Detection of RTK pathway activation in Drosophila using anti-dpERK immunofluorescence staining

Cinnamic acids as promising bioactive compounds for cancer therapy by targeting MAPK3: a computational simulation study

OBJECTIVES

Mitogen-activated protein kinase-3 (MAPK3) is the upstream regulator in the MAPK cascade and is involved in many critical signaling pathways and biological processes, such as cell proliferation, survival, and apoptosis. MAPK3 overexpression is linked to onset, development, metastasis, and drug resistance in several human cancers. Thus, identifying novel and effective MAPK3 inhibitors is highly demanded. Herein, we aimed to discover organic compounds from cinnamic acid derivatives as potential MAPK3 inhibitors.

METHODS

The binding affinity of 20 cinnamic acids to the MAPK3 active site was tested using the AutoDock 4.0 software. Top-ranked cinnamic acids were ranked based on the ΔG binding values between the ligands and the receptor's active site. Interaction modes between top-ranked cinnamic acids and MAPK3 catalytic site were indicated using the Discovery Studio Visualizer tool. Molecular dynamics (MD) simulation was carried out to study the stability of the docked pose for the most potent MAPK3 inhibitor in this study.

RESULTS

Cynarin, chlorogenic acid, rosmarinic acid, caffeic acid 3-glucoside, and cinnamyl caffeate exhibited a salient binding affinity to the MAPK3 active site with the criteria of ΔG binding <-10 k cal/mol. Further, the inhibition constant value for cynarin was calculated at the picomolar concentration. The docked pose of cynarin within the MAPK3 catalytic domain was stable in 100 ns simulation.

CONCLUSIONS

Cynarin, chlorogenic acid, rosmarinic acid, caffeic acid 3-glucoside, and cinnamyl caffeate might be helpful in cancer therapy by inhibiting MAPK3.

Novel interplay between JNK and Egfr signaling in Drosophila dorsal closure

Dorsal closure (DC) is a developmental process in which two contralateral epithelial sheets migrate to seal a large hole in the dorsal ectoderm of the Drosophila embryo. Two signaling pathways act sequentially to orchestrate this dynamic morphogenetic process. First, c-Jun N-terminal kinase (JNK) signaling activity in the dorsal-most leading edge (LE) cells of the epidermis induces expression of decapentaplegic (dpp). Second, Dpp, a secreted TGF-β homolog, triggers cell shape changes in the adjacent, ventrally located lateral epidermis, that guide the morphogenetic movements and cell migration mandatory for DC. Here we uncover a cell non-autonomous requirement for the Epidermal growth factor receptor (Egfr) pathway in the lateral epidermis for sustained dpp expression in the LE. Specifically, we demonstrate that Egfr pathway activity in the lateral epidermis prevents expression of the gene scarface (scaf), encoding a secreted antagonist of JNK signaling. In embryos with compromised Egfr signaling, upregulated Scaf causes reduction of JNK activity in LE cells, thereby impeding completion of DC. Our results identify a new developmental role for Egfr signaling in regulating epithelial plasticity via crosstalk with the JNK pathway.

Genome-wide genetic screen identified the link between dG9a and epidermal growth factor receptor signaling pathway in vivo

G9a is one of the histone H3 Lys 9 (H3K9) specific methyltransferases first identified in mammals. Drosophila G9a (dG9a) has been reported to induce H3K9 dimethylation in vivo, and the target genes of dG9a were identified during embryonic and larval stages. Although dG9a is important for a variety of developmental processes, the link between dG9a and signaling pathways are not addressed yet. Here, by genome-wide genetic screen, taking advantage of the rough eye phenotype of flies that over-express dG9a in eye discs, we identified 16 genes that enhanced the rough eye phenotype induced by dG9a over-expression. These 16 genes included Star, anterior open, bereft and F-box and leucine-rich repeat protein 6 which are components of epidermal growth factor receptor (EGFR) signaling pathway. When dG9a over-expression was combined with mutation of Star, differentiation of R7 photoreceptors in eye imaginal discs as well as cone cells and pigment cells in pupal retinae was severely inhibited. Furthermore, the dG9a over-expression reduced the activated ERK signals in eye discs. These data demonstrate a strong genetic link between dG9a and the EGFR signaling pathway.

Ligand-binding and constitutive FGF receptors in single Drosophila tracheal cells: Implications for the role of FGF in collective migration

BACKGROUND

The migration of individual cells relies on their capacity to evaluate differences across their bodies and to move either toward or against a chemoattractant or a chemorepellent signal respectively. However, the direction of collective migration is believed to depend on the internal organization of the cell cluster while the role of the external signal is limited to single out some cells in the cluster, conferring them with motility properties.

RESULTS

Here we analyzed the role of Fibroblast Growth Factor (FGF) signaling in collective migration in the Drosophila trachea. While ligand-binding FGF receptor (FGFR) activity in a single cell can drive migration of a tracheal cluster, we show that activity from a constitutively activated FGFR cannot-an observation that contrasts with previously analyzed cases.

CONCLUSIONS

Our results indicate that individual cells in the tracheal cluster can "read" differences in the distribution of FGFR activity and lead migration of the cluster accordingly. Thus, FGF can act as a chemoattractant rather than as a motogen in collective cell migration. This finding has many implications in both development and pathology.

Spen is required for pigment cell survival during pupal development in Drosophila

Apoptosis is required during development to eliminate superfluous cells and sculpt tissues; spatial and timed control of apoptosis ensures that the necessary number of cells is eliminated at a precise time in a given tissue. The elimination of supernumerary pigment or inter-ommatidial cells (IOCs) depends on cell-cell communication and is necessary for the formation of the honeycomb-like structure of the Drosophila eye. However, the mechanisms occurring during pupal development and controlling apoptosis of superfluous IOC in space and time remain unclear. Here, we found that split-ends (spen) is required for IOC survival at the time of removal of superfluous IOCs. Loss of spen function leads to abnormal removal of IOCs by apoptosis. We show that spen is required non-autonomously in cone cells for the survival of IOCs by positively regulating the Spitz/EGFR pathway. We propose that Spen is an important survival factor that ensures spatial control of the apoptotic wave that is necessary for the correct patterning and formation of the Drosophila eye.

RTK signaling modulates the Dorsal gradient

The dorsoventral (DV) axis of the Drosophila embryo is patterned by a nuclear gradient of the Rel family transcription factor, Dorsal (Dl), that activates or represses numerous target genes in a region-specific manner. Here, we demonstrate that signaling by receptor tyrosine kinases (RTK) reduces nuclear levels and transcriptional activity of Dl, both at the poles and in the mid-body of the embryo. These effects depend on wntD, which encodes a Dl antagonist belonging to the Wingless/Wnt family of secreted factors. Specifically, we show that, via relief of Groucho- and Capicua-mediated repression, the Torso and EGFR RTK pathways induce expression of WntD, which in turn limits Dl nuclear localization at the poles and along the DV axis. Furthermore, this RTK-dependent control of Dl is important for restricting expression of its targets in both contexts. Thus, our results reveal a new mechanism of crosstalk, whereby RTK signals modulate the spatial distribution and activity of a developmental morphogen in vivo.

A secreted MMP is required for reepithelialization during wound healing

Matrix metalloproteinases (MMPs) are extracellular proteases highly expressed at wound sites. However, the precise function of MMPs during reepithelialization in vivo has been elusive in mammalian models because of the high level of redundancy among the 24 mammalian MMPs. For this reason we used Drosophila melanogaster, whose genome encodes only two MMPs-one secreted type (Mmp1) and one membrane-anchored type (Mmp2)-to study the function and regulation of the secreted class of MMPs in vivo. In the absence of redundancy, we found that the Drosophila secreted MMP, Mmp1, is required in the epidermis to facilitate reepithelialization by remodeling the basement membrane, promoting cell elongation and actin cytoskeletal reorganization, and activating extracellular signal-regulated kinase signaling. In addition, we report that the jun N-terminal kinase (JNK) pathway upregulates Mmp1 expression after wounding, but that Mmp1 is expressed independent of the JNK pathway in unwounded epidermis. When the JNK pathway is ectopically activated to overexpress Mmp1, the rate of healing is accelerated in an Mmp1-dependent manner. A primary function of Mmp1, under the control of the JNK pathway, is to promote basement membrane repair, which in turn may permit cell migration and the restoration of a continuous tissue.