Overexpression of the secretory small GTPase Rab27B in human breast cancer correlates closely with lymph node metastasis and predicts poor prognosis

Regulation of autophagy by Rab27B in colorectal cancer

Autophagy is a cellular recycling process that is associated with tumor growth, anti-tumor immune responses, and therapy resistance in colorectal cancer (CRC). In this report, we identify the small GTPase Rab27B to control the autophagy process in CRC. Depletion of Rab27B showed an abnormal accumulation of autophagy vesicles and increased autophagy markers in CRC cells, indicating autophagy dysregulation. Image analysis indicated that autophagy flux is blocked at the autophagosome/lysosome fusion step when Rab27B is lost. While Rab27B deficient cells are proficient at growth under 2D in vitro conditions, cell growth was significantly impacted in both in vitro 3D growth and in vivo tumorigenesis studies. Together, these results demonstrate a new role of Rab27B in the autophagy trafficking process in CRC and identify Rab27B as a potential therapeutic target for CRC.

Tectoridin inhibits the growth of bladder cancer by regulating PI3K/MAPK pathway through RAB27B

Bladder cancer (BC) is a common and malignant tumor of the urinary tract, and its treatment options are limited. Tectoridin (TEC) has antitumor activity against prostate and colon cancer, but its effects on BC are poorly understood. BC cells were treated with increasing concentrations of TEC, and its effects on cell proliferation, migration, invasiveness, and apoptosis were assessed. Xenograft mouse model was used to evaluate the influences of TEC on BC tumor growth. Western blot analysis was conducted to explore the downstream pathways affected by TEC. TEC treatment decreased BC cell viability in a dose-dependent manner (IC50 ≈ 25 μM), and inhibited cell proliferation, migration, and invasiveness while promoting apoptosis. Clinical analysis revealed high expression of RAB27B in BC tumor tissues, particularly in advanced stages, correlating with an unfavorable prognosis. In vitro experiments demonstrated that TEC suppressed the PI3K/MAPK pathway by targeting RAB27B, and overexpression of RAB27B counteracted the antitumor effects of TEC. In xenograft models, TEC administration suppressed tumor growth, reduced tumor volume, inhibited cell proliferation, and suppressed the PI3K/MAPK pathway, highlighting its potential as an inhibitor of tumor growth. TEC suppresses BC tumor growth by targeting RAB27B and inactivating the PI3K/MAPK signaling and may provide a promising therapeutic target for BC treatment.

Membrane trafficking alterations in breast cancer progression

Breast cancer (BC) is the most common type of cancer in women, and remains one of the major causes of death in women worldwide. It is now well established that alterations in membrane trafficking are implicated in BC progression. Indeed, membrane trafficking pathways regulate BC cell proliferation, migration, invasion, and metastasis. The 22 members of the ADP-ribosylation factor (ARF) and the >60 members of the rat sarcoma (RAS)-related in brain (RAB) families of small GTP-binding proteins (GTPases), which belong to the RAS superfamily, are master regulators of membrane trafficking pathways. ARF-like (ARL) subfamily members are involved in various processes, including vesicle budding and cargo selection. Moreover, ARFs regulate cytoskeleton organization and signal transduction. RABs are key regulators of all steps of membrane trafficking. Interestingly, the activity and/or expression of some of these proteins is found dysregulated in BC. Here, we review how the processes regulated by ARFs and RABs are subverted in BC, including secretion/exocytosis, endocytosis/recycling, autophagy/lysosome trafficking, cytoskeleton dynamics, integrin-mediated signaling, among others. Thus, we provide a comprehensive overview of the roles played by ARF and RAB family members, as well as their regulators in BC progression, aiming to lay the foundation for future research in this field. This research should focus on further dissecting the molecular mechanisms regulated by ARFs and RABs that are subverted in BC, and exploring their use as therapeutic targets or prognostic markers.

Anticancer Therapy Targeting Cancer-Derived Extracellular Vesicles

Extracellular vesicles (EVs) are natural lipid nanoparticles secreted by most types of cells. In malignant cancer, EVs derived from cancer cells contribute to its progression and metastasis by facilitating tumor growth and invasion, interfering with anticancer immunity, and establishing premetastasis niches in distant organs. In recent years, multiple strategies targeting cancer-derived EVs have been proposed to improve cancer patient outcomes, including inhibiting EV generation, disrupting EVs during trafficking, and blocking EV uptake by recipient cells. Developments in EV engineering also show promising results in harnessing cancer-derived EVs as anticancer agents. Here, we summarize the current understanding of the origin and functions of cancer-derived EVs and review the recent progress in anticancer therapy targeting these EVs.

Sex-Specific Silica Nanoparticle Protein Corona Compositions Exposed to Male and Female BALB/c Mice Plasmas

As various nanoparticles (NPs) are increasingly being used in nanomedicine products for more effective and less toxic therapy and diagnosis of diseases, there is a growing need to understand their biological fate in different sexes. Herein, we report a proof-of-concept result of sex-specific protein corona compositions on the surface of silica NPs as a function of their size and porosity upon incubation with plasma proteins of female and male BALB/c mice. Our results demonstrate substantial differences between male and female protein corona profiles on the surface of silica nanoparticles. By comparing protein abundances between male and female protein coronas of mesoporous silica nanoparticles and Stöber silica nanoparticles of ∼100, 50, and 100 nm in diameter, respectively, we detected 17, 4, and 4 distinct proteins, respectively, that were found at significantly different concentrations for these constructs. These initial findings demonstrate that animal sex can influence protein corona formation on silica NPs as a function of the physicochemical properties. A more thorough consideration of the role of plasma sex would enable nanomedicine community to design and develop safer and more efficient diagnostic and therapeutic nanomedicine products for both sexes.

RAB27B expression in pancreatic cancer is predictive of poor survival but good response to chemotherapy

BACKGROUND

Pancreatic cancer is the 4th leading cause of cancer-related death with poor survival even after curative resection. RAB27A and RAB27B are key players in the exosome pathway where they play important roles in exosome secretion. Evidence suggests that RAB27A and RAB27B expression not only leads to tumor proliferation and invasion, but also plays an important role in antigen transfer necessary for anticancer immunity.

OBJECTIVE

In this study, we analyze the expression of RAB27A and RAB27B in patients after pancreatic cancer surgery with or without adjuvant chemotherapy and its influence on overall survival.

METHODS

We analyzed a total of 167 patients with pancreatic cancer for their RAB27A and RAB27B expression. We dichotomized the patients along the median and compared survival in patients with high and low RAB27A and RAB27B expression with or without adjuvant chemotherapy treatment.

RESULTS

We found a significant improvement in overall survival in patients with a negative resection margin (p= 0.037) and in patients who received adjuvant chemotherapy (p= 0.039). The survival benefit after chemotherapy was dependent on RAB27B expression status: only the subgroup of patients with high RAB27B expression benefited from adjuvant chemotherapy (p= 0.006), but not the subgroup with low RAB27B expression (p= 0.59). Patients with high RAB27B expression who did not receive adjuvant chemotherapy showed a trend towards worse survival compared to the other subgroups. This difference was abolished after treatment with adjuvant chemotherapy.

CONCLUSION

These results suggest that RAB27B expression in pancreatic cancer might identify a subgroup of patients with poor survival who might respond well to adjuvant chemotherapy. If resectable, these patients could be considered for neoadjuvant chemotherapy to minimize the risk of not receiving adjuvant chemotherapy. Further prospective studies are needed to confirm these findings.

Rab GTPases: Central Coordinators of Membrane Trafficking in Cancer

Tumor progression involves invasion, migration, metabolism, autophagy, exosome secretion, and drug resistance. Cargos transported by membrane vesicle trafficking underlie all of these processes. Rab GTPases, which, through coordinated and dynamic intracellular membrane trafficking alongside cytoskeletal pathways, determine the maintenance of homeostasis and a series of cellular functions. The mechanism of vesicle movement regulated by Rab GTPases plays essential roles in cancers. Therefore, targeting Rab GTPases to adjust membrane trafficking has the potential to become a novel way to adjust cancer treatment. In this review, we describe the characteristics of Rab GTPases; in particular, we discuss the role of their activation in the regulation of membrane transport and provide examples of Rab GTPases regulating membrane transport in tumor progression. Finally, we discuss the clinical implications and the potential as a cancer therapeutic target of Rab GTPases.

The calcium sensing receptor (CaSR) promotes Rab27B expression and activity to control secretion in breast cancer cells

Chemotactic and angiogenic factors secreted within the tumor microenvironment eventually facilitate the metastatic dissemination of cancer cells. Calcium-sensing receptor (CaSR) activates secretory pathways in breast cancer cells via a mechanism driven by vesicular trafficking of this receptor. However, it remains to be elucidated how endosomal proteins in secretory vesicles are controlled by CaSR. In the present study, we demonstrate that CaSR promotes expression of Rab27B and activates this secretory small GTPase via PI3K, PKA, mTOR and MADD, a guanine nucleotide exchange factor, also known as DENN/Rab3GEP. Active Rab27B leads secretion of various cytokines and chemokines, including IL-6, IL-1β, IL-8, IP-10 and RANTES. Expression of Rab27B is stimulated by CaSR in MDA-MB-231 and MCF-7 breast epithelial cancer cells, but not in non-cancerous MCF-10A cells. This regulatory mechanism also occurs in HeLa and PC3 cells. Our findings provide insightful information regarding how CaSR activates a Rab27B-dependent mechanism to control secretion of factors known to intervene in paracrine communication circuits within the tumor microenvironment.

Prognostic significance of Rab27 expression in solid cancer: a systematic review and meta-analysis

Rab27 is an essential molecule of vesicle fusion and trafficking in exosome secretion process, which plays important roles in cancer progression and metastasis. Recent studies reported that Rab27 expression is also associated with cancer prognosis. Therefore, we performed a meta-analysis to reveal the prognostic significance of Rab27 expression in solid cancer. Data were extracted by searching on PubMed, Embase and Cochrane library until February 15 2020. Pooled hazard ratio (HR) with confidence interval (CI) was calculated to evaluate the association between Rab27 expression and survival in solid cancer. Ten studies with 1434 cancer patients were including for this meta-analysis. High expression of Rab27 was associated with poor survival (HR 2.67, 95% CI 1.52-4.69, p = 0.001). High expression of Rab27A was significantly associated with lymph node metastasis (HR 1.53, 95% CI 1.00-2.34, p = 0.048). High expression of Rab27B was significantly correlated with lymph node and distant metastasis (HR 2.15, 95% CI 1.56-2.95, p < 0.001; HR 6.80, 95% CI 3.12-14.85, p < 0.001), and higher TNM stage (HR 2.55, 95% CI 1.78-3.65, p < 0.001). This meta-analysis revealed that Rab27 expression could be a potential prognostic marker in solid cancer.

Androgen Receptor Signaling Reduces the Efficacy of Bacillus Calmette-Guérin Therapy for Bladder Cancer via Modulating Rab27b-Induced Exocytosis

Although intravesical bacillus Calmette-Guérin (BCG) immunotherapy has been the gold standard for nonsurgical management of non-muscle-invasive bladder cancer, a considerable number of patients exhibit resistance to the adjuvant treatment with unexplained mechanisms. This study aimed to investigate whether and how androgen receptor (AR) signals modulate BCG cytotoxicity in bladder cancer. AR knockdown or overexpression in bladder cancer lines resulted in induction or reduction, respectively, in intracellular BCG quantity and its cytotoxic activity. Microarray screening identified Rab27b, a small GTPase known to mediate bacterial exocytosis, which was upregulated in BCG-resistant cells and downregulated in AR-shRNA cells. Knockdown of Rab27b, or its effector SYTL3, or overexpression of Rab27b also induced or reduced, respectively, BCG quantity and cytotoxicity. In addition, treatment with GW4869, which was previously shown to inhibit Rab27b-dependent secretion, induced them and reduced Rab27b expression in bladder cancer cells. Meanwhile, AR expression was upregulated in BCG-resistant lines, compared with respective controls. In a mouse orthotopic xenograft model, Rab27b/SYTL3 knockdown or GW4869 treatment enhanced the amount of BCG within tumors and its suppressive effect on tumor growth. Moreover, in non-muscle-invasive bladder cancer specimens from patients subsequently undergoing BCG therapy, positivity of AR/Rab27b expression was associated with significantly higher risks of tumor recurrence. AR activation thus correlates with resistance to BCG treatment, presumably via upregulating Rab27b expression. Mechanistically, it is suggested that BCG elimination from urothelial cells is induced by Rab27b/SYTL3-mediated exocytosis. Accordingly, Rab27b inactivation, potentially via antiandrogenic drugs and/or exocytosis inhibition are anticipated to sensitize the efficacy of BCG therapy, especially in patients with BCG-refractory AR/Rab27b-positive bladder cancer.

Upregulation of Rab31 is associated with poor prognosis and promotes colorectal carcinoma proliferation via the mTOR/p70S6K/Cyclin D1 signalling pathway

AIMS

Rab31, a Rab5 subfamily member, has emerged as a modulator of membrane trafficking. Our study serves to clarify the role and mechanism of Rab31 in colorectal carcinoma (CRC) pathogenesis.

MATERIALS AND METHODS

The differential expression of Rab31 was examined in paired normal and cancerous colonic tissues by quantitative PCR, western blot and immunochemistry. The prognostic significance of Rab31 was analysed by univariate and multivariate survival analyses. We also investigated the effects of Rab31 on tumour growth in vitro.

KEY FINDINGS

We observed that Rab31, which is related to histological differentiation in CRC, was markedly overexpressed in CRC cells. Moreover, patients who showed higher Rab31 levels had a shortened survival period relative to those with low Rab31 levels. Rab31 knockdown significantly downregulated cyclin D1, p-mTOR, and p-p70S6K expression. Moreover, the expression of Rab31-induced p-p70S6K was almost inhibited by rapamycin, a well-established inhibitor of mTOR. Similarly, rapamycin also significantly decreased the stimulatory effect of Rab31 on the expression of cyclin D1.

SIGNIFICANCE

These findings suggested that Rab31 enhanced proliferation, promoted cell cycle progression, and inhibited apoptosis of colorectal carcinoma cells through the mTOR pathway.

Extracellular Vesicles and Metastasis

Secretion of cell contents through extracellular vesicles (EVs), such as exosomes and microvesicles, is a fundamental cell behavior. Compared with their normal counterparts, cancer cells are different in the amount and composition of EVs they secrete as a result of intrinsic and extrinsic (microenvironmental) alterations. Although EVs were originally recognized as a means to remove undesired cell components, recent studies show their critical role in mediating intercellular interaction through cargo transport. In cancer, EVs can be transferred between different cancer cell subpopulations and between cancer and normal cells localized inside and outside of the tumor. By regulating various aspects of cellular functions, EVs contribute to tumor heterogeneity and plasticity, vascular remodeling, cancer-niche coevolution, immunomodulation, and establishment of premetastatic niche, all of which are important to the process of metastasis. Recent discoveries on EV-mediated mechanisms lead to a new understanding of the multifaceted changes in tumor and nontumor tissues before and after cancer metastasis, paving the way for new therapeutic strategies.

Oncogenic effects of RAB27B through exosome independent function in renal cell carcinoma including sunitinib-resistant

Exosomes are 40–100 nm nano-sized extracellular vesicles. They are released from many cell types and move into the extracellular space, thereby transferring their components to recipient cells. Exosomes are receiving increasing attention as novel structures participating in intracellular communication. RAB27B is one of the leading proteins involved in exosome secretion, and oncogenic effects have been reported in several cancers. In recent years, molecularly targeted agents typified by sunitinib are widely used for the treatment of metastatic or recurrent renal cell carcinoma (RCC). However, intrinsic or acquired resistance to sunitinib has become a major issue. The present study aimed to elucidate the role of RAB27B in RCC including sunitinib-resistant and its role in exosomes. Bioinformatic analyses revealed that high expression of RAB27B correlates with progression of RCC. The expression of RAB27B protein in RCC cell lines was significantly enhanced compared with that in normal kidney cell lines. Furthermore, RAB27B protein expression was enhanced in all of the tested sunitinib-resistant RCC cell lines compared to parental cells. Although no specific effect of RAB27B on exosomes was identified in RCC cells, loss-of-function studies demonstrated that knockdown of RAB27B suppressed cell proliferation, migration and invasive activities. Moreover, anti-tumor effects of RAB27B downregulation were also observed in sunitinib-resistant RCC cells. RNA sequence and pathway analysis suggested that the oncogenic effects of RAB27B might be associated with MAPK and VEGF signaling pathways. These results showed that RAB27B is a prognostic marker and a novel therapeutic target in sunitinib-sensitive and -resistant RCCs. Further analyses should improve our understanding of sunitinib resistance in RCC.

Posttraumatic stress disorder and breast cancer: Risk factors and the role of inflammation and endocrine function

A breast cancer diagnosis can be a life-changing and stressful experience that can lead to chronic mental health conditions such as posttraumatic stress disorder (PTSD). Greater than one-third of patients initially diagnosed with PTSD after a diagnosis of breast cancer continue to have persistent or worsening PTSD symptoms after 4 years. An emerging body of literature has indicated several key environmental and biological risk factors for PTSD among survivors of breast cancer. Well-recognized risk factors include having a history of childhood trauma, being nonwhite, obesity, younger age at the time of diagnosis, diagnosis with a higher stage of breast cancer, and short time since treatment. Of the emerging risk factors related to fear circuitry in the brain, 2 pathways of particular importance are the stress-driven activation of inflammatory pathways and the long-term effect of antiendocrine therapies. These central and peripheral responses during and after stress exposure are important because increased fear and anxiety can lead to the maintenance of PTSD and worse patient outcomes. Given the poor outcomes associated with PTSD and the high prevalence of breast cancer in women, more research to identify those women at heightened risk of PTSD after breast cancer is warranted to reduce the number of diagnoses and lessen the negative impact of this chronic mental health condition.

Exosomes, new biomarkers in early cancer detection

Exosomes are endosomal-derived vesicles, playing a major role in cell-to-cell communication. Multiple cells secret these vesicles to induce and inhibit different cellular and molecular pathways. Cancer-derived exosomes have been shown to affect development of cancer in different stages and contribute to the recruitment and reprogramming of both proximal and distal tissues. The growing interest in defining the clinical relevance of these nano-sized particles in cancers, has led to the identification of either tissue- or disease-specific exosomal contents, such as nucleic acids, proteins and lipids as a source of new biomarkers which propose the diagnostic potentials of exosomes in early detection of cancers. In this review, we have discussed some aspects of exosomes including their contents, applications and isolation techniques in the field of early cancer detection. Although, exosomes are considered as ideal biomarkers in cancer diagnosis, due to their unique characteristics, there is still a long way in the development of exosome-based assays.

Insights into the roles of miRNAs; miR-193 as one of small molecular silencer in osteosarcoma therapy

Today, cancer is one of the most common causes of death. Osteosarcoma (OS) is a tumor in long bones and its prevalence is high in teenagers and young people. Among the methods that used to treat cancer, one can name chemotherapy, surgery, and radiotherapy. Since these methods have some disadvantages and they are not absolutely successful, the use of microRNAs (miRNAs) is very useful in diagnosis and treatment of OS. MiRNAs are small non-coding RNA molecules, containing 18-25 nucleotides, which are involved in the regulation of gene expression via binding to messenger RNA (mRNA). These RNAs are divided into two classes of suppressors and oncogenes. During OS, there is aberrant expression of several miRNAs. Among these miRNAs are downregulation of miR-193 that has been associated with cancer occurrence. The aim of the current manuscript is to have overview on the treatment approaches of OS with special focus on miR-193.

Rab27b Is a Potential Indicator for Lymph Node Metastasis and Unfavorable Prognosis in Lung Adenocarcinoma

Rab27b is reported to associate with the development and progression of several types of human cancers. However, the relationship between Rab27b expression and the clinical characteristics of lung adenocarcinoma (LUAD) is rarely explored. In this present study, the TCGA database was consulted, followed by one-step quantitative reverse transcription polymerase chain reaction (qPCR), Western blot, and immunohistochemistry (IHC) analyses in LUAD cell lines and tissue samples. Rab27b expression levels were statistically higher in LUAD cell lines and tissue samples compared with a noncancerous cell line and tissue samples (p < 0.05). Rab27b expression was statistically correlated with lymph node metastasis (p = 0.016) and TNM stage (p = 0.019). Survival analysis and Kaplan-Meier curve revealed that Rab27b expression (p = 0.006) and TNM stage (p = 0.027) were independently associated with the unfavorable overall survival of patients with LUAD. These results indicate that high expression of Rab27b correlates with malignant attributes of LUAD and Rab27b may be identified as a potential indicator of metastasis and prognosis for LUAD.

Functional implications of Rab27 GTPases in Cancer

Background

The Rab27 family of small GTPases promotes the progression of breast cancer, melanoma, and other human cancers. In this review, we discuss the role of Rab27 GTPases in cancer progression and the potential applications of these targets in cancer treatment.

Main body

Elevated expression of Rab27 GTPases is associated with poor prognosis and cancer metastasis. Moreover, these GTPases govern a variety of oncogenic functions, including cell proliferation, cell motility, and chemosensitivity. In addition, small GTPases promote tumor growth and metastasis by enhancing exosome secretion, which alters intracellular microRNA levels, signaling molecule expression, and the tumor microenvironment.

Conclusion

Rab27 GTPases may have applications as prognostic markers and therapeutic targets in cancer treatment.

The role of the oncogenic Rab35 in cancer invasion, metastasis, and immune evasion, especially in leukemia

The study of cancer has allowed researchers to describe some biological characteristics that tumor cells acquire during their development, known as the “hallmarks of cancer” but more research is needed to expand our knowledge about cancer biology and to generate new strategies of treatment. The role that RabGTPases might play in some hallmarks of cancer represents interesting areas of study since these proteins are frequently altered in cancer. However, their participation is not well known. Recently, Rab35was recognized as an oncogenic RabGTPase and and because of its association with different cellular functions, distinctly important in immune cells, a possible role of Rab35 in leukemia can be suggested. Nevertheless, the involvement of Rab35 in cancer remains poorly understood and its possible specific role in leukemia remains unknown. In this review, we analyze general aspects of the participation of RabGTPases in cancer, and especially, the plausible role of Rab35 in leukemia.

Platform-independent gene expression signature differentiates sessile serrated adenomas/polyps and hyperplastic polyps of the colon

Background

Sessile serrated adenomas/polyps are distinguished from hyperplastic colonic polyps subjectively by their endoscopic appearance and histological morphology. However, hyperplastic and sessile serrated polyps can have overlapping morphological features resulting in sessile serrated polyps diagnosed as hyperplastic. While sessile serrated polyps can progress into colon cancer, hyperplastic polyps have virtually no risk for colon cancer. Objective measures, differentiating these types of polyps would improve cancer prevention and treatment outcome.

Methods

RNA-seq training data set and Affimetrix, Illumina testing data sets were obtained from Gene Expression Omnibus (GEO). RNA-seq single-end reads were filtered with FastX toolkit. Read mapping to the human genome, gene abundance estimation, and differential expression analysis were performed with Tophat-Cufflinks pipeline. Background correction, normalization, and probe summarization steps for Affimetrix arrays were performed using the robust multi-array method (RMA). For Illumina arrays, log₂-scale expression data was obtained from GEO. Pathway analysis was implemented using Bioconductor package GSAR. To build a platform-independent molecular classifier that accurately differentiates sessile serrated and hyperplastic polyps we developed a new feature selection step. We also developed a simple procedure to classify new samples as either sessile serrated or hyperplastic with a class probability assigned to the decision, estimated using Cantelli’s inequality.

Results

The classifier trained on RNA-seq data and tested on two independent microarray data sets resulted in zero and three errors. The classifier was further tested using quantitative real-time PCR expression levels of 45 blinded independent formalin-fixed paraffin-embedded specimens and was highly accurate. Pathway analyses have shown that sessile serrated polyps are distinguished from hyperplastic polyps and normal controls by: up-regulation of pathways implicated in proliferation, inflammation, cell-cell adhesion and down-regulation of serine threonine kinase signaling pathway; differential co-expression of pathways regulating cell division, protein trafficking and kinase activities.

Conclusions

Most of the differentially expressed pathways are known as hallmarks of cancer and likely to explain why sessile serrated polyps are more prone to neoplastic transformation than hyperplastic. The new molecular classifier includes 13 genes and may facilitate objective differentiation between two polyps.

Electronic supplementary material

The online version of this article (10.1186/s12920-017-0317-7) contains supplementary material, which is available to authorized users.

Cancer-derived extracellular vesicles: the 'soil conditioner' in breast cancer metastasis?

It has been recognized that cancer-associated mortality is more often a result of the disrupted physiological functions in multiple organs following metastatic dissemination of cancer cells, rather than the presence and growth of the primary tumor. Despite advances in our understanding of the events leading to cancer initiation, growth, and acquisition of invasive properties, we are still unable to effectively treat metastatic disease. It is now being accepted that the secretion of extracellular vesicles, such as exosomes from cancer cells, has a profound impact on the initiation and propagation of metastatic breast cancer. These cancer-secreted vesicles differ from other means of cellular communication due to their capability of bulk delivery and organotropism. Here, we provide an overview of the role of extracellular vesicles in breast cancer metastasis and discuss key areas that may facilitate our understanding of metastatic breast cancer to guide our efforts towards providing better therapies.

Effects of Rab27A and Rab27B on Invasion, Proliferation, Apoptosis, and Chemoresistance in Human Pancreatic Cancer Cells

OBJECTIVES

Rab family members are key regulatory factors that function as molecular switches in multiple phases of vesicular trafficking. Our previous study demonstrated that Rab27A and Rab27B overexpression may predict a poor outcome of pancreatic ductal adenocarcinoma. The purpose of this study was to investigate the role of Rab27A and Rab27B in the progression of pancreatic cancer.

METHODS

We down-regulated Rab27A and Rab27B expression in pancreatic cancer cell lines. The regulatory effects of knockdown Rab27A and Rab27B on pancreatic cancer cell were measured by cisplatin assay, invasion assay, proliferation assay, and Western blot assay.

RESULTS

Rab27A and Rab27B down-regulation enhances sensitivity to cisplatin and induces apoptosis in ASPC-1 and PANC-1 cells. In addition, down-regulation of Rab27A reduced the invasive and proliferative ability of ASPC-1 cells, and Rab27B knockdown significantly prevented cancer invasion and proliferation in PANC-1 cells.

CONCLUSIONS

Our findings provide evidence that Rab27A and Rab27B play significant roles in cell invasion, proliferation, and apoptosis, as well as in chemotherapy resistance.

MiR-20a-5p promotes radio-resistance by targeting Rab27B in nasopharyngeal cancer cells

BACKGROUND

MicroRNAs (miRNAs) was reported to be involved in cancer radio-resistance, which remains a major obstacle for effective cancer therapy.

METHODS

The differently expressed miRNAs were detected by RNA-seq experiment in nasopharyngeal cancer (NPC) cells. MiR-20a-5p was selected as our target, which was subject to finding its target gene Rab27B via bioinformatics analysis. The qRT-PCR, western blot and the luciferase reporter assays were performed to confirm Rab27B as the target of miR-20a-5p. In addition, the roles of miR-20a-5p in NPC radio-resistance were detected by transfection of either miR-20a-5p-mimic or miR-20a-5p-antagomiR. The involvement of Rab27B with NPC radio-resistance was also detected by the experiments with siRNA-mediated repression of Rab27B or over-expression of GFP-Rab27B. Wound healing and invasion assays were performed to detect the roles of both miR-20a-5p and Rab27B.

RESULTS

MiR-20a-5p promotes NPC radio-resistance. We identified that its target gene Rab27B negatively correlates with miR-20a-5p-mediated NPC radio-resistance by systematic studies of a radio-sensitive (CNE-2) and resistant (CNE-1) NPC cell lines. Repression of Rab27B by siRNA suppresses cell apoptosis and passivates CNE-2 cells, whereas over-expression of Rab27B triggered cell apoptosis and sensitizes CNE-1 cells.

CONCLUSIONS

MiR-20a-5p and its target gene Rab27B might be involved in the NPC radio-resistance. Thus the key players and regulators involved in this pathway might be the potential targets for developing effective therapeutic strategies against NPC.

RAB27A, RAB27B and VPS36 are downregulated in advanced prostate cancer and show functional relevance in prostate cancer cells

Paracrine and long-range signaling via extracellular vesicles, such as exosomes and microvesicles, is deemed crucial for tumorigenesis, invasion and spread of solid tumors. The ESCRT machinery (endosomal sorting complexes required for transport) and Rab-proteins act as key players in vesicular trafficking and secretion. Yet, their role in prostate cancer (PCa) is unknown. Therefore, this study aimed to elucidate the relevance of these components in PCa. In silico reanalysis of genes with known involvement in vesicular trafficking and secretion in an existing microarray dataset revealed low expression of RAB27A, RAB27B and VPS36 to be predictive for reduced BCR-free survival in patients with localized PCa (p=0.033, 0.025 and 0.005). In the same microarray dataset underexpression of RAB27A, RAB27B and VPS36 was seen in distant metastases (p<0.001; p=0.003; p<0.001). This was consistent in two further microarray datasets. qRT-PCR-validation in two independent cohorts of PCa specimens (n=90) showed low expression of VPS36 in PCa tissue (p=0.023), especially in castration-resistant tumors (p=0.002). In all five datasets there were significant correlations between the expression of at least two of the candidates. Upon knockdown of VPS36 an increase of RAB27A and RAB27B expression, but not vice versa, was observed in both prostate and breast cancer cells (PC3, MDA-MB‑231). In PC3 cell knockdown of RAB27B and VPS36 dramatically reduced colony formation (-52.2%, p<0.001; -71.1%, p<0.001) and, controversial to reports in other tumor entities, increased the release of extracellular particles (+25.3%, p=0.014; +45.6%, p<0.001). Taken together RAB27A, RAB27B and VPS36 are frequently underexpressed in advanced PCa and are inversely correlated with PCa outcome. There seems to be a close relationship in the expression of RAB27A, RAB27B and VPS36, with RAB27A and RAB27B being dependent on VPS36. Changes in colony formation and particle release upon RNAi indicate an involvement in paracrine cell-cell communication.

Overexpression of Rab27B is correlated with distant metastasis and poor prognosis in ovarian cancer

The secretory small guanosine-5'-triphosphate-binding enzyme, Rab27B, has been identified to be an oncogene that is involved in the progression of certain tumors. The current study was designed to evaluate the expression pattern of Rab27B in ovarian cancer (OC), borderline tumors and benign ovarian adenoid tumors, as well as its association with survival prognosis and clinical parameters. The expression of Rab27B protein was examined by immunohistochemistry in 204 patients who had undergone ovarian resection without preoperative systemic chemotherapy at the Surgical Department of the Affiliated Hospital of Nantong University (Nantong, China), including 57 benign ovarian adenoid tumors, 44 borderline tumors and 103 malignant tumors. Rab27B expression and clinicopathological features were analyzed with the χ² test. Patient survival rate was analyzed with the Kaplan-Meier method. Univariate and multivariate analysis of the prognostic factors was performed using the Cox regression model. Increased expression of Rab27B was positively correlated with histological type (P=0.012), level of differentiation (P=0.015), lymph node metastasis (P=0.024), distant metastasis (P<0.001) and International Federation of Gynecology and Obstetrics stage (P=0.001). Survival analysis revealed an association between Rab27B-positivity and poor overall survival rate. Multivariate analysis indicated that Rab27B (P<0.031) and distant metastases (P=0.031) were independent prognostic factors for OC patients' survival. The results of the present study supported the hypothesis that Rab27B may be a valuable prognostic indicator in patients with OC.

High expression of small GTPase Rab3D promotes cancer progression and metastasis

Rab GTPases control exocytic and endocytic membrane trafficking such as exosomes release. As a secretory small GTPase, Rab3D is a vital regulator for protein secretion. However, the role of Rab3D in cancer was never systematically studied. The aim of this study is to examine its function and mechanism in cancer, especially metastasis. We detected protein levels of Rab3D in nine cancer cell lines and twelve types of clinical cancer specimens. Subsequently, we established in vitro migration and in vivo orthotopic metastatic mouse models to study the role of Rab3D in tumor metastasis. Here, we reported that the expression levels of Rab3D were dysregulated in cancer cells and highly correlated with tumor malignancies in the clinical samples. Increased expressions of Rab3D led to tumor invasion in vitro and lung metastasis in vivo, whereas Rab3D knockdown suppressed the tumor cell motility. Mechanistic studies revealed that Rab3D activated intracellular the AKT/GSK3β signaling to induce the EMT process. In addition, it also regulated the extracellular secretion of Hsp90α to promote tumor cell migration and invasion. These results prove that Rab3D is a key molecule to regulate tumor metastasis, suggesting that blocking the Rab3D function can be a potential therapeutic approach for cancer metastasis.

MiR-193a-3p and miR-193a-5p suppress the metastasis of human osteosarcoma cells by down-regulating Rab27B and SRR, respectively

MicroRNAs have been identified as key players in the development and progression of osteosarcoma, which is the most common primary malignancy of bone. Sequencing-based miR-omic and quantitative real-time PCR analyses suggested that the expression of miR-193a-3p and miR-193a-5p was decreased by DNA methylation at their promoter region in a highly metastatic osteosarcoma cell line (MG63.2) relative to their expression in the less metastatic MG63 cell line. Further wound-healing and invasion assays demonstrated that both miR-193a-3p and miR-193a-5p suppressed osteosarcoma cell migration and invasion. Moreover, introducing miR-193a-3p and miR-193a-5p mimics into MG63.2 cells or antagomiRs into MG63 cells confirmed their critical roles in osteosarcoma metastasis. Additionally, bioinformatics prediction along with biochemical assay results clearly suggested that the secretory small GTPase Rab27B and serine racemase (SRR) were direct targets of miR-193a-3p and miR-193a-5p, respectively. These two targets are indeed involved in the miR-193a-3p- and miR-193a-5p-induced suppression of osteosarcoma cell migration and invasion. MiR-193a-3p and miR-193a-5p play important roles in osteosarcoma metastasis through down-regulation of the Rab27B and SRR genes and therefore may serve as useful biomarkers for the diagnosis of osteosarcoma and as potential candidates for the treatment of metastatic osteosarcoma.

Correlation Between RAB27B and p53 Expression and Overall Survival in Pancreatic Cancer

OBJECTIVES

RAB27B is a member of the Rab family GTPases involved in vesicle trafficking, and p53 has recently been implicated in regulating the exosome secretion pathway. Because exosome secretion plays an important role in modulating tumor microenvironment and invasive growth, we hypothesized that RAB27B and p53 expression might be associated with the aggressive behavior in pancreatic ductal adenocarcinoma, one of the most deadly human malignancies.

METHODS

We determined protein expression of RAB27B and p53 in 260 pancreatic tissues (186 malignant and 74 normal or benign) by immunohistochemistry analysis on tissue microarray and their correlation with patients' clinical parameters and overall survival.

RESULTS

We found that a high RAB27B protein expression (RAB27B) was significantly associated with perineural and vascular invasion, as well as distant metastasis. Patients with a high RAB27B expression had significantly poorer overall survival in both univariate and multivariate analyses. A significant correlation between RAB27B and p53 expression was observed.

CONCLUSIONS

Our data indicate that RAB27B expression is an independent prognostic marker for pancreatic ductal adenocarcinoma and suggest that RAB27B-regulated exosome secretion pathway represents a novel therapeutic target in pancreatic cancer.

Rab27b is a potential predictor for metastasis and prognosis in colorectal cancer

Objective. Rab27b is reported to correlate with cancer development and progression. However, the association between Rab27b expression and the clinical characteristics of colorectal cancer (CRC) is barely investigated. Methods. One-step quantitative reverse transcription-polymerase chain reaction (qPCR) test with 18 fresh-frozen CRC samples and immunohistochemistry (IHC) analysis in 113 CRC cases were performed to explore the relationship between Rab27b expression and the clinicopathological features of CRC. Cox regression and Kaplan-Meier survival analyses were executed to evaluate the prognosis of CRC. Results. The results demonstrated that the expression levels of Rab27b mRNA and protein were significantly higher in CRC tissues than that in matched noncancerous tissues (P < 0.05). Rab27b protein expression in CRC was statistically correlated with serum CEA level (P = 0.004), lymph node metastasis (P = 0.001), distant metastasis (P = 0.009), and TNM stage (P = 0.001). Cox multifactor analysis and Kaplan-Meier method suggested that higher Rab27b protein expression (P = 0.041) and tumor differentiation (P = 0.001) were significantly associated with the overall survival of CRC patients. Conclusions. The data indicated that higher expression of Rab27b was observed in CRC tissues and Rab27b may be identified as a useful predictor of metastasis and prognosis for CRC.

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.

Prognostic value of Rab27B nuclear expression in gastrointestinal stromal tumors

Rab proteins of the endocytosis and exocytosis pathways both play critical roles in cancer progression, and Rab27B has a significant relationship with several types of human cancer. However, the association between Rab27B expression and clinical features to determine its clinicopathological significance in gastrointestinal tumor (GIST) has not been investigated. To examine the expression of Rab27B in GIST and investigate the association between its expression and patient prognosis, immunohistochemistry analysis with tissue microarray was used to evaluate expression of Rab27B in 162 patients with GIST. The relationship between Rab27B expression and patient prognosis was analyzed. High nuclear staining of Rab27B was detected in 88 of 162 (54.32%) GIST tissues. Positive staining of Rab27B was significantly associated with tumor size (P = 0.006), mitotic index (P = 0.013), Armed Forces Institute of Pathology Miettinen risk classification (P = 0.002), and tumor grade (P = 0.021). Kaplan-Meier survival curves showed that GIST patients with low Rab27B nuclear expression (P = 0.038) and mitotic index <5 per 50 high-power fields (P = 0.029) had a more favorable prognosis. These findings indicate that Rab27B nuclear expression is correlated with several clinicopathological features of GIST patients, and it may serve as an unfavorable prognostic marker.

MicroRNAs transported by exosomes in body fluids as mediators of intercellular communication in cancer

Cancer-cell communication is an important and complex process, achieved through a diversity of mechanisms that allows tumor cells to mold and influence their environment. In recent years, evidence has accumulated indicating that cells communicate via the release and delivery of microRNAs (miRNAs) packed into tumor-released (TR) exosomes. Understanding the role and mode of action of miRNAs from TR exosomes is of paramount importance in the field of cancer biomarker discovery and for the development of new biomedical applications for cancer therapeutics. In this review, we focus on miRNAs secreted via TR exosomes, which by acting in a paracrine or endocrine manner, facilitate a diversity of signaling mechanisms between cancer cells. We address their contribution as signaling molecules, to the establishment, maintenance, and enhancement of the tumor microenvironment and the metastatic niche in cancer. Finally, we address the potential role of these molecules as biomarkers in cancer diagnosis and prognosis and their impact as a biomedical tool in cancer therapeutics.

Rab27 effectors, pleiotropic regulators in secretory pathways

Rab27, a member of the small GTPase Rab family, is widely conserved in metazoan, and two Rab27 isoforms, Rab27A and Rab27B, are present in vertebrates. Rab27A was the first Rab protein whose dysfunction was found to cause a human hereditary disease, type 2 Griscelli syndrome, which is characterized by silvery hair and immunodeficiency. The discovery in the 21st century of three distinct types of mammalian Rab27A effectors [synaptotagmin-like protein (Slp), Slp homologue lacking C2 domains (Slac2), and Munc13-4] that specifically bind active Rab27A has greatly accelerated our understanding not only of the molecular mechanisms of Rab27A-mediated membrane traffic (e.g. melanosome transport and regulated secretion) but of the symptoms of Griscelli syndrome patients at the molecular level. Because Rab27B is widely expressed in various tissues together with Rab27A and has been found to have the ability to bind all of the Rab27A effectors that have been tested, Rab27A and Rab27B were initially thought to function redundantly by sharing common Rab27 effectors. However, recent evidence has indicated that by interacting with different Rab27 effectors Rab27A and Rab27B play different roles in special types of secretion (e.g. exosome secretion and mast cell secretion) even within the same cell type. In this review article, I describe the current state of our understanding of the functions of Rab27 effectors in secretory pathways.

Rab27 GTPases distribute extracellular nanomaps for invasive growth and metastasis: implications for prognosis and treatment

The Rab27 family of small GTPases regulates exocytosis of distinct vesicle types including multivesicular endosomes, which results in the release of exosomes. Exosomes are nanometer-sized membrane vesicles that enclose soluble factors such as proteins and nucleic acids within a lipid bilayer and can travel toward distant tissues to influence multiple aspects of cell behavior. In our view that tumors are endocrine organs producing exosomes, Rab27 GTPases and their effector proteins are critical determinants for invasive growth and metastasis. Rab27 proteins and their effectors may serve as prognostic biomarkers or as targets for patient-tailored therapy.