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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.08.025 Byline: Nicola A. Grzeschik (a)(b), Nancy Amin (a)(b), Julie Secombe (c), Anthony M. Brumby (a)(b)(c), Helena E. Richardson (a)(b)(c) Keywords: Drosophila; Eye development; Proliferation; Apico-basal cell polarity; Apoptosis; lgl; cyclin E Abstract: In homozygous mutants of Drosophila lethal-2-giant larvae (lgl), tissues lose apico-basal cell polarity and exhibit ectopic proliferation. Here, we use clonal analysis in the developing eye to investigate the effect of lgl null mutations in the context of surrounding wild-type tissue. lgl.sup.- clones in the larval eye disc exhibit ectopic expression of the G1-S regulator, Cyclin E, and ectopic proliferation, but do not lose apico-basal cell polarity. Decreasing the perdurance of Lgl protein in larval eye disc clones, by forcing extra proliferation of lgl.sup.- tissue (using a Minute background), leads to a loss in cell polarity and to more extreme ectopic cell proliferation. Later in development at the pupal stage, lgl mutant photoreceptor cells show aberrant apico-basal cell polarity, but this is not associated with ectopic proliferation, presumably because cells are differentiated. Thus in a clonal context, the ectopic proliferation and cell polarity defects of lgl.sup.- mutants are separable. Furthermore, lgl.sup.- mosaic eye discs have alterations in the normal patterns of apoptosis: in larval discs some lgl.sup.- and wild-type cells at the clonal boundary undergo apoptosis and are excluded from the epithelia, but apoptosis is decreased elsewhere in the disc, and in pupal retinas lgl.sup.- tissue shows less apoptosis. Author Affiliation: (a) Peter MacCallum Cancer Center, Melbourne, Victoria, Australia (b) Anatomy and Cell Biology Department, University of Melbourne, Melbourne, Victoria, Australia (c) Genetics Department, University of Adelaide, Adelaide, South Australia, Australia Article History: Received 22 February 2007; Revised 6 August 2007; Accepted 7 August 2007

Cyclin E together with its kinase partner Cdk2 is a critical regulator of entry into S phase. To identify novel genes that regulate the G1- to S-phase transition within a whole animal we made use of a hypomorphic cyclin E mutation, Dmcyc[E.sup.JP], which results in a rough eye phenotype. We screened the X and third chromosome deficiencies, tested candidate genes, and carried out a genetic screen of 55,000 EMS or X-ray-mutagenized flies for second or third chromosome mutations that dominantly modified the Dmcyc[E.sup.JP] rough eye phenotype. We have focused on the Dmcyc[E.sup.JP] suppressors, S(Dmcyc[E.sup.JP]), to identify novel negative regulators of S-phase entry. There are 18 suppressor gene groups with more than one allele and several genes that are represented by only a single allele. All S(Dmcyc[E.sup.JP]) tested suppress the Dmcyc[E.sup.JP] rough eye phenotype by increasing the number of S phases in the postmorphogenetic furrow S-phase band. By testing candidates we have identified several modifier genes from the mutagenic screen as well as from the deficiency screen. Dmcyc[E.sup.JP] suppressor genes fall into the classes of: (1) chromatin remodeling or transcription factors; (2) signaling pathways; and (3) cytoskeletal, (4) cell adhesion, and (5) cytoarchitectural tumor suppressors. The cytoarchitectural tumor suppressors include scribble, lethal-2-giant-larvae (lgl), and discs-large (dlg), loss of function of which leads to neoplastic tumors and disruption of apical-basal cell polarity. We further explored the genetic interactions of scribble with S(Dmcyc[E.sup.JP]) genes and show that bypomorphic scribble mutants exhibit genetic interactions with lgl, scab ([alpha]PS3-integrin--cell adhesion), phyllopod (signaling), dEB1 (microtubule-binding protein--cytoskeletal)' and moira (chromatin remodeling). These interactions of the cytoarchitectural suppressor gene, scribble, with cell adhesion, signaling, cytoskeletal, and chromatin remodeling genes, suggest that these genes may act in a common pathway to negatively regulate cyclin E or S-phase entry.

Abstract Background Metastatic neoplasias are characterized by excessive cell proliferation and disruptions to apico-basal cell polarity and tissue architecture. Understanding how alterations in cell polarity can impact upon tumour development is, therefore, a central issue in cancer biology. The Drosophila gene scribble (scrib) encodes a PDZ-domain scaffolding protein that regulates cell polarity and acts as a tumour suppressor in flies. Increasing evidence also implicates the loss of human Scrib in cancer. In this report, we investigate how loss of Scrib promotes epithelial tumourigenesis in Drosophila, both alone and in cooperation with oncogenic mutations. Results We find that genetically distinct atypical protein kinase C (aPKC)-dependent and Jun N-terminal kinase (JNK)-dependent alterations in scrib mutants drive epithelial tumourigenesis. First, we show that over-expression of the apical cell polarity determinants Crumbs (Crb) or aPKC induces similar cell morphology defects and over-proliferation phenotypes as scrib loss-of-function. However, the morphological and proliferative defects in scrib mutants are independent of Crb function, and instead can be rescued by a dominant negative (kinase dead) aPKC transgene. Secondly, we demonstrate that loss of Scrib promotes oncogene-mediated transformation through both aPKC and JNK-dependent pathways. JNK normally promotes apoptosis of scrib mutant cells. However, in cooperation with oncogenic activated Ras or Notch signalling, JNK becomes an essential driver of tumour overgrowth and invasion. aPKC-dependent signalling in scrib mutants cooperates with JNK to significantly enhance oncogene-mediated tumour overgrowth. Conclusion These results demonstrate distinct aPKC and JNK-dependent pathways through which loss of Scrib promotes tumourigenesis in Drosophila. This is likely to have a direct relevance to the way in which human Scrib can similarly restrain an oncogene-mediated transformation and, more generally, on how the outcome of oncogenic signalling can be profoundly perturbed by defects in apico-basal epithelial cell polarity.

Background: Metastasis underlies most colorectal cancer mortality. Cancer cells spread through the body as single cells or small clusters of cells that have an invasive, mesenchymal, nonproliferative phenotype. At the secondary site, they revert to a proliferative “tumor constructing” epithelial phenotype to rebuild a tumor. We previously developed a unique in vitro three‐dimensional model, called LIM1863‐Mph, which faithfully recapitulates these reversible transitions that underpin colorectal cancer metastasis. Wnt signaling plays a key role in these transitions and is initiated by the coupling of extracellular Wnt to Frizzled (FZD). Using the LIM1863‐Mph model system we demonstrated that the Wnt receptor FZD7 is necessary for mesenchymal to epithelial transition (MET). Here we investigate the role of Wnt in MET. Results: Wnt secretion is dependent on palmitoylation by Porcupine (PORC). A PORC inhibitor (IWP2) that prevents Wnt secretion, blocked the epithelial transition of mesenchymal LIM1863‐Mph cells. Wnt gene array analysis identified several Wnts that are upregulated in epithelial compared with mesenchymal LIM1863‐Mph cells, suggesting these ligands in MET. Wnt2B was the most abundant differentially expressed Wnt gene. Indeed, recombinant Wnt2B could overcome the IWP2‐mediated block in epithelial transition of mesenchymal LIM1863‐Mph cells. Conclusions: Wnt2B co‐operates with Frizzled7 to mediate MET in colorectal cancer. Developmental Dynamics 247:521–530, 2018. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Background: Metastatic neoplasias are characterized by excessive cell proliferation and disruptions to apico-basal cell polarity and tissue architecture. Understanding how alterations in cell polarity can impact upon tumour development is, therefore, a central issue in cancer biology. The Drosophila gene scribble (scrib) encodes a PDZ-domain scaffolding protein that regulates cell polarity and acts as a tumour suppressor in flies. Increasing evidence also implicates the loss of human Scrib in cancer. In this report, we investigate how loss of Scrib promotes epithelial tumourigenesis in Drosophila, both alone and in cooperation with oncogenic mutations., Results: We find that genetically distinct atypical protein kinase C (aPKC)-dependent and Jun N-terminal kinase (JNK)-dependent alterations in scrib mutants drive epithelial tumourigenesis. First, we show that over-expression of the apical cell polarity determinants Crumbs (Crb) or aPKC induces similar cell morphology defects and over-proliferation phenotypes as scrib loss-of-function. However, the morphological and proliferative defects in scrib mutants are independent of Crb function, and instead can be rescued by a dominant negative (kinase dead) aPKC transgene. Secondly, we demonstrate that loss of Scrib promotes oncogene-mediated transformation through both aPKC and JNK-dependent pathways. JNK normally promotes apoptosis of scrib mutant cells. However, in cooperation with oncogenic activated Ras or Notch signalling, JNK becomes an essential driver of tumour overgrowth and invasion. aPKC-dependent signalling in scrib mutants cooperates with JNK to significantly enhance oncogene-mediated tumour overgrowth., Conclusion: These results demonstrate distinct aPKC and JNK-dependent pathways through which loss of Scrib promotes tumourigenesis in Drosophila. This is likely to have a direct relevance to the way in which human Scrib can similarly restrain an oncogene-mediated transformation and, more generally, on how the outcome of oncogenic signalling can be profoundly perturbed by defects in apico-basal epithelial cell polarity.