EHD2 mediates trafficking from the plasma membrane by modulating Rac1 activity

EH domain-containing protein 2 (EHD2): Overview, biological function, and therapeutic potential

EH domain-containing protein 2 (EHD2) is a member of the EHD protein family and is mainly located in the plasma membrane, but can also be found in the cytoplasm and endosomes. EHD2 is also a nuclear-cytoplasmic shuttle protein. After entering the cell nuclear, EHD2 acts as a corepressor of transcription to inhibit gene transcription. EHD2 regulates a series of biological processes. As a key regulator of endocytic transport, EHD2 is involved in the formation and maintenance of endosomal tubules and vesicles, which are critical for the intracellular transport of proteins and other substances. The N-terminal of EHD2 is attached to the cell membrane, while its C-terminal binds to the actin-binding protein. After binding, EHD2 connects with the actin cytoskeleton, forming the curvature of the membrane and promoting cell endocytosis. EHD2 is also associated with membrane protein trafficking and receptor signaling, as well as in glucose metabolism and lipid metabolism. In this review, we highlight the recent advances in the function of EHD2 in various cellular processes and its potential implications in human diseases such as cancer and metabolic disease. We also discussed the prospects for the future of EHD2. EHD2 has a broad prospect as a therapeutic target for a variety of diseases. Further research is needed to explore its mechanism, which could pave the way for the development of targeted treatments.

mRNA transcriptome profiling of human hepatocellular carcinoma cells HepG2 treated with Catharanthus roseus-silver nanoparticles

BACKGROUND

The demand for the development of cancer nanomedicine has increased due to its great therapeutic value that can overcome the limitations of conventional cancer therapy. However, the presence of various bioactive compounds in crude plant extracts used for the synthesis of silver nanoparticles (AgNPs) makes its precise mechanisms of action unclear.

AIM

To assessed the mRNA transcriptome profiling of human HepG2 cells exposed to Catharanthus roseus G. Don (C. roseus)-AgNPs.

METHODS

The proliferative activity of hepatocellular carcinoma (HepG2) and normal human liver (THLE3) cells treated with C. roseusAgNPs were measured using MTT assay. The RNA samples were extracted and sequenced using BGIseq500 platform. This is followed by data filtering, mapping, gene expression analysis, differentially expression genes analysis, Gene Ontology analysis, and pathway analysis.

RESULTS

The mean IC₅₀ values of C. roseusAgNPs on HepG2 was 4.38 ± 1.59 μg/mL while on THLE3 cells was 800 ± 1.55 μg/mL. Transcriptome profiling revealed an alteration of 296 genes. C. roseusAgNPs induced the expression of stress-associated genes such as MT, HSP and HMOX-1. Cellular signalling pathways were potentially activated through MAPK, TNF and TGF pathways that are responsible for apoptosis and cell cycle arrest. The alteration of ARF6, EHD2, FGFR3, RhoA, EEA1, VPS28, VPS25, and TSG101 indicated the uptake of C. roseus-AgNPs via both clathrin-dependent and clathrin-independent endocytosis.

CONCLUSION

This study provides new insights into gene expression study of biosynthesised AgNPs on cancer cells. The cytotoxicity effect is mediated by the aberrant gene alteration, and more interestingly the unique selective antiproliferative properties indicate the C. roseusAgNPs as an ideal anticancer candidate.

In Mitosis You Are Not: The NIMA Family of Kinases in Aspergillus, Yeast, and Mammals

The Never in mitosis gene A (NIMA) family of serine/threonine kinases is a diverse group of protein kinases implicated in a wide variety of cellular processes, including cilia regulation, microtubule dynamics, mitotic processes, cell growth, and DNA damage response. The founding member of this family was initially identified in Aspergillus and was found to play important roles in mitosis and cell division. The yeast family has one member each, Fin1p in fission yeast and Kin3p in budding yeast, also with functions in mitotic processes, but, overall, these are poorly studied kinases. The mammalian family, the main focus of this review, consists of 11 members named Nek1 to Nek11. With the exception of a few members, the functions of the mammalian Neks are poorly understood but appear to be quite diverse. Like the prototypical NIMA, many members appear to play important roles in mitosis and meiosis, but their functions in the cell go well beyond these well-established activities. In this review, we explore the roles of fungal and mammalian NIMA kinases and highlight the most recent findings in the field.

Hypoxia-induced macropinocytosis represents a metabolic route for liver cancer

Hepatocellular carcinoma (HCC) invariably exhibits inadequate O₂ (hypoxia) and nutrient supply. Hypoxia-inducible factor (HIF) mediates cascades of molecular events that enable cancer cells to adapt and propagate. Macropinocytosis is an endocytic process initiated by membrane ruffling, causing the engulfment of extracellular fluids (proteins), protein digestion and subsequent incorporation into the biomass. We show that macropinocytosis occurs universally in HCC under hypoxia. HIF-1 activates the transcription of a membrane ruffling protein, EH domain-containing protein 2 (EHD2), to initiate macropinocytosis. Knockout of HIF-1 or EHD2 represses hypoxia-induced macropinocytosis and prevents hypoxic HCC cells from scavenging protein that support cell growth. Germline or somatic deletion of Ehd2 suppresses macropinocytosis and HCC development in mice. Intriguingly, EHD2 is overexpressed in HCC. Consistently, HIF-1 or macropinocytosis inhibitor suppresses macropinocytosis and HCC development. Thus, we show that hypoxia induces macropinocytosis through the HIF/EHD2 pathway in HCC cells, harnessing extracellular protein as a nutrient to survive.

Cancer cells rely on macropinocytosis to scavenge extracellular proteins for growth. Here the authors show that macropinocytosis supports the survival of hypoxic hepatocellular carcinoma cells and this is dependent on HIF-1, which in turns activates the transcription of a membrane ruffling protein, EH domain-containing protein 2.

EHD2 Overexpression Suppresses the Proliferation, Migration, and Invasion in Human Colon Cancer

Background: To investigate how EHD2 influences the development of colon cancer.Methods: Immunohistochemistry of 90 colon cancer tissue specimens were determined the expression of EHD2. The lentivirus-EHD2-transfected colon cancer cells were conducted to evaluate the biological behaviors.Results: EHD2 was closely associated with clinic pathological parameters (p < 0.001). EHD2 upregulation was relative with a longer overall survival. The results of the univariate and multivariate analyses indicated that EHD2 could be an independent prognosis marker. EHD2 overexpression suppressed cell invasion and proliferation, but enhanced cell apoptosis and cell cycle arrest.Conclusions: EHD2 might represent a therapeutic target of colon cancer.IMPACT STATEMENTWhat is already known on this subject? Membrane trafficking is crucial for cell proliferation, differentiation and apoptosis, especially tumorigenesis and development. EHD2 proteins play an important role in the regulation of membrane trafficking in endocytosis. EHD2 has been suggested to participate in the occurrence of some malignancies.What are the new findings? EHD2 could be an independent prognosis marker in colon cancer. EHD2 overexpression suppressed cell invasion and proliferation, but enhanced cell apoptosis and cell cycle arrest in vitro. EHD2 overexpression markedly increased the expression of EMT marker E-cadherin in colon cancer.How might it impact on clinical practice in the foreseeable future? EHD2 overexpression may inhibit tumorigenesis in colon cancer through the modulation of E-cadherin, the critical marker of EMT which is closely related to invasion and distant metastasis of tumor cells.

Eps15 Homology Domain Protein 4 (EHD4) is required for Eps15 Homology Domain Protein 1 (EHD1)-mediated endosomal recruitment and fission

Upon internalization, receptors are trafficked to sorting endosomes (SE) where they undergo sorting and are then packaged into budding vesicles that undergo fission and transport within the cell. Eps15 Homology Domain Protein 1 (EHD1), the best-characterized member of the Eps15 Homology Domain Protein (EHD) family, has been implicated in catalyzing the fission process that releases endosome-derived vesicles for recycling to the plasma membrane. Indeed, recent studies suggest that upon receptor-mediated internalization, EHD1 is recruited from the cytoplasm to endosomal membranes where it catalyzes vesicular fission. However, the mechanism by which this recruitment occurs remains unknown. Herein, we demonstrate that the EHD1 paralog, EHD4, is required for the recruitment of EHD1 to SE. We show that EHD4 preferentially dimerizes with EHD1, and knock-down of EHD4 expression by siRNA, shRNA or by CRISPR/Cas9 gene-editing leads to impaired EHD1 SE-recruitment and enlarged SE. Moreover, we demonstrate that at least 3 different asparagine-proline-phenylalanine (NPF) motif-containing EHD binding partners, Rabenosyn-5, Syndapin2 and MICAL-L1, are required for the recruitment of EHD1 to SE. Indeed, knock-down of any of these SE-localized EHD interaction partners leads to enlarged SE, presumably due to impaired endosomal fission. Overall, we identify a novel mechanistic role for EHD4 in recruitment of EHD1 to SE, thus positioning EHD4 as an essential component of the EHD1-fission machinery at SE.

The trafficking protein, EHD2, positively regulates cardiac sarcolemmal KATP channel surface expression: role in cardioprotection

ATP-sensitive K⁺ (K_ATP) channels uniquely link cellular energy metabolism to membrane excitability and are expressed in diverse cell types that range from the endocrine pancreas to neurons and smooth, skeletal, and cardiac muscle. A decrease in the surface expression of K_ATP channels has been linked to various disorders, including dysregulated insulin secretion, abnormal blood pressure, and impaired resistance to cardiac injury. In contrast, up-regulation of K_ATP channel surface expression may be protective, for example, by mediating the beneficial effect of ischemic preconditioning. Molecular mechanisms that regulate K_ATP channel trafficking are poorly understood. Here, we used cellular assays with immunofluorescence, surface biotinylation, and patch clamping to demonstrate that Eps15 homology domain-containing protein 2 (EHD2) is a novel positive regulator of K_ATP channel trafficking to increase surface K_ATP channel density. EHD2 had no effect on cardiac Na⁺ channels (Nav1.5). The effect is specific to EHD2 as other members of the EHD family-EHD1, EHD3, and EHD4-had no effect on K_ATP channel surface expression. EHD2 did not directly affect K_ATP channel properties as unitary conductance and ATP sensitivity were unchanged. Instead, we observed that the mechanism by which EHD2 increases surface expression is by stabilizing K_ATP channel-containing caveolar structures, which results in a reduced rate of endocytosis. EHD2 also regulated K_ATP channel trafficking in isolated cardiomyocytes, which validated the physiologic relevance of these observations. Pathophysiologically, EHD2 may be cardioprotective as a dominant-negative EHD2 mutant sensitized cardiomyocytes to ischemic damage. Our findings highlight EHD2 as a potential pharmacologic target in the treatment of diseases with K_ATP channel trafficking defects.-Yang, H. Q., Jana, K., Rindler, M. J., Coetzee, W. A. The trafficking protein, EHD2, positively regulates cardiac sarcolemmal K_ATP channel surface expression: role in cardioprotection.

Inhibition of Rac1 ameliorates neuronal oxidative stress damage via reducing Bcl-2/Rac1 complex formation in mitochondria through PI3K/Akt/mTOR pathway

Although the neuroprotective effects of Rac1 inhibition have been reported in various cerebral ischemic models, the molecular mechanisms of action have not yet been fully elucidated. In this study, we investigated whether the inhibition of Rac1 provided neuroprotection in a diabetic rat model of focal cerebral ischemia and hyperglycemia-exposed PC-12 cells. Intracerebroventricular administration of lentivirus expressing the Rac1 small hairpin RNA (shRNA) and specific Rac1 inhibitor NSC23766 not only decreased the infarct volumes and improved neurologic deficits with a correlated significant activation of mitochondrial DNA specific proteins, such as OGG1 and POLG, but also elevated Bcl-2 S70 phosphorylation in mitochondria. Furthermore, the levels of p-PI3K, p-Akt and p-mTOR increased, while 8-OHdG, ROS production and Bcl-2/Rac1 complex formation in mitochondria reduced in both Rac1-shRNA- and NSC23766-treated rats. Moreover, to confirm our in vivo observations, inhibition of Rac1 activity by NSC23766 suppressed the interactions between Bcl-2 and Rac1 in the mitochondria of PC-12 cells cultured in high glucose conditions and protected PC-12 cells from high glucose-induced neurotoxicity. More importantly, these beneficial effects of Rac1 inhibition were abolished by PI3K inhibitor LY294002. In contrast to NSC23766 treatment, LY294002 had little effect on the decrement of p-PTEN level. Taken together, these findings revealed novel neuroprotective roles of Rac1 inhibition against cerebral ischemic reperfusion injury in vivo and high glucose-induced neurotoxicity in PC-12 cells in vitro, by reducing Bcl-2/Rac1 complex formation in mitochondria through the activation of PI3K/Akt/mTOR survival pathway.

Past1 Modulates Drosophila Eye Development

Endocytosis is a multi-step process involving a large number of proteins, both general factors, such as clathrin and adaptor protein complexes, and unique proteins, which modulate specialized endocytic processes, like the EHD proteins. EHDs are a family of Eps15 Homology Domain containing proteins that consists of four mammalian homologs, one C. elegans, one Drosophila melanogaster and two plants orthologs. These membrane-associated proteins are involved in different steps of endocytic trafficking pathways. We have previously shown that the Drosophila EHD ortholog, PAST1, associates predominantly with the plasma membrane. Mutations in Past1 result in defects in endocytosis, male sterility, temperature sensitivity and premature death of the flies. Also, Past1 genetically interacts with Notch. In the present study, we investigated the role of PAST1 in the developing fly eye. In mutant flies lacking PAST1, abnormal differentiation of photoreceptors R1, R6 and R7 was evident, with partial penetrance. Likewise, five cone cells were present instead of four. Expression of transgenic PAST1 resulted in a dominant negative effect, with a phenotype similar to that of the deletion mutant, and appearance of additional inter-ommatidial pigment cells. Our results strongly suggest a role for PAST1 in differentiation of photoreceptors R1/R6/R7 and cone cells of the fly ommatidia.

Phosphatidylinositol glycan anchor biosynthesis, class X containing complex promotes cancer cell proliferation through suppression of EHD2 and ZIC1, putative tumor suppressors

We identified phosphatidylinositol glycan anchor biosynthesis, class X (PIGX), which plays a critical role in the biosynthetic pathway of glycosylphosphatidylinositol (GPI)-anchor motif, to be upregulated highly and frequently in breast cancer cells. Knockdown of PIGX as well as reticulocalbin 1 (RCN1) and reticulocalbin 2 (RCN2), which we found to interact with PIGX and was indicated to regulate calcium-dependent activities, significantly suppressed the growth of breast cancer cells. We also identified PIGX to be a core protein in an RCN1/PIGX/RCN2 complex. Microarray analysis revealed that the expression of two putative tumor suppressor genes, Zic family member 1 (ZIC1) and EH-domain containing 2 (EHD2), were upregulated commonly in cells in which PIGX, RCN1, or RCN2 was knocked down, suggesting that this RCN1/PIGX/RCN2 complex could negatively regulate the expression of these two genes and thereby contribute to human breast carcinogenesis. Our results imply that PIGX may be a good candidate molecule for development of novel anticancer drugs for breast cancer.

SUMOylation of EHD3 Modulates Tubulation of the Endocytic Recycling Compartment

Endocytosis defines the entry of molecules or macromolecules through the plasma membrane as well as membrane trafficking in the cell. It depends on a large number of proteins that undergo protein-protein and protein-phospholipid interactions. EH Domain containing (EHDs) proteins formulate a family, whose members participate in different stages of endocytosis. Of the four mammalian EHDs (EHD1-EHD4) EHD1 and EHD3 control traffic to the endocytic recycling compartment (ERC) and from the ERC to the plasma membrane, while EHD2 modulates internalization. Recently, we have shown that EHD2 undergoes SUMOylation, which facilitates its exit from the nucleus, where it serves as a co-repressor. In the present study, we tested whether EHD3 undergoes SUMOylation and what is its role in endocytic recycling. We show, both in-vitro and in cell culture, that EHD3 undergoes SUMOylation. Localization of EHD3 to the tubular structures of the ERC depends on its SUMOylation on lysines 315 and 511. Absence of SUMOylation of EHD3 has no effect on its dimerization, an important factor in membrane localization of EHD3, but has a dominant negative effect on its appearance in tubular ERC structures. Non-SUMOylated EHD3 delays transferrin recycling from the ERC to the cell surface. Our findings indicate that SUMOylation of EHD3 is involved in tubulation of the ERC membranes, which is important for efficient recycling.

Role of the EHD2 unstructured loop in dimerization, protein binding and subcellular localization

The C-terminal Eps 15 Homology Domain proteins (EHD1-4) play important roles in regulating endocytic trafficking. EHD2 is the only family member whose crystal structure has been solved, and it contains an unstructured loop consisting of two proline-phenylalanine (PF) motifs: KPFRKLNPF. In contrast, despite EHD2 having nearly 70% amino acid identity with its paralogs, EHD1, EHD3 and EHD4, the latter proteins contain a single KPF or RPF motif, but no NPF motif. In this study, we sought to define the precise role of each PF motif in EHD2’s homo-dimerization, binding with the protein partners, and subcellular localization. To test the role of the NPF motif, we generated an EHD2 NPF-to-NAF mutant to mimic the homologous sequences of EHD1 and EHD3. We demonstrated that this mutant lost both its ability to dimerize and bind to Syndapin2. However, it continued to localize primarily to the cytosolic face of the plasma membrane. On the other hand, EHD2 NPF-to-APA mutants displayed normal dimerization and Syndapin2 binding, but exhibited markedly increased nuclear localization and reduced association with the plasma membrane. We then hypothesized that the single PF motif of EHD1 (that aligns with the KPF of EHD2) might be responsible for both binding and localization functions of EHD1. Indeed, the EHD1 RPF motif was required for dimerization, interaction with MICAL-L1 and Syndapin2, as well as localization to tubular recycling endosomes. Moreover, recycling assays demonstrated that EHD1 RPF-to-APA was incapable of supporting normal receptor recycling. Overall, our data suggest that the EHD2 NPF phenylalanine residue is crucial for EHD2 localization to the plasma membrane, whereas the proline residue is essential for EHD2 dimerization and binding. These studies support the recently proposed model in which the EHD2 N-terminal region may regulate the availability of the unstructured loop for interactions with neighboring EHD2 dimers, thus promoting oligomerization.

Role of EHD2 in migration and invasion of human breast cancer cells

Eps15 homology domain-containing 2 (EHD2) is a tumor suppressor gene, overexpressed in several solid tumors, including ovarian cancer and esophageal squamous cell carcinoma. The current study examined the expression and the role of EHD2 in human breast cancer. EHD2 expression was determined by Western blot and immunohistochemistry (IHC) in 80 breast cancer and paired noncancerous breast tissues. Correlations between clinicopathologic variables, overall survival, and EHD2 expression were analyzed. We investigated the role of EHD2 in breast cancer migration and invasion by wound healing assay and trans-well invasion assays. A notably lower level of EHD2 expression was found in breast cancer tissues. EHD2 expression was associated with histological grade, lymph node metastasis, and tumor size. Expression of EHD2 was found to be an independent prognostic factor in breast cancer patients. Furthermore, overexpression of EHD2 suppressed, while elimination of EHD2 promoted, the migration and invasion of breast cancer cells. Molecular data showed that EHD2 inhibited breast cancer migration and invasion probably by dampening the expression of Ras-related C3 botulinum toxin substrate 1 (Rac1). Downregulation of EHD2 was associated with migration and invasion by abrogating the expression of Rac1 in breast cancer patients. EHD2 may serve as a prognostic marker in breast cancer.

Identification of gene regulation patterns underlying both oestrogen- and tamoxifen-stimulated cell growth through global gene expression profiling in breast cancer cells

PURPOSE

A c-Src inhibitor blocks oestrogen (E2)-induced stress and converts E2 responses from inducing apoptosis to growth stimulation in E2-deprived breast cancer cells. A reprogrammed cell line, MCF-7:PF, results in a functional oestrogen receptor (ER). We addressed the question of whether the selective ER modulator 4-hydroxytamoxifen (4-OHT) could target ER to prevent E2-stimulated growth in MCF-7:PF cells.

METHODS

Expression of mRNA was measured through real-time RT-PCR. Global gene expression profile was analysed through microarray. Transcriptome profiles were screened by RNA-sequencing.

RESULTS

Unexpectedly, both 4-OHT and E2 stimulated cell growth in a concentration-dependent manner. Expression profiling showed a remarkable overlap in genes regulated in the same direction by E2 and 4-OHT. Pathway enrichment analysis of the 280 genes commonly deregulated in MCF-7:PF cells by 4-OHT and E2 revealed functions mainly related to membrane, cytoplasm and metabolic processes. Further analysis of 98 genes up-regulated by both 4-OHT and E2 uncovered a significant enrichment in genes associated with membrane remodelling, cytoskeleton reorganisation, cytoplasmic adapter proteins, cytoplasm organelle proteins and related processes. 4-OHT was more potent than E2 in up-regulating some membrane remodelling molecules, such as EHD2, FHL2, HOMER3 and RHOF. In contrast, 4-OHT acted as an antagonist to inhibit expression of the majority of enriched membrane-associated genes in wild-type MCF-7 cells.

CONCLUSIONS

Long-term selection pressure has changed the cell population responses to 4-OHT. Membrane-associated signalling is critical for 4-OHT-stimulated cell growth in MCF-7:PF cells. This study provides a rationale for the further investigation of target therapy for tamoxifen resistant patients.

“Stop Ne(c)king around”: How interactomics contributes to functionally characterize Nek family kinases

Aside from Polo and Aurora, a third but less studied kinase family involved in mitosis regulation is the never in mitosis-gene A (NIMA)-related kinases (Neks). The founding member of this family is the sole member NIMA of Aspergillus nidulans, which is crucial for the initiation of mitosis in that organism. All 11 human Neks have been functionally assigned to one of the three core functions established for this family in mammals: (1) centrioles/mitosis; (2) primary ciliary function/ciliopathies; and (3) DNA damage response (DDR). Recent findings, especially on Nek 1 and 8, showed however, that several Neks participate in parallel in at least two of these contexts: primary ciliary function and DDR. In the core section of this in-depth review, we report the current detailed functional knowledge on each of the 11 Neks. In the discussion, we return to the cross-connections among Neks and point out how our and other groups’ functional and interactomics studies revealed that most Neks interact with protein partners associated with two if not all three of the functional contexts. We then raise the hypothesis that Neks may be the connecting regulatory elements that allow the cell to fine tune and synchronize the cellular events associated with these three core functions. The new and exciting findings on the Nek family open new perspectives and should allow the Neks to finally claim the attention they deserve in the field of kinases and cell cycle biology.

Upregulation of EHD2 after intracerebral hemorrhage in adult rats

EHD2, a member of the Eps15 homology domain (EH domain) family, is important for protein interactions during vesicular trafficking. Previous studies have proved that EHD2 can regulate trafficking from the plasma membrane in the process of endocytosis. However, its function in central nervous system diseases is still with limited understanding. In this frame, we found that EHD2 expression was upregulated in the perihematomal caudate in adult rats after intracerebral hemorrhage (ICH). Double immunofluorescence staining revealed that EHD2 was colocalized with neurons and activated microglias after ICH. Besides, we detected that neuronal apoptosis markers (TUNEL and caspase-3), and microglial activation marker (CD68), also known as a marker of macrophage, were colocated with EHD2. The vitro study also indicated that EHD2 was linked with neuronal apoptosis and microglial phagocytosis. All our findings suggested that EHD2 might be involved in the pathophysiology of ICH.

The function of EHD2 in endocytosis and defense signaling is affected by SUMO

Post-translational modification of target proteins by the small ubiquitin-like modifier protein (SUMO) regulates many cellular processes. SUMOylation has been shown to regulate cellular localization and function of a variety of proteins, in some cases affecting nuclear import or export. We have previously characterized two EHDs (EH domain containing proteins) in Arabidospis and showed their involvement in plant endocytosis. AtEHD2 has an inhibitory effect on endocytosis of transferrin, FM-4-64, and the leucine rich repeat receptor like protein LeEix2, an effect that requires and intact coiled-coil domain. Inhibition of endocytosis of LeEix2 by EHD2 is effective in inhibiting defense responses mediated by the LeEix2 receptor in response to its ligand EIX. In the present work we demonstrate that SUMOylation of EHD2 appears to be required for EHD2-induced inhibition of LeEix2 endocytosis. Indeed, we found that a mutant form of EHD2, possessing a defective SUMOylation site, has an increased nuclear abundance, can no longer be SUMOylated and is no longer effective in inhibiting LeEix2 endocytosis or defense signaling in response to EIX.

Scratching the surface: actin' and other roles for the C-terminal Eps15 homology domain protein, EHD2

The C-terminal Eps15 homology domain-containing (EHD) proteins participate in multiple aspects of endocytic membrane trafficking. Of the four mammalian EHD proteins, EHD2 appears to be the most disparate, both in terms of sequence homology, and in subcellular localization/function. Since its initial description as a plasma membrane-associated protein, the precise function of EHD2 has remained enigmatic. Various reports have suggested roles for EHD2 at the plasma membrane, within the endocytic transport system, and even in the nucleus. For example, EHD2 facilitates membrane fusion/repair in muscle cells. Recently the focus has shifted to the role of EHD2 in regulating caveolae. Indeed, EHD2 is highly expressed in tissues rich in caveolae, including fat, muscle and blood vessels. This review highlights cumulative evidence linking EHD2 to actin-rich structures at the plasma membrane, where the plasma membrane-associated phospholipid phosphatidylinositol 4,5-bisphosphate controls EHD2 recruitment. Herein we examine the key pathways where EHD2 might function, and address its potential involvement in these processes.

Tiam-1, a GEF for Rac1, plays a critical role in metformin-mediated glucose uptake in C2C12 cells

Metformin is known to stimulate glucose uptake, but the mechanism for this action is not fully understood. In this study, AMPK activators (AICAR and metformin) increased the expression of T-lymphoma invasion and metastasis-inducing protein-1 (Tiam-1), a Rac1 specific guanine nucleotide exchange factor (GEF), mRNA and protein in skeletal muscle C2C12 cells. Metformin increases the serine-phosphorylation of Tiam-1 by AMPK and induces interaction between Tiam-1 and 14-3-3. Pharmacologic inhibition of AMPK blocks this interaction, indicating that 14-3-3 may be required for induction of Tiam-1 by AMPK. Metformin also increases the phosphorylation of p21-activated kinase 1 (PAK1), a direct downstream target of Rac1, dependent on AMPK. Tiam-1 is down-regulated at high glucose concentrations in cultured cells and in the db/db mouse model of hyperglycemia. Furthermore, Tiam-1 knock-down blocked metformin-induced increase in glucose uptake. These findings suggest that metformin promotes cellular glucose uptake in part through Tiam-1 induction.

A snapshot of the physical and functional wiring of the Eps15 homology domain network in the nematode

Protein interaction modules coordinate the connections within and the activity of intracellular signaling networks. The Eps15 Homology (EH) module, a protein-protein interaction domain that is a key feature of the EH-network, was originally identified in a few proteins involved in endocytosis and vesicle trafficking, and has subsequently also been implicated in actin reorganization, nuclear shuttling, and DNA repair. Here we report an extensive characterization of the physical connections and of the functional wirings of the EH-network in the nematode. Our data show that one of the major physiological roles of the EH-network is in neurotransmission. In addition, we found that the proteins of the network intersect, and possibly coordinate, a number of “territories” of cellular activity including endocytosis/recycling/vesicle transport, actin dynamics, general metabolism and signal transduction, ubiquitination/degradation of proteins, DNA replication/repair, and miRNA biogenesis and processing.

Effects of EHD2 interference on migration of esophageal squamous cell carcinoma

C-Terminal EH domain-containing protein 2 (EHD2) of the EHD family is associated with plasma membrane. We investigated the expression of EHD2 in human esophageal squamous cell carcinoma (ESCC) and the EHD2 expression to study the therapeutic effect of chemotherapy drugs. Western blot and immunohistochemistry were used to measure the expression of EHD2 protein in ESCC and adjacent normal tissue in 98 patients. EHD2 protein level was reduced in ESCC tissues in comparison with adjacent normal tissues. Under-expression of EHD2 increased the motility property of ESCC cell TE1 in vitro by wound-healing assays and transwell migration assays, and it was concurrent with the decreased expression of epithelial marker E-cadherin. Under-expression of EHD2 in TE1 can cause resistance to cisplatin. Our results suggested that EHD2 low expression is involved in the pathogenesis of ESCC, and it might be a favorable independent poor prognostic parameter for ESCC.

EHD2 shuttles to the nucleus and represses transcription

EHD {EH [Eps15 (epidermal growth factor receptor substrate 15) homology]-domain-containing} proteins participate in several endocytic events, such as the internalization and the recycling processes. There are four EHD proteins in mammalian cells, EHD1–EHD4, each with diverse roles in the recycling pathway of endocytosis. EHD2 is a plasma-membrane-associated member of the EHD family that regulates internalization. Since several endocytic proteins have been shown to undergo nucleocytoplasmic shuttling and have been assigned roles in regulation of gene expression, we tested the possibility that EHD proteins also shuttle to the nucleus. Our results showed that, among the three EHD proteins (EHD1–EHD3) that were tested, only EHD2 accumulates in the nucleus under nuclear export inhibition treatment. Moreover, the presence of a NLS (nuclear localization signal) was essential for its entry into the nucleus. Nuclear exit of EHD2 depended partially on its NES (nuclear export signal). Elimination of a potential SUMOylation site in EHD2 resulted in a major accumulation of the protein in the nucleus, indicating the involvement of SUMOylation in the nuclear exit of EHD2. We confirmed the SUMOylation of EHD2 by employing co-immunoprecipitation and the yeast two-hybrid system. Using GAL4-based transactivation assay as well as a KLF7 (Krüppel-like factor 7)-dependent transcription assay of the p21WAF1/Cip1 [CDKN1A (cyclin-dependent kinase inhibitor 1A)] gene, we showed that EHD2 represses transcription. qRT-PCR (quantitative real-time PCR) of RNA from cells overexpressing EHD2 or of RNA from cells knocked down for EHD2 confirmed that EHD2 represses transcription of the p21WAF1/Cip1 gene.

Oligomers of the ATPase EHD2 confine caveolae to the plasma membrane through association with actin

Caveolae are plasma membrane microdomains that play important roles in signalling and endocytosis. The ATPase EHD2 shuttles on and off the static population of caveolae in an ATPase cycledependent manner and links caveolae to actin filaments confining them to the plasma membrane.

Caveolae are specialized domains present in the plasma membrane (PM) of most mammalian cell types. They function in signalling, membrane regulation, and endocytosis. We found that the Eps-15 homology domain-containing protein 2 (EHD2, an ATPase) associated with the static population of PM caveolae. Recruitment to the PM involved ATP binding, interaction with anionic lipids, and oligomerization into large complexes (60–75S) via interaction of the EH domains with intrinsic NPF/KPF motifs. Hydrolysis of ATP was essential for binding of EHD2 complexes to caveolae. EHD2 was found to undergo dynamic exchange at caveolae, a process that depended on a functional ATPase cycle. Depletion of EHD2 by siRNA or expression of a dominant-negative mutant dramatically increased the fraction of mobile caveolar vesicles coming from the PM. Overexpression of EHD2, in turn, caused confinement of cholera toxin B in caveolae. The confining role of EHD2 relied on its capacity to link caveolae to actin filaments. Thus, EHD2 likely plays a key role in adjusting the balance between PM functions of stationary caveolae and the role of caveolae as vesicular carriers.