HES6 promotes prostate cancer aggressiveness independently of Notch signalling

Notch signalling is implicated in the pathogenesis of a variety of cancers, but its role in prostate cancer is poorly understood. However, selected Notch pathway members are overrepresented in high‐grade prostate cancers. We comprehensively profiled Notch pathway components in prostate cells and found prostate cancer‐specific up‐regulation of NOTCH3 and HES6. Their expression was particularly high in androgen responsive lines. Up‐ and down‐regulating Notch in these cells modulated expression of canonical Notch targets, HES1 and HEY1, which could also be induced by androgen. Surprisingly, androgen treatment also suppressed Notch receptor expression, suggesting that androgens can activate Notch target genes in a receptor‐independent manner. Using a Notch‐sensitive Recombination signal binding protein for immunoglobulin kappa J region (RBPJ) reporter assay, we found that basal levels of Notch signalling were significantly lower in prostate cancer cells compared to benign cells. Accordingly pharmacological Notch pathway blockade did not inhibit cancer cell growth or viability. In contrast to canonical Notch targets, HES6, a HES family member known to antagonize Notch signalling, was not regulated by Notch signalling, but relied instead on androgen levels, both in cultured cells and in human cancer tissues. When engineered into prostate cancer cells, reduced levels of HES6 resulted in reduced cancer cell invasion and clonogenic growth. By molecular profiling, we identified potential roles for HES6 in regulating hedgehog signalling, apoptosis and cell migration. Our results did not reveal any cell‐autonomous roles for canonical Notch signalling in prostate cancer. However, the results do implicate HES6 as a promoter of prostate cancer progression.     

A mechanism for morphogen-controlled domain growth

Many developmental systems are organised via the action of graded distributions of morphogens. In the Drosophila wing disc, for example, recent experimental evidence has shown that graded expression of the morphogen Dpp controls cell proliferation and hence disc growth. Our goal is to explore a simple model for regulation of wing growth via the Dpp gradient: we use a system of reaction-diffusion equations to model the dynamics of Dpp and its receptor Tkv, with advection arising as a result of the flow generated by cell proliferation. We analyse the model both numerically and analytically, showing that uniform domain growth across the disc produces an exponentially growing wing disc.     

Induction of cellular growth by the axon guidance regulators Netrin A and Semaphorin‐1a

Although neurite outgrowth has been linked to axon guidance regulators, the effects of guidance molecules on cellular growth are not well understood. Use of the Drosophila wing imaginal disc, an epithelial tissue and a well‐characterized system for analysis of cellular growth regulation, permits analysis of the impacts of guidance molecules on cellular growth in a setting in which axon guidance is not a confounding factor. In this investigation, the impacts of Netrin A (NetA) and Semaphorin‐1a (Sema1a) signaling on cellular growth are examined during wing development. Levels of these genes were modulated in somatic clones in the developing wing disc, and clone areas, as well as individual sizes of clonal cells were assessed. NetA and Sema1a signaling were found to induce cellular growth in these assays. Furthermore, immunohistochemical analyses indicated that NetA and Sema1a signaling induce expression of several growth regulators, including myc, cycD, cdk4, PCNA, and MapK in the wing disc. These data illustrate that NetA and Sema1a can specifically promote growth through induction of key cellular growth regulators. The abilities of NetA and Sema1a to regulate cellular growth are likely critical to their functions in both nervous system development and oncogenesis. © 2010 Wiley Periodicals, Inc. Develop Neurobiol 70:473–484, 2010     

A novel interaction between hedgehog and Notch promotes proliferation at the anterior-posterior organizer of the Drosophila wing

Notch has multiple roles in the development of the Drosophila melanogaster wing imaginal disc. It helps specify the dorsal-ventral compartment border, and it is needed for the wing margin, veins, and sensory organs. Here we present evidence for a new role: stimulating growth in response to Hedgehog. We show that Notch signaling is activated in the cells of the anterior-posterior organizer that produce the region between wing veins 3 and 4, and we describe strong genetic interactions between the gene that encodes the Hedgehog pathway activator Smoothened and the Notch pathway genes Notch, presenilin, and Suppressor of Hairless and the Enhancer of split complex. This work thus reveals a novel collaboration by the Hedgehog and Notch pathways that regulates proliferation in the 3-4 intervein region independently of Decapentaplegic.     

Fringe, Notch, and making developmental boundaries.

Multiple mechanisms are involved in positioning and restricting specialized dorsal-ventral border cells in the Drosophila wing, including modulation of Notch signaling by Fringe, autonomous inhibition by Notch ligands, and inhibition of Notch target genes by Nubbin. Recent studies have revealed that Fringe also modulates a Notch-mediated signaling process between dorsal and ventral cells in the Drosophila eye, establishing an organizer of eye growth and patterning along the dorsal-ventral midline. Fringe-dependent modulation of Notch signaling also plays a key role in Drosophila leg segmentation and growth. Lunatic Fringe has been shown to be required for vertebrate somitogenesis, where it appears to act as a crucial link between a molecular clock and the regulation of Notch signaling.     

The Transcription Factor Optomotor-Blind Antagonizes Drosophila Haltere Growth by Repressing Decapentaplegic and Hedgehog Targets

In Drosophila, decapentaplegic, which codes for a secreted signaling molecule, is activated by the Hedgehog signaling pathway at the anteroposterior compartment border of the two dorsal primordia; the wing and the haltere imaginal discs. In the wing disc, Decapentaplegic and Hedgehog signaling targets are implicated in cell proliferation and cell survival. However, most of their known targets in the wing disc are not expressed in the haltere disc due to their repression by the Hox gene Ultrabithorax. The T-box gene optomotor-blind escapes this repression in the haltere disc, and therefore is expressed in both the haltere and wing discs. Optomotor-blind is a major player during wing development and its function has been intensely investigated in this tissue, however, its role in haltere development has not been reported so far. Here we show that Optomotor-blind function in the haltere disc differs from that in the wing disc. Unlike its role in the wing, Optomotor-blind does not prevent apoptosis in the haltere but rather limits growth by repressing several Decapentaplegic and Hedgehog targets involved both in wing proliferation and in modulating the spread of morphogens similar to Ultrabithorax function but without disturbing Ultrabithorax expression.     

Distinct functions of the Drosophila genes Serrate and Delta revealed by ectopic expression during wing development

 The Drosophila gene Serrate encodes a transmembrane protein with 14 epidermal growth factor-(EGF)-like repeats in its extracellular portion. It has been suggested to act as a signal in the developing wing from the dorsal side to induce the organising centre at the dorsal/ventral compartment boundary, which is required for growth and patterning of the wing. Ectopic expression of Serrate during wing development induces ectopic outgrowth of ventral wing tissue and the formation of an additional wing margin. Here we present data to suggest that both events are mediated by genes that are required for normal wing development, including Notch as receptor. In order for Serrate to elicit these responses the concomitant expression of wingless seems to be required. The lack of wings in flies devoid of Serrate function can be partially restored by Gal4-mediated expression of Serrate, whilst expression of wingless is not sufficient. Ectopic expression of Delta, which encodes a structurally very similar transmembrane protein with EGF-like repeats, provokes wing outgrowth and induction of a new margin under all conditions tested here, both on the dorsal and ventral side. Our data further suggest that Serrate can act as an activating ligand for the Notch receptor only under certain circumstances; it inhibits Notch function under other conditions. Received: 26 april 1996 / Accepted: 24 May 1996     

Compartments and the control of growth in the Drosophila wing imaginal disc

The mechanisms that control organ growth are among the least known in development. This is particularly the case for the process in which growth is arrested once final size is reached. We have studied this problem in the wing disc of Drosophila, the developmental and growth parameters of which are well known. We have devised a method to generate entire fast-growing Minute(+) (M(+)) discs or compartments in slow developing Minute/+ (M/+) larvae. Under these conditions, a M(+) wing disc gains at least 20 hours of additional development time. Yet it grows to the same size of Minute/+ discs developing in M/+ larvae. We have also generated wing discs in which all the cells in either the anterior (A) or the posterior (P) compartment are transformed from M/+ to M(+). We find that the difference in the cell division rate of their cells is reflected in autonomous differences in the developmental progression of these compartments: each grows at its own rate and manifests autonomous regulation in the expression of the developmental genes wingless and vestigial. In spite of these differences, ;mosaic' discs comprising fast and slow compartments differentiate into adult wings of the correct size and shape. Our results demonstrate that imaginal discs possess an autonomous mechanism with which to arrest growth in anterior and posterior compartments, which behave as independent developmental units. We propose that this mechanism does not act by preventing cell divisions, but by lengthening the division cycle.