Bmx tyrosine kinase transgene induces skin hyperplasia, inflammatory angiogenesis, and accelerated wound healing

ErbB4 Is a Potential Key Regulator of the Pathways Activated by NTRK-Fusions in Thyroid Cancer

NTRK gene fusions are drivers of tumorigenesis events that specific Trk-inhibitors can target. Current knowledge of the downstream pathways activated has been previously limited to the pathways of regulator proteins phosphorylated directly by Trk receptors. Here, we aimed to detect genes whose expression is increased in response to the activation of these pathways. We identified and analyzed differentially expressed genes in thyroid cancer samples with NTRK1 or NTRK3 gene fusions, and without any NTRK fusions, versus normal thyroid gland tissues, using data from the Cancer Genome Atlas, the DESeq2 tool, and the Genome Enhancer and geneXplain platforms. Searching for the genes activated only in samples with an NTRK fusion as opposed to those without NTRK fusions, we identified 29 genes involved in nervous system development, including AUTS2, DTNA, ERBB4, FLRT2, FLRT3, RPH3A, and SCN4A. We found that genes regulating the expression of the upregulated genes (i.e., upstream regulators) were enriched in the “signaling by ERBB4” pathway. ERBB4 was also one of three genes encoding master regulators whose expression was increased only in samples with an NTRK fusion. Moreover, the algorithm searching for positive feedback loops for gene promoters and transcription factors (a so-called “walking pathways” algorithm) identified the ErbB4 protein as the key master regulator. ERBB4 upregulation (p-value = 0.004) was confirmed in an independent sample of ETV6-NTRK3-positive FFPE specimens. Thus, ErbB4 is the potential key regulator of the pathways activated by NTRK gene fusions in thyroid cancer. These results are preliminary and require additional biochemical validation.

Fas signaling in adipocytes promotes low-grade inflammation and lung metastasis of colorectal cancer through interaction with Bmx

Obesity is a global public health issue. Obesity-related chronic low-grade inflammation (meta-inflammation) can lead to aberrant adipokine release and promote cardiometabolic diseases and obesity-related tumors. However, the mechanisms involved in the initiation of inflammatory responses in obesity and obesity-related tumors as well as metastasis are not fully understood. In this study, we found that the increased tumor necrosis factor-alpha (TNF-α) in adipocytes promoted the lung metastasis of MC38 colon cancer cells via Fas signaling. The release of TNF-α and interleukin (IL)-6 by Fas signaling in adipocytes was caused by the activation of the nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways mediated by the interaction of Fas with Bmx, a non-receptor tyrosine kinase. Moreover, the Fas/Bmx complex is involved in the inflammation of adipocytes via Fas at the Tyr189 site and SH2 domain of Bmx. This is the first study to report the interaction between Fas and Bmx in adipocyte inflammation, which may provide clues for the development of potential new treatment strategies for obesity-related diseases.

Emerging Kinase Therapeutic Targets in Pancreatic Ductal Adenocarcinoma and Pancreatic Cancer Desmoplasia

Kinase drug discovery represents an active area of therapeutic research, with previous pharmaceutical success improving patient outcomes across a wide variety of human diseases. In pancreatic ductal adenocarcinoma (PDAC), innovative pharmaceutical strategies such as kinase targeting have been unable to appreciably increase patient survival. This may be due, in part, to unchecked desmoplastic reactions to pancreatic tumors. Desmoplastic stroma enhances tumor development and progression while simultaneously restricting drug delivery to the tumor cells it protects. Emerging evidence indicates that many of the pathologic fibrotic processes directly or indirectly supporting desmoplasia may be driven by targetable protein tyrosine kinases such as Fyn-related kinase (FRK); B lymphoid kinase (BLK); hemopoietic cell kinase (HCK); ABL proto-oncogene 2 kinase (ABL2); discoidin domain receptor 1 kinase (DDR1); Lck/Yes-related novel kinase (LYN); ephrin receptor A8 kinase (EPHA8); FYN proto-oncogene kinase (FYN); lymphocyte cell-specific kinase (LCK); tec protein kinase (TEC). Herein, we review literature related to these kinases and posit signaling networks, mechanisms, and biochemical relationships by which this group may contribute to PDAC tumor growth and desmoplasia.

Transcriptome analysis during photostimulated recrudescence reveals distinct patterns of gene regulation in Siberian hamster ovaries†

In Siberian hamsters, exposure to short days (SDs, 8 h light:16 h dark) reduces reproductive function centrally by decreasing gonadotropin secretion, whereas subsequent transfer of photoinhibited hamsters to stimulatory long days (LDs, 16 L:8 D) promotes follicle stimulating hormone (FSH) release inducing ovarian recrudescence. Although differences between SD and LD ovaries have been investigated, a systematic investigation of the ovarian transcriptome across photoperiod groups to identify potentially novel factors that contribute to photostimulated restoration of ovarian function had not been conducted. Hamsters were assigned to one of four photoperiod groups: LD to maintain ovarian cyclicity, SD to induce ovarian regression, or post transfer (PT), where females housed in SD for 14-weeks were transferred to LD for 2-days or 1-week to reflect photostimulated ovaries prior to (PTd2) and following (PTw1) the return of systemic FSH. Ovarian RNA was extracted to create RNA-sequencing libraries and short-read sequencing Illumina assays that mapped and quantified the ovarian transcriptomes (n = 4/group). Ovarian and uterine masses, plasma FSH, and numbers of antral follicles and corpora lutea decreased in SD as compared to LD ovaries (P < 0.05). When reads were aligned to the mouse genome, 18 548 genes were sufficiently quantified. Most of the differentially expressed genes noted between functional LD ovaries and regressed SD ovaries; however, five main expression patterns were identified across photoperiod groups. These results, generally corroborated by select protein immunostaining, provide a map of photoregulated ovary function and identify novel genes that may contribute to the photostimulated resumption of ovarian activity.

Nuclear localization of the tyrosine kinase BMX mediates VEGFR2 expression

Vascular endothelial growth factor receptors (VEGFRs) are major contributors to angiogenesis and lymphangiogenesis through the binding of VEGF ligands. We have previously shown that the bone marrow tyrosine kinase BMX is critical for inflammatory angiogenesis via its direct transactivation of VEGFR2. In the present study, we show that siRNA-mediated silencing of BMX led to a significant decrease in the total levels of VEGFR2 mRNA and protein, without affecting their stability, in human endothelial cells (ECs). Interestingly, BMX was detected in the nuclei of ECs, and the SH3 domain of BMX was necessary for its nuclear localization. Luciferase assays showed a significant decrease in the Vegfr2 (kdr) gene promoter activity in ECs after BMX silencing, indicating that BMX is necessary for Vegfr2 transcription. In addition, we found that wild-type BMX, but not a catalytic inactive mutant BMX-K445R, promoted Vegfr2 promoter activity and VEGF-induced EC migration and tube sprouting. Mechanistically, we show that the enhancement of Vegfr2 promoter activity by BMX was mediated by Sp1, a transcription factor critical for the Vegfr2 promoter. Loss of BMX significantly reduced Sp1 binding to the Vegfr2 promoter as assayed by chromatin immunoprecipitation assays. Wild-type BMX, but not a kinase-inactive form of BMX, associated with and potentially phosphorylated Sp1. Moreover, a nuclear-targeted BMX (NLS-BMX), but not cytoplasm-localized form (NES-BMX), bound to Sp1 and augmented VEGFR2 expression. In conclusion, we uncovered a novel function of nuclear-localized BMX in regulating VEGFR2 expression and angiogenesis, suggesting that BMX is a therapeutic target for angiogenesis-related diseases.

Genomic analysis reveals variant association with high altitude adaptation in native chickens

Native chickens are endangered genetic resources that are kept by farmers for different purposes. Native chickens distributed in a wide range of altitudes, have developed adaptive mechanisms to deal with hypoxia. For the first time, we report variants associated with high-altitude adaptation in Iranian native chickens by whole genome sequencing of lowland and highland chickens. We found that these adaptive variants are involved in DNA repair, organs development, immune response and histone binding. Amazingly, signature selection analysis demonstrated that differential variants are adaptive in response to hypoxia and are not due to other evolutionary pressures. Cellular component analysis of variants showed that mitochondrion is the most important organelle for hypoxia adaptation. A total of 50 variants was detected in mtDNA for highland and lowland chickens. High-altitude associated with variant discovery highlighted the importance of COX3, a gene involved in cell respiration, in hypoxia adaptation. The results of study suggest that MIR6644-2 is involved in hypoxia and high-altitude adaptations by regulation of embryo development. Finally, 3877 novel SNVs including the mtDNA ones, were submitted to EBI (PRJEB24944). Whole-genome sequencing and variant discovery of native chickens provided novel insights about adaptation mechanisms and highlights the importance of valuable genomic variants in chickens.

Optimization of novel reversible Bruton's tyrosine kinase inhibitors identified using Tethering-fragment-based screens

Since the approval of ibrutinib for the treatment of B-cell malignancies in 2012, numerous clinical trials have been reported using covalent inhibitors to target Bruton's tyrosine kinase (BTK) for oncology indications. However, a formidable challenge for the pharmaceutical industry has been the identification of reversible, selective, potent molecules for inhibition of BTK. Herein, we report application of Tethering-fragment-based screens to identify low molecular weight fragments which were further optimized to improve on-target potency and ADME properties leading to the discovery of reversible, selective, potent BTK inhibitors suitable for pre-clinical proof-of-concept studies.

BMX-Mediated Regulation of Multiple Tyrosine Kinases Contributes to Castration Resistance in Prostate Cancer

Prostate cancer responds to therapies that suppress androgen receptor (AR) activity (androgen deprivation therapy, ADT) but invariably progresses to castration-resistant prostate cancer (CRPC). The Tec family nonreceptor tyrosine kinase BMX is activated downstream of PI3K and has been implicated in regulation of multiple pathways and in the development of cancers including prostate cancer. However, its precise mechanisms of action, and particularly its endogenous substrates, remain to be established. Here, we demonstrate that BMX expression in prostate cancer is suppressed directly by AR via binding to the BMX gene and that BMX expression is subsequently rapidly increased in response to ADT. BMX contributed to CRPC development in cell line and xenograft models by positively regulating the activities of multiple receptor tyrosine kinases through phosphorylation of a phosphotyrosine-tyrosine (pYY) motif in their activation loop, generating pYpY that is required for full kinase activity. To assess BMX activity in vivo, we generated a BMX substrate-specific antibody (anti-pYpY) and found that its reactivity correlated with BMX expression in clinical samples, supporting pYY as an in vivo substrate. Inhibition of BMX with ibrutinib (developed as an inhibitor of the related Tec kinase BTK) or another BMX inhibitor BMX-IN-1 markedly enhanced the response to castration in a prostate cancer xenograft model. These data indicate that increased BMX in response to ADT contributes to enhanced tyrosine kinase signaling and the subsequent emergence of CRPC, and that combination therapies targeting AR and BMX may be effective in a subset of patients.Significance: The tyrosine kinase BMX is negatively regulated by androgen and contributes to castration-resistant prostate cancer by enhancing the phosphorylation and activation of multiple receptor tyrosine kinases following ADT. Cancer Res; 78(18); 5203-15. ©2018 AACR.

Glucose-Dependent Insulinotropic Polypeptide Ameliorates Mild Traumatic Brain Injury-Induced Cognitive and Sensorimotor Deficits and Neuroinflammation in Rats

Mild traumatic brain injury (mTBI) is a major public health issue, representing 75-90% of all cases of TBI. In clinical settings, mTBI, which is defined as a Glascow Coma Scale (GCS) score of 13-15, can lead to various physical, cognitive, emotional, and psychological-related symptoms. To date, there are no pharmaceutical-based therapies to manage the development of the pathological deficits associated with mTBI. In this study, the neurotrophic and neuroprotective properties of glucose-dependent insulinotropic polypeptide (GIP), an incretin similar to glucagon-like peptide-1 (GLP-1), was investigated after its steady-state subcutaneous administration, focusing on behavior after mTBI in an in vivo animal model. The mTBI rat model was generated by a mild controlled cortical impact (mCCI) and used to evaluate the therapeutic potential of GIP. We used the Morris water maze and novel object recognition tests, which are tasks for spatial and recognition memory, respectively, to identify the putative therapeutic effects of GIP on cognitive function. Further, beam walking and the adhesive removal tests were used to evaluate locomotor activity and somatosensory functions in rats with and without GIP administration after mCCI lesion. Lastly, we used immunohistochemical (IHC) staining and Western blot analyses to evaluate the inflammatory markers, glial fibrillary acidic protein (GFAP), amyloid-β precursor protein (APP), and bone marrow tyrosine kinase gene in chromosome X (BMX) in animals with mTBI. GIP was well tolerated and ameliorated mTBI-induced memory impairments, poor balance, and sensorimotor deficits after initiation in the post-injury period. In addition, GIP mitigated mTBI-induced neuroinflammatory changes on GFAP, APP, and BMX protein levels. These findings suggest GIP has significant benefits in managing mTBI-related symptoms and represents a novel strategy for mTBI treatment.

Targets for Ibrutinib Beyond B Cell Malignancies

Ibrutinib (Imbruvica^™) is an irreversible, potent inhibitor of Bruton's tyrosine kinase (BTK). Over the last few years, ibrutinib has developed from a promising drug candidate to being approved by FDA for the treatment of three B cell malignancies, a truly remarkable feat. Few, if any medicines are monospecific and ibrutinib is no exception; already during ibrutinib's initial characterization, it was found that it could bind also to other kinases. In this review, we discuss the implications of such interactions, which go beyond the selective effect on BTK in B cell malignancies. In certain cases, the outcome of ibrutinib treatment likely results from the combined inhibition of BTK and other kinases, causing additive or synergistic, effects. Conversely, there are also examples when the clinical outcome seems unrelated to inhibition of BTK. Thus, more specifically, adverse effects such as enhanced bleeding or arrhythmias could potentially be explained by different interactions. We also predict that during long‐term treatment bone homoeostasis might be affected due to the inhibition of osteoclasts. Moreover, the binding of ibrutinib to molecular targets other than BTK or effects on cells other than B cell‐derived malignancies could be beneficial and result in new indications for clinical applications.

Endothelial Bmx tyrosine kinase activity is essential for myocardial hypertrophy and remodeling

Cardiac hypertrophy accompanies many forms of heart disease, including ischemic disease, hypertension, heart failure, and valvular disease, and it is a strong predictor of increased cardiovascular morbidity and mortality. Deletion of bone marrow kinase in chromosome X (Bmx), an arterial nonreceptor tyrosine kinase, has been shown to inhibit cardiac hypertrophy in mice. This finding raised the possibility of therapeutic use of Bmx tyrosine kinase inhibitors, which we have addressed here by analyzing cardiac hypertrophy in gene-targeted mice deficient in Bmx tyrosine kinase activity. We found that angiotensin II (Ang II)-induced cardiac hypertrophy is significantly reduced in mice deficient in Bmx and in mice with inactivated Bmx tyrosine kinase compared with WT mice. Genome-wide transcriptomic profiling showed that Bmx inactivation suppresses myocardial expression of genes related to Ang II-induced inflammatory and extracellular matrix responses whereas expression of RNAs encoding mitochondrial proteins after Ang II administration was maintained in Bmx-inactivated hearts. Very little or no Bmx mRNA was expressed in human cardiomyocytes whereas human cardiac endothelial cells expressed abundant amounts. Ang II stimulation of endothelial cells increased Bmx phosphorylation, and Bmx gene silencing inhibited downstream STAT3 signaling, which has been implicated in cardiac hypertrophy. Furthermore, activation of the mechanistic target of rapamycin complex 1 pathway by Ang II treatment was decreased in the Bmx-deficient hearts. Our results demonstrate that inhibition of the cross-talk between endothelial cells and cardiomyocytes by Bmx inactivation suppresses Ang II-induced signals for cardiac hypertrophy. These results suggest that the endothelial Bmx tyrosine kinase could provide a target to attenuate the development of cardiac hypertrophy.

BMX Negatively Regulates BAK Function, Thereby Increasing Apoptotic Resistance to Chemotherapeutic Drugs

The ability of chemotherapeutic agents to induce apoptosis, predominantly via the mitochondrial (intrinsic) apoptotic pathway, is thought to be a major determinant of the sensitivity of a given cancer to treatment. Intrinsic apoptosis, regulated by the BCL2 family, integrates diverse apoptotic signals to determine cell death commitment and then activates the nodal effector protein BAK to initiate the apoptotic cascade. In this study, we identified the tyrosine kinase BMX as a direct negative regulator of BAK function. BMX associates with BAK in viable cells and is the first kinase to phosphorylate the key tyrosine residue needed to maintain BAK in an inactive conformation. Importantly, elevated BMX expression prevents BAK activation in tumor cells treated with chemotherapeutic agents and is associated with increased resistance to apoptosis and decreased patient survival. Accordingly, BMX expression was elevated in prostate, breast, and colon cancers compared with normal tissue, including in aggressive triple-negative breast cancers where BMX overexpression may be a novel biomarker. Furthermore, BMX silencing potentiated BAK activation, rendering tumor cells hypersensitive to otherwise sublethal doses of clinically relevant chemotherapeutic agents. Our finding that BMX directly inhibits a core component of the intrinsic apoptosis machinery opens opportunities to improve the efficacy of existing chemotherapy by potentiating BAK-driven cell death in cancer cells.

The influence of BMX gene polymorphisms on clinical symptoms after mild traumatic brain injury

Mild traumatic brain injury (mTBI) is one of the most common neurological disorders. Most patients diagnosed with mTBI could fully recover, but 15% of patients suffer from persistent symptoms. In recent studies, genetic factors were found to be associated with recovery and clinical outcomes after TBI. In addition, results from our previous research have demonstrated that the bone marrow tyrosine kinase gene in chromosome X (BMX), a member of the Tec family of kinases, is highly expressed in rats with TBI. Therefore, our aim in this study was to identify the association between genetic polymorphisms of BMX and clinical symptoms following mTBI. Four tagging single nucleotide polymorphisms (tSNPs) of BMX with minimum allele frequency (MAF) >1% were selected from the HapMap Han Chinese database. Among these polymorphisms, rs16979956 was found to be associated with the Beck anxiety inventory (BAI) and dizziness handicap inventory (DHI) scores within the first week after head injury. Additionally, another SNP, rs35697037, showed a significant correlation with dizziness symptoms. These findings suggested that polymorphisms of the BMX gene could be a potential predictor of clinical symptoms following mTBI.

Tyrosine kinase BMX phosphorylates phosphotyrosine-primed motif mediating the activation of multiple receptor tyrosine kinases

The nonreceptor tyrosine kinase BMX (bone marrow tyrosine kinase gene on chromosome X) is abundant in various cell types and activated downstream of phosphatidylinositol-3 kinase (PI3K) and the kinase Src, but its substrates are unknown. Positional scanning peptide library screening revealed a marked preference for a priming phosphorylated tyrosine (pY) in the -1 position, indicating that BMX substrates may include multiple tyrosine kinases that are fully activated by pYpY sites in the kinase domain. BMX phosphorylated focal adhesion kinase (FAK) at Tyr⁵⁷⁷ subsequent to its Src-mediated phosphorylation at Tyr⁵⁷⁶. Loss of BMX by RNA interference or by genetic deletion in mouse embryonic fibroblasts (MEFs) markedly impaired FAK activity. Phosphorylation of the insulin receptor in the kinase domain at Tyr¹¹⁸⁹ and Tyr¹¹⁹⁰, as well as Tyr¹¹⁸⁵, and downstream phosphorylation of the kinase AKT at Thr³⁰⁸ were similarly impaired by BMX deficiency. However, insulin-induced phosphorylation of AKT at Ser⁴⁷³ was not impaired in Bmx knockout MEFs or liver tissue from Bmx knockout mice, which also showed increased insulin-stimulated glucose uptake, possibly because of decreased abundance of the phosphatase PHLPP (PH domain leucine-rich repeat protein phosphatase). Thus, by identifying the pYpY motif as a substrate for BMX, our findings suggest that BMX functions as a central regulator among multiple signaling pathways mediated by tyrosine kinases.

Different sham procedures for rats in traumatic brain injury experiments induce corresponding increases in levels of trauma markers

BACKGROUND

In traumatic brain injury animal models, sham or naïve control groups are often used for the analysis of injured animals; however, the existence and/or significance of differences in the control groups has yet to be studied. In addition, recent controversies regarding the decompressive craniectomy trial in which decompressive craniectomies in patients with severe traumatic brain injury and refractory increased intracranial pressure remains unsettled. Although the report demonstrated that the procedure may result in less favorable long-term outcomes despite the decrease in intracranial pressure and shorter length of intensive care unit stay, the study has been criticized, and the debate is still inconclusive partly because of a lack of mechanistic explanation. We have recently discovered epithelial and endothelial tyrosine kinase (Etk) to exhibit upregulation after traumatic neural injury and will compare the effects of craniectomy procedure with those of other procedures inducing different levels of severity.

MATERIALS AND METHODS

Four groups of rats receiving different procedures (controlled cortical impact, craniectomy, bicortical drilling, and unicortical drilling [UD]) were compared. Polymerase chain reaction, Western blot analysis, and immunoflorescence staining of Etk, S100, and glial fibrillary acidic protein levels were used to analyze the results and compare the different groups.

RESULTS

Etk upregulation was statistically significant between craniectomy and UD groups. The level of change for glial fibrillary acidic protein and S100 was only significant when cortex was impacted.

CONCLUSIONS

UD may be preferable as a sham control procedure over craniectomy or bicortical drilling. Increases in the expression of Etk in the craniectomy group suggest a possible mechanism by which unfavorable outcome occurs in patients receiving craniectomy procedures.

Location and level of Etk expression in neurons are associated with varied severity of traumatic brain injury

Background

Much recent research effort in traumatic brain injury (TBI) has been devoted to the discovery of a reliable biomarker correlating with severity of injury. Currently, no consensus has been reached regarding a representative marker for traumatic brain injury. In this study, we explored the potential of epithelial/endothelial tyrosine kinase (Etk) as a novel marker for TBI.

Methodology/Principal Findings

TBI was induced in Sprague Dawley (SD) rats by controlled cortical impact. Brain tissue samples were analyzed by Western blot, Q-PCR, and immunofluorescence staining using various markers including glial fibrillary acidic protein, and epithelial/endothelial tyrosine kinase (Etk). Results show increased Etk expression with increased number and severity of impacts. Expression increased 2.36 to 7-fold relative to trauma severity. Significant upregulation of Etk appeared at 1 hour after injury. The expression level of Etk was inversely correlated with distance from injury site. Etk and trauma/inflammation related markers increased post-TBI, while other tyrosine kinases did not.

Conclusion/Significance

The observed correlation between Etk level and the number of impacts, the severity of impact, and the time course after impact, as well as its inverse correlation with distance away from injury site, support the potential of Etk as a possible indicator of trauma severity.

Deletion of the endothelial Bmx tyrosine kinase decreases tumor angiogenesis and growth

Bmx, [corrected] also known as Etk, is a member of the Tec family of nonreceptor tyrosine kinases. Bmx is expressed mainly in arterial endothelia and in myeloid hematopoietic cells. Bmx regulates ischemia-mediated arteriogenesis and lymphangiogenesis, but its role in tumor angiogenesis is not known. In this study, we characterized the function of Bmx in tumor growth using both Bmx knockout and transgenic mice. Isogenic colon, lung, and melanoma tumor xenotransplants showed reductions in growth and tumor angiogenesis in Bmx gene-deleted ((-/-)) mice, whereas developmental angiogenesis was not affected. In addition, growth of transgenic pancreatic islet carcinomas and intestinal adenomas was also slower in Bmx(-/-) mice. Knockout mice showed high levels of Bmx expression in endothelial cells of tumor-associated and peritumoral arteries. Moreover, endothelial cells lacking Bmx showed impaired phosphorylation of extracellular signal-regulated kinase (Erk) upon VEGF stimulation, indicating that Bmx contributes to the transduction of vascular endothelial growth factor signals. In transgenic mice overexpressing Bmx in epidermal keratinocytes, tumors induced by a two-stage chemical skin carcinogenesis treatment showed increased growth and angiogenesis. Our findings therefore indicate that Bmx activity contributes to tumor angiogenesis and growth.

Suppression of Etk/Bmx Protects against Ischemic Brain Injury

Etk/Bmx (epithelial and endothelial tyrosine kinase, also known as BMX), a member of the Tec (tyrosine kinase expressed in hepatocellular carcinoma) family of protein-tyrosine kinases, is an important regulator of signal transduction for the activation of cell growth, differentiation, and development. We have previously reported that activation of Etk leads to apoptosis in MDA-MB-468 cells. The purpose of this study was to examine the role of Etk in neuronal injury induced by H2O2 or ischemia. Using Western blot analysis and immunohistochemistry, we found that treatment with H2O2 significantly enhanced phosphorylation of Etk and its downstream signaling molecule Stat1 in primary cortical neurons. Inhibiting Etk activity by LFM-A13 or knocking down Etk expression by a specific shRNA increased the survival of primary cortical neurons. Similarly, at 1 day after a 60-min middle cerebral artery occlusion (MCAo) in adult rats, both phosphorylated Etk and Stat1 were coexpressed with apoptotic markers in neurons in the penumbra. Pretreatment with LFM-A13 or an adenoviral vector encoding the kinase deletion mutant EtkΔk attenuated caspase-3 activity and infarct volume in ischemic brain. All together, our data suggest that Etk is activated after neuronal injury. Suppressing Etk activity protects against neurodegeneration in ischemic brain.

Nonreceptor tyrosine kinase BMX maintains self-renewal and tumorigenic potential of glioblastoma stem cells by activating STAT3

Glioblastomas display cellular hierarchies containing tumor-propagating glioblastoma stem cells (GSCs). STAT3 is a critical signaling node in GSC maintenance but molecular mechanisms underlying STAT3 activation in GSCs are poorly defined. Here we demonstrate that the bone marrow X-linked (BMX) nonreceptor tyrosine kinase activates STAT3 signaling to maintain self-renewal and tumorigenic potential of GSCs. BMX is differentially expressed in GSCs relative to nonstem cancer cells and neural progenitors. BMX knockdown potently inhibited STAT3 activation, expression of GSC transcription factors, and growth of GSC-derived intracranial tumors. Constitutively active STAT3 rescued the effects of BMX downregulation, supporting that BMX signals through STAT3 in GSCs. These data demonstrate that BMX represents a GSC therapeutic target and reinforces the importance of STAT3 signaling in stem-like cancer phenotypes.

Compensatory upregulation of tyrosine kinase Etk/BMX in response to androgen deprivation promotes castration-resistant growth of prostate cancer cells

We previously showed that targeted expression of non-receptor tyrosine kinase Etk/BMX in mouse prostate induces prostate intraepithelial neoplasia, implying a possible causal role of Etk in prostate cancer development and progression. Here, we report that Etk is upregulated in both human and mouse prostates in response to androgen ablation. Etk expression seems to be differentially regulated by androgen and interleukin 6 (IL-6), which is possibly mediated by the androgen receptor (AR) in prostate cancer cells. Our immunohistochemical analysis of tissue microarrays containing 112 human prostate tumor samples revealed that Etk expression is elevated in hormone-resistant prostate cancer and positively correlated with tyrosine phosphorylation of AR (Pearson correlation coefficient rho = 0.71, P < 0.0001). AR tyrosine phosphorylation is increased in Etk-overexpressing cells, suggesting that Etk may be another tyrosine kinase, in addition to Src and Ack-1, which can phosphorylate AR. We also showed that Etk can directly interact with AR through its Src homology 2 domain, and such interaction may prevent the association of AR with Mdm2, leading to stabilization of AR under androgen-depleted conditions. Overexpression of Etk in androgen-sensitive LNCaP cells promotes tumor growth while knocking down Etk expression in hormone-insensitive prostate cancer cells by a specific shRNA that inhibits tumor growth under androgen-depleted conditions. Taken together, our data suggest that Etk may be a component of the adaptive compensatory mechanism activated by androgen ablation in prostate and may play a role in hormone resistance, at least in part, through direct modulation of the AR signaling pathway.

Etk/Bmx regulates proteinase-activated-receptor1 (PAR1) in breast cancer invasion: signaling partners, hierarchy and physiological significance

BACKGROUND

While protease-activated-receptor 1 (PAR(1)) plays a central role in tumor progression, little is known about the cell signaling involved.

METHODOLOGY/PRINCIPAL FINDINGS

We show here the impact of PAR(1) cellular activities using both an orthotopic mouse mammary xenograft and a colorectal-liver metastasis model in vivo, with biochemical analyses in vitro. Large and highly vascularized tumors were generated by cells over-expressing wt hPar1, Y397Z hPar1, with persistent signaling, or Y381A hPar1 mutant constructs. In contrast, cells over-expressing the truncated form of hPar1, which lacks the cytoplasmic tail, developed small or no tumors, similar to cells expressing empty vector or control untreated cells. Antibody array membranes revealed essential hPar1 partners including Etk/Bmx and Shc. PAR(1) activation induces Etk/Bmx and Shc binding to the receptor C-tail to form a complex. Y/A mutations in the PAR(1) C-tail did not prevent Shc-PAR(1) association, but enhanced the number of liver metastases compared with the already increased metastases obtained with wt hPar1. We found that Etk/Bmx first binds via the PH domain to a region of seven residues, located between C378-S384 in PAR(1) C-tail, enabling subsequent Shc association. Importantly, expression of the hPar1-7A mutant form (substituted A, residues 378-384), which is incapable of binding Etk/Bmx, resulted in inhibition of invasion through Matrigel-coated membranes. Similarly, knocking down Etk/Bmx inhibited PAR(1)-induced MDA-MB-435 cell migration. In addition, intact spheroid morphogenesis of MCF10A cells is markedly disrupted by the ectopic expression of wt hPar1. In contrast, the forced expression of the hPar1-7A mutant results in normal ball-shaped spheroids. Thus, by preventing binding of Etk/Bmx to PAR(1) -C-tail, hPar1 oncogenic properties are abrogated.

CONCLUSIONS/SIGNIFICANCE

This is the first demonstration that a cytoplasmic portion of the PAR(1) C-tail functions as a scaffold site. We identify here essential signaling partners, determine the hierarchy of binding and provide a platform for therapeutic vehicles via definition of the critical PAR(1)-associating region in the breast cancer signaling niche.

Bone marrow X kinase-mediated signal transduction in irradiated vascular endothelium

Radiation-induced activation of the phosphatidyl inositol-3 kinase/Akt signal transduction pathway requires Akt binding to phosphatidyl-inositol phosphates (PIP) on the cell membrane. The tyrosine kinase bone marrow X kinase (Bmx) binds to membrane-associated PIPs in a manner similar to Akt. Because Bmx is involved in cell growth and survival pathways, it could contribute to the radiation response within the vascular endothelium. We therefore studied Bmx signaling within the vascular endothelium. Bmx was activated rapidly in response to clinically relevant doses of ionizing radiation. Bmx inhibition enhanced the efficacy of radiotherapy in endothelial cells as well as tumor vascular endothelium in lung cancer tumors in mice. Retroviral shRNA knockdown of Bmx protein enhanced human umbilical vascular endothelial cell (HUVEC) radiosensitization. Furthermore, pretreatment of HUVEC with a pharmacologic inhibitor of Bmx, LFM-A13, produced significant radiosensitization of endothelial cells as measured by clonogenic survival analysis and apoptosis as well as functional assays including cell migration and tubule formation. In vivo, LFM-A13, when combined with radiation, resulted in significant tumor microvascular destruction as well as enhanced tumor growth delay. Bmx therefore represents a molecular target for the development of novel radiosensitizing agents.

Tyrosine kinase Etk/BMX is up-regulated in human prostate cancer and its overexpression induces prostate intraepithelial neoplasia in mouse

The nonreceptor tyrosine kinase Etk/BMX was originally identified from the human prostate xenograft CWR22. Here, we report that Etk is up-regulated in human prostate tumor specimens surveyed. Knocking down Etk expression by a specific small interfering RNA (siRNA) in prostate cancer cells attenuates cell proliferation, suggesting an essential role of Etk for prostate cancer cell survival and growth. Targeted expression of Etk in mouse prostate epithelium results in pathologic changes resembling human prostatic intraepithelial neoplasia, indicating that up-regulation of Etk may contribute to prostate cancer development. A marked increase of luminal epithelial cell proliferation was observed in the Etk transgenic prostate, which may be attributed in part to the elevated activity of Akt and signal transducers and activators of transcription 3 (STAT3). More interestingly, the expression level of acetyltransferase cyclic AMP-responsive element binding protein-binding protein (CBP) is also increased in the Etk transgenic prostate as well as in a prostate cancer cell line overexpressing Etk, concomitant with elevated histone 3 acetylation at lysine 18 (H3K18Ac). Down-modulation of Etk expression by a specific siRNA leads to a decrease of H3 acetylation in prostate cancer cell lines. Our data suggest that Etk may also modulate chromatin remodeling by regulating the activity of acetyltransferases, such as CBP. Given that Etk may exert its effects in prostate through modulation of multiple signaling pathways altered in human prostate cancer, the Etk transgenic mouse model may be a useful tool for studying the functions of Etk and identification of new molecular markers and drug targets relevant to human diseases.

Posterolateral intertransverse lumbar fusion in a mouse model: surgical anatomy and operative technique

BACKGROUND CONTEXT

Animal models are frequently used for studying the effect of bone graft substitutes or allogeneic materials on osterolateral lumbar fusion. Transgenic technology in the mouse provides a unique opportunity to further understand the biology of spine fusion.

PURPOSE

To describe pertinent lumbar spine anatomy and formulate a surgical protocol for posterolateral fusion in the mouse model.

STUDY DESIGN

Diagnostic model: development of an animal model for biologic evaluation of posterolateral spine fusion.

METHOD

Ten mice were killed to study relevant lumbar spine anatomy and develop a protocol for lumbar spine fusion. The L4-L6 fusion protocol was validated in 46 mice for ease of exposure, preparation of the posterolateral fusion bed, introduction of bone inductive agents, and perioperative care.

RESULTS

Anatomy and surgical technique for posterolateral intertransverse lumbar fusion in the mouse model are described. A paraspinal approach allows exposure of the transverse processes, decortication, and graft placement at the L4-L6 intertransverse fusion site. Decortication alone did not result in fusion, whereas the use of bone graft resulted in satisfactory fusion rates. Perioperative morbidity and mortality rates were low.

CONCLUSION

The mouse posterolateral lumbar spine fusion model is reproducible, inexpensive, and has low complication rates. Knowledge of the relevant anatomy and adherence to a well-defined surgical protocol provides a reliable and reproducible experimental spine fusion model.

Critical function of Bmx/Etk in ischemia-mediated arteriogenesis and angiogenesis

Bmx/Etk non-receptor tyrosine protein kinase has been implicated in endothelial cell migration and tube formation in vitro. However, the role of Bmx in vivo is not known. Bmx is highly induced in the vasculature of ischemic hind limbs. We used both mice with a genetic deletion of Bmx (Bmx-KO mice) and transgenic mice expressing a constitutively active form of Bmx under the endothelial Tie-2 enhancer/promoter (Bmx-SK-Tg mice) to study the role of Bmx in ischemia-mediated arteriogenesis/angiogenesis. In response to ischemia, Bmx-KO mice had markedly reduced, whereas Bmx-SK-Tg mice had enhanced, clinical recovery, limb perfusion, and ischemic reserve capacity when compared with nontransgenic control mice. The functional outcomes in these mice were correlated with ischemia-initiated arteriogenesis, capillary formation, and vessel maturation as well as Bmx-dependent expression/activation of TNF receptor 2- and VEGFR2-mediated (TNFR2/VEGFR2-mediated) angiogenic signaling in both hind limb and bone marrow. More importantly, results of bone marrow transplantation studies showed that Bmx in bone marrow-derived cells plays a critical role in the early phase of ischemic tissue remodeling. Our study provides the first demonstration to our knowledge that Bmx in endothelium and bone marrow plays a critical role in arteriogenesis/angiogenesis in vivo and suggests that Bmx may be a novel target for the treatment of vascular diseases such as coronary artery disease and peripheral arterial disease.

Human single-domain neutralizing intrabodies directed against Etk kinase: a novel approach to impair cellular transformation

Etk, the 70-kDa member of the Tec family of nonreceptor protein tyrosine kinases, is expressed in a variety of hematopoietic, epithelial, and endothelial cells and was shown to be involved in several cellular processes, including proliferation, differentiation, and motility. In this study, we describe a novel approach using a human single-domain antibody phage display library for the generation of intrabodies directed against Etk. These single-domain antibodies bind specifically to recombinant Etk and efficiently block its kinase activity. When expressed in transformed cells, these antibodies associated tightly with Etk, leading to significant blockade of Etk enzymatic activity and inhibition of clonogenic cell growth in soft agar. Our results indicate that Etk may play a role in Src-induced cellular transformation and thus may represent a good target for cancer intervention. Furthermore, our single-domain antibody-based intrabody system proves to be an excellent tool for future intracellular targeting of other signaling molecules.

Cytokine gene expression in a murine wound healing model

Inflammatory mediators have been shown to play a major role in the complex series of co-ordinated events that occur in wound healing responses following injury. However, to date most of the studies carried out have addressed the expression, interactions and role of only one or two cytokines that are thought to be involved in wound repair. This study has evaluated, in murine skin samples taken at 0, 3, 12, 18, 24, 48, 72, 120 and 168 h post-wounding, the expression of a wide range of cytokines with potential for a role in wound repair. Various techniques (reverse transcription polymerase chain reaction (RT-PCR), bioassays and ELISA) were used to evaluate cytokine expression in these samples at both the mRNA and protein expressions level. Semi-quantitative analysis using RT-PCR revealed that IL-1beta, IP10, bFGF, and TGFbeta3 up-regulated in wounded samples, compared to non-injured control samples. Expression of mRNA for other cytokines and inflammatory mediators, IL-1alpha, IL-6, TGFbeta1, TNFalpha, MIP-1alpha, MIP-2, JE, KC, PDGFalpha and PDGFbeta, were found to be down-regulated in injured adult murine samples compared to normal control samples. Interestingly we failed to find evidence of mRNA expression for the cytokines IL-2, IL-4, IL-12, GM-CSF, IFNgamma and RANTES, in both non-injured and injured samples. These observations were also generally supported by the results obtained using bioassays for IL-1 and IL-6 and ELISA for IL-1alpha, IL-1beta, IL-6, TNFalpha, and IFNgamma.

Etk/Bmx mediates expression of stress-induced adaptive genes VEGF, PAI-1, and iNOS via multiple signaling cascades in different cell systems

We recently showed that Etk/Bmx, a member of the Tec family of nonreceptor protein tyrosine kinases, promotes tight junction formation during chronic hypoxic exposure and augments normoxic VEGF expression via a feedforward mechanism. Here we further characterized Etk's role in potentiating hypoxia-induced gene expression in salivary epithelial Pa-4 cells. Using transient transfection in conditionally activated Etk (DeltaEtk:ER) cells, we demonstrated that Etk enhances hypoxia-response element-dependent reporter activation in normoxia and hypoxia. This Etk-driven reporter activation is ameliorated by treatment with wortmannin or LFM-A13. Using lentivirus-mediated gene delivery and small interfering RNA, we provided direct evidence that hypoxia leads to transient Etk and Akt activation and hypoxia-mediated Akt activation is Etk dependent. Northern blot analyses confirmed that Etk activation led to induction of steady-state mRNA levels of endogenous VEGF and plasminogen activator inhibitor (PAI)-1, a hallmark of hypoxia-mediated gene regulation. We also demonstrated that Etk utilizes a phosphatidylinositol 3-kinase/Akt pathway to promote reporter activation driven by NF-kappaB, another oxygen-sensitive transcription factor, and to augment cytokine-induced inducible nitric oxide synthase expression in endothelial cells. To establish the clinical relevance of Etk-induced, hypoxia-mediated gene regulation, we examined Etk expression in keloid, which has elevated VEGF and PAI-1. We found that Etk is overexpressed in keloid (but not normal skin) tissues. The differential steady-state Etk protein levels were further confirmed in primary fibroblast cultures derived from these tissues, suggesting an Etk role in tissue fibrosis. Our results provide further understanding of Etk function within multiple signaling cascades to govern adaptive cytoprotection against extracellular stress in different cell systems, salivary epithelial cells, brain endothelial cells, and dermal fibroblasts.