aPKCzeta cortical loading is associated with Lgl cytoplasmic release and tumor growth in Drosophila and human epithelia

The Drosophila tumour suppressor Lgl and Vap33 activate the Hippo pathway through a dual mechanism

The tumour suppressor, Lethal (2) giant larvae [Lgl; also known as L(2)gl], is an evolutionarily conserved protein that was discovered in the vinegar fly Drosophila, where its depletion results in tissue overgrowth and loss of cell polarity. Lgl links cell polarity and tissue growth through regulation of the Notch and the Hippo signalling pathways. Lgl regulates the Notch pathway by inhibiting V-ATPase activity via Vap33. How Lgl regulates the Hippo pathway was unclear. In this current study, we show that V-ATPase activity inhibits the Hippo pathway, whereas Vap33 acts to activate Hippo signalling. Vap33 physically and genetically interacts with the actin cytoskeletal regulators RtGEF (Pix) and Git, which also bind to the Hippo protein (Hpo) and are involved in the activation of the Hippo pathway. Additionally, we show that the ADP ribosylation factor Arf79F (Arf1), which is a Hpo interactor, is involved in the inhibition of the Hippo pathway. Altogether, our data suggest that Lgl acts via Vap33 to activate the Hippo pathway by a dual mechanism: (1) through interaction with RtGEF, Git and Arf79F, and (2) through interaction and inhibition of the V-ATPase, thereby controlling epithelial tissue growth.

Apoptosis inhibition restrains primary malignant traits in different Drosophila cancer models

Tumor cells exploit multiple mechanisms to evade apoptosis, hence the strategies aimed at reactivating cell death in cancer. However, recent studies are revealing that dying cells play remarkable pro-oncogenic roles. Among the mechanisms promoting cell death, cell competition, elicited by disparities in MYC activity in confronting cells, plays the primary role of assuring tissue robustness during development from Drosophila to mammals: cells with high MYC levels (winners) overproliferate while killing suboptimal neighbors (losers), whose death is essential to process completion. This mechanism is coopted by tumor cells in cancer initiation, where host cells succumb to high-MYC-expressing precancerous neighbors. Also in this case, inhibition of cell death restrains aberrant cell competition and rescues tissue structure. Inhibition of apoptosis may thus emerge as a good strategy to counteract cancer progression in competitive contexts; of note, we recently found a positive correlation between cell death amount at the tumor/stroma interface and MYC levels in human cancers. Here we used Drosophila to investigate the functional role of competition-dependent apoptosis in advanced cancers, observing dramatic changes in mass dimensions and composition following a boost in cell competition, rescued by apoptosis inhibition. This suggests the role of competition-dependent apoptosis be not confined to the early stages of tumorigenesis. We also show that apoptosis inhibition, beside restricting cancer mass, is sufficient to rescue tissue architecture and counteract cell migration in various cancer contexts, suggesting that a strong activation of the apoptotic pathways intensifies cancer burden by affecting distinct phenotypic traits at different stages of the disease.

Silencing of LLGL2 Suppresses the Estradiol-Induced BPH-1 Cell Proliferation through the Regulation of Autophagy

Lethal giant larvae (Lgl) is an apical-basal polarity gene first identified in Drosophila. LLGL2 is one of the mammalian homologs of Lgl. However, little is known about its function in the prostate. In this study, to explore the new role of LLGL2 in the prostate, we examined the proliferative activity of a BPH-1 cell line, a well-established model for the human prostate biology of benign prostatic hyperplasia (BPH). The expression of LLGL2 was dose-dependently increased in BPH-1 cells after treatment with 17β-estradiol (E2). Additionally, E2 treatment increased the proliferation of the BPH-1 cells. However, the knockdown of LLGL2 with siRNA significantly suppressed the proliferation of the E2-treated BPH-1 cells. Moreover, si-llgl2 treatment up-regulated the expression of LC-3B, ATG7, and p-beclin, which are known to play a pivotal role in autophagosome formation in E2-treated BPH-1 cells. Overexpression of LLGL2 was able to further prove these findings by showing the opposite results from the knockdown of LLGL2 in E2-treated BPH-1 cells. Collectively, our results suggest that LLGL2 is closely involved in the proliferation of prostate cells by regulating autophagosome formation. These results provide a better understanding of the mechanism involved in the effect of LLGL2 on prostate cell proliferation. LLGL2 might serve as a potential target in the diagnosis and/or treatment of human BPH.

Caenorhabditis elegans LET-413 Scribble is essential in the epidermis for growth, viability, and directional outgrowth of epithelial seam cells

The conserved adapter protein Scribble (Scrib) plays essential roles in a variety of cellular processes, including polarity establishment, proliferation, and directed cell migration. While the mechanisms through which Scrib promotes epithelial polarity are beginning to be unraveled, its roles in other cellular processes including cell migration remain enigmatic. In C. elegans, the Scrib ortholog LET-413 is essential for apical–basal polarization and junction formation in embryonic epithelia. However, whether LET-413 is required for postembryonic development or plays a role in migratory events is not known. Here, we use inducible protein degradation to investigate the functioning of LET-413 in larval epithelia. We find that LET-413 is essential in the epidermal epithelium for growth, viability, and junction maintenance. In addition, we identify a novel role for LET-413 in the polarized outgrowth of the epidermal seam cells. These stem cell-like epithelial cells extend anterior and posterior directed apical protrusions in each larval stage to reconnect to their neighbors. We show that the role of LET-413 in seam cell outgrowth is likely mediated largely by the junctional component DLG-1 discs large, which we demonstrate is also essential for directed outgrowth of the seam cells. Our data uncover multiple essential functions for LET-413 in larval development and show that the polarized outgrowth of the epithelial seam cells is controlled by LET-413 Scribble and DLG-1 Discs large.

Most cells in multicellular organisms are organized along a directional axis of cell polarity. One protein that is important for this polarized organization is the conserved polarity regulator Scribble. This protein has several functions, including forming the basolateral domains of cells, promoting the formation of cell junctions, and promoting cell migration. How Scribble performs these functions is not fully understood. In this paper we study the role of Scribble during larval development of the small nematode Caenorhabditis elegans using an inducible protein degradation system. We show that Scribble, called LET-413 in C. elegans, is essential in the epidermal epithelium for animal development, as depletion of LET-413 in only this tissue blocks growth. We also demonstrate that LET-413 is required for the polarized outgrowth of an epithelial cell type called the seam cells, a process resembling cell migration. Finally, we show that one major function of LET-413 in seam cell outgrowth is the localization of the junctional component Discs large (DLG-1), which we demonstrate is also essential for this process. Our data thus uncover multiple essential functions for LET-413 in larval development and provide new insights into how the directional outgrowth of epithelial seam cells is controlled.

LLGL2 Increases Ca2+ Influx and Exerts Oncogenic Activities via PI3K/AKT Signaling Pathway in Hepatocellular Carcinoma

Background

Lethal giant larvae (Lgl), scaffolding proteins, regulate the epithelial cell apicobasal polarity in Drosophila. They play important roles in asymmetric cell division, cell migration, and progenitor cells self-renewal as tumor suppressors. One of Lgl mammalian homologues proteins, LLGL2 overexpression has been reported in ER+ breast cancer and promotes tumor proliferation through regulating leucine uptake. Nonetheless, the role of LLGL2 in hepatocellular carcinoma (HCC) is still unknown.

Methods

TCGA dataset mining, qRT-PCR, Western blot along with immunohistochemistry assays were employed to explore LLGL2 expression in human HCC samples and cell lines. Moreover, the clinical value of LLGL2 was investigated in 156 HCC patients. Furthermore, the role as well as the molecular mechanism of LLGL2 in the progression of HCC was explored through a series of in vitro and in vivo experiments.

Results

LLGL2 was up-regulated in HCC tissues, which was related with certain clinicopathological features including tumor number, vascular invasion as well as advanced stage. High expression of LLGL2 predicted poor prognosis after hepatectomy. LLGL2 promoted HCC cells proliferation, migration and invasion through PI3K/ATK signaling by promoting calcium ion influx.

Conclusion

Our study identified that LLGL2 is a tumor promoter in HCC for the first time, which could potentially be utilized as a new biomarker and a therapeutic target for HCC.

Human giant larvae-1 promotes migration and invasion of malignant glioma cells by regulating N-cadherin

Human giant larvae-1 (Hugl-1) is a human homologue of Drosophila tumor suppressor lethal (2)-giant larvae and has been reported to be involved in the development of human malignancies. Previous studies performed by our group demonstrated that Hugl-1 inhibits glioma cell proliferation in an intracranial model of nude mice. However, the exact molecular mechanisms underlying the participation of Hugl-1 in glioma invasion and migration, and in the depolarizing process remain largely unknown. Utilizing the U251-MG cells with stable expression of Hugl-1, the present study used wound healing, Transwell invasion and western blot assays to explore the role and specific mechanism of Hugl-1 in glioma invasion and migration. The results of the present study demonstrated that overexpression of Hugl-1 decreased cell-cell adhesion and increased cell-cell extracellular matrix adhesion. In addition, overexpression of Hugl-1 promoted pseudopodia formation, glioma cell migration and invasion. The molecular mechanism of action involved the negative regulation of N-cadherin protein levels by Hugl-1. Overexpression or knockdown of N-cadherin partially suppressed or enhanced the effects of Hugl-1 on glioma cell migration and invasion, respectively. Furthermore, Hugl-1 inhibited cell proliferation, while promoting cell migration, which suggests that it may serve a two-sided biological role in cellular processes. Taken together, these results suggest that Hugl-1 promotes the migration and invasion of malignant glioma cells by decreasing N-cadherin expression. Thus, Hugl-1 may be applied in the development of targeted and personalized treatment.

DNA methylation of Hugl-2 is a prognostic biomarker in kidney renal clear cell carcinoma

It has been reported that loss of Hugl-2 contributes to tumour formation and progression in vitro and in vivo. However, whether Hugl-2 levels decrease during kidney renal clear cell carcinoma (KIRC) and the mechanism involved remain unknown. This study aimed to investigate whether DNA methylation of Hugl-2 reduces its expression, leading to the progression and poor prognosis of KIRC. Hugl-2 methylation and mRNA expression and KIRC clinicopathological data were extracted from The Cancer Genome Atlas (TCGA), and relationships among these factors were analyzed using UALCAN, MethHC, Wanderer and LinkedOmics web tools. We found that Hugl-2 mRNA and protein levels were reduced in KIRC tissues. Moreover, Hugl-2 mRNA levels were related to tumour grade and overall survival, and Hugl-2 methylation was increased in KIRC. According to the results of methylation-specific PCR, KIRC cells had higher Hugl-2 DNA methylation levels than HKC cells. Moreover, Hugl-2 DNA methylation correlated negatively with Hugl-2 mRNA and was also related to the pathology and T stage of KIRC patients. KIRC patients with high Hugl-2 DNA methylation also had shorter overall survival. Additionally, methylation of cg08827674, a Hugl-2 probe, was related to pathologic stage, T stage, neoplasm histologic grade, serum calcium level without laterality, M stage, N stage, and ethnicity. Furthermore, treatment with the DNA methylation inhibitor decitabine resulted in upregulation of Hugl-2 mRNA and protein levels in KIRC cell lines. These results indicate that Hugl-2 DNA methylation may be both a prognostic marker and a therapeutic target in KIRC.

Lgl cortical dynamics are independent of binding to the Scrib-Dlg complex but require Dlg-dependent restriction of aPKC

Apical-basal polarity underpins the formation of epithelial barriers that are crucial for metazoan physiology. Although apical-basal polarity is long known to require the basolateral determinants Lethal Giant Larvae (Lgl), Discs Large (Dlg) and Scribble (Scrib), mechanistic understanding of their function is limited. Lgl plays a role as an aPKC inhibitor, but it remains unclear whether Lgl also forms complexes with Dlg or Scrib. Using fluorescence recovery after photobleaching, we show that Lgl does not form immobile complexes at the lateral domain of Drosophila follicle cells. Optogenetic depletion of plasma membrane PIP₂ or dlg mutants accelerate Lgl cortical dynamics. However, Dlg and Scrib are required only for Lgl localization and dynamic behavior in the presence of aPKC function. Furthermore, light-induced oligomerization of basolateral proteins indicates that Lgl is not part of the Scrib-Dlg complex in the follicular epithelium. Thus, Scrib and Dlg are necessary to repress aPKC activity in the lateral domain but do not provide cortical binding sites for Lgl. Our work therefore highlights that Lgl does not act in a complex but in parallel with Scrib-Dlg to antagonize apical determinants.

Pard3 suppresses glioma invasion by regulating RhoA through atypical protein kinase C/NF-κB signaling

Partitioning defective protein 3 (Pard3) has been reported to inhibit the progression of numerous human cancer cell types. However, the role of Pard3 in glioma progression remains unclear. In this study, the expression of Pard3 was measured in human gliomas of different grades by both quantitative polymerase chain reaction and Western blotting. The effect of Pard3 on glioma progression was tested using cell counting kit‐8 assays, EdU assays, colony formation assays, cell migration, and invasion assays and tumor xenografts. The effect of Pard3 on Ras homolog family member A (RhoA) protein levels, subcellular localization, and transcriptional activity was measured by immunoblotting and immunofluorescence. Our results indicate that Pard3 functions as a tumor suppressor in gliomas and that the loss of Pard3 protein is strongly associated with a higher grade and poorer outcome. Pard3 overexpression inhibits glioma progression by upregulating RhoA protein levels. However, the level of GTP‐RhoA protein remained unchanged. Further evidence demonstrates that Pard3 regulates RhoA protein levels, subcellular localization and transcriptional activity by activating atypical protein kinase C/NF‐κB signaling. Mouse modeling experiments show that Pard3 overexpression inhibits glioma cell growth in vivo. Taken together, these findings identify RhoA as a novel target of Pard3 in gliomas and substantiate a novel regulatory role for Pard3 in glioma progression. This study reveals that Pard3 plays an inhibitory role in gliomas by regulating RhoA, which reveals a potential benefit for Pard3 activators in the prevention and therapy of gliomas.

Drosophila melanogaster: A Model Organism to Study Cancer

Cancer is a multistep disease driven by the activation of specific oncogenic pathways concomitantly with the loss of function of tumor suppressor genes that act as sentinels to control physiological growth. The conservation of most of these signaling pathways in Drosophila, and the ability to easily manipulate them genetically, has made the fruit fly a useful model organism to study cancer biology. In this review we outline the basic mechanisms and signaling pathways conserved between humans and flies responsible of inducing uncontrolled growth and cancer development. Second, we describe classic and novel Drosophila models used to study different cancers, with the objective to discuss their strengths and limitations on their use to identify signals driving growth cell autonomously and within organs, drug discovery and for therapeutic approaches.

Lgl reduces endosomal vesicle acidification and Notch signaling by promoting the interaction between Vap33 and the V-ATPase complex

Epithelial cell polarity is linked to the control of tissue growth and tumorigenesis. The tumor suppressor and cell polarity protein lethal-2-giant larvae (Lgl) promotes Hippo signaling and inhibits Notch signaling to restrict tissue growth in Drosophila melanogaster Notch signaling is greater in lgl mutant tissue than in wild-type tissue because of increased acidification of endosomal vesicles, which promotes the proteolytic processing and activation of Notch by γ-secretase. We showed that the increased Notch signaling and tissue growth defects of lgl mutant tissue depended on endosomal vesicle acidification mediated by the vacuolar adenosine triphosphatase (V-ATPase). Lgl promoted the activity of the V-ATPase by interacting with Vap33 (VAMP-associated protein of 33 kDa). Vap33 physically and genetically interacted with Lgl and V-ATPase subunits and repressed V-ATPase-mediated endosomal vesicle acidification and Notch signaling. Vap33 overexpression reduced the abundance of the V-ATPase component Vha44, whereas Lgl knockdown reduced the binding of Vap33 to the V-ATPase component Vha68-3. Our data indicate that Lgl promotes the binding of Vap33 to the V-ATPase, thus inhibiting V-ATPase-mediated endosomal vesicle acidification and thereby reducing γ-secretase activity, Notch signaling, and tissue growth. Our findings implicate the deregulation of Vap33 and V-ATPase activity in polarity-impaired epithelial cancers.

Ubiquitin-specific protease 11 functions as a tumor suppressor by modulating Mgl-1 protein to regulate cancer cell growth

The Lethal giant larvae (Lgl) gene encodes a cortical cytoskeleton protein, Lgl, and is involved in maintaining cell polarity and epithelial integrity. Previously, we observed that Mgl-1, a mammalian homologue of the Drosophila tumor suppressor protein Lgl, is subjected to degradation via ubiquitin-proteasome pathway, and scaffolding protein RanBPM prevents the turnover of the Mgl-1 protein. Consequently, overexpression of RanBPM enhances Mgl-1-mediated cell proliferation and migration. Here, we analyzed the ability of ubiquitin-specific protease 11 (USP11) as a novel regulator of Mgl-1 and it requires RanBPM to regulate proteasomal degradation of Mgl-1. USP11 showed deubiquitinating activity and stabilized Mgl-1 protein. However, USP11-mediated Mgl-1 stabilization was inhibited in RanBPM-knockdown cells. Furthermore, in the cancer cell migration, the regulation of Mgl-1 by USP11 required RanBPM expression. In addition, an in vivo study revealed that depletion of USP11 leads to tumor formation. Taken together, the results indicated that USP11 functions as a tumor suppressor through the regulation of Mgl-1 protein degradation via RanBPM.

Tumorigenic Properties of Drosophila Epithelial Cells Mutant for lethal giant larvae

BACKGROUND

Mutations in Drosophila tumor suppressor genes (TSGs) lead to the formation of invasive tumors in the brain and imaginal discs.

RESULTS

Here we studied the tumorigenic properties of imaginal discs mutant for the TSG gene lethal giant larvae (lgl). lgl mutant cells display the characteristic features of mammalian tumor cells: they can proliferate indefinitely, induce additional tracheogenesis (an insect counterpart of vasculogenesis) and invade neighboring tissues. Lgl mutant tissues exhibit high apoptotic levels, which lead to the activation of the Jun-N-Terminal Kinase (JNK) pathway. We propose that JNK is a key factor in the acquisition of these tumorigenic properties; it promotes cell proliferation and induces high levels of Mmp1 and confers tumor cells capacity to invade wild-type tissue. Noteworthy, lgl RNAi-mediated down-regulation does not produce similar transformations in the central nervous system (CNS), thereby indicating a fundamental difference between the cells of developing imaginal discs and those of differentiated organs. We discuss these results in the light of the "single big-hit origin" of some human pediatric or developmental cancers.

CONCLUSIONS

Down-regulation of lgl in imaginal discs is sufficient to enhance tracheogenesis and to promote invasion and colonization of other larval structures including the CNS. Developmental Dynamics 245:834-843, 2016. © 2016 Wiley Periodicals, Inc.

High MYC Levels Favour Multifocal Carcinogenesis

The term "field cancerisation" describes the formation of tissue sub-areas highly susceptible to multifocal tumourigenesis. In the earlier stages of cancer, cells may indeed display a series of molecular alterations that allow them to proliferate faster, eventually occupying discrete tissue regions with irrelevant morphological anomalies. This behaviour recalls cell competition, a process based on a reciprocal fitness comparison: when cells with a growth advantage arise in a tissue, they are able to commit wild-type neighbours to death and to proliferate at their expense. It is known that cells expressing high MYC levels behave as super-competitors, able to kill and replace less performant adjacent cells; given MYC upregulation in most human cancers, MYC-mediated cell competition is likely to pioneer field cancerisation. Here we show that MYC overexpression in a sub-territory of the larval wing epithelium of Drosophila is sufficient to trigger a number of cellular responses specific to mammalian pre-malignant tissues. Moreover, following induction of different second mutations, high MYC-expressing epithelia were found to be susceptible to multifocal growth, a hallmark of mammalian pre-cancerous fields. In summary, our study identified an early molecular alteration implicated in field cancerisation and established a genetically amenable model which may help study the molecular basis of early carcinogenesis.

Human Cancer Cells Signal Their Competitive Fitness Through MYC Activity

MYC-mediated cell competition is a cell-cell interaction mechanism known to play an evolutionary role during development from Drosophila to mammals. Cells expressing low levels of MYC, called losers, are committed to die by nearby cells with high MYC activity, called winners, that overproliferate to compensate for cell loss, so that the fittest cells be selected for organ formation. Given MYC's consolidated role in oncogenesis, cell competition is supposed to be relevant to cancer, but its significance in human malignant contexts is largely uncharacterised. Here we show stereotypical patterns of MYC-mediated cell competition in human cancers: MYC-upregulating cells and apoptotic cells were indeed repeatedly found at the tumour-stroma interface and within the tumour parenchyma. Cell death amount in the stromal compartment and MYC protein level in the tumour were highly correlated regardless of tumour type and stage. Moreover, we show that MYC modulation in heterotypic co-cultures of human cancer cells is sufficient as to subvert their competitive state, regardless of genetic heterogeneity. Altogether, our findings suggest that the innate role of MYC-mediated cell competition in development is conserved in human cancer, with malignant cells using MYC activity to colonise the organ at the expense of less performant neighbours.

Characterization of MicroRNA-200 pathway in ovarian cancer and serous intraepithelial carcinoma of fallopian tube

BACKGROUND

Ovarian cancer is the leading cause of death among gynecologic diseases in Western countries. We have previously identified a miR-200-E-cadherin axis that plays an important role in ovarian inclusion cyst formation and tumor invasion. The purpose of this study was to determine if the miR-200 pathway is involved in the early stages of ovarian cancer pathogenesis by studying the expression levels of the pathway components in a panel of clinical ovarian tissues, and fallopian tube tissues harboring serous tubal intraepithelial carcinomas (STICs), a suggested precursor lesion for high-grade serous tumors.

METHODS

RNA prepared from ovarian and fallopian tube epithelial and stromal fibroblasts was subjected to quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) to determine the expression of miR-200 families, target and effector genes and analyzed for clinical association. The effects of exogenous miR-200 on marker expression in normal cells were determined by qRT-PCR and fluorescence imaging after transfection of miR-200 precursors.

RESULTS

Ovarian epithelial tumor cells showed concurrent up-regulation of miR-200, down-regulation of the four target genes (ZEB1, ZEB2, TGFβ1 and TGFβ2), and up-regulation of effector genes that were negatively regulated by the target genes. STIC tumor cells showed a similar trend of expression patterns, although the effects did not reach significance because of small sample sizes. Transfection of synthetic miR-200 precursors into normal ovarian surface epithelial (OSE) and fallopian tube epithelial (FTE) cells confirmed reduced expression of the target genes and elevated levels of the effector genes CDH1, CRB3 and EpCAM in both normal OSE and FTE cells. However, only FTE cells had a specific induction of CA125 after miR-200 precursor transfection.

CONCLUSIONS

The activation of the miR-200 pathway may be an early event that renders the OSE and FTE cells more susceptible to oncogenic mutations and histologic differentiation. As high-grade serous ovarian carcinomas (HGSOC) usually express high levels of CA125, the induction of CA125 expression in FTE cells by miR-200 precursor transfection is consistent with the notion that HGSOC has an origin in the distal fallopian tube.

APT2 Inhibition Restores Scribble Localization and S-Palmitoylation in Snail-Transformed Cells

The multidomain scaffolding protein Scribble (Scrib) organizes key signaling complexes to specify basolateral cell polarity and suppress aberrant growth. In many human cancers, genetically normal Scrib mislocalizes from cell-cell junctions to the cytosol, correlating with enhanced growth signaling and malignancy. Here we confirm that expression of the epithelial-to-mesenchymal transcription factor (EMT-TF) Snail in benign epithelial cells leads to Scrib displacement from the plasma membrane, mimicking the mislocalization observed in aggressive cancers. Upon further examination, Snail promotes a transcriptional program that targets genes in the palmitoylation cycle, repressing many protein acyl transferases and elevating expression and activity of protein acyl thioesterase 2 (APT2). APT2 isoform-selective inhibition or knockdown rescued Scrib membrane localization and palmitoylation while attenuating MEK activation. Overall, inhibiting APT2 restores balance to the Scrib palmitoylation cycle, promoting membrane re-localization and growth attenuation. These findings emphasize the importance of S-palmitoylation as a post-translational gatekeeper of cell polarity-mediated tumor suppression.

Failure of the PTEN/aPKC/Lgl Axis Primes Formation of Adult Brain Tumours in Drosophila

Different regions in the mammalian adult brain contain immature precursors, reinforcing the concept that brain cancers, such as glioblastoma multiforme (GBM), may originate from cells endowed with stem-like properties. Alterations of the tumour suppressor gene PTEN are very common in primary GBMs. Very recently, PTEN loss was shown to undermine a specific molecular axis, whose failure is associated with the maintenance of the GBM stem cells in mammals. This axis is composed of PTEN, aPKC, and the polarity determinant Lethal giant larvae (Lgl): PTEN loss promotes aPKC activation through the PI3K pathway, which in turn leads to Lgl inhibition, ultimately preventing stem cell differentiation. To find the neural precursors responding to perturbations of this molecular axis, we targeted different neurogenic regions of the Drosophila brain. Here we show that PTEN mutation impacts aPKC and Lgl protein levels also in Drosophila. Moreover, we demonstrate that PI3K activation is not sufficient to trigger tumourigenesis, while aPKC promotes hyperplastic growth of the neuroepithelium and a noticeable expansion of the type II neuroblasts. Finally, we show that these neuroblasts form invasive tumours that persist and keep growing in the adult, leading the affected animals to untimely death, thus displaying frankly malignant behaviours.

Modeling Human Cancers in Drosophila

Cancer is a complex disease that affects multiple organs. Whole-body animal models provide important insights into oncology that can lead to clinical impact. Here, we review novel concepts that Drosophila studies have established for cancer biology, drug discovery, and patient therapy. Genetic studies using Drosophila have explored the roles of oncogenes and tumor-suppressor genes that when dysregulated promote cancer formation, making Drosophila a useful model to study multiple aspects of transformation. Not limited to mechanism analyses, Drosophila has recently been showing its value in facilitating drug development. Flies offer rapid, efficient platforms by which novel classes of drugs can be identified as candidate anticancer leads. Further, we discuss the use of Drosophila as a platform to develop therapies for individual patients by modeling the tumor's genetic complexity. Drosophila provides both a classical and a novel tool to identify new therapeutics, complementing other more traditional cancer tools.

Hugl-1 inhibits glioma cell growth in intracranial model

Drosophila lethal (2) giant larvae (lgl) has been reported as a tumor suppressor and could regulate the Drosophila hippo signaling. Human giant larvae-1(Hugl-1), one human homologue of Drosophila lgl, also has been reported to be involved in the development of some human cancers. However, whether Hugl-1 is associated with the pathogenesis of malignant gliomas remains poorly understood. In the present work, we examined the effect of Hugl-1 on glioma cell growth both in vitro and in vivo. Firstly, we found that Hugl-1 protein levels decreased in the human glioma tissues, suggesting that Hugl-1 is involved in glioma progression. Unfortunately, either stably or transiently over-expressing Hugl-1 did not affect glioma cell proliferation in vitro. In addition, Hugl-1 over-expression did not regulate hippo signaling pathway. Interestingly, over-expression of Hugl-1 not only inhibited gliomagenesis but also markedly inhibited cell proliferation and promoted the apoptosis of U251 cells in an orthotopic model of nude mice. Taken together, this study provides the evidence that Hugl-1 inhibits glioma cell growth in intracranial model of nude mice, suggesting that Hugl-1 might be a potential tumor target for glioma therapy.

Atypical protein kinase C induces cell transformation by disrupting Hippo/Yap signaling

Epithelial cells are major sites of malignant transformation. Atypical protein kinase C (aPKC) isoforms are overexpressed and activated in many cancer types. Using normal, highly polarized epithelial cells (MDCK and NMuMG), we report that aPKC gain of function overcomes contact inhibited growth and is sufficient for a transformed epithelial phenotype. In 2D cultures, aPKC induced cells to grow as stratified epithelia, whereas cells grew as solid spheres of nonpolarized cells in 3D culture. aPKC associated with Mst1/2, which uncoupled Mst1/2 from Lats1/2 and promoted nuclear accumulation of Yap1. Of importance, Yap1 was necessary for aPKC-mediated overgrowth but did not restore cell polarity defects, indicating that the two are separable events. In MDCK cells, Yap1 was sequestered to cell-cell junctions by Amot, and aPKC overexpression resulted in loss of Amot expression and a spindle-like cell phenotype. Reexpression of Amot was sufficient to restore an epithelial cobblestone appearance, Yap1 localization, and growth control. In contrast, the effect of aPKC on Hippo/Yap signaling and overgrowth in NMuMG cells was independent of Amot. Finally, increased expression of aPKC in human cancers strongly correlated with increased nuclear accumulation of Yap1, indicating that the effect of aPKC on transformed growth by deregulating Hippo/Yap1 signaling may be clinically relevant.

The tumor suppressor Lgl1 regulates front-rear polarity of migrating cells

Cell migration is a highly integrated, multistep process that plays an important role in physiological and pathological processes. The migrating cell is highly polarized, with complex regulatory pathways that integrate its component processes spatially and temporally. The Drosophila tumor suppressor, Lethal (2) giant larvae (Lgl), regulates apical-basal polarity in epithelia and asymmetric cell division. But little is known about the role of Lgl in establishing cell polarity in migrating cells. Recently, we showed that the mammalian Lgl1 interacts directly with non-muscle myosin IIA (NMIIA), inhibiting its ability to assemble into filaments in vitro. Lgl1 also regulates the cellular localization of NMIIA, the maturation of focal adhesions, and cell migration. We further showed that phosphorylation of Lgl1 by aPKCζ prevents its interaction with NMIIA and is important for Lgl1 and acto-NMII cytoskeleton cellular organization. Lgl is a critical downstream target of the Par6-aPKC cell polarity complex; we showed that Lgl1 forms two distinct complexes in vivo, Lgl1-NMIIA and Lgl1-Par6-aPKCζ in different cellular compartments. We further showed that aPKCζ and NMIIA compete to bind directly to Lgl1 through the same domain. These data provide new insights into the role of Lgl1, NMIIA, and Par6-aPKCζ in establishing front-rear polarity in migrating cells. In this commentary, I discuss the role of Lgl1 in the regulation of the acto-NMII cytoskeleton and its regulation by the Par6-aPKCζ polarity complex, and how Lgl1 activity may contribute to the establishment of front-rear polarity in migrating cells.

Atypical protein kinase C zeta: potential player in cell survival and cell migration of ovarian cancer

Ovarian cancer is one of the most aggressive gynaecological cancers, thus understanding the different biological pathways involved in ovarian cancer progression is important in identifying potential therapeutic targets for the disease. The aim of this study was to investigate the potential roles of Protein Kinase C Zeta (PRKCZ) in ovarian cancer. The atypical protein kinase C isoform, PRKCZ, is involved in the control of various signalling processes including cell proliferation, cell survival, and cell motility, all of which are important for cancer development and progression. Herein, we observe a significant increase in cell survival upon PRKCZ over-expression in SKOV3 ovarian cancer cells; additionally, when the cells are treated with small interference RNA (siRNA) targeting PRKCZ, the motility of SKOV3 cells decreased. Furthermore, we demonstrate that over-expression of PRKCZ results in gene and/or protein expression alterations of insulin-like growth factor 1 receptor (IGF1R) and integrin beta 3 (ITGB3) in SKOV3 and OVCAR3 cells. Collectively, our study describes PRKCZ as a potential regulatory component of the IGF1R and ITGB3 pathways and suggests that it may play critical roles in ovarian tumourigenesis.

Multiple strategies of oxygen supply in Drosophila malignancies identify tracheogenesis as a novel cancer hallmark

Angiogenesis is the term used to describe all the alterations in blood vessel growth induced by a tumour mass following hypoxic stress. The occurrence of multiple strategies of vessel recruitment favours drug resistance, greatly complicating the treatment of certain tumours. In Drosophila, oxygen is conveyed to the internal organs by the tracheal system, a closed tubular network whose role in cancer growth is so far unexplored. We found that, as observed in human cancers, Drosophila malignant cells suffer from oxygen shortage, release pro-tracheogenic factors, co-opt nearby vessels and get incorporated into the tracheal walls. We also found that the parallelisms observed in cellular behaviours are supported by genetic and molecular conservation. Finally, we identified a molecular circuitry associated with the differentiation of cancer cells into tracheal cells. In summary, our findings identify tracheogenesis as a novel cancer hallmark in Drosophila, further expanding the power of the fly model in cancer research.

Control of stem cell self-renewal and differentiation by the heterochronic genes and the cellular asymmetry machinery in Caenorhabditis elegans

Transitions between asymmetric (self-renewing) and symmetric (proliferative) cell divisions are robustly regulated in the context of normal development and tissue homeostasis. To genetically assess the regulation of these transitions, we used the postembryonic epithelial stem (seam) cell lineages of Caenorhabditis elegans. In these lineages, the timing of these transitions is regulated by the evolutionarily conserved heterochronic pathway, whereas cell division asymmetry is conferred by a pathway consisting of Wnt (Wingless) pathway components, including posterior pharynx defect (POP-1)/TCF, APC related/adenomatosis polyposis coli (APR-1)/APC, and LIT-1/NLK (loss of intestine/Nemo-like kinase). Here we explore the genetic regulatory mechanisms underlying stage-specific transitions between self-renewing and proliferative behavior in the seam cell lineages. We show that mutations of genes in the heterochronic developmental timing pathway, including lin-14 (lineage defect), lin-28, lin-46, and the lin-4 and let-7 (lethal defects)-family microRNAs, affect the activity of LIT-1/POP-1 cellular asymmetry machinery and APR-1 polarity during larval development. Surprisingly, heterochronic mutations that enhance LIT-1 activity in seam cells can simultaneously also enhance the opposing, POP-1 activity, suggesting a role in modulating the potency of the cellular polarizing activity of the LIT-1/POP-1 system as development proceeds. These findings illuminate how the evolutionarily conserved cellular asymmetry machinery can be coupled to microRNA-regulated developmental pathways for robust regulation of stem cell maintenance and proliferation during the course of development. Such genetic interactions between developmental timing regulators and cell polarity regulators could underlie transitions between asymmetric and symmetric stem cell fates in other systems and could be deregulated in the context of developmental disorders and cancer.

Deregulation of the cell polarity protein Lethal giant larvae 2 (Lgl2) correlates with gastric cancer progression

BACKGROUND

We investigated the roles of Lethal giant larvae 2 (Lgl2), an epithelial cell polarity protein, during gastric carcinogenesis and gastric cancer (GC) progression and evaluated the correlation of Lgl2 with epithelial-mesenchymal transition (EMT) markers.

METHODS

Lgl2 protein and mRNA expression were determined by immunohistochemistry and mRNA in situ hybridization in a large series of GC and preneoplastic lesions. Additionally, expression of 7 EMT markers was examined by immunohistochemistry.

RESULTS

Loss of membrane Lgl2 staining in GC was observed in 347 of 409 GCs. Lgl2 loss was associated with diffuse histological type (P < 0.001), advanced stage (P = 0.021), and worse prognosis (P = 0.047). Furthermore, Lgl2 loss correlated with reduced E-cadherin expression (P < 0.01) and increased expression of vimentin (P < 0.01). Combined analysis of Lgl2 and the EMT markers, S100A4 and MMP2, improved predictions of patient outcomes. During gastric carcinogenesis, membrane expression of Lgl2 was progressively lost in 4 % of normal mucosa, 75 % of intestinal metaplasia, 58 % of gastric dysplasia, 69 % of intestinal type GC, and 96 % of diffuse type GC.

CONCLUSIONS

Our results suggest that Lgl2 loss occurs at an early stage of gastric carcinogenesis and contributes to GC progression.

Drosophila Myc: A master regulator of cellular performance

The identification of the Drosophila homolog of the human MYC oncogene has fostered a series of studies aimed to address its functions in development and cancer biology. Due to its essential roles in many fundamental biological processes it is hard to imagine a molecular mechanism in which MYC function is not required. For this reason, the easily manipulated Drosophila system has greatly helped in the dissection of the genetic and molecular pathways that regulate and are regulated by MYC function. In this review, we focus on studies of MYC in the fruitfly with particular emphasis on metabolism and cell competition, highlighting the contributions of this model system in the last decade to our understanding of MYC's complex biological nature. This article is part of a Special Issue entitled: Myc proteins in cell biology and pathology.

Establishment of epithelial polarity--GEF who's minding the GAP?

Cell polarization is a fundamental process that underlies epithelial morphogenesis, cell motility, cell division and organogenesis. Loss of polarity predisposes tissues to developmental disorders and contributes to cancer progression. The formation and establishment of epithelial cell polarity is mediated by the cooperation of polarity protein complexes, namely the Crumbs, partitioning defective (Par) and Scribble complexes, with Rho family GTPases, including RhoA, Rac1 and Cdc42. The activation of different GTPases triggers distinct downstream signaling pathways to modulate protein-protein interactions and cytoskeletal remodeling. The spatio-temporal activation and inactivation of these small GTPases is tightly controlled by a complex interconnected network of different regulatory proteins, including guanine-nucleotide-exchange factors (GEFs), GTPase-activating proteins (GAPs), and guanine-nucleotide-dissociation inhibitors (GDIs). In this Commentary, we focus on current understanding on how polarity complexes interact with GEFs and GAPs to control the precise location and activation of Rho GTPases (Crumbs for RhoA, Par for Rac1, and Scribble for Cdc42) to promote apical-basal polarization in mammalian epithelial cells. The mutual exclusion of GTPase activities, especially that of RhoA and Rac1, which is well established, provides a mechanism through which polarity complexes that act through distinct Rho GTPases function as cellular rheostats to fine-tune specific downstream pathways to differentiate and preserve the apical and basolateral domains. This article is part of a Minifocus on Establishing polarity.

Rewiring cell polarity signaling in cancer

Disrupted cell polarity is a feature of epithelial cancers. The Crumbs, Par and Scribble polarity complexes function to specify and maintain apical and basolateral membrane domains, which are essential to organize intracellular signaling pathways that maintain epithelial homeostasis. Disruption of apical-basal polarity proteins facilitates rewiring of oncogene and tumor suppressor signaling pathways to deregulate proliferation, apoptosis, invasion and metastasis. Moreover, apical-basal polarity integrates intracellular signaling with the microenvironment by regulating metabolic signaling, extracellular matrix remodeling and tissue level organization. In this review, we discuss recent advances in our understanding of how polarity proteins regulate diverse signaling pathways throughout cancer progression from initiation to metastasis.

Hugl-1 induces apoptosis in esophageal carcinoma cells both in vitro and in vivo

AIM: To determine whether the human giant larvae homolog 1 gene (Hugl-1/Llg1/Lgl1) exerts tumor suppressor effects in esophageal cancer.

METHODS: We constructed a Hugl-1 expression plasmid, pEZ-M29-Hugl1, for gene transfection. We transfected the pEZ-M29-Hugl1 plasmid into Eca109 esophageal cancer cell lines with Lipofectamine 2000 to overexpress Hugl-1. Real-time reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting were performed to determine the effects of the plasmid on Hugl-1 expression. In vitro cell proliferation and apoptosis were examined separately by cell counting Kit-8 (CCK-8) assay, flow cytometry, and Western blotting before and after the transfection of the plasmid into Eca109 cells. Cell cycle distribution was assessed with flow cytometry. The effect of Hugl-1 overexpressing on tumor growth in vivo was performed with a xenograft tumor model in nude mice. Expression of Hugl-1 in xenograft tumor was analyzed by immunohistochemistry. The transferase-mediated dUTP nick end-labeling (TUNEL) technique was performed to detect and quantitate apoptotic cell.

RESULTS: The transfection efficiency was confirmed with real-time RT-PCR and Western blotting. Our results show that compared with control groups the mRNA levels and protein levels of Hugl-1 in pEZ-M29-Hugl1-treated group were remarkably increased (P < 0.05). The CCK-8 assay demonstrated that the growth of cells overexpressing Hugl-1 was significantly lower than control cells. Cell cycle distribution showed there was a G₀/G₁ cell cycle arrest in cells overexpressing Hugl-1 (64.09% ± 3.14% vs 50.32% ± 4.60%, 64.09% ± 3.14% vs 49.13% ± 2.24%). Annexin V-fluorescein isothiocyanate revealed that apoptosis was significantly increased in cells overexpressing Hugl-1 compared with control group (17.33% ± 4.76% vs 6.90% ± 1.61%, 17.33% ± 4.76% vs 6.27% ± 0.38%). Moreover, we found that Hugl-1 changes the level of the anti-apoptotic protein Bcl-2 and the pro-apoptotic protein Bax and the activation of both caspase-3 and caspase-9. With a TUNEL assay, we found that Hugl-1 markedly increased the apoptosis rate of Eca109 cells in vivo (60.50% ± 9.11% vs 25.00% ± 12.25%). It was shown that Hugl-1 represents a significantly more effective tumor suppressor gene alone in a xenograft tumor mouse model. This data suggest that Hugl-1 inhibited tumor growth and induced cell apoptosis in vivo.

CONCLUSION: These results suggest that Hugl-1 induces growth suppression and apoptosis in a human esophageal squamous cell carcinoma cell line both in vitro and in vivo.

Phosphorylation of serine 399 in LKB1 protein short form by protein kinase Cζ is required for its nucleocytoplasmic transport and consequent AMP-activated protein kinase (AMPK) activation

Two splice variants of LKB1 exist: LKB1 long form (LKB1(L)) and LKB1 short form (LKB1(S)). In a previous study, we demonstrated that phosphorylation of Ser-428/431 (in LKB1(L)) by protein kinase Cζ (PKCζ) was essential for LKB1-mediated activation of AMP-activated protein kinase (AMPK) in response to oxidants or metformin. Paradoxically, LKB1S also activates AMPK although it lacks Ser-428/431. Thus, we hypothesized that LKB1(S) contained additional phosphorylation sites important in AMPK activation. Truncation analysis and site-directed mutagenesis were used to identify putative PKCζ phosphorylation sites in LKB1(S). Substitution of Ser-399 to alanine did not alter the activity of LKB1(S), but abolished peroxynitrite- and metformin-induced activation of AMPK. Furthermore, the phosphomimetic mutation (S399D) increased the phosphorylation of AMPK and its downstream target phospho-acetyl-coenzyme A carboxylase (ACC). PKCζ-dependent phosphorylation of Ser-399 triggered nucleocytoplasmic translocation of LKB1(S) in response to metformin or peroxynitrite treatment. This effect was ablated by pharmacological and genetic inhibition of PKCζ, by inhibition of CRM1 activity and by substituting Ser-399 with alanine (S399A). Overexpression of PKCζ up-regulated metformin-mediated phosphorylation of both AMPK (Thr-172) and ACC (Ser-79), but the effect was ablated in the S399A mutant. We conclude that, similar to Ser-428/431 (in LKB1(L)), Ser-399 (in LKB1(S)) is a PKCζ-dependent phosphorylation site essential for nucleocytoplasmic export of LKB1(S) and consequent AMPK activation.

The Par complex and integrins direct asymmetric cell division in adult intestinal stem cells

The adult Drosophila midgut is maintained by intestinal stem cells (ISCs) that generate both self-renewing and differentiating daughter cells. How this asymmetry is generated is currently unclear. Here, we demonstrate that asymmetric ISC division is established by a unique combination of extracellular and intracellular polarity mechanisms. We show that Integrin-dependent adhesion to the basement membrane induces cell-intrinsic polarity and results in the asymmetric segregation of the Par proteins Par-3, Par-6, and aPKC into the apical daughter cell. Cell-specific knockdown and overexpression experiments suggest that increased activity of aPKC enhances Delta/Notch signaling in one of the two daughter cells to induce terminal differentiation. Perturbing this mechanism or altering the orientation of ISC division results in the formation of intestinal tumors. Our data indicate that mechanisms for intrinsically asymmetric cell division can be adapted to allow for the flexibility in lineage decisions that is required in adult stem cells.

Disruption of precise regulation of αPKC expression and cellular localization is associated with cervical cancer progression

PURPOSE

To understand the pathogenesis of cervical cancer (CC) associated with polarity protein αPKC and the potential roles of αPKC in clinical management of CC.

METHODS

Tissue samples were collected from women who received colposcopy biopsy or hysterectomy surgery, including 9 CIN1, 8 CIN2, 15 CIN3, and 12 invasive cervical squamous cancer (ICC). 16 normal controls were from the normal region of tumor samples, HE and immunofluorescence staining of αPKC were performed on these samples. ANOVA and Kruslal-wallis test were used to quantitate the abnormal distribution and expression level of αPKC among different cervical lesions.

RESULTS

Disruption of polarized apical localization and increased cytoplasmic accumulation of αPKC were identified in cervical lesions. In normal cervical epithelium, αPKC was detected on the apical membrane of endocervical columnar epithelial cells and of exocervical epithelial cells located at basal layer of squamous epithelium. While in squamous metaplasia, a precancerous lesion of cervical neoplasia, the polarized apical membrane localization of αPKC was disrupted, and intensed cytoplasmic accumulation was identified in the immature squamous metaplastic cells. Compared with normal cervix, number of epithelial cells with abnormal αPKC distribution was progressively increased in CINs and ICC (P < 0.05), and cytoplasmic accumulation of αPKC was increased in CIN2, CIN3, and ICC compared with CIN1 (P < 0.05).

CONCLUSIONS

Disruption of polarized apical localization and increased cytoplasmic accumulation of αPKC were associated with CC progression, indicating that precise regulation of αPKC may play important roles in CC progression, and αPKC may be a potential molecular target for clinical diagnoses and treatment of CC.

High expression of KIBRA in low atypical protein kinase C-expressing gastric cancer correlates with lymphatic invasion and poor prognosis

Overexpression of atypical protein kinase Cλ/ι (aPKCλ/ι), a regulator of cell polarity, is frequently associated with the poor prognoses of several cancers, including gastric cancer. Recent studies revealed a molecular link between aPKC and KIBRA, an upstream regulator of tumor suppressor Hippo pathway that regulates cell proliferation and apoptosis. Further, KIBRA directly inhibits the kinase activity of aPKC to regulate epithelial cell polarity. These observations suggest that the KIBRA-aPKC connection plays a role in cancer progression; however, clinical significance of the correlation between these factors remains unclear. Here we examined the correlation between KIBRA/aPKCλ/ι expression, as detected by immunohistochemistry, and clinicopathological outcomes in 164 gastric cancer patients using Fisher's exact test and Kaplan-Meier log-rank test. We found an intimate correlation between the expression level of KIBRA and aPKCλ/ι (P = 0.012). Furthermore, high expression of KIBRA is correlated with lymphatic (P = 0.046) and venous invasion (P = 0.039). The expression level of KIBRA by itself did not correlate with the prognosis; however, high expression of KIBRA in low aPKCλ/ι-expressing gastric cancer correlated with disease-specific (P = 0.037) and relapse-free survival (P = 0.041) by Kaplan-Meier with log-rank test and higher lymphatic invasion cases by Fisher's exact test (P = 0.042). Furthermore, overexpression of the aPKC-binding region of KIBRA disrupted tight junctions in epithelial cells. These results suggest that high expression of KIBRA in low aPKC-expressing cells causes massive loss of aPKC activity, leading to loss of polarity and invasiveness of gastric cancer cells.

The Scribble-Dlg-Lgl polarity module in development and cancer: from flies to man

The Scribble, Par and Crumbs modules were originally identified in the vinegar (fruit) fly, Drosophila melanogaster, as being critical regulators of apico-basal cell polarity. In the present chapter we focus on the Scribble polarity module, composed of Scribble, discs large and lethal giant larvae. Since the discovery of the role of the Scribble polarity module in apico-basal cell polarity, these proteins have also been recognized as having important roles in other forms of polarity, as well as regulation of the actin cytoskeleton, cell signalling and vesicular trafficking. In addition to these physiological roles, an important role for polarity proteins in cancer progression has also been uncovered, with loss of polarity and tissue architecture being strongly correlated with metastatic disease.

Epithelial cell polarity: what flies can teach us about cancer

Epithelial cells are polarized along their apical-basal axis. Much of the cellular machinery that goes into establishing and maintaining epithelial cell polarity is evolutionarily conserved. Model organisms, including the fruit fly, Drosophila melanogaster, are thus particularly useful for the study of cell polarity. Work in Drosophila has identified several important components of the polarity machinery and has also established the surprising existence of a secondary cell polarity pathway required only under conditions of energetic stress. This work has important implications for the understanding of human cancer. Most cancers are epithelial in origin, and the loss of cell polarity is a critical step towards malignancy. Thus a better understanding of how polarity is established and maintained in epithelial cells will help us to understand the process of malignant transformation and may lead to improved therapies. In the present chapter we discuss the current understanding of how epithelial cell polarity is regulated and the known associations between polarity factors and cancer.

Cytoplasmic Trop-1/Ep-CAM overexpression is associated with a favorable outcome in node-positive breast cancer

OBJECTIVE

Trop-1/Ep-CAM modulates growth and survival of transformed cells, and it is highly expressed in most carcinomas including breast cancer. Only membranous staining is typically considered in evaluating Trop-1/epithelial cell adhesion molecule (Ep-CAM) expression in tumor cells. However, there is evidence of retention of Trop-1/Ep-CAM, as functionally incompetent molecules, in intra-cytoplasmic vesicles. Hence, we investigated whether cytoplasmic immunostaining may have an independent clinical significance with respect to membranous staining.

METHODS

Membranous and cytoplasmic Trop-1/Ep-CAM expression was immunohistochemically investigated in 642 unilateral breast cancers from patients with a 99-month median follow-up. Multiple correspondence analysis was used to investigate the association between Trop-1/Ep-CAM and other biological variables. The impact of Trop-1/Ep-CAM expression on the patient's outcome was evaluated as event-free survival by the Kaplan-Meier method and proportional hazard Cox model.

RESULTS

While tumors with intermediate/strong membranous staining were mostly associated with concomitant cytoplasmic Trop-1/Ep-CAM expression (97%), tumors with weak-to-nil membranous staining showed intermediate/high cytoplasmic expression in 23% of cases. Cytoplasmic overexpression was associated with a favorable outcome, especially in node-positive patients, regardless of the adjuvant therapy received.

CONCLUSION

Trop-1/Ep-CAM expression may have different clinical implications according to its subcellular localization.

Tumor type-dependent function of the par3 polarity protein in skin tumorigenesis

Cell polarization is crucial during development and tissue homeostasis and is regulated by conserved proteins of the Scribble, Crumbs, and Par complexes. In mouse skin tumorigenesis, Par3 deficiency results in reduced papilloma formation and growth. Par3 mediates its tumor-promoting activity through regulation of growth and survival, since Par3 deletion increases apoptosis and reduces growth in vivo and in vitro. In contrast, Par3-deficient mice are predisposed to formation of keratoacanthomas, cutaneous tumors thought to originate from different cellular origin and frequently observed in humans. Par3 expression is reduced in both mouse and human keratoacanthomas, indicating tumor-suppressive properties of Par3. Our results identify a dual function of Par3 in skin cancer, with both pro-oncogenic and tumor-suppressive activity depending on the tumor type.

The human Lgl polarity gene, Hugl-2, induces MET and suppresses Snail tumorigenesis

Lethal giant larvae proteins have key roles in regulating polarity in a variety of cell types and function as tumour suppressors. A transcriptional programme initiated by aberrant Snail expression transforms epithelial cells to potentially aggressive cancer cells. Although progress in defining the molecular determinants of this programme has been made, we have little knowledge as to how the Snail-induced phenotype can be suppressed. In our studies we identified the human lethal giant larvae homologue 2, Hugl-2, (Llgl2/Lgl2) polarity gene as downregulated by Snail. Snail binds E-boxes in the Hugl-2 promoter and represses Hugl-2 expression, whereas removal of the E-boxes releases Hugl-2 from Snail repression. We demonstrate that inducing Hugl-2 in cells with constitutive Snail expression reverses the phenotype including changes in morphology, motility, tumour growth and dissemination in vivo, and expression of epithelial markers. Hugl-2 expression reduced the nuclear localization of Snail and thus binding of Snail to its target promoters. Our results placing Hugl-2 within the Snail network as well as its ability to suppress Snail carcinogenesis identifies Hugl-2 as a target molecule driving cascades, which may have preventative and therapeutic promise to minimize cancer progression.

Cell polarity proteins and cancer

Cell polarity is essential in many biological processes and required for development as well as maintenance of tissue integrity. Loss of polarity is considered both a hallmark and precondition for human cancer. Three conserved polarity protein complexes regulate different modes of polarity that are conserved throughout numerous cell types and species. These complexes are the Crumbs, Par and Scribble complex. Given the importance of cell polarity for normal tissue homeostasis, aberrant polarity signaling is suggested to contribute to the multistep processes of human cancer. Most human cancers are formed from epithelial cells. Evidence confirming the roles for polarity proteins in different phases of the oncogenic trajectory comes from functional studies using mammalian cells as well as Drosophila and zebrafish models. Furthermore, several reports have revealed aberrant expression and localization of polarity proteins in different human tumors. In this review we will give an overview on the current data available that couple polarity signaling to tumorigenesis, particularly in epithelial cells.

Drosophila cancer models

Cancer is driven by complex genetic and cellular mechanisms. Recently, the Drosophila community has become increasingly interested in exploring cancer issues. The Drosophila field has made seminal contributions to many of the mechanisms that are fundamental to the cancer process; several of these mechanisms have already been validated in vertebrates. Less well known are the Drosophila field's early direct contributions to the cancer field: some of the earliest tumor suppressors were identified in flies. In this review, we identify major contributions that Drosophila studies have made toward dissecting the pathways and mechanisms underlying tumor progression. We also highlight areas, such as drug discovery, where we expect Drosophila studies to make a major scientific impact in the future.

Drosophila lethal giant larvae neoplastic mutant as a genetic tool for cancer modeling

Drosophila lethal giant larvae (lgl) is a tumour suppressor gene whose function in establishing apical-basal cell polarity as well as in exerting proliferation control in epithelial tissues is conserved between flies and mammals. Individuals bearing lgl null mutations show a gradual loss of tissue architecture and an extended larval life in which cell proliferation never ceases and no differentiation occurs, resulting in prepupal lethality. When tissues from those individuals are transplanted into adult normal recipients, a subset of cells, possibly the cancer stem units, are again able to proliferate and give rise to metastases which migrate to distant sites killing the host. This phenotype closely resembles that of mammalian epithelial cancers, in which loss of cell polarity is one of the hallmarks of a malignant, metastatic behaviour associated with poor prognosis. Lgl protein shares with its human counterpart Human giant larvae-1 (Hugl-1) significant stretches of sequence similarity that we demonstrated to translate into a complete functional conservation, pointing out a role in cell proliferation control and tumorigenesis also for the human homologue. The functional conservation and the power of fly genetics, that allows the researcher to manipulate the fly genome at a level of precision that exceeds that of any other multicellular genetic system, make this Drosophila mutant a very suitable model in which to investigate the mechanisms underlying epithelial tumour formation, progression and metastatisation. In this review, we will summarise the results obtained in these later years using this model for the study of cancer biology. Moreover, we will discuss how recent advances in developmental genetics techniques have succeeded in enhancing the similarities between fly and human tumorigenesis, giving Drosophila a pivotal role in the study of such a complex genetic disease.

Mammalian Llgl2 is necessary for proper branching morphogenesis during placental development

Cell polarity plays a critical role in the development of all metazoans; however, the mechanisms of cell polarity and the specific role of cell polarity pathways in mammalian organisms are still poorly understood. Lethal giant larvae (Lgl) is an apical-basal polarity gene identified in Drosophila, where it functions as a tumor suppressor controlling self-renewal and differentiation of progenitor cells. There are two orthologs of Lgl in mammalian genomes: Llgl1 and Llgl2. While mammalian Lgls are assumed to be tumor suppressor genes, little is known about their function in vivo. Here we report the functional analysis of murine Llgl2. We generated Llgl2(-/-) mice and found that Llgl2 functions as a polarity protein required for proper branching morphogenesis during placental development. Llgl2(-/-) pups are born as runts but quickly catch up in size and grow into normal-size adults. Surprisingly, no prominent phenotypes or spontaneous tumors were observed in adult Llgl2(-/-) mice. Analyses of placental trophoblasts reveal a critical role for Llgl2 in cell polarization and polarized cell invasion. We conclude that mammalian Llgl2 is required for proper polarized invasion of trophoblasts and efficient branching morphogenesis during placental development, but, unlike its Drosophila ortholog, it does not function as a canonical tumor suppressor gene.

The Hippo pathway and apico–basal cell polarity

The establishment and maintenance of apico–basal cell polarity is a pre-requisite for the formation of a functioning epithelial tissue. Many lines of evidence suggest that cell polarity perturbations favour cancer formation, even though the mechanistic basis for this link remains unclear. Studies in Drosophila have uncovered complex interactions between the conserved Hpo (Hippo) tumour suppressor pathway and apico–basal polarity determinants. The Hpo pathway is a crucial growth regulatory network whose inactivation in Drosophila epithelial tissues induces massive overproliferation. Its core consists of a phosphorylation cascade (comprising the kinases Hpo and Warts) that mediates the inactivation of the pro-growth transcriptional co-activator Yki [Yorkie; YAP (Yes-associated protein) in mammals]. Several apically located proteins, such as Merlin, Expanded or Kibra, have been identified as upstream regulators of the Hpo pathway, leading to the notion that an apical multi-molecular complex modulates core kinase activity and promotes Yki/YAP inactivation. In the present review, we explore the links between apico–basal polarity and Hpo signalling. We focus on the regulation of Yki/YAP by apical proteins, but also on how the Hpo pathway might in turn influence apical domain size as part of a regulatory feedback loop.

Aberrant overexpression of the cell polarity module scribble in human cancer

Human Scribble (Scrib) is an evolutionary-conserved cell polarity protein, but its potential role in human cancer is controversial. Herein, we show that Scrib is nearly universally overexpressed in cultured tumor cell lines and genetically disparate cancer patient series compared with matched normal tissues in vivo. Instead of a membrane association seen in normal epithelia, tumor-associated Scrib is mislocalized and found predominantly in the cytosol. Small-interfering RNA silencing of Scrib in model lung adenocarcinoma A549 cells inhibited cell migration in wound-healing assays, suppressed tumor cell invasion across Matrigel-coated inserts, and down-regulated the expression of cell motility markers and mediators of epithelial-mesenchymal transition. These data uncover a previously unrecognized exploitation of Scrib for aberrant tumor cell motility and invasion, thus potentially contributing to disease progression in humans.

Protein complexes that control renal epithelial polarity

Establishment of epithelial apicobasal polarity is crucial for proper kidney development and function. In recent years, there have been important advances in our understanding of the factors that mediate the initiation of apicobasal polarization. Key among these are the polarity complexes that are evolutionarily conserved from simple organisms to humans. Three of these complexes are discussed in this review: the Crumbs complex, the Par complex, and the Scribble complex. The apical Crumbs complex consists of three proteins, Crumbs, PALS1, and PATJ, whereas the apical Par complex consists of Par-3, Par-6, and atypical protein kinase C. The lateral Scribble complex consists of Scribble, discs large, and lethal giant larvae. These complexes modulate kinase and small G protein activity such that the apical and basolateral complexes signal antagonistically, leading to the segregation of the apical and basolateral membranes. The polarity complexes also serve as scaffolds to direct and retain proteins at the apical membrane, the basolateral membrane, or the intervening tight junction. There is plasticity in apicobasal polarity, and this is best seen in the processes of epithelial-to-mesenchymal transition and the converse mesenchymal-to-epithelial transition. These transitions are important in kidney disease as well as kidney development, and modulation of the polarity complexes are critical for these transitions.

Faulty epithelial polarity genes and cancer

Epithelial architecture is formed in tissues and organs when groups of epithelial cells are organized into polarized structures. The epithelial function and integrity as well as signaling across the epithelial layer is orchestrated by apical junctional complexes (AJCs), which are landmarks for PAR/CRUMBS and lateral SCRIB polarity modules and by dynamic interactions of the cells with underlying basement membrane (BM). These highly organized epithelial architectures are demolished in cancer. In all advanced epithelial cancers, malignant cells have lost polarity and connections to the basement membrane and they have become proliferative, motile, and invasive. Clearly, loss of epithelial integrity associates with tumor progression but does it contribute to tumor development? Evidence from studies in Drosophila and recently also in vertebrate models have suggested that even the oncogene-driven enforced cell proliferation can be conditional, dependant on the influence of cell-cell or cell-microenvironment contacts. Therefore, loss of epithelial integrity may not only be an obligate consequence of unscheduled proliferation of malignant cells but instead, malignant epithelial cells may need to acquire capacity to break free from the constraints of integrity to freely and autonomously proliferate. We discuss how epithelial polarity complexes form and regulate epithelial integrity, highlighting the roles of enzymes Rho GTPases, aPKCs, PI3K, and type II transmembrane serine proteases (TTSPs). We also discuss relevance of these pathways to cancer in light of genetic alterations found in human cancers and review molecular pathways and potential pharmacological strategies to revert or selectively eradicate disorganized tumor epithelium.