Regulation of Son of sevenless by the membrane-actin linker protein ezrin

Ezrin gone rogue in cancer progression and metastasis: An enticing therapeutic target

Cancer metastasis is the primary cause of morbidity and mortality in cancer as it remains the most complicated, devastating, and enigmatic aspect of cancer. Several decades of extensive research have identified several key players closely associated with metastasis. Among these players, cytoskeletal linker Ezrin (the founding member of the ERM (Ezrin-Radixin-Moesin) family) was identified as a critical promoter of metastasis in pediatric cancers in the early 21st century. Ezrin was discovered 40 years ago as a aminor component of intestinal epithelial microvillus core protein, which is enriched in actin-containing cell surface structures. It controls gastric acid secretion and plays diverse physiological roles including maintaining cell polarity, regulating cell adhesion, cell motility and morphogenesis. Extensive research for more than two decades evinces that Ezrin is frequently dysregulated in several human cancers. Overexpression, altered subcellular localization and/or aberrant activation of Ezrin are closely associated with higher metastatic incidence and patient mortality, thereby justifying Ezrin as a valuable prognostic biomarker in cancer. Ezrin plays multifaceted role in multiple aspects of cancer, with its significant contribution in the complex metastatic cascade, through reorganizing the cytoskeleton and deregulating various cellular signaling pathways. Current preclinical studies using genetic and/or pharmacological approaches reveal that inactivation of Ezrin results in significant inhibition of Ezrin-mediated tumor growth and metastasis as well as increase in the sensitivity of cancer cells to various chemotherapeutic drugs. In this review, we discuss the recent advances illuminating the molecular mechanisms responsible for Ezrin dysregulation in cancer and its pleiotropic role in cancer progression and metastasis. We also highlight its potential as a prognostic biomarker and therapeutic target in various cancers. More importantly, we put forward some potential questions, which we strongly believe, will stimulate both basic and translational research to better understand Ezrin-mediated malignancy, ultimately leading to the development of Ezrin-targeted cancer therapy for the betterment of human life.

A somatic mutation in moesin drives progression into acute myeloid leukemia

Acute myeloid leukemia (AML) arises when leukemia-initiating cells, defined by a primary genetic lesion, acquire subsequent molecular changes whose cumulative effects bypass tumor suppression. The changes that underlie AML pathogenesis not only provide insights into the biology of transformation but also reveal novel therapeutic opportunities. However, backtracking these events in transformed human AML samples is challenging, if at all possible. Here, we approached this question using a murine in vivo model with an MLL-ENL fusion protein as a primary molecular event. Upon clonal transformation, we identified and extensively verified a recurrent codon-changing mutation (Arg²⁹⁵Cys) in the ERM protein moesin that markedly accelerated leukemogenesis. Human cancer-associated moesin mutations at the conserved arginine-295 residue similarly enhanced MLL-ENL-driven leukemogenesis. Mechanistically, the mutation interrupted the stability of moesin and conferred a neomorphic activity to the protein, which converged on enhanced extracellular signal-regulated kinase activity. Thereby, our studies demonstrate a critical role of ERM proteins in AML, with implications also for human cancer.

Osimertinib-resistant NSCLC cells activate ERBB2 and YAP/TAZ and are killed by neratinib

We performed additional mechanistic analyses to redefine neratinib biology and determined the mechanisms by which the multi-kinase inhibitor neratinib interacted with the thymidylate synthase inhibitor pemetrexed to kill NSCLC cells expressing either mutant KRAS (G12S; Q61H; G12A; G12C) or mutant NRAS (Q61K) or mutant ERBB1 (L858R; L858R T790M; exon 19 deletion). Neratinib rapidly reduced KRASG12V and RAC1G12V nanoclustering which was followed by KRASG12V, but not RAC1G12V, being extensively mislocalized away from the plasma membrane. This correlated with reduced levels of, and reorganized membrane localization of phosphatidylserine and cholesterol. Reduced nanoclustering was not associated with inactivation of ERBB1, Merlin or Ezrin. The drug combination killed cells expressing mutant KRAS, NRAS or mutant ERBB1 proteins. Afatinib or osimertinib resistant cells were killed with a similar efficacy to non-resistant cells. Compared to osimertinib-resistant cells, sensitive cells had less ERBB2 Y1248 phosphorylation. In osimertinib resistant H1975 cells, the drug combination was less capable of inactivating AKT, mTOR, STAT3, STAT5, ERK1/2 whereas it gained the ability to inactivate ERBB3. In resistant H1650 cells, the drug combination was less capable of inactivating JAK2 and STAT5. Sensitive cells exhibited elevated basal phosphorylation of YAP and TAZ. In resistant cells, portions of YAP and TAZ were localized in the nucleus. [Neratinib + pemetrexed] increased phosphorylation of YAP and TAZ, caused their nuclear exit, and enhanced ERBB2 degradation. Thus, neratinib targets an unidentified protein whose functional inhibition directly results in RAS inactivation and tumor cell killing. Our data prove that, albeit indirectly, oncogenic RAS proteins are druggable by neratinib.

Decrease in membrane fluidity and traction force induced by silica-coated magnetic nanoparticles

Background

Nanoparticles are being increasingly used in biomedical applications owing to their unique physical and chemical properties and small size. However, their biophysical assessment and evaluation of side-effects remain challenging. We addressed this issue by investigating the effects of silica-coated magnetic nanoparticles containing rhodamine B isothiocyanate [MNPs@SiO₂(RITC)] on biophysical aspects, such as membrane fluidity and traction force of human embryonic kidney 293 (HEK293) cells. We further extended our understanding on the biophysical effects of nanoparticles on cells using a combination of metabolic profiling and transcriptomic network analysis.

Results

Overdose (1.0 μg/µL) treatment with MNPs@SiO₂(RITC) induced lipid peroxidation and decreased membrane fluidity in HEK293 cells. In addition, HEK293 cells were morphologically shrunk, and their aspect ratio was significantly decreased. We found that each traction force (measured in micropillar) was increased, thereby increasing the total traction force in MNPs@SiO₂(RITC)-treated HEK293 cells. Due to the reduction in membrane fluidity and elevation of traction force, the velocity of cell movement was also significantly decreased. Moreover, intracellular level of adenosine triphosphate (ATP) was also decreased in a dose-dependent manner upon treatment with MNPs@SiO₂(RITC). To understand these biophysical changes in cells, we analysed the transcriptome and metabolic profiles and generated a metabotranscriptomics network, which revealed relationships among peroxidation of lipids, focal adhesion, cell movement, and related genes and metabolites. Furthermore, in silico prediction of the network showed increment in the peroxidation of lipids and suppression of focal adhesion and cell movement.

Conclusion

Taken together, our results demonstrated that overdose of MNPs@SiO₂(RITC) impairs cellular movement, followed by changes in the biophysical properties of cells, thus highlighting the need for biophysical assessment of nanoparticle-induced side-effects.

Merlin cooperates with neurofibromin and Spred1 to suppress the Ras-Erk pathway

The Ras-Erk pathway is frequently overactivated in human tumors. Neurofibromatosis types 1 and 2 (NF1, NF2) are characterized by multiple tumors of Schwann cell origin. The NF1 tumor suppressor neurofibromin is a principal Ras-GAP accelerating Ras inactivation, whereas the NF2 tumor suppressor merlin is a scaffold protein coordinating multiple signaling pathways. We have previously reported that merlin interacts with Ras and p120RasGAP. Here, we show that merlin can also interact with the neurofibromin/Spred1 complex via merlin-binding sites present on both proteins. Further, merlin can directly bind to the Ras-binding domain (RBD) and the kinase domain (KiD) of Raf1. As the third component of the neurofibromin/Spred1 complex, merlin cannot increase the Ras-GAP activity; rather, it blocks Ras binding to Raf1 by functioning as a 'selective Ras barrier'. Merlin-deficient Schwann cells require the Ras-Erk pathway activity for proliferation. Accordingly, suppression of the Ras-Erk pathway likely contributes to merlin's tumor suppressor activity. Taken together, our results, and studies by others, support targeting or co-targeting of this pathway as a therapy for NF2 inactivation-related tumors.

Silica-Coated Magnetic Nanoparticles Decrease Human Bone Marrow-Derived Mesenchymal Stem Cell Migratory Activity by Reducing Membrane Fluidity and Impairing Focal Adhesion

For stem cell-based therapies, the fate and distribution of stem cells should be traced using non-invasive or histological methods and a nanomaterial-based labelling agent. However, evaluation of the biophysical effects and related biological functions of nanomaterials in stem cells remains challenging. Here, we aimed to investigate the biophysical effects of nanomaterials on stem cells, including those on membrane fluidity, using total internal reflection fluorescence microscopy, and traction force, using micropillars of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) labelled with silica-coated magnetic nanoparticles incorporating rhodamine B isothiocyanate (MNPs@SiO₂(RITC)). Furthermore, to evaluate the biological functions related to these biophysical changes, we assessed the cell viability, reactive oxygen species (ROS) generation, intracellular cytoskeleton, and the migratory activity of MNPs@SiO₂(RITC)-treated hBM-MSCs. Compared to that in the control, cell viability decreased by 10% and intracellular ROS increased by 2-fold due to the induction of 20% higher peroxidized lipid in hBM-MSCs treated with 1.0 µg/µL MNPs@SiO₂(RITC). Membrane fluidity was reduced by MNPs@SiO₂(RITC)-induced lipid oxidation in a concentration-dependent manner. In addition, cell shrinkage with abnormal formation of focal adhesions and ~30% decreased total traction force were observed in cells treated with 1.0 µg/µL MNPs@SiO₂(RITC) without specific interaction between MNPs@SiO₂(RITC) and cytoskeletal proteins. Furthermore, the migratory activity of hBM-MSCs, which was highly related to membrane fluidity and cytoskeletal abnormality, decreased significantly after MNPs@SiO₂(RITC) treatment. These observations indicated that the migratory activity of hBM-MSCs was impaired by MNPs@SiO₂(RITC) treatment due to changes in stem-cell biophysical properties and related biological functions, highlighting the important mechanisms via which nanoparticles impair migration of hBM-MSCs. Our findings indicate that nanoparticles used for stem cell trafficking or clinical applications should be labelled using optimal nanoparticle concentrations to preserve hBM-MSC migratory activity and ensure successful outcomes following stem cell localisation.

Extracellular Signal-Regulated Kinase: A Regulator of Cell Growth, Inflammation, Chondrocyte and Bone Cell Receptor-Mediated Gene Expression

Extracellular signal-regulated kinase (ERK) is a member of the mitogen-activated protein kinase family of signaling molecules. ERK is predominantly found in two forms, ERK1 (p44) and ERK2 (p42), respectively. There are also several atypical forms of ERK, including ERK3, ERK4, ERK5 and ERK7. The ERK1/2 signaling pathway has been implicated in many and diverse cellular events, including proliferation, growth, differentiation, cell migration, cell survival, metabolism and transcription. ERK1/2 is activated (i.e., phosphorylated) in the cytosol and subsequently translocated to the nucleus, where it activates transcription factors including, but not limited to, ETS, c-Jun, and Fos. It is not surprising that the ERK1/2 signaling cascade has been implicated in many pathological conditions, namely, cancer, arthritis, chronic inflammation, and osteoporosis. This narrative review examines many of the cellular events in which the ERK1/2 signaling cascade plays a critical role. It is anticipated that agents designed to inhibit ERK1/2 activation or p-ERK1/2 activity will be developed for the treatment of those diseases characterized by dysregulated gene expression through ERK1/2 activation.

The NF2 tumor suppressor merlin interacts with Ras and RasGAP, which may modulate Ras signaling

Inactivation of the tumor suppressor NF2/merlin underlies neurofibromatosis type 2 (NF2) and some sporadic tumors. Previous studies have established that merlin mediates contact inhibition of proliferation; however, the exact mechanisms remain obscure and multiple pathways have been implicated. We have previously reported that merlin inhibits Ras and Rac activity during contact inhibition, but how merlin regulates Ras activity has remained elusive. Here we demonstrate that merlin can directly interact with both Ras and p120RasGAP (also named RasGAP). While merlin does not increase the catalytic activity of RasGAP, the interactions with Ras and RasGAP may fine-tune Ras signaling. In vivo, loss of RasGAP in Schwann cells, unlike the loss of merlin, failed to promote tumorigenic growth in an orthotopic model. Therefore, modulation of Ras signaling through RasGAP likely contributes to, but is not sufficient to account for, merlin’s tumor suppressor activity. Our study provides new insight into the mechanisms of merlin-dependent Ras regulation and may have additional implications for merlin-dependent regulation of other small GTPases.

Gamma secretase dependent release of the CD44 cytoplasmic tail upregulates IFI16 in cd44-/- tumor cells, MEFs and macrophages

The adhesion molecule and co-receptor of receptor tyrosine kinases, CD44, is expressed in all cells of the immune system, but also in numerous non-immune cells. CD44 plays roles in the cellular response to different pathogens. The molecular actions of CD44 during these processes are by and large still unknown. The CD44 molecule undergoes a sequential proteolytic cleavage which leads to the release of a soluble intracellular domain (CD44-ICD). Previous reports had shown that the CD44-ICD is taken up into the nucleus where it enhances transcription of specific target genes. By RNA profiling we identified a CD44-dependent transcriptional increase of interferon-responsive genes, among them IFI16. IFI16 is important in the innate immune response. It senses and binds pathogenic DNA and, together with cGAS, activates the cGAS-cGAMP-STING pathway and induces the expression of genes relevant for the response, e.g. IFN-β. Our results show that the enhancement of IFI16 expression depended on CD44 cleavage. A CD44-negative tumor cell line, embryonic fibroblasts and bone marrow-derived macrophages from cd44^-/- mice were reduced in their response to IFN-γ, to viral DNA fragments and to Listeria monocytogenes infection. We could rescue the deficiency of CD44 negative RPM-MC cells and cd44^-/- MEFs by expressing only the soluble CD44-ICD in the absence of any other CD44 domain. Expression of the CD44-ICD carrying a mutation that prevented the uptake into the nucleus, could not rescue the absence of CD44. This molecular aspect of regulation by CD44 may explain part of the immune phenotypes of mice with cd44 gene disruption.

CPI-17 drives oncogenic Ras signaling in human melanomas via Ezrin-Radixin-Moesin family proteins

Hyperactive Ras signaling has strong oncogenic effects causing several different forms of cancer. Hyperactivity is frequently induced by mutations within Ras itself, which account for up to 30% of all human cancers. In addition, hyperactive Ras signaling can also be triggered independent of Ras by either mutation or by misexpression of various upstream regulators and immediate downstream effectors. We have previously reported that C-kinase potentiated protein phosphatase-1 inhibitor of 17 kDa (CPI-17) can drive Ras activity and promote tumorigenic transformation by inhibition of the tumor suppressor Merlin. We now describe an additional element of this oncogenic mechanism in the form of the ezrin-radixin-moesin (ERM) protein family, which exhibits opposing roles in Ras activity control. Thus, CPI-17 drives Ras activity and tumorigenesis in a two-fold way; inactivation of the tumor suppressor merlin and activation of the growth promoting ERM family. The in vivo significance of this oncogenic switch is highlighted by demonstrating CPI-17's involvement in human melanoma pathogenesis.

Regulation of ErbB2 localization and function in breast cancer cells by ERM proteins

The ERM protein family is implicated in processes such as signal transduction, protein trafficking, cell proliferation and migration. Consequently, dysregulation of ERM proteins has been described to correlate with carcinogenesis of different cancer types. However, the underlying mechanisms are poorly understood. Here, we demonstrate a novel functional interaction between ERM proteins and the ErbB2 receptor tyrosine kinase in breast cancer cells. We show that the ERM proteins ezrin and radixin are associated with ErbB2 receptors at the plasma membrane, and depletion or functional inhibition of ERM proteins destabilizes the interaction of ErbB2 with ErbB3, Hsp90 and Ebp50. Accompanied by the dissociation of this protein complex, binding of ErbB2 to the ubiquitin-ligase c-Cbl is increased, and ErbB2 becomes dephosphorylated, ubiquitinated and internalized. Furthermore, signaling via Akt- and Erk-mediated pathways is impaired upon ERM inhibition. Finally, interference with ERM functionality leads to receptor degradation and reduced cellular levels of ErbB2 and ErbB3 receptors in breast cancer cells.

A Novel Invasive-Related Biomarker in Three Subtypes of Nonfunctioning Pituitary Adenomas

OBJECTIVE

To identify biomarkers key to invasiveness of the 3 subtypes of nonfunctioning pituitary adenomas (NFPAs) and provide a guidance for therapeutic decision making and identification of potential adjuvant drugs.

METHODS

Fifty NFPA tumor tissues obtained from transsphenoidal surgery were used in the study. Three invasive NFPAs and 4 noninvasive NFPAs were used for gene expression microarray analyses. In addition, there are 5 invasive NFPAs and 4 noninvasive NFPAs used for proteomic analyses. Invasive-related biomarkers were identified by bioinformatics analysis by integrating the transcriptomics and proteomics data sets. All 3 subtypes of NFPAs (null cell adenomas, oncocytomas, and gonadotroph adenomas) were used to validate differentially expressed candidate biomarkers by means of quantitative real-time reverse transcription polymerase chain reaction and Western blot. The level of EZR was downregulated in pituitary adenoma cell line GH3 to investigate the invasive effect of EZR on GH3 cells by using the RNA interference technique.

RESULTS

Eight genes involved in the invasion function were found by bioinformatics analysis, and the EZR gene was identified as a novel invasive-related biomarker in the 3 subtypes of NFPAs. The expression level of EZR was found higher in terms of invasiveness than the noninvasive ones of the 3 subtypes of NFPAs. Moreover, the knockdown of EZR inhibited the invasion of GH3 cells in vitro.

CONCLUSIONS

EZR is a novel biomarker in terms of invasion among the 3 subtypes of NFPAs, and it is a promising guide for therapeutic decision making as well.

Regulation of E3 ubiquitin ligase-1 (WWP1) by microRNA-452 inhibits cancer cell migration and invasion in prostate cancer

Background:

MicroRNA-224 (miR-224) and microRNA-452 (miR-452) are closely located on the human chromosome Xq28 region. miR-224 functions as a tumour suppressor by targeting tumour protein D52 (TPD52) in prostate cancer (PCa). Here, we aimed to investigate the functional significance of miR-452 in PCa cells.

Methods:

Functional studies of PCa cells were performed using transfection with mature miRNAs or siRNAs. Genome-wide gene expression analysis, in silico analysis, and dual-luciferase reporter assays were applied to identify miRNA targets. The association between miR-452 levels and overall patient survival was estimated by the Kaplan–Meier method.

Results:

Expression of miR-452 was significantly downregulated in PCa tissues. Transfection with mature miR-452 inhibited the migration and invasion of PCa cells. Kaplan–Meier survival curves showed that low expression of miR-452 predicted a short duration of progression to castration-resistant PCa. WW domain-containing E3 ubiquitin protein ligase-1 (WWP1) was a direct target of miR-452, and knockdown of WWP1 inhibited the migration and invasion of PCa cells. WWP1 was upregulated in PCa clinical specimens.

Conclusions:

Regulation of the miR-452–WWP1 axis contributed to PCa cell migration and invasion, and elucidation of downstream signalling of this axis will provide new insights into the mechanisms of PCa oncogenesis and metastasis.

Role of Merlin/NF2 inactivation in tumor biology

Merlin (Moesin-ezrin-radixin-like protein, also known as schwannomin) is a tumor suppressor protein encoded by the neurofibromatosis type 2 gene NF2. Loss of function mutations or deletions in NF2 cause neurofibromatosis type 2 (NF2), a multiple tumor forming disease of the nervous system. NF2 is characterized by the development of bilateral vestibular schwannomas. Patients with NF2 can also develop schwannomas on other cranial and peripheral nerves, as well as meningiomas and ependymomas. The only potential treatment is surgery/radiosurgery, which often results in loss of function of the involved nerve. There is an urgent need for chemotherapies that slow or eliminate tumors and prevent their formation in NF2 patients. Interestingly NF2 mutations and merlin inactivation also occur in spontaneous schwannomas and meningiomas, as well as other types of cancer including mesothelioma, glioma multiforme, breast, colorectal, skin, clear cell renal cell carcinoma, hepatic and prostate cancer. Except for malignant mesotheliomas, the role of NF2 mutation or inactivation has not received much attention in cancer, and NF2 might be relevant for prognosis and future chemotherapeutic approaches. This review discusses the influence of merlin loss of function in NF2-related tumors and common human cancers. We also discuss the NF2 gene status and merlin signaling pathways affected in the different tumor types and the molecular mechanisms that lead to tumorigenesis, progression and pharmacological resistance.

Targeted Chemotherapy in Bone and Soft-Tissue Sarcoma

Historically surgical intervention has been the mainstay of therapy for bone and soft-tissue sarcomas, augmented with adjuvant radiation for local control. Although cytotoxic chemotherapy revolutionized the treatment of many sarcomas, classic treatment regimens are fraught with side effects while outcomes have plateaued. However, since the approval of imatinib in 2002, research into targeted chemotherapy has increased exponentially. With targeted therapies comes the potential for decreased side effects and more potent, personalized treatment options. This article reviews the evolution of medical knowledge regarding sarcoma, the basic science of sarcomatogenesis, and the major targets and pathways now being studied.

Tumor Suppressor NF2 Blocks Cellular Migration by Inhibiting Ectodomain Cleavage of CD44

Ectodomain cleavage (shedding) of transmembrane proteins by metalloproteases (MMP) generates numerous essential signaling molecules, but its regulation is not totally understood. CD44, a cleaved transmembrane glycoprotein, exerts both antiproliferative or tumor-promoting functions, but whether proteolysis is required for this is not certain. CD44-mediated contact inhibition and cellular proliferation are regulated by counteracting CD44 C-terminal interacting proteins, the tumor suppressor protein merlin (NF2) and ERM proteins (ezrin, radixin, moesin). We show here that activation or overexpression of constitutively active merlin or downregulation of ERMs inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced [as well as serum, hepatocyte growth factor (HGF), or platelet-derived growth factor (PDGF)] CD44 cleavage by the metalloprotease ADAM10, whereas overexpressed ERM proteins promoted cleavage. Merlin- and ERM-modulated Ras or Rac activity was not required for this function. However, latrunculin (an actin-disrupting toxin) or an ezrin mutant which is unable to link CD44 to actin, inhibited CD44 cleavage, identifying a cytoskeletal C-terminal link as essential for induced CD44 cleavage. Cellular migration, an important tumor property, depended on CD44 and its cleavage and was inhibited by merlin. These data reveal a novel function of merlin and suggest that CD44 cleavage products play a tumor-promoting role. Neuregulin, an EGF ligand released by ADAM17 from its pro-form NRG1, is predominantly involved in regulating cellular differentiation. In contrast to CD44, release of neuregulin from its pro-form was not regulated by merlin or ERM proteins. Disruption of the actin cytoskeleton however, also inhibited NRG1 cleavage. This current study presents one of the first examples of substrate-selective cleavage regulation.

IMPLICATIONS

Investigating transmembrane protein cleavage and their regulatory pathways have provided new molecular insight into their important role in cancer formation and possible treatment.

Novel mechanism of JNK pathway activation by adenoviral E1A

The adenoviral oncoprotein E1A influences cellular regulation by interacting with a number of cellular proteins. In collaboration with complementary oncogenes, E1A fully transforms primary cells. As part of this action, E1A inhibits transcription of c-Jun:Fos target genes while promoting that of c-Jun:ATF2-dependent genes including jun. Both c-Jun and ATF2 are hyperphosphorylated in response to E1A. In the current study, E1A was fused with the ligand binding domain of the estrogen receptor (E1A-ER) to monitor the immediate effect of E1A activation. With this approach we now show that E1A activates c-Jun N-terminal kinase (JNK), the upstream kinases MKK4 and MKK7, as well as the small GTPase Rac1. Activation of the JNK pathway requires the N-terminal domain of E1A, and, importantly, is independent of transcription. In addition, it requires the presence of ERM proteins. Downregulation of signaling components upstream of JNK inhibits E1A-dependent JNK/c-Jun activation. Taking these findings together, we show that E1A activates the JNK/c-Jun signaling pathway upstream of Rac1 in a transcription-independent manner, demonstrating a novel mechanism of E1A action.

An intimate look at LET-23 EGFR trafficking in the vulval cells of live C. elegans larvae

Precise cell fate specification is essential for organ formation. A simple view is that one or several signal sending cells emit a ligand to a group of signal receiving cells that express the corresponding receptor, which transduces the signal through intracellular enzyme pathways. All these events must be spatio-temporally regulated to achieve the proper strength, duration and output of the signaling pathways. In particular, the production and secretion of the ligand has to be coordinated with the expression and accessibility of the receptor in the signal receiving cells. Furthermore, removal of the ligand or receptor is key to achieve proper signal termination and prevent excess cell differentiation and proliferation. Improper regulation of any of these events may cause developmental defects and human disease. C. elegans is an excellent model to systematically identify genes that control the localization and activity of the Epidermal Growth Factor Receptor (EGFR) homolog LET-23. To identify regulators of LET-23 trafficking, Haag et al. observed LET-23 localization in the vulva precursor cells (VPCs) of RNAi treated larvae by live fluorescent microscopy. In this comment, we provide an overview of the newly identified regulators of LET-23 trafficking and discuss the role of the Ezrin/Radixin/Moesin homolog ERM-1 as a temporal regulator of EGFR signaling.