Flotillin2 expression correlates with HER2 levels and poor prognosis in gastric cancer

The scaffolding protein flot2 promotes cytoneme-based transport of wnt3 in gastric cancer

The Wnt/β-catenin signalling pathway regulates multiple cellular processes during development and many diseases, including cell proliferation, migration, and differentiation. Despite their hydrophobic nature, Wnt proteins exert their function over long distances to induce paracrine signalling. Recent studies have identified several factors involved in Wnt secretion; however, our understanding of how Wnt ligands are transported between cells to interact with their cognate receptors is still debated. Here, we demonstrate that gastric cancer cells utilise cytonemes to transport Wnt3 intercellularly to promote proliferation and cell survival. Furthermore, we identify the membrane-bound scaffolding protein Flotillin-2 (Flot2), frequently overexpressed in gastric cancer, as a modulator of these cytonemes. Together with the Wnt co-receptor and cytoneme initiator Ror2, Flot2 determines the number and length of Wnt3 cytonemes in gastric cancer. Finally, we show that Flotillins are also necessary for Wnt8a cytonemes during zebrafish embryogenesis, suggesting a conserved mechanism for Flotillin-mediated Wnt transport on cytonemes in development and disease.

Preclinical evaluation of MRG002, a novel HER2-targeting antibody-drug conjugate with potent antitumor activity against HER2-positive solid tumors

Background

ERBB2 is a proto-oncogene of multiple cancers including breast and gastric cancers with HER2 protein overexpression or gene amplification and has been proven clinically as a valid target for these cancers. HER2-targeting agents such as Herceptin®, Kadcyla® and ENHERTU® have been approved by the FDA for the treatment of breast cancer, but these drugs still face the challenge of acquired resistance and/or severe adverse reactions in clinical use. Therefore, there is significant unmet medical need for developing new agents that are more effective and safer for patients with advanced HER2-positive solid tumors including breast and gastric cancers.

Methods

We report here the making of MRG002, a novel HER2-targeted antibody drug conjugate (ADC), and preclinical characterization including pharmacology, pharmacodynamics and toxicology and discuss its potential as a novel agent for treating patients with HER2-positive solid tumors.

Results

MRG002 exhibited similar antigen binding affinity but much reduced antibody-dependent cellular cytotoxicity (ADCC) activity compared to trastuzumab. In addition to potent in vitro cytotoxicity, MRG002 showed tumor regression in both high- and medium-to-low HER2 expressing in vivo xenograft models. Furthermore, MRG002 showed enhanced antitumor activity when used in combination with an anti-PD-1 antibody. Main findings from toxicology studies are related to the payload and are consistent with literature report of other ADCs with monomethyl auristatinE.

Conclusion

MRG002 has demonstrated a favorable toxicity profile and potent antitumor activities in the breast and gastric PDX models with varying levels of HER2 expression, and/or resistance to trastuzumab or T-DM1. A phase I clinical study of MRG002 in patients with HER2-positive solid tumors is ongoing (CTR20181778).

Flotillin membrane domains in cancer

Flotillins 1 and 2 are two ubiquitous, highly conserved homologous proteins that assemble to form heterotetramers at the cytoplasmic face of the plasma membrane in cholesterol- and sphingolipid-enriched domains. Flotillin heterotetramers can assemble into large oligomers to form molecular scaffolds that regulate the clustering of at the plasma membrane and activity of several receptors. Moreover, flotillins are upregulated in many invasive carcinomas and also in sarcoma, and this is associated with poor prognosis and metastasis formation. When upregulated, flotillins promote plasma membrane invagination and induce an endocytic pathway that allows the targeting of cargo proteins in the late endosomal compartment in which flotillins accumulate. These late endosomes are not degradative, and participate in the recycling and secretion of protein cargos. The cargos of this Upregulated Flotillin–Induced Trafficking (UFIT) pathway include molecules involved in signaling, adhesion, and extracellular matrix remodeling, thus favoring the acquisition of an invasive cellular behavior leading to metastasis formation. Thus, flotillin presence from the plasma membrane to the late endosomal compartment influences the activity, and even modifies the trafficking and fate of key protein cargos, favoring the development of diseases, for instance tumors. This review summarizes the current knowledge on flotillins and their role in cancer development focusing on their function in cellular membrane remodeling and vesicular trafficking regulation.

Membrane Compartmentalization and Scaffold Proteins in Leukocyte Migration

Leukocyte migration across vessels into and within peripheral and lymphoid tissues is essential for host defense against invading pathogens. Leukocytes are specialized in sensing a variety of guidance cues and to integrate environmental stimuli to navigate in a timely and spatially controlled manner. These extracellular signals must be transmitted across the leukocyte’s plasma membrane in a way that intracellular signaling cascades enable directional cell movement. Therefore, the composition of the membrane in concert with proteins that influence the compartmentalization of the plasma membrane or contribute to delineate intracellular signaling molecules are key in controlling leukocyte navigation. This becomes evident by the fact that mislocalization of membrane proteins is known to deleteriously affect cellular functions that may cause diseases. In this review we summarize recent advances made in the understanding of how membrane cholesterol levels modulate chemokine receptor signaling and hence leukocyte trafficking. Moreover, we provide an overview on the role of membrane scaffold proteins, particularly tetraspanins, flotillins/reggies, and caveolins in controlling leukocyte migration both in vitro and in vivo.

Flotillin-2 predicts poor prognosis and promotes tumor invasion in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma (iCCA) is a highly malignant neoplasm arising from the intrahepatic bile ducts. As a scaffold protein of lipid rafts, flotillin-2 is upregulated in several types of cancer and promotes tumor progression and metastasis. To the best of our knowledge, the present study was the first to detect the upregulation of flotillin-2 in iCCA tissues compared with matched adjacent non-tumor tissues. In addition, immunohistochemistry was used to investigate the expression of flotillin-2 in a microarray consisting of 92 iCCA tissues. A total of 59 samples (64.1%) exhibited high flotillin-2 expression, which was significantly related to lymph node metastasis (P=0.029) and tumor-node-metastasis stage (P=0.016). Further in vitro study demonstrated that knockdown of flotillin-2 inhibited the invasive capability of iCCA cell lines, further supporting the participation of flotillin-2 in cancer invasion and metastasis. Moreover, Kaplan-Meier analysis showed patients with high flotillin-2 expression had worse overall survival outcomes. The multivariate Cox proportional hazards model further revealed that high flotillin-2 expression was an independent indicator (P=0.005) of poor prognosis for patients with iCCA. Collectively, the present study revealed that as a promoter of invasion and an independent marker of poor prognosis, flotillin-2 may serve as a potential target for the development of novel therapeutic agents for iCCA.

MicroRNA-351 eases insulin resistance and liver gluconeogenesis via the PI3K/AKT pathway by inhibiting FLOT2 in mice of gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is known as different degree glucose intolerance that is initially identified during pregnancy. MicroRNAs (miRs) may be a potential candidate for treatment of GDM. Herein, we suggested that miR‐351 could be an inhibitor in the progression of GDM via the phosphoinositide 3‐kinase/protein kinase B (PI3K/AKT) pathway. Microarray analysis was used to identify differentially expressed genes and predict miRs regulating flotillin 2 (FLOT2). Target relationship between miR‐351 and FLOT2 was verified. Gestational diabetes mellitus mice were treated with a series of mimic, inhibitor and small interfering RNA to explore the effect of miR‐351 on insulin resistance (IR), cell apoptosis in pancreatic tissues and liver gluconeogenesis through evaluating GDM‐related biochemical indexes, as well as expression of miR‐351, FLOT2, PI3K/AKT pathway‐, IR‐ and liver gluconeogenesis‐related genes. MiR‐351 and FLOT2 were reported to be involved in GDM. FLOT2 was the target gene of miR‐351. Gestational diabetes mellitus mice exhibited IR and liver gluconeogenesis, up‐regulated FLOT2, activated PI3K/AKT pathway and down‐regulated miR‐351 in liver tissues. Additionally, miR‐351 overexpression and FLOT2 silencing decreased the levels of FLOT2, phosphoenolpyruvate carboxykinase, glucose‐6‐phosphatase, fasting blood glucose, fasting insulin, total cholesterol, triglyceride, glyeosylated haemoglobin and homeostasis model of assessment for IR index (HOMA‐IR), extent of PI3K and AKT phosphorylation, yet increased the levels of HOMA for islet β‐cell function, HOMA for insulin sensitivity index and glucose transporter 2 expression, indicating reduced cell apoptosis in pancreatic tissues and alleviated IR and liver gluconeogenesis. Our results reveal that up‐regulation of miR‐351 protects against IR and liver gluconeogenesis by repressing the PI3K/AKT pathway through regulating FLOT2 in GDM mice, which identifies miR‐351 as a potential therapeutic target for the clinical management of GDM.

Roles of flotillins in tumors

The identification and use of molecular biomarkers have greatly improved the diagnosis and treatment of malignant tumors. However, a much deeper understanding of oncogenic proteins is needed for the benefit to cancer patients. The lipid raft marker proteins, flotillin-1 and flotillin-2, were first found in goldfish retinal ganglion cells during axon regeneration. They have since been found in a variety of cells, mainly on the inner surface of cell membranes, and not only act as a skeleton to provide a platform for protein-protein interactions, but also are involved in signal transduction, nerve regeneration, endocytosis, and lymphocyte activation. Previous studies have shown that flotillins are closely associated with tumor development, invasion, and metastasis. In this article, we review the functions of flotillins in relevant cell processes, their underlying mechanisms of action in a variety of tumors, and their potential applications to tumor molecular diagnosis and targeted therapy.

MT1-MMP targeting to endolysosomes is mediated by upregulation of flotillins

Tumor cell invasion and metastasis formation are the major cause of death in cancer patients. These processes rely on extracellular matrix (ECM) degradation mediated by organelles termed invadopodia, to which the transmembrane matrix metalloproteinase MT1-MMP (also known as MMP14) is delivered from its reservoir, the RAB7-containing endolysosomes. How MT1-MMP is targeted to endolysosomes remains to be elucidated. Flotillin-1 and -2 are upregulated in many invasive cancers. Here, we show that flotillin upregulation triggers a general mechanism, common to carcinoma and sarcoma, which promotes RAB5-dependent MT1-MMP endocytosis and its delivery to RAB7-positive endolysosomal reservoirs. Conversely, flotillin knockdown in invasive cancer cells greatly reduces MT1-MMP accumulation in endolysosomes, its subsequent exocytosis at invadopodia, ECM degradation and cell invasion. Our results demonstrate that flotillin upregulation is necessary and sufficient to promote epithelial and mesenchymal cancer cell invasion and ECM degradation by controlling MT1-MMP endocytosis and delivery to the endolysosomal recycling compartment.

Prognostic value of flotillins (flotillin-1 and flotillin-2) in human cancers: A meta-analysis

Increasing evidence indicates that flotillins which associate with cell infiltration and metastasis are overexpressed in multiple tumors. The prognostic role of flotillins remains controversial. We conducted a comprehensive meta-analysis of published research to investigate the prognostic value of flotillins in patients with cancer. Pooled HRs (hazard ratio) with 95% CIs (confidence interval) were collected to estimate the prognostic value. Twenty-seven studies with 4803 cancer patients were finally identified. The results indicated that: (1) elevated flotillins predicted poorer OS (overall survival) (HR = 2.17, 95% CI 1.87 to 2.52; HR = 1.61, 95% CI 1.44 to 1.81) and DFS (disease-free survival) (HR = 2.41, 95% CI 1.83 to 3.18; HR = 3.01, 95% CI 2.12 to 4.27) in patients with cancer; (2) Subgroup analysis showed that the prognostic value of flotillin-1 on OS and DFS in the investigated tumors were not altered by tumor type (such as digestive system cancers, renal cell cancer, lung cancer, or others), country (China or Canada), cutoff value, detection method, analysis type or paper quality and flotillin-2 overexpression indicates poor OS in human cancers except for nasopharyngeal carcinoma. Flotillins are promising as new biomarkers to predict poor prognosis of patients with tumors. This conclusion needs more clinical studies with different types of cancer to be proven.

Flot2 promotes tumor growth and metastasis through modulating cell cycle and inducing epithelial-mesenchymal transition of hepatocellular carcinoma

Flotillin-2 (Flot2) is a highly conserved and ubiquitously expressed protein that resides on the cytoplasmic side of the cell membrane within specific cholesterol rich microdomains. Some studies have reported that overexpression of Flot2 is related to cancer progression. However, the role of Flot2 in hepatocellular carcinoma (HCC) remains unclarified. In this study, we aim to explore the correlation between Flot2 expression and HCC progression and the underlying mechanism. In the present study, overexpression of Flot2 in HCC tissues and cell lines was detected, and forced overexpression of Flot2 significantly promoted the proliferation, migration, invasion and metastasis of HCC in vitro and in vivo by modulating cell cycle and inducing EMT, which was mediated via up-regulation of Twist as a result of Raf/MEK/ERK1/2 pathway activation. In contrast, silencing Flot2 expression inhibited these biological processes. Furthermore, high expression of Flot2 was significantly correlated with poor prognosis of HCC patients after curative resection and is an independent risk factor. In conclusion, Flot2 promoted tumor growth and metastasis of HCC through modulating cell cycle and inducing EMT. The expression of Flot2 may play a key role in HCC progression and may be regarded as a potential poor prognostic marker for HCC.

HER2 Testing and Clinical Decision Making in Gastroesophageal Adenocarcinoma: Guideline From the College of American Pathologists, American Society for Clinical Pathology, and the American Society of Clinical Oncology

Context ERBB2 (erb-b2 receptor tyrosine kinase 2 or HER2) is currently the only biomarker established for selection of a specific therapy for patients with advanced gastroesophageal adenocarcinoma (GEA). However, there are no comprehensive guidelines for the assessment of HER2 in patients with GEA. Objectives To establish an evidence-based guideline for HER2 testing in patients with GEA, formalize the algorithms for methods to improve the accuracy of HER2 testing while addressing which patients and tumor specimens are appropriate, and to provide guidance on clinical decision making. Design The College of American Pathologists (CAP), American Society for Clinical Pathology (ASCP), and the American Society of Clinical Oncology (ASCO) convened an Expert Panel to conduct a systematic review of the literature to develop an evidence-based guideline with recommendations for optimal HER2 testing in patients with GEA. Results The Panel is proposing 11 recommendations with strong agreement from the open comment participants. Recommendations The Panel recommends that tumor specimen(s) from all patients with advanced GEA, who are candidates for HER2-targeted therapy, should be assessed for HER2 status before the initiation of HER2-targeted therapy. Clinicians should offer combination chemotherapy and an HER2-targeted agent as initial therapy for all patients with HER2-positive advanced GEA. For pathologists, guidance is provided for morphologic selection of neoplastic tissue, testing algorithms, scoring methods, interpretation and reporting of results, and laboratory quality assurance. Conclusion This guideline provides specific recommendations for assessment of HER2 in patients with advanced GEA while addressing pertinent technical issues and clinical implications of the results.

HER2 Testing and Clinical Decision Making in Gastroesophageal Adenocarcinoma: Guideline From the College of American Pathologists, American Society for Clinical Pathology, and American Society of Clinical Oncology

CONTEXT

- ERBB2 (erb-b2 receptor tyrosine kinase 2 or HER2) is currently the only biomarker established for selection of a specific therapy for patients with advanced gastroesophageal adenocarcinoma (GEA). However, there are no comprehensive guidelines for the assessment of HER2 in patients with GEA.

OBJECTIVES

- To establish an evidence-based guideline for HER2 testing in patients with GEA, to formalize the algorithms for methods to improve the accuracy of HER2 testing while addressing which patients and tumor specimens are appropriate, and to provide guidance on clinical decision making.

DESIGN

- The College of American Pathologists, American Society for Clinical Pathology, and American Society of Clinical Oncology convened an expert panel to conduct a systematic review of the literature to develop an evidence-based guideline with recommendations for optimal HER2 testing in patients with GEA.

RESULTS

- The panel is proposing 11 recommendations with strong agreement from the open-comment participants.

RECOMMENDATIONS

- The panel recommends that tumor specimen(s) from all patients with advanced GEA, who are candidates for HER2-targeted therapy, should be assessed for HER2 status before the initiation of HER2-targeted therapy. Clinicians should offer combination chemotherapy and a HER2-targeted agent as initial therapy for all patients with HER2-positive advanced GEA. For pathologists, guidance is provided for morphologic selection of neoplastic tissue, testing algorithms, scoring methods, interpretation and reporting of results, and laboratory quality assurance.

CONCLUSIONS

- This guideline provides specific recommendations for assessment of HER2 in patients with advanced GEA while addressing pertinent technical issues and clinical implications of the results.

HER2 Testing and Clinical Decision Making in Gastroesophageal Adenocarcinoma: Guideline From the College of American Pathologists, American Society for Clinical Pathology, and American Society of Clinical Oncology

CONTEXT

ERBB2 (erb-b2 receptor tyrosine kinase 2 or HER2) is currently the only biomarker established for selection of a specific therapy for patients with advanced gastroesophageal adenocarcinoma (GEA). However, there are no comprehensive guidelines for the assessment of HER2 in patients with GEA.

OBJECTIVES

To establish an evidence-based guideline for HER2 testing in patients with GEA, to formalize the algorithms for methods to improve the accuracy of HER2 testing while addressing which patients and tumor specimens are appropriate, and to provide guidance on clinical decision making.

DESIGN

The College of American Pathologists, American Society for Clinical Pathology, and American Society of Clinical Oncology convened an expert panel to conduct a systematic review of the literature to develop an evidence-based guideline with recommendations for optimal HER2 testing in patients with GEA.

RESULTS

The panel is proposing 11 recommendations with strong agreement from the open-comment participants.

RECOMMENDATIONS

The panel recommends that tumor specimen(s) from all patients with advanced GEA, who are candidates for HER2-targeted therapy, should be assessed for HER2 status before the initiation of HER2-targeted therapy. Clinicians should offer combination chemotherapy and a HER2-targeted agent as initial therapy for all patients with HER2-positive advanced GEA. For pathologists, guidance is provided for morphologic selection of neoplastic tissue, testing algorithms, scoring methods, interpretation and reporting of results, and laboratory quality assurance.

CONCLUSIONS

This guideline provides specific recommendations for assessment of HER2 in patients with advanced GEA while addressing pertinent technical issues and clinical implications of the results.

Flotillin-2 promotes nasopharyngeal carcinoma metastasis and is necessary for the epithelial-mesenchymal transition induced by transforming growth factor-β

Transforming growth factor-β (TGF-β) promotes cancer metastasis via the epithelial-mesenchymal transition (EMT) but the underlying mechanisms in nasopharyngeal carcinoma (NPC) remain unclear. Flotillin-2 (Flot2), a specialized lipid raft domain in cellular membrane, was reported to promote cancer metastasis. Recently, in neuropathy, it was also suggested that Flot2 was involved in Src activation, which is known as the downstream signal of TGF-β. Therefore, we intended to find out the relationship between Flot2 and TGF-β in the process of nasopharyngeal carcinoma (NPC) metastasis. In this study, we found that Flot2 expression level positively correlated with the cancer stage in NPC tissues. Elevated Flot2 in tumor tissue was an independent prognostic marker, and higher Flot2 expression level showed shorter overall survival time in 181 NPC patients. In NPC cells, silencing Flot2 reversed the metastatic effect induced by TGF-β. Moreover, TGF-β-induced Src phosphorylation was significantly inhibited by Flot2 knocking down. As the consequence of Flot2 inhibition, the expression of the epithelial biomarker E-cadherin was upregulated, while the mesenchymal marker vimentin and signaling transducer β-catenin was suppressed. In conclusions, Flot2 is an indispensable member for TGF-β signaling, which is essential for the EMT process in NPC metastasis. Suppressing Flot2 may be a novel way against TGF-β-induced EMT.

An anti-HER2 antibody conjugated with monomethyl auristatin E is highly effective in HER2-positive human gastric cancer

Antibody-drug conjugate (ADC) is a novel class of therapeutics for cancer target therapy. This study assessed antitumor activity of ADC with an antimitotic agent, monomethyl auristatin E (MMAE) and a humanized monoclonal anti-HER2 antibody, hertuzumab, in gastric cancer. The efficacy of hertuzumab-MC-Val-Cit-PAB-MMAE (hertuzumab-vcMMAE) on human epidermal growth factor receptor 2 (HER2) positive human gastric cancer cells, NCI-N87, was evaluated in vitro and in vivo. The cytotoxicity of hertuzumab was significantly enhanced after conjugation with MMAE. Compared to trastuzumab, hertuzumab had a higher affinity to HER2 and had more potent antibody-dependent cell-mediated cytotoxicity (ADCC) activity in vitro. After conjugation with MMAE, the binding specificity for HER2 was not affected. Furthermore, the internalization of hertuzumab-vcMMAE in HER2 positive gastric cancer cells was verified. Although the conjugation of hertuzumab and MMAE decreased the ADCC effect, the overall cytotoxicity was dramatically increased in HER2 positive gastric cancer cells. In vitro data on this hertuzumab-vcMMAE has exerted much stronger antitumor activity compared to trastuzumab-DM1 in HER2 positive gastric cancer cells. A single administration of hertuzumab-vcMMAE at 5 or 10 mg/kg showed high potency and a sustained tumor inhibitory effect on NCI-N87 xenografts in mice. In conclusion, hertuzumab-vcMMAE conjugate is a highly effective anti-HER2 targeted therapy for HER2-positive gastric cancer.

Flotillin-2 Gene Is Associated with Coronary Artery Disease in Chinese Han Population

BACKGROUND

Flotillin-2, an important protein of vesicular endocytosis, is commonly used as a marker protein for lipid microdomains. It plays an essential role in cellular cholesterol uptake and biliary cholesterol reabsorption. Excessive cholesterol intake could cause dyslipidemia, which is a major risk factor of coronary artery disease (CAD).

AIMS

To investigate the association between the human flotillin-2 gene polymorphism and CAD in the Chinese Han population.

MATERIALS AND METHODS

Three single-nucleotide polymorphisms (SNPs; rs10205, rs3816848 and rs8081659) of the flotillin-2 gene were genotyped by real-time polymerase chain reaction in 307 CAD patients and 441 control subjects.

RESULTS

The genotypic distribution of these three SNPs was significantly different between CAD patients and control subjects (all p < 0.05). There were significant differences in the plasma levels of total cholesterol (TC) among different genotypes in the CAD group and control group. For rs3816848, CAD patients with the GG genotype had a higher level of TC than those with an AG or AA genotype (p < 0.001). For rs8081659, CAD patients with TT genotype had a higher level of TC than those with a CT or CC genotype (p < 0.001). Multiple logistic regression analysis showed that the GG genotype of rs3816848 was an independent risk factor for CAD (odds ratio [OR] = 1.786; 95% CI = 1.099-2.902; p = 0.019).

CONCLUSION

There was a strong association between polymorphisms of flotillin-2 gene and CAD in the Chinese Han population. Persons with the GG genotype of rs3816848 may have a higher risk of CAD. Moreover, the plasma levels of TC were significantly different among the different genotypes of the rs3816848 and rs8081659 SNPs in the CAD group as well as the control group.

Impact of c-erbB-2 protein on 5-year survival rate of gastric cancer patients after surgery: a cohort study and meta-analysis

OBJECTIVE

To explore the association of c-erbB-2 protein expression with clinicopathological characteristics and prognosis of gastric cancer (GC) after surgery.

METHODS

A total of 133 patients undergoing surgical resection for GC between March 2006 and January 2009 in the Second Affiliated Hospital of Wenzhou Medical University were included in this study. c-erbB-2 protein expression was determined by immunohistochemistry. Afterwards, a meta-analysis was performed to further confirm the association between c-erbB-2 protein expression and GC by employing stringent inclusion and exclusion criteria. All data analyses were conducted with STATA 12.0 and SPSS 19.0.

RESULTS

There was no significant difference in c-erbB-2 expression among patients with various parameters including age, gender and histological types (all p>0.05). Among 133 GC patients, 32 patients presented c-erbB-2-positive expression and 101 presented c-erbB-2-negative expression (24.1% vs. 75.9%). The c-erbB-2-positive expression rate was significantly higher in GC tissues of patients with lymph node metastasis than those without. Similarly, a significant increase in c-erbB-2 expression was observed in well/moderately differentiated GC tissues compared with poorly differentiated GC. Patients with negative c-erbB-2 expression had a higher 5-year survival rate than those with positive c-erbB-2 expression, which was consistent with the results of the meta-analysis (OR = 0.54, 95% CI 0.37-0.80, p = 0.002).

CONCLUSIONS

Our study demonstrated that high expression of c-erbB-2 protein was strongly associated with lymph node metastasis, histological differentiation and 5-year survival rate in GC patients after surgery.

Flotillin-2 promotes metastasis of nasopharyngeal carcinoma by activating NF-κB and PI3K/Akt3 signaling pathways

Lipid raft proteins have been confirmed to be important in cell signal transduction. Some reports have shown that the aberrant expression of lipid raft proteins is associated with malignant phenotypes in some cancers. However, the role of the lipid raft protein flotillin-2 (Flot-2) in nasopharyngeal carcinoma (NPC) remains to be comprehensively characterized. Here, overexpression of Flot-2 in NPC tissues and cell lines was detected by immunostaining, and Flot-2 expression was found to be positively associated with NPC metastasis. Furthermore, inhibiting Flot-2 expression impaired the malignancy of the highly metastatic NPC cell line 5-8F by constraining its growth and proliferation, mobility and migration, and decreasing the capacity of 5-8F cells to metastasize in nude mice. In contrast, forced overexpression of Flot-2 increased the malignancy of 6-10B, a non-metastatic NPC cell line that weakly expresses Flot-2. Moreover, in 5-8F-shFlot-2 cells, which have inhibited Flot-2 expression, the NF-κB and PI3K/Akt3 pathways were inactivated. Subsequently, MMPs expression were decreased, and Foxo1 activity was increased. In addition, enhanced NF-κB and PI3K/Akt3 activities were observed in Flot-2 overexpressing 6-10B cells. Thus, Flot-2 exerts a pro-neoplastic role in NPC and is involved in tumor progression and metastasis. Moreover, Flot-2 exerts its role through NF-κB and PI3K/Akt3 signaling.

Flot-2 Expression Correlates with EGFR Levels and Poor Prognosis in Surgically Resected Non-Small Cell Lung Cancer

We previously reported that expression of Flotillin 2 (Flot-2), a protein isolated from caveolae/lipid raft domains, increased significantly in nasopharyngeal carcinoma (NPC) compared with normal tissues. Signal transduction through epidermal growth factor receptors (EGFR) and Flot-2 play an important role in cancer development, but their precise role in lung cancer has not been investigated. In this study, we have investigated the correlation between the expression of Flot-2 and EGFR, which increase significantly in non-small cell lung cancer (NSCLC) patients (n=352) compared with non-cancer tissues. Additionally, patients with advanced stages of NSCLC had higher positive expression of Flot-2 and EGFR than patients with early stages. NSCLC patients with increased expression of Flot-2 and EGFR had significantly less overall survival rates than patients with less expression of Flot-2 and EGFR. Taken together, our data suggest that increased expression of Flot-2 and EGFR in NSCLC patients is inversely proportional to the disease prognosis and that increased expression of Flot-2 associated with increased EGFR may serve as a biomarker to predict poor disease prognosis.

FLOT-2 is an independent prognostic marker in oral squamous cell carcinoma

Flotillin-2 (Flot-2) is an important component of cellular membrane, which involves in various cellular processes and recent studies have revealed that Flot-2 played important roles in cancer progression. The expression and prognostic impact of Flot-2 in oral squamous cell carcinoma (OSCC) have not been well studied. So, a tissue microarray (TMA) based on immunohistochemical analysis of surgical resection of tumor tissues of 78 cases of OSCC patients and 27 cases of adjacent non-cancerous squamous epithelium tissues was conducted. This study focused on detecting Flot-2 expression and analyzing its prognostic impact on OSCC. The result showed that the positive percentage of Flot-2 expression in OSCC (74.4%, 58/78) was significantly higher than that in adjacent non-cancerous squamous epithelium tissues (25.9%, 7/27) (P<0.001). Additionally, the positive expression of Flot-2 in OSCC patients with a history of alcohol consumption was significantly higher than those nonusers (P=0.027). Both univariate and multivariate survival analysis indicated that increased expression Flot-2 protein was significantly correlated inversely with overall survival rates in OSCC patients (P=0.046, P=0.002). Taken together, positive expression of Flot-2 protein may be an independent biomarker for poor prognosis in OSCC.

Plasma membrane proteomic analysis of human Gastric Cancer tissues: revealing flotillin 1 as a marker for Gastric Cancer

Background

Gastric cancer remains the second leading cause of cancer-related deaths in the world. Successful early gastric cancer detection is hampered by lack of highly sensitive and specific biomarkers. Plasma membrane proteins participate and/or have a central role in the metastatic process of cancer cells and are potentially useful for cancer therapy due to easy accessibility of the targets.

Methods

In the present research, TMT method followed by mass spectrometry analysis was used to compare the relative expression levels of plasma membrane proteins between noncancer and gastric cancer tissues.

Results

Of a total data set that included 501 identified proteins, about 35% of the identified proteins were found to be plasma membrane and associated proteins. Among them, 82 proteins were at least 1.5-fold up- or down-regulated in gastric cancer compared with the adherent normal tissues.

Conclusions

A number of markers (e.g. annexin A6, caveolin 1, epidermal growth factor receptor, integrin beta 4) were previously reported as biomarkers of GC. Additionally, several potential biomarkers participated in endocytosis pathway and integrin signaling pathways were firstly identified as differentially expressed proteins in GC samples. Our findings also supported the notion that flotillin 1 is a potential biomarker that could be exploited for molecular imaging-based detection of gastric cancer. Together, the results show that subcellular proteomics of tumor tissue is a feasible and promising avenue for exploring oncogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1343-5) contains supplementary material, which is available to authorized users.

Clinicopathological significance of cytoplasmic transducer of ErbB2. 1 expression in gastric cancer

The aim of the present study was to investigate the expression of transducer of ErbB2. 1 (TOB1) in gastric carcinoma and to clarify the association between TOB1 expression and the clinical significance of this expression in patients with gastric carcinoma. Western blot analysis was performed to confirm the expression of TOB1 in gastric cancer. Immunohistochemistry (IHC) was performed on a tissue microarray containing 90 pairs of primary gastric cancer and adjacent normal tissue samples. TOB1 expression was evaluated separately with cytoplasmic and nuclear staining. Western blot analysis revealed significantly lower expression levels of TOB1 in gastric cancer tissues than those in adjacent normal tissues in 91.7% of cases. This was confirmed by IHC, which revealed decreased cytoplasmic TOB1 expression in cancer tissues compared with those of normal tissue samples in 84.4% of cases. The IHC data also revealed low cytoplasmic expression of TOB1 in 67.8% of human gastric cancer samples. Nuclear TOB1 expression exhibited no significant association with specific pathological features. However, a significant association was identified between cytoplasmic expression levels of TOB1 and clinicopathological characteristics, including the depth of invasion (P=0.017), differentiation grade (P=0.034) and tumor-node-metastasis stage (P<0.000). In conclusion, cytoplasmic TOB1 expression was suggested to be significant in angiogenesis and cell differentiation in gastric cancer tissues and may be used as a potential prognostic marker.

High expression of flotillin-2 is associated with poor clinical survival in cervical carcinoma

AIMS

To investigate the expression and clinical significance of flotillin-2 (FLOT2) in cervical cancer (CC).

METHODS

We examined FLOT2 mRNA levels in 10 pairs of cervical cancer and adjacent normal tissues. Immunohistochemistry was performed to analyze FLOT2 protein expression in 115 archived cervical cancer samples. The association between FLOT2 levels, clinicopathologic factors and prognosis was analyzed statistically as well.

RESULTS

The cancer tissues of CC patients had clearly increased expression of FLOT2 at mRNA level as compared to adjacent nontumorous tissues. Survival analysis of CC patients indicated that FLOT2 expression was significantly associated with poor overall and local recurrence-free survival (P = 0.025 and P = 0.028, respectively). Moreover, FLOT2 expression was significantly correlated with clinical stage, tumor differentiation, and lymph nodes metastasis. Multivariate analysis revealed that FLOT2 expression was an independent prognostic factor for overall survival in CC patients.

CONCLUSION

FLOT2 may serve as an oncogene in the development of CC, and may serve as a clinicopathologic biomarker for prognosis in CC patients.

Flotillins in intercellular adhesion - from cellular physiology to human diseases

Flotillin 1 and 2 are ubiquitous and highly conserved proteins. They were initially discovered in 1997 as being associated with specific caveolin-independent cholesterol- and glycosphingolipid-enriched membrane microdomains and as being expressed during axon regeneration. Flotillins have a role in a large number of physiopathological processes, mainly through their function in membrane receptor clustering and in the regulation of clathrin-independent endocytosis. In this Commentary, we summarize the research performed so far on the role of flotillins in cell-cell adhesion. Recent studies have demonstrated that flotillins directly regulate the formation of cadherin complexes. Indeed, flotillin microdomains are required for the dynamic association and stabilization of cadherins at cell-cell junctions and also for cadherin signaling. Moreover, because flotillins regulate endocytosis and also the actin cytoskeleton, they could have an indirect role in the assembly and stabilization of cadherin complexes. Because it has also recently been shown that flotillins are overexpressed during neurodegenerative diseases and in human cancers, where their upregulation is associated with metastasis formation and poor prognosis, understanding to what extent flotillin upregulation participates in the development of such pathologies is thus of particular interest, as well as how, at the molecular level, it might affect cell adhesion processes.

Increased expression of flotillin-2 protein as a novel biomarker for lymph node metastasis in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a head and neck malignant tumor rare throughout most of the world but common in Southeast Asia, especially in Southern China. Flotillin-2 (Flot-2) is not only an important component of cellular membrane, but also involves in various cellular processes such as membrane trafficking, T cell and B cell activation, regulation of several signaling pathways associated with cell growth and malignant transformation, keeping structure and junction of epidermal cells and formation of filopodia. Although such molecular effects of Flot-2 have been reported, whether the expression of Flot-2 protein is associated with clinicopathologic implication for NPC has not been reported. The purpose of this research is to investigate the expression of Flot-2 protein in NPC and control nasopharyngeal epithelial tissues by immunohistochemistry and elucidate the association between the expression of Flot-2 protein and clinicopathological characteristics of NPC. The results showed that the positive percentage of Flot-2 expression in the NPC, nasopharyngeal epithelia with atypical hyperplasia and in the control nasopharyngeal mucosa epithelia was 88.8% (119/134), 76.9% (10/13) and 5.7% (5/88), respectively. There was significantly higher expression of Flot-2 protein in NPC and nasopharyngeal epithelia with atypical hyperplasia compared to the control nasopharyngeal mucosa epithelia (P<0.001, respectively). The positive percentage of Flot-2 protein expression in NPC patients with lymph node metastasis was significantly higher than those without lymph node metastasis. Increasing of Flot-2 expression was obviously correlated with clinical stages of NPC patients. The expression of Flot-2 was proved to be the independent predicted factor for lymph node metastasis by multivariate analysis. The sensitivity of Flot-2 for predicting lymph node metastasis of NPC patients was 93%. Taken together, our results suggest that the increased expression of Flot-2 protein is a novel higher sensitivity biomarker that can predict lymph node metastases in NPC.

Flotillin depletion affects ErbB protein levels in different human breast cancer cells

The ErbB3 receptor is an important regulator of cell growth and carcinogenesis. Among breast cancer patients, up to 50-70% have ErbB3 overexpression and 20-30% show overexpressed or amplified ErbB2. ErbB3 has also been implicated in the development of resistance to several drugs used against cancers driven by ErbB1 or ErbB2. One of the main challenges in ErbB-targeting therapy is to inactivate signaling mediated by ErbB2-ErbB3 oncogenic receptor complexes. We analyzed the regulatory role of flotillins on ErbB3 levels and ErbB2-ErbB3 complexes in SKBR3, MCF7 and MDA-MB-134-VI human breast cancer cells. Recently, we described a mechanism for interfering with ErbB2 signaling in breast cancer and demonstrated a molecular complex of flotillin scaffolding proteins with ErbB2 and Hsp90. In the present study, flotillins were found to be in a molecular complex with ErbB3, even in cells without the presence of ErbB2 or other ErbB receptors. Depletion of either flotillin-1 or flotillin-2 resulted in downregulation of ErbB3 and a selective reduction of ErbB2-ErbB3 receptor complexes. Moreover, flotillin-2 depletion resulted in reduced activation of Akt and MAPK signaling cascades, and as a functional consequence of flotillin depletion, breast cancer cells showed an impaired cell migration. Altogether, we provide data demonstrating a novel and functional role of flotillins in the regulation of ErbB protein levels and stabilization of ErbB2-ErbB3 receptor complexes. Thus, flotillins are crucial regulators for oncogenic ErbB function and potential targets for cancer treatment.

Flotillins in receptor tyrosine kinase signaling and cancer

Flotillins are highly conserved proteins that localize into specific cholesterol rich microdomains in cellular membranes. They have been shown to be associated with, for example, various signaling pathways, cell adhesion, membrane trafficking and axonal growth. Recent findings have revealed that flotillins are frequently overexpressed in various types of human cancers. We here review the suggested functions of flotillins during receptor tyrosine kinase signaling and in cancer. Although flotillins have been implicated as putative cancer therapy targets, we here show that great caution is required since flotillin ablation may result in effects that increase instead of decrease the activity of specific signaling pathways. On the other hand, as flotillin overexpression appears to be related with metastasis formation in certain cancers, we also discuss the implications of these findings for future therapy aspects.

Phosphatidylinositol 3-Kinase dependent upregulation of the epidermal growth factor receptor upon Flotillin-1 depletion in breast cancer cells

BACKGROUND

Flotillin-1 and flotillin-2 are two homologous and ubiquitously expressed proteins that are involved in signal transduction and membrane trafficking. Recent studies have reported that flotillins promote breast cancer progression, thus making them interesting targets for breast cancer treatment. In the present study, we have investigated the underlying molecular mechanisms of flotillins in breast cancer.

METHODS

Human adenocarcinoma MCF7 breast cancer cells were stably depleted of flotillins by means of lentivirus mediated short hairpin RNAs. Western blotting, immunofluorescence and quantitative real-time PCR were used to analyze the expression of proteins of the epidermal growth factor receptor (EGFR) family. Western blotting was used to investigate the effect of EGFR stimulation or inhibition as well as phosphatidylinositol 3-kinase (PI3K) inhibition on mitogen activated protein kinase (MAPK) signaling. Rescue experiments were performed by stable transfection of RNA intereference resistant flotillin proteins.

RESULTS

We here show that stable knockdown of flotillin-1 in MCF7 cells resulted in upregulation of EGFR mRNA and protein expression and hyperactivation of MAPK signaling, whereas ErbB2 and ErbB3 expression were not affected. Treatment of the flotillin knockdown cells with an EGFR inhibitor reduced the MAPK signaling, demonstrating that the increased EGFR expression and activity is the cause of the increased signaling. Stable ectopic expression of flotillins in the knockdown cells reduced the increased EGFR expression, demonstrating a direct causal relationship between flotillin-1 expression and EGFR amount. Furthermore, the upregulation of EGFR was dependent on the PI3K signaling pathway which is constitutively active in MCF7 cells, and PI3K inhibition resulted in reduced EGFR expression.

CONCLUSIONS

This study demonstrates that flotillins may not be suitable as cancer therapy targets in cells that carry certain other oncogenic mutations such as PI3K activating mutations, as unexpected effects are prone to emerge upon flotillin knockdown which may even facilitate cancer cell growth and proliferation.