The membrane protein CD9/DRAP 27 potentiates the juxtacrine growth factor activity of the membrane-anchored heparin-binding EGF-like growth factor

The Multiple Functions of HB-EGF in Female Reproduction and Related Cancer: Molecular Mechanisms and Targeting Strategies

Heparin-binding growth factor (HB-EGF) is a member of the epidermal growth factor (EGF) ligand family which has a crucial role in women's health. However, there is a lack of comprehensive review to summarize the significance of HB-EGF. Therefore, this work first described the expression patterns of HB-EGF in the endometrium and ovary of different species and gestational time. Then, the focus was on exploring how it promotes the successful implantation and regulates the process of decidualization and the function of ovarian granulosa cells as an intermediate molecule. Otherwise, we also focused on the clinical and prognostic significance of HB-EGF in female-related cancers (including ovarian cancer, cervical cancer, and endometrial cancer) and breast cancer. Lastly, the article also summarizes the current drugs targeting HB-EGF in the treatment of ovarian cancer and breast cancer. Overall, these studies found that the expression of HB-EGF in the endometrium is spatiotemporal and species-specific. And it mediates the dialogue between the blastocyst and endometrium, promoting synchronous development of the blastocyst and endometrium as an intermediate molecule. HB-EGF may serve as a potentially valuable prognostic clinical indicator in tumors. And the specific inhibitor of HB-EGF (CRM197) has a certain anti-tumor ability, which can exert synergistic anti-tumor effects with conventional chemotherapy drugs. However, it also suggests that more research is needed in the future to elucidate its specific mechanisms and to accommodate clinical studies with a larger sample size to clarify its clinical value.

High expression of CD9 and Epidermal Growth Factor Receptor promotes the development of tongue cancer

Tongue cancer is distinguished by aggressive behavior, a high risk of recurrence, lymph, and distant metastases. Hypoxia-Induced Factor 1 α functions as a CD9 transcription factor. CD9 is a transmembrane protein that may be found on the cell membrane. It can modulate the expression of the Epidermal Growth Factor Receptor (EGFR) pathway. ELISA was used to measure serum CD9, p-EGFR, and p-Akt levels in 70 tongue cancer patients and 35 healthy controls. RT-PCR was used to analyze the gene expression of the related genes. The gene as well as protein expression of CD9, EGFR/p-EGFR, and Akt/p-Akt was significantly higher in case subjects when compared with the controls. The expression of CD9 was higher in case subjects who were smokers/alcoholics when to control subjects who were smokers/alcoholics. Overexpression of CD9 due to hypoxic conditions leads to the activation of EGFR-signaling pathway resulting in cancer progression, resistance to chemotherapy. Hence, CD9 could be a potential target to suppress cancer progression.

Tetraspanin CD9: A friend or foe of head and neck cancer (Review)

Head and neck cancers are diverse and complex diseases characterised by unregulated growth of tumour cells in various parts of the head and neck region, such as in the buccal mucosa, floor of the mouth, tongue, oropharynx, hypopharynx, oesophagus, nasopharynx and salivary glands. Partial or total glossectomy, radiation or chemotherapy greatly affect patient quality of life. However, even following treatment, patients may relapse. Nicotine-derived nitrosamines and alcohol are the major etiological factors underlying this deadly disease. These compounds induce DNA damage that may lead to mutation in crucial genes, such as p53 and p21, which are important to regulate cell proliferation, thus leading to cancer. CD9 is a tetraspanin, which are a group of transmembrane proteins that have a role in cell motility and adhesion. The present review aimed to explore the role of CD9 in head and neck cancer. Epidermal growth factor receptor activity and cell proliferation are regulated by the CD9-integrin/CD9-transforming growth factor interaction. Hence, CD9 can play a dual role in various types of cancer.

Methods for the Assembly and Characterization of Polyelectrolyte Multilayers as Microenvironments to Modulate Human Mesenchymal Stromal Cell Response

Thin films are of interest in materials design because they allow for the modification of surface properties of materials while the bulk properties of the material are largely unaffected. In this work, we outline methods for the assembly of thin films using a technique known as layer-by-layer (LbL). Furthermore, their interactions with human mesenchymal stromal cells (hMSCs) are discussed. hMSCs are a subject of growing interest because of their potential to treat or cure diseases, given their immunosuppressive properties, multipotent differentiation capabilities, and tissue regeneration capabilities. Numerous improvements and modifications have been suggested for the harvesting, treatment, and culture of hMSCs prior to their administration in human subjects. Here, we discuss methods to assess the interactions of hMSCs with thin LbL-assembled films of heparin and collagen. Three different methods are discussed. The first details the preparation of heparin/collagen multilayers on different surfaces and the seeding of cells on these multilayers. The second method details the characterization of multilayers, including techniques to assess the thickness, roughness, and surface charge of the multilayers, as well as in situ deposition of multilayers. The third method details the analysis of cell interactions with the multilayers, including techniques to assess proliferation, viability, real-time monitoring of hMSC behavior, analysis of hMSC-adhesive proteins on the multilayers, immunomodulatory factor expression of hMSCs, and cytokine expression on heparin/collagen multilayers. We propose that the methods described in this work will assist in the design and characterization of LbL-assembled thin films and the analysis of hMSCs cultured on these thin films.

Cooperation and Interplay between EGFR Signalling and Extracellular Vesicle Biogenesis in Cancer

Epidermal growth factor receptor (EGFR) takes centre stage in carcinogenesis throughout its entire cellular trafficking odyssey. When loaded in extracellular vesicles (EVs), EGFR is one of the key proteins involved in the transfer of information between parental cancer and bystander cells in the tumour microenvironment. To hijack EVs, EGFR needs to play multiple signalling roles in the life cycle of EVs. The receptor is involved in the biogenesis of specific EV subpopulations, it signals as an active cargo, and it can influence the uptake of EVs by recipient cells. EGFR regulates its own inclusion in EVs through feedback loops during disease progression and in response to challenges such as hypoxia, epithelial-to-mesenchymal transition and drugs. Here, we highlight how the spatiotemporal rules that regulate EGFR intracellular function intersect with and influence different EV biogenesis pathways and discuss key regulatory features and interactions of this interplay. We also elaborate on outstanding questions relating to EGFR-driven EV biogenesis and available methods to explore them. This mechanistic understanding will be key to unravelling the functional consequences of direct anti-EGFR targeted and indirect EGFR-impacting cancer therapies on the secretion of pro-tumoural EVs and on their effects on drug resistance and microenvironment subversion.

Mechanisms of Action of EGFR Tyrosine Kinase Receptor Incorporated in Extracellular Vesicles

EGFR and some of the cognate ligands extensively traffic in extracellular vesicles (EVs) from different biogenesis pathways. EGFR belongs to a family of four homologous tyrosine kinase receptors (TKRs). This family are one of the major drivers of cancer and is involved in several of the most frequent malignancies such as non-small cell lung cancer, breast cancer, colorectal cancer and ovarian cancer. The carrier EVs exert crucial biological effects on recipient cells, impacting immunity, pre-metastatic niche preparation, angiogenesis, cancer cell stemness and horizontal oncogene transfer. While EV-mediated EGFR signalling is important to EGFR-driven cancers, little is known about the precise mechanisms by which TKRs incorporated in EVs play their biological role, their stoichiometry and associations to other proteins relevant to cancer pathology and EV biogenesis, and their means of incorporation in the target cell. In addition, it remains unclear whether different subtypes of EVs incorporate different complexes of TKRs with specific functions. A raft of high spatial and temporal resolution methods is emerging that could solve these and other questions regarding the activity of EGFR and its ligands in EVs. More importantly, methods are emerging to block or mitigate EV activity to suppress cancer progression and drug resistance. By highlighting key findings and areas that remain obscure at the intersection of EGFR signalling and EV action, we hope to cross-fertilise the two fields and speed up the application of novel techniques and paradigms to both.

Ablation of Fat Cells in Adult Mice Induces Massive Bone Gain

Adipocytes control bone mass, but the mechanism is unclear. To explore the effect of postnatal adipocyte elimination on bone cells, we mated mice expressing an inducible primate diphtheria toxin receptor (DTR) to those bearing adiponectin (ADQ)-Cre. DTR activation eliminates peripheral and marrow adipocytes in these DTR^ADQ mice. Within 4 days of DTR activation, the systemic bone mass of DTR^ADQ mice began to increase due to stimulated osteogenesis, with a 1,000% expansion by 10-14 days post-DTR treatment. This adipocyte ablation-mediated enhancement of skeletal mass reflected bone morphogenetic protein (BMP) receptor activation following the elimination of its inhibitors, associated with simultaneous epidermal growth factor (EGF) receptor signaling. DTR^ADQ-induced osteosclerosis is not due to ablation of peripheral adipocytes but likely reflects the elimination of marrow ADQ-expressing cells. Thus, anabolic drugs targeting BMP receptor inhibitors with short-term EGF receptor activation may be a means of profoundly increasing skeletal mass to prevent or reverse pathological bone loss.

Tetraspanins: useful multifunction proteins for the possible design and development of small-molecule therapeutic tools

Tetraspanins constitute a well-conserved superfamily of four-span small membrane proteins (TM4SF), with >30 members in humans, with important roles in numerous mechanisms of cell biology. Moreover, tetraspanins associate with either specific partner proteins or another tetraspanin, generating a network of interactions involved in cell and membrane compartmentalization and having a role in cellular development, proliferation, activation, motility, and membrane fusions. Therefore, tetraspanins are considered regulators of cellular signaling and are often depicted as 'molecular facilitators'. In view of these many physiological functions, it is likely that these molecules are important actors in pathological processes. In this review, we present the main characteristics of this superfamily, providing a more detailed description of some significant representatives and discuss their relevance as potential targets for the design and development of small-molecule therapeutics in different pathologies.

ADAM17: An Emerging Therapeutic Target for Lung Cancer

Lung cancer is the leading cause of cancer-related mortality, which histologically is classified into small-cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). NSCLC accounts for approximately 85% of all lung cancer diagnoses, with the majority of patients presenting with lung adenocarcinoma (LAC). KRAS mutations are a major driver of LAC, and are closely related to cigarette smoking, unlike mutations in the epidermal growth factor receptor (EGFR) which arise in never-smokers. Although the past two decades have seen fundamental progress in the treatment and diagnosis of NSCLC, NSCLC still is predominantly diagnosed at an advanced stage when therapeutic interventions are mostly palliative. A disintegrin and metalloproteinase 17 (ADAM17), also known as tumour necrosis factor-α (TNFα)-converting enzyme (TACE), is responsible for the protease-driven shedding of more than 70 membrane-tethered cytokines, growth factors and cell surface receptors. Among these, the soluble interleukin-6 receptor (sIL-6R), which drives pro-inflammatory and pro-tumourigenic IL-6 trans-signaling, along with several EGFR family ligands, are the best characterised. This large repertoire of substrates processed by ADAM17 places it as a pivotal orchestrator of a myriad of physiological and pathological processes associated with the initiation and/or progression of cancer, such as cell proliferation, survival, regeneration, differentiation and inflammation. In this review, we discuss recent research implicating ADAM17 as a key player in the development of LAC, and highlight the potential of ADAM17 inhibition as a promising therapeutic strategy to tackle this deadly malignancy.

DTR-mediated conditional cell ablation-Progress and challenges

Cell ablation is a valuable complement to mutagenesis for experimentally defining specific cell functions in physiology and pathophysiology in small animal models. One of the most popular ablation strategies involves transgenic expression of a primate diphtheria toxin receptor (DTR) on murine cells that are otherwise resistant to the bacterial exotoxin. The efforts of many laboratories using the DTR approach over the years have yielded numerous valuable insights into specific cell functions. Here, we will discuss the technical aspects of the DTR approach, including the strengths, pitfalls, and future strategies to overcome the shortcomings, highlighting a recent paper published in the European Journal of Immunology [El Hachem et al. Eur. J. Immunol. 2018 https://doi.org/10.1002/eji.201747351]. A particular focus will be given to the application of DTR approach to decipher in vivo functions of the murine myeloid cell compartment.

Characterization of a Novel Anti-Human HB-EGF Monoclonal Antibody Applicable for Paraffin-Embedded Tissues and Diagnosis of HB-EGF-Related Cancers

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family of growth factors that bind to and activate the EGF receptor (EGFR/ErbB1) and ErbB4. HB-EGF plays pivotal roles in pathophysiological processes, including cancer. Thus, monoclonal antibodies (mAbs) for HB-EGF detection could be an important tool in the therapeutic diagnosis of HB-EGF-related cancers and other diseases. However, few mAbs, especially those applicable for immunohistochemistry (IHC), have been established to date. In this study, we generated a clone of hybridoma-derived mAb 2-108 by immunizing mice with recombinant human HB-EGF protein expressed by human cells. The mAb 2-108 specifically bound to human HB-EGF but not to mouse HB-EGF and was successful in immunoblotting, even under reducing conditions, immunoprecipitation, and immunofluorescence for unfixed as well as paraformaldehyde-fixed cells. Notably, this mAb was effective in IHC of paraffin-embedded tumor specimens. Epitope mapping analysis showed that mAb 2-108 recognized the N-terminal prodomain in HB-EGF. These results indicate that this new anti-HB-EGF mAb 2-108 would be useful in the diagnosis of HB-EGF-related cancers and would be a strong tool in both basic and clinical research on HB-EGF.

The significance of membrane fluidity of feeder cell-derived substrates for maintenance of iPS cell stemness

The biological activity of cell-derived substrates to maintain undifferentiated murine-induced pluripotent stem (iPS) cells was correlated to membrane fluidity as a new parameter of cell culture substrates. Murine embryonic fibroblasts (MEFs) were employed as feeder cells and their membrane fluidity was tuned by chemical fixation using formaldehyde (FA). Membrane fluidity was evaluated by real-time single-molecule observations of green fluorescent protein-labeled epidermal growth factor receptors on chemically fixed MEFs. Biological activity was monitored by colony formation of iPS cells. Treatment with a low concentration of FA sustained the membrane fluidity and biological activity, which were comparable to those of mitomycin C-treated MEFs. The biological activity was further confirmed by sustained expression of alkaline phosphatase, SSEA-1, and other pluripotency markers in iPS cells after 3-5 days of culture on FA-fixed MEFs. Chemical fixation of feeder cells has several advantages such as providing ready-to-use culture substrates without contamination by proliferating feeder cells. Therefore, our results provide an important basis for the development of chemically fixed culture substrates for pluripotent stem cell culture as an alternative to conventional treatment by mitomycin C or x-ray irradiation.

Novel CD9-targeted therapies in gastric cancer

There are 33 human tetraspanin proteins, emerging as key players in malignancy, the immune system, fertilization, cellular signaling, adhesion, morphology, motility, proliferation, and tumor invasion. CD9, a member of the tetraspanin family, associates with and influences a variety of cell-surface molecules. Through these interactions, CD9 modifies multiple cellular events, including adhesion, migration, proliferation, and survival. CD9 is therefore considered to play a role in several stages during cancer development. Reduced CD9 expression is generally related to venous vessel invasion and metastasis as well as poor prognosis. We found that treatment of mice bearing human gastric cancer cells with anti-CD9 antibody successfully inhibited tumor progression via antiproliferative, proapoptotic, and antiangiogenic effects, strongly indicating that CD9 is a possible therapeutic target in patients with gastric cancer. Here, we describe the possibility of CD9 manipulation as a novel therapeutic strategy in gastric cancer, which still shows poor prognosis.

Regulation of stem cell fate by nanomaterial substrates

Stem cells are increasingly studied because of their potential to underpin a range of novel therapies, including regenerative strategies, cell type-specific therapy and tissue repair, among others. Bionanomaterials can mimic the stem cell environment and modulate stem cell differentiation and proliferation. New advances in these fields are presented in this review. This work highlights the importance of topography and elasticity of the nano-/micro-environment, or niche, for the initiation and induction of stem cell differentiation and proliferation.

Design of growth factor sequestering biomaterials

Growth factors (GFs) are major regulatory proteins that can govern cell fate, migration, and organization. Numerous aspects of the cell milieu can modulate cell responses to GFs, and GF regulation is often achieved by the native extracellular matrix (ECM). For example, the ECM can sequester GFs and thereby control GF bioavailability. In addition, GFs can exert distinct effects depending on whether they are sequestered in solution, at two-dimensional interfaces, or within three-dimensional matrices. Understanding how the context of GF sequestering impacts cell function in the native ECM can instruct the design of soluble or insoluble GF sequestering moieties, which can then be used in a variety of bioengineering applications. This Feature Article provides an overview of the natural mechanisms of GF sequestering in the cell milieu, and reviews the recent bioengineering approaches that have sequestered GFs to modulate cell function. Results to date demonstrate that the cell response to GF sequestering depends on the affinity of the sequestering interaction, the spatial proximity of sequestering in relation to cells, the source of the GF (supplemented or endogenous), and the phase of the sequestering moiety (soluble or insoluble). We highlight the importance of context for the future design of biomaterials that can leverage endogenous molecules in the cell milieu and mitigate the need for supplemented factors.

MiR-212 exerts suppressive effect on SKOV3 ovarian cancer cells through targeting HBEGF

MicroRNAs (miRNAs) play critical roles in the development and progression of ovarian cancer. We found that miR-212 was significantly downregulated in serum and tissues from epithelial ovarian cancer (EOC) patients. Overexpression of miR-212 in ovarian cancer cells inhibited cell proliferation, migration, and invasion. Luciferase reporter assay confirmed HBEGF as a direct target of miR-212. Overexpression of miR-212 decreased HBEGF expression at both the protein and messenger RNA (mRNA) levels. Knockdown of HBEGF expression in SKOV3 cell line significantly inhibited cell growth, migration, and invasion. HBEGF mRNA level was upregulated in EOC tissues and inversely correlated with miR-212 expression in tissues. Upregulation of HBEGF could attenuate the effect induced by miR-212. These findings indicate that miR-212 displays a tumor-suppressive effect in human ovarian cancer. And miR-212 suppresses cell proliferation, migration, and invasion by targeting the HBEGF transcript, highlighting the therapeutic potential of miR-212 and HBEGF in epithelial ovarian cancer treatment.

Tetraspanins at a glance

Tetraspanins are a family of proteins with four transmembrane domains that play a role in many aspects of cell biology and physiology; they are also used by several pathogens for infection and regulate cancer progression. Many tetraspanins associate specifically and directly with a limited number of proteins, and also with other tetraspanins, thereby generating a hierarchical network of interactions. Through these interactions, tetraspanins are believed to have a role in cell and membrane compartmentalization. In this Cell Science at a Glance article and the accompanying poster, we describe the basic principles underlying tetraspanin-based assemblies and highlight examples of how tetraspanins regulate the trafficking and function of their partner proteins that are required for the normal development and function of several organs, including, in humans, the eye, the kidney and the immune system.

Gene expression profiling of Drosophila tracheal fusion cells

The Drosophila trachea is a premier genetic system to investigate the fundamental mechanisms of tubular organ formation. Tracheal fusion cells lead the branch fusion process to form an interconnected tubular network. Therefore, fusion cells in the Drosophila trachea will be an excellent model to study branch fusion in mammalian tubular organs, such as kidneys and blood vessels. The fusion process is a dynamic cellular process involving cell migration, adhesion, vesicle trafficking, cytoskeleton rearrangement, and membrane fusion. To understand how these cellular events are coordinated, we initiated the critical step to assemble a gene expression profile of fusion cells. For this study, we analyzed the expression of 234 potential tracheal-expressed genes in fusion cells during fusion cell development. 143 Tracheal genes were found to encode transcription factors, signal proteins, cytoskeleton and matrix proteins, transporters, and proteins with unknown function. These genes were divided into four subgroups based on their levels of expression in fusion cells compared to neighboring non-fusion cells revealed by in situ hybridization: (1) genes that have relative high abundance in fusion cells, (2) genes that are dynamically expressed in fusion cells, (3) genes that have relative low abundance in fusion cells, and (4) genes that are expressed at similar levels in fusion cells and non-fusion tracheal cells. This study identifies the expression profile of fusion cells and hypothetically suggests genes which are necessary for the fusion process and which play roles in distinct stages of fusion, as indicated by the location and timing of expression. These data will provide the basis for a comprehensive understanding of the molecular and cellular mechanisms of branch fusion.

From wavy hair to naked proteins: the role of transforming growth factor alpha in health and disease

Since its discovery in 1978 and cloning in 1984, transforming growth factor-alpha (TGF-α, TGFA) has been one of the most extensively studied EGF receptor (EGFR) ligands. In this review, we provide a historical perspective on TGFA-related studies, highlighting what we consider important advances related to its function in normal and disease states.

Stem cell culture using cell-derived substrates

There have been great efforts to develop cell culture systems using chemically-fixed cells or decellularized matrices to regulate stem cell functions.

Regulation of receptor tyrosine kinase ligand processing

A primary mode of regulating receptor tyrosine kinase (RTK) signaling is to control access of ligand to its receptor. Many RTK ligands are synthesized as transmembrane proteins. Frequently, the active ligand must be released from the membrane by proteolysis before signaling can occur. Here, we discuss RTK ligand shedding and describe the proteases that catalyze it in flies and mammals. We focus principally on the control of EGF receptor ligand shedding, but also refer to ligands of other RTKs. Two prominent themes emerge. First, control by regulated trafficking and cellular compartmentalization of the proteases and their ligand substrates plays a key role in shedding. Second, many external signals converge on the shedding proteases and their control machinery. Proteases therefore act as regulatory hubs that integrate information that the cell receives and translate it into precise outgoing signals. The activation of signaling by proteases is therefore an essential element of the cellular communication machinery.

Recombinant receptor-binding domain of diphtheria toxin increases the potency of curcumin by enhancing cellular uptake

Diphtheria toxin (DT) binds to a specific cell surface receptor, gets internalized, and causes cytotoxicity through its catalytic domain. The toxicity of DT is used in several therapeutic molecules. Here, we have exploited the receptor-binding ability of DT to increase cellular uptake of curcumin, a hydrophobic molecule with low bioavailability and cellular uptake. We have expressed only the receptor-binding domain of DT (RDT) in Escherichia coli. Purified RDT binds to the receptor with an affinity equivalent to that of full-length DT. It also binds to curcumin forming a curcumin-RDT complex, and this increases the fluorescence intensity and fluorescence lifetime of curcumin. The curcumin-RDT complex binds to the receptor and associates with human glioblastoma cells (U-87 MG) expressing the receptor. The cellular uptake of curcumin is higher for the curcumin-RDT complex than curcumin alone. This increase in uptake enhances the antiproliferative effect of curcumin and induces apoptosis of these cells even at a lower dose.

Trafficking of epidermal growth factor receptor ligands in polarized epithelial cells

A largely unilamellar epithelial layer lines body cavities and organ ducts such as the digestive tract and kidney tubules. This polarized epithelium is composed of biochemically and functionally separate apical and basolateral surfaces. The epidermal growth factor receptor (EGFR) signaling pathway is a critical regulator of epithelial homeostasis and is perturbed in a number of epithelial disorders. It is underappreciated that in vivo EGFR signaling is most often initiated by cell-surface delivery and processing of one of seven transmembrane ligands, resulting in release of the soluble form that binds EGFR. In polarized epithelial cells, EGFR is restricted largely to the basolateral surface, and apical or basolateral ligand delivery therefore has important biological consequences. In vitro approaches have been used to study the biosynthesis, cell-surface delivery, proteolytic processing, and release of soluble EGFR ligands in polarized epithelial cells. We review these results, discuss their relevance to normal physiology, and demonstrate the pathophysiological consequences of aberrant trafficking. These studies have uncovered a rich diversity of apico-basolateral trafficking mechanisms among the EGFR ligands, provided insights into the pathogenesis of an inherited magnesium-wasting disorder of the kidney (isolated renal hypomagnesemia), and identified a new mode of EGFR ligand signaling via exosomes.

Roles for HB-EGF and CD9 in multiple sclerosis

Early events in multiple sclerosis (MS) lesion formation are loss of blood-brain barrier (BBB) integrity, immune cell trafficking into the central nervous system, and demyelination. To date, the molecular mechanisms underlying these pathogenic events are poorly understood. Heparin-binding epidermal growth factor (HB-EGF) is a trophic factor that is induced by inflammatory stimuli and has previously been shown to interact with tetraspanins (TSPs), a family of transmembrane proteins that are involved in cellular migration and adhesion. Given the known roles of TSPs and HB-EGF, we hypothesized that HB-EGF and TSPs may play a role in the processes that underlie MS lesion formation. We examined the expression of HB-EGF and the TSPs CD9 and CD81 in MS brain and found that HB-EGF was highly induced in reactive astrocytes in active lesions. TSPs were constitutively expressed throughout normal appearing white matter and control white matter. In contrast, CD9 was reduced in demyelinated lesions and increased on blood vessels in lesion areas. In vitro studies revealed that expression of HB-EGF and TSPs is regulated during inflammation. Importantly, blocking either HB-EGF or CD9 significantly reduced the migration of monocytes across brain endothelial cell monolayers. Moreover, blocking CD9 strongly enhanced the barrier function of the BBB in vitro. Together, we demonstrate that these molecules are likely implicated in processes that are highly relevant for MS lesion formation, and therefore, HB-EGF and TSPs are promising therapeutic targets.

Immunolocalization of heparin-binding EGF-like growth factor (HB-EGF) as a possible immunotarget in diagnosis of some soft tissue sarcomas

Heparin-binding EGF-like growth factor (HB-EGF), a member of the family of epidermal growth factors (EGFs), is involved in several biological processes and tumor formation. Several lines of evidence show that HB-EGF plays a key role in the acquisition of malignant phenotype. Studies show that HB-EGF expression is essential in oncogenesis of cancer-derived cell lines. HB-EGF is a promising target for cancer therapy. The aim of this study was to find new insights on the biological features of the soft tissue sarcomas, in order to consider the possibility to use HB-EGF as an immuno-target in histotype characterization and to facilitate therapeutic intervention. In our study we did HB-EGF-immunostaining on tissue samples collected from 43 human soft tissue sarcomas. We analyzed HB-EGF immunoexpression in some types of tumors such as clear cell sarcomas, leiomyosarcomas, phyllodes sarcomas, chondrosarcomas and liposarcomas. In relation to the different histotypes, we detected different immunostaining localization. From our results it was evident that pleomorphic cells, a signal of tumor progression, were HB-EGF immunostained, and this was accompanied by an extracellular matrix immunostaining. Moreover statistical analysis showed a correlation between HB-EGF immunostaining and the different types of analyzed soft tissue sarcomas. In conclusion, in some types of soft tissue sarcoma HB-EGF could be considered a useful diagnostic marker for their characterization.

Capture and printing of fixed stromal cell membranes for bioactive display on PDMS surfaces

Poly(dimethylsiloxane) (PDMS) has emerged as an extremely useful polymer for various biological applications. The conjugation of PDMS with bioactive molecules to create functional surfaces is feasible yet limited to a single-molecule display with imprecise localization of the molecules on PDMS. Here we report a robust technique that can transfer and print the membrane surface of glutaraldehyde-fixed stromal cells intact onto a PDMS substrate using an intermediate polyvinylalcohol (PVA) film as a transporter system. The cell-PVA film capturing the entirety of surface molecules can be peeled off and subsequently printed onto PDMS while maintaining the spatial display of the original cell surface molecules. Proof-of-concept studies are described using human bone marrow stromal cell membranes including a demonstration of the bioactivity of transferred membranes to capture and adhere hematopoietic cells. The presented process is applicable to virtually any adherent cell and can broaden the functional display of biomolecules on PDMS for biotechnology applications.

Heparin-binding EGF-like growth factor enhances the activity of invasion and metastasis in thyroid cancer cells

Thyroid cancer sometimes contains poorly differentiated components, which have the potential of invasion and metastasis. We evaluated the possible roles of heparin-binding EGF-like growth factor (HB-EGF), a member of the epidermal growth factor (EGF) family, in cell growth and invasion of thyroid cancer cells, and demonstrated that HB-EGF is not only a potent mitogen but also a chemotactic factor in the thyroid cancer cells 8305C and SW579. The HB-EGF-mediated chemotaxis was inhibited by neutralizing antibody against the EGF receptor (EGFR/HER1/ErbB1) or tyrphostin AG1478, a specific inhibitor of the EGFR tyrosine kinase. The HB-EGF mRNA and protein expression was also analyzed using RT-PCR and immunofluorescence methods, respectively. In addition, in clinical immunohistochemical study, increased expression of HB-EGF and its receptors, HER1 and EGFR4 (HER4/ErbB4), was observed in thyroid carcinoma cells. Our findings suggest that HB-EGF acts as a potent paracrine and/or autocrine chemotactic factor as well as a mitogen that mediates HER1 and/or HER4 in the invasion and metastasis of thyroid carcinoma cells, including poorly differentiated papillary carcinomas or undifferentiated/anaplastic carcinomas. These data may aid in the development of novel therapeutic strategies for thyroid cancer.

Notch increases the shedding of HB-EGF by ADAM12 to potentiate invadopodia formation in hypoxia

Hypoxia increases the levels of ADAM12 in a Notch-dependent manner, leading to increased ectodomain shedding of HB-EGF and subsequent promotion of invadopodia formation.

Notch regulates cell–cell contact-dependent signaling and is activated by hypoxia, a microenvironmental condition that promotes cellular invasion during both normal physiology and disease. The mechanisms by which hypoxia and Notch regulate cellular invasion are not fully elucidated. In this paper, we show that, in cancer cells, hypoxia increased the levels and activity of the ADAM12 metalloprotease in a Notch signaling–dependent manner, leading to increased ectodomain shedding of the epidermal growth factor (EGF) receptor (EGFR) ligand heparin-binding EGF-like growth factor. Released HB-EGF induced the formation of invadopodia, cellular structures that aid cancer cell invasion. Thus, we describe a signaling pathway that couples cell contact–dependent signaling with the paracrine activation of the EGFR, indicating cross talk between the Notch and EGFR pathways in promoting cancer cell invasion. This signaling pathway might regulate the coordinated acquisition of invasiveness by neighboring cells and mediate the communication between normoxic and hypoxic areas of tumors to facilitate cancer cell invasion.

Tetraspanin protein CD9 interacts with metalloprotease CD10 and enhances its release via exosomes

Tetraspanins interact with a wide variety of transmembrane and intracellular proteins called molecular partners, and modulate their function. In this article, we describe a new partner of tetraspanin web, membrane metalloprotease CD10, which is selectively associated with CD9. By constructing chimeras between tetraspanins CD9 and CD82 (the latter does not interact with CD10) or by using site-directed mutagenesis, we determined that a portion of the large extracellular loop from the CCG motif to transmembrane domain 4, as well as the C-terminal tail of CD9, are involved in the interaction with CD10. The stable expression of wild-type CD9 in K562 CD10-positive cells enhanced the level of CD10 released with exosomes five-fold. In contrast, the expression of chimeric CD9, which contained the cytoplasmic C-terminal domain from CD82, had little effect on CD10 release. Short hairpin RNA knockdown of CD9 expression in Nalm-6 pre-B cells resulted in a two-fold reduction in the amount of endogenous CD10 released with microvesicles. The peptidase activity of CD10 measured either on cells or on exosomes correlated with the level of CD10 expression, and was not significantly modulated by CD9 expression as such. Our data suggest that the interaction of CD10 with tetraspanin CD9 can play an important role in the redistribution of peptidase activity from the cell surface to outer microenvironments. In bone marrow, where CD10 presumably contributes to the maturation of pre-B cells and migration of B cells to the blood circulation, release of CD10 peptidase activity with exosomes may effectively regulate extracellular matrix microenvironments.

Identification of the cancer cell proliferation and survival functions of proHB-EGF by using an anti-HB-EGF antibody

PURPOSE

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the epidermal growth factor family. The membrane-bound proHB-EGF is known to be a precursor of the soluble form of HB-EGF (sHB-EGF), which promotes cell proliferation and survival. While the functions of sHB-EGF have been extensively studied, it is not yet fully understood if proHB-EGF is also involved in cellular signaling events. In this study, we utilized the anti-HB-EGF monoclonal antibodies Y-142 and Y-073, which have differential specificities toward proHB-EGF, in order to elucidate proHB-EGF functions in cancer cells.

EXPERIMENTAL DESIGN

The biological activities of proHB-EGF were assessed in cell proliferation, caspase activation, and juxtacrine activity assays by using a 3D spheroid culture of NUGC-3 cells.

RESULTS

Y-142 and Y-073 exhibited similar binding and neutralizing activities for sHB-EGF. However, only Y-142 bound to proHB-EGF. We could detect the function of endogenously expressed proHB-EGF in a 3D spheroid culture. Blocking proHB-EGF with Y-142 reduced spheroid formation, suppressed cell proliferation, and increased caspase activation in the 3D spheroid culture of NUGC-3 cells.

CONCLUSIONS

Our results show that proHB-EGF acts as a cell proliferation and cell survival factor in cancer cells. The results suggest that proHB-EGF may play an important role in tumor progression.

Who decides when to cleave an ectodomain?

Many life-essential molecules such as growth factors, cytokines, ectoenzymes, and decoy receptors are produced by ectodomain cleavage of transmembrane precursor molecules. Not surprisingly, misregulation of such essential functions is linked to numerous diseases. Ectodomain cleavage is the function of transmembrane ADAMs (a disintegrin and metalloprotease) and other membrane-bound metalloproteases, which have an extracellular catalytic domain. Almost all work on ectodomain cleavage regulation has focused on the control of enzyme activity determined by substrate cleavage as surrogate. However, the number of substrates far exceeds the number of enzymes. Specificity can therefore not be achieved by solely modulating enzyme activity. Here, we argue that specific regulatory pathways must exist to control the availability and susceptibility of substrates.

Tetraspanin CD82 inhibits protrusion and retraction in cell movement by attenuating the plasma membrane-dependent actin organization

To determine how tetraspanin KAI1/CD82, a tumor metastasis suppressor, inhibits cell migration, we assessed which cellular events critical for motility are altered by KAI1/CD82 and how KAI1/CD82 regulates these events. We found that KAI1/CD82-expressing cells typically exhibited elongated cellular tails and diminished lamellipodia. Live imaging demonstrated that the polarized protrusion and retraction of the plasma membrane became deficient upon KAI1/CD82 expression. The deficiency in developing these motility-related cellular events was caused by poor formations of actin cortical network and stress fiber and by aberrant dynamics in actin organization. Rac1 activity was reduced by KAI1/CD82, consistent with the diminution of lamellipodia and actin cortical network; while the growth factor-stimulated RhoA activity was blocked by KAI1/CD82, consistent with the loss of stress fiber and attenuation in cellular retraction. Upon KAI1/CD82 expression, Rac effector cofilin was not enriched at the cell periphery to facilitate lamellipodia formation while Rho kinase exhibited a significantly lower activity leading to less retraction. Phosphatidylinositol 4, 5-biphosphate, which initiates actin polymerization from the plasma membrane, became less detectable at the cell periphery in KAI1/CD82-expressing cells. Moreover, KAI1/CD82-induced phenotypes likely resulted from the suppression of multiple signaling pathways such as integrin and growth factor signaling. In summary, at the cellular level KAI1/CD82 inhibited polarized protrusion and retraction events by disrupting actin reorganization; at the molecular level, KAI1/CD82 deregulated Rac1, RhoA, and their effectors cofilin and Rho kinase by perturbing the plasma membrane lipids.

A potent anti-HB-EGF monoclonal antibody inhibits cancer cell proliferation and multiple angiogenic activities of HB-EGF

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the epidermal growth factor family and has a variety of physiological and pathological functions. Modulation of HB-EGF activity might have a therapeutic potential in the oncology area. We explored the therapeutic possibilities by characterizing the in vitro biological activity of anti-HB-EGF monoclonal antibody Y-142. EGF receptor (EGFR) ligand and species specificities of Y-142 were tested. Neutralizing activities of Y-142 against HB-EGF were evaluated in EGFR and ERBB4 signaling. Biological activities of Y-142 were assessed in cancer cell proliferation and angiogenesis assays and compared with the anti-EGFR antibody cetuximab, the HB-EGF inhibitor CRM197, and the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab. The binding epitope was determined with alanine scanning. Y-142 recognized HB-EGF as well as the EGFR ligand amphiregulin, and bound specifically to human HB-EGF, but not to rodent HB-EGF. In addition, Y-142 neutralized HB-EGF-induced phosphorylation of EGFR and ERBB4, and blocked their downstream ERK1/2 and AKT signaling. We also found that Y-142 inhibited HB-EGF-induced cancer cell proliferation, endothelial cell proliferation, tube formation, and VEGF production more effectively than cetuximab and CRM197 and that Y-142 was superior to bevacizumab in the inhibition of HB-EGF-induced tube formation. Six amino acids in the EGF-like domain were identified as the Y-142 binding epitope. Among the six amino acids, the combination of F115 and Y123 determined the amphiregulin cross-reactivity and that F115 accounted for the species selectivity. Furthermore, it was suggested that the potent neutralizing activity of Y-142 was derived from its recognition of R142 and Y123 and its high affinity to HB-EGF. Y-142 has a potent HB-EGF neutralizing activity that modulates multiple biological activities of HB-EGF including cancer cell proliferation and angiogenic activities. Y-142 may have a potential to be developed into a therapeutic agent for the treatment of HB-EGF-dependent cancers.

Tetraspanin CO-029 inhibits colorectal cancer cell movement by deregulating cell-matrix and cell-cell adhesions

Alterations in tetraspanin CO-029 expression are associated with the progression and metastasis of cancers in the digestive system. However, how CO-029 promotes cancer metastasis is still poorly understood. To determine the mechanism, we silenced CO-029 expression in HT29 colon cancer cells and found that the CO-029 knockdown significantly reduced cell migratory ability. The diminished cell migration was accompanied by the upregulation of both integrin-dependent cell-matrix adhesion on laminin and calcium-dependent cell-cell adhesion. The cell surface levels of laminin-binding integrin α3β1 and fibronectin-integrin α5β1 were increased while the level of CD44 was decreased upon CO-029 silencing. These changes contribute to the altered cell-matrix adhesion. The deregulated cell-cell adhesion results, at least partially, from increased activity of cadherins and reduced level of MelCAM. In conclusion, CO-029 functions as a regulator of both cell-matrix and cell-cell adhesion. During colon cancer progression, CO-029 promotes cancer cell movement by deregulating cell adhesions.

Feeder cells support the culture of induced pluripotent stem cells even after chemical fixation

Chemically fixed mouse embryonic fibroblasts (MEFs), instead of live feeder cells, were applied to the maintenance of mouse induced pluripotent stem (miPS) cells. Formaldehyde and glutaraldehyde were used for chemical fixation. The chemically fixed MEF feeders maintained the pluripotency of miPS cells, as well as their undifferentiated state. Furthermore, the chemically fixed MEF feeders were reused several times without affecting their functions. These results indicate that chemical fixation can be applied to modify biological feeders chemically, without losing their original functions. Chemically fixed MEF feeders will be applicable to other stem cell cultures as a reusable extracellular matrix candidate that can be preserved on a long-term basis.

Functional interplay between tetraspanins and proteases

Several recent publications have described examples of physical and functional interations between tetraspanins and specific membrane proteases belonging to the TM-MMP and α-(ADAMs) and γ-secretases families. Collectively, these examples constitute an emerging body of evidence supporting the notion that tetraspanin-enriched microdomains (TEMs) represent functional platforms for the regulation of key cellular processes including the release of surface protein ectodomains ("shedding"), regulated intramembrane proteolysis ("RIPing") and matrix degradation and assembly. These cellular processes in turn play a crucial role in an array of physiological and pathological phenomena. Thus, TEMs may represent new therapeutical targets that may simultaneously affect the proteolytic activity of different enzymes and their substrates. Agonistic or antagonistic antibodies and blocking soluble peptides corresponding to tetraspanin functional regions may offer new opportunities in the treatment of pathologies such as chronic inflammation, cancer, or Alzheimer's disease. In this review article, we will discuss all these aspects of functional regulation of protease activities by tetraspanins.

Efficient CRM197-mediated drug targeting to monocytes

Efficient delivery of drugs to specific cellular reservoirs is of particular importance for therapeutics that are not able to pass cellular barriers and that may have unwanted side effects in off-target tissues. Heparin-binding epidermal growth factor (HB-EGF) is expressed on leukocytes and may be targeted for specific drug delivery using cross-reacting material (CRM)197, a non-toxic variant of diphtheria toxin and exogenous substrate for HB-EGF. We used fluorescently labeled CRM197 and CRM197-coated liposomes to investigate their potential use for drug delivery to leukocytes. We demonstrate that CRM197-guided systems are efficiently taken up by human leukocytes in vitro. CRM197 was also found to specifically target leukocytes in vivo in mice with components of the human immune system (HIS mice) and hamsters. Monocytes represent the most prominent subset of leukocytes that showed highly specific CRM197-mediated uptake. We therefore propose the application of CRM197 as a novel targeting approach in diseases that require the selective treatment of monocytes.

Membrane proteases and tetraspanins

TEMs (tetraspanin-enriched microdomains) are specialized platforms in the plasma membrane that include adhesion receptors and enzymes. Insertion into TEMs dictates the local concentration of these molecules, regulates their internalization rate, their interaction and cross-talk with other receptors at the plasma membrane and provides links with certain signalling pathways. We focus on the associations described for tetraspanins with membrane proteases and their substrates, reviewing the emerging evidence in the literature that suggests that TEMs might be essential platforms for regulating protein shedding, RIP (regulated intramembrane proteolysis) and matrix degradation and assembly.

HB-EGF function in cardiac valve development requires interaction with heparan sulfate proteoglycans

HB-EGF, a member of the EGF family of growth factors, plays an important role in cardiac valve development by suppressing mesenchymal cell proliferation. Here, we show that HB-EGF must interact with heparan sulfate proteoglycans (HSPGs) to properly function in this process. In developing valves, HB-EGF is synthesized in endocardial cells but accumulates in the mesenchyme by interacting with HSPGs. Disrupting the interaction between HB-EGF and HSPGs in an ex vivo model of endocardial cushion explants resulted in increased mesenchymal cell proliferation. Moreover, homozygous knock-in mice (HBΔhb/Δhb) expressing a mutant HB-EGF that cannot bind to HSPGs developed enlarged cardiac valves with hyperproliferation of mesenchymal cells; this resulted in a phenotype that resembled that of Hbegf-null mice. Interestingly, although Hbegf-null mice had abnormal heart chambers and lung alveoli, HBΔhb/Δhb mice did not exhibit these defects. These results indicate that interactions with HSPGs are essential for the function of HB-EGF, especially in cardiac valve development, in which HB-EGF suppresses mesenchymal cell proliferation.

The tetraspanins CD9 and CD81 regulate CD9P1-induced effects on cell migration

CD9P-1 is a cell surface protein with immunoglobulin domains and an unknown function that specifically associates with tetraspanins CD9 and CD81. Overexpression of CD9P-1 in HEK-293 cells induces dramatic changes in cell spreading and migration on various matrices. Experiments using time-lapse videomicroscopy revealed that CD9P-1 expression has led to higher cell motility on collagen I but lower motility on fibronectin through a beta1-integrins dependent mechanism. On collagen I, the increase in cell motility induced by CD9P-1 expression was found to involve integrin alpha2beta1 and CD9P-1 was observed to associate with this collagen receptor. The generation of CD9P-1 mutants demonstrated that the transmembrane and the cytoplasmic domains are necessary for inducing effects on cell motility. On the other hand, expression of tetraspanins CD9 or CD81 was shown to reverse the effects of CD9P-1 on cell motility on collagen I or fibronectin with a concomitant association with CD9P-1. Thus, the ratio of expression levels between CD9P-1 and its tetraspanin partners can regulate cell motility.

Down-regulation of CD9 expression and its correlation to tumor progression in B lymphomas

Histological transformation, a pivotal event in the natural history of cancers including lymphomas, is typically associated with more aggressive clinical behavior. L3055, a B lymphoma cell line of germinal center (GC) origin, is dependent on follicular dendritic cells (FDCs) for survival and proliferation, similar to GC-B cells. However, L3055 cells become less FDC-dependent after prolonged culture, which is analogous to transformation in vivo. Comparison of two L3055 subclones (i.e., the FDC-dependent indolent clone 12 and the FDC-independent aggressive clone 33) by DNA microarray revealed that CD9 was the most differentially expressed gene (P = 0.05). L3055-12 expresses high levels of CD9 while L3055-33 does not. Reduced levels or loss of CD9 expression is also observed in other CD9-positive B lymphoma cell lines. The resultant CD9-negative cells grow faster than CD9-positive cells due to their greater resistance to apoptosis. Furthermore, CD9-negative cells are less dependent on FDCs for their survival and growth compared with CD9-positive cells. CD9 down-regulation in B lymphomas appears to be controlled epigenetically, mainly through histone modifications. These findings imply that CD9 is inversely correlated with B lymphoma progression, and CD9 inactivation may play an important role in B lymphoma transformation.

The heparin-binding domain of HB-EGF mediates localization to sites of cell-cell contact and prevents HB-EGF proteolytic release

Heparin-binding EGF-like growth factor (HB-EGF) is a ligand for EGF receptor (EGFR) and possesses the ability to signal in juxtacrine, autocrine and/or paracrine mode, with these alternatives being governed by the degree of proteolytic release of the ligand. Although the spatial range of diffusion of released HB-EGF is restricted by binding heparan-sulfate proteoglycans (HSPGs) in the extracellular matrix and/or cellular glycocalyx, ascertaining mechanisms governing non-released HB-EGF localization is also important for understanding its effects. We have employed a new method for independently tracking the localization of the extracellular EGF-like domain of HB-EGF and the cytoplasmic C-terminus. A striking observation was the absence of the HB-EGF transmembrane pro-form from the leading edge of COS-7 cells in a wound-closure assay; instead, this protein localized in regions of cell-cell contact. A battery of detailed experiments found that this localization derives from a trans interaction between extracellular HSPGs and the HB-EGF heparin-binding domain, and that disruption of this interaction leads to increased release of soluble ligand and a switch in cell phenotype from juxtacrine-induced growth inhibition to autocrine-induced proliferation. Our results indicate that extracellular HSPGs serve to sequester the transmembrane pro-form of HB-EGF at the point of cell-cell contact, and that this plays a role in governing the balance between juxtacrine versus autocrine and paracrine signaling.

The overexpression of heparin-binding epidermal growth factor is responsible for Th17-induced airway remodeling in an experimental asthma model

Th17 cells that produce IL-17 have been found to participate in the development of allergy-triggered asthma. However, whether they play a causative role in the pathogenesis of airway remodeling in chronic asthma remains unclear. In this study, we investigated the role of Th17 cells in airway remodeling and the possible involvement of epidermal growth factor (EGF) receptor signals downstream of Th17. We established a C57BL/6 mouse model of prolonged allergen challenge that exhibits many characteristics of airway remodeling. Prolonged allergen challenge induced a progressive increase in the number of airway-infiltrating Th17 cells, and Th17 counts positively correlated with the severity of airway remodeling. Increases in mucus production, airway smooth muscle (ASM) mass, peribronchial collagen deposition, and airway heparin-binding EGF (HB-EGF) expression have been observed in sensitized mice following prolonged allergen exposure or adoptive Th17 transfer; remarkably, these effects can be abrogated by treatment with anti-IL-17 mAb. Both the EFGR inhibitor AG1478 and an anti-HB-EGF mAb ameliorated all of these effects, except for peribronchial collagen deposition in the presence of high levels of IL-17. In vitro, Th17 cells enhanced the airway epithelial expression of HB-EGF in a coculture of the two cells. The conditioned medium obtained from this coculture system effectively promoted ASM proliferation; this response was dramatically abolished by anti-HB-EGF mAb but not Abs against other EGF receptor ligands or IL-17. These observations demonstrated that overexpression of airway HB-EGF induced by IL-17 secreted from redundant expanding Th17 cells might contribute to excessive mucus expression and ASM proliferation in chronic asthma.

Loss of Bicc1 impairs tubulomorphogenesis of cultured IMCD cells by disrupting E-cadherin-based cell-cell adhesion

The Bicaudal-C (Bic-C) gene was originally discovered in Drosophila melanogaster. The gene product Bic-C is thought to serve as an RNA-binding molecule targeting diverse proteins at the post-transcriptional level. Recent research has shown this gene to be conserved in many species, from Caenorhabditis elegans to humans. Disruption of this protein can disturb the normal migration direction of the anterior follicle cell of Drosophila oocytes, while mutation of a mouse Bicc1 (a mouse homologue of Bic-C) results in phenotypes mimicking human hereditary polycystic kidney disease (PKD). However, the cellular function of Bicc1 gene products in mammalian systems remains largely unknown. In this study, we established stable IMCD (mouse inner medullary collecting duct) cell lines, in which Bicc1 was silenced by short hairpin RNA inhibition (shRNA). We show that inhibition of Bicc1 disrupted normal tubulomorphogenesis and induced cystogenesis of IMCD cells grown in three dimensional cultures. To determine what factors contributed to the defect, we systematically examined biological changes of Bicc1-silenced IMCD cells. We found that the cells had significant defects in E-cadherin-based cell-cell adhesion, along with abnormalities in actin cytoskeleton organization, cell-extracellular matrix interactions, cell proliferation, and apoptosis. These findings suggest that lack of Bicc1 leads to disruption of normal cell-cell junctions, which in turn impedes establishment of epithelial polarity. These cellular defects may initiate abnormal tubulomorphogenesis and cystogenesis of IMCD cells grown in vitro. The observation of aberrant cellular behaviors in Bicc1-silenced IMCD cells reveal functions for Bicc1 in renal epithelial cells and provides insight into a potential pathogenic mechanism of polycystic kidney disease.