Rab5a overexpression promoting ovarian cancer cell proliferation may be associated with APPL1-related epidermal growth factor signaling pathway

The expression of Rab5 and its effect on invasion, migration and exosome secretion in triple negative breast cancer

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer and current therapeutic strategies are limited in their effectiveness. The expressions of Rab5 and the M2 tumor-associated macrophage marker CD163 in tissues were detected by Western blot. The migration and invasion of cells were determined using a Transwell assay. The expressions of the exosome markers were evaluated by Western blot. The polarization of human macrophages (THP-1) was determined by incubation of THP-1 cells with conditioned medium or exosomes collected from MDA-MB-231 cells with indicated transfections or by a coculture system of THP-1 and MDA-MB-231 cells. The M1 and M2 macrophage markers were evaluated by qRT-PCR. The expression of Rab5 in TNBC was significantly higher than that in normal breast tissue. Rab5 expressions in triple-negative and luminal A breast cancer were higher than those in other molecular subtypes. Higher CD163 expression was observed in triple-negative breast cancer and in triple-negative and luminal B subtypes. Rab5 knockdown suppressed but Rab5 overexpression promoted the migration and invasion capacity of MDA-MB-231 cells. The levels of CD63 and CD9 in the medium of Rab5 knockdown cells were lower than those in control cells, whereas higher levels of CD63 and CD9 were observed in Rab5 overexpression cells. Rab5 knockdown decreased the excretion but did not alter the diameter of the exosomes. Knockdown of Rab5 facilitated the anti-tumor polarization of macrophages, which was partially reversed by Rab5 overexpression. Therefore, Rab5 is expected to be a potential therapeutic target for triple-negative breast cancer.

RAB5C, a new mRNA binding target of HuR, regulates breast cancer cell proliferation

The posttranscriptional control of gene expression mediated by RNA-binding proteins (RBPs) is essential to determine tumor cell fate. HuR is an RBP with increased expression in various cancer types. This study aimed to clarify the regulatory mechanism of HuR's contribution to breast cancer (BC) cell proliferation by inducing RAB5C expression. First, we analyzed the expression level of HuR and RAB5C in BC tissues and cell lines by immunohistochemistry, qRT-PCR, and western blot. Next, to further investigate the effect of HuR on RAB5C expression, we used short hairpin RNAs (shRNAs) to silence endogenous HuR expression in BC cell lines MCF7 and MDA-MB-231. The binding site of RAB5C mRNA and HuR was confirmed by RNA immunoprecipitation. Finally, the function of RAB5C was investigated using flow cytometry, colony formation, and MTT assays. We found that the expression of HuR and RAB5C was significantly upregulated in BC tissues and MCF-7 and MDA-MB231 cell lines. Importantly, RAB5C mRNA stability was increased through binding of HuR to its 3'UTR. Inhibition of HuR expression using shRNA decreased RAB5C mRNA, suggesting that HuR plays a role in regulating RAB5C expression level. In addition, suppression of RAB5C expression reduced BC cell growth. These results suggest RAB5C functions as an oncogene in BC cells, HuR promoted BC cell survival by facilitating RAB5C expression. Our findings suggest that HuR and RAB5C play important roles in BC cell survival.

Persistent Properties of a Subpopulation of Cancer Cells Overexpressing the Hedgehog Receptor Patched

Despite the development of new therapeutic strategies, cancer remains one of the leading causes of mortality worldwide. One of the current major challenges is the resistance of cancers to chemotherapy treatments inducing metastases and relapse of the tumor. The Hedgehog receptor Patched (Ptch1) is overexpressed in many types of cancers. We showed that Ptch1 contributes to the efflux of doxorubicin and plays an important role in the resistance to chemotherapy in adrenocortical carcinoma (ACC), a rare cancer which presents strong resistance to the standard of care chemotherapy treatment. In the present study, we isolated and characterized a subpopulation of the ACC cell line H295R in which Ptch1 is overexpressed and more present at the cell surface. This cell subpopulation is more resistant to doxorubicin, grows as spheroids, and has a greater capability of clonogenicity, migration, and invasion than the parental cells. Xenograft experiments performed in mice and in ovo showed that this cell subpopulation is more tumorigenic and metastatic than the parental cells. These results suggest that this cell subpopulation has cancer stem-like or persistent cell properties which were strengthened by RNA-seq. If present in tumors from ACC patients, these cells could be responsible for therapy resistance, relapse, and metastases.

Hsa_circ_0001756 promotes ovarian cancer progression through regulating IGF2BP2-mediated RAB5A expression and the EGFR/MAPK signaling pathway

Hsa_circ_0001756 was reported to be upregulated in serum samples of ovarian cancer (OC) patients and may serve as a potential OC biomarker. This study aimed to investigate the role and molecular mechanisms of hsa_circ_0001756 in OC procession. Herein, we detected the expression of hsa_circ_0001756 in OC tissues and cell lines with RT-qPCR assay, which showed that hsa_circ_0001756 was upregulated in OC tissues and cell lines. Then small interfering RNA targeting hsa_circ_0001756 (si-hsa_circ_0001756) was transfected into SKOV3 and A2780 cells, and the proliferation, invasion, and expression of epithelial-mesenchymal transition (EMT) marker proteins were determined with CCK-8, Transwell and Western blotting assays, respectively. We found that hsa_circ_0001756 knockdown inhibited OC cell proliferation, invasion and EMT. Moreover, RNA pull-down assay verified the binding between hsa_circ_0001756 and IGF2 mRNA binding protein 2 (IGF2BP2), and rescue experiments indicated that IGF2BP2 overexpression reversed the effects of has_circ_0001756 knockdown on OC cell functions. Co-IP assay verified IGF2BP2 could interact with RAB GTPase 5A (RAB5A) protein. Then SKOV3 cells were transfected with si-IGF2BP2 alone or together with pcDNA-RAB5A, followed by the detection of SKOV3 cell functions. We found that IGF2BP2 knockdown inhibited OC cell proliferation, invasion, and EMT, while RAB5A overexpression reversed these effects. Finally, SKOV3 cells transfected with si-hsa_circ_0001756 were injected into nude mice through tail vein. Hsa_circ_0001756 knockdown significantly inhibited the xenograft tumor growth of OC in vivo. In conclusion, hsa_circ_0001756 knockdown inhibits OC cell proliferation, invasion, and EMT, and reduces xenograft tumor growth by suppressing IGF2BP2-mediated RAB5A expression and blocking the EGFR/MAPK signaling pathway.

CHML targeted by miR-199a-3p promotes non-small cell lung cancer cell growth via binding to Rab5A

Choroideremia-like (CHML) has been demonstrated to be related to the development of urothelial carcinoma, multiple myeloma, and hepatocellular carcinoma. Whereas, the association between CHML and lung cancer remains dimness. CHML expression was analyzed in NSCLC patients from TCGA dataset and evaluated in our collected NSCLC tissues and NSCLC cell lines. The effects of CHML on the proliferation and apoptosis of NSCLC were investigated in A549 and H1299 cells that downregulation of CHML as well as in H1299-induced xenograft mouse model. An upstream miRNA of CHML was further analyzed. Moreover, bioinformatics analysis and co-immunoprecipitation assay were carried out to explore the mechanism of CHML in NSCLC. We found CHML expression was upregulated in NSCLC patients and cell lines compared with their controls. Knockdown of CHML suppressed the viability and BrdU-positive cell number, and elevated the proportion of Tunel-positive cells and levels of Bax/Bcl-2 and cleaved-caspase-3 in NSCLC cells. In mouse models, downregulation of CHML decreased tumor volume and weight, attenuated Ki-67 staining, whereas elevated numbers of Tunel-positive cells, and upregulated levels of Bax/Bcl-2 and cleaved-caspase-3. CHML was demonstrated to be a target of miR-199a-3p. miR-199a-3p inhibitor significantly promoted the proliferation, and attenuated the apoptosis of H1299 cells, which were abrogated by CHML silencing. CHML promoted the proliferation of NSCLC cells via directly binding to Rab5A. Taken together, this study revealed that CHML was an oncogene in NSCLC and it could promote the proliferation and inhibit apoptosis of NSCLC cells through binding to Rab5A. CHML was targeted by miR-199a-3p in this cancer.

Direct interaction between Rab5a and Rab4a enhanced epidermal growth factor-stimulated proliferation of gastric cancer cells

BACKGROUND

Gastric cancer (GC) is one of the leading causes of cancer-related death worldwide. Although targeted therapies such as antibodies against human epidermal growth factor receptor 2 or vascular endothelial growth factor receptor 2 have been widely used in the treatment of metastatic cancer, the overall outcomes are poor. Therefore, elucidation of the mechanism underlying cancer progression is important to improve prognosis. Overexpression of the Rab5a gene has been confirmed to correlate with tumorigenesis of many cancers, but the mechanism underling, especially of GC, is still unclear.

AIM

To investigate the effects of Rab5a overexpression on the tumorigenesis of GC.

METHODS

First, the expression levels of Rab5a and Rab4a in primary tumorous tissues of GC patients diagnosed between 2015 and 2018 were analyzed. Then we constructed HGC-27 cell lines overexpressing green fluorescent protein-Rab5a or red fluorescent protein-Rab4a and investigated the interaction between Rab5a or Rab4a using Western blotting, co-immunoprecipitation, confocal microscopy, and colocalization analysis. Finally, epidermal growth factor-stimulated proliferation of these cell lines was analyzed using cell counting kit-8 cell viability assay.

RESULTS

Compared with normal gastric tissues, the expression levels of Rab5a and Rab4a increased progressively both in paracancerous tissues and in advanced cancerous tissues. Epidermal growth factor could promote the proliferation of HGC-27 cells, especially Rab5a-overexpressing HGC-27 cells. Notably, Rab5a and Rab4a co-overexpression promoted the proliferation of HGC-27 cells to the greatest extent. Further analysis identified a direct interaction between Rab5a and Rab4a in HGC-27 cells.

CONCLUSION

Co-overexpression of Rab5a and Rab4a in GC may promote the endosomal recycling of epidermal growth factor receptor, which in turn contributes to poor prognosis and tumor progression in GC patients. Inhibition of Rab5a or Rab4a expression might be a promising therapy for refractory GC.

Rab6c is a new target of miR‑218 that can promote the progression of bladder cancer

Bladder cancer has high morbidity and mortality rates among the male genitourinary system tumor types. MicroRNA‑218 (miR‑218) is associated with the development of a variety of cancer types, including bladder cancer. Rab6c is a member of the Rab family and is involved in drug resistance in MCF7 cells. The aim of the present study was to clarify the relationship between Rab6c and miR‑218 in bladder cancer cell lines. In this study, the expression levels of miR‑218 and Rab6c were evaluated via reverse transcription‑quantitative PCR and western blotting, respectively. The association between Rab6c and miR‑218 was recognized via TargetScan analysis and dual luciferase reporter gene detection. Cell proliferation was analyzed using Cell Counting Kit‑8 and colony formation assays, and the invasive ability was measured via Transwell assays. Rab6c was highly expressed in bladder cancer, while miR‑218 had abnormally low expression in bladder cancer. In addition, there was a mutual regulation between Rab6c and miR‑218 in bladder cancer. It was found that overexpression of Rab6c significantly enhanced the proliferation, colony formation and invasion of T24 and EJ cells. Furthermore, miR‑218 overexpression blocked the promoting effects of Rab6c on the malignant behavior of bladder cancer cells. Thus, Rab6c promotes the proliferation and invasion of bladder cancer cells, while miR‑218 has the opposite effect, which may provide a novel insight for the treatment of bladder cancer.

Crystal Structure of Human APPL BAR-PH Heterodimer Reveals a Flexible Dimeric BAR curve: Implication in Mutual Regulation of Endosomal Targeting

The APPL (adaptor proteins containing pleckstrin homology domain, phosphotyrosine binding domain and a leucine zipper motif) family consists of two isoforms, APPL1 and APPL2. By binding to curved plasma membrane, these adaptor proteins associate with multiple transmembrane receptors and recruit various downstream signaling components. They are involved in the regulation of signaling pathways evoked by a variety of extracellular stimuli, such as adiponectin, insulin, FSH (follicle stimulating hormone), EGF (epidermal growth factor). And they play important roles in cell proliferation, apoptosis, glucose uptake, insulin secretion and sensitivity. However, emerging evidence suggests that APPL1 and APPL2 perform different or even opposite functions and the underlying mechanism remains unclear. As APPL proteins can either homodimerize or heterodimerize in vivo, we hypothesized that heterodimerization of APPL proteins might account for the mechanism. By solving the crystal structure of APPL1-APPL2 BAR-PH heterodimer, we find that the overall structure is crescent-shaped with a longer curvature radius of 76 Å, compared to 55 Å of the APPL1 BAR-PH homodimer. However, there is no significant difference of the curvature between APPL BAR-PH heterodimer and APPL2 homodimer. The data suggest that the APPL1 BAR-PH homodimer, APPL2 BAR-PH homodimer and APPL1/APPL2 BAR-PH heterodimer may bind to endosomes of different sizes.   Different positive charge distribution is observed on the concave surface of APPL BAR-PH heterodimer than the homodimers, which may change the affinity of membrane association and subcellular localization. Collectively, APPL2 may regulate APPL1 function through altering the preference of endosome binding by heterodimerization.

Long non-coding RNA MIAT promotes gastric cancer proliferation and metastasis via modulating the miR-331-3p/RAB5B pathway

Gastric cancer (GC) remains a threat to the health of the global population. The present study investigated the effects and mechanisms of the long non-coding RNA myocardial infarction associated transcript (MIAT) on the proliferation, apoptosis and metastasis of GC (HGC-27 and AGS) cells. The expression levels of MIAT, micoRNA (miR)-331-3p and RAB5B mRNA were analyzed using reverse transcription-quantitative PCR analysis. Cell growth, apoptosis, migration and invasion were measured using 5-ethynyl-2′-deoxyuridine, flow cytometry, wound healing and Transwell assays, respectively. A luciferase assay was used to determine whether miR-331-3p targeted MIAT and RAB5B. The results indicated that MIAT levels were significantly upregulated in GC tissues and cells, correlated with RAB5B levels and inversely associated with miR-331-3p levels. MIAT overexpression promoted proliferation and metastasis, and inhibited the apoptosis of GC cells. MIAT knockdown had the opposite effect on GC cells. The rescue experiments revealed that the effects of MIAT knockdown on the biological behaviour of GC cells were attenuated by RAB5B overexpression. These data suggest that MIAT promotes GC progression via modulating miR-331-3p/RAB5B pathway.

Rab5 regulates the proliferation, migration and invasion of glioma cells via cyclin E

Glioma is the most common and lethal type of primary brain tumor, with a high mortality and recurrence rate. Rab5, which serves as a classic ontogenetic gene, is highly expressed in various types of tumor, including lung cancer, hepatocellular carcinoma and ovarian cancer. However, the exact role and the underlying mechanism of Rab5 in glioma remain unknown. Herein, the role of Rab5 in the tumorigenesis and metastasis of glioma cells was investigated. The upregulation of Rab5 in glioma tissues and cells was observed. The expression of Rab5 was positively associated with proliferation, migration and invasion of glioma cells. Moreover, Rab5 was involved in the cell cycle of glioma cells via the regulation of cyclin E. Data presented in the present study suggest Rab5 as a potential novel diagnostic and prognosis marker of glioma.

Nuclear accumulation of β-catenin is associated with endosomal sequestration of the destruction complex and increased activation of Rab5 in oral dysplasia

Potentially malignant lesions, commonly referred to as dysplasia, are associated with malignant transformation by mechanisms that remain unclear. We recently reported that increased Wnt secretion promotes the nuclear accumulation of β-catenin and expression of target genes in oral dysplasia. However, the mechanisms accounting for nuclear re-localization of β-catenin in oral dysplasia remain unclear. In this study, we show that endosomal sequestration of the β-catenin destruction complex allows nuclear accumulation of β-catenin in oral dysplasia, and that these events depended on the endocytic protein Rab5. Tissue immunofluorescence analysis showed aberrant accumulation of enlarged early endosomes in oral dysplasia biopsies, when compared with healthy oral mucosa. These observations were confirmed in cell culture models, by comparing dysplastic oral keratinocytes (DOK) and non-dysplastic oral keratinocytes (OKF6). Intriguingly, DOK depicted higher levels of active Rab5, a critical regulator of early endosomes, when compared with OKF6. Increased Rab5 activity in DOK was necessary for nuclear localization of β-catenin and Tcf/Lef-dependent transcription, as shown by expression of dominant negative and constitutively active mutants of Rab5, along with immunofluorescence, subcellular fractionation, transcription, and protease protection assays. Mechanistically, elevated Rab5 activity in DOK accounted for endosomal sequestration of components of the destruction complex, including GSK3β, Axin, and adenomatous polyposis coli (APC), as observed in Rab5 dominant negative experiments. In agreement with these in vitro observations, tissue immunofluorescence analysis showed increased co-localization of GSK3β, APC, and Axin, with early endosome antigen 1- and Rab5-positive early endosomes in clinical samples of oral dysplasia. Collectively, these data indicate that increased Rab5 activity and endosomal sequestration of the β-catenin destruction complex leads to stabilization and nuclear accumulation of β-catenin in oral dysplasia.

Drugging the Small GTPase Pathways in Cancer Treatment: Promises and Challenges

Small GTPases are a family of low molecular weight GTP-hydrolyzing enzymes that cycle between an inactive state when bound to GDP and an active state when associated to GTP. Small GTPases regulate key cellular processes (e.g., cell differentiation, proliferation, and motility) as well as subcellular events (e.g., vesicle trafficking), making them key participants in a great array of pathophysiological processes. Indeed, the dysfunction and deregulation of certain small GTPases, such as the members of the Ras and Arf subfamilies, have been related with the promotion and progression of cancer. Therefore, the development of inhibitors that target dysfunctional small GTPases could represent a potential therapeutic strategy for cancer treatment. This review covers the basic biochemical mechanisms and the diverse functions of small GTPases in cancer. We also discuss the strategies and challenges of inhibiting the activity of these enzymes and delve into new approaches that offer opportunities to target them in cancer therapy.

Probing the molecular regulation of lipopolysaccharide stress in piglet liver by comparative proteomics analysis

Lipopolysaccharide (LPS) can induce inflammatory responses in piglets, causing immunological stress and tissue damage. However, chronic LPS infection may lead to LPS-induced immunological stress resistance. The molecular mechanisms underlying LPS stress have not been fully elucidated. Here, we conducted a global comparative proteomics analysis to investigate the molecular regulation of LPS stress using an immunological stress model of weaned piglets. A shotgun-based SWATH-MS workflow was used for global proteomes of the piglet livers after 15-day LPS treatment. Out of 3700 quantified proteins, 93 proteins showed differential changes under LPS stress. Bioinformatics analysis indicated that the differentially expressed proteins were mainly involved in inflammatory response, oxidation-redox processes and defense reactions, and were enriched in a phagosome pathway. Several key proteins associated with oxidative stress (SOD2), inflammation response (STEAP4 and S100 family) and the phagosome pathway were verified by activity and targeted-MS analyses. The observed responses appear to mitigate hepatic damage due to excessive oxidative stress, inflammation, and repression of the phagosome pathway. Our results reveal that an increased STEAP4 expression in piglets appears involved in cellular regulation by LPS stress and subsequent immunological stress resistance. This study sheds new light on the mechanism of prevention and relieving injury by LPS-induced immune responses.

Rab5a is overexpressed in oral cancer and promotes invasion through ERK/MMP signaling

Ras-related protein Rab-5A (Rab5a) has been identified to be overexpressed in several types of human cancer. However, its clinical significance and biological roles in oral cancer remain unclear. In the present study, the protein expression of Rab5a was examined in 79 cases of oral squamous cell carcinoma samples using immunohistochemistry. It was demonstrated that Rab5a protein was upregulated in 49.3% (39/79) of cancer samples. Small interfering RNA knockdown was performed on Detroit 562 cells with high endogenous expression. Rab5a transfection was performed in FaDu cells with low endogenous levels. Rab5a depletion was revealed to inhibit cell growth, invasion and colony formation while its overexpression facilitated cell growth, invasion, and colony formation. In addition, Rab5a facilitated cell cycle progression and cell migration. It was also demonstrated that Rab5a depletion downregulated and its overexpression upregulated the expression levels of various cell cycle-associated proteins, and matrix metalloproteinase-2 (MMP-2). Furthermore, Rab5a positively regulated the extracellular signal-regulated kinase (ERK) signaling pathway and promoted epithelial-mesenchymal transition (EMT). ERK inhibitor PD98059 partially inhibited the role of Rab5a on MMP-2, cyclin D1, cell proliferation and invasion. The results of the present study suggest that Rab5a is overexpressed in oral cancer tissue samples and promotes the malignant phenotype through EMT and the ERK/MMP-2 signaling pathway.

Expression of Rab5a correlates with tumor progression in pancreatic carcinoma

Rab family protein Rab5a has been implicated in cancer progression. To date, its expression pattern in human pancreatic cancer has not been investigated. This study aims to examine clinical significance, biological role, and potential mechanism of action of mRab5a in human pancreatic cancer. We analyzed Rab5a protein in cancer tissue of 111 cases of pancreatic cancer using immunohistochemistry. The results show that Rab5a overexpression correlates with high T stage, positive nodal status, and advanced TNM stage. We performed knockdown of Rab5a through transfection of Rab5a-specific siRNA in the Capan-2 cell line, which shows high endogenous expression, and of Rab5a plasmid in the CFPAC-1 cell line, which shows low endogenous expression. Rab5a knockdown inhibited cell proliferation and invasion while its overexpression promoted cell proliferation and invasion. In addition, overexpression of Rab5a induced resistance to 5-FU and gemcitabine while its knockdown reduced resistance to 5-FU and gemcitabine. Furthermore, our results show that Rab5a overexpression upregulates Wnt signaling and expression of Wnt target genes including c-myc and MMP7. Blocking Wnt signaling abolished the effects of Rab5a on Wnt targets and on cancer cell proliferation. In summary, our results show that Rab5a is overexpressed in pancreatic cancer and promotes aggressive biological behavior through regulation of the Wnt/β-catenin signaling pathway.

Targeting Rabs as a novel therapeutic strategy for cancer therapy

Rab GTPases constitute the largest family of small GTPases. Rabs regulate not only membrane trafficking but also cell signaling, growth and survival, and development. Increasingly, Rabs and their effectors are shown to be overexpressed or subject to loss-of-function mutations in a variety of disease settings, including cancer progression. This review provides an overview of dysregulated Rab proteins in cancer, and highlights the signaling and secretory pathways in which they operate, with the aim of identifying potential avenues for therapeutic intervention. Recent progress and perspectives for direct and/or indirect targeting of Rabs are also summarized.

Rab14 is overexpressed in ovarian cancers and promotes ovarian cancer proliferation through Wnt pathway

The Rab GTPase family protein Rab14 has been implicated in cancer development. However, its clinical significance in ovarian cancers and its biological effects have not been examined. The present study aims to examine the clinical significance, biological roles, and molecular mechanism of Rab14 in ovarian cancer progression. We examined expression pattern of Rab14 in 122 cases of ovarian cancer specimens using immunohistochemistry and found Rab14 overexpression correlated with FIGO stage (p = 0.0041). We depleted Rab14 in SKOV3 cells using siRNA and overexpressed Rab14 in SW626 cells. Knockdown of Rab14 inhibited cell growth and invasion while its overexpression facilitated cell growth and invasion. In addition, Rab14 overexpression increased paclitaxel resistance in SW626 cells while its depletion reduced drug resistance. Then, we investigated the role of Rab14 in the regulation of WNT/β-catenin signaling, demonstrating Rab14 overexpression regulated GSK3β phosphorylation and nuclear β-catenin accumulation. Rab14 depletion inhibited while its overexpression enhanced TCF transcriptional activity with corresponding change of Wnt target genes including MMP7 and c-myc. Wnt inhibitor abolished the effect of Rab14 on cell proliferation and Wnt target genes. In conclusion, the present study demonstrated that Rab14 promotes aggressiveness of ovarian cancer cell through, at least partly, Wnt signaling pathway.

Rab5a‑mediated autophagy regulates the phenotype and behavior of vascular smooth muscle cells

Rab5a, a key member of the Rab family of GTPases, was determined to be a regulator of vascular smooth muscle cell (VSMC) proliferation and migration. However, the exact regulatory mechanism remains unclear. As Rab5a has been shown to be associated with autophagy, which is essential for the conversion of VSMCs from a contractile to a synthetic phenotype in order to prevent cell death due to oxidative stress. The present study hypothesized that autophagy may be responsible for the proliferation and migration of VSMCs via the Rab5a protein. The aim of the present study was to evaluate the effect of Rab5a on autophagy in VSMCs. The human aorta vascular smooth muscle cell line, T/G HA-VSMCs, was treated with small interfering (si)RNA against Rab5a and/or platelet-derived growth factor (PDGF). Following treatment, the phenotype transition of the VSMCs was evaluated by detecting the mRNA and protien expression levels of VSMC molecular markers using reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. In addition, autophagy in VSMCs was evaluated by western blotting for autophagy-associated proteins, flow cytometry of acidic vesicular organelles, punctate fluorescence of microtubule associated protein light chain 3 and transmission electron microscopy of typical scattered double-membrane vacuolar structures. Additionally, the proliferation, migration, cell cycle and apoptotic response of VSMCs were detected by sulforhodamine B assay, transwell assay and flow cytometry, respectively. The results revealed that transfection with siRNA against Rab5a led to a significant decrease in Rab5a protein expression, while the reduced expression trend of Rab5a was rescued by intervention with PDGF. Furthermore, cells transfected with siRNA against Rab5a inhibited the autophagy of VSMCs. Downregulated Rab5a inhibited the phenotype transition of VSMCs. Additionally, downregulated Rab5a led to slowed cell growth, decreased numbers of migrated cells, decreased numbers of cells at the G0-G1 phase and a higher apoptosis rate. However, PDGF significantly rescued these phenomena caused by siRNA against Rab5a. These results indicated that Rab5a-mediated autophagy may regulate the phenotype transition and cell behavior of VSMCs through the activation of the extracellular-regulated kinase 1/2 signaling pathway.

Expression of APPL1 is correlated with clinicopathologic characteristics and poor prognosis in patients with gastric cancer

BACKGROUND

Although appl1 is overexpressed in many cancers, its status in gastric cancer (gc) is not known. In the present study, we used relevant pathologic and clinical data to investigate appl1 expression in patients with gc.

METHODS

In 47 gc and 27 non-gc surgical specimens, immunohistochemistry was used to detect the expression of appl1, and reverse-transcriptase polymerase chain reaction (rt-pcr) was used to detect messenger rna (mrna). A scatterplot visualized the relationship between survival time and mrna expression in gc patients. The log-rank test and other survival statistics were used to determine the association of appl1 expression with the pathologic features of the cancer and clinical outcomes.

RESULTS

In gc, appl1 was expressed in 28 of 47 specimens (59.6%), and in non-gc, it was expressed in 7 of 23 specimens (30.4%, p < 0.05). The expression of mrna in gc was 0.82 [95% confidence interval (ci): 0.78 to 0.86], and in non-gc, it was 0.73 (95% ci: 0.69 to 0.77; p < 0.05). Immunohistochemistry demonstrated that, in gc, appl1 expression was correlated with depth of infiltration (p = 0.005), lymph node metastasis (p = 0.017), and TNM stage (p = 0.022), but not with pathologic type (p = 0.41). Testing by rt-pcr demonstrated that, in gc, appl1 mrna expression was correlated with depth of infiltration (p = 0.042), lymph node metastasis (p = 0.031), and TNM stage (p = 0.04), but again, not with pathologic type (p = 0.98). The correlation coefficient between survival time and mrna expression was -0.83 (p < 0.01). Overexpression of appl1 protein (hazard ratio: 3.88; 95% ci: 1.07 to 14.09) and mrna (hazard ratio: 4.23; 95% ci: 3.09 to 15.11) was a risk factor for death in patients with gc.

CONCLUSIONS

Expression of appl1 is increased in gc. Overexpression is prognostic for a lethal outcome.

APPL1-Mediating Leptin Signaling Contributes to Proliferation and Migration of Cancer Cells

Leptin has been implicated in tumorigenesis and tumor progression, particularly in obese patients. As a multifunctional adaptor protein, APPL1 (containing pleckstrin homology domain, phosphotyrosine binding domain, and a leucine zipper motif 1) plays a critical role in regulating adiponectin and insulin signaling pathways. Currently, high APPL1 level has been suggested to be related to metastases and progression of some types of cancer. However, the intercourse between leptin signaling pathway and APPL1 remains poorly understood. Here, we show that the protein levels and phosphorylation statues of APPL1were highly expressed in tissues from human hepatocellular carcinoma and triple-positive breast cancer. Leptin stimulated APPL1 phosphorylation in a time-dependent manner in both human hepatocellular carcinoma HepG2 cell and breast cancer MCF-7 cell. Overexpression or suppression of APPL1 promoted or attenuated, respectively, leptin-induced phosphorylation of STAT3, ERK1/2, and Akt in the cancer cells, accompanied with enhanced or mitigated cell proliferation and migration. In addition, we identified that APPL1 directly bound to both leptin receptor and STAT3. This interaction was significantly enhanced by leptin stimulation. Our results suggested that APPL1 positively mediated leptin signaling and promoted leptin-induced proliferation and migration of cancer cells. This finding reveals a novel mechanism by which leptin promotes the motility and growth of cancer cells.

Overexpression of Rab5a promotes hepatocellular carcinoma cell proliferation and invasion via FAK signaling pathway

Rab5a was reported to be overexpressed in human malignancy and associated with the malignant phenotype. To data, its expression pattern and biological function in hepatocellular carcinoma (HCC) have not been studied. We analyzed Rab5a protein expression in 98 cases of HCC tissues and four HCC cell lines. We found that Rab5a expression was upregulated in HCC tissues and cell lines. Rab5a overexpression correlated with TNM stage and nodal metastasis (p < 0.05). To confirm the biological function of Rab5a in HCC cell lines, Rab5a siRNA was employed in SK-Hep-1 cell line and plasmid transfection was performed in Huh7 cell line. CCK-8 assay showed that Rab5a depletion blocked cell growth rate while Rab5a overexpression facilitated proliferation. Transwell and migration assay showed that Rab5a positively regulated cell invasion and migration. To explore the molecular mechanism underlying the biological effects of Rab5a, we checked several signaling pathways and found that Rab5a overexpression upregulated cyclin D1, cyclin E expression, FAK (Tyr397), and AKT (Ser473) phosphorylation. Blockage of FAK using inhibitor PF573228 abolished the role of Rab5a on cyclin D1. In conclusion, Rab5a is overexpressed in human HCC and contributes to cancer cell proliferation and invasion through regulation of FAK and AKT signaling.

The role of endocytic Rab GTPases in regulation of growth factor signaling and the migration and invasion of tumor cells

Metastasis is characterized pathologically by uncontrolled cell invasion, proliferation, migration and angiogenesis. It is a multistep process that encompasses the modulation of membrane permeability and invasion, cell spreading, cell migration and proliferation of the extracellular matrix, increase in cell adhesion molecules and interaction, decrease in cell attachment and induced survival signals and propagation of nutrient supplies (blood vessels). In cancer, a solid tumor cannot expand and spread without a series of synchronized events. Changes in cell adhesion receptor molecules (e.g., integrins, cadherin-catenins) and protease expressions have been linked to tumor invasion and metastasis. It has also been determined that ligand-growth factor receptor interactions have been associated with cancer development and metastasis via the endocytic pathway. Specifically, growth factors, which include IGF-1 and IGF-2 therapy, have been associated with most if not all of the features of metastasis. In this review, we will revisit some of the key findings on perhaps one of the most important hallmarks of cancer metastasis: cell migration and cell invasion and the role of the endocytic pathway in mediating this phenomenon.

The role of the small GTPase Rab31 in cancer

Members of the small GTPase family Rab are emerging as potentially important factors in cancer development and progression. A good number of Rabs have been implicated or associated with various human cancers, and much recent excitement has been associated with the roles of the Rab11 subfamily member Rab25 and its effector, the Rab coupling protein (RCP), in tumourigenesis and metastasis. In this review, we focus on a Rab5 subfamily member, Rab31, and its implicated role in cancer. Well recognized as a breast cancer marker with good prognostic value, recent findings have provided some insights as to the mechanism underlying Rab31's influence on oncogenesis. Levels of Oestrogen Receptor α (ERα)- responsive Rab31 could be elevated through stabilization of its transcript by the RNA binding protein HuR, or though activation by the oncoprotein mucin1-C (MUC1-C), which forms a transcriptional complex with ERα. Elevated Rab31 stabilizes MUC1-C levels in an auto-inductive loop that could lead to aberrant signalling and gene expression associated with cancer progression. Rab31 and its guanine nucleotide exchange factor GAPex-5 have, however, also been shown to enhance early endosome-late endosome transport and degradation of the epidermal growth factor receptor (EGFR). The multifaceted action and influences of Rab31 in cancer is discussed in the light of its new interacting partners and pathways.

RABEX-5 is upregulated and plays an oncogenic role in gastric cancer development by activating the VEGF signaling pathway

RABEX-5, a guanine-nucleotide exchange factor (GEF) for RAB-5, is implicated in tumorigenesis and in the development of certain human cancers. Here, we report that RABEX-5 promotes tumor growth and the metastatic ability of gastric cancer cells both in vitro and in vivo. Expression of RABEX-5 is significantly higher in gastric cancer tissues and is associated with tumor size and lymph node metastasis. In addition, targeted silencing of RABEX-5 reduced gastric cancer cell proliferation and colony formation in vitro via the induction of a G0/G1 phase arrest, and stimulated gastric cancer cell apoptosis. Knockdown of RABEX-5 also inhibited wound healing, migration and the invasive abilities of gastric cancer cells. The results of in vivo animal experiments were also consistent with these in vitro findings. Silencing of RABEX-5 led to decreased expression of VEGF. These results indicate that RABEX-5 is upregulated and plays an oncogenic role in gastric cancer development by activating the VEGF signaling pathway.

Downregulation of miR-101-3p by hepatitis B virus promotes proliferation and migration of hepatocellular carcinoma cells by targeting Rab5a

RAB GTPase 5A (RAB5A), a member of the Rab subfamily of small GTPases, acts as an oncogene and has been associated with various key cellular functions, including cell growth, differentiation, apoptosis and angiogenesis. Recently, it has been reported that the Rab5a gene is involved in the progression of cancer. Hepatocellular carcinoma (HCC) is one of the most common and aggressive cancers, and it is usually associated with persistent hepatitis B virus (HBV) infections. Emerging evidence suggests that HBV alters microRNA (miRNA) expression profiles, but the mechanisms underlying this process have not yet been fully elucidated. Here, we examine how HBV affects the production of miR-101-1, which has been shown to be downregulated in HCC. We found that HBV could repress miR-101-3p by inhibiting its promoter activity. Downregulation of miR-101-3p promoted cancer cell growth and migration, and a specific miR-101-3p inhibitor was able to enhance proliferation and migration. Moreover, we identified Rab5a was one of the target genes of miR-101-3p in HBV-related HCC. Forced expression of miR-101-3p in liver cell lines resulted in a marked reduction of the expression of Rab5a at both the mRNA and protein level by directly targeting the 3'untranslated region of Rab5a. Overexpression of Rab5a resulted in a reversal of the suppression of proliferation and migration of SMMC-7721 cells mediated by miR-101-3p. Taken together, our data show that HBV can downregulate miR-101-3p expression by inhibiting its promoter activity and that downregulation of miR-101-3p promotes HCC cell proliferation and migration by targeting Rab5a. This provides new insights into the mechanisms of HBV-related HCC pathogenesis.

Epigenetic control of autophagy by microRNAs in ovarian cancer

Autophagy is a lysosomal-driven catabolic process that contributes to the preservation of cell homeostasis through the regular elimination of cellular damaged, aged, and redundant molecules and organelles. Autophagy plays dual opposite roles in cancer: on one hand it prevents carcinogenesis; on the other hand it confers an advantage to cancer cells to survive under prohibitive conditions. Autophagy has been implicated in ovarian cancer aggressiveness and in ovarian cancer cell chemoresistance and dormancy. Small noncoding microRNAs (miRNAs) regulate gene expression at posttranscriptional level, thus playing an important role in many aspects of cell pathophysiology, including cancerogenesis and cancer progression. Certain miRNAs have recently emerged as important epigenetic modulators of autophagy in cancer cells. The mRNA of several autophagy-related genes contains, in fact, the target sequence for miRNAs belonging to different families, with either oncosuppressive or oncogenic activities. MiRNA profiling studies have identified some miRNAs aberrantly expressed in ovarian cancer tissues that can impact autophagy. In addition, plasma and stroma cell-derived miRNAs in tumour-bearing patients can regulate the expression of relevant autophagy genes in cancer cells. The present review focuses on the potential implications of miRNAs regulating autophagy in ovarian cancer pathogenesis and progression.

miRNA-130a regulates C/EBP-ε expression during granulopoiesis

CCAAT/enhancer binding protein-ε (C/EBP-ε) is considered a master transcription factor regulating terminal neutrophil maturation. It is essential for expression of secondary granule proteins, but it also regulates proliferation, cell cycle, and maturation during granulopoiesis. Cebpe(-/-) mice have incomplete granulocytic differentiation and increased sensitivity toward bacterial infections. The amount of C/EBP-ε messenger RNA (mRNA) increases with maturation from myeloblasts with peak level in myelocytes (MC)/metamyelocytes (MM), when the cells stop proliferating followed by a decline in more mature cells. In contrast, C/EBP-ε protein is virtually detectable only in the MC/MM population, indicating that expression in more immature cells could be inhibited by microRNAs (miRNAs). We found that miRNA-130a (miR-130a) regulates C/EBP-ε protein expression in both murine and human granulocytic precursors. Overexpression of miR-130a in a murine cell line downregulated C/EBP-ε protein and lactoferrin (Ltf), cathelicidin antimicrobial protein (Camp), and lipocalin-2 (Lcn2) mRNA expression giving rise to cells with a more immature phenotype, as seen in the Cebpe(-/-) mouse. Introduction of a C/EBP-ε mRNA without target site for miR-130a restored both C/EBP-ε production, expression of Camp and Lcn2, and resulted in the cells having a more mature phenotype. We conclude that miR-130a is important for the regulation of the timed expression of C/EBP-ε during granulopoiesis.

RABEX-5 plays an oncogenic role in breast cancer by activating MMP-9 pathway

BACKGROUND

RABEX-5, a guanine nucleotide exchange factor (GEF) for RAB-5, plays an important role in cell mobility and altered expression associated with tumor metastasis. This study aimed to investigate the role of RABEX-5 in proliferation and metastasis of breast cancer in vitro and ex vivo.

METHODS

RABEX-5 expression was examined in breast cancer, benign tumor and normal breast tissues by immunohistochemistry and western blot. Two stable cell lines were established, the MCF-7/NC negative control cell line and the MCF-7/KD cell line, which stably expressed an RNA interference (RNAi) construct that induced downregulation of RABEX-5 expression. These cell lines were utilized to evaluate the role of RABEX-5 in cell proliferation and migration in vitro and tumorigenicity in vivo. The possible role of RABEX-5 in the regulation of matrix metallopeptidase 9 (MMP-9) was evaluated using western blot and real-time PCR.

RESULTS

RABEX-5 expression was found to be significantly higher in breast cancer tissues compared with benign tumor and normal breast tissues. High levels of RABEX-5 expression were associated with axillary lymph node metastasis. In addition, RABEX-5 silencing significantly reduced cancer cell proliferation, colony formation and migration ability in vitro and inhibited tumor growth in vivo. RABEX -5 knockdown also attenuated the migration of breast cancer cells via modulation of MMP-9 transcriptional activity.

CONCLUSIONS

Our results indicate that RABEX-5 plays an oncogenic role in breast cancer by modulating the proliferation and metastasis potential of breast cancer cells. Thus, RABEX-5 is a promising prognostic indicator for patients with breast cancer.

Reconstruction of an integrated genome-scale co-expression network reveals key modules involved in lung adenocarcinoma

Our goal of this study was to reconstruct a “genome-scale co-expression network” and find important modules in lung adenocarcinoma so that we could identify the genes involved in lung adenocarcinoma. We integrated gene mutation, GWAS, CGH, array-CGH and SNP array data in order to identify important genes and loci in genome-scale. Afterwards, on the basis of the identified genes a co-expression network was reconstructed from the co-expression data. The reconstructed network was named “genome-scale co-expression network”. As the next step, 23 key modules were disclosed through clustering. In this study a number of genes have been identified for the first time to be implicated in lung adenocarcinoma by analyzing the modules. The genes EGFR, PIK3CA, TAF15, XIAP, VAPB, Appl1, Rab5a, ARF4, CLPTM1L, SP4, ZNF124, LPP, FOXP1, SOX18, MSX2, NFE2L2, SMARCC1, TRA2B, CBX3, PRPF6, ATP6V1C1, MYBBP1A, MACF1, GRM2, TBXA2R, PRKAR2A, PTK2, PGF and MYO10 are among the genes that belong to modules 1 and 22. All these genes, being implicated in at least one of the phenomena, namely cell survival, proliferation and metastasis, have an over-expression pattern similar to that of EGFR. In few modules, the genes such as CCNA2 (Cyclin A2), CCNB2 (Cyclin B2), CDK1, CDK5, CDC27, CDCA5, CDCA8, ASPM, BUB1, KIF15, KIF2C, NEK2, NUSAP1, PRC1, SMC4, SYCE2, TFDP1, CDC42 and ARHGEF9 are present that play a crucial role in cell cycle progression. In addition to the mentioned genes, there are some other genes (i.e. DLGAP5, BIRC5, PSMD2, Src, TTK, SENP2, PSMD2, DOK2, FUS and etc.) in the modules.

Rab5 activation promotes focal adhesion disassembly, migration and invasiveness in tumor cells

Migration and invasion are essential steps associated with tumor cell metastasis and increasing evidence points towards endosome trafficking being essential in this process. Indeed, the small GTPase Rab5, a crucial regulator of early endosome dynamics, promotes cell migration in vitro and in vivo. Precisely how Rab5 participates in these events remains to be determined. Considering that focal adhesions represent structures crucial to cell migration, we specifically asked whether Rab5 activation promoted focal adhesion disassembly and thereby facilitated migration and invasion of metastatic cancer cells. Pulldown and biosensor assays revealed that Rab5-GTP loading increased at the leading edge of migrating tumor cells. Additionally, targeting of Rab5 by different shRNA sequences, but not control shRNA, decreased Rab5-GTP levels, leading to reduced cell spreading, migration and invasiveness. Re-expression in knockdown cells of wild-type Rab5, but not the S34N mutant (GDP-bound), restored these properties. Importantly, Rab5 association with the focal adhesion proteins vinculin and paxillin increased during migration, and expression of wild-type, but not GDP-bound Rab5, accelerated focal adhesion disassembly, as well as FAK dephosphorylation on tyrosine 397. Finally, Rab5-driven invasiveness required focal adhesion disassembly, as treatment with the FAK inhibitor number 14 prevented Matrigel invasion and matrix metalloproteinase release. Taken together, these observations show that Rab5 activation is required to enhance cancer cell migration and invasion by promoting focal adhesion disassembly.

Hepatitis B virus X protein upregulates oncogene Rab18 to result in the dysregulation of lipogenesis and proliferation of hepatoma cells

Hepatitis B virus X protein (HBx) contributes to the development of hepatocellular carcinoma (HCC) through inducing dysregulation of lipogenesis. However, the mechanism by which HBx induces the abnormal lipogenesis is not well known. In this study, we report that the oncogene Rab18, a member of Ras family, enhances the HBx-induced hepatocarcinogenesis through inducing dysregulation of lipogenesis and proliferation. Our data showed that the expression levels of Rab18 were positively associated with those of HBx in clinical HCC tissues. HBx was able to upregulate the expression of Rab18 in p21-HBx transgenic mice and hepatoma cell lines. Next, we identified the mechanism by which HBx upregulated Rab18. The results demonstrated that cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) were able to stimulate Rab18 promoter through activating transcription factor activator protein 1 (AP-1) and cyclic adenosine 3',5'-monophosphate response element-binding (CREB). In addition, we identified another pathway that HBx activated Rab18. We found that miR-429 was able to directly target the 3' untranslated region of Rab18, suggesting that Rab18 is one of the target genes of miR-429. Then, we found that HBx was able to downregulate miR-429 in hepatoma cells. The oil red O staining showed that HBx resulted in the dysregulation of lipogenesis through Rab18. Moreover, Rab18 contributed to the HBx-enhanced proliferation of hepatoma cells in vitro and in vivo. HBx enhances hepatocarcinogenesis through leading to the dysregulation of lipogenesis and proliferation of hepatoma cells, involving two pathways such as HBx/COX-2/5-LOX/AP-1/CREB/Rab18 and HBx/miR-429/Rab18.

Involvement of autophagy in ovarian cancer: a working hypothesis

Autophagy is a lysosomal-driven catabolic process that contributes to preserve cell and tissue homeostases through the regular elimination of damaged, aged and redundant self-constituents. In normal cells, autophagy protects from DNA mutation and carcinogenesis by preventive elimination of pro-oxidative mitochondria and protein aggregates. Mutations in oncogenes and oncosuppressor genes dysregulate autophagy. Up-regulated autophagy may confer chemo- and radio-resistance to cancer cells, and also a pro-survival advantage in cancer cells experiencing oxygen and nutrient shortage. This fact is the rationale for using autophagy inhibitors along with anti-neoplastic therapies. Yet, aberrant hyper-induction of autophagy can lead to cell death, and this phenomenon could also be exploited for cancer therapy. The actual level of autophagy in the cancer cell is greatly affected by vascularization, inflammation, and stromal cell infiltration. In addition, small non-coding microRNAs have recently emerged as important epigenetic modulators of autophagy. The present review focuses on the potential involvement of macroautophagy, and on its genetic and epigenetic regulation, in ovarian cancer pathogenesis and progression.

Optimizing molecular-targeted therapies in ovarian cancer: the renewed surge of interest in ovarian cancer biomarkers and cell signaling pathways

The hallmarks of ovarian cancer encompass the development of resistance, disease recurrence and poor prognosis. Ovarian cancer cells express gene signatures which pose significant challenges for cancer drug development, therapeutics, prevention and management. Despite enhancements in contemporary tumor debulking surgery, tentative combination regimens and abdominal radiation which can achieve beneficial response rates, the majority of ovarian cancer patients not only experience adverse effects, but also eventually relapse. Therefore, additional therapeutic possibilities need to be explored to minimize adverse events and prolong progression-free and overall response rates in ovarian cancer patients. Currently, a revival in cancer drug discovery is devoted to identifying diagnostic and prognostic ovarian cancer biomarkers. However, the sensitivity and reliability of such biomarkers may be complicated by mutations in the BRCA1 or BRCA2 genes, diverse genetic risk factors, unidentified initiation and progression elements, molecular tumor heterogeneity and disease staging. There is thus a dire need to expand existing ovarian cancer therapies with broad-spectrum and individualized molecular targeted approaches. The aim of this review is to profile recent developments in our understanding of the interrelationships among selected ovarian tumor biomarkers, heterogeneous expression signatures and related molecular signal transduction pathways, and their translation into more efficacious targeted treatment rationales.

Expression of adaptor protein containing PH domain, PTB domain and leucine zipper motif 1 in colorectal carcinogenesis

AIM: To investigate the relationship between expression of adaptor protein containing PH domain, PTB domain and leucine zipper motif 1(APPL1) and clinicopathological parameters of colorectal cancer.

METHODS: Expression of APPL1 protein and mRNA in 35 surgical specimens of colorectal carcinoma (CRC) and 27 normal colorectal tissue specimens was detected by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR), respectively.

RESULTS: The expression of APPL1 in CRC was significantly higher than that in normal mucosa. APPL1 expression was correlated with histological differentiation, lymph node metastasis and TNM stage (all P < 0.05), but not with sex, age, or tumor size (all P > 0.05) in patients with CRC.

CONCLUSION: The expression of APPL1 protein is increased in CRC. APPL1 protein expression is closely related with tumor differentiation, lymph node metastasis and TNM stage in patients with colorectal cancer. APPL1 may be a novel therapeutic target for CRC.

Rab5A is associated with axillary lymph node metastasis in breast cancer patients

The expression of Rab proteins has been associated with cancer. However, few data are available on Rab5A expression in human breast cancer or its impact on disease progression. First, we examined the functional role of Rab5A in breast cancer cells. The expression of Rab5A in MDA-MB-231 cells can be stimulated by epidermal growth factor in a dose-dependent manner. The epidermal growth factor-induced increase of Rab5A expression correlated well with enhanced migration in wound healing migration assays in these cells. Furthermore, we evaluated the expression of Rab5A in breast cancer specimens using immunohistochemical staining, then analyzed the relationship between the expression of Rab5A and clinicopathological parameters. The increased expression of Rab5A protein in 123 breast cancer samples was associated with higher histological grade (P = 0.004), more lymphovascular invasion (P = 0.027), more axillary lymph node (LN) metastasis (P = 0.008), and a higher number of axillary LN metastases (P = 0.043). Among 218 axillary LNs of more than 10 breast cancer patients with node metastases, 167 metastatic LNs were found to have increased Rab5A expression. Rab5A is associated with axillary LN metastasis in breast cancer patients.

microRNA-101 is a potent inhibitor of autophagy

Autophagy is an evolutionarily conserved mechanism of cellular self-digestion in which proteins and organelles are degraded through delivery to lysosomes. Defects in this process are implicated in numerous human diseases including cancer. To further elucidate regulatory mechanisms of autophagy, we performed a functional screen in search of microRNAs (miRNAs), which regulate the autophagic flux in breast cancer cells. In this study, we identified the tumour suppressive miRNA, miR-101, as a potent inhibitor of basal, etoposide- and rapamycin-induced autophagy. Through transcriptome profiling, we identified three novel miR-101 targets, STMN1, RAB5A and ATG4D. siRNA-mediated depletion of these genes phenocopied the effect of miR-101 overexpression, demonstrating their importance in autophagy regulation. Importantly, overexpression of STMN1 could partially rescue cells from miR-101-mediated inhibition of autophagy, indicating a functional importance for this target. Finally, we show that miR-101-mediated inhibition of autophagy can sensitize breast cancer cells to 4-hydroxytamoxifen (4-OHT)-mediated cell death. Collectively, these data establish a novel link between two highly important and rapidly growing research fields and present a new role for miR-101 as a key regulator of autophagy.