Apicobasal Polarity Research Articles

Drosophila Models of Cell Polarity and Cell Competition in Tumourigenesis.

Cell competition is an important surveillance mechanism that measures relative fitness between cells in a tissue during development, homeostasis, and disease. Specifically, cells that are "less fit" (losers) are actively eliminated by relatively "more fit" (winners) neighbours, despite the less fit cells otherwise being able to survive in a genetically uniform tissue. Originally described in the epithelial tissues of Drosophila larval imaginal discs, cell competition has since been shown to occur in other epithelial and non-epithelial Drosophila tissues, as well as in mammalian model systems. Many genes and signalling pathways have been identified as playing conserved roles in the mechanisms of cell competition. Among them are genes required for the establishment and maintenance of apico-basal cell polarity: the Crumbs/Stardust/Patj (Crb/Sdt/Patj), Bazooka/Par-6/atypical Protein Kinase C (Baz/Par-6/aPKC), and Scribbled/Discs large 1/Lethal (2) giant larvae (Scrib/Dlg1/L(2)gl) modules. In this chapter, we describe the concepts and mechanisms of cell competition, with emphasis on the relationship between cell polarity proteins and cell competition, particularly the Scrib/Dlg1/L(2)gl module, since this is the best described module in this emerging field.

Mesenchymal-epithelial transition in development and reprogramming.

During organogenesis, epithelial cells can give rise to mesenchymal cells through epithelial-mesenchymal transition. The reverse process, mesenchymal-epithelial transition (MET), can similarly generate epithelial cells. Transitions between epithelial and mesenchymal states are also critical for the induction of pluripotent stem cells from somatic cells. This Review discusses the relatively less characterized process of MET, focusing on the genesis of apicobasal cell polarity and exploring the roles of MET in development and reprogramming.

Functional Assessment of Patient-Derived Retinal Pigment Epithelial Cells Edited by CRISPR/Cas9.

Retinitis pigmentosa is the most common form of inherited blindness and can be caused by a multitude of different genetic mutations that lead to similar phenotypes. Specifically, mutations in ubiquitously expressed splicing factor proteins are known to cause an autosomal dominant form of the disease, but the retina-specific pathology of these mutations is not well understood. Fibroblasts from a patient with splicing factor retinitis pigmentosa caused by a missense mutation in the PRPF8 splicing factor were used to produce three diseased and three CRISPR/Cas9-corrected induced pluripotent stem cell (iPSC) clones. We differentiated each of these clones into retinal pigment epithelial (RPE) cells via directed differentiation and analyzed the RPE cells in terms of gene and protein expression, apicobasal polarity, and phagocytic ability. We demonstrate that RPE cells can be produced from patient-derived and corrected cells and they exhibit morphology and functionality similar but not identical to wild-type RPE cells in vitro. Functionally, the RPE cells were able to establish apicobasal polarity and phagocytose photoreceptor outer segments at the same capacity as wild-type cells. These data suggest that patient-derived iPSCs, both diseased and corrected, are able to differentiate into RPE cells with a near normal phenotype and without differences in phagocytosis, a result that differs from previous mouse models. These RPE cells can now be studied to establish a disease-in-a-dish system relevant to retinitis pigmentosa.

FGFR1 regulates trophectoderm development and facilitates blastocyst implantation

FGF signaling plays important roles in many aspects of mammalian development. Fgfr1-/- and Fgfr1-/-Fgfr2-/- mouse embryos on a 129S4 co-isogenic background fail to survive past the peri-implantation stage, whereas Fgfr2-/- embryos die at midgestation and show defects in limb and placental development. To investigate the basis for the Fgfr1-/- and Fgfr1-/-Fgfr2-/- peri-implantation lethality, we examined the role of FGFR1 and FGFR2 in trophectoderm (TE) development. In vivo, Fgfr1-/- TE cells failed to downregulate CDX2 in the mural compartment and exhibited abnormal apicobasal E-Cadherin polarity. In vitro, we were able to derive mutant trophoblast stem cells (TSCs) from Fgfr1-/- or Fgfr2-/- single mutant, but not from Fgfr1-/-Fgfr2-/- double mutant blastocysts. Fgfr1-/- TSCs however failed to efficiently upregulate TE differentiation markers upon differentiation. These results suggest that while the TE is specified in Fgfr1-/- mutants, its differentiation abilities are compromised leading to defects at implantation.

Cell competition: Emerging mechanisms to eliminate neighbors.

Cell competition is a context-dependent cell elimination through short-range cell-cell interaction, in which cells with higher fitness eliminate neighboring less-fit or oncogenic cells within the growing tissue. Cell competition can be triggered by many different factors such as heterozygous mutations in the ribosomal protein genes (which are called "Minute" mutations), elevated Myc, Yorkie/YAP, Wg/Wnt, JAK-STAT, Ras, or Src activity, and loss of Mahjong/VprBP, endocytic pathway components, or apicobasal cell polarity. Studies on the mechanisms and roles of cell competition have suggested that cell competition can be divided into two types: selection of fitter cells or elimination of oncogenic cells. The former type of cell competition includes Minute or Myc-induced cell competition that is considered to be dependent on the relative level of protein synthesis. The later type of cell competition includes tumor-suppressive cell competition triggered by loss of cell polarity genes such as scribble (scrib) or discs large (dlg). Genetic studies in Drosophila during the past decade have provided significant progress in understanding the mechanisms of these phenomena. At the same time, these studies have now raised new questions; how do different mechanisms contribute or cooperate to drive cell competition, do common mechanisms exist in different types of cell competition, and what are the physiological roles of these cell competition phenomena?

Src-transformed cells hijack mitosis to extrude from the epithelium

At the initial stage of carcinogenesis single mutated cells appear within an epithelium. Mammalian in vitro experiments show that potentially cancerous cells undergo live apical extrusion from normal monolayers. However, the mechanism underlying this process in vivo remains poorly understood. Mosaic expression of the oncogene vSrc in a simple epithelium of the early zebrafish embryo results in extrusion of transformed cells. Here we find that during extrusion components of the cytokinetic ring are recruited to adherens junctions of transformed cells, forming a misoriented pseudo-cytokinetic ring. As the ring constricts, it separates the basal from the apical part of the cell releasing both from the epithelium. This process requires cell cycle progression and occurs immediately after vSrc-transformed cell enters mitosis. To achieve extrusion, vSrc coordinates cell cycle progression, junctional integrity, cell survival and apicobasal polarity. Without vSrc, modulating these cellular processes reconstitutes vSrc-like extrusion, confirming their sufficiency for this process.

A Tuba/Cdc42/Par6A complex is required to ensure singularity in apical domain formation during enterocyte polarization.

Apico-basal polarity establishment is a seminal process in tissue morphogenesis. To function properly it is often imperative that epithelial cells limit apical membrane formation to a single domain. We previously demonstrated that signaling by the small GTPase Cdc42, together with its guanine nucleotide exchange factor (GEF) Tuba, is required to prevent the formation of multiple apical domains in polarized Ls174T:W4 cells, a single cell model for enterocyte polarization. To further chart the molecular signaling mechanisms that safeguard singularity during enterocyte polarization we generated knockout cells for the Cdc42 effector protein Par6A. Par6A loss results in the formation of multiple apical domains, similar to loss of Cdc42. In Par6A knockout cells, we find that active Cdc42 is more mobile at the apical membrane compared to control cells and that wild type Cdc42 is more diffusely localized throughout the cell, indicating that Par6A is required to restrict Cdc42 signaling. Par6A, Cdc42 and its GEF Tuba bind in a co-immunoprecipitation experiment and they partially colocalize at the apical membrane in polarized Ls174T:W4 cells, suggesting the formation of a trimeric complex. Indeed, in a rescue experiment using Par6A mutants, we show that the ability to establish this trimeric complex correlates with the ability to restore singularity in Par6A knockout cells. Together, these experiments therefore indicate that a Tuba/Cdc42/Par6A complex is required to ensure the formation of a single apical domain during enterocyte polarization.

Epithelial cells release adenosine to promote local TNF production in response to polarity disruption

Disruption of epithelial integrity contributes to chronic inflammatory disorders through persistent activation of stress signalling. Here we uncover a mechanism whereby disruption of apico-basal polarity promotes stress signalling. We show that depletion of Scribbled (Scrib), a baso-lateral determinant, causes epithelial cells to release adenosine through equilibrative channels into the extracellular space. Autocrine activation of the adenosine receptor leads to transcriptional upregulation of TNF, which in turn boosts the activity of JNK signalling. Thus, disruption of cell polarity feeds into a well-established stress pathway through the intermediary of an adenosine signalling branch. Although this regulatory input could help ensuring an effective response to acute polarity stress, we suggest that it becomes deleterious in situations of low-grade chronic disruption by provoking a private inflammatory-like TNF-driven response within the polarity-deficient epithelium.

RHOA activity in expanding blastocysts is essential to regulate HIPPO-YAP signaling and to maintain the trophectoderm-specific gene expression program in a ROCK/actin filament-independent manner.

What molecular signals are required to maintain the functional trophectoderm (TE) during blastocyst expansion of the late stage of preimplantation development? The activity of ras homology family member A (RHOA) GTPases is necessary to retain the expanded blastocyst cavity and also to sustain the gene expression program specific to TE. At the early stages of preimplantation development, the precursor of the TE lineage is generated through the molecular signals that integrate RHOA, RHO-associated coiled-coil containing protein kinase (ROCK), the apicobasal cell polarity, and the HIPPO-Yes-associated protein (YAP) signaling pathway. By contrast, molecular mechanisms regulating the maintenance of the TE characteristics at the later stage, which is crucial for blastocyst hatching and implantation, are scarcely understood. Expanding mouse blastocysts, obtained from crosses of the F1 (C57BL6 × DBA/2) strain, were exposed to chemical agents that interfere with RHOA, ROCK, or the actin cytoskeleton for up to 8 h, and effects on the blastocyst cavity, HIPPO-YAP signaling, and cell lineage-specific gene expression profiles were examined. Mouse embryos at the embryonic stage E3.5 (expanding blastocysts) and E4.5 (fully expanded blastocysts) were treated with RHOA inhibitor (C3 exoenzyme), ROCK inhibitor (Y27632), or actin filament disruptors (cytochalasin B and latrunculin A). The integrity of the blastocyst cavity was evaluated based on the gross morphology. Effects on HIPPO-YAP signaling were assessed based on the presence of nuclearized YAP protein by immunofluorescence staining and the expression of YAP/TEA domain family member (TEAD) target genes by quantitative RT-PCR (qRT-PCR). The impact of these disruptors on cell lineages was evaluated based on expression of the TE-specific and inner cell mass-specific marker genes by qRT-PCR. The integrity of the apicobasal cell polarity was assessed by localization of protein kinase C zeta (PRKCZ; apical) and scribbled planar cell polarity (SCRIB; basal) proteins by immunofluorescence staining. For comparisons, cultured cell lines, NIH/3T3 (mouse fibroblast) and P19C5 (mouse embryonal carcinoma), were also treated with RHOA inhibitor, ROCK inhibitor, and actin filament disruptors for up to 8 h, and effects on HIPPO-YAP signaling were assessed based on expression of YAP/TEAD target genes by qRT-PCR. Each experiment was repeated using three independent batches of embryos (n = 40-80 per batch) or cell collections. Statistical analyses of data were performed, using one-way ANOVA and two-sample t-test. Inhibition of RHOA deflated the cavity, diminished nuclear YAP (P < 0.01), and down-regulated the YAP/TEAD target and TE-specific marker genes in both E3.5 and E4.5 blastocysts (P < 0.05), indicating that the maintenance of the key TE characteristics is dependent on RHOA activity. However, inhibition of ROCK or disruption of actin filament only deflated the blastocyst cavity, but did not alter HIPPO-YAP signaling or lineage-specific gene expressions, suggesting that the action of RHOA to sustain the TE-specific gene expression program is not mediated by ROCK or the actomyosin cytoskeleton. By contrast, ROCK inhibitor and actin filament disruptors diminished YAP/TEAD target gene expressions in cultured cells to a greater extent than RHOA inhibitor, implicating that the regulation of HIPPO-YAP signaling in expanding blastocysts is distinctly different from that in the cell lines. Furthermore, the apicobasal cell polarity proteins in the expanding blastocyst were mislocalized by ROCK inhibition but not by RHOA inhibition, indicating that cell polarity is not linked to regulation of HIPPO-YAP signaling. Taken together, our study suggests that RHOA activity is essential to maintain the TE lineage in the expanding blastocyst and it regulates HIPPO-YAP signaling and the lineage-specific gene expression program through mechanisms that are independent of ROCK or actomyosin cytoskeleton. Not applicable. This study was conducted using one species, the mouse. Direct translation of the experiments and findings to human fertility preservation and ART requires further investigations. The elucidation of the mechanisms of TE formation is highly pertinent to fertility preservation in women. Our findings may raise awareness among providers of ART that the TE is sensitive to disturbance even in the late stage of blastocyst expansion and that rational approaches should be devised to avoid conditions that may impair the TE and its function. This study was funded by grants from the Ingeborg v.F. McKee Fund of the Hawaii Community Foundation (16ADVC-78882 to V.B.A.), and the National Institutes of Health (P20 GM103457 and R03 HD088839 to V.B.A.). The authors have no conflict of interest to declare.

Abstract B57: Microtubule dynamics regulates mammary gland morphogenesis and tumorigenesis via stathmin

Abstract Microtubule (MT) dynamics is essential to provide a correct apico-basal polarization of epithelial cells, by regulating the movement of vesicles and proteins within the cell and by ensuring a correct orientation of the mitotic spindle during cell division. The dynamics of MT is governed by the activity of MT-stabilizing and destabilizing proteins, generally known as MT-acting proteins. Little is known about the role of the MT-dynamics and of MT-acting proteins during development of the mammary gland, a dynamic organ that displays a complex and finely organized apico-basal architecture. Stathmin, a MT-destabilizing protein, is often overexpressed in breast cancer (BC). By studying knockout (STM KO) mice we observed that STM KO females were unable to nurse their offspring. This phenotype was accompanied by defective development of the mammary gland, particularly evident during pregnancy and postpartum phases. Our results showed that stathmin absence mainly impinged on two key features of the mammary epithelial organization, polarity and proliferation. In vitro, normal mammary epithelial cells silenced for stathmin were not able to form organized acini in 3D-matrices. In vivo, when stathmin was KO, many molecules involved in mammary gland functions were not properly localized, indicating a disruption of the apico-basal polarity. Furthermore, loss of stathmin strongly decreased proliferation and induced disoriented positioning of the mitotic spindle in dividing epithelial cells of the developing alveolus, preventing the correct orientation of the daughter cells. Loss of polarity and deregulated proliferation are tightly linked to tumorigenesis. We therefore decided to examine the role of stathmin also in the context of HER2-driven tumorigenesis. To this end, we used a transgenic mouse model expressing a constitutively active form of HER2 (Δ16HER2), which is an alternatively spliced, very aggressive form of HER2, and intercrossed them with STM WT and KO mice. We analyzed the role of stathmin in both early and late stages of tumorigenesis. STM KO mice displayed a significantly reduced number of preneoplastic foci and this phenotype was maintained also in late stages of tumorigenesis. In WT mice, preneoplastic lesions expressed high level of stathmin compared with normal tissue, supporting the idea that stathmin played an active role in tumor initiation. Analysis of proliferation in tumors revealed that loss of stathmin strongly decreased the mitotic rate of Δ16HER2-transformed cells. Furthermore, by syngeneic injection of tumor cells in recipient mice of the two different genotypes, we could assess that stathmin plays a cell-autonomous function in tumor initiation. Our study has shed new light on the field of mammary gland development and of breast cancer biology. Collectively, our data indicate that loss of stathmin by altering the dynamics of microtubules causes a profound disorganization of the normal mammary gland architecture and a delay in initiation of the tumorigenic process. We have uncovered new functions of stathmin that could have important implications in BC, also considering that several microtubule-acting drugs are currently employed in the therapy of BC patients. Citation Format: Ilenia Segatto, Mara De Marco Zompit, Gian Luca Rampioni Vinciguerra, Giorgia Mungo, Sara D’Andrea, Tiziana Perin, Gustavo Baldassarre, Barbara Belletti. Microtubule dynamics regulates mammary gland morphogenesis and tumorigenesis via stathmin [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr B57.

Nephron-specific knockin of the PIKfyve-binding-deficient Vac14L156R mutant results in albuminuria and mesangial expansion.

Intracellular trafficking processes play a key role for the establishment and maintenance of membrane surfaces in renal epithelia. Therefore, dysfunctions of these trafficking processes could be key events and important determinants in the onset and progression of diseases. The presence of cellular vacuoles-observed in many histologic analyses of renal diseases-is a macroscopic hint for disturbed intracellular trafficking processes. However, how vacuoles develop and which intracellular pathways are directly affected remain largely unknown. Previous studies showed that in some cases, vacuolization is linked to malfunction of the Vac14 complex. This complex, including the scaffold protein Vac14, the lipid kinase PIKfyve, and its counteracting lipid phosphatase Fig4, regulates intracellular phosphatidylinositol phosphate levels, which in turn, control the maturation of early-into-late endosomes, as well as the processing of autophagosomes into autophagolysosomes. Here, we analyzed the role of Vac14 in mice and observed that the nephron-specific knockin of the PIKfyve-binding-deficient Vac14L156R mutant led to albuminuria, accompanied by mesangial expansion, increased glomerular size, and an elevated expression of several kidney injury markers. Overexpression of this Vac14 variant in podocytes did not reveal a strong in vivo phenotype, indicating that Vac14-dependent trafficking processes are more important for tubular than for glomerular processes in the kidney. In vitro overexpression of Vac14L156R in Madin-Darby canine kidney cells had no impact on apico-basal polarity defects but resulted in a faster reassembly of junctional structures after Ca2+ depletion and delayed endo- and transcytosis rates. Taken together, our data suggest that increased albuminuria of Vac14L156R-overexpressing mice is a consequence of a lowered endo- and transcytosis of albumin in renal tubules.

Polarity and morphogenesis of the eye epithelium requires the adhesion junction associated adaptor protein Traf4

ABSTRACTDuring development, neuroepithelial progenitors acquire apico-basal polarity and adhere to one another via apically located tight and adherens junction complexes. This polarized neuroepithelium must continue to integrate cells arising through cell divisions and intercalation, and allow for cell movements, at the same time as undergoing morphogenesis. Cell proliferation, migration and intercalation all occur in the morphing embryonic eye. To understand how eye development might depend on dynamic epithelial adhesion, we investigated the function of a known regulator of junctional plasticity, Tumour necrosis factor receptor-associated factor 4 (Traf4). traf4a mRNA is expressed in the developing eye vesicle over the period of optic cup morphogenesis, and Traf4a loss leads to disrupted evagination and elongation of the eye vesicles, and aberrant organization and apico-basal polarity of the eye epithelium. We propose a model whereby Traf4a regulates apical junction plasticity in nascent eye epithelium, allowing for its polarization and morphogenesis.Symbols and Abbreviations: AB: apico-basal; aPKC: atypical protein kinase-C; CRISPR: clustered regularly-interspaced short palindromic repeats; GFP: green fluorescent protein; hpf: hours post-fertilization; MO: antisense morpholino oligonucleotide; pHH3: phospho histone H3; ss: somite stage; Traf4: Tumour necrosis factor receptor-associated factor 4; ZO-1: zona occludens-1

The regulation of junctional actin dynamics by cell adhesion receptors.

The formation of cell-cell junctions and the development of stable cell-cell adhesion require the association of actin filaments with the sites of cell-cell adhesion. From the initial formation of cell-cell junctions, which appear as punctate, spot-like junctions, to the formation of a stable actin belt that runs adjacent to cell-cell junctions, the actin cytoskeleton is closely associated with the adhesion apparatus. Importantly, the junctional actin is highly dynamic, even after the maturation of intercellular junctions and the development of apico-basal polarity. Regulators of both branched actin networks and of linear actin cables have been identified at cell-cell junctions, in particular at adherens junctions but also at tight junctions. These regulators of actin dynamics are often directly or indirectly associated with cell adhesion receptors, suggesting a critical role for cell adhesion molecules for the recruitment of regulators of actin dynamics to cell-cell junctions. Here, we review the recent developments on the role of cell adhesion molecules at epithelial and endothelial cell-cell junctions in the regulation of junctional actin dynamics.

Abstract 1460: Stathmin regulates mammary gland morphogenesis and tumorigenesis

Abstract Microtubule (MT) dynamics is essential to provide a correct apico-basal polarization of epithelial cells, by regulating the movement of vesicles and proteins within the cell and by ensuring a correct orientation of the mitotic spindle during cell division. Little is known about the role of the MT-dynamics and of MT-regulating proteins during development of the mammary gland, a dynamic organ that displays a complex and finely organized apico-basal architecture. Stathmin, a MT-destabilizing protein, is often overexpressed in breast cancer (BC). By studying knockout (STM KO) mice we observed that STM KO females were unable to nurse their offspring. This phenotype was accompanied by defective development of the mammary gland, particularly evident during pregnancy and post-partum phases. Our results showed that stathmin absence mainly impinged on two key features of the mammary epithelial organization, polarity and proliferation. In vitro, normal mammary epithelial cells silenced for stathmin were not able to form organized acini in 3D-matrices. In vivo, when stathmin was KO, many molecules involved in mammary gland functions were not properly localized, indicating a disruption of the apico-basal polarity. Furthermore, loss of stathmin strongly decreased proliferation and induced disoriented positioning of the mitotic spindle in dividing epithelial cells, preventing the correct orientation of the daughter cells. Loss of polarity and deregulated proliferation are tightly linked to tumorigenesis. We therefore examined the role of stathmin also in the context of HER2-driven tumorigenesis. To this end, we used a transgenic mouse model expressing a constitutively active form of HER2 (Δ16HER2), which is an alternatively spliced, very aggressive form of HER2, and intercrossed them with STM WT and KO mice. We analyzed the role of stathmin in both early and late stages of tumorigenesis. STM KO mice displayed a significantly reduced number of pre-neoplastic foci and this phenotype was maintained also in late stages of tumorigenesis. In WT mice, pre-neoplastic lesions expressed high level of stathmin compared with normal tissue supporting the idea that stathmin played an active role in tumor initiation. Analysis of proliferation in tumors revealed that loss of stathmin strongly decreased the mitotic rate of Δ16HER2-transformed cells. Furthermore, we assessed that stathmin plays a cell autonomous function in tumor initiation. Our study has shed new light in the field of mammary gland development and of breast cancer biology. Collectively, our data indicate that loss of stathmin by altering the dynamics of microtubules, causes a profound disorganization of the normal mammary gland architecture and a delay in initiation of the tumorigenic process. We have uncovered new functions of stathmin that could have important implications in BC, also in consideration that several microtubules acting drugs are currently employed in the therapy of BC patients Citation Format: Ilenia Segatto, Mara De Marco Zompit, Gian Luca Rampioni Vinciguerra, Francesca Citron, Sara D'Andrea, Tiziana Perin, Gustavo Baldassarre, Barbara Belletti. Stathmin regulates mammary gland morphogenesis and tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1460.

Abstract 3338: BP1 induces an epithelial to mesenchymal transition in breast cancer cells by modulating the Twist/IL6 pathway

Abstract Background. BP1 (Beta Protein 1) belongs to the Distal-less family of homeobox genes. We have demonstrated that BP1 is activated in over 80% of invasive ductal breast tumors, where it is associated with breast cancer progression. The mechanism(s) of BP1 involvement in breast cancer progression, invasion and metastasis are still not known. Homeobox genes contribute to the epithelial to mesenchymal transition (EMT). During EMT, epithelial cells acquire mesenchymal features which lead to motility, invasiveness and resistance to apoptosis. EMT is also characterized by changes in apico-basal polarity and a dramatic remodeling of the cytoskeleton. During progression toward metastasis, cancer cells acquire a mesenchymal gene expression phenotype and increased motility. This transition allows the tumor cells to metastasize and establish secondary tumors at distant sites. One of the drivers of the EMT is the transcription factor Twist. Twist is a member of highly conserved family of basic helix-loop-helix transcription factors and is involved in the specification and differentiation of mesenchymal tissue in embryos. Twist overexpression can induce EMT, generate cancer stem cells, and promote metastasis in vivo. We hypothesized that BP1 might promote cancer metastasis and invasiveness mediated though Twist and the EMT. Methods. We generated BP1 overexpressing cell lines, MCF-7/BP1 and HS578T/BP1, along with the associated vector controls. Expression of BP1 was tested by both protein and transcript levels by Western blotting and qRT-PCR, respectively. BP1 binding to Twist was assayed by chromatin immunoprecipitation. Confocal microscopy was used to localize BP1 expression and Boyden chamber assays were employed to assess the migratory and invasive ability of these cells. ELISA assays were employed to study IL6 expression in BP1 expressing cells. Results. BP1 expression led to an increase in Twist expression. Mechanistically, we demonstrated that BP1 bound proximally to the Twist promoter and regulated its expression. BP1 induced an EMT in both cell lines as seen by (a) lack of expression of E-cadherin, and an increase of vimentin and fibronectin expression, as well as (b) morphological changes, including a spindle-like, and more migratory phenotype. We also observed that BP1 induced expression of the cytokine IL6 in both cell lines. We conclude that BP1 regulates the EMT in breast cancer cells via the Twist and IL6 pathways. Citation Format: Farhad Vesuna, Bin-Jin Hwang, Jinguen Rheey, Mamta Giri, Mandeep Gill, Sidney W. Fu, Ashley Irving, Ala Lisok, Yehudit Bergman, Venu Raman, Patricia E. Berg. BP1 induces an epithelial to mesenchymal transition in breast cancer cells by modulating the Twist/IL6 pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3338.

Insane in the apical membrane: Trafficking events mediating apicobasal epithelial polarity during tube morphogenesis.

The creation of cellular tubes is one of the most vital developmental processes, resulting in the formation of most organ types. Cells have co-opted a number of different mechanisms for tube morphogenesis that vary among tissues and organisms; however, generation and maintenance of cell polarity is fundamental for successful lumenogenesis. Polarized membrane transport has emerged as a key driver not only for establishing individual epithelial cell polarity, but also for coordination of epithelial polarization during apical lumen formation and tissue morphogenesis. In recent years, much work has been dedicated to identifying membrane trafficking regulators required for lumenogenesis. In this review we will summarize the findings from the past couple of decades in defining the molecular machinery governing lumenogenesis both in 3D tissue culture models and during organ development in vivo.

A New Approach to Design Artificial 3D Microniches with Combined Chemical, Topographical, and Rheological Cues

AbstractThe in vitro methods to recapitulate environmental cues around cells are usually optimized to test a specific property of the environment (biochemical nature or the stiffness of the extracellular matrix (ECM), or nanotopography) for its capability to induce defined cell behaviors (lineage commitment, migration). Approaches that combine different environmental cues in 3D to assess the biological response of cells to the spatial organization of different biophysical and biochemical cues are growingly being developed. It is demonstrated how the lamination of through‐hole polymeric biofunctionalized membranes can be implemented to create complex bona fide microniches with differential 3D environmental properties using photoactive materials. The approach enables to create microniches ranging in size from single cells to cell aggregates. They are biofunctionalized in 3D simultaneously with topographical featured, protein patterns and structured ECM surrogate with 1 µm resolution. It is demonstrated how these niches extend in 3D the ability to pattern cells. It is exemplified how they can be used to standardize cells' shapes in 3D and to trigger the apicobasal polarization of single epithelial cells.

Small GTPase R-Ras participates in neural tube formation in zebrafish embryonic spinal cord

Ras related (R-Ras), a small GTPase, is involved in the maintenance of apico-basal polarity in neuroepithelial cells of the zebrafish hindbrain, axonal collapse in cultured murine hippocampal neurons, and maturation of blood vessels in adult mice. However, the role of R-Ras in neural tube formation remains unknown. Using antisense morpholino oligonucleotides (AMOs), we found that in the spinal cord of zebrafish embryos, the lumen was formed bilaterally in rras morphants, whereas it was formed at the midline in control embryos. As AMO can cause off-target effects, we generated rras mutant zebrafish lines using CRISPR/Cas9 technology. Although these rras mutant embryos did not have a bilateral lumen in the spinal cord, the following findings suggest that the phenotype is unlikely due to an off-target effect of rras AMO: 1) The rras morphant phenotype was rescued by an injection of AMO-resistant rras mRNA, and 2) a bilaterally segregated spinal cord was not observed in rras mutant embryos injected with rras AMO. The results suggest that the function of other ras family genes may be redundant in rras mutants. Previous research reported a bilaterally formed lumen in the spinal cord of zebrafish embryos with a mutation in a planar cell polarity (PCP) gene, van gogh-like 2 (vangl2). In the present study, in cultured cells, R-Ras was co-immunoprecipitated with Vangl2 but not with another PCP regulator, Pricke1. Interestingly, the interaction between R-Ras and Vangl2 was stronger in guanine-nucleotide free point mutants of R-Ras than in wild-type or constitutively active (GTP-bound) forms of R-Ras. R-Ras may regulate neural tube formation in cooperation with Vangl2 in the developing zebrafish spinal cord.

Perturbation of epithelial apicobasal polarity by rhomboid family‐1 gene overexpression

The human rhomboid family (RHBDF)1 gene is highly expressed in breast cancer under clinical conditions but not in normal mammary gland tissues. Silencing the RHBDF1 gene in breast cancer xenograft tumors leads to inhibition of tumor growth. We show in this study that artificially raising RHBDF1 protein levels in the mammary epithelial cells MCF-10A results in severe perturbations of the ability of the cells to form lumen-containing acini, either in 3-dimensional cell cultures or implanted in mouse mammary fat pads. Knocking down RHBDF1 with short hairpin (sh)RNA leads to restoration of acinus formation. Consistently, RHBDF1 overexpression gives rise to disordered distribution of polarity markers GM130 and laminin-5, which otherwise are located in apical and basal positions, respectively, in the acini. Further investigations reveal that RHBDF1 directly binds to Par6a, a component of a protein complex consisting of partitioning-defective scaffold protein (Par)6, Par3, renin-angiotensin system-related C3 botulinum toxin substrate (Rac)1, and cell-division cycle (Cdc)42, which is structurally critical to the formation of apicobasal polarity. RHBDF1 binding to Par6a results in collapse of the protein complex and thus disruption of polarity formation. Since early stages of breast cancer are characterized by the loss of mammary gland epithelial cell polarity, our findings indicate that perturbations of apicobasal polarity by high levels of RHBDF1 is a significant attribute in the development of breast neoplasia.-Peng, X.-M., Gao, S., Deng, H.-T., Cai, H.-X., Zhou, Z., Xiang, R., Zhang, Q.-Z., Li, L.-Y. Perturbation of epithelial apicobasal polarity by rhomboid family-1 gene overexpression.

Patient-iPSC-Derived Kidney Organoids Show Functional Validation of a Ciliopathic Renal Phenotype and Reveal Underlying Pathogenetic Mechanisms

Despite the increasing diagnostic rate of genomic sequencing, the genetic basis of more than 50% of heritable kidney disease remains unresolved. Kidney organoids differentiated from induced pluripotent stem cells (iPSCs) of individuals affected by inherited renal disease represent a potential, but unvalidated, platform for the functional validation of novel gene variants and investigation of underlying pathogenetic mechanisms. In this study, trio whole-exome sequencing of a prospectively identified nephronophthisis (NPHP) proband and her parents identified compound-heterozygous variants in IFT140, a gene previously associated with NPHP-related ciliopathies. IFT140 plays a key role in retrograde intraflagellar transport, but the precise downstream cellular mechanisms responsible for disease presentation remain unknown. A one-step reprogramming and gene-editing protocol was used to derive both uncorrected proband iPSCs and isogenic gene-corrected iPSCs, which were differentiated to kidney organoids. Proband organoid tubules demonstrated shortened, club-shaped primary cilia, whereas gene correction rescued this phenotype. Differential expression analysis of epithelial cells isolated from organoids suggested downregulation of genes associated with apicobasal polarity, cell-cell junctions, and dynein motor assembly in proband epithelial cells. Matrigel cyst cultures confirmed a polarization defect in proband versus gene-corrected renal epithelium. As such, this study represents a "proof of concept" for using proband-derived iPSCs to model renal disease and illustrates dysfunctional cellular pathways beyond the primary cilium in the setting of IFT140 mutations, which are established for other NPHP genotypes.