Flotillins Regulate Focal Adhesions by Interacting with α-Actinin and by Influencing the Activation of Focal Adhesion Kinase

Flotillins affect LPS-induced TLR4 signaling by modulating the trafficking and abundance of CD14

Lipopolysaccharide (LPS) induces a strong pro-inflammatory reaction of macrophages upon activation of Toll-like receptor 4 (TLR4) with the assistance of CD14 protein. Considering a key role of plasma membrane rafts in CD14 and TLR4 activity and the significant impact exerted on that activity by endocytosis and intracellular trafficking of the both LPS acceptors, it seemed likely that the pro-inflammatory reaction could be modulated by flotillins. Flotillin-1 and -2 are scaffolding proteins associated with the plasma membrane and also with endo-membranes, affecting both the plasma membrane dynamics and intracellular protein trafficking. To verify the above hypothesis, a set of shRNA was used to down-regulate flotillin-2 in Raw264 cells, which were found to also become deficient in flotillin-1. The flotillin deficiency inhibited strongly the TRIF-dependent endosomal signaling of LPS-activated TLR4, and to a lower extent also the MyD88-dependent one, without affecting the cellular level of TLR4. The flotillin depletion also inhibited the pro-inflammatory activity of TLR2/TLR1 and TLR2/TLR6 but not TLR3. In agreement with those effects, the depletion of flotillins down-regulated the CD14 mRNA level and the cellular content of CD14 protein, and also inhibited constitutive CD14 endocytosis thereby facilitating its shedding. Ultimately, the cell-surface level of CD14 was markedly diminished. Concomitantly, CD14 recycling was enhanced via EEA1-positive early endosomes and golgin-97-positive trans-Golgi network, likely to compensate for the depletion of the cell-surface CD14. We propose that the paucity of surface CD14 is the reason for the down-regulated signaling of TLR4 and the other TLRs depending on CD14 for ligand binding.

Distinct Brain Proteomic Signatures in Cerebral Small Vessel Disease Rat Models of Hypertension and Cerebral Amyloid Angiopathy

Cerebral small vessel diseases (CSVDs) are prominent contributors to vascular cognitive impairment and dementia and can arise from a range of etiologies. Cerebral amyloid angiopathy (CAA) and hypertension (HTN), both prevalent in the elderly population, lead to cerebral microhemorrhages, macrohemorrhages, and white matter damage. However, their respective underlying mechanisms and molecular events are poorly understood. Here, we show that the transgenic rat model of CAA type 1 (rTg-DI) exhibits perivascular inflammation that is lacking in the spontaneously hypertensive stroke-prone (SHR-SP) rat model of HTN. Alternatively, SHR-SP rats display notable dilation of arteriolar perivascular spaces. Comparative proteomics analysis revealed few shared altered proteins, with key proteins such as ANXA3, H2A, and HTRA1 unique to rTg-DI rats, and Nt5e, Flot-1 and Flot-2 unique to SHR-SP rats. Immunolabeling confirmed that upregulation of ANXA3, HTRA1, and neutrophil extracellular trap proteins were distinctly associated with rTg-DI rats. Pathway analysis predicted activation of TGF-β1 and TNFα in rTg-DI rat brain, while insulin signaling was reduced in the SHR-SP rat brain. Thus, we report divergent protein signatures associated with distinct cerebral vessel pathologies in the SHR-SP and rTg-DI rat models and provide new mechanistic insight into these different forms of CSVD.

Heterostructured Metal-Organic Frameworks/Polydopamine Coating Endows Polyetheretherketone Implants with Multimodal Osteogenicity and Photoswitchable Disinfection

Clinically, bacteria-induced contagion and insufficient osseointegrative property inevitably elicit the failure of orthopedic implants. Herein, a heterostructured coating consisting of simvastatin (SIM)-laden metal-organic frameworks and polydopamine nanolayers is created on a porous bioinert polyetheretherketone implant. The heterostructured coating significantly promotes cytocompatibility and osteogenic differentiation through multimodal osteogenicity mechanisms of zinc ion (Zn²⁺ ) therapy, SIM drug therapy, and surface micro-/nano-topological stimulation. Under the illumination of near-infrared (NIR) light, singlet oxygen (¹ O₂ ) and local hyperthermia are produced; besides, NIR light dramatically accelerates the release of Zn²⁺ ions from heterostructured coatings. Gram-positive and -negative bacteria are effectively eradicated by the synergy of photothermal/photodynamic effects and photo-induced accelerated delivery of Zn²⁺ ions. The superior osteogenicity and osseointegration, as well as photoswitchable disinfection controlled by NIR light are corroborated via in vivo results. This work highlights the great potential of photoresponsive heterostructured orthopedic implants in treatment of the noninvasive bone reconstruction of bacteria-associated infectious tissues through multimodal phototherapy and photoswitchable ion-therapy.

Identification of novel proteins and mechanistic pathways associated with early-onset hypertension by deep proteomic mapping of resistance arteries

Resistance arteries are small blood vessels that create resistance to blood flow. In hypertension, resistance arteries undergo remodeling, affecting their ability to contract and relax appropriately. To date, no study has mapped the hypertension-related proteomic changes in resistance arteries. Using a novel data-independent acquisition–mass spectrometry (DIA-MS) approach, we determined the proteomic changes in small mesenteric and renal arteries in pre- and early-onset hypertension from the spontaneously hypertensive rat (SHR) model, which represents human primary hypertension. Compared with normotensive controls, mesenteric arteries from 12-week-old SHRs had 286 proteins that were significantly up- or downregulated, whereas 52 proteins were identified as up- or downregulated in mesenteric arteries from 6-week-old SHRs. Of these proteins, 18 were also similarly regulated in SHR renal arteries. Our pathway analyses reveal several novel pathways in the pathogenesis of hypertension. Finally, using a matrisome database, we identified 38 altered extracellular-matrix-associated proteins, many of which have never previously been associated with hypertension. Taken together, this study reveals novel proteins and mechanisms that are associated with early-onset hypertension, thereby providing novel insights into disease progression.

Identification of UBE2T as an independent prognostic biomarker for gallbladder cancer

Gallbladder cancer is the most common biliary tract malignant tumor, with unfavorable patient outcomes. The present study aimed to identify potential diagnostic or prognostic biomarkers for gallbladder cancer. To do so, differentially expressed genes in the gallbladder walls and tumor tissues of patients with gallbladder cancer were analyzed via microarray. Furthermore, a protein-protein interaction network was constructed and genes with a degree score >10 were selected as hub genes. As ubiquitin conjugating enzyme E2T (UBE2T) was considered to be a hub gene, its expression was assessed via reverse transcription-quantitative (RT-q)PCR and immunohistochemistry (IHC). In addition, the association between UBE2T expression and the clinicopathological characteristics of patients with gallbladder cancer was analyzed using the χ² test. Furthermore, all patients were divided into high- and low groups based on UBE2T expression level and overall survival analysis was performed. Univariate and multivariate Cox regression analyses were performed to determine whether UBE2T may serve as an independent risk factor for gallbladder cancer. The results demonstrated that UBE2T expression was upregulated in the gallbladder walls and tumor tissues of patients with gallbladder cancer. Furthermore, UBE2T expression level was confirmed to be upregulated following RT-qPCR, and results from IHC demonstrated that UBE2T was predominantly expressed in the cytoplasm of gallbladder cancer cells. In addition, high UBE2T expression level was associated with clinical stage, T classification, N classification and M classification. The results from Univariate and multivariate analyses indicated that UBE2T expression level may be considered as an independent risk factor for gallbladder cancer. Taken together, the findings from this study suggested that high UBE2T expression level may contribute to the poor prognosis of patients with gallbladder cancer, and that UBE2T may act as an independent prognostic biomarker for these patients.

Membrane dynamics in cell migration

Migration of cells is required in multiple tissue-level processes, such as in inflammation or cancer metastasis. Endocytosis is an extremely regulated cellular process by which cells uptake extracellular molecules or internalise cell surface receptors. While the role of endocytosis of focal adhesions (FA) and plasma membrane (PM) turnover at the leading edge of migratory cells is wide known, the contribution of endocytic proteins per se in migration has been frequently disregarded. In this review, we describe the novel functions of the most well-known endocytic proteins in cancer cell migration, focusing on clathrin, caveolin, flotillins and GRAF1. In addition, we highlight the relevance of the macropinocytic pathway in amoeboid-like cell migration.

Flotillins: At the Intersection of Protein S-Palmitoylation and Lipid-Mediated Signaling

Flotillin-1 and flotillin-2 are ubiquitously expressed, membrane-associated proteins involved in multifarious cellular events from cell signaling, endocytosis, and protein trafficking to gene expression. They also contribute to oncogenic signaling. Flotillins bind the cytosolic leaflet of the plasma membrane and endomembranes and, upon hetero-oligomerization, serve as scaffolds facilitating the assembly of multiprotein complexes at the membrane-cytosol interface. Additional functions unique to flotillin-1 have been discovered recently. The membrane-binding of flotillins is regulated by S-palmitoylation and N-myristoylation, hydrophobic interactions involving specific regions of the polypeptide chain and, to some extent, also by their oligomerization. All these factors endow flotillins with an ability to associate with the sphingolipid/cholesterol-rich plasma membrane domains called rafts. In this review, we focus on the critical input of lipids to the regulation of the flotillin association with rafts and thereby to their functioning. In particular, we discuss how the recent developments in the field of protein S-palmitoylation have contributed to the understanding of flotillin1/2-mediated processes, including endocytosis, and of those dependent exclusively on flotillin-1. We also emphasize that flotillins affect directly or indirectly the cellular levels of lipids involved in diverse signaling cascades, including sphingosine-1-phosphate and PI(4,5)P₂. The mutual relations between flotillins and distinct lipids are key to the regulation of their involvement in numerous cellular processes.

Involvement of lipid microdomains in human endothelial cells infected by Streptococcus agalactiae type III belonging to the hypervirulent ST-17

BACKGROUND

Streptococcus agalactiae capsular type III strains are a leading cause of invasive neonatal infections. Many pathogens have developed mechanisms to escape from host defense response using the host membrane microdomain machinery. Lipid rafts play an important role in a variety of cellular functions and the benefit provided by interaction with lipid rafts can vary from one pathogen to another.

OBJECTIVES

This study aims to evaluate the involvement of membrane microdomains during infection of human endothelial cell by S. agalactiae.

METHODS

The effects of cholesterol depletion and PI3K/AKT signaling pathway activation during S. agalactiae-human umbilical vein endothelial cells (HUVEC) interaction were analysed by pre-treatment with methyl-β-cyclodextrin (MβCD) or LY294002 inhibitors, immunofluorescence and immunoblot analysis. The involvement of lipid rafts was analysed by colocalisation of bacteria with flotillin-1 and caveolin-1 using fluorescence confocal microscopy.

FINDINGS

In this work, we demonstrated the importance of the integrity of lipid rafts microdomains and activation of PI3K/Akt pathway during invasion of S. agalactiae strain to HUVEC cells. Our results suggest the involvement of flotillin-1 and caveolin-1 during the invasion of S. agalactiae strain in HUVEC cells.

CONCLUSIONS

The collection of our results suggests that lipid microdomain affects the interaction of S. agalactiae type III belonging to the hypervirulent ST-17 with HUVEC cells through PI3K/Akt signaling pathway.

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.

Protein phosphatase 2A-mediated flotillin-1 dephosphorylation up-regulates endothelial cell migration and angiogenesis regulation

Endothelial cells have key functions in endothelial barrier integrity and in responses to angiogenic signals that promote cell proliferation, cell migration, cytoskeletal reorganization, and formation of new blood vessels. These functions highly depend on protein-protein interactions in cell-cell junction and cell attachment complexes and on interactions with cytoskeletal proteins. Protein phosphatase 2A (PP2A) dephosphorylates several target proteins involved in cytoskeletal dynamics and cell adhesion. Our goal was to find new interacting and substrate proteins of the PP2A-B55α holoenzyme in bovine pulmonary endothelial cells. Using LC-MS/MS analysis, we identified flotillin-1 as a protein that binds recombinant GSH S-transferase-tagged PP2A-B55α. Immunoprecipitation experiments, proximity ligation assays, and immunofluorescent staining confirmed the interaction between these two endogenous proteins in endothelial cells. Originally, flotillins were described as regulatory proteins for axon regeneration, but they appear to function in many cellular processes, such as membrane receptor signaling, endocytosis, and cell adhesion. Ser³¹⁵ is a known PKC-targeted site in flotillin-1. Utilizing phosphomutants of flotillin-1 and the NanoBiT luciferase assay, we show here that phosphorylation/dephosphorylation of Ser³¹⁵ in flotillin-1 significantly affects its interaction with PP2A-B55α and that PP2A-B55α dephosphorylates phospho-Ser³¹⁵ Spreading, attachment, migration, and in vitro tube formation rates of S315A variant-overexpressing cells were faster than those of nontransfected or S315D-transfected cells. These results indicate that the PP2A-flotillin-1 interaction identified here affects major physiological activities of pulmonary endothelial cells.

LIN28B increases neural crest cell migration and leads to transformation of trunk sympathoadrenal precursors

The RNA-binding protein LIN28B regulates developmental timing and determines stem cell identity by suppressing the let-7 family of microRNAs. Postembryonic reactivation of LIN28B impairs cell commitment to differentiation, prompting their transformation. In this study, we assessed the extent to which ectopic lin28b expression modulates the physiological behavior of neural crest cells (NCC) and governs their transformation in the trunk region of developing embryos. We provide evidence that the overexpression of lin28b inhibits sympathoadrenal cell differentiation and accelerates NCC migration in two vertebrate models, Xenopus leavis and Danio rerio. Our results highlight the relevance of ITGA5 and ITGA6 in the LIN28B-dependent regulation of the invasive motility of tumor cells. The results also establish that LIN28B overexpression supports neuroblastoma onset and the metastatic potential of malignant cells through let-7a-dependent and let-7a-independent mechanisms.

The Flot2 component of the lipid raft changes localization during neural differentiation of P19C6 cells

Background

Flotillin-2 (Flot2) is a lipid raft scaffold protein that is thought to be related to neural differentiation. Flot2 is phosphorylated by Fyn, a Src kinase, and causes raft-dependent endocytosis; however, the exact role of Flot2 in neural differentiation remains unclear. To reveal the roles of lipid raft-associated proteins during neural differentiation, we tried to analyze the expression and localization.

Results

In this study, we found that the expression levels of the Flot2 and Fyn proteins increased in whole-cell lysates of P19C6 cells after neural differentiation. In addition, sucrose density fractionation and immunofluorescence experiments revealed an increase in the localization of Flot2 and Fyn to lipid rafts after neural differentiation. We also found that Fyn partially colocalized with Flot2 lipid rafts in neural cells.

Conclusion

The observed distribution of Fyn and level of inactivated Fyn and/or c-Src in detergent–resistant membrane (DRM) fractions suggests that the amount of activated Fyn might increase in DRM fractions after neural differentiation. Overall these findings suggest that Flot2 lipid rafts are associated with Fyn, and that Fyn phosphorylates Flot2 during neural differentiation of P19C6 cells.

Electronic supplementary material

The online version of this article (10.1186/s12860-019-0225-0) contains supplementary material, which is available to authorized users.

NPTX1 promotes metastasis via integrin/FAK signaling in gastric cancer

PURPOSE

This study aimed to investigate the effect of NPTX1 on the prognosis of gastric cancer (GC), as well as the metastatic process in GC.

MATERIALS AND METHODS

The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases were used to analyze the association between NPTX1 expression and prognosis in GC. Quantitative real-time polymerase chain reaction and Western blots were applied to examine the expression of NPTX1 in GC cell lines and expression of genes in downstream pathways. The role of NPTX1 on the migration, invasion, adhesion, and proliferation of GC cell lines was investigated with the transwell assay, the adhesion assay, and the MTT assay. Immunofluorescence staining was used to observe the effect of NPTX1 knockdown on the morphology of cells.

RESULTS

According to the review of TCGA and GEO databases of GC, we found that the expression of NPTX1 increased in cancer tissues and high NPTX1 expression was correlated with poor overall survival, which was associated with lymph node stage in clinicopathologic parameters. Knockdown of NPTX1 attenuated the migration, invasion, and adhesion abilities of GC cells. According to gene set enrichment analysis, NPTX1 was found to be positively related to integrin and focal adhesion (FA). Additionally, NPTX1 knockdown decreased the expression of integrin α1 and integrin α7, followed by deregulation of the expression of p-Src, p-Akt, p-Erk, MMP2, and MMP7, as well as inhibiting the formation of FA complexes and decreasing the length of pseudopods in GC cells.

CONCLUSION

Our study provides strong evidence that NPTX1 plays a crucial role in promoting metastasis and acts as a prognostic indicator in GC.

Insufficient radiofrequency ablation promotes the metastasis of residual hepatocellular carcinoma cells via upregulating flotillin proteins

Purpose

Radiofrequency ablation (RFA) therapy has proven to be effective and feasible for early-stage hepatocellular carcinoma (HCC); however, rapid progression of residual tumor cells after RFA has been confirmed, but the molecular mechanisms of this phenomenon are poorly understood. This study evaluated the effect of the lipid raft proteins known as flotillins on the invasive and metastatic potential of residual HCC.

Methods

The human HCC cell line HCCLM3 was used to establish insufficient RFA models in vivo and in vitro. Changes in cellular morphology, soft agar colony formation, motility, metastasis, and epithelial–mesenchymal transition (EMT) markers after insufficient RFA intervention in vitro and in vivo were detected by real-time PCR, western blotting, immunohistochemistry and transwell assays.

Results

The results showed that flotillin-1 and flotillin-2 expression were upregulated in HCCLM3 cells following 45 °C heat treatment and in residual HCCLM3 xenografts cells after insufficient RFA. Knocking down flotillin-1 or flotillin-2 in HCCLM3 cells by shRNA significantly lowered insufficient RFA-induced tumor growth, EMT changes, and metastasis in vitro and in vivo. Furthermore, mechanism studies indicated that flotillins altered the EMT status and metastatic potential of heat-treated HCCLM3 cells by activating the Akt/Wnt/β-catenin signaling pathway.

Conclusions

Our findings present new evidence that flotillins play a key role in the aggressive behaviors of residual cancer cells after insufficient RFA and provide new insights into the regulatory mechanism of Wnt/β-catenin signaling.

Electronic supplementary material

The online version of this article (10.1007/s00432-019-02852-z) contains supplementary material, which is available to authorized users.