Jun Kinase Pathway Research Articles

Abstract 228: Patient-derived gbm organoids reflect tumour heterogeneity and treatment sensitivity in patients

Abstract Glioblastoma (GBM) is the most common and incurable adult primary brain tumour. Treatment resistance and relapse is the primary cause of death in GBM. Tumour heterogeneity is one of the significant determinants of treatment failure. Patient-derived cancer organoids have been shown to maintain genetic and phenotypic tumour features and recapitulate intratumoral heterogeneity. Here, we report the development and molecular characterisation of patient-derived GBM organoid (PGO) models to study treatment response to existing and new treatment combinations. GBM biopsies were dissociated, suspended in Cultrex, and cultured in a brain stem cell medium. PGOs were characterised by whole-exome (WES) single-cell karyotype (scKaryoSeq) and RNA sequencing. The IC-50 and viability of PGO upon temozolomide (TMZ) and small molecule inhibitors were determined. Gene expression profiling was performed before and after TMZ treatment. Single-cell spatial heterogeneity was determined using Multiplex Immunostaining of PGO and matched patient samples. PGOs were established with a success rate of 80% (n=31). WES analysis between PGOs from the same patient at multiple time points (1-3 months) showed high maintenance of Single Nucleotide Variants (92.3%-97.7%). In PGOs key somatic oncogene variants and copy number variations were retained compared to the primary tumour (58%-90%). scKaryoseq (N=7) of different clinical GBM subtypes showed a high degree of genetic heterogeneity, with some PGO having up to 10 subclones. Single-cell phenotypic landscaping of patient biopsies showed mixed cellular states maintained after long-term culture in the matched PGO. PGOs showed a differential response to TMZ, corresponding with MGMT methylation and patient mutation status. RNAseq of PGO revealed TMZ-responsive genes, including upregulation of the prognostic JUN kinase pathway. Combination treatment of a JUN kinase inhibitor and TMZ showed a synergistic effect. In addition, PGOs were screened for their sensitivity to clinically approved brain-penetrable small molecule inhibitors targeting key GBM driver pathways. Combining small molecular inhibitors of MEK/PI-3/CDK4/EGFR kinase strongly reduced cell viability and activation of cell death pathways. phosphoKinome screens detected compensatory pathway activation upon kinase inhibition (MEK/CDK4 inhibitor) in several PGO. Data will show novel kinase interaction pathways that increase drug sensitivity in PGO. These data show that PGOs can be used as a stable phenotypic and genetic representative of the patient's tumour and have the potential to function as patient avatars for adaptive treatment selection and actionable drug target discovery. Citation Format: Marc A. Vooijs, Linde Hoosemans, Jolanda Piepers, Maikel Verduin, Maxime Vanmechelen, Mike Van Heumen, Frederik De Smet, Ann Hoeben. Patient-derived gbm organoids reflect tumour heterogeneity and treatment sensitivity in patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 228.

Puckered and JNK signaling in pioneer neurons coordinates the motor activity of the Drosophila embryo

Central nervous system organogenesis is a complex process that obeys precise architectural rules. The impact that nervous system architecture may have on its functionality remains, however, relatively unexplored. To clarify this problem, we analyze the development of the Drosophila embryonic Ventral Nerve Cord (VNC). VNC morphogenesis requires the tight control of Jun kinase (JNK) signaling in a subset of pioneer neurons, exerted in part via a negative feedback loop mediated by the dual specificity phosphatase Puckered. Here we show that the JNK pathway autonomously regulates neuronal electrophysiological properties without affecting synaptic vesicle transport. Manipulating JNK signaling activity in pioneer neurons during early embryogenesis directly influences their function as organizers of VNC architecture and, moreover, uncovers a role in the coordination of the embryonic motor circuitry that is required for hatching. Together, our data reveal critical links, mediated by the control of the JNK signaling cascade by Puckered, between the structural organization of the VNC and its functional optimization.

Early Response Transcription Factors in Erythroid Regeneration

Acute anemia activates distinct mechanisms from physiological erythropoiesis to increase red blood cell production. While erythroid regeneration in this context requires some critical cytokines (e.g., BMP-4), little is known about transcription factors (TFs) connecting growth factor stimulation to anemia-specific gene expression and cellular responses. We previously discovered that GATA1 and TAL1 control a cohort of composite cis-elements which are anemia-activated in erythroid progenitors and precursors during regeneration. Intriguingly, cis-regulatory activity and gene activation at these loci are delayed by several days following initial anemia onset by the red blood cell lysing chemical phenylhydrazine. This delay suggested that these elements were utilized for erythroid precursor expansion but not activation. We hypothesize that distinct TF mechanisms are early responders to erythroid regeneration. To identify early anemia response TFs, we compared transcript levels in mouse spleen Kit + erythroid progenitors at days 0 and 1 post-anemia (anemia upregulated genes; p<0.05, fold change>1.5). Among upregulated genes, only 10 were TFs, and 3 of them ( Jun, Junb, Fos) are components of Activator protein 1 (AP-1) transcription factor. All 3 transcripts were subsequently downregulated at 3 days after anemia. In physiological hematopoiesis, AP-1 is highly expressed in most cells but low within the erythroid lineage. These findings suggested transient anemia-activated AP-1 may initiate erythroid regeneration. While AP-1 is a big family, only JUN and FOS family exhibited transient anemia-activation. Genes containing AP-1 binding motifs were cell intrinsically upregulated post-anemia in Jun and Fos-expressing cells. To determine Jun TF activity in anemia, we performed phospho-flow cytometry in Lin- spleen cells from mice after inducing anemia. We discovered that at Day 1 vs Control, the median fluorescence intensity (MFI) of Kit +CD71 +Ter119 + cells stained with total Jun or phospho-Jun (p-Jun) antibodies increased 2.0-fold (p=0.03) and 2.9-fold (p=0.04), respectively. Concurring with transcript levels, both total and p-Jun protein increased between 6- and 24-hours post-anemia and decreased at 72 hours. These changes post-anemia were absent in non-erythroid (CD71 -Ter119 -) and Kit - cells. These data demonstrated a transient increase in JUN TF activity early during the anemia response in erythroid progenitor/precursors. AP-1 activity is commonly elevated in response to a variety of stressors, including hypoxia and inflammation. Given the limited sets of transcripts upregulated at early anemia time points, direct AP-1 targets may be required for establishing an anemia-dependent transcriptome. To identify AP-1 target genes in erythroid regeneration, we selected genetic loci nearby (distance <100kb) AP-1-occupied cis-elements in human erythroleukemia (K562) or mouse erythroid progenitor cells (GEO: GSE31477, 208960, 170378, 172818). 50 potential AP-1 target genes were upregulated in stress erythroid precursors on day 3 vs day 1 post-anemia. Seven anemia-regulated transcription factors (SOX6, E2F2, TAL1, TFDP2, FOXO3, GFI1B, MAFG) reside at loci containing candidate AP-1 cis-elements. The T-cell Acute Lymphoblastic Leukemia-1 (TAL1) TF cooperates with GATA1 at E-box-GATA composite cis-elements to promote transcription of a number of erythroid-specific genes, several of which are needed for effective erythroid regeneration. Knockdown approaches will be used to test whether Jun expression and activity promotes the anemia-dependent transcriptome, stress erythroid precursor differentiation, and cell survival during erythroid regeneration. Given that Jun can be activated by BMP-4 signaling via the Jun kinase (JNK) pathway, and the requirement for BMP-4 in erythroid regeneration, we are investigating whether BMP-4 stimulation (or other cytokines) phosphorylates Jun to establish the regenerative transcriptome at early time points post-anemia. These studies will improve our understanding of transcriptional mechanisms driving erythroid regenerative responses, which can be useful for identifying new therapeutic targets for acute/chronic anemias.

Differences within the Immune Microenvironment May Account for Poorer Outcomes in African American AML Patients Compared to European American Patients with AML

Background: Acute myeloid leukemia (AML) is an aggressive hematological malignancy arising from an immature myeloid progenitor with notoriously poor outcomes. A critical factor responsible for the difficulty in treating this disease evasion of the host immune system by AML. Both the innate and adaptive immune systems have been shown to be dysfunctional in AML with poor type I interferon responses, decreased STING signaling and increased populations of granulocytic and monocytic myeloid derived suppressor cells ultimately leading to poor adaptive response. Studies in solid tumors have demonstrated that variation in immunity contributes to racial disparities in cancer and outcomes. This is felt to be due to variation in geographic ancestry leading to differences in the innate immune genome required due to the need for protection against environmental pathogens. However, no data exists comparing innate and adaptive immunity by race in patients (pts) with AML. Here we sought to characterize the immune microenvironment with treatment outcomes in racially diverse AML pts. Methods: Adults with newly diagnosed AML were identified who had corresponding cryopreserved bone marrow mononuclear cells available within Roswell Park Hematologic Procurement bank. Pts were matched as closely as possible for age, gender, cytogenetic risk per ELN 2017 and molecular profile. Transcriptional differences between African American (AA, n=26) and European American (EA, n=26) AML pts and healthy controls (n=10) were analyzed using transcriptomics data from NanoString Pan Cancer Immune Profile panels. AA and EA AML samples were compared to each other, as well as their race-matched healthy controls. The ‘Limma’ package in R was utilized for differential gene expression analysis. Research was conducted according to the Declaration of Helsinki in accordance with the Institutional Review Board regulated protocol. Results: The median age of the entire cohort (n=52) was 65 years (range: 28-92), with 28 female patients (53.8%) ( Table 1). Within the AA cohort, the majority of pts had intermediate risk cytogenetics per ELN 2017 (n=19; 73.1%, and 6 pts had FLT3 mut (26.1%). Three pts (11.5%) underwent allogeneic stem cell transplant, with a median overall survival (OS) censoring for transplant of 5 months (range; 0.5-68 months) ( Figure 1). Within the EA cohort, most pts had poor risk cytogenetics (n=15; 57.7%). Six pts had FLT3 mut (26.1%), and three pts had TP53 mut (12%). Five pts underwent allogeneic stem cell transplant (19.2%), with a median OS of 16.4 months (range; 0.8-67 months). Sixty-nine significantly (p<0.05, |logFC|>1.5) differentially expressed genes in AA vs. EA pts were identified. Gene set enrichment analysis (GSEA) revealed alterations to Interferon, Jun kinase and STAT signaling pathways in AA pts. In contrast, EA pt samples were enriched for pathways related to amyloid metabolism and other T and B cell immune pathways. Master regulator analysis using LISA highlighted transcriptional dysregulation attributed to PDGB5, CTCF, AR, and NOTCH in AA pts and to GLIS2, SMAD1 and NFE2 in EA pts. Conclusions: As previously reported, we found that a clinically matched cohort of AA AML patients experienced significantly worse OS as compared to EA counterparts. We have identified several significant alterations within the immune microenvironment between cohorts, which may potentially explain this discrepancy in survival in AA patients. These differences could potentially serve as targetable alterations for therapeutic purposes. This work represents the first of its kind evaluating the immune microenvironment by race in AML patients and are awaiting confirmation in a larger cohort.

A Preliminary Study in Immune Response of BALB/c and C57BL/6 Mice with a Locally Allergic Rhinitis Model.

BALB/c and C57BL/6 mouse strains are commonly used in allergy research. The current study investigated the immunological differences between these two mouse strains with a locally allergic rhinitis model. Eighteen BALB/c and eighteen C57BL/6 mice received different doses of ovalbumin (OVA) intranasally for eight weeks (each mouse strain has three subgroups, 25 mg/mL group, 0.25 mg/mL group, and the PBS group). The allergic symptoms, OVA-specific serum antibody (IgE, IgG1, IgG2a), cytokines (IL-4, IFN-γ, IL-10) in the splenic culture supernatant, infiltrating eosinophils and goblet cells in local nasal mucosa were measured. RNA-seq technology was applied to detect differential gene expression in the local nasal mucosa. With the same dose of OVA stimulation, the exacerbation of allergic symptoms was more pronounced in C57BL/6 than in BALB/c. BALB/c serum IgE, IgG1, and IgG2a gradually increased, and C57BL/6 produced fewer serum antibodies IgE and IgG1, while IgG2a never increased. BALB/c spleen cell culture supernatant IL-4 and IL-10 increased with increasing dose, and IFN-γ increased significantly in the intermediate dose group, while IL-4, IL-10, and IFN-γ did not increase in C57BL/6. The infiltration of eosinophils and goblet cells in both mice was proportional to the dose, while C57BL/6 was elevated more than BALB/c. RNA-seq suggested that the innate immune response, immune system process function, Jun kinase (JNK) pathway, and MAPKK pathway were upregulated in C57BL/6 compared to BALB/c. The core genes responsible for the differential immune response in both mice with allergic rhinitis were Kng2, Kng1, Gnb3, Lpar3, Lpar1, Pik3r1, Pf4, Apob, Rps9, and Fbxo2. There are significant differences in the immunologic responses between BALB/c mice and C57BL/6 mice. BALB/c mice developed mild local allergic inflammatory reactions and strong systemic immune responses. In contrast, C57BL/6 mice had stronger local allergic inflammatory responses and relatively mild systemic immune responses. Different mice strains can be selected according to the research purpose.

Somatic support cells regulate germ cell survival through the Baz/aPKC/Par6 complex.

ABSTRACTLocal signals and structural support from the surrounding cellular microenvironment play key roles in directing development in both embryonic organs and adult tissues. In Drosophila, male germ cells are intimately associated and co-differentiate with supporting somatic cells. Here, we show that the function of the Baz/aPKC/Par6 apical polarity complex in somatic cyst cells is required stage specifically for survival of the germ cells they enclose. Although spermatogonia enclosed by cyst cells in which the function of the Par complex had been knocked down survived and proliferated, newly formed spermatocytes enclosed by cyst cells lacking Par complex proteins died soon after onset of meiotic prophase. Loss of Par complex function resulted in stage-specific overactivation of the Jun-kinase (JNK) pathway in cyst cells. Knocking down expression of JNK pathway components or the GTPase Rab35 in cyst cells lacking Par complex function rescued the survival of neighboring spermatocytes, suggesting that action of the apical polarity complex ensures germ cell survival by preventing JNK pathway activation, and that the mechanism by which cyst cells lacking Par complex function kill neighboring spermatocytes requires intracellular trafficking in somatic cyst cells.

A Kinome RNAi Screen in Drosophila Identifies Novel Genes Interacting with Lgl, aPKC, and Crb Cell Polarity Genes in Epithelial Tissues.

In both Drosophila melanogaster and mammalian systems, epithelial structure and underlying cell polarity are essential for proper tissue morphogenesis and organ growth. Cell polarity interfaces with multiple cellular processes that are regulated by the phosphorylation status of large protein networks. To gain insight into the molecular mechanisms that coordinate cell polarity with tissue growth, we screened a boutique collection of RNAi stocks targeting the kinome for their capacity to modify Drosophila “cell polarity” eye and wing phenotypes. Initially, we identified kinase or phosphatase genes whose depletion modified adult eye phenotypes associated with the manipulation of cell polarity complexes (via overexpression of Crb or aPKC). We next conducted a secondary screen to test whether these cell polarity modifiers altered tissue overgrowth associated with depletion of Lgl in the wing. These screens identified Hippo, Jun kinase (JNK), and Notch signaling pathways, previously linked to cell polarity regulation of tissue growth. Furthermore, novel pathways not previously connected to cell polarity regulation of tissue growth were identified, including Wingless (Wg/Wnt), Ras, and lipid/Phospho-inositol-3-kinase (PI3K) signaling pathways. Additionally, we demonstrated that the “nutrient sensing” kinases Salt Inducible Kinase 2 and 3 (SIK2 and 3) are potent modifiers of cell polarity phenotypes and regulators of tissue growth. Overall, our screen has revealed novel cell polarity-interacting kinases and phosphatases that affect tissue growth, providing a platform for investigating molecular mechanisms coordinating cell polarity and tissue growth during development.

Oxidation resistance 1 (OXR1) participates in silkworm defense against bacterial infection through the JNK pathway.

Bacterial infection causes enhanced reactive oxygen species (ROS) levels in insects. Oxidation resistance 1 (OXR1) plays an antioxidant role in eukaryotic organisms, including insects. In this report, we demonstrated that Pseudomonas aeruginosa and Staphylococcus aureus infection and hydrogen peroxide (H2 O2 ) injection induced the expression of specific transcriptional isoforms of OXR1 in larval silkworms. We further showed that a Jun kinase (JNK) pathway inhibitor, SP600125, down-regulated expression of OXR1 during infection, leading to elevated H2 O2 levels in the hemolymph, resulting in lower viability of the injected bacteria inside the silkworm larvae. Our study suggests that OXR1 participates in protecting larval silkworms from oxidative stress and bacterial infection through the JNK pathway.

Apelin-13 upregulates Egr-1 expression in rat vascular smooth muscle cells through the PI3K/Akt and PKC signaling pathways

Previous studies have shown that Apelin-13 upregulates early growth response factor-1 (Egr-1) via the extracellular signal-regulated protein kinase (ERK) signaling pathway. Apelin-13 induces proliferation and migration of vascular smooth muscle cells (VSMCs) as well as the upregulation of osteopontin (OPN) via the upregulation of Egr-1. This study was designed to further explore the activity of Apelin-13 in VSMCs by investigating members of the mitogen-activated protein kinase (MAPK) family, in particular Jun kinase (JNK) and p38 mitogen-activated protein kinase (P38). We also examined whether the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt) and protein kinase C (PKC) signaling pathways were involved in the regulation of Egr-1 by Apelin-13. We treated rat aortic VSMCs with Apelin-13 and examined the expression of JNK, p-JNK, P38, and p-P38 to investigate whether Apelin-13-mediated increases in Egr-1 occurred through the JNK and P38 signaling pathways. We then pretreated VSMCs with the Gi protein inhibitor pertussis toxin (PTX) and the Gq inhibitor YM254890, added Apelin-13 and looked for changes in Egr-1 expression. Finally, we pretreated with the PI3K inhibitor LY294002 and the PKC inhibitor GF109203X, and treated with Apelin-13. Our results showed that JNK and P38 did not participate in Apelin-13-mediated increase in Egr-1. Instead, Apelin-13 upregulation of Egr-1 was mediated by a PTX-sensitive Gi protein. Apelin-13 did increase ERK phosphorylation through the PI3K/Akt and PKC signaling pathways, resulting in changes in Egr-1 expression. These data provide important targets for future studies to modulate vascular remodeling.

Widespread JNK-dependent alternative splicing induces a positive feedback loop through CELF2-mediated regulation of MKK7 during T-cell activation.

Alternative splicing is prevalent among genes encoding signaling molecules; however, the functional consequence of differential isoform expression remains largely unknown. Here we demonstrate that, in response to T-cell activation, the Jun kinase (JNK) kinase MAP kinase kinase 7 (MKK7) is alternatively spliced to favor an isoform that lacks exon 2. This isoform restores a JNK-docking site within MKK7 that is disrupted in the larger isoform. Consistently, we show that skipping of MKK7 exon 2 enhances JNK pathway activity, as indicated by c-Jun phosphorylation and up-regulation of TNF-α. Moreover, this splicing event is itself dependent on JNK signaling. Thus, MKK7 alternative splicing represents a positive feedback loop through which JNK promotes its own signaling. We further show that repression of MKK7 exon 2 is dependent on the presence of flanking sequences and the JNK-induced expression of the RNA-binding protein CELF2, which binds to these regulatory elements. Finally, we found that ∼25% of T-cell receptor-mediated alternative splicing events are dependent on JNK signaling. Strikingly, these JNK-dependent events are also significantly enriched for responsiveness to CELF2. Together, our data demonstrate a widespread role for the JNK-CELF2 axis in controlling splicing during T-cell activation, including a specific role in propagating JNK signaling.

The Drosophila retinoblastoma protein, Rbf1, induces a Debcl- and Drp1-dependent mitochondrial apoptosis.

In accordance with its tumor suppressor role, the retinoblastoma protein pRb can ensure pro-apoptotic functions. Rbf1, the Drosophila homolog of Rb, also displays a pro-apoptotic activity in proliferative cells. We have previously shown that the Rbf1 pro-apoptotic activity depends on its ability to decrease the level of anti-apoptotic proteins such as the Bcl-2 family protein Buffy. Buffy often acts in an opposite manner to Debcl, the other Drosophila Bcl-2-family protein. Both proteins can localize at the mitochondrion, but the way they control apoptosis still remains unclear. Here, we demonstrate that Debcl and the pro-fission gene Drp1 are necessary downstream of Buffy to trigger a mitochondrial fragmentation during Rbf1-induced apoptosis. Interestingly, Rbf1-induced apoptosis leads to a Debcl- and Drp1-dependent reactive oxygen species production, which in turn activates the Jun Kinase pathway to trigger cell death. Moreover, we show that Debcl and Drp1 can interact and that Buffy inhibits this interaction. Notably, Debcl modulates Drp1 mitochondrial localization during apoptosis. These results provide a mechanism by which Drosophila Bcl-2 family proteins can control apoptosis, and shed light on a link between Rbf1 and mitochondrial dynamics in vivo.

Inhibition of basal JNK activity by small interfering RNAs enhances cisplatin sensitivity and decreases DNA repair in T98G glioblastoma cells.

Inhibition of basal Jun kinase (JNK) activity by small interfering RNAs (siRNAs) enhances cisplatin sensitivity and decreases DNA repair in T98G glioblastoma cells. Although the JNK pathway has been extensively studied in recent years, little is known concerning the signaling pathways that control their expression in glioma cells. The aim of the present study was to assess the role of c-Jun-NH2-terminal kinases (JNKs) in the regulation of T98G glioblastoma cells treated with cisplatin in the presence or absence of siRNAs against JNK1 and JNK2. Addition of either small interfering JNK1-siRNA or JNK2-siRNA induced decreased DNA repair and sensitized the T98G glioblastoma cells to the DNA damaging drug cisplatin (cis-diamminedichloroplatinum). This effect was associated with reduced cell survival and loss of anchorage‑independent colony formation. The results indicate that effective inhibition of the JNK pathway significantly sensitizes glioblastoma cells to cisplatin, a compound of proven clinical value whose spectrum of application is limited by resistance phenomena.

Telomere-Homologous G-Rich Oligonucleotides Sensitize Human Ovarian Cancer Cells to TRAIL-Induced Growth Inhibition and Apoptosis

G-rich T-oligos (GT-oligos; oligonucleotides with homology to telomeres) elicit a DNA damage response in cells and induce cytotoxic effects in certain tumor cell lines. We have previously shown that GT-oligo inhibits growth, arrests cell cycle, and induces apoptosis in ovarian, pancreatic, and prostate cancer cells. However, not all ovarian cancer cell lines are susceptible to GT-oligo exposure. GT-oligo was found to induce transcript expression of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors DR-4 and DR-5, which are generally silenced in ovarian cancer cells, rendering them insensitive to TRAIL. Exposure of TRAIL- and GT-oligo-resistant cell lines to GT-oligo rendered them sensitive to the cytotoxic effects of TRAIL, producing more than additive inhibition of growth. An intracellular inhibitor of the extrinsic apoptotic pathway, FLICE-like Inhibitory Protein-Short (FLIPs), was down-regulated and Jun kinase (JNK) was activated by exposure to GT-oligo. JNK inhibition partially reversed the growth inhibition caused by the combination of GT-oligo and TRAIL indicating partial involvement of the Jun kinase pathway in the resulting cytotoxic effect. Both capase-8 and caspases 3/7 were activated by exposure to GT-oligo plus TRAIL, consistent with activation of the extrinsic apoptotic pathway. These results demonstrate a novel way of sensitizing resistant ovarian cancer cells to TRAIL-mediated cytotoxicity.

Death takes a holiday—non‐apoptotic role for caspases in cell migration and invasion

Many types of cancer exhibit significantly elevated caspase activity and this is positively correlated with tumour aggression. In this issue of EMBO Reports, Cagan and colleagues reveal a non‐apoptotic role for active caspase in cell migration in Drosophila.

InDrosophila, RhoGEF2 cooperates with activated Ras in tumorigenesis through a pathway involving Rho1–Rok–Myosin-II and JNK signalling

SUMMARYThe Ras oncogene contributes to ∼30% of human cancers, but alone is not sufficient for tumorigenesis. In a Drosophila screen for oncogenes that cooperate with an activated allele of Ras (RasACT) to promote tissue overgrowth and invasion, we identified the GTP exchange factor RhoGEF2, an activator of Rho-family signalling. Here, we show that RhoGEF2 also cooperates with an activated allele of a downstream effector of Ras, Raf (RafGOF). We dissect the downstream pathways through which RhoGEF2 cooperates with RasACT (and RafGOF), and show that RhoGEF2 requires Rho1, but not Rac, for tumorigenesis. Furthermore, of the Rho1 effectors, we show that RhoGEF2 + Ras (Raf)-mediated tumorigenesis requires the Rho kinase (Rok)–Myosin-II pathway, but not Diaphanous, Lim kinase or protein kinase N. The Rho1–Rok–Myosin-II pathway leads to the activation of Jun kinase (JNK), in cooperation with RasACT. Moreover, we show that activation of Rok or Myosin II, using constitutively active transgenes, is sufficient for cooperative tumorigenesis with RasACT, and together with RasACT leads to strong activation of JNK. Our results show that Rok–Myosin-II activity is necessary and sufficient for Ras-mediated tumorigenesis. Our observation that activation of Myosin II, which regulates Filamentous actin (F-actin) contractility without affecting F-actin levels, cooperates with RasACT to promote JNK activation and tumorigenesis, suggests that increased cell contractility is a key factor in tumorigenesis. Furthermore, we show that signalling via the Tumour necrosis factor (TNF; also known as Egr)-ligand–JNK pathway is most likely the predominant pathway that activates JNK upon Rok activation. Overall, our analysis highlights the need for further analysis of the Rok–Myosin-II pathway in cooperation with Ras in human cancers.

Drosophila Heat Shock Response Requires the JNK Pathway and Phosphorylation of Mixed Lineage Kinase at a Conserved Serine-Proline Motif

Defining context specific requirements for proteins and pathways is a major challenge in the study of signal transduction. For example, the stress-activated protein kinase (SAPK) pathways are comprised of families of closely related transducers that are activated in a variety of tissues and contexts during development and organismal homeostasis. Consequently, redundant and pleiotropic effects have hampered a complete understanding of the individual contributions of transducers in distinct contexts. Here, we report on the function of a context-specific regulatory phosphorylation site, PXSP, in the Drosophila mixed lineage kinase protein, Slpr, a mitogen-activated protein kinase kinase kinase (MAP3K) in the Jun Kinase (JNK) pathway. Genetic analysis of the function of non-phosphorylatable (PXAP) and phosphomimetic mutant (PXEP) Slpr transgenes in several distinct contexts revealed minimal effects in JNK-dependent tissue closure processes but differential requirements in heat stress response. In particular, PXAP expression resulted in sensitivity of adults to sustained heat shock, like p38 and JNK pathway mutants. In contrast, PXEP overexpression conferred some resistance. Indeed, phosphorylation of the PXSP motif is enriched under heat shock conditions and requires in part, the p38 kinases for the enrichment. These data suggest that coordination of signaling between p38 and Slpr serves to maintain JNK signaling during heat stress. In sum, we demonstrate a novel role for JNK signaling in the heat shock response in flies and identify a posttranslational modification on Slpr, at a conserved site among MAP3K mixed lineage kinase family members, which bolsters stress resistance with negligible effects on JNK-dependent developmental processes.

Spontaneous Age-Related Neurite Branching in Caenorhabditis elegans

The analysis of morphological changes that occur in the nervous system during normal aging could provide insight into cognitive decline and neurodegenerative disease. Previous studies have suggested that the nervous system of Caenorhabditis elegans maintains its structural integrity with age despite the deterioration of surrounding tissues. Unexpectedly, we observed that neurons in aging animals frequently displayed ectopic branches and that the prevalence of these branches increased with time. Within age-matched populations, the branching of mechanosensory neurons correlated with decreased response to light touch and decreased mobility. The incidence of branching was influenced by two pathways that can affect the rate of aging, the Jun kinase pathway and the insulin/IGF-1 pathway. Loss of Jun kinase signaling, which slightly shortens lifespan, dramatically increased and accelerated the frequency of neurite branching. Conversely, inhibition of the daf-2 insulin/IGF-1-like signaling pathway, which extends lifespan, delayed and suppressed branching, and this delay required DAF-16/FOXO activity. Both JNK-1 and DAF-16 appeared to act within neurons in a cell-autonomous manner to influence branching, and, through their tissue-specific expression, it was possible to disconnect the rate at which branching occurred from the overall rate of aging of the animal. Old age has generally been associated with the decline and deterioration of different tissues, except in the case of tumor cell growth. To our knowledge, this is the first indication that aging can potentiate another form of growth, the growth of neurite branches, in normal animals.

Identification of Novel Ras-Cooperating Oncogenes in Drosophila melanogaster: A RhoGEF/Rho-Family/JNK Pathway Is a Central Driver of Tumorigenesis

We have shown previously that mutations in the apico-basal cell polarity regulators cooperate with oncogenic Ras (Ras(ACT)) to promote tumorigenesis in Drosophila melanogaster and mammalian cells. To identify novel genes that cooperate with Ras(ACT) in tumorigenesis, we carried out a genome-wide screen for genes that when overexpressed throughout the developing Drosophila eye enhance Ras(ACT)-driven hyperplasia. Ras(ACT)-cooperating genes identified were Rac1 Rho1, RhoGEF2, pbl, rib, and east, which encode cell morphology regulators. In a clonal setting, which reveals genes conferring a competitive advantage over wild-type cells, only Rac1, an activated allele of Rho1 (Rho1(ACT)), RhoGEF2, and pbl cooperated with Ras(ACT), resulting in reduced differentiation and large invasive tumors. Expression of RhoGEF2 or Rac1 with Ras(ACT) upregulated Jun kinase (JNK) activity, and JNK upregulation was essential for cooperation. However, in the whole-tissue system, upregulation of JNK alone was not sufficient for cooperation with Ras(ACT), while in the clonal setting, JNK upregulation was sufficient for Ras(ACT)-mediated tumorigenesis. JNK upregulation was also sufficient to confer invasive growth of Ras(V12)-expressing mammalian MCF10A breast epithelial cells. Consistent with this, HER2(+) human breast cancers (where human epidermal growth factor 2 is overexpressed and Ras signaling upregulated) show a significant correlation with a signature representing JNK pathway activation. Moreover, our genetic analysis in Drosophila revealed that Rho1 and Rac are important for the cooperation of RhoGEF2 or Pbl overexpression and of mutants in polarity regulators, Dlg and aPKC, with Ras(ACT) in the whole-tissue context. Collectively our analysis reveals the importance of the RhoGEF/Rho-family/JNK pathway in cooperative tumorigenesis with Ras(ACT).

Expression and function of EZH2 in synovial fibroblasts: epigenetic repression of the Wnt inhibitor SFRP1 in rheumatoid arthritis

ObjectivesTo study the expression, regulation and function of the histone methyltransferase enhancer of zeste homologue 2 (EZH2) in synovial fibroblasts (SF) from patients with rheumatoid arthritis (RA) and osteoarthritis (OA).MethodsSF...

Regulation of Hippo signaling by Jun kinase signaling during compensatory cell proliferation and regeneration, and in neoplastic tumors

When cells undergo apoptosis, they can stimulate the proliferation of nearby cells, a process referred to as compensatory cell proliferation. The stimulation of proliferation in response to tissue damage or removal is also central to epimorphic regeneration. The Hippo signaling pathway has emerged as an important regulator of growth during normal development and oncogenesis from Drosophila to humans. Here we show that induction of apoptosis in the Drosophila wing imaginal disc stimulates activation of the Hippo pathway transcription factor Yorkie in surviving and nearby cells, and that Yorkie is required for the ability of the wing to regenerate after genetic ablation of the wing primordia. Induction of apoptosis activates Yorkie through the Jun kinase pathway, and direct activation of Jun kinase signaling also promotes Yorkie activation in the wing disc. We also show that depletion of neoplastic tumor suppressor genes, including lethal giant larvae and discs large, or activation of aPKC, activates Yorkie through Jun kinase signaling, and that Jun kinase activation is necessary, but not sufficient, for the disruption of apical-basal polarity associated with loss of lethal giant larvae. Our observations identify Jnk signaling as a modulator of Hippo pathway activity in wing imaginal discs, and implicate Yorkie activation in compensatory cell proliferation and disc regeneration.