Small guanosine triphosphatase Rho/Rho-associated kinase as a novel regulator of intracellular redistribution of lysosomes in invasive tumor cells

RhoA Signaling in Neurodegenerative Diseases

Ras homolog gene family member A (RhoA) is a small GTPase of the Rho family involved in regulating multiple signal transduction pathways that influence a diverse range of cellular functions. RhoA and many of its downstream effector proteins are highly expressed in the nervous system, implying an important role for RhoA signaling in neurons and glial cells. Indeed, emerging evidence points toward a role of aberrant RhoA signaling in neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, and amyotrophic lateral sclerosis. In this review, we summarize the current knowledge of RhoA regulation and downstream cellular functions with an emphasis on the role of RhoA signaling in neurodegenerative diseases and the therapeutic potential of RhoA inhibition in neurodegeneration.

Lederer C, Kleanthous M, Drousiotou A, Malekkou A. Acid Ceramidase Depletion Impairs Neuronal Survival and Induces Morphological Defects in Neurites Associated with Altered Gene Transcription and Sphingolipid Content

The ASAH1 gene encodes acid ceramidase (AC), an enzyme that is implicated in the metabolism of ceramide (Cer). Mutations in the ASAH1 gene cause two different disorders, Farber disease (FD), a rare lysosomal storage disorder, and a rare form of spinal muscular atrophy combined with progressive myoclonic epilepsy (SMA-PME). In the absence of human in vitro neuronal disease models and to gain mechanistic insights into pathological effects of ASAH1 deficiency, we established and characterized a stable ASAH1 knockdown (ASAH1KD) SH-SY5Y cell line. ASAH1KD cells displayed reduced proliferation due to elevated apoptosis and G1/S cell cycle arrest. Distribution of LAMP1-positive lysosomes towards the cell periphery and significantly shortened and less branched neurites upon differentiation, implicate AC for lysosome positioning and neuronal development, respectively. Lipidomic analysis revealed changes in the intracellular levels of distinct sphingolipid species, importantly without Cer accumulation, in line with altered gene transcription within the sphingolipid pathway. Additionally, the transcript levels for Rho GTPases (RhoA, Rac1, and Cdc42), which are key regulators of axonal orientation, neurite branching and lysosome positioning were found to be dysregulated. This study shows the critical role of AC in neurons and suggests how AC depletion leads to defects seen in neuropathology of SMA-PME and FD.

Lysosome trafficking is necessary for EGF-driven invasion and is regulated by p38 MAPK and Na+/H+ exchangers

Background

Tumor invasion through a basement membrane is one of the earliest steps in metastasis, and growth factors, such as Epidermal Growth Factor (EGF) and Hepatocyte Growth Factor (HGF), stimulate this process in a majority of solid tumors. Basement membrane breakdown is one of the hallmarks of invasion; therefore, tumor cells secrete a variety of proteases to aid in this process, including lysosomal proteases. Previous studies demonstrated that peripheral lysosome distribution coincides with the release of lysosomal cathepsins.

Methods

Immunofluorescence microscopy, western blot, and 2D and 3D cell culture techniques were performed to evaluate the effects of EGF on lysosome trafficking and cell motility and invasion.

Results

EGF-mediated lysosome trafficking, protease secretion, and invasion is regulated by the activity of p38 mitogen activated protein kinase (MAPK) and sodium hydrogen exchangers (NHEs). Interestingly, EGF stimulates anterograde lysosome trafficking through a different mechanism than previously reported for HGF, suggesting that there are redundant signaling pathways that control lysosome positioning and trafficking in tumor cells.

Conclusions

These data suggest that EGF stimulation induces peripheral (anterograde) lysosome trafficking, which is critical for EGF-mediated invasion and protease release, through the activation of p38 MAPK and NHEs. Taken together, this report demonstrates that anterograde lysosome trafficking is necessary for EGF-mediated tumor invasion and begins to characterize the molecular mechanisms required for EGF-stimulated lysosome trafficking.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3660-3) contains supplementary material, which is available to authorized users.

A Novel High Content Imaging-Based Screen Identifies the Anti-Helminthic Niclosamide as an Inhibitor of Lysosome Anterograde Trafficking and Prostate Cancer Cell Invasion

Lysosome trafficking plays a significant role in tumor invasion, a key event for the development of metastasis. Previous studies from our laboratory have demonstrated that the anterograde (outward) movement of lysosomes to the cell surface in response to certain tumor microenvironment stimulus, such as hepatocyte growth factor (HGF) or acidic extracellular pH (pHe), increases cathepsin B secretion and tumor cell invasion. Anterograde lysosome trafficking depends on sodium-proton exchanger activity and can be reversed by blocking these ion pumps with Troglitazone or EIPA. Since these drugs cannot be advanced into the clinic due to toxicity, we have designed a high-content assay to discover drugs that block peripheral lysosome trafficking with the goal of identifying novel drugs that inhibit tumor cell invasion. An automated high-content imaging system (Cellomics) was used to measure the position of lysosomes relative to the nucleus. Among a total of 2210 repurposed and natural product drugs screened, 18 "hits" were identified. One of the compounds identified as an anterograde lysosome trafficking inhibitor was niclosamide, a marketed human anti-helminthic drug. Further studies revealed that niclosamide blocked acidic pHe, HGF, and epidermal growth factor (EGF)-induced anterograde lysosome redistribution, protease secretion, motility, and invasion of DU145 castrate resistant prostate cancer cells at clinically relevant concentrations. In an effort to identify the mechanism by which niclosamide prevented anterograde lysosome movement, we found that this drug exhibited no significant effect on the level of ATP, microtubules or actin filaments, and had minimal effect on the PI3K and MAPK pathways. Niclosamide collapsed intralysosomal pH without disruption of the lysosome membrane, while bafilomycin, an agent that impairs lysosome acidification, was also found to induce JLA in our model. Taken together, these data suggest that niclosamide promotes juxtanuclear lysosome aggregation (JLA) via modulation of pathways involved in lysosome acidification. In conclusion, we have designed a validated reproducible high-content assay to screen for drugs that inhibit lysosome trafficking and reduce tumor invasion and we summarize the action of one of these drugs.

Scavenger receptor-recognized and enzyme-responsive nanoprobe for fluorescent labeling of lysosomes in live cells

Lysosomal imaging represents a potent tool for investigating the organization of related cellular events and their modulation via diagnostic and therapeutic approaches. However, specific labeling of the lysosome in live cells is a significant challenge. Taking advantage of the inherent lysosomal entry of nanoparticles and unique digestive inclusions in the lysosome, we developed a nanoparticle-based, enzyme-switchable fluorescence OFF-ON strategy for specific labeling of the lysosome and further imaging of extracellular acidification-induced lysosome trafficking in living cells. The nanoprobe comprised a 16 nm spherical gold nanoparticle as the core and an enzyme-responsive oligomer of fluorescein-conjugated oligo(4-vinyl-phenyl phosphate) as the shell. Due to quenching of the core gold nanoparticle, the nanoprobe was non-fluorescent. After incubation with cancer cells, the nanoprobe was rapidly internalized via scavenger receptor-mediated endocytosis and significantly shuffled into the lysosome. The nanoprobe specifically lighted up the lysosome owing to lysosome-induced fluorescence enhancement. Specifically, digestive inclusions in the lysosome hydrolyzed and released gold-quenched fluorescein molecules, leading to significant augmentation of fluorescence. On account of specific lysosomal labeling, the nanoprobe effectively facilitated imaging of a 4-6 μm anterograde trafficking event of the lysosome from the perinuclear region to the cell surface when an acidic extracellular environment developed. Our findings collectively highlight the use of nanoprobes for lysosomal imaging.

A novel role of Rho-kinase in the regulation of ligand-induced phosphorylated EGFR endocytosis via the early/late endocytic pathway in human fibrosarcoma cells

The small GTPase RhoA and its downstream effectors, the Rho-associated kinase (Rho-kinase) family, are known to regulate cell morphology, motility, and tumor progression via the regulation of actin cytoskeleton rearrangement. In the present study, we evaluated the role of Rho-kinase in the intracellular endocytic trafficking of ligand-induced phosphorylated epidermal growth factor receptor (pEGFR). We investigated the time course of the internalization fate of EGF-induced pEGFR via the early/late endocytic pathway in human fibrosarcoma cell line HT1080 cells using Y-27632, a selective Rho-kinase inhibitor. We found, using confocal immunofluorescence microscopy and Western blot analysis, a large accumulation of pEGFR in the nuclei of HT1080 cells. In contrast, we observed decreased amounts of the pEGFR-positive staining in the nuclei along with an accumulation of cytosolic pEGFR staining when the cells were incubated for 15-30 min in the presence of Y-27632, implying that an aberrant endocytic trafficking mechanism of pEGFR occurs in HT1080 cells whereby pEGFR might be selectively translocated into the nucleus. Moreover, we demonstrated that after 15-min of stimulation with Texas Red-EGF, increasing numbers of pEGFR-positive staining that had colocalized with Texas Red-EGF-positive punctate staining were seen in the cytoplasm of HT1080 cells but after 30-min of stimulation, most of this staining had disappeared from the cytoplasm and a large accumulation of pEGFR-positive staining appeared in the nucleus. Thus, nuclear accumulation of pEGFR appears to occur in an EGF-dependent manner. In contrast, such nuclear pEGFR-positive staining was not seen in the Y-27632-treated cells. Furthermore, silencing of RhoA or Rho-kinases I/II by sequence specific siRNAs considerably inhibited the EGF-dependent nuclear accumulation of pEGFR. Collectively, these results provide the first evidence that Rho-kinase signaling pathway plays a suppressive role in the intracellular vesicle trafficking of pEGFR via the endocytic pathway and that an increased Rho-kinase activity leads to the attenuation of the normal endocytic vesicular traffic of pEGFR via the early/late endocytic pathway, instead causing pEGFR to be trafficked out of the endocytic vesicles into the nucleus.

Na+/H+ exchangers and RhoA regulate acidic extracellular pH-induced lysosome trafficking in prostate cancer cells

Acidic extracellular pH (pHe) is a common feature of the tumor microenvironment and has been implicated in tumor invasion through the induction of protease secretion.Since lysosomes constitute the major storehouse of cellular proteases, the trafficking of lysosomes to the cell periphery may be required in order to secrete proteases. We demonstrate that a pHe of 6.4-6.8 induced the trafficking of lysosomes to membrane protrusions in the cell periphery. This trafficking event depended upon the PI3K pathway, the GTPase RhoA and sodium-proton exchange activity, resulting in lysosomal exocytosis. Acidic pHe induced a cytoplasmic acidification (although cytoplasmic acidification was not sufficient for acidic pHe-induced lysosome trafficking and exocytosis) and inhibition of NHE activity with the amiloride derivative, EIPA or the anti-diabetic agent troglitazone prevented lysosome trafficking to the cell periphery. Interestingly, using the more specific NHE1 and NHE3 inhibitors, cariporide and s3226 respectively, we show that multiple NHE isoforms are involved in acidic pHe-induced lysosome trafficking and exocytosis. Moreover, in cells expressing NHE1 shRNA, although basal NHE activity was decreased, lysosomes still underwent acidic pHe-induced trafficking,suggesting compensation by other NHE family members.Together these data implicate proton exchangers, especially NHE1 and NHE3, in acidic pHe-induced lysosome trafficking and exocytosis.

Inhibition of Rho kinases enhances the degradation of mutant huntingtin

Huntington disease (HD) is a fatal hereditary neurodegenerative disease caused by an expansion of the polyglutamine (polyQ) stretch in huntingtin (htt). Whereas the pathological significance of the expanded polyQ has been clearly established and a tremendous effort to develop therapeutic tools for HD has been exerted, there is yet no effective cure. Whereas many molecules able to reduce the polyQ accumulation and aggregation have been identified, including several Rho kinase (ROCK) inhibitors, it remains very important to determine the mechanism of action of the potential drugs. ROCK inhibitors, including Y-27632 were reported to decrease aggregation of htt and androgen receptor (AR) through ROCK1 and protein kinase C-related protein kinase-2 (PRK-2). A downstream effector of ROCK1, actin-binding factor profilin, was shown to inhibit the mutant htt aggregation but not AR by direct interaction. We found that the anti-aggregation effect of ROCK inhibitors was not limited to the mutant htt and AR and that Y-27632 was also able to reduce the aggregation of ataxin-3 and atrophin-1 with expanded polyQ. These results suggested that in addition to the mechanism reported for htt and AR, there might also be other common mediators involved in the reduced aggregation of different polyQ proteins. In this study, we show that Y-27632 not only reduced the mutant htt aggregation by enhancing its degradation, but surprisingly was able to activate the main cellular degradation pathways, proteasome, and macroautophagy. We also show that this unique effect was mediated by ROCK1 and ROCK2.

Statins stimulate in vitro membrane FasL expression and lymphocyte apoptosis through RhoA/ROCK pathway in murine melanoma cells

The capacity of FasL molecules expressed on melanoma cells to induce lymphocyte apoptosis contributes to either antitumor immune response or escape depending on their expression level. Little is known, however, about the mechanisms regulating FasL protein expression. Using the murine B16F10 melanoma model weakly positive for FasL, we demonstrated that in vitro treatment with statins, inhibitors of 3-hydroxy-3-methylgutaryl CoA reductase, enhances membrane FasL expression. C3 exotoxin and the geranylgeranyl transferase I inhibitor GGTI-298, but not the farnesyl transferase inhibitor FTI-277, mimic this effect. The capacity of GGTI-298 and C3 exotoxin to inhibit RhoA activity prompted us to investigate the implication of RhoA in FasL expression. Inhibition of RhoA expression by small interfering RNA (siRNA) increased membrane FasL expression, whereas overexpression of constitutively active RhoA following transfection of RhoAV14 plasmid decreased it. Moreover, the inhibition of a RhoA downstream effector p160ROCK also induced this FasL overexpression. We conclude that the RhoA/ROCK pathway negatively regulates membrane FasL expression in these melanoma cells. Furthermore, we have shown that B16F10 cells, through the RhoA/ROCK pathway, promote in vitro apoptosis of Fas-sensitive A20 lymphoma cells. Our results suggest that RhoA/ROCK inhibition could be an interesting target to control FasL expression and lymphocyte apoptosis induced by melanoma cells.

The EGFR inhibitor gefitinib suppresses ligand-stimulated endocytosis of EGFR via the early/late endocytic pathway in non-small cell lung cancer cell lines

The drug gefitinib (Iressa), which is a specific inhibitor of EGFR tyrosine kinase, has been shown to suppress the activation of EGFR signaling for survival and proliferation in non-small cell lung cancer (NSCLC) cell lines. A recent study demonstrated rapid down-regulation of ligand-induced EGFR in a gefitinib-sensitive cell line and inefficient down-regulation of EGFR in a gefitinib-resistant cell line in the exponential phase of growth; this implies that each cell type employs a different unknown down-regulation mechanism occurs. However, the mechanism of drug sensitivity to gefitinib remains unclear. In this study, to further substantiate the effect of gefitinib on the EGFR down-regulation pathway and to understand the detailed internalization mechanism of gefitinib-sensitive PC9 and gefitinib-resistant QG56 cell lines, we examined the internalization of Texas red-EGF in the absence or presence of gefitinib in both cell lines. The distribution of internalized Texas red-EGF, early endosomes, and late endosomes/lysosomes was then assessed by confocal immunofluorescence microscopy. Here, we provide novel evidence that efficient endocytosis of EGF-EGFR occurs via the endocytic pathway in the PC9 cells, because the internalized Texas red-EGF-positive small punctate vesicles were transported to the late endosomes/lysosomes and then degraded within the lysosomes after 60 min of internalization. Additionally, gefitinib exerted a strong inhibitory effect on the endocytosis of EGFR in PC9 cells, and the internalization rate of EGFR from the plasma membrane via the early endosomes to the late endosomes/lysosomes was considerably delayed. This indicates that gefitinib efficiently suppresses ligand-stimulated endocytosis of EGFR via the early/late endocytic pathway in PC9 cells. In contrast, the internalization rate of ligand-induced EGFR was not significantly changed by gefitinib in QG56 cells because even in the absence of gefitinib, internalized EGFR accumulation was noted in the early and late endosomes after 60 min of internalization instead of its delivery to the lysosomes in QG56 cells. This suggests that the endocytic machinery of EGFR might be basically impaired at the level of the early/late endosomes. Taken together, this is the first report demonstrating that the suppressive effect of gefitinib on the endocytosis of EGFR is much stronger with PC9 cells than QG56 cells. Thus, impairment in some steps of the EGF-EGFR traffic out of early endosomes toward the late endosomes/lysosomes might confer gefitinib-resistance in NSCLC cell lines.

A role of LIM kinase 1/cofilin pathway in regulating endocytic trafficking of EGF receptor in human breast cancer cells

We have previously shown that overexpression of LIM kinase1 (LIMK1) resulted in a marked retardation of the internalization of the receptor-mediated endocytic tracer, Texas red-labeled epidermal growth factor (EGF) in low-invasive human breast cancer cell MCF-7. We thereby postulate that LIMK1 signaling plays an important role in the regulation of ligand-induced endocytosis of EGF receptor (EGFR) in tumor cells by reorganizing and influencing actin-filament dynamics. In the present study, we further assessed the effect of wild-type LIMK1, a kinase-deficient dominant negative mutant of LIMK1 (DN-LIMK1) and an active, unphosphorylatable cofilin mutant (S3A cofilin) on internalization of EGF-EGFR in MDA-MB-231, a highly invasive human breast cancer cell line. We demonstrate here that a marked delay in the receptor-mediated internalization of Texas red-labeled EGF was observed in the wild-type LIMK1 transfectants, and that most of the internalized EGF staining were accumulated within transferrin receptor-positive early endosomes even after 30 min internalization. In contrast, the expression of dominant-negative LIMK1 mutant rescued the efficient endocytosis of Texas red-EGF, and large amounts of Texas red-EGF staining already reached LIMPII-positive late endosomes/lysosomal vacuoles after 15 min internalization. We further analyzed the effect of S3A cofilin mutant on EGFR trafficking, and found an efficient delivery of Texas red-EGF into late endosomes/lysosomes at 15-30 min after internalization. Taken together, our novel findings presented in this paper implicate that LIMK1 signaling indeed plays a pivotal role in the regulation of EGFR trafficking through the endocytic pathway in invasive tumor cells.

Cysteine cathepsins: multifunctional enzymes in cancer

Cysteine cathepsins are highly upregulated in a wide variety of cancers by mechanisms ranging from gene amplification to post-transcriptional modification. Their localization within intracellular lysosomes often changes during neoplastic progression, resulting in secretion of both inactive and active forms and association with binding partners on the tumour cell surface. Secreted, cell-surface and intracellular cysteine cathepsins function in proteolytic pathways that increase neoplastic progression. Direct proof for causal roles in tumour growth, migration, invasion, angiogenesis and metastasis has been shown by downregulating or ablating the expression of individual cysteine cathepsins in tumour cells and in transgenic mouse models of human cancer.

LIM kinase 1: evidence for a role in the regulation of intracellular vesicle trafficking of lysosomes and endosomes in human breast cancer cells

LIM kinase (LIMK) plays a critical role in stimulus-induced remodeling of the actin cytoskeleton by linking signals from the Rho family GTPases to changes in cofilin activity. Recent studies have shown an important role for LIMK1 signaling in tumor cell invasion through regulating actin dynamics. In this study, we investigate the role of LIMK1 in intracellular vesicle trafficking of lysosomes/endosomes. We analyzed by confocal immunofluorescence microscopy the cellular distribution of lysosomal proteins and the endocytosis of an endocytic tracer, epidermal growth factor (EGF), in LIMK1-transfected cells. We found in these cells an abnormal dispersed translocation of lysosomes stained for LIMPII and cathepsin D throughout the cytoplasm. The small punctate structures that stained for these lysosomal proteins were redistributed to the periphery of the cell. Computational 3D-image analysis of confocal immunofluorescence micrographs further demonstrated that these vesicles did not colocalize with the transferrin receptor, an early endosomal marker. Furthermore, LIMPII-positive lysosomes did not colocalize with early endosomes labeled with endocytosed Texas red-transferrin. These results indicate that there is no mixing between dispersed lysosomes and early endosomes in the LIMK1-transfected cells. Moreover, LIMK1 overexpression resulted in a marked retardation in the receptor-mediated internalization of Texas red-labeled EGF in comparison with mock-transfected cells. At 30 min after internalization, most of the Texas red-EGF staining overlapped with LIMPII-positive late endosomes/lysosomes in mock-transfected cells, whereas in LIMK1 transfectants only a small fraction of internalized EGF colocalized with LIMPII-positive structures in the perinuclear region. Taken together, the findings presented in this paper suggest that LIMK1 has a role in regulating vesicle trafficking of lysosomes and endosomes in invasive tumor cells.

Overexpression of ROCK in human breast cancer cells: evidence that ROCK activity mediates intracellular membrane traffic of lysosomes

Small GTPase Rho and its downstream effectors, ROCK family of Rho-associated serine-threonine kinases, are thought to participate in cell morphology, motility, and tumor progression through regulating the rearrangement of actin cytoskeleton. Here we present evidence that transfection of human breast cancer cells with cDNA encoding a dominant active mutant of ROCK causes dispersal of lysosomal vesicles throughout the cytoplasm without perturbing the machinery of the endocytic pathway. The intracellular distribution of lysosomes and endocytosed transferrin, an early endosomal marker, were further assessed by confocal immunofluorescence microscopy. In the active ROCK transfected cells the lysosomal proteins, cathepsin D, LIMPII, and LAMP1, were found throughout the cytoplasm in dispersed small vesicles, which were accessible to the endocytosed Texas Red-labeled transferrin. 3D-image analysis of lysosomal distribution in the active ROCK transfectants revealed abundant punctate signals in the peripheral region of the basal plasma membrane. Cells expressing vector alone did not exhibit these alterations. Wortmannin, a phosphatidylinositol 3-kinase inhibitor, induced LIMPII-positive/ transferrin negative large vacuoles in the perinuclear region, and disappearence of the dispersed small vesicular structures. To our knowledge, this is the first evidence that increasing ROCK expression contributes to selective cellular dispersion of lysosomes in invasive breast cancer cells.

Dynamic regulation of microtubule coils in ADP-induced platelet shape change by p160ROCK (Rho-kinase)

Platelet shape change is an extremely rapid process mediated by both the calcium-sensitive and p160ROCK pathways. The present study examines how different features of shape change studied by scanning electron microscopy clearly correlate to changes in the pattern of light absorbance measured in an aggregometer. Platelets change shape from the initial 'disc' form by producing: membrane 'blebs', sphere formation (cell-rounding), filopodia extension, and surface membrane folding. The presentation of these features was dramatically slower in the absence of intracellular calcium mobilization. In the presence of the p160ROCK-inhibitor, Y-27632, shape change was initially normal but platelets rapidly transformed back to smooth discs with extended filopodia. The reappearance of the disc shape is reflected by an increase in the amplitude of oscillations in the aggregometer shape change tracing. The kinetics of actin/cytoskeleton association correlated with filopodia formation but not with disc to sphere transformation. Changes in the level of tubulin polymerization correlated with changes from disc to sphere morphology. These experiments are consistent with a role for a RhoA/Rho kinase-regulated pathway in the maintenance of a spherical platelet shape after agonist-dependent activation. Continued disruption of the cytoskeletal microtubule ring, appears to be a Rhokinase-dependent event involved in the transformation of discoid platelets into spheres.

A role for small GTPase RhoA in regulating intracellular membrane traffic of lysosomes in invasive rat hepatoma cells

Small GTPase RhoA regulates signal transduction from receptors in the membrane to a variety of cellular events related to cell morphology, motility, cytoskeletal dynamics, cytokinesis, and tumour progression, but it is unclear how RhoA regulates intracellular membrane dynamics of lysosomes. We showed previously by confocal immunofluorescence microscopy that the transfection of dominant active RhoA in MM1 cells causes the dispersal translocation of lysosomes stained for cathepsin D throughout the cytoplasm. Y-27632, a selective inhibitor of p160ROCK, impeded the cellular redistribution of lysosomes and promoted reclustering of lysosomes toward the perinuclear region. Here we have further investigated whether the acidic lysosomal vesicles dispersed throughout the cytoplasm are applied to the early endosomes in the endocytic pathway, and we demonstrate that the dispersed lysosomes were accessible to endocytosed molecule such as dextran, and their acidity was not changed, as determined by increased accumulation of the acidotropic probe LysoTracker Red. Brefeldin A did not induce the tabulation of these dispersed lysosomes, but it caused early endosomes to form an extensive tubular network. The dispersed lysosomes associated with cathepsin D and LIMPII were not colocalized with early endosomes, and these vesicles were not inaccessible to the endocytosed anti-transferrin receptor antibody. Moreover, wortmannin, an inhibitor of phosphatidylinositol 3-kinase, induced a dramatic change in LIMPII-containing structures in which LIMPII-positive swollen large vacuoles were increased and small punctate structures disappeared in the cytoplasm. These swollen vacuoles were not doubly positive for LIMPII and transferrin receptor, and were not inaccessible to the internalized anti-transferrin receptor antibody. Therefore, our novel findings presented in this paper indicate that RhoA activity causes a selective translocation of lysosomes without perturbing the machinery of endocytic pathway.