Regulation of vesicle trafficking in madin-darby canine kidney cells by Rab11a and Rab25

Rab25 is involved in hypospadias via the β1 integrin/EGFR pathway

BACKGROUND

Hypospadias is a common congenital abnormality of the penile. Abnormal regulation of critical genes involved in urethral development leads to hypospadias. We used the Rab25-/- mice and foreskin fibroblasts transfected with lentivirus in vitro and in vivo to investigate the role of Rab25 in hypospadias.

METHODS

The expression levels of various molecules in tissue samples and foreskin fibroblasts were confirmed using molecular biology methods (western blotting, PCR, immunohistochemistry, etc.). A scanning electron microscope (SEM) was used to visualize the external morphology of genital tubercles (GTs) of gestation day (GD) 18.5 male wild-type (WT) and Rab25-/- mice.

RESULTS

An expanded distal cleft and V-shaped urethral opening were observed in GD 18.5 Rab25-/- mice. We demonstrated that Rab25 mediated hypospadias through the β1 integrin/EGFR pathway. In addition, silencing Rab25 inhibited cell proliferation and migration and promoted apoptosis in the foreskin fibroblasts; Ki-67- and TUNEL-positive cells were mainly concentrated near the urethral seam.

CONCLUSION

These findings suggest that Rab25 plays an essential role in hypospadias by activation of β1 integrin/EGFR pathway, and Rab25 is a critical mediator of urethral seam formation in GD18.5 male fetal mice.

Coronavirus M Protein Trafficking in Epithelial Cells Utilizes a Myosin Vb Splice Variant and Rab10

The membrane (M) glycoprotein of coronaviruses (CoVs) serves as the nidus for virion assembly. Using a yeast two-hybrid screen, we identified the interaction of the cytosolic tail of Murine Hepatitis Virus (MHV-CoV) M protein with Myosin Vb (MYO5B), specifically with the alternative splice variant of cellular MYO5B including exon D (MYO5B+D), which mediates interaction with Rab10. When co-expressed in human lung epithelial A549 and canine kidney epithelial MDCK cells, MYO5B+D co-localized with the MHV-CoV M protein, as well as with the M proteins from Porcine Epidemic Diarrhea Virus (PEDV-CoV), Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome 2 (SARS-CoV-2). Co-expressed M proteins and MYO5B+D co-localized with endogenous Rab10 and Rab11a. We identified point mutations in MHV-CoV M that blocked the interaction with MYO5B+D in yeast 2-hybrid assays. One of these point mutations (E121K) was previously shown to block MHV-CoV virion assembly and its interaction with MYO5B+D. The E to K mutation at homologous positions in PEDV-CoV, MERS-CoV and SARS-CoV-2 M proteins also blocked colocalization with MYO5B+D. The knockdown of Rab10 blocked the co-localization of M proteins with MYO5B+D and was rescued by re-expression of CFP-Rab10. Our results suggest that CoV M proteins traffic through Rab10-containing systems, in association with MYO5B+D.

RAB11A and RAB11B control mitotic spindle function in intestinal epithelial progenitor cells

RAB11 small GTPases and associated recycling endosome have been localized to mitotic spindles and implicated in regulating mitosis. However, the physiological significance of such regulation has not been observed in mammalian tissues. We have used newly engineered mouse models to investigate intestinal epithelial renewal in the absence of single or double isoforms of RAB11 family members: Rab11a and Rab11b. Comparing with single knockouts, mice with compound ablation demonstrate a defective cell cycle entry and robust mitotic arrest followed by apoptosis, leading to a total penetrance of lethality within 3 days of gene ablation. Upon Rab11 deletion ex vivo, enteroids show abnormal mitotic spindle formation and cell death. Untargeted proteomic profiling of Rab11a and Rab11b immunoprecipitates has uncovered a shared interactome containing mitotic spindle microtubule regulators. Disrupting Rab11 alters kinesin motor KIF11 function and impairs bipolar spindle formation and cell division. These data demonstrate that RAB11A and RAB11B redundantly control mitotic spindle function and intestinal progenitor cell division, a mechanism that may be utilized to govern the homeostasis and renewal of other mammalian tissues.

Sonic hedgehog is basolaterally sorted from the TGN and transcytosed to the apical domain involving Dispatched-1 at Rab11-ARE

Hedgehog proteins (Hhs) secretion from apical and/or basolateral domains occurs in different epithelial cells impacting development and tissue homeostasis. Palmitoylation and cholesteroylation attach Hhs to membranes, and Dispatched-1 (Disp-1) promotes their release. How these lipidated proteins are handled by the complex secretory and endocytic pathways of polarized epithelial cells remains unknown. We show that polarized Madin-Darby canine kidney cells address newly synthesized sonic hedgehog (Shh) from the TGN to the basolateral cell surface and then to the apical domain through a transcytosis pathway that includes Rab11-apical recycling endosomes (Rab11-ARE). Both palmitoylation and cholesteroylation contribute to this sorting behavior, otherwise Shh lacking these lipid modifications is secreted unpolarized. Disp-1 mediates first basolateral secretion from the TGN and then transcytosis from Rab11-ARE. At the steady state, Shh predominates apically and can be basolaterally transcytosed. This Shh trafficking provides several steps for regulation and variation in different epithelia, subordinating the apical to the basolateral secretion.

Endosomal recycling protein Rab11 in Parkin and Pink1 signaling in Drosophila model of Parkinson's disease

Neurodegenerative diseases are progressive disorders of the nervous system primarily affecting the loss of neuronal cells present in the brain. Although most neurodegenerative cases are sporadic, some familial genes are found to be involved in the neurodegenerative diseases. The extensively studied parkin and pink1 gene products are known to be involved in the removal of damaged mitochondria via autophagy (mitophagy), a quality control process. If the function of any of these genes is somehow disrupted, accumulation of damaged mitochondria occurs in the forms of protein aggregates in the cytoplasm, leading to formation of the Lewy-bodies. Autophagy is an important catabolic process where the endosomal Rab proteins are seen to be involved. Rab11, an endosomal recycling protein, serves as an ATG9A carrier that helps in autophagosome formation and maturation. Earlier studies have reported that loss of Rab11 prevents the fusion of autophagosomes with the late endosomes hampering the autophagy pathway resulting in apoptosis of cells. In this study, we have emphasized on the importance and functional role of Rab11 in the molecular pathway of Parkin/Pink1 in Parkinson's disease.

Polarized trafficking and copper transport activity of ATP7B: a mutational approach to establish genotype-phenotype correlation in Wilson disease

Mutation in ATP7B gene causes Wilson disease (WD) that is characterized by severe hepatic and neurological symptoms. ATP7B localizes at the trans-Golgi Network (TGN) transporting copper to copper-dependent enzymes and traffics in apically targeted vesicles upon intracellular copper elevation. To decode the cellular underpinnings of WD manifestation we investigated copper-responsive polarized trafficking and copper transport activity of fifteen WD causing point mutations in ATP7B. Amino-terminal mutations Gly85Val, Leu168Pro and Gly591Asp displayed TGN and sub-apical localization whereas, Leu492Ser mislocalized at the basolateral region. The actuator domain mutation Gly875Arg shows retention in the endoplasmic reticulum (ER), Ala874Val and Leu795Phe show partial targeting to TGN and post-Golgi vesicles. The Nucleotide-Binding Domain mutations His1069Gln and Leu1083Phe also display impaired targeting. The C-terminal mutations Leu1373Pro/Arg is arrested at ER but Ser1423Asn shows TGN localization. Transmembrane mutant Arg778Leu resides in ER and TGN while Arg969Gln is exclusively ER localized. Cellular Cu level does not alter the targeting of any of the studied mutations. Mutants that traffic to TGN exhibits biosynthetic function. Finally, we correlated cellular phenotypes with the clinical manifestation of the two most prevalent mutations; the early onset and more aggressive WD caused by Arg778Leu and the milder form of WD caused by mutation His1069Gln. This article is protected by copyright. All rights reserved.

Autophagy gene ATG7 regulates albumin transcytosis in renal tubule epithelial cells

Receptor-mediated albumin transport in proximal tubule epithelial cells (PTECs) is important to control proteinuria. Autophagy is an evolutionarily conserved degradation pathway, and its role in intracellular trafficking through interactions with the endocytic pathway has recently been highlighted. Here, we determined whether autophagy regulates albumin transcytosis in PTECs and suppresses albumin-induced cytotoxicity using human proximal tubule (HK-2) cells. The neonatal Fc receptor (FcRn), a receptor for albumin transcytosis, is partially colocalized with autophagosomes. Recycling of FcRn was attenuated, and FcRn accumulated in autophagy-related 7 (ATG7) knockdown HK-2 cells. Colocalization of FcRn with RAB7-positive late endosomes and RAB11-positive recycling endosomes was reduced in ATG7 knockdown cells, which decreased recycling of FcRn to the plasma membrane. In ATG7 or autophagy-related 5 (ATG5) knockdown cells and Atg5 or Atg7 knockout mouse embryonic fibroblasts, albumin transcytosis was significantly reduced and intracellular albumin accumulation was increased. Finally, the release of kidney injury molecule-1, a marker of tubule injury, from ATG7 or ATG5 knockdown cells was increased in response to excess albumin. In conclusion, suppression of autophagy in tubules impairs FcRn transport, thereby inhibiting albumin transcytosis. The resulting accumulation of albumin induces cytotoxicity in tubules.NEW & NOTEWORTHY Albumin transport in proximal tubule epithelial cells (PTECs) is important to control proteinuria. The neonatal Fc receptor (FcRn), a receptor for albumin transcytosis, is partially colocalized with autophagosomes. Recycling of FcRn to the plasma membrane was decreased in autophagy-related 7 (ATG7) knockdown cells. In addition, albumin transcytosis was decreased in ATG7 or autophagy-related 5 (ATG5) knockdown PTECs. Finally, release of kidney injury molecule-1 from ATG7 or ATG5 knockdown cells was increased in response to excess albumin.

Epithelial-to-Mesenchymal Plasticity in Circulating Tumor Cell Lines Sequentially Derived from a Patient with Colorectal Cancer

Simple Summary

Metastasis is a complex dynamic multistep process; however, our knowledge is still limited. Very few circulating tumor cells (CTCs) are metastatic precursor cells and represent the intermediate stage of metastasis. Epithelial–mesenchymal plasticity (EMP) has crucial roles in tissue development and homeostasis, and also in metastasis formation. In this study, we explored the EMP phenotype of a unique series of CTC lines, obtained from a patient with colon cancer during the disease course and treatment, by detecting markers involved in the epithelial–mesenchymal and mesenchymal–epithelial (MET) transitions. This study shows that these colon CTC lines have acquired only few mesenchymal features to migrate and intravasate, whereas an increase of MET-related markers was observed, suggesting that metastasis-competent CTCs need to revert quickly to the epithelial phenotype to reinitiate a tumor at a distant site.

Abstract

Metastasis is a complicated and only partially understood multi-step process of cancer progression. A subset of cancer cells that can leave the primary tumor, intravasate, and circulate to reach distant organs are called circulating tumor cells (CTCs). Multiple lines of evidence suggest that in metastatic cancer cells, epithelial and mesenchymal markers are co-expressed to facilitate the cells’ ability to go back and forth between cellular states. This feature is called epithelial-to-mesenchymal plasticity (EMP). CTCs represent a unique source to understand the EMP features in metastatic cascade biology. Our group previously established and characterized nine serial CTC lines from a patient with metastatic colon cancer. Here, we assessed the expression of markers involved in epithelial–mesenchymal (EMT) and mesenchymal–epithelial (MET) transition in these unique CTC lines, to define their EMP profile. We found that the oncogenes MYC and ezrin were expressed by all CTC lines, but not SIX1, one of their common regulators (also an EMT inducer). Moreover, the MET activator GRHL2 and its putative targets were strongly expressed in all CTC lines, revealing their plasticity in favor of an increased MET state that promotes metastasis formation.

Rab11-FIP1 and Rab11-FIP5 Regulate pIgR/pIgA Transcytosis through TRIM21-Mediated Polyubiquitination

Polymeric immunoglobulin receptor (pIgR)-mediated polymeric immunoglobulin A (pIgA) transcytosis across mucosal epithelial cells plays an essential role in mucosal immunity. The general trafficking process has been well investigated, yet the elaborate regulatory mechanisms remain enigmatic. We identified a new pIgR interacting protein, the Rab11 effector Rab11-FIP1. Rab11-FIP1 and Rab11-FIP5 knockdown additively impaired pIgA transcytosis in both polarized and incompletely polarized cells. Moreover, Rab11-FIP1 and Rab11-FIP5 knockdown exhibited more significant inhibitory effects on pIgA transcytosis in incompletely polarized cells than in polarized cells. Interestingly, the trafficking process of pIgA in incompletely polarized cells is distinct from that in polarized cells. In incompletely polarized cells, the endocytic pIgR/pIgA was first transported from the basolateral plasma membrane to the vicinity of the centrosome where Rab11-FIP1 and Rab11-FIP5 bound to it, before the Rab11a-positive endosomes containing pIgR/pIgA, Rab11-FIP1 and Rab11-FIP5 were further transported to the apical plasma membrane via Golgi apparatus. During the trafficking process, TRIM21 mediated the K11-linked polyubiquitination of Rab11-FIP1 and the K6-linked polyubiquitination of Rab11-FIP5 to promote their activation and pIgA transcytosis. This study indicates that polyubiquitinated Rab11-FIP1 and Rab11-FIP5 mediated by TRIM21 cooperatively facilitate pIgA transcytosis and provides new insights into the intracellular trafficking process of pIgA in incompletely polarized cells.

CD13 orients the apical-basal polarity axis necessary for lumen formation

Polarized epithelial cells can organize into complex structures with a characteristic central lumen. Lumen formation requires that cells coordinately orient their polarity axis so that the basolateral domain is on the outside and apical domain inside epithelial structures. Here we show that the transmembrane aminopeptidase, CD13, is a key determinant of epithelial polarity orientation. CD13 localizes to the apical membrane and associates with an apical complex with Par6. CD13-deficient cells display inverted polarity in which apical proteins are retained on the outer cell periphery and fail to accumulate at an intercellular apical initiation site. Here we show that CD13 is required to couple apical protein cargo to Rab11-endosomes and for capture of endosomes at the apical initiation site. This role in polarity utilizes the short intracellular domain but is independent of CD13 peptidase activity.

HIV-1 Hijacking of Host ATPases and GTPases That Control Protein Trafficking

The human immunodeficiency virus (HIV-1) modifies the host cell environment to ensure efficient and sustained viral replication. Key to these processes is the capacity of the virus to hijack ATPases, GTPases and the associated proteins that control intracellular protein trafficking. The functions of these energy-harnessing enzymes can be seized by HIV-1 to allow the intracellular transport of viral components within the host cell or to change the subcellular distribution of antiviral factors, leading to immune evasion. Here, we summarize how energy-related proteins deviate from their normal functions in host protein trafficking to aid the virus in different phases of its replicative cycle. Recent discoveries regarding the interplay among HIV-1 and host ATPases and GTPases may shed light on potential targets for pharmacological intervention.

Hherisomes, Hedgehog specialized recycling endosomes, are required for high level Hedgehog signaling and tissue growth

In metazoans, tissue growth and patterning is partly controlled by the Hedgehog (Hh) morphogen. Using immuno-electron microscopy on Drosophila wing imaginal discs, we identified a cellular structure, the Hherisomes, which contain the majority of intracellular Hh. Hherisomes are recycling tubular endosomes, and their formation is specifically boosted by overexpression of Hh. Expression of Rab11, a small GTPase involved in recycling endosomes, boosts the size of Hherisomes and their Hh concentration. Conversely, increased expression of the transporter Dispatched, a regulator of Hh secretion, leads to their clearance. We show that increasing Hh density in Hherisomes through Rab11 overexpression enhances both the level of Hh signaling and disc pouch growth, whereas Dispatched overexpression decreases high-level Hh signaling and growth. We propose that, upon secretion, a pool of Hh triggers low-level signaling, whereas a second pool of Hh is endocytosed and recycled through Hherisomes to stimulate high-level signaling and disc pouch growth. Altogether, our data indicate that Hherisomes are required to sustain physiological Hh activity necessary for patterning and tissue growth in the wing disc.

Rab27b regulates extracellular vesicle production in cells infected with Kaposi's sarcoma-associated herpesvirus to promote cell survival and persistent infection

Extracellular vesicles (EVs) play a crucial role in cell-to-cell communication. EVs and viruses share several properties related to their structure and the biogenesis machinery in cells. EVs from virus-infected cells play a key role in virus spread and suppression using various loading molecules, such as viral proteins, host proteins, and microRNAs. However, it remains unclear how and why viruses regulate EV production inside host cells. The purpose of this study is to investigate the molecular mechanisms underlying EV production and their roles in Kaposi's sarcoma-associated herpesvirus (KSHV)-infected cells. Here, we found that KSHV induced EV production in human endothelial cells via Rab-27b upregulation. The suppression of Rab27b expression in KSHV-infected cells enhanced cell death by increasing autophagic flux and autolysosome formation. Our results indicate that Rab27b regulates EV biogenesis to promote cell survival and persistent viral infection during KSHV infection, thereby providing novel insights into the crucial role of Rab-27b in the KSHV life cycle.

RAB11-Mediated Trafficking and Human Cancers: An Updated Review

Simple Summary

The small GTPase RAB11 is a master regulator of both vesicular trafficking and membrane dynamic defining the surface proteome of cellular membranes. As a consequence, the alteration of RAB11 activity induces changes in both the sensory and the transduction apparatuses of cancer cells leading to tumor progression and invasion. Here, we show that this strictly depends on RAB11′s ability to control the sorting of signaling receptors from endosomes. Therefore, RAB11 is a potential therapeutic target over which to develop future therapies aimed at dampening the acquisition of aggressive traits by cancer cells.

Abstract

Many disorders block and subvert basic cellular processes in order to boost their progression. One protein family that is prone to be altered in human cancers is the small GTPase RAB11 family, the master regulator of vesicular trafficking. RAB11 isoforms function as membrane organizers connecting the transport of cargoes towards the plasma membrane with the assembly of autophagic precursors and the generation of cellular protrusions. These processes dramatically impact normal cell physiology and their alteration significantly affects the survival, progression and metastatization as well as the accumulation of toxic materials of cancer cells. In this review, we discuss biological mechanisms ensuring cargo recognition and sorting through a RAB11-dependent pathway, a prerequisite to understand the effect of RAB11 alterations in human cancers.

A conserved LDL-receptor motif regulates corin and CD320 membrane targeting in polarized renal epithelial cells

Selective protein distribution on distinct plasma membranes is important for epithelial cell function. To date, how proteins are directed to specific epithelial cell surface is not fully understood. Here we report a conserved DSSDE motif in LDL-receptor (LDLR) modules of corin (a transmembrane serine protease) and CD320 (a receptor for vitamin B12 uptake), which regulates apical membrane targeting in renal epithelial cells. Altering this motif prevents specific apical corin and CD320 expression in polarized Madin-Darby canine kidney (MDCK) cells. Mechanistic studies indicate that this DSSDE motif participates in a Rab11a-dependent mechanism that specifies apical sorting. In MDCK cells, inhibition of Rab11a, but not Rab11b, expression leads to corin and CD320 expression on both apical and basolateral membranes. Together, our results reveal a novel molecular recognition mechanism that regulates LDLR module-containing proteins in their specific apical expression in polarized renal epithelial cells.

Dysregulated Plasma Membrane Turnover Underlying Dendritic Pathology in Neurodegenerative Diseases

Due to their enormous surface area compared to other cell types, neurons face unique challenges in properly handling supply and retrieval of the plasma membrane (PM)-a process termed PM turnover-in their distal areas. Because of the length and extensiveness of dendritic branches in neurons, the transport of materials needed for PM turnover from soma to distal dendrites will be inefficient and quite burdensome for somatic organelles. To meet local demands, PM turnover in dendrites most likely requires local cellular machinery, such as dendritic endocytic and secretory systems, dysregulation of which may result in dendritic pathology observed in various neurodegenerative diseases (NDs). Supporting this notion, a growing body of literature provides evidence to suggest the pathogenic contribution of dysregulated PM turnover to dendritic pathology in certain NDs. In this article, we present our perspective view that impaired dendritic endocytic and secretory systems may contribute to dendritic pathology by encumbering PM turnover in NDs.

VISTA: a novel immunotherapy target for normalizing innate and adaptive immunity

V-domain Ig suppressor of T cell activation (VISTA) is a novel checkpoint regulator with limited homology to other B7 family members. The constitutive expression of VISTA on both the myeloid and T lymphocyte lineages coupled to its important role in regulating innate and adaptive immune responses, qualifies VISTA to be a promising target for immunotherapeutic intervention. Studies have shown differential impact of agonistic and antagonistic targeting of VISTA, providing a unique landscape for influencing the outcome of cancer and inflammatory diseases.

Rab GTPases: Emerging Oncogenes and Tumor Suppressive Regulators for the Editing of Survival Pathways in Cancer

The Rab GTPase family of proteins are mediators of membrane trafficking, conferring identity to the cell membranes. Recently, Rab and Rab-associated factors have been recognized as major regulators of the intracellular positioning and activity of signaling pathways regulating cell growth, survival and programmed cell death or apoptosis. Membrane trafficking mediated by Rab proteins is controlled by intracellular localization of Rab proteins, Rab-membrane interactions and GTP-activation processes. Aberrant expression of Rab proteins has been reported in multiple cancers such as lung, brain and breast malignancies. Mutations in Rab-coding genes and/or post-translational modifications in their protein products disrupt the cellular vesicle trafficking network modulating tumorigenic potential, cellular migration and metastatic behavior. Conversely, Rabs also act as tumor suppressive factors inducing apoptosis and inhibiting angiogenesis. Deconstructing the signaling mechanisms modulated by Rab proteins during apoptosis could unveil underlying molecular mechanisms that may be exploited therapeutically to selectively target malignant cells.

Quantitative live cell imaging reveals influenza virus manipulation of Rab11A transport through reduced dynein association

Assembly of infectious influenza A viruses (IAV) is a complex process involving transport from the nucleus to the plasma membrane. Rab11A-containing recycling endosomes have been identified as a platform for intracellular transport of viral RNA (vRNA). Here, using high spatiotemporal resolution light-sheet microscopy (~1.4 volumes/second, 330 nm isotropic resolution), we quantify Rab11A and vRNA movement in live cells during IAV infection and report that IAV infection decreases speed and increases arrest of Rab11A. Unexpectedly, infection with respiratory syncytial virus alters Rab11A motion in a manner opposite to IAV, suggesting that Rab11A is a common host component that is differentially manipulated by respiratory RNA viruses. Using two-color imaging we demonstrate co-transport of Rab11A and IAV vRNA in infected cells and provide direct evidence that vRNA-associated Rab11A have altered transport. The mechanism of altered Rab11A movement is likely related to a decrease in dynein motors bound to Rab11A vesicles during IAV infection.

Rab25 Deficiency Perturbs Epidermal Differentiation and Skin Barrier Function in Mice

Rab25, a member of the Rab11 small GTPase family, is central to achieving cellular polarity in epithelial tissues. Rab25 is highly expressed in epithelial cells of various tissues including breast, vagina, cervix, the gastrointestinal tract, and skin. Rab25 plays key roles in tumorigenesis, mainly by regulating epithelial differentiation and proliferation. However, its role in skin physiology is relatively unknown. In this study, we demonstrated that Rab25 knock-out (KO) mice show a skin barrier dysfunction with high trans-epidermal water loss and low cutaneous hydration. To examine this observation, we investigated the histology and epidermal differentiation markers of the skin in Rab25 KO mice. Rab25 KO increased cell proliferation at the basal layer of epidermis, whereas the supra-basal layer remained unaffected. Ceramide, which is a critical lipid component for skin barrier function, was not altered by Rab25 KO in its distribution or amount, as determined by immunohistochemistry. Notably, levels of epidermal differentiation markers, including loricrin, involucrin, and keratins (5, 14, 1, and 10) increased prominently in Rab25 KO mice. In line with this, depletion of Rab25 with single hairpin RNA increased the expression of differentiation markers in a human keratinocyte cell line, HaCaT. Transcriptomic analysis of the skin revealed increased expression of genes associated with skin development, epidermal development, and keratinocyte differentiation in Rab25 KO mice. Collectively, these results suggested that Rab25 is involved in the regulation of epidermal differentiation and proliferation.

Loss of Rab25 promotes the development of skin squamous cell carcinoma through the dysregulation of integrin trafficking

Rab25 can function as both a tumor suppressor and a tumor promoter across different tissues. This study sought to clarify the role of Rab25 as a tumor suppressor in skin squamous cell carcinoma (SCC). Rab25 loss was closely associated with neoplastic transition in both humans and mice. Rab25 loss was well correlated with increased cell proliferation and poor differentiation in human SCC. While Rab25 knockout (KO) in mice did not induce spontaneous tumor formation, it did significantly accelerate tumor generation and promote malignant transformation in a mouse two-stage skin carcinogenesis model. Xenografting of a Rab25-deficient human keratinocyte cell line, HaCaT, also elicited neoplastic transformation. Notably, Rab25 deficiency led to dysregulation of integrins β1, β4, and α6, which matched well with increased epidermal proliferation and impaired desmosome-tight junction formation. Rab25 deficiency induced impairment of integrin recycling, leading to the improper expression of integrins. In line with this, significant attenuation of integrin β1, β4, and α6 expression was identified in human SCCs where Rab25 was deficient. Collectively, these results suggest that loss of Rab25 promotes the development and neoplastic transition of SCC through dysregulation of integrin trafficking. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

New approaches for solving old problems in neuronal protein trafficking

Fundamental cellular properties are determined by the repertoire and abundance of proteins displayed on the cell surface. As such, the trafficking mechanisms for establishing and maintaining the surface proteome must be tightly regulated for cells to respond appropriately to extracellular cues, yet plastic enough to adapt to ever-changing environments. Not only are the identity and abundance of surface proteins critical, but in many cases, their regulated spatial positioning within surface nanodomains can greatly impact their function. In the context of neuronal cell biology, surface levels and positioning of ion channels and neurotransmitter receptors play essential roles in establishing important properties, including cellular excitability and synaptic strength. Here we review our current understanding of the trafficking pathways that control the abundance and localization of proteins important for synaptic function and plasticity, as well as recent technological advances that are allowing the field to investigate protein trafficking with increasing spatiotemporal precision.

Tolerogenic properties of the Fc portion of IgG and its relevance to the treatment and management of hemophilia

Hemophilia, or inherited genetic deficiencies in coagulation factors, results in uncontrolled bleeding requiring replacement therapy with recombinant proteins given preventively or on demand. However, a major problem with these approaches is the potential for development of immune responses to the administered proteins due to the underlying genetic deficiency of the factor(s) throughout life. As such, there is great interest in developing strategies that avoid immunogenicity and induce immune tolerance. Recently, recombinant factor VIII (rFVIII) and rFIX fused to the crystallizable fragment (Fc) domain of immunoglobulin G (IgG) have been developed as therapeutic agents for hemophilia A and B, respectively. Although it is well known that the possession of an Fc domain confers IgG's longer-lasting circulating half-life, it is not generally appreciated that the Fc domain also confers immunoregulatory properties that are associated with the induction of tolerance. Here, we review some of the latest advances in our understanding of the tolerogenic abilities of IgG Fc and the impact of Fc-fusion proteins of rFVIII on the treatment of hemophilia.

Transcellular vesicular transport in epithelial and endothelial cells: Challenges and opportunities

Vesicle-mediated transcellular transport or simply "transcytosis" is a cellular process used to shuttle macromolecules such as lipoproteins, antibodies, and albumin from one surface of a polarized cell to the other. This mechanism is in contrast to the transit of small molecules such as anions, cations and amino acids that occur via uptake, diffusion through the cytosol and release and is also distinct from paracellular leak between cells. Importantly, transcytosis has evolved as a process to selectively move macromolecules between 2 neighboring yet unique microenvironments within a multicellular organism. Examples include the movement of lipoproteins out of the circulatory system and into tissues and the delivery of immunoglobulins to mucosal surfaces. Regardless of whether the transport is conducted by endothelial or epithelial cells, the process often involves receptor-mediated uptake of a ligand into an endocytic vesicle, regulated transit of the carrier through the cytoplasm and release of the cargo via an exocytic event. While transcytosis has been examined in detail in epithelial cells, for both historical and technical reasons, the process is less understood in endothelial cells. Here, we spotlight aspects of epithelial transcytosis including recent findings and review the comparative dearth of knowledge regarding the process in endothelial cells highlighting the opportunity for further study.

Stapled peptide inhibitors of RAB25 target context-specific phenotypes in cancer

Recent evidence has established a role for the small GTPase RAB25, as well as related effector proteins, in enacting both pro-oncogenic and anti-oncogenic phenotypes in specific cellular contexts. Here we report the development of all-hydrocarbon stabilized peptides derived from the RAB-binding FIP-family of proteins to target RAB25. Relative to unmodified peptides, optimized stapled peptides exhibit increased structural stability, binding affinity, cell permeability, and inhibition of RAB25:FIP complex formation. Treatment of cancer cell lines in which RAB25 is pro-oncogenic with an optimized stapled peptide, RFP14, inhibits migration, and proliferation in a RAB25-dependent manner. In contrast, RFP14 treatment augments these phenotypes in breast cancer cells in which RAB25 is tumor suppressive. Transcriptional profiling identified significantly altered transcripts in response to RAB25 expression, and treatment with RFP14 opposes this expression profile. These data validate the first cell-active chemical probes targeting RAB-family proteins and support the role of RAB25 in regulating context-specific oncogenic phenotypes.

The Ras-family small GTPase RAB25 can exert both pro- and anti-oncogenic functions. Here, the authors develop all-hydrocarbon stabilized peptides targeting RAB25 and influencing the context-specificity phenotypes in cancer cell lines.

Membrane Transport across Polarized Epithelia

Polarized epithelial cells line diverse surfaces throughout the body forming selective barriers between the external environment and the internal milieu. To cross these epithelial barriers, large solutes and other cargoes must undergo transcytosis, an endocytic pathway unique to polarized cell types, and significant for the development of cell polarity, uptake of viral and bacterial pathogens, transepithelial signaling, and immunoglobulin transport. Here, we review recent advances in our knowledge of the transcytotic pathway for proteins and lipids. We also discuss briefly the promise of harnessing the molecules that undergo transcytosis as vehicles for clinical applications in drug delivery.

RIN1 promotes renal cell carcinoma malignancy by activating EGFR signaling through Rab25

We previously identified the important role of RIN1 expression in the prognosis of clear cell renal cell carcinoma (ccRCC). The role of RIN1 in ccRCC malignancy and underlying molecular mechanisms remain unclear. Here we report that ccRCC cells and tissues expressed more RIN1 than normal controls. Gain‐of‐function and loss‐of‐function studies demonstrated that RIN1 enhanced ccRCC cell growth, migration and invasion abilities in vitro and promoted tumor growth and metastasis in vivo. Mechanistic studies revealed that RIN1 has an activating effect on EGFR signaling in ccRCC. In addition, we unveil Rab25, a critical GTPase in ccRCC malignancy, as a functional RIN1 interacting partner. Knockdown of Rab25 eliminated the augmentation of carcinoma cell proliferation, migration and invasion by ectopic RIN1. We also confirmed that RIN1 and Rab25 expression correlates with the overall‐survival of ccRCC patients from TCGA. These findings suggest that RIN1 plays an important oncogenic role in ccRCC malignancy by activation of EGFR signaling through interacting with Rab25, and RIN1 could be employed as an effective therapeutic target for ccRCC.

The role of small GTPases and EPAC-Rap signaling in the regulation of the blood-brain and blood-retinal barriers

Maintenance and regulation of the vascular endothelial cell junctional complex is critical for proper barrier function of the blood-brain barrier (BBB) and the highly related blood-retinal barrier (BRB) that help maintain proper neuronal environment. Recent research has demonstrated that the junctional complex is actively maintained and can be dynamically regulated. Studies focusing on the mechanisms of barrier formation, maintenance, and barrier disruption have been of interest to understanding development of the BBB and BRB and identifying a means for therapeutic intervention for diseases ranging from brain tumors and dementia to blinding eye diseases. Research has increasingly revealed that small GTPases play a critical role in both barrier formation and disruption mechanisms. This review will summarize the current data on small GTPases in barrier regulation with an emphasis on the EPAC-Rap1 signaling pathway to Rho in endothelial barriers, as well as explore its potential involvement in paracellular flux and transcytosis regulation.

Knockdown of Ras-Related Protein 25 (Rab25) Inhibits the In Vitro Cytotoxicity and In Vivo Antitumor Activity of Human Glioblastoma Multiforme Cells

Ras-related protein 25 (Rab25) is a member of the Rab family, and it has been reported to play an important role in tumorigenesis. However, its direct involvement in human glioblastoma multiforme (GBM) is still unclear. The aim of the current study was to investigate the potential role of Rab25 in the growth, proliferation, invasion, and migration of human GBM. Our results showed that Rab25 expression was significantly higher in human GBM cell lines compared with a normal astrocyte cell line. In vitro functional studies revealed that knockdown of Rab25 reduced cell proliferation and inhibited invasion and migration of GBM cells. In vivo experiments showed that knockdown of Rab25 attenuated the tumor growth in nude mice. Finally, knockdown of Rab25 significantly inhibited the phosphorylation levels of PI3K and AKT in GBM cells. Taken together, these findings indicate that Rab25 may act as a tumor promoter in human GBM and that approaches to target Rab25 may provide a novel strategy to treat this disease.

A targeted RNAi screen identifies factors affecting diverse stages of receptor-mediated transcytosis

Transcytosis plays an important role in establishing cell polarity and in mediating transport of large cargo across epithelial barriers, but its molecular basis is unclear. Nelms et al. present a new dataset of genes involved in receptor-mediated transcytosis and show that the apical and basolateral recycling and transcytotic pathways are genetically separable.

Endosome transport by transcytosis is the primary mechanism by which proteins and other large cargo traverse epithelial barriers in normal tissue. Transcytosis is also essential for establishing and maintaining membrane polarity in epithelia and other polarized cells. To identify novel components of this pathway, we conducted a high-throughput RNA interference screen for factors necessary for the bidirectional transcytosis of IgG by the Fcγ receptor FcRn. This screen identified 23 genes whose suppression resulted in a reproducible decrease in FcRn-mediated transcytosis. Pulse-chase kinetic transport assays on four of the top-ranking genes (EXOC2, EXOC7, PARD6B, and LEPROT) revealed distinct effects on the apical and basolateral recycling and transcytotic pathways, demonstrating that these pathways are genetically separable. We also found a strong dependence on PARD6B for apical, but not basolateral, recycling, implicating this cell polarity gene in assembly or maintenance of the apical endosomal system. This dataset yields insights into how vesicular transport is adapted to the specialized functions of differentiated cell types and opens new research avenues into epithelial trafficking.

Annexin A6 in the liver: From the endocytic compartment to cellular physiology

Annexin A6 (AnxA6) belongs to the conserved annexin family - a group of Ca²⁺-dependent membrane binding proteins. AnxA6 is the largest of all annexins and highly expressed in smooth muscle, hepatocytes, endothelial cells and cardiomyocytes. Upon activation, AnxA6 binds to negatively charged phospholipids in a wide range of intracellular localizations, in particular the plasma membrane, late endosomes/pre-lysosomes, but also synaptic vesicles and sarcolemma. In these cellular sites, AnxA6 is believed to contribute to the organization of membrane microdomains, such as cholesterol-rich lipid rafts and confer multiple regulatory functions, ranging from vesicle fusion, endocytosis and exocytosis to programmed cell death and muscle contraction. Growing evidence supports that Ca²⁺ and Ca²⁺-binding proteins control endocytosis and autophagy. Their regulatory role seems to operate at the level of the signalling pathways that initiate autophagy or at later stages, when autophagosomes fuse with endolysosomal compartments. The convergence of the autophagic and endocytic vesicles to lysosomes shares several features that depend on Ca²⁺ originating from lysosomes/late endosomes and seems to depend on proteins that are subsequently activated by this cation. However, the involvement of Ca²⁺ and its effector proteins in these autophagic and endocytic stages still remains poorly understood. Although AnxA6 makes up almost 0.25% of total protein in the liver, little is known about its function in hepatocytes. Within the endocytic route, we identified AnxA6 in endosomes and autophagosomes of hepatocytes. Hence, AnxA6 and possibly other annexins might represent new Ca²⁺ effectors that regulate converging steps of autophagy and endocytic trafficking in hepatocytes. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Exosomes from the tumor microenvironment as reciprocal regulators that enhance prostate cancer progression

Distant organ metastasis of prostate cancer is a puzzle, and various theories have successively arisen to explain the mechanism of lethal cancer progression. While perhaps agreeable to many cancer biologists, the very statement of "seed and soil" proposed by Stephan Paget in 1881 is arguably still the major statement for organ-specific cancer metastasis. Since recent studies showed important correlations of regulation of cancer cells and the microenvironment, exosomes from cancer and stromal cells seem to create another important niche for metastasis. Stromal cells pretreated with exosomes from metastatic cancer cells increase the potential of change stromal cells. The poorly metastatic cancer cells could also enhance malignancy through transfer of proteins, microribonucleic acid and messenger ribonucleic acid to recipient cancer cells. Herein, we reviewed extracellular exosomes as a factor involved in cross-talk between stromal and prostate cancer epithelial cells.

Complex Polarity: Building Multicellular Tissues Through Apical Membrane Traffic

The formation of distinct subdomains of the cell surface is crucial for multicellular organism development. The most striking example of this is apical-basal polarization. What is much less appreciated is that underpinning an asymmetric cell surface is an equally dramatic intracellular endosome rearrangement. Here, we review the interplay between classical cell polarity proteins and membrane trafficking pathways, and discuss how this marriage gives rise to cell polarization. We focus on those mechanisms that regulate apical polarization, as this is providing a number of insights into how membrane traffic and polarity are regulated at the tissue level.

The fast-recycling receptor Megalin defines the apical recycling pathway of epithelial cells

The basolateral recycling and transcytotic pathways of epithelial cells were previously defined using markers such as transferrin (TfR) and polymeric IgA (pIgR) receptors. In contrast, our knowledge of the apical recycling pathway remains fragmentary. Here we utilize quantitative live-imaging and mathematical modelling to outline the recycling pathway of Megalin (LRP-2), an apical receptor with key developmental and renal functions, in MDCK cells. We show that, like TfR, Megalin is a long-lived and fast-recycling receptor. Megalin enters polarized MDCK cells through segregated apical sorting endosomes and subsequently intersects the TfR and pIgR pathways at a perinuclear Rab11-negative compartment termed common recycling endosomes (CRE). Whereas TfR recycles to the basolateral membrane from CRE, Megalin, like pIgR, traffics to subapical Rab11-positive apical recycling endosomes (ARE) and reaches the apical membrane in a microtubule- and Rab11-dependent manner. Hence, Megalin defines the apical recycling pathway of epithelia, with CRE as its apical sorting station.

Molecular mechanism of constitutively active Rab11A was revealed by crystal structure of Rab11A S20V

Rab11A is a small GTP-binding protein involved in the regulation of vesicle trafficking during recycling of endosomes. Substitution of S20 to V (S20V) at Rab11A inhibits the GTP hydrolysis activity of Rab11A. This mutation is known to be constitutively in an active form. Here, we report the crystal structure of the human Rab11A S20V mutant form complexed with GTP at a resolution of 2.4 Å. Without adding any substrate, Rab11A contained non-hydrolyzed natural substrate GTP in the nucleotide binding pocket with Mg(2+). In our observations, substituted V20 of Rab11A was found to interfere with proper localization of the water molecule, which mediated GTP hydrolysis, resulting in GTP being locked in an active form of Rab11A S20V.

Regulation of ENaC trafficking in rat kidney

The epithelial Na channel (ENaC) forms a pathway for Na(+) reabsorption in the distal nephron, and regulation of these channels is essential for salt homeostasis. In the rat kidney, ENaC subunits reached the plasma membrane in both immature and fully processed forms, the latter defined by either endoglycosidase H-insensitive glycosylation or proteolytic cleavage. Animals adapted to a low-salt diet have increased ENaC surface expression that is specific for the mature forms of the subunit proteins and is similar (three- to fourfold) for α, β, and γENaC. Kidney membranes were fractionated using differential centrifugation, sucrose-gradient separation, and immunoabsorption. Endoplasmic reticulum membranes, isolated using an antibody against calnexin, expressed immature γENaC, and the content decreased with Na depletion. Golgi membranes, isolated with an antibody against the cis-Golgi protein GM130, expressed both immature and processed γENaC; Na depletion increased the content of processed γENaC in this fraction by 3.8-fold. An endosomal compartment isolated using an antibody against Rab11 contained both immature and processed γENaC; the content of processed subunit increased 2.4-fold with Na depletion. Finally, we assessed the content of γENaC in the late endocytic compartments indirectly using urinary exosomes. All of the γENaC in these exosomes was in the fully cleaved form, and its content increased by 4.5-fold with Na depletion. These results imply that stimulation of ENaC surface expression results at least in part from increased rates of formation of fully processed subunits in the Golgi and subsequent trafficking to the apical membrane.

Rab11-FIP1A regulates early trafficking into the recycling endosomes

The Rab11 family of small GTPases, along with the Rab11-family interacting proteins (Rab11-FIPs), are critical regulators of intracellular vesicle trafficking and recycling. We have identified a point mutation of Threonine-197 site to an Alanine in Rab11-FIP1A, which causes a dramatic dominant negative phenotype when expressed in HeLa cells. The normally perinuclear distribution of GFP-Rab11-FIP1A was condensed into a membranous cisternum with almost no GFP-Rab11-FIP1A(T197A) remaining outside of this central locus. Also, this condensed GFP-FIP1A(T197A) altered the distribution of proteins in the Rab11a recycling pathway including endogenous Rab11a, Rab11-FIP1C, and transferrin receptor (CD71). Furthermore, this condensed GFP-FIP1A(T197A)-containing structure exhibited little movement in live HeLa cells. Expression of GFP-FIP1A(T197A) caused a strong blockade of transferrin recycling. Treatment of cells expressing GFP-FIP1A(T197A) with nocodazole did not disperse the Rab11a-containing recycling system. We also found that Rab5 and EEA1 were accumulated in membranes by GFP-Rab11-FIP1A but Rab4 was unaffected, suggesting that a direct pathway may exist from early endosomes into the Rab11a-containing recycling system. Our study of a potent inhibitory trafficking mutation in Rab11-FIP1A shows that Rab11-FIP1A associates with and regulates trafficking at an early step in the process of membrane recycling.

Critical role of Rab11a-mediated recycling endosomes in the assembly of type I parainfluenza viruses

Paramyxoviruses replicate in the cytoplasm of infected cells and newly synthesized viral nucleocapsids (vRNPs) are transported to the plasma membrane to be incorporated into progeny virions. In this study, we analyzed the impact of the Rab11-mediated recycling pathway in Sendai virus (SeV) and human parainfluenza virus type 1 (hPIV1) vRNP transport. We found that suppression of Rab11 expression caused vRNP aggregation in the cytoplasm and reduced progeny virion formation. Overexpression of constitutively active Rab11Q70L, but not dominant negative Rab11S25N co-localized with vRNP, showing that vRNP specifically recognizes the GTP-bound active form of Rab11. Moreover, Rab11Q70L co-localized with the dominant negative tails of all three subtypes of myosins, Va, Vb, and Vc, while SeV and hPIV1 vRNPs co-localized with only myosin Vb and Vc. These results highlight the critical role of Rab11 in vRNP trafficking, and suggest a specificity in the recycling endosomes parainfluenza viruses utilize for virus assembly.

Polarized protein transport and lumen formation during epithelial tissue morphogenesis

One of the major challenges in biology is to explain how complex tissues and organs arise from the collective action of individual polarized cells. The best-studied model of this process is the cross talk between individual epithelial cells during their polarization to form the multicellular epithelial lumen during tissue morphogenesis. Multiple mechanisms of apical lumen formation have been proposed. Some epithelial lumens form from preexisting polarized epithelial structures. However, de novo lumen formation from nonpolarized cells has recently emerged as an important driver of epithelial tissue morphogenesis, especially during the formation of small epithelial tubule networks. In this review, we discuss the latest findings regarding the mechanisms and regulation of de novo lumen formation in vitro and in vivo.

Structural and functional analysis of endosomal compartments in epithelial cells

Epithelial cells display segregated early endosomal compartments, termed apical sorting endosomes and basolateral sorting endosomes, that converge into a common late endosomal-lysosomal degradative compartment and common recycling endosomes (CREs). Unlike recycling endosomes of nonpolarized cells, CREs have the ability to sort apical and basolateral plasma membrane proteins into distinct apical and basolateral recycling routes, utilizing mechanisms similar to those employed by the trans Golgi network in the biosynthetic pathway. The apical recycling route includes an additional compartment, the apical recycling endosomes, consisting of multiple vesicles bundled around the basal body. Recent evidence indicates that, in addition to their role in internalizing ligands and recycling their receptors back to the cell surface, endosomal compartments act as intermediate stations in the biosynthetic routes to the plasma membrane. Here we review methods employed by our laboratory to study the endosomal compartments of epithelial cells and their multiple trafficking roles.

Downregulation of Rab25 activates Akt1 in head and neck squamous cell carcinoma

Several studies have suggested that Ras-associated binding 25 protein (Rab25) is involved in the pathogenesis of human cancer. Although it has been demonstrated that the development of head and neck squamous cell carcinoma (HNSCC) is the result of an accumulation of multiple sequential genetic and epigenetic alterations in key genes with important functions in cell growth and the cell cycle, recent studies have indicated that HNSCC is a complex and heterogenous disease. To the best of our knowledge, there is no data regarding the regulation of the Rab25 gene at the mRNA or protein level in HNSCC. Furthermore, available data on Rab25 expression in other types of cancer are conflicting. The aim of the present study was to investigate whether Rab25 is involved in the development and/or progression of HNSCC, and to analyze the mechanisms underlying its effects in this type of cancer. The expression of Rab25 mRNA in HNSCC tissues and adjacent non-tumor tissue samples was measured using reverse transcription-quantitative polymerase chain reaction, while the level of the Rab25, Akt1 and phosphorylated-Akt1 proteins was measured using western blotting. Expression of Rab25 mRNA and protein was downregulated in 69.1% and 56.1% of tumor tissue samples, respectively. This downregulation was associated with an increase in p-Akt1 expression, in the absence of a change in total Akt1 protein levels, in tumor tissues compared with normal tissues. The current findings suggest that Rab25 acts as a tumor suppressor in HNSCC.

Neisseria meningitidis subverts the polarized organization and intracellular trafficking of host cells to cross the epithelial barrier

Translocation of the nasopharyngeal barrier by Neisseria meningitidis occurs via an intracellular microtubule-dependent pathway and represents a crucial step in its pathogenesis. Despite this fact, the interaction of invasive meningococci with host subcellular compartments and the resulting impact on their organization and function have not been investigated. The influence of serogroup B strain MC58 on host cell polarity and intracellular trafficking system was assessed by confocal microscopy visualization of different plasma membrane-associated components (such as E-cadherin, ZO-1 and transferrin receptor) and evaluation of the transferrin uptake and recycling in infected Calu-3 monolayers. Additionally, the association of N. meningitidis with different endosomal compartments was evaluated through the concomitant staining of bacteria and markers specific for Rab11, Rab22a, Rab25 and Rab3 followed by confocal microscopy imaging. Subversion of the host cell architecture and intracellular trafficking system, denoted by mis-targeting of cell plasma membrane components and perturbations of transferrin transport, was shown to occur in response to N. meningitidis infection. Notably, the appearance of all of these events seems to positively correlate with the efficiency of N. meningitidis to cross the epithelial barrier. Our data reveal for the first time that N. meningitidis is able to modulate the host cell architecture and function, which might serve as a strategy of this pathogen for overcoming the nasopharyngeal barrier without affecting the monolayer integrity.

CCM-3/STRIPAK promotes seamless tube extension through endocytic recycling

The mechanisms governing apical membrane assembly during biological tube development are poorly understood. Here, we show that extension of the C. elegans excretory canal requires cerebral cavernous malformation 3 (CCM-3), independent of the CCM1 orthologue KRI-1. Loss of ccm-3 causes canal truncations and aggregations of canaliculular vesicles, which form ectopic lumen (cysts). We show that CCM-3 localizes to the apical membrane, and in cooperation with GCK-1 and STRIPAK, promotes CDC-42 signalling, Golgi stability and endocytic recycling. We propose that endocytic recycling is mediated through the CDC-42-binding kinase MRCK-1, which interacts physically with CCM-3-STRIPAK. We further show canal membrane integrity to be dependent on the exocyst complex and the actin cytoskeleton. This work reveals novel in vivo roles of CCM-3·STRIPAK in regulating tube extension and membrane integrity through small GTPase signalling and vesicle dynamics, which may help explain the severity of CCM3 mutations in patients.

Rab25 upregulation correlates with the proliferation, migration, and invasion of renal cell carcinoma

Renal cell carcinoma (RCC) is a common urological cancer with a poor prognosis. A recent cohort study revealed that the median survival of RCC patients was only 1.5 years and that <10% of the patients in the study survived up to 5 years. In tumor development, Rab GTPase are known to play potential roles such as regulation of cell proliferation, migration, invasion, communication, and drug resistance in multiple tumors. However, the correlation between Rabs expression and the occurrence, development, and metastasis of RCC remains unclear. In this study, we analyzed the transcriptional levels of 52 Rab GTPases in RCC patients. Our results showed that high levels of Rab25 expression were significantly correlated with RCC invasion classification (P < 0.01), lymph-node metastasis (P < 0.001), and pathological stage (P < 0.01). Conversely, in 786-O and A-498 cells, knocking down Rab25 protein expression inhibited cell proliferation, migration, and invasion. Our results also demonstrated that Rab25 is a target gene of let-7d, and further suggested that Rab25 upregulation in RCC is due to diminished expression of let-7d. These findings indicate that Rab25 might be a novel candidate molecule involved in RCC development, thus identifying a potential biological therapeutic target for RCC.

Rab25 is responsible for phosphoinositide 3-kinase/AKT‑mediated cisplatin resistance in human epithelial ovarian cancer cells

Rab25, a member of the Rab family of small guanosine triphosphatase, was reported to have an essential role in the development of human epithelial ovarian cancer. The present study demonstrated that Rab25 mediated the sensitivity of ovarian cancer to cisplatin, a first‑line chemotherapeutic agent for the treatment of ovarian cancer in the clinic. Overexpression of Rab25 and increased phosphoinositide 3‑kinase (PI3K)/AKT signaling were detected in cisplatin‑resistant SKOV‑3 cells compared with those in cisplatin‑sensitive ES‑2 cells. The results of the present study indicated that cisplatin resistance was primarily due to reduced G1 cell cycle arrest following cisplatin treatment in SKOV‑3 cells. By contrast, the corresponding phenomenon was not observed following treatment with a Rab25‑specific small interfering RNA or treatment with the PI3K/AKT inhibitor LY294002. Of note, inhibition of the PI3K/AKT pathway reduced Rab25 gene expression and sensitized SKOV‑3 cells to cisplatin. Furthermore, knockdown of Rab25 showed an effect comparable with blocking the PI3K/AKT pathway. In conclusion, the results of the present study demonstrated that PI3K/AKT and Rab25 significantly contributed to cisplatin resistance in human epithelial ovarian cancer; in addition, silencing Rab25 or inhibiting the PI3K/AKT pathway markedly increased the sensitivity of these cells to cisplatin.

Rab11, but not Rab4, facilitates cyclic AMP- and tauroursodeoxycholate-induced MRP2 translocation to the plasma membrane

Rab proteins (Ras homologous for brain) play an important role in vesicle trafficking. Rab4 and Rab11 are involved in vesicular trafficking to the plasma membrane from early endosomes and recycling endosomes, respectively. Tauroursodeoxycholate (TUDC) and cAMP increase bile formation, in part, by increasing plasma membrane localization of multidrug resistance-associated protein 2 (MRP2). The goal of the present study was to determine the role of these Rab proteins in the trafficking of MRP2 by testing the hypothesis that Rab11 and/or Rab4 facilitate cAMP- and TUDC-induced MRP2 translocation to the plasma membrane. Studies were conducted in HuH-NTCP cells (HuH7 cells stably transfected with human NTCP), which constitutively express MRP2. HuH-NTCP cells were transfected with Rab11-WT and GDP-locked dominant inactive Rab11-GDP or with Rab4-GDP to study the role of Rab11 and Rab4. A biotinylation method and a GTP overlay assay were used to determine plasma membrane MRP2 and activation of Rab proteins (Rab11 and Rab4), respectively. Cyclic AMP and TUDC increased plasma membrane MRP2 and stimulated Rab11 activity. Plasma membrane translocation of MRP2 by cAMP and TUDC was increased and inhibited in cells transfected with Rab11-WT and Rab11-GDP, respectively. Cyclic AMP (previous study) and TUDC increased Rab4 activity. However, cAMP- and TUDC-induced increases in MRP2 were not inhibited by Rab4-GDP. Taken together, these results suggest that Rab11 is involved in cAMP- and TUDC-induced MRP2 translocation to the plasma membrane.

Global ablation of the mouse Rab11a gene impairs early embryogenesis and matrix metalloproteinase secretion

Rab11a has been conceived as a prominent regulatory component of the recycling endosome, which acts as a nexus in the endo- and exocytotic networks. The precise in vivo role of Rab11a in mouse embryonic development is unknown. We globally ablated Rab11a and examined the phenotypic and molecular outcomes in Rab11a(null) blastocysts and mouse embryonic fibroblasts. Using multiple trafficking assays and complementation analyses, we determined, among multiple important membrane-associated and soluble cargos, the critical contribution of Rab11a vesicular traffic to the secretion of multiple soluble MMPs. Rab11a(null) embryos were able to properly form normal blastocysts but died at peri-implantation stages. Our data suggest that Rab11a critically controls mouse blastocyst development and soluble matrix metalloproteinase secretion.