Protein 4.1R regulates cell adhesion, spreading, migration and motility of mouse keratinocytes by modulating surface expression of beta1 integrin

Cytoskeletal Protein 4.1R in Health and Diseases

The protein 4.1R is an essential component of the erythrocyte membrane skeleton, serving as a key structural element and contributing to the regulation of the membrane's physical properties, including mechanical stability and deformability, through its interaction with spectrin-actin. Recent research has uncovered additional roles of 4.1R beyond its function as a linker between the plasma membrane and the membrane skeleton. It has been found to play a crucial role in various biological processes, such as cell fate determination, cell cycle regulation, cell proliferation, and cell motility. Additionally, 4.1R has been implicated in cancer, with numerous studies demonstrating its potential as a diagnostic and prognostic biomarker for tumors. In this review, we provide an updated overview of the gene and protein structure of 4.1R, as well as its cellular functions in both physiological and pathological contexts.

The Role of Cytoskeleton Protein 4.1 in Immunotherapy

Cytoskeleton protein 4.1 is an essential class of skeletal membrane protein, initially found in red blood cells, and can be classified into four types: 4.1R (red blood cell type), 4.1N (neuronal type), 4.1G (general type), and 4.1B (brain type). As research progressed, it was discovered that cytoskeleton protein 4.1 plays a vital role in cancer as a tumor suppressor. Many studies have also demonstrated that cytoskeleton protein 4.1 acts as a diagnostic and prognostic biomarker for tumors. Moreover, with the rise of immunotherapy, the tumor microenvironment as a treatment target in cancer has attracted great interest. Increasing evidence has shown the immunoregulatory potential of cytoskeleton protein 4.1 in the tumor microenvironment and treatment. In this review, we discuss the role of cytoskeleton protein 4.1 within the tumor microenvironment in immunoregulation and cancer development, with the intention of providing a new approach and new ideas for future cancer diagnosis and treatment.

Suppression of 4.1R enhances the potency of NKG2D-CAR T cells against pancreatic carcinoma via activating ERK signaling pathway

Pancreatic carcinoma (PC) is one of the most common malignancies. Chimeric antigen receptor (CAR)-modified T cells has achieved remarkable efficacy in the treatment of hematological malignancies. However, lack of tumor-specific targets and the existence of inhibitory factors limit the function of CAR T cells when treating solid tumors. 4.1R has been reported to suppress the anti-tumor activity of T cell responses. In this study, we investigated the anti-tumor activity of 4.1R deletion in natural killer group 2D (NKG2D)-CAR T cells against PC. The CAR T cells were obtained by transfecting T cells with lentiviral vector carrying NKG2D-CAR, NC-NKG2D-CAR, or KD2-NKG2D-CAR. In vitro, NKG2D-CAR T cells showed higher cytotoxicity than Mock T cells. However, compared to NKG2D-CAR T cells, furtherly higher cytotoxicity against PC cells in a dose-dependent manner was found in KD2-NKG2D-CAR T cells. In addition, the proliferation rate and cytotoxic activity of KD2-NKG2D-CAR T cells were significantly higher than those of NKG2D-CAR T cells. Besides, the inhibitory receptors PD-1 and TIM-3 were expressed in lower level on KD2-NKG2D-CAR T cells. In vivo, KD2-NKG2D-CAR T cells suppressed tumor growth more effectively in a xenograft model compared to NKG2D-CAR T cells. Mechanistically, 4.1R regulated CAR T cell function via activating ERK signaling pathway. Therefore, the study provides a new idea to enhance the anti-tumor efficiency of CAR T therapy.

Protein 4.1R negatively regulates P815 cells proliferation by inhibiting C-Kit-mediated signal transduction

The proliferation of mast cells (MCs) plays a crucial role in either physiological or pathological progression of human physical. C-Kit-mediated signaling pathway has been confirmed to play a key role in MCs proliferation, and the regulatory mechanisms of C-Kit-mediated MCs proliferation need to be further explored. Our previous study found that protein 4.1R could negatively regulate T cell receptor (TCR) mediated signal pathways in CD4+ T cells. Little is known about the function of 4.1R in C-Kit-mediated proliferation of MCs. In this study, P815-4.1R-/- cells were constructed by using CRISPR/Cas9 technique. Lack of 4.1R significantly enhanced P815 cells proliferation by accelerating the progression of cell cycle. 4.1R could also significantly alleviate the clinical symptoms of systemic mastocytosis (SM) and improve the overall survival of SM mice. Further study showed that 4.1R could interact directly with C-Kit to inhibit the activation of C-Kit-mediated Ras-Raf-MAPKs and PI3K-AKT signal pathways. Taken together, our findings demonstrate that protein 4.1R, a novel negative regulator, negatively regulates MCs proliferation by inhibiting C-Kit-mediated signal transduction, which maybe provide a potential target to the prevention and treatment of abnormal MCs proliferation-related diseases.

Silencing EPB41 Gene Expression Leads to Cell Cycle Arrest, Migration Inhibition, and Upregulation of Cell Surface Antigen in DC2.4 Cells

BACKGROUND Protein 4.1R (EPB41) is the main cytoskeleton component of the erythrocyte membrane and may be involved in cell migration and adhesion. Previous research discovered overexpression of 4.1R in the thymus of patients with myasthenia gravis (MG). The protein 4.1R on dendritic cells may play a pivotal role in MG pathogenesis. This research investigated the effects of small interfering RNA 4.1R-siRNA on cell migration, cell cycle, and surface antigen expression of DC2.4 mouse dendritic cells, thus providing a new direction for the study of MG pathogenesis. MATERIAL AND METHODS Three 4.1R-specific siRNAs were designed, and the expression of 4.1R was detected by real-time PCR at the mRNA level and Western blot analysis at the protein level to select out the most efficient siRNAs. Changes in cell morphology were observed and cell migration ability was analyzed by Transwell assay. Cell cycle and surface antigen were both analyzed by flow cytometry. RESULTS The cell bodies of DC2.4 diminished, the synapses were increased, and protuberance became more obvious after being transfected with 4.1R-siRNA. After knockdown of 4.1R, cell migration ability decreased and the proportion of cells in S phase significantly increased (both P<0.05). The expression levels of MHCII, CD80, and CD86 were all increased in DC2.4 cells (all <0.05). CONCLUSIONS Silencing the expression of 4.1R in dendritic cells resulted in inhibition of migration ability, cell cycle arrest, and increase in surface antigens, which suggest that 4.1R participates in MG autoimmunity.

Deficiency of αII-spectrin affects endothelial cell-matrix contact and migration leading to impairment of angiogenesis in vitro

Background

Precise coordination of cytoskeletal components and dynamic control of cell adhesion and migration are required for crucial cell processes such as differentiation and morphogenesis. We investigated the potential involvement of αII-spectrin, a ubiquitous scaffolding element of the membrane skeleton, in the adhesion and angiogenesis mechanism.

Methods

The cell models were primary human umbilical vein endothelial cells (HUVECs) and a human dermal microvascular endothelial cell line (HMEC-1). After siRNA- and shRNA-mediated knockdown of αII-spectrin, we assessed its expression and that of its partners and adhesion proteins using western blotting. The phenotypes of the control and spectrin-depleted cells were examined using immunofluorescence and video microscopy. Capillary tube formation was assessed using the thick gel Matrigel matrix-based method and a microscope equipped with a thermostatic chamber and a Nikon Biostation System camera.

Results

Knockdown of αII-spectrin leads to: modified cell shape; actin cytoskeleton organization with the presence of peripheral actin patches; and decreased formation of stress fibers. Spectrin deficiency affects cell adhesion on laminin and fibronectin and cell motility. This included modification of the localization of adhesion molecules, such as αVβ3- and α5-integrins, and organization of adhesion structures, such as focal points. Deficiency of αII-spectrin can also affect the complex mechanism of in vitro capillary tube formation, as demonstrated in a model of angiogenesis. Live imaging revealed that impairment of capillary tube assembly was mainly associated with a significant decrease in cell projection length and stability. αII-spectrin depletion is also associated with significantly decreased expression of three proteins involved in capillary tube formation and assembly: VE-cadherin, MCAM and β3-integrin.

Conclusion

Our data confirm the role of αII-spectrin in the control of cell adhesion and spreading. Moreover, our findings further support the participation of αII-spectrin in capillary tube formation in vitro through control of adhesion molecules, such as integrins. This indicates a new function of αII-spectrin in angiogenesis.

Cytoskeletal Protein 4.1R Is a Positive Regulator of the FcεRI Signaling and Chemotaxis in Mast Cells

Protein 4.1R, a member of the 4.1 family, functions as a bridge between cytoskeletal and plasma membrane proteins. It is expressed in T cells, where it binds to a linker for activation of T cell (LAT) family member 1 and inhibits its phosphorylation and downstream signaling events after T cell receptor triggering. The role of the 4.1R protein in cell activation through other immunoreceptors is not known. In this study, we used 4.1R-deficient (4.1R-KO) and 4.1R wild-type (WT) mice and explored the role of the 4.1R protein in the high-affinity IgE receptor (FcεRI) signaling in mast cells. We found that bone marrow mast cells (BMMCs) derived from 4.1R-KO mice showed normal growth in vitro and expressed FcεRI and c-KIT at levels comparable to WT cells. However, 4.1R-KO cells exhibited reduced antigen-induced degranulation, calcium response, and secretion of tumor necrosis factor-α. Chemotaxis toward antigen and stem cell factor (SCF) and spreading on fibronectin were also reduced in 4.1R-KO BMMCs, whereas prostaglandin E₂-mediated chemotaxis was not affected. Antibody-induced aggregation of tetraspanin CD9 inhibited chemotaxis toward antigen in WT but not 4.1R-KO BMMCs, implying a CD9-4.1R protein cross-talk. Further studies documented that in the absence of 4.1R, antigen-mediated phosphorylation of FcεRI β and γ subunits was not affected, but phosphorylation of SYK and subsequent signaling events such as phosphorylation of LAT1, phospholipase Cγ1, phosphatases (SHP1 and SHIP), MAP family kinases (p38, ERK, JNK), STAT5, CBL, and mTOR were reduced. Immunoprecipitation studies showed the presence of both LAT1 and LAT2 (LAT, family member 2) in 4.1R immunocomplexes. The positive regulatory role of 4.1R protein in FcεRI-triggered activation was supported by in vivo experiments in which 4.1R-KO mice showed the normal presence of mast cells in the ears and peritoneum, but exhibited impaired passive cutaneous anaphylaxis. The combined data indicate that the 4.1R protein functions as a positive regulator in the early activation events after FcεRI triggering in mast cells.

Cell Adhesion by Integrins

Integrins are heterodimeric cell surface receptors ensuring the mechanical connection between cells and the extracellular matrix. In addition to the anchorage of cells to the extracellular matrix, these receptors have critical functions in intracellular signaling, but are also taking center stage in many physiological and pathological conditions. In this review, we provide some historical, structural, and physiological notes so that the diverse functions of these receptors can be appreciated and put into the context of the emerging field of mechanobiology. We propose that the exciting journey of the exploration of these receptors will continue for at least another new generation of researchers.

[Construction of a stable 4.1R gene knockout cell model in RAW264.7 cells using CRISPR/Cas9 technique]

OBJECTIVE

To construct a cell model of 4.1R gene knockout in murine macrophage cell line RAW264.7 using CRISPR/Cas9 technique.

METHODS

Three high?grade small?guide RNAs (sgRNAs) that could specifically identify 4.1R gene were synthesized and inserted into lentiCRISPRv2 plasmid. RAW264.7 cells were infected with sgRNA?Cas9 lentivirus from 293T cells transfected with the recombinant sgRNA?lentiCRISPRv2 plasmid, and the positive cells were screened using puromycin and the monoclonal cells were obtained. The expression of 4.1R protein in the monoclonal cells was measured by Western blotting, and the mutation site was confirmed by sequence analysis. Result A 4.1R gene knockout RAW264.7 cell line was obtained, which showed a 19?bp deletion mutation in the 4.1R gene sequence and obviously enhanced proliferation.

CONCLUSION

We successfully constructed a 4.1R gene knockout macrophage cell line using CRISPR/Cas9 technique, which may facilitate further investigation of the function of 4.1R in macrophages.

[Construction of a stable 4.1R gene knockout cell model in RAW264.7 cells using CRISPR/Cas9 technique]

OBJECTIVE

To construct a cell model of 4.1R gene knockout in murine macrophage cell line RAW264.7 using CRISPR/Cas9 technique.

METHODS

Three high?grade small?guide RNAs (sgRNAs) that could specifically identify 4.1R gene were synthesized and inserted into lentiCRISPRv2 plasmid. RAW264.7 cells were infected with sgRNA?Cas9 lentivirus from 293T cells transfected with the recombinant sgRNA?lentiCRISPRv2 plasmid, and the positive cells were screened using puromycin and the monoclonal cells were obtained. The expression of 4.1R protein in the monoclonal cells was measured by Western blotting, and the mutation site was confirmed by sequence analysis. Result A 4.1R gene knockout RAW264.7 cell line was obtained, which showed a 19?bp deletion mutation in the 4.1R gene sequence and obviously enhanced proliferation.

CONCLUSION

We successfully constructed a 4.1R gene knockout macrophage cell line using CRISPR/Cas9 technique, which may facilitate further investigation of the function of 4.1R in macrophages.

Kindlin-1 contributes to EGF-induced re-epithelialization in skin wound healing

The commercial use of epidermal growth factor (EGF) is extensive and has been shown to be effective for skin wound healing in clinical practice. There is evidence to indicate that the topical administration of EGF significantly accelerates re-epithelialization by promoting keratinocyte mitogenesis and migration following acute injury; however, the mechanisms involved remain to be elucidated. Thus, in this study, we focused on Kindlin-1, a four-point-one, ezrin, radixin, moesin (FERM)-domain-containing adaptor protein, and report its contribution to EGF-induced re-epithelialization in skin wound healing. In tissue samples, the expression of Kindlin-1 was induced upon EGF treatment compared to that in the natural healing group. In immortalized human keratinocytes (HaCaT cells), we further proved that Kindlin-1 was necessary for mediating EGF-induced activation signals, including integrin β1 activation, focal adhesion kinase (FAK) phosphorylation and actin re-organization, which finally led to enhanced cell proliferation and migration. These results indicate that Kindlin-1 is essential in EGF-induced re-epithelialization in skin wound healing and provide additional rationale for the clinical application of EGF in the treatment of acute wounds.

Alternative polyadenylation in a family of paralogous EPB41 genes generates protein 4.1 diversity

Alternative polyadenylation (APA) is a step in mRNA 3'-end processing that contributes to the complexity of the transcriptome by generating isoforms that differ in either their coding sequence or their 3'-untranslated regions (UTRs). The EPB41 genes, EPB41, EPB41L2, EPB41L3 and EPB41L1, encode an impressively complex array of structural adaptor proteins (designated 4.1R, 4.1G, 4.1B and 4.1N, respectively) by using alternative transcriptional promoters and tissue-specific alternative pre-mRNA splicing. The great variety of 4.1 proteins mainly results from 5'-end and internal processing of the EPB41 pre-mRNAs. Thus, 4.1 proteins can vary in their N-terminal extensions but all contain a highly homologous C-terminal domain (CTD). Here we study a new group of EPB41-related mRNAs that originate by APA and lack the exons encoding the CTD characteristic of prototypical 4.1 proteins, thereby encoding a new type of 4.1 protein. For the EPB41 gene, this type of processing was observed in all 11 human tissues analyzed. Comparative genomic analysis of EPB41 indicates that APA is conserved in various mammals. In addition, we show that APA also functions for the EPB41L2, EPB41L3 and EPB41L1 genes, but in a more restricted manner in the case of the latter 2 than it does for the EPB41 and EPB41L2 genes. Our study shows alternative polyadenylation to be an additional mechanism for the generation of 4.1 protein diversity in the already complex EPB41-related genes. Understanding the diversity of EPB41 RNA processing is essential for a full appreciation of the many 4.1 proteins expressed in normal and pathological tissues.

Epithelial deletion of podoplanin is dispensable for re-epithelialization of skin wounds

The mucin-like transmembrane protein podoplanin (PDPN) is prominently represented in tumor-associated gene expression signatures of numerous types of cancer including squamous cell carcinoma, and gain-of-function and knockdown approaches in tissue culture strongly suggested an important role of PDPN in cell proliferation, migration and adhesion. PDPN is absent during epidermal homeostasis but is highly expressed in basal keratinocytes during cutaneous wound healing. Enhanced motility of immortalized keratinocytes upon ectopic PDPN overexpression argues for wound healing defects upon podoplanin deficiency in keratinocytes; however, in vivo data that unequivocally define the impact of PDPN by functional studies in a physiologically relevant system are still missing. Here, we have applied an in vivo loss-of-function approach by generating a novel transgenic mouse line with keratinocyte-specific podoplanin deficiency. Performing cutaneous full-thickness excisional wounds to examine re-epithelialization capacity, unexpectedly, no defects were observed in wound healing properties of mutant mice. Similarly, PDPN-deficient primary keratinocytes showed no impairment in migration, adhesion or proliferation. Thus, PDPN function is not rate-limiting for re-epithelialization but may be functionally compensated by an as yet unknown protein. Our data also call for in vivo functional studies on PDPN in settings of skin tumor development and progression to clarify PDPN's role in skin pathology.

Proximity biotinylation provides insight into the molecular composition of focal adhesions at the nanometer scale

Focal adhesions are protein complexes that link metazoan cells to the extracellular matrix through the integrin family of transmembrane proteins. Integrins recruit many proteins to these complexes, referred to as the "adhesome." We used proximity-dependent biotinylation (BioID) in U2OS osteosarcoma cells to label proteins within 15 to 25 nm of paxillin, a cytoplasmic focal adhesion protein, and kindlin-2, which directly binds β integrins. Using mass spectrometry analysis of the biotinylated proteins, we identified 27 known adhesome proteins and 8 previously unknown components close to paxillin. However, only seven of these proteins interacted directly with paxillin, one of which was the adaptor protein Kank2. The proteins in proximity to β integrin included 15 of the adhesion proteins identified in the paxillin BioID data set. BioID also correctly established kindlin-2 as a cell-cell junction protein. By focusing on this smaller data set, new partners for kindlin-2 were found, namely, the endocytosis-promoting proteins liprin β1 and EFR3A, but, contrary to previous reports, not the filamin-binding protein migfilin. A model adhesome based on both data sets suggests that focal adhesions contain fewer components than previously suspected and that paxillin lies away from the plasma membrane. These data not only illustrate the power of using BioID and stable isotope-labeled mass spectrometry to define macromolecular complexes but also enable the correct identification of therapeutic targets within the adhesome.

Protein 4.1G Regulates Cell Adhesion, Spreading, and Migration of Mouse Embryonic Fibroblasts through the β1 Integrin Pathway

Protein 4.1G is a membrane skeletal protein that can serve as an adapter between transmembrane proteins and the underlying membrane skeleton. The function of 4.1G remains largely unexplored. Here, using 4.1G knockout mouse embryonic fibroblasts (MEFs) as a model system, we explored the function of 4.1G in motile cells. We show that the adhesion, spreading, and migration of 4.1G(-/-) MEF cells are impaired significantly. We further show that, although the total cellular expression of β1 integrin is unchanged, the surface expression of β1 integrin and its active form are decreased significantly in 4.1G(-/-) MEF cells. Moreover, the phosphorylation of focal adhesion kinase, a downstream component of the integrin-mediated signal transduction pathway, is suppressed in 4.1G(-/-) MEF cells. Co-immunoprecipitation experiments and in vitro binding assays showed that 4.1G binds directly to β1 integrin via its membrane-binding domain. These findings identified a novel role of 4.1G in cell adhesion, spreading, and migration in MEF cells by modulating the surface expression of β1 integrin and subsequent downstream signal transduction.

αII-spectrin regulates invadosome stability and extracellular matrix degradation

Invadosomes are actin-rich adhesion structures involved in tissue invasion and extracellular matrix (ECM) remodelling. αII-Spectrin, an ubiquitous scaffolding component of the membrane skeleton and a partner of actin regulators (ABI1, VASP and WASL), accumulates highly and specifically in the invadosomes of multiple cell types, such as mouse embryonic fibroblasts (MEFs) expressing SrcY527F, the constitutively active form of Src or activated HMEC-1 endothelial cells. FRAP and live-imaging analysis revealed that αII-spectrin is a highly dynamic component of invadosomes as actin present in the structures core. Knockdown of αII-spectrin expression destabilizes invadosomes and reduces the ability of the remaining invadosomes to digest the ECM and to promote invasion. The ECM degradation defect observed in spectrin-depleted-cells is associated with highly dynamic and unstable invadosome rings. Moreover, FRAP measurement showed the specific involvement of αII-spectrin in the regulation of the mobile/immobile β3-integrin ratio in invadosomes. Our findings suggest that spectrin could regulate invadosome function and maturation by modulating integrin mobility in the membrane, allowing the normal processes of adhesion, invasion and matrix degradation. Altogether, these data highlight a new function for spectrins in the stability of invadosomes and the coupling between actin regulation and ECM degradation.

Integrins in Wound Healing

Significance: Regulation of cell adhesions during tissue repair is fundamentally important for cell migration, proliferation, and protein production. All cells interact with extracellular matrix proteins with cell surface integrin receptors that convey signals from the environment into the nucleus, regulating gene expression and cell behavior. Integrins also interact with a variety of other proteins, such as growth factors, their receptors, and proteolytic enzymes. Re-epithelialization and granulation tissue formation are crucially dependent on the temporospatial function of multiple integrins. This review explains how integrins function in wound repair. Recent Advances: Certain integrins can activate latent transforming growth factor beta-1 (TGF-β1) that modulates wound inflammation and granulation tissue formation. Dysregulation of TGF-β1 function is associated with scarring and fibrotic disorders. Therefore, these integrins represent targets for therapeutic intervention in fibrosis. Critical Issues: Integrins have multifaceted functions and extensive crosstalk with other cell surface receptors and molecules. Moreover, in aberrant healing, integrins may assume different functions, further increasing the complexity of their functionality. Discovering and understanding the role that integrins play in wound healing provides an opportunity to identify the mechanisms for medical conditions, such as excessive scarring, chronic wounds, and even cancer. Future Directions: Integrin functions in acute and chronic wounds should be further addressed in models better mimicking human wounds. Application of any products in acute or chronic wounds will potentially alter integrin functions that need to be carefully considered in the design.

ICln: a new regulator of non-erythroid 4.1R localisation and function

To optimise the efficiency of cell machinery, cells can use the same protein (often called a hub protein) to participate in different cell functions by simply changing its target molecules. There are large data sets describing protein-protein interactions (“interactome”) but they frequently fail to consider the functional significance of the interactions themselves. We studied the interaction between two potential hub proteins, ICln and 4.1R (in the form of its two splicing variants 4.1R⁸⁰ and 4.1R¹³⁵), which are involved in such crucial cell functions as proliferation, RNA processing, cytoskeleton organisation and volume regulation. The sub-cellular localisation and role of native and chimeric 4.1R over-expressed proteins in human embryonic kidney (HEK) 293 cells were examined. ICln interacts with both 4.1R⁸⁰ and 4.1R¹³⁵ and its over-expression displaces 4.1R from the membrane regions, thus affecting 4.1R interaction with ß-actin. It was found that 4.1R⁸⁰ and 4.1R¹³⁵ are differently involved in regulating the swelling activated anion current (I_Cl,swell) upon hypotonic shock, a condition under which both isoforms are dislocated from the membrane region and thus contribute to I_Cl,swell current regulation. Both 4.1R isoforms are also differently involved in regulating cell morphology, and ICln counteracts their effects. The findings of this study confirm that 4.1R plays a role in cell volume regulation and cell morphology and indicate that ICln is a new negative regulator of 4.1R functions.

Protein 4.1R attenuates autoreactivity in experimental autoimmune encephalomyelitis by suppressing CD4(+) T cell activation

Immune synapse components contribute to multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) pathogenesis as they play important role in autoreactive T cell activation. Protein 4.1R, a red cell membrane cytoskeletal protein, recently was identified as an important component of immunological synapse (IS) and acted as the negative regulator of CD4(+) T cell activation. However, the pathological role of 4.1R in the MS/EAE pathogenesis is still not elucidated. In this study, we investigated the potential role of protein 4.1R in pathologic processes of EAE by using 4.1R knockout mouse model. Our results suggest that 4.1R can prevent pathogenic autoimmunity in MS/EAE progression by suppressing the CD4(+) T cell activation.

Comprehensive characterization of protein 4.1 expression in epithelium of large intestine

The protein 4.1 family consists of four members, 4.1R, 4.1N, 4.1B and 4.1G, each encoded by a distinct gene. All 4.1 mRNAs undergo extensive alternative splicing. Functionally, they usually serve as adapters that link actin-based cytoskeleton to plasma membrane proteins. It has been reported that 4.1 proteins are expressed in most animal cell types and tissues including epithelial cells and epithelial tissues. However, the expression of 4.1 proteins in large intestine has not been well characterized. In the present study, we performed RT-PCR, western blot and immunohistochemistry analysis to characterize the transcripts, the protein expression and cellular localization of 4.1 proteins in the epithelia of mouse large intestine. We show that multiple transcripts derive from each gene, including eight 4.1R isoforms, four 4.1N isoforms, four 4.1B isoforms and six 4.1G isoforms. However, at the protein level, only one or two major bands were detected, implying that not all transcripts are translated and/or the proteins do not accumulate at detectable levels. Immunohistochemistry revealed that 4.1R, 4.1N and 4.1B are all expressed at the lateral membrane as well as cytoplasm of epithelial cells, suggesting a potentially redundant role of these proteins. Our findings not only provide new insights into the structure of protein 4.1 genes but also lay the foundation for future functional studies.

FERM family proteins and their importance in cellular movements and wound healing (review)

Motility is a requirement for a number of biological processes, including embryonic development, neuronal development, immune responses, cancer progression and wound healing. Specific to wound healing is the migration of endothelial cells, fibroblasts and other key cellular players into the wound space. Aberrations in wound healing can result in either chronic wounds or abnormally healed wounds. The protein 4.1R, ezrin, radixin, moesin (FERM) superfamily consists of over 40 proteins all containing a three lobed N-terminal FERM domain which binds a variety of cell-membrane associated proteins and lipids. The C-terminal ends of these proteins typically contain an actin-binding domain (ABD). These proteins therefore mediate the linkage between the cell membrane and the actin cytoskeleton, and are involved in cellular movements and migration. Certain FERM proteins have been shown to promote cancer metastasis via this very mechanism. Herein we review the effects of a number of FERM proteins on wound healing and cancer. We show how these proteins typically aid wound healing through their effects on increasing cellular migration and movements, but also typically promote metastasis in cancer. We conclude that FERM proteins play important roles in cellular migration, with markedly different outcomes in the context of cancer and wound healing.

The Protein 4.1 family: hub proteins in animals for organizing membrane proteins

Proteins of the 4.1 family are characteristic of eumetazoan organisms. Invertebrates contain single 4.1 genes and the Drosophila model suggests that 4.1 is essential for animal life. Vertebrates have four paralogues, known as 4.1R, 4.1N, 4.1G and 4.1B, which are additionally duplicated in the ray-finned fish. Protein 4.1R was the first to be discovered: it is a major mammalian erythrocyte cytoskeletal protein, essential to the mechanochemical properties of red cell membranes because it promotes the interaction between spectrin and actin in the membrane cytoskeleton. 4.1R also binds certain phospholipids and is required for the stable cell surface accumulation of a number of erythrocyte transmembrane proteins that span multiple functional classes; these include cell adhesion molecules, transporters and a chemokine receptor. The vertebrate 4.1 proteins are expressed in most tissues, and they are required for the correct cell surface accumulation of a very wide variety of membrane proteins including G-Protein coupled receptors, voltage-gated and ligand-gated channels, as well as the classes identified in erythrocytes. Indeed, such large numbers of protein interactions have been mapped for mammalian 4.1 proteins, most especially 4.1R, that it appears that they can act as hubs for membrane protein organization. The range of critical interactions of 4.1 proteins is reflected in disease relationships that include hereditary anaemias, tumour suppression, control of heartbeat and nervous system function. The 4.1 proteins are defined by their domain structure: apart from the spectrin/actin-binding domain they have FERM and FERM-adjacent domains and a unique C-terminal domain. Both the FERM and C-terminal domains can bind transmembrane proteins, thus they have the potential to be cross-linkers for membrane proteins. The activity of the FERM domain is subject to multiple modes of regulation via binding of regulatory ligands, phosphorylation of the FERM associated domain and differential mRNA splicing. Finally, the spectrum of interactions of the 4.1 proteins overlaps with that of another membrane-cytoskeleton linker, ankyrin. Both ankyrin and 4.1 link to the actin cytoskeleton via spectrin, and we hypothesize that differential regulation of 4.1 proteins and ankyrins allows highly selective control of cell surface protein accumulation and, hence, function. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé

A 130-kDa protein 4.1B regulates cell adhesion, spreading, and migration of mouse embryo fibroblasts by influencing actin cytoskeleton organization

Protein 4.1B is a member of protein 4.1 family, adaptor proteins at the interface of membranes and the cytoskeleton. It is expressed in most mammalian tissues and is known to be required in formation of nervous and cardiac systems; it is also a tumor suppressor with a role in metastasis. Here, we explore functions of 4.1B using primary mouse embryonic fibroblasts (MEF) derived from wild type and 4.1B knock-out mice. MEF cells express two 4.1B isoforms: 130 and 60-kDa. 130-kDa 4.1B was absent from 4.1B knock-out MEF cells, but 60-kDa 4.1B remained, suggesting incomplete knock-out. Although the 130-kDa isoform was predominantly located at the plasma membrane, the 60-kDa isoform was enriched in nuclei. 130-kDa-deficient 4.1B MEF cells exhibited impaired cell adhesion, spreading, and migration; they also failed to form actin stress fibers. Impaired cell spreading and stress fiber formation were rescued by re-expression of the 130-kDa 4.1B but not the 60-kDa 4.1B. Our findings document novel, isoform-selective roles for 130-kDa 4.1B in adhesion, spreading, and migration of MEF cells by affecting actin organization, giving new insight into 4.1B functions in normal tissues as well as its role in cancer.

Mapping the extracellular and membrane proteome associated with the vasculature and the stroma in the embryo

In order to map the extracellular or membrane proteome associated with the vasculature and the stroma in an embryonic organism in vivo, we developed a biotinylation technique for chicken embryo and combined it with mass spectrometry and bioinformatic analysis. We also applied this procedure to implanted tumors growing on the chorioallantoic membrane or after the induction of granulation tissue. Membrane and extracellular matrix proteins were the most abundant components identified. Relative quantitative analysis revealed differential protein expression patterns in several tissues. Through a bioinformatic approach, we determined endothelial cell protein expression signatures, which allowed us to identify several proteins not yet reported to be associated with endothelial cells or the vasculature. This is the first study reported so far that applies in vivo biotinylation, in combination with robust label-free quantitative proteomics approaches and bioinformatic analysis, to an embryonic organism. It also provides the first description of the vascular and matrix proteome of the embryo that might constitute the starting point for further developments.

Expressed in high metastatic cells (Ehm2) is a positive regulator of keratinocyte adhesion and motility: The implication for wound healing

BACKGROUND

Multiple factors have been shown to delay dermal wound healing. These resultant wounds pose a significant problem in terms of morbidity and healthcare spend. Recently, an increasing volume of research has focused on the molecular perturbations underlying non-healing wounds.

OBJECTIVES

This study investigates the effect of a novel cancer promoter, Ehm2, in wound healing. Ehm2 belongs to the FERM family of proteins, known to be involved in membrane-cytoskeletal interactions, and has been shown to promote cancer metastasis in melanoma, prostate cancer and breast cancer.

METHODS

Ehm2 mRNA levels were analysed using qRT-PCR, standardised to GAPDH, from either acute or chronic wounds, and normal skin. IHC analysis was also undertaken from wound edge biopsies. An anti-Ehm2 transgene was created and transfected into the HaCaT cell line. The effect of Ehm2 knockdown on migration, adhesion, growth, cell cycle progression and apoptosis was analysed using standard laboratory methods. Western Blot analysis was used to investigate potential downstream protein interactions.

RESULTS

Ehm2 is expressed nearly three times higher in acute wound tissues, compared to chronic wound tissues. Increased Ehm2 expression is found in wounds undergoing healing, especially at the leading wound edge. In vitro, Ehm2 knockdown reduces cellular adhesion, migration and motility, without affecting growth, cell cycle and apoptosis. Finally, Ehm2 knockdown results in reduced NWasp protein expression.

CONCLUSION

These results suggest Ehm2 may be an important player in the wound healing process, and show that Ehm2 knockdown downregulates the expression of NWasp, through which it may have its effect on cellular migration.

Band 4.1 proteins regulate integrin-dependent cell spreading

Integrins link the extracellular matrix (ECM) to the cytoskeleton to control cell behaviors including adhesion, spreading and migration. Band 4.1 proteins contain 4.1, ezrin, radixin, moesin (FERM) domains that likely mediate signaling events and cytoskeletal reorganization via integrins. However, the mechanisms by which Band 4.1 proteins and integrins are functionally interconnected remain enigmatic. Here we have investigated roles for Band 4.1 proteins in integrin-mediated cell spreading using primary astrocytes as a model system. We demonstrate that Proteins 4.1B and 4.1G show dynamic patterns of sub-cellular localization in astrocytes spreading on fibronectin. During early stages of cell spreading Proteins 4.1B and 4.1G are enriched in ECM adhesion sites but become more diffusely localized at later stages of spreading. Combinatorial inactivation of Protein 4.1B and 4.1G expression leads to impaired astrocyte spreading. Furthermore, in exogenous expression systems we show that the isolated Protein 4.1 FERM domain significantly enhances integrin-mediated cell spreading. Protein 4.1B is dispensable for reactive astrogliosis in experimental models of cortical injury, likely due to functional compensation by related Protein 4.1 family members. Collectively, these findings reveal that Band 4.1 proteins are important intracellular components for integrin-mediated cell spreading.

Expression of ezrin correlates with malignant phenotype of lung cancer, and in vitro knockdown of ezrin reverses the aggressive biological behavior of lung cancer cells

Ezrin, one of the ezrin-radixin-moesin proteins, is involved in the formation of cell membrane processes such as lamellipodia and filopodia and acts as a membrane-cytoskeleton linker. Its aberrant expression correlates with development and progression of several human cancers. However, the expression of ezrin and its role in lung cancer are currently unknown. In this study, we performed ezrin small interfering RNA transfection in two lung cancer cell lines and examined the effects on malignant phenotypes in cancer cells by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, wound healing, and chamber transwell assays. Ezrin knockdown significantly reduced the proliferation, migration, and invasion of lung cancer cells in vitro. To address the possible mechanisms, we evaluated the expression of adhesion molecules E-cadherin and β-catenin by Western blot and reverse transcriptase-polymerase chain reaction analyses. The results demonstrated that downregulation of ezrin reduced β-catenin and increased E-cadherin at the protein level but had no effects on their mRNA levels, suggesting posttranscriptional regulation of these two adhesion molecules. Immunofluorescence assays revealed that ezrin knockdown restored membranous expression of E-cadherin and decreased cytoplasmic β-catenin in lung cancer cells. In addition, ezrin expression was immunohistochemically evaluated on 135 normal and 183 lung cancer tissues. The expression of ezrin was significantly higher in cancer samples than paired autologous normal lung tissues. In normal bronchial epithelium, ezrin was mainly localized on the apical membrane, while in lung cancers and metastatic foci, ezrin was primarily distributed in cytoplasm. Among lung cancer tissues, expression of ezrin was higher in the invasive front of primary lesions and the highest in lymphatic metastasis. Statistical analysis demonstrated that ezrin expression correlated significantly with lymphatic metastasis and advanced TNM stage. Our data suggest that ezrin may play a crucial role in governing the biological behavior of lung cancer.