19-induced Src maintains cholesterol homeostasis and protects against atherosclerosis.

Blockade of HMGB1 signaling pathway by ethyl pyruvate inhibits tumor growth in diffuse large B-cell lymphoma

High mobility group box 1 (HMGB1) protein in the tumor microenvironment actively contributes to tumor progression but its role in diffuse large B-cell lymphoma (DLBCL) is unknown. The aim of this study was to determine the mechanism by which HMGB1 promotes tumor growth in DLBCL and whether blockade of HMGB1 signaling pathway could inhibit tumorigenesis. We report that HMGB1 promotes proliferation of DLBCL cells by activation of AKT, extracellular signal-regulated kinases 1/2 (ERK1/2), signal transducer and activator of transcription 3 (STAT3) and SRC Proto-Oncogene, Non-Receptor Tyrosine Kinase (Src). Ethyl pyruvate (EP), an anti-inflammatory agent, inhibits HMGB1 active release from DLBCL cells and significantly inhibited proliferation of DLBCL cells in vitro. Treatment with EP significantly prevented and inhibited tumor growth in vivo and prolonged DLBCL-bearing mice survival. EP significantly downregulated HMGB1 expression and phosphorylation of Src and ERK1/2 in mice lymphoma tissue. EP induced accumulation of the cell cycle inhibitor p27 but downregulated expression of cyclin-dependent kinase 2 (CDK2). Increased nuclear translocation of p27 interacted with CDK2 and cyclin A, which led to blockade of cell cycle progression at the G1 to S phase transition. In conclusion, we demonstrated for the first time that blockade of HMGB1-mediated signaling pathway by EP effectively inhibited DLBCL tumorigenesis and disease progression.

Exploring the functional role of Nlrp12's interaction with Hck

The members of the family of Nucleotide‐binding oligomerization domain‐Like Receptor proteins (NLR) are composed of a N‐terminal domain, a central nucleotide‐binding domain, and a C‐terminal ligand‐binding domain. They are generally known to be involved in regulating NF‐kB pathway. A yeast two‐hybrid screen was performed with the pyrin plus nucleotide binding domain of NLR family pyrin domain‐containing12 protein (Nlrp12) as a bait and human leucocyte proteins a prey. It revealed that Hck, a src non‐receptor tyrosine kinase family member was the top hit. Further experiments confirmed that: 1) the C‐terminal 40 amino acids of Hck specifically binds to Nlrp12's pyrin plus nucleotide binding domains; 2) the last 30 amino acids of Hck is sufficient to bind to Nlrp12's pyrin plus nucleotide binding domains, but neither to Nlrp12's pyrin domain alone nor Nlrp12's nucleotide‐binding domain alone; and, 3) the last 40 amino acids of dephosphorylated, but not phosphorylated, Hck preferentially binds to full‐length Nlrp12. Nlrp12 co‐immunoprecipitated with Hck when both are heterologously overexpressed in 293T cells. Using the same system, Nlrp12 and Hck are co‐localized by immunofluorescence. In addition, in Raw 264.7, U937, and THP‐1 cells, endogenous Hck co‐immunoprecipitated with transfected Nlrp12. Since Csk is a tyrosine kinase of members of the src family that specifically binds to the tyrosine negative regulatory residue at the C‐terminal of src family kinases and phosphorylates Hck to inactivate it in mammalian cells, it is hypothesized that Nlrp12 competes with Csk binding to Hck, thereby activating Hck. Since Nlrp12 also inhibits the NF‐kB pathway, an alternative hypothesis is that Hck rescues cells from Nlrp12's inhibition of NF‐kB activity. An NF‐kB luciferase assay confirmed that overexpression of Hck alone does not inhibit NF‐kB, but overexpression of Hck plus Nlrp12 rescued Nlrp12's inhibition of the NF‐kB pathway.Support or Funding InformationUSC School of Pharmacy Mutual Funds 2017–2019This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.