Regulation offlotillin-1in the establishment of NIH-3T3 cell-cell interactions1

Simultaneous expression of flotillin-1, flotillin-2, stomatin and caveolin-1 in non-small cell lung cancer and soft tissue sarcomas

BACKGROUND

At the present time, there is a lack of data about the involvement of flotillins and stomatin in the development of non-small cell lung cancer (NSCLC) and soft tissue sarcomas (STS). Moreover, changes in expression of members of different families of the microdomain-forming proteins (caveolins and SPFH-domain containing family) are usually investigated independently of each other. In this study we performed a combined analysis of flotillins, stomatin, and caveolin-1 expression in these pathologies and evaluated correlations between generated data and clinicopathological characteristics of the specimens.

METHODS

The protein and mRNA expression was analyzed by Western blotting and real-time PCR, respectively, in tissue specimens of patients undergoing surgery for non-small cell lung cancer and soft tissue sarcomas. Association between expression of studied proteins and patient clinicopathological characteristics or outcome was evaluated.

RESULTS

Stomatin protein expression was down-regulated in 80% of NSCLC samples and this decrease significantly associated with presence of lymph node metastases. Flotillin-2 protein expression was up-regulated in the majority of NSCLC samples whereas caveolin-1α expression was decreased. We revealed a strong correlation between STOM and FLOT-1 mRNA expression in both pathologies, although the gene expression changes were diverse.

CONCLUSIONS

Our data demonstrate for the first time that expression of stomatin, a poorly studied microdomain-forming protein, significantly changes in human tumors, thus pointing to its importance in the progression of NSCLC. We also suggest the existence of some relationship between the expression of these proteins.

Transcriptional regulation of flotillins by the extracellularly regulated kinases and retinoid X receptor complexes

Flotillin-1 and flotillin-2 are important regulators of signal transduction pathways such as growth factor signaling. Flotillin expression is increased under pathological conditions such as neurodegenerative disorders and cancer. Despite their importance for signal transduction, very little is known about the transcriptional regulation of flotillins. Here, we analyzed the expression of flotillins at transcriptional level and identified flotillins as downstream targets of the mitogen activated kinases ERK1/2. The promoter activity of flotillins was increased upon growth factor stimulation in a MAPK dependent manner. Overexpression of serum response factor or early growth response gene 1 resulted in increased flotillin mRNA and protein expression. Furthermore, both promoter activity and expression of endogenous flotillins were increased upon treatment with retinoic acid or by overexpression of the retinoid X receptor and its binding partners RARα and PPARγ. Our data indicate that the expression of flotillins, which can be detected in all cultured cells, is fine-tuned in response to various external stimuli. This regulation may be critical for the outcome of signaling cascades in which flotillins are known to be involved.

Enterocytic differentiation is modulated by lipid rafts-dependent assembly of adherens junctions

Integrity of the epithelial barrier is determined by apical junctional complexes which also participate in the signalling pathways inducing intestinal cell differentiation. Lipid rafts (LR) have been proposed to play a role in the organization and the function of these intercellular complexes. This study investigated potential mechanisms by which LR could participate in the establishment of adherens junctions (AJ) and the initiation of enterocytic differentiation. We showed that the differentiation of epithelial cells in rat colons correlates with the emergence of LR. Using HT-29 cells we demonstrated that during the differentiation process, LR are required for the recruitment and the association of p120ctn to E-cadherin. Silencing of flotillin-1, a LR component, alters the recruitment of AJ proteins in LR and delays the expression of differentiation markers. Furthermore, the ability of p120ctn/E-cadherin complexes to support cell differentiation is altered in HT-29 Rac1N17 cells. These results show a contributory role of LR in the enterocytic differentiation process, which serve as signalling platforms for Rac1-mediated organization of AJ. A better understanding of the mechanism involved in the establishment of junctional complex and their role in enterocytic differentiation provides new insights into the regulation of intestinal homeostasis.

Flotillins are involved in the polarization of primitive and mature hematopoietic cells

Background

Migration of mature and immature leukocytes in response to chemokines is not only essential during inflammation and host defense, but also during development of the hematopoietic system. Many molecules implicated in migratory polarity show uniform cellular distribution under non-activated conditions, but acquire a polarized localization upon exposure to migratory cues.

Methodology/Principal Findings

Here, we present evidence that raft-associated endocytic proteins (flotillins) are pre-assembled in lymphoid, myeloid and primitive hematopoietic cells and accumulate in the uropod during migration. Furthermore, flotillins display a polarized distribution during immunological synapse formation. Employing the membrane lipid-order sensitive probe Laurdan, we show that flotillin accumulation in the immunological synapse is concomittant with membrane ordering in these regions.

Conclusions

Together with the observation that flotillin polarization does not occur in other polarized cell types such as polarized epithelial cells, our results suggest a specific role for flotillins in hematopoietic cell polarization. Based on our results, we propose that in hematopoietic cells, flotillins provide intrinsic cues that govern segregation of certain microdomain-associated molecules during immune cell polarization.

Ethanol mimics ligand-mediated activation and endocytosis of IL-1RI/TLR4 receptors via lipid rafts caveolae in astroglial cells

We have recently reported that ethanol-induced inflammatory processes in the brain and glial cells are mediated via the activation of interleukin-1 beta receptor type I (IL-1RI)/toll-like receptor type 4 (TLR4) signalling. The mechanism(s) by which ethanol activates these receptors in astroglial cells remains unknown. Recently, plasma membrane microdomains, lipid rafts, have been identified as platforms for receptor signalling and, in astrocytes, rafts/caveolae constitute an important integrators of signal events and trafficking. Here we show that stimulation of astrocytes with IL-1beta, lipopolysaccharide or ethanol (10 and 50 mM), triggers the translocation of IL-1RI and/or TLR4 into lipid rafts caveolae-enriched fractions, promoting the recruitment of signalling molecules (phospho-IL-1R-associated kinase and phospho-extracellular regulated-kinase) into these microdomains. With confocal microscopy, we further demonstrate that IL-1RI is internalized by caveolar endocytosis via enlarged caveosomes organelles upon IL-1beta or ethanol treatment, which sorted their IL-1RI cargo into the endoplasmic reticulum-Golgi compartment and into the nucleus of astrocytes. In short, our findings demonstrate that rafts/caveolae are critical for IL-1RI and TLR4 signalling in astrocytes, and reveal a novel mechanism by which ethanol, by interacting with lipid rafts caveolae, promotes IL-1RI and TLR4 receptors recruitment, triggering their endocytosis via caveosomes and downstream signalling stimulation. These results suggest that TLRs receptors are important targets of ethanol-induced inflammatory damage in the brain.

Changes in Vinexin Expression Patterns in the Mouse Testis Induced by Developmental Exposure to 17Beta-Estradiol1

In the seminiferous epithelium, numerous cell interactions between Sertoli cells and Sertoli-germ cells are established by specialized proteins so as to maintain the functionality of the testis. Exogenous estrogen exposure can result in alterations to these interactions and cause pathologies, including impaired spermatogenesis and tumorigenesis. In the present study, with the aim of finding markers of the action of estrogenic compounds in the mammalian testis, we focused on investigating molecules that are linked to cellular junctions. We found that the testicular vinexin (sorbin and SH3 domain-containing protein 3, encoded by the Sorbs3 gene) pattern underwent significant changes after developmental exposure to 17beta-estradiol (E(2)). Vinexin is an adaptor protein that is implicated in cell adhesion and actin-cytoskeletal reorganization. We characterized, at the protein and mRNA levels, the expression patterns of vinexin isoforms during testis development and in defined cell types from the seminiferous tubule. The protein expression patterns of vinexin-interacting proteins flotillin 1 and vinculin were also analyzed. Thus, we have identified a novel association between a vinexin isoform and germ cells, which contrasts with the predominant localization of the gamma isoform in Sertoli cells. The effects of E(2) on the testes of developmentally exposed mice were evident, with total depletion of the germ-cell-associated vinexin isoform and a noticeable decrease in Sertoli-cell-related vinexin gamma.

Flotillin-1 localization on sporozoites oF Eimeria tenella

In an attempt to identify parasite surface components involved in the interaction with the host cell, the present research focuses on the rafts of Eimeria tenella that might be involved in the host cell invasion process. To that end, this study was undertaken to investigate the expression of flotillin-1, which is an important component and marker of lipid rafts at the plasma membrane of sporozoites of E. tenella. The expression of this plasma membrane protein was identified by an antibody that specifically reacts with flotillin- and was studied by electron microscopy. Flotillin-1 was found to occur in patches on the surface of E. tenella sporozoites. Immunoblot analysis of the total proteins of the sporozoites showed only 1 band of approximately 48 kDa. This indicates that the antibody exclusively recognized the molecules of flotillin-1 expressed on the surface of E. tenella sporozoites. The presence of flotillin-1 on the cellular membrane of sporozoites predominantly at the apical tip suggests that flotillin-1 belongs to the invasion machinery of E. tenella.

EXPRESSION OF FLOTILLIN-1 ON EIMERIA TENELLA SPOROZOITES AND ITS ROLE IN HOST CELL INVASION

Lipid rafts are detergent-resistant, liquid-ordered microdomains in plasma membranes that are enriched in cholesterol and sphingolipids and involved in intracellular signal transduction, membrane trafficking, and molecular sorting. In this study, we investigated the possibility that lipid rafts on Eimeria tenella sporozoites may act as platforms for host cell invasion. Flotillin-1, a resident protein of lipid rafts, was identified on E. tenella sporozoites and was prominently expressed at the apex of the cells, a region mediating host cell invasion. Pretreatment of sporozoites with antibody against flotillin-1 blocked parasite invasion. Furthermore, the anticoccidial drug, monensin, disrupted the localization of flotillin-1 within raft structures resulting in loss of invasion. We conclude that Eimeria sporozoites utilize lipid rafts containing flotillin-1 for internalization into host cells.

Loss- and gain-of-function analysis of the lipid raft proteins Reggie/Flotillin in Drosophila: They are posttranslationally regulated, and misexpression interferes with wing and eye development

Reggie/Flotillin proteins are upregulated after optic nerve dissection and evolutionary highly conserved components of lipid rafts. Whereas many biochemical and cell culture studies suggest an involvement in the assembly of multiprotein complexes at cell contact sites, not much is known about their biological in vivo functions. We therefore set out to study the expression pattern and the effects of loss- and gain-of-function in the Drosophila melanogaster model system. We found that in flies these proteins are mainly expressed in axons at the root of fiber tracts, in places where strong fasciculation is required, e.g. at the neck of the peduncle of the mushroom bodies and in the optic chiasms. Despite their evolutionary conservation which implies fundamental and important functions, a P-element-induced null mutant (KG00210) of reggie1/flotillin2 (reggie1/flo2) in D. melanogaster shows no apparent phenotypic defects. This was even more surprising as we show that in this reggie1/flo2 null mutant the paralogous Reggie2/Flo1 protein is unstable and degraded, while the transcript is still present. The requirement of Reggie1/Flo2 for Reggie2/Flo1 stabilization is confirmed by misexpression experiments. Reggie2/Flo1 can only be misexpressed when Reggie1/Flo2 is provided as well. Conversely, Reggie1/Flo2 immunoreactivity can be detected, when its transgene is misexpressed alone. Using appropriate Gal4 driver lines, misexpression of Reggie1/Flo2 alone or together with Reggie2/Flo1 in the eye imaginal disc results in a specific and severe mislocalization of cell adhesion molecules of the immunoglobulin superfamily (IgCAMs) (while DE-Cadherin is unaffected) and in differentiation defects pointing to impaired signaling. In the wing imaginal disc, global overexpression of Reggie/Flotillin proteins leads to a significant extension of the Wingless signal and severely disrupts normal wing development. Our data support the notion that Reggie/Flotillin proteins are implicated in signaling processes at cellular contact sites.

Identification of CCR2, flotillin, and gp49B genes as new G-CSF targets during neutrophilic differentiation

Granulocyte colony-stimulating factor (G-CSF) is a cytokine that stimulates myeloid progenitor cells to proliferate and differentiate into neutrophilic granulocytes. To identify genes induced by G-CSF during neutrophil differentiation, interleukin-3-dependent murine myeloid precursor FDC-P1 cells expressing the G-CSF receptor were stimulated with G-CSF, and the gene expression profile was characterized by DNA microarray analysis. In addition to known signal transducer and activator of transcription-3 target genes, such as suppressor of cytokine signaling-3 (SOCS3), JunB, and p19(INK4D), we newly identified several G-CSF targets, including genes for the CC chemokine receptor-2 (CCR2), raft proteins flotillin-1 and flotillin-2, and immunoglobulin-like receptor gp49B. Real-time, quantitative polymerase chain reaction analyses revealed that the expression of these genes was induced in various myeloid cell lines by G-CSF. Furthermore, when HoxA9-immortalized bone marrow progenitors were induced by G-CSF to differentiate into mature neutrophils, all of these genes were strongly activated. These genes could be categorized into three groups based on their time-course of expression: immediate-early (approximately 20 min, SOCS3), mid-early (2-4 h, flotillin-1/2 and gp49B), and late (>12 h, CCR2). This suggests that different transcriptional mechanisms are involved in the regulation of these genes. We show that bone marrow neutrophils express functional CCR2, which suggest that CC chemokines may play previously unknown roles in neutrophil activation and chemotaxis.

Restricted expression of reggie genes and proteins during early zebrafish development

Reggies are plasma membrane-associated proteins and characteristic markers of lipid-raft microdomains. They are highly conserved from flies to humans and have been implicated in axon regeneration and cell process and contact formation, possibly providing functional platforms for cell-signaling in neurons and other cell types. We analyzed reggie mRNA and protein expression patterns during early zebrafish development. All three zebrafish genes, re-1a, -2a, and -2b, span a considerably diverse set of expression patterns, and their proteins are induced maternally, showing ubiquitous expression at early stages. Although re-2a mRNA can be observed in differentiating neurons in the brain, spinal cord, and neurogenic placodes, re-2b is transcribed mainly in head mesoderm, in neural crest derivates, and along somite boundaries. re-1a mRNA is present at high levels in expression domains that overlap with the combined expression pattern of both re-2 genes except at the somites, where it complements the pattern of re-2b. Immunostaining on embryos reveals reggie protein localization at the cell membrane, at cell-cell contacts, and along all early axon tracts. The early phase of reggie expression suggests a basic and ubiquitous function during the first stages of embryogenesis and into the gastrula period. Upon segmentation, a second phase of expression shows distinctly localized expression patterns, indicating tissue-specific roles and an involvement of re-1a/re-2a in neural development.

A simplified method for the preparation of detergent-free lipid rafts

Lipid rafts are small plasma membrane domains that contain high levels of cholesterol and sphingolipids. Traditional methods for the biochemical isolation of lipid rafts involve the extraction of cells with nonionic detergents followed by the separation of a low-density, detergent-resistant membrane fraction on density gradients. Because of concerns regarding the possible introduction of artifacts through the use of detergents, it is important to develop procedures for the isolation of lipid rafts that do not involve detergent extraction. We report here a simplified method for the purification of detergent-free lipid rafts that requires only one short density gradient centrifugation, but yields a membrane fraction that is highly enriched in cholesterol and protein markers of lipid rafts, with no contamination from nonraft plasma membrane or intracellular membranes.

Lipid rafts-protein association and the regulation of protein activity

Lipid rafts are membrane microdomains enriched in saturated phospholipids, sphingolipids, and cholesterol. They have a varied but distinct protein composition and have been implicated in diverse cellular processes including polarized traffic, signal transduction, endo- and exo-cytoses, entrance of obligate intracellular pathogens, and generation of pathological forms of proteins associated with Alzheimer's and prion diseases. Raft proteins can be permanently or temporarily associated to lipid rafts. Here, we review recent advances on the biochemical and cell biological characterization of rafts, and on the emerging concept of the temporary residency of proteins in rafts as a regulatory mechanism of their biological activity.