CD98hc (SLC3A2) drives integrin-dependent renal cancer cell behavior

Empagliflozin drives ferroptosis in anoikis-resistant cells by activating miR-128-3p dependent pathway and inhibiting CD98hc in breast cancer

A tumour suppressor miRNA, miR-128-3p, is widely involved in various biological processes and has been found to get downregulated in breast cancer patients. We previously published that ectopically expressed miR-128-3p suppressed migration, invasion, cell cycle arrest, and breast cancer stem cells. In the present study, we explored the role of Empagliflozin (EMPA) as a miR-128-3p functionality-mimicking drug in inducing ferroptosis by inhibiting CD98hc. Given that CD98hc is one of the proteins critical in triggering ferroptosis, we confirmed that miR-128-3p and EMPA inhibited SP1, leading to inhibition of CD98hc expression. Further, transfection with siCD98hc, miR-128-3p mimics, and inhibitors was performed to assess their involvement in the ferroptosis of anoikis-resistant cells. We proved that anoikis-resistant cells possess high ROS and iron levels. Further, miR-128-3p and EMPA treatments induced ferroptosis by inhibiting GSH and enzymatic activity of GPX4 and also induced lipid peroxidation. Moreover, EMPA suppressed bioluminescence of 4T1-Red-FLuc induced thoracic cavity, peritoneal tumour burden and lung nodules in an in-vivo metastatic model of breast cancer. Collectively, we revealed that EMPA sensitized the ECM detached cells to ferroptosis by synergically activating miR-128-3p and lowering the levels of SP1 and CD98hc, making it a potential adjunct drug for breast cancer chemotherapy.

A novel SLC3A2-targeting antibody-drug conjugate exerts potent antitumor efficacy in head and neck squamous cell cancer

The development of innovative therapeutic strategies for head and neck squamous cell carcinoma (HNSCC) is a critical medical requirement. Antibody-drug conjugates (ADC) targeting tumor-specific surface antigens have demonstrated clinical effectiveness in treating hematologic and solid malignancies. Our investigation revealed high expression levels of SLC3A2 in HNSCC tissue and cell lines. This study aimed to develop a novel anti-SLC3A2 ADC and assess its antitumor effects on HNSCC both in vitro and in vivo. This study developed a potent anti-SLC3A2 ADC (19G4-MMAE) and systematically investigated its drug delivery potential and antitumor efficacy in preclinical models. This study revealed that 19G4-MMAE exhibited specific binding to SLC3A2 and effectively targeted lysosomes. Moreover, 19G4-MMAE induced a significant accumulation of reactive oxygen species (ROS) and apoptosis in SLC3A2-positive HNSCC cells. The compound demonstrated potent antitumor effects derived from MMAE against SLC3A2-expressing HNSCC in preclinical models, displaying a favorable safety profile. These findings suggest that targeting SLC3A2 with an anti-SLC3A2 ADC could be a promising therapeutic approach for treating HNSCC patients.

Prognostic and therapeutic model based on disulfidptosis-related genes for patients with clear cell renal cell carcinoma

Disulfidptosis, a newly discovered mode of cell death caused by excessive accumulation of intracellular disulfide compounds, is closely associated with tumor development. This study focused on the relationship between disulfidptosis and clear cell renal cell carcinoma (ccRCC). Firstly, the characterizations of disulfidptosis-related genes (DRGs) in ccRCC were showed, which included number variation (CNV), single nucleotide variation (SNV), DNA methylation, mRNA expression and gene mutation. Then, the ccRCC samples were classified into three clusters through unsupervised clustering based on DRGs. Survival and pathway enrichment differences were evaluated among the three clusters. Subsequently, the differentially expressed genes (DEGs) among the three clusters were screened by univariate Cox, LASSO, and multivariate Cox analysis, and five key DEGs were obtained. Based on the five key DEGs, the ccRCC samples were reclassified into two geneclusters and the survival differences and immune cell infiltration between two geneclusters was investigated. In next step, ccRCC samples were divided into two groups according to PCA scores of five key DEGs, namely high PCA score group (HPSG) and low PCA score group (LPSG). On this basis, differences in survival prognosis, immune cell infiltration and correlation with immune checkpoint, as well as differences in sensitivity to targeted drugs were compared between HPSG and LPSG. The expression levels of four immune checkpoints were higher in HPSG than in LPSG, whereas the LPSG was more sensitive to targeted drug therapy than the HPSG. Finally, validation experiments on HDAC4 indicated that HDAC4 could increase the proliferation and colony formation ability of ccRCC cells.

Amino acid transporters within the solute carrier superfamily: Underappreciated proteins and novel opportunities for cancer therapy

BACKGROUND

Solute carrier (SLC) transporters, a diverse family of membrane proteins, are instrumental in orchestrating the intake and efflux of nutrients including amino acids, vitamins, ions, nutrients, etc, across cell membranes. This dynamic process is critical for sustaining the metabolic demands of cancer cells, promoting their survival, proliferation, and adaptation to the tumor microenvironment (TME). Amino acids are fundamental building blocks of cells and play essential roles in protein synthesis, nutrient sensing, and oncogenic signaling pathways. As key transporters of amino acids, SLCs have emerged as crucial players in maintaining cellular amino acid homeostasis, and their dysregulation is implicated in various cancer types. Thus, understanding the intricate connections between amino acids, SLCs, and cancer is pivotal for unraveling novel therapeutic targets and strategies.

SCOPE OF REVIEW

In this review, we delve into the significant impact of amino acid carriers of the SLCs family on the growth and progression of cancer and explore the current state of knowledge in this field, shedding light on the molecular mechanisms that underlie these relationships and highlighting potential avenues for future research and clinical interventions.

MAJOR CONCLUSIONS

Amino acids transportation by SLCs plays a critical role in tumor progression. However, some studies revealed the tumor suppressor function of SLCs. Although several studies evaluated the function of SLC7A11 and SLC1A5, the role of some SLC proteins in cancer is not studied well. To exert their functions, SLCs mediate metabolic rewiring, regulate the maintenance of redox balance, affect main oncogenic pathways, regulate amino acids bioavailability within the TME, and alter the sensitivity of cancer cells to therapeutics. However, different therapeutic methods that prevent the function of SLCs were able to inhibit tumor progression. This comprehensive review provides insights into a rapidly evolving area of cancer biology by focusing on amino acids and their transporters within the SLC superfamily.

Metabolic Responses of Lung Adenocarcinoma Cells to Survive under Stressful Conditions Associated with Tumor Microenvironment

Solid tumors frequently present a heterogeneous tumor microenvironment. Because tumors have the potential to proliferate quickly, the consequence is a reduction in the nutrients, a reduction in the pH (<6.8), and a hypoxic environment. Although it is often assumed that tumor clones show a similar growth rate with little variations in nutrient consumption, the present study shows how growth-specific rate (µ), the specific rates of glucose, lactate, and glutamine consumption (qS), and the specific rates of lactate and glutamate production (qP) of 2D-cultured lung tumor cells are affected by changes in their environment. We determined in lung tumor cells (A427, A549, Calu-1, and SKMES-1) the above mentioned kinetic parameters during the exponential phase under different culture conditions, varying the predominant carbon source, pH, and oxygen tension. MCF-7 cells, a breast tumor cell line that can consume lactate, and non-transformed fibroblast cells (MRC-5) were included as controls. We also analyzed how cell-cycle progression and the amino acid transporter CD98 expression were affected. Our results show that: (1) In glucose presence, μ increased, but qS Glucose and qP Lactate decreased when tumor cells were cultured under acidosis as opposed to neutral conditions; (2) most lung cancer cell lines consumed lactate under normoxia or hypoxia; (3) although qS Glutamine diminished under hypoxia or acidosis, it slightly increased in lactate presence, a finding that was associated with CD98 upregulation; and (4) under acidosis, G0/G1 arrest was induced in A427 cancer cells, although this phenomenon was significantly increased when glucose was changed by lactate as the predominant carbon-source. Hence, our results provide an understanding of metabolic responses that tumor cells develop to survive under stressful conditions, providing clues for developing promising opportunities to improve traditional cancer therapies.

CD98 heavy chain as a prognostic biomarker and target for cancer treatment

The SLC3A2 gene encodes for a cell-surface transmembrane protein CD98hc (4F2). CD98hc serves as a chaperone for LAT1 (SLC7A5), LAT2 (SLC7A8), y+LAT1 (SLC7A7), y+LAT2 (SLC7A6), xCT (SLC7A11) and Asc1 (SLC7A10) providing their recruitment to the plasma membrane. Together with the light subunits, it constitutes heterodimeric transmembrane amino acid transporters. CD98hc interacts with other surface molecules, such as extracellular matrix metalloproteinase inducer CD147 (EMMPRIN) and adhesion receptors integrins, and regulates glucose uptake. In this way, CD98hc connects the signaling pathways sustaining cell proliferation and migration, biosynthesis and antioxidant defense, energy production, and stem cell properties. This multifaceted role makes CD98hc one of the critical regulators of tumor growth, therapy resistance, and metastases. Indeed, the high expression levels of CD98hc were confirmed in various tumor tissues, including head and neck squamous cell carcinoma, glioblastoma, colon adenocarcinoma, pancreatic ductal adenocarcinoma, and others. A high expression of CD98hc has been linked to clinical prognosis and response to chemo- and radiotherapy in several types of cancer. In this mini-review, we discuss the physiological functions of CD98hc, its role in regulating tumor stemness, metastases, and therapy resistance, and the clinical significance of CD98hc as a tumor marker and therapeutic target.

Anti-proliferation and anti-migration effects of Yishen Tongbi decoction in experimental rheumatoid arthritis by suppressing SLC3A2/integrin β3 signaling pathways

BACKGROUND

Yishen Tongbi (YSTB) decoction is a patented herbal formula that is used in China to treat rheumatoid arthritis (RA); however, the exact mechanism of its anti-synovial hyperplasia efficacy has not been fully elucidated.

PURPOSE

Based on our previous proteomics study, we aimed to reveal whether YSTB inhibits the proliferation and migration of RA-FLSs through the SLC3A2/integrin β3 pathway in vivo and in vitro.

STUDY DESIGN

The study design consists of three parts, a comparison of the expression of SLC3A2 and integrin β3 in synovial tissues of RA and OA patients; an animal experiment to verify the pharmacodynamic effect of YSTB, and in vitro experiment to elucidate the specific mechanism of YSTB.

METHODS

The expression of SLC3A2 and integrin β3 in the synovial tissues of patients with RA and osteoarthritis (OA) patients were detected by immunohistochemistry (IHC). In vitro, firstly, the proliferation and migration abilities of HFLS (human fibroblast-like synoviocytes) and HFLS-RA (human fibroblast-like synoviocytes-RA) cells were compared by EdU staining and wound healing assays, respectively, and the differences in the expression and localization of SLC3A2, integrin β3, p-FAK and p-Src between HFLS and HFLS-RA cells were detected by IF and WB. In vivo, DBA/1 mice were injected with bovine collagen II to construct a CIA mouse model. Paw swelling, body weight and the arthritis index (AI) were used as basic treatment evaluation indicators for YSTB. Micro-CT and histopathological analyses of the knee and ankle joints were also performed. In addition, the expression of SLC3A2, integrin β3, p-FAK and p-Src in the synovial tissue of mice was detected by IHC. Subsequently, CCK-8 was used to screen for suitable concentrations of YSTB for use in HFLS-RA cells. EdU staining and transwell migration assays were performed to evaluate the inhibitory effect of YSTB on cell proliferation and migration, and WB was conducted to assess whether YSTB inhibited HFLS-RA migration through downregulation of the SLC3A2/integrin β3 pathways.

RESULTS

IHC showed that the expression of SLC3A2 and integrin β3 was higher in RA synovial tissues than in OA tissues. In vivo experiments showed that YSTB inhibited synovial hyperplasia, prevented bone destruction, and reduced the expression of SLC3A2, integrin β3, p-FAK and p-Src. In vitro experiments showed that YSTB inhibited HFLS-RA migration and proliferation by inhibiting the expression of SLC3A2/integrin β3 and downstream signaling molecules.

CONCLUSION

YSTB inhibits the proliferation and migration of synovial fibroblasts in RA by downregulating the SLC3A2/integrin β3 pathways.

Identification of the target protein and molecular mechanism of honokiol in anti-inflammatory action

BACKGROUND

Searching the targets of natural products is very important for drug discovery and elucidating the mechanism of drug action and disease. Honokiol (HK), as the major active component of Magnolia officinalis Rehder & E.H.Wilson, has been widely used in medicine and cosmetics. Among its bioactivities, its anti-inflammatory activity is particularly impressive. However, the target protein of HK in anti-inflammatory action and its regulatory mechanism are unclear.

PURPOSE

Here, we identified the target protein and molecular mechanism of the anti- inflammatory action of HK.

METHODS

First, an LPS-induced septic shock model and DSS-induced ulcerative colitis model were used to assess the anti-inflammatory efficacy of HK. Second, the drug affinity responsive target stability, proteomics analysis, thermal shift assays and cellular thermal shift assays were used to identify and validate the target of HK. Finally, western blot, ELISA, LDH immunofluorescence staining, shRNA and LC/MS for L-leucine analysis were performed to determine the mechanism of the anti-inflammatory action of HK.

RESULTS

This study revealed that HK significantly alleviated LPS-induced septic shock and DSS-induced ulcerative colitis in vivo, suggesting that HK has significant anti-inflammatory activity. HK treatment dramatically reduced IL-1β release and caspase-1 activation at different time points, showing that HK could inhibit both NLRP3 inflammasome priming and activation processes in cells. HK also suppressed adaptor apoptosis speck-like protein oligomerization. Mechanistically, SLC3A2 was identified as a direct target of HK in THP-1 cells. HK downregulated SLC3A2 expression by promoting its degradation via proteasome-mediated proteolysis. Further study demonstrated that HK triggered SLC3A2 to suppress NLRP3 inflammasome activation by significantly reducing the content of L-leucine transported into cells and lysosomes to block the mTORC1 pathway.

CONCLUSIONS

Our work identified HK as a promising anti-inflammatory drug candidate through the SLC3A2/L-leucine/mTORC1/NLRP3 pathways.

Both In Situ and Circulating SLC3A2 Could Be Used as Prognostic Markers for Human Lung Squamous Cell Carcinoma and Lung Adenocarcinoma

Simple Summary

With the continuous progress of diagnosis and treatment technology, the early diagnosis rate and survival rate of lung cancer have improved, but the incidence rate and mortality rate of lung cancer are still very high. Therefore, it has become an urgent problem to analyze the molecular mechanism of lung cancer and to determine the markers related to early diagnosis. SLC3A2 protein is a cell-surface marker that plays an important role in tumorigenesis and development, and it is expected to become a new target for the treatment of tumors. The in-depth study of SLC3A2 can provide a new molecular target for the early diagnosis, treatment, and prognosis of lung cancer.

Abstract

SLC3A2, the heavy chain of the CD98 protein, is highly expressed in many cancers, including lung cancer. It can regulate the proliferation and the metastasis of cancer cells via the integrin signaling pathway. Liquid biopsy is a novel method for tumor diagnosis. The diagnostic or prognostic roles of serum SLC3A2 in lung cancer are still not clear. In this study, we analyzed SLC3A2 mRNA levels in human lung squamous cell carcinoma (LUSC) and lung adenocarcinoma (LUAD) using the TCGA database and serum SLC3A2 protein levels using ELISA. We confirmed high SLC3A2 levels in both the serum and tissue of LUAD and LUSC patients. Both serum and tissue SLC3A2 could be used as prognostic markers for overall LUAD and subgroups of LUSC patients. SLC3A2 induced tumorigenesis via the MEK/ERK signaling pathway in LUAD and LUSC cells.

Expression of CD98hc in Pancreatic Cancer and Its Role in Cancer Cell Behavior

Background: Cluster of differentiation 98 heavy chain (CD98hc) is a transmembrane protein, which functions both as a coreceptor of ß-integrins, enhancing intracellular integrin-dependent downstream signaling, and as a transporter of branched-chain and aromatic amino acids. As such, it is pivotal in cell cycle regulation and protection of oxidative, nutritional and DNA replication stress. Overexpression of CD98hc occurs widely in cancer cells and is associated with poor clinical prognosis. The role of CD98hc in pancreatic cancer remains to be elucidated. The aim of this study was to determine the expression of CD98hc in pancreatic ductal adenocarcinoma and to define its potential functional role in cancer cell biology.

Methods: Immunohistochemical staining for CD98hc was performed on 222 tissue samples of patients with pancreatic ductal adenocarcinoma. The pancreatic cancer cell lines PANC-1 and BxPC-3 were used to determine the effect of CD98hc expression on cancer cell behavior using cell adhesion, cell trans-migration and cell spreading assays. Flow cytometry was performed to study the rate of apoptosis after detachment or serum starvation. shRNA-lentiviral constructs were used to knock down or reconstitute full length or mutated CD98hc.

Results: Up to 20% of pancreatic ductal adenocarcinomas express CD98hc in the acinar cells (13%) and islet cells (20%) embedded in tumor tissue. Although expression of CD98hc in tumor tissue was not associated with a particular tumor stage or grade, our data show a trend towards longer overall survival of pancreatic cancer patients without CD98hc expression as compared to those with immunohistochemical positivity. In vitro downregulation of CD98hc in the pancreatic cancer cell lines PANC-1 and BxPC-3 significantly inhibits cell proliferation (p<0.05), self-renewal (p<0.05) and anchorage-independent growth (p<0.05).

Conclusion: CD98hc is expressed in a remarkable percentage of pancreatic ductal adenocarcinomas. Due to its important role in cell behavior and malignant cell transformation, it may be a promising molecular target for potential new therapeutic approaches in pancreatic cancer in the future.

CD98hc has a pivotal role in maintaining the immuno-barrier integrity of basal layer cells in esophageal epithelium

OBJECTIVES

The current study aims to find the linker between esophageal epithelial carcinogenesis and chronic inflammation and the origin of hyperproliferative cells in precancerous lesions of esophageal squamous cell carcinoma (ESCC).

MATERIALS AND METHODS

Twenty one normal esophageal tissues from cadavers and 180 paired tissues from 60 surgical resected ESCC specimens were utilized for immunohistochemistry staining against CK14, CK6, CD98hc and Ki67. NE6 cell line was treated with H₂O₂ to mimic chronic inflammation microenvironment and TPA for malignant orientated transformation. Cell proliferation and CD98hc mRNA were assessed by CCK8 assay and RT-qPCR.

RESULTS

CD98hc expression was correlated with chronic inflammation severity, precancerous lesion stage, and epithelial cell proliferative activity. CD98hc expression and proliferation rate of NE6 were up regulated by low dose H₂O₂ treatment and long term TPA treatment. The proliferating cells in hyperplastic and dysplastic tissues could be divided into two patterns by the expression of CK14, CD98hc, CK6 and Ki67: CK14⁺CD98hc⁺CK6^-Ki67^- in basal cells with CK14^-CD98hc^-CK6⁺Ki67⁺ in proliferating cells and CK14⁺CD98hc⁺CK6⁺Ki67⁺ in both basal cells and proliferating cells.

CONCLUSIONS

Our study revealed that CD98hc was a marker of cells originated from basal cell in esophagus, ectopic expression of CD98hc in hyperplastic/dysplastic cells by chronic inflammation stimulation crippled the linkage between basal cell and basement membrane, sabotaged the integrity of the barrier in between lamina propria and epithelium, subsequentially initiate carcinogenesis.

SLC3A2 inhibits ferroptosis in laryngeal carcinoma via mTOR pathway

Objective

This study aimed to explore the mRNA and protein expression of SLC3A2 in laryngeal carcinoma cells and tissues, and functional regulatory mechanism of SLC3A2 in cell ferroptosis of laryngeal carcinoma.

Methods

We chose the key gene-SLC3A2 of DEGs from TCGA by bioinformatics analysis, and then we constructed stable knockdown of SLC3A2 in laryngeal carcinoma cells. MTT assay and clonogenic assay were used to determine cell viability and cell growth, respectively. The mRNA and protein expression were determined by RT-qPCR and western blotting, respectively. Xenograft tumor model was used to determine the role of SLC3A2 in tumor growth.

Results

The results of limma analysis recovered that 92 genes were involved in both upregulated DEGs and high risk of poor prognosis, whereas 36 genes were involved in both downregulated DEGs and low risk of poor prognosis. Pathway enrichment analysis indicated that mTOR signaling pathway and ferroptosis exerted a role in regulating these intersection genes. Moreover, SLC3A2 is a key gene in ferroptosis in laryngeal carcinoma. SLC3A2 is highly expressed in laryngeal carcinoma tissues and cells. Patients with high SLC3A2 expression exerted poor survival. SLC3A2 deficiency inhibited cell proliferation and foci formation. Furthermore, knockdown of SLC3A2 expression induced the efficacy of ferroptosis and suppressed ferroptosis related proteins expression. Mechanically, SLC3A2 deficiency facilitated ferroptosis through upregulating the expression of mTOR and P70S6K, whereas inhibited p-mTOR and p-P70S6K expression in laryngeal carcinoma cells. SLC3A2 deficiency inhibited tumorigenesis in nude mice.

Conclusion

Our study suggests that SLC3A2 negatively regulates ferroptosis through mTOR pathway in laryngeal carcinoma.

The Ectodomains of rBAT and 4F2hc Are Fake or Orphan α-Glucosidases

It is known that 4F2hc and rBAT are the heavy subunits of the heteromeric amino acid transporters (HATs). These heavy subunits are N-glycosylated proteins, with an N-terminal domain, one transmembrane domain and a bulky extracellular domain (ectodomain) that belongs to the α-amylase family. The heavy subunits are covalently linked to a light subunit from the SLC7 family, which is responsible for the amino acid transport activity, forming a heterodimer. The functions of 4F2hc and rBAT are related mainly to the stability and trafficking of the HATs in the plasma membrane of vertebrates, where they exert the transport activity. Moreover, 4F2hc is a modulator of integrin signaling, has a role in cell fusion and it is overexpressed in some types of cancers. On the other hand, some mutations in rBAT are found to cause the malfunctioning of the b0,+ transport system, leading to cystinuria. The ectodomains of 4F2hc and rBAT share both sequence and structure homology with α-amylase family members. Very recently, cryo-EM has revealed the structure of several HATs, including the ectodomains of rBAT and 4F2hc. Here, we analyze available data on the ectodomains of rBAT and 4Fhc and their relationship with the α-amylase family. The physiological relevance of this relationship remains largely unknown.

Role of CD98 in liver disease

CD98 is a multifunctional glycoprotein that is involved in various biological processes such as amino acid transport, cell adhesion, diffusion, adhesion, and proliferation. The role of CD98 in liver disease has not thoroughly been examined and is limited reports in the literature. Among these reports, direct association for CD98 in nonalcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC) have been reported. Our lab has reported that targeting CD98 in high fat diet mice reduced steatosis and inflammation in NAFLD. Other reports associate CD98 in HCC due in part to the role of CD98 in activating integrin signaling. Herein, we present CD98 staining on liver biopsies from NAFLD, chronic active hepatitis, cirrhosis, and 3 stages of HCC to demonstrate the upregulation of CD98 expression throughout liver disease progression. In addition, we analyze current literature to elucidate roles and potential roles of CD98 with each stage of liver disease.

Amino acid transporter LAT1 (SLC7A5) as a molecular target for cancer diagnosis and therapeutics

Cancer cells require a massive supply of nutrients, including sugars and amino acids-the upregulation of transporters for each nutrient contributes to meet the demand. Distinct from glucose transporters, amino acid transporters include ones whose expression is specific to cancer cells. For example, LAT1 (SLC7A5) displays protein expression mostly limited to the plasma membrane of cancer cells. The exceptions are the placental barrier and the blood-brain barrier, where immunohistochemical and mass spectrometric studies have shown LAT1 expression, although their levels are supposed to be lower than those in cancers. The expression of LAT1 has been reported in cancers from various tissue origins, where high LAT1 expression is related to the poor prognosis of patients. LAT1 is essential for cancer cell growth because the pharmacologic inhibition and knockdown/knockout of LAT1 suppress the proliferation of cancer cells and the growth of xenograft tumors. The inhibition of LAT1 suppresses protein synthesis by downregulating the mTORC1 signaling pathway and mobilizing the general amino acid control (GAAC) pathway in cancer cells. LAT1 is, thus, a candidate molecular target for the diagnosis and therapeutics of cancers. ¹⁸F-labeled 3-fluoro-l-α-methyl-tyrosine (FAMT) is used as a LAT1-specific PET probe for cancer detection due to the LAT1 specificity of α-methyl aromatic amino acids. FAMT accumulation is cancer-specific and avoids non-cancer lesions, including inflammation, confirming the cancer-specific expression of LAT1 in humans. Due to the cancer-specific nature, LAT1 can also be used for cancer-specific delivery of anti-tumor agents such as l-para-boronophenylalanine used for boron neutron capture therapy and α-emitting nuclide-labeled LAT1 substrates developed for nuclear medicine treatment. Based on the importance of LAT1 in cancer progression, high-affinity LAT1-specific inhibitors have been developed for anti-tumor drugs. JPH203 (KYT0353) is such a compound designed based on the structure-activity relationship of LAT1 ligands. It is one of the highest-affinity inhibitors with less affecting other transporters. It suppresses tumor growth in vivo without significant toxicity in preclinical studies at doses enough to suppress tumor growth. In the phase-I clinical trial, JPH203 appeared to provide promising activity. Because the mechanisms of action of LAT1 inhibitors are novel, with or without combination with other anti-tumor drugs, they could contribute to the treatment of cancers that do not respond to current therapy. The LAT1-specific PET probe could also be used as companion diagnostics of the LAT1-targeting therapies to select patients to whom therapeutic benefits could be expected. Recently, the cryo-EM structure of LAT1 has been solved, which would facilitate the understanding of the mechanisms of the dynamic interaction of ligands and the binding site, and further designing new compounds with higher activity.

Effects of Donor-Recipient Age Difference in Renal Transplantation, an Investigation on Renal Function and Fluid Proteome

Introduction

Our previous study revealed that a young internal environment ameliorated kidney aging by virtue of an animal model of heterochronic parabiosis and a model of heterochronic renal transplantation. In this research, we used proteome to investigate the effects of donor-recipient age difference in clinical renal transplantation.

Methods

This study included 10 pairs of renal transplantation donors and recipients with an age difference of greater than 20 years to their corresponding recipients/donors. All recipients have received transplantation more than 3 years ago. Renal function and the serum/urine proteomes of the donors and recipients were analyzed.

Results

The renal function was similar between the young recipients and the old donors. In contrast, the renal function of the young donors was significantly superior to that of the old recipients. Furthermore, 497 and 975 proteins were identified in the serum and urine proteomes, respectively. The content of SLC3A2 in the blood was found to be related to aging, while the contents of SERPINA1 and SERPINA3 in the urine were related to immune functions after renal transplantation.

Conclusion

This study demonstrated that, in the human body, a younger internal environment could ameliorate kidney aging and provided not only clinical evidence for increasing the age limit of kidney transplant donors but also new information for kidney aging research.

Oncogenic transformation of NIH/3T3 cells by the overexpression of L-type amino acid transporter 1, a promising anti-cancer target

L-type amino acid transporter 1 (LAT1)/SLC7A5 is the first identified CD98 light chain disulfide linked to the CD98 heavy chain (CD98hc/SLC3A2). LAT1 transports large neutral amino acids, including leucine, which activates mTOR, and is highly expressed in human cancers. We investigated the oncogenicity of human LAT1 introduced to NIH/3T3 cells by retrovirus infection. NIH/3T3 cell lines stably expressing human native (164C) or mutant (164S) LAT1 (naLAT1/3T3 or muLAT1/3T3, respectively) were established. We confirmed that endogenous mouse CD98hc forms a disulfide bond with exogenous human LAT1 in naLAT1/3T3, but not in muLAT1/3T3. Endogenous mouse CD98hc mRNA increased in both naNIH/3T3 and muLAT1/3T3, and a similar amount of exogenous human LAT1 protein was detected in both cell lines. Furthermore, naLAT1/3T3 and muLAT1/3T3 cell lines were evaluated for cell growth-related phenotypes (phosphorylation of ERK, cell-cycle progression) and cell malignancy-related phenotypes (anchorage-independent cell growth, tumor formation in nude mice). naLAT1/3T3 had stronger growth- and malignancy- related phenotypes than NIH/3T3 and muLAT1/3T3, suggesting the oncogenicity of native LAT1 through its interaction with CD98hc. Anti-LAT1 monoclonal antibodies significantly inhibited in vitro cell proliferation and in vivo tumor growth of naLAT1/3T3 cells in nude mice, demonstrating LAT1 to be a promising anti-cancer target.

Identification of Tumor Microenvironment-Related Alternative Splicing Events to Predict the Prognosis of Endometrial Cancer

Background

Endometrial cancer (EC) is one of the most common female malignant tumors. The immunity is believed to be associated with EC patients’ survival, and growing studies have shown that aberrant alternative splicing (AS) might contribute to the progression of cancers.

Methods

We downloaded the clinical information and mRNA expression profiles of 542 tumor tissues and 23 normal tissues from The Cancer Genome Atlas (TCGA) database. ESTIMATE algorithm was carried out on each EC sample, and the OS-related different expressed AS (DEAS) events were identified by comparing the high and low stromal/immune scores groups. Next, we constructed a risk score model to predict the prognosis of EC patients. Finally, we used unsupervised cluster analysis to compare the relationship between prognosis and tumor immune microenvironment.

Results

The prognostic risk score model was constructed based on 16 OS-related DEAS events finally identified, and then we found that compared with high-risk group the OS in the low-risk group was notably better. Furthermore, according to the results of unsupervised cluster analysis, we found that the better the prognosis, the higher the patient’s ESTIMATE score and the higher the infiltration of immune cells.

Conclusions

We used bioinformatics to construct a gene signature to predict the prognosis of patients with EC. The gene signature was combined with tumor microenvironment (TME) and AS events, which allowed a deeper understanding of the immune status of EC patients, and also provided new insights for clinical patients with EC.

Epigenetic Alterations in Renal Cell Cancer With TKIs Resistance: From Mechanisms to Clinical Applications

The appearance of tyrosine kinase inhibitors (TKIs) has been a major breakthrough in renal cell carcinoma (RCC) therapy. Unfortunately, a portion of patients with TKIs resistance experience disease progression after TKIs therapy. Epigenetic alterations play an important role in the development of TKIs resistance. Current evidence suggests that epigenetic alterations occur frequently in RCC patients with poor response to TKIs therapy, and modulation of them could enhance the cytotoxic effect of antitumor therapy. In this review, we summarize the currently known epigenetic alterations relating to TKIs resistance in RCC, focusing on DNA methylation, non-coding RNAs (ncRNAs), histone modifications, and their interactions with TKIs treatment. In addition, we discuss application of epigenetic alteration analyses in the clinical setting to predict prognosis of patients with TKIs treatment, and the potential use of epigenetics-based therapies to surmount TKIs resistance.

Identification of AR-V7 downstream genes commonly targeted by AR/AR-V7 and specifically targeted by AR-V7 in castration resistant prostate cancer

Primary prostate cancer (PC) progresses to castration-resistant PC (CRPC) under androgen deprivation therapy, by mechanisms e.g. expression of androgen receptor (AR) splice variant-7 (AR-V7). Here we conducted comprehensive epigenome and transcriptome analyses comparing LNCaP, primary PC cells, and LNCaP95, AR-V7-expressing CRPC cells derived from LNCaP. Of 399 AR-V7 target regions identified through ChIP-seq analysis, 377 could be commonly targeted by hormone-stimulated AR, and 22 were specifically targeted by AR-V7. Among genes neighboring to these AR-V7 target regions, 78 genes were highly expressed in LNCaP95, while AR-V7 knockdown led to significant repression of these genes and suppression of growth of LNCaP95. Of the 78 AR-V7 target genes, 74 were common AR/AR-V7 target genes and 4 were specific AR-V7 target genes; their most suppressed genes by AR-V7 knockdown were NUP210 and SLC3A2, respectively, and underwent subsequent analyses. NUP210 and SLC3A2 were significantly upregulated in clinical CRPC tissues, and their knockdown resulted in significant suppression of cellular growth of LNCaP95 through apoptosis and growth arrest. Collectively, AR-V7 contributes to CRPC proliferation by activating both common AR/AR-V7 target and specific AR-V7 target, e.g. NUP210 and SLC3A2.

Regulation of stem cell function and neuronal differentiation by HERV-K via mTOR pathway

Stem cells are capable of unlimited proliferation but can be induced to form brain cells. Factors that specifically regulate human development are poorly understood. We found that human stem cells expressed high levels of the envelope protein of an endogenized human-specific retrovirus (HERV-K, HML-2) from loci in chromosomes 12 and 19. The envelope protein was expressed on the cell membrane of the stem cells and was critical in maintaining the stemness via interactions with CD98HC, leading to triggering of human-specific signaling pathways involving mammalian target of rapamycin (mTOR) and lysophosphatidylcholine acyltransferase (LPCAT1)-mediated epigenetic changes. Down-regulation or epigenetic silencing of HML-2 env resulted in dissociation of the stem cell colonies and enhanced differentiation along neuronal pathways. Thus HML-2 regulation is critical for human embryonic and neurodevelopment, while it's dysregulation may play a role in tumorigenesis and neurodegeneration.

LncRNA SNHG1 contributes to sorafenib resistance by activating the Akt pathway and is positively regulated by miR-21 in hepatocellular carcinoma cells

Background

Acquired resistance to sorafenib greatly limits its therapeutic efficiency in the treatment of hepatocellular carcinoma (HCC). Increasing evidence indicates that long noncoding RNAs (lncRNAs) play important roles in the resistance to anti-cancer drugs. The present study aims to explore the involvement of lncRNA SNHG1 (small nucleolar RNA host gene 1) in sorafenib resistance and how SNHG1 is associated with overexpressed microRNA-21 (miR-21) and the activated Akt pathway, which have been demonstrated to mediate this resistance in HCC cells.

Methods

Sorafenib-resistant HCC (SR-HCC) cells were generated and their sorafenib-resistant properties were confirmed by cell viability and apoptosis assays. Potential lncRNAs were screened by using multiple bioinformatics analyses and databases. The expression of genes and proteins was detected by qRT-PCR, Western blot and in situ hybridization. Gene silencing was achieved by specific siRNA or lncRNA Smart Silencer. The effects of anti-SNHG1 were evaluated in vitro and in experimental animals by using quantitative measures of cell proliferation, apoptosis and autophagy. The binding sites of miR-21 and SNHG1 were predicted by using the RNAhybrid algorithm and their interaction was verified by luciferase assays.

Results

The Akt pathway was highly activated by overexpressed miR-21 in SR-HCC cells compared with parental HCC cells. Among ten screened candidates, SNHG1 showed the largest folds of alteration between SR-HCC and parental cells and between vehicle- and sorafenib-treated cells. Overexpressed SNHG1 contributes to sorafenib resistance by activating the Akt pathway via regulating SLC3A2. Depletion of SNHG1 enhanced the efficacy of sorafenib to induce apoptosis and autophagy of SR-HCC cells by inhibiting the activation of Akt pathway. Sorafenib induced translocation of miR-21 to the nucleus, where it promoted the expression of SNHG1, resulting in upregulation of SLC3A2, leading to the activation of Akt pathway. In contrast, SNHG1 was shown to have little effect on the expression of miR-21, which downregulated the expression of PTEN, leading to the activation of the Akt pathway independently of SNHG1.

Conclusions

The present study has demonstrated that lncRNA SNHG1 contributes to sorafenib resistance by activating the Akt pathway and its nuclear expression is promoted by miR-21, whose nuclear translocation is induced by sorafenib. These results indicate that SNHG1 may represent a potentially valuable target for overcoming sorafenib resistance for HCC.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1177-0) contains supplementary material, which is available to authorized users.

The combined expression of solute carriers is associated with a poor prognosis in highly proliferative ER+ breast cancer

PURPOSE

Breast cancer (BC) is a heterogeneous disease characterised by variant biology, metabolic activity, and patient outcome. Glutamine availability for growth and progression of BC is important in several BC subtypes. This study aimed to evaluate the biological and prognostic role of the combined expression of key glutamine transporters, SLC1A5, SLC7A5, and SLC3A2 in BC with emphasis on the intrinsic molecular subtypes.

METHODS

SLC1A5, SLC7A5, and SLC3A2 were assessed at the protein level, using immunohistochemistry on tissue microarrays constructed from a large well-characterised BC cohort (n = 2248). Patients were stratified into accredited clusters based on protein expression and correlated with clinicopathological parameters, molecular subtypes, and patient outcome.

RESULTS

Clustering analysis of SLC1A5, SLC7A5, and SLC3A2 identified three clusters low SLCs (SLC1A5-/SLC7A5-/SLC3A2-), high SLC1A5 (SLC1A5+/SLC7A5-/SLC3A2-), and high SLCs (SLC1A5+/SLC7A5+/SLC3A2+) which had distinct correlations to known prognostic factors and patient outcome (p < 0.001). The key regulator of tumour cell metabolism, c-MYC, was significantly expressed in tumours in the high SLC cluster (p < 0.001). When different BC subtypes were considered, the association with the poor outcome was observed in the ER+ high proliferation/luminal B class only (p = 0.003). In multivariate analysis, SLC clusters were independent risk factor for shorter BC-specific survival (p = 0.001).

CONCLUSION

The co-operative expression of SLC1A5, SLC7A5, and SLC3A2 appears to play a role in the aggressive subclass of ER+ high proliferation/luminal BC, driven by c-MYC, and therefore have the potential to act as therapeutic targets, particularly in synergism.

Anti-tumor effects of mAb against L-type amino acid transporter 1 (LAT1) bound to human and monkey LAT1 with dual avidity modes

l‐Type amino acid transporter 1 (LAT1) disulfide linked to CD98 heavy chain (hc) is highly expressed in most cancer cells, but weakly expressed in normal cells. In the present study, we developed novel anti‐LAT1 mAbs and showed internalization activity, inhibitory effects of amino acid uptake and cell growth and antibody‐dependent cellular cytotoxicity, as well as in vivo antitumor effects in athymic mice. Furthermore, we examined the reactivity of mAbs with LAT1 of Macaca fascicularis to evaluate possible side‐effects of antihuman LAT1 mAbs in clinical trials. Antihuman LAT1 mAbs reacted with ACHN human and MK.P3 macaca kidney‐derived cells, and this reactivity was significantly decreased by siRNAs against LAT1. Macaca LAT1 cDNA was cloned from MK.P3, and only two amino acid differences between human and macaca LAT1 were seen. RH7777 rat hepatoma and HEK293 human embryonic kidney cells expressing macaca LAT1 were established as stable transfectants, and antihuman LAT1 mAbs were equivalently reactive against transfectants expressing human or macaca LAT1. Dual (high and low) avidity modes were detected in transfectants expressing macaca LAT1, MK.P3, ACHN and HCT116 human colon cancer cells, and K_A values were increased by anti‐CD98hc mAb, suggesting anti‐LAT1 mAbs detect an epitope on LAT1‐CD98hc complexes on the cell surface. Based on these results, LAT1 may be a promising anticancer target and Macaca fascicularis can be used in preclinical studies with antihuman LAT1 mAbs.

CircSLC3A2 functions as an oncogenic factor in hepatocellular carcinoma by sponging miR-490-3p and regulating PPM1F expression

Background

Non-coding RNAs (ncRNAs) have been reported to participate in tumor progression by regulating gene expression. Previous studies showed that protein phosphatase Mg2⁺/Mn2⁺ dependent 1F (PPM1F) acts a dual role in cancer growth and metastasis. But, the underlying mechanisms by which ncRNAs regulate PPM1F expression in hepatocellular carcinoma (HCC) are poorly understood.

Methods

The association between PPM1F or miR-490-3p expression and clinicopathological features and prognosis in patients with HCC was analyzed by TCGA RNA-sequencing data. CircSLC3A2 was identified to bind with miR-490-3p by bioinformatic analysis, and the binding sites between miR-490-3p and PPM1F or circSLC3A2 were confirmed by dual luciferase report and RNA immunoprecipitation (RIP) assays. The localization and clinical significance of miR-490-3p and circSLC3A2 in patients with HCC were investigated by fluorescence in situ hybridization (FISH). MTT, Agar, and Transwell assays were conducted to evaluate the effects of miR-490-3p or circSLC3A2 on cell proliferation and invasive potential.

Results

The expression of PPM1F or miR-490-3p was associated with poor survival and tumor recurrence, and acted as an independent prognostic factor in patients with HCC. Re-expression of miR-490-3p inhibited HCC cell proliferation and invasion by targeting PPM1F, but its inhibitor reversed these effects. Moreover, circSLC3A2, predominantly localized in the cytoplasm, exhibited an oncogenic role by sponging miR-490-3p and regulating PPM1F expression, and harbored a positive correlation with poor survival in patients with HCC.

Conclusion

CircSLC3A2 acts as an oncogenic factor in HCC by sponging miR-490-3p and regulating PPM1F expression.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0909-7) contains supplementary material, which is available to authorized users.

Overexpression of CD98 in intestinal epithelium dysregulates miRNAs and their targeted proteins along the ileal villus-crypt axis

CD98 has been implicated in the experimental model of inflammatory bowel disease. We have previously shown that IEC-specific overexpression of CD98 mediates intestinal inflammation and intestinal epithelial barrier dysfunction. Mice overexpressing CD98 exhibited severe colitis and a greater susceptibility to CAC. Here we demonstrated CD98 overexpression to dysregulate homeostatic gradient profile of miRNA and protein expression along the ileal villus-crypt axis. Using miRNA-target gene prediction module, we observed differentially expressed miRNAs to target proteins of villus and crypt profoundly affected by CD98 overexpression. We have utilized online bioinformatics as methods to further scrutinize the biological meanings of miRNA-target data. We identified significant interactions among the differentially regulated proteins targeted by altered miRNAs in Tg mice. The biological processes affected by the predicted targets of miRNAs deviate from the homeostatic functions of the miRNA-gene-protein axis of the wildtype mice. Our results emphasize a dynamic perturbation of miRNA and protein expression in villus-crypt axis contributing to potential biological consequences of altering CD98 expression. Our findings also suggest the need for a consideration of arrays of interacting biological entities (i.e. miRNAs-mRNAs, protein-protein interaction) or a combination comparison for a better understanding of the disease pathology which is necessary for an effective therapeutic target development.

Hepatitis C Virus Modulates Solute carrier family 3 member 2 for Viral Propagation

Hepatitis C virus (HCV) exploits an extensive network of host proteins to maintain chronic infection. Using RNA-Seq technology, we identified 30 host genes that were differentially expressed in cell culture grown HCV (HCVcc)-infected cells. Of these candidate genes, we selected solute carrier family 3 member 2 (SLC3A2) for further investigation. SLC3A2, also known as CD98hc, is a member of the solute carrier family and encodes a subunit of heterodimeric amino acid transporter. SLC3A2 and LAT1 constitute a heterodimeric transmembrane protein complex that catalyzes amino acid transport. In this study, we showed that HCV upregulated both mRNA and protein expression levels of SLC3A2 and this upregulation occurred through NS3/4A-mediated oxidative stress. HCV also elevated SLC3A2/LAT1 complex level and thus mammalian target of rapamycin complex 1 (mTORC1) signaling was activated. We further showed that L-leucine transport level was significantly increased in Jc1-infected cells as compared with mock-infected cells. Using RNA interference technology, we demonstrated that SLC3A2 was specifically required for the entry step but not for other stages of the HCV life cycle. These data suggest that SLC3A2 plays an important role in regulating HCV entry. Collectively, HCV exploits SLC3A2 for viral propagation and upregulation of SLC3A2 may contribute to HCV-mediated pathogenesis.

Prazosin induced lysosomal tubulation interferes with cytokinesis and the endocytic sorting of the tumour antigen CD98hc

The quinazoline based drug prazosin (PRZ) is a potent inducer of apoptosis in human cancer cells. We recently reported that PRZ enters cells via endocytosis and induces tubulation of the endolysosomal system. In a proteomics approach aimed at identifying potential membrane proteins with binding affinity to quinazolines, we detected the oncoprotein CD98hc. We confirmed shuttling of CD98hc towards lysosomes and upregulation of CD98hc expression in PRZ treated cells. Gene knockout (KO) experiments revealed that endocytosis of PRZ still occurs in the absence of CD98hc - suggesting that PRZ does not enter the cell via CD98hc but misroutes the protein towards tubular lysosomes. Lysosomal tubulation interfered with completion of cytokinesis and provoked endoreplication. CD98hc KO cells showed reduced endoreplication capacity and lower sensitivity towards PRZ induced apoptosis than wild type cells. Thus, loss of CD98hc does not affect endocytosis of PRZ and lysosomal tubulation, but the ability for endoreplication and survival of cells. Furthermore, we found that glutamine, lysomototropic agents - namely chloroquine and NH4Cl - as well as inhibition of v-ATPase, interfere with the intracellular transport of CD98hc. In summary, our study further emphasizes lysosomes as target organelles to inhibit proliferation and to induce cell death in cancer. Most importantly, we demonstrate for the first time that the intracellular trafficking of CD98hc can be modulated by small molecules. Since CD98hc is considered as a potential drug target in several types of human malignancies, our study possesses translational significance suggesting, that old drugs are able to act on a novel target.

A proteomic analysis of chemoresistance development via sequential treatment with doxorubicin reveals novel players in MCF‑7 breast cancer cells

Breast cancer exhibits the highest incidence of all cancer types and is the 2nd leading cause of cancer mortality in women. Up to 82% of breast cancer patients receive a chemotherapy-containing treatment regimen. However, numerous breast tumors recur within 10 years following an initial response and are frequently resistant to previous therapeutic agents. Thus, to analyze the crucial factors, and whether the development of resistance in tumor cells follows certain patterns, is of great importance. In the present study, the clinical treatment schedule of the frequently used chemotherapeutic drug doxorubicin was applied in an in vitro model, the Molecular Evolution Assay (MEA), leading to resistance formation. By investigating the alterations in protein expression in MCF-7 breast cancer cells with three biological replicates, it was observed that the development of resistance to doxorubicin is a multi-directed process. The number and composition of the differentially expressed proteins varied, in addition to the pathways involved in chemoresistance, leading to only a small number of proteins and pathways being commonly regulated in all the MEAs. The proteins 60S ribosomal export protein NMD3 and 4F2 cell-surface antigen heavy chain (SLC3A2) were identified to be the most promising differentially expressed targets; the gene ontology term 'apoptotic signaling pathway' was reduced and 'cell redox homeostasis' was upregulated. Based on the present findings in vitro, it may be hypothesized that the development of resistance in patients is an even more complex process, emphasizing the need for further investigations of resistance development in the clinic to eventually improve patient outcomes.

The multifunctional solute carrier 3A2 (SLC3A2) confers a poor prognosis in the highly proliferative breast cancer subtypes

Breast cancer (BC) is a heterogeneous disease characterised by variant biology, metabolic activity and patient outcome. This study aimed to evaluate the biological and prognostic value of the membrane solute carrier, SLC3A2 in BC with emphasis on the intrinsic molecular subtypes. SLC3A2 was assessed at the genomic level, using METABRIC data (n = 1980), and at the proteomic level, using immunohistochemistry on tissue microarray (TMA) sections constructed from a large well-characterised primary BC cohort (n = 2500). SLC3A2 expression was correlated with clinicopathological parameters, molecular subtypes and patient outcome. SLC3A2 mRNA and protein expression were strongly correlated with higher tumour grade and poor Nottingham prognostic index (NPI). High expression of SLC3A2 was observed in triple-negative (TN), HER2+ and ER+ high-proliferation subtypes. SLC3A2 mRNA and protein expression were significantly associated with the expression of c-MYC in all BC subtypes (p < 0.001). High expression of SLC3A2 protein was associated with poor patient outcome (p < 0.001), but only in the ER+ high-proliferation (p = 0.01) and TN (p = 0.04) subtypes. In multivariate analysis SLC3A2 protein was an independent risk factor for shorter BC-specific survival (p < 0.001). SLC3A2 appears to play a role in the aggressive BC subtypes driven by MYC and could act as a potential prognostic marker. Functional assessment is necessary to reveal its potential therapeutic value in the different BC subtypes.

Curcumin modulates chronic myelogenous leukemia exosomes composition and affects angiogenic phenotype via exosomal miR-21

Tumor derived exosomes are vesicles which contain proteins and microRNAs that mediate cell-cell communication and are involved in angiogenesis and tumor progression. Curcumin derived from the plant Curcuma longa, shows anticancer effects. Exosomes released by CML cells treated with Curcumin contain a high amount of miR-21 that is shuttled into the endothelial cells in a biologically active form. The treatment of HUVECs with CML Curcu-exosomes reduced RhoB expression and negatively modulated endothelial cells motility. We showed that the addition of CML control exosomes to HUVECs caused an increase in IL8 and VCAM1 levels, but Curcu-exosomes reversed these effects thus attenuating their angiogenic properties. This antiangiogenic effect was confirmed with in vitro and in vivo vascular network formation assays. SWATH analysis of the proteomic profile of Curcu-exosomes revealed that Curcumin treatment deeply changes their molecular properties, in particular, Curcumin induces a release of exosomes depleted in pro-angiogenic proteins and enriched in proteins endowed with anti-angiogenic activity. Among the proteins differential expressed we focused on MARCKS, since it was the most modulated protein and a target of miR-21. Taken together our data indicated that also Curcumin attenuates the exosome's ability to promote the angiogenic phenotype and to modulate the endothelial barrier organization.

Methylmercury Uptake into BeWo Cells Depends on LAT2-4F2hc, a System L Amino Acid Transporter

The organic mercury compound methylmercury (MeHg) is able to target the fetal brain. However, the uptake of the toxicant into placental cells is incompletely understood. MeHg strongly binds to thiol-S containing molecules such as cysteine. This MeHg-l-cysteine exhibits some structural similarity to methionine. System L plays a crucial role in placental transport of essential amino acids such as leucine and methionine and thus has been assumed to also transport MeHg-l-cysteine across the placenta. The uptake of methylmercury and tritiated leucine and methionine into the choriocarcinoma cell line BeWo was examined using transwell assay and small interfering (si)RNA mediated gene knockdown. Upon the downregulation of large neutral amino acids transporter (LAT)2 and 4F2 cell-surface antigen heavy chain (4F2hc), respectively, the levels of [³H]leucine in BeWo cells are significantly reduced compared to controls treated with non-targeting siRNA (p < 0.05). The uptake of [³H]methionine was reduced upon LAT2 down-regulation as well as methylmercury uptake after 4F2hc silencing (p < 0.05, respectively). These findings suggest an important role of system L in the placental uptake of the metal. Comparing the cellular accumulation of mercury, leucine, and methionine, it can be assumed that (1) MeHg is transported through system L amino acid transporters and (2) system L is responsible for the uptake of amino acids and MeHg primarily at the apical membrane of the trophoblast. The findings together can explain why mercury in contrast to other heavy metals such as lead or cadmium is efficiently transported to fetal blood.

SLC3A2, antigen of mAb 3G9, promotes migration and invasion by upregulating of mucins in gastric cancer

Solute carrier family 3 member 2 (SLC3A2) has been reported to be highly expressed in a variety of carcinomas. However, the function of SLC3A2 in gastric carcinoma (GC) has not been well explored. Monoclonal antibody (mAb) 3G9, generated from immunogen of various human GC cell lines, has been shown to bind to GC tissues specifically. In this study, we identified the target antigen of mAb 3G9 as SLC3A2, and detected the expression profile of SLC3A2 in a panel of gastric cancer cell lines and GC tumor tissues. We found that the increased expression of SLC3A2 was associated with serosal invasion in GC patients. Knockout of SLC3A2 suppressed the migration and invasion of BGC-823 cells in vitro and in vivo, whereas overexpression of SLC3A2 in NCI-N87 cells promoted the migration and invasion in vitro and in vivo. Mechanistic investigations suggested that MUC1, MUC16 and MUC5B were the downstream genes of SLC3A2 in GC cells. Taken together, our data suggested that SLC3A2 promoted the aggressive phenotype of GC by upregulating several mucin genes expression and may serve as a potential biomarker for diagnosis and target therapy.

TGFβ1-induced leucine limitation uncovered by differential ribosome codon reading

Cancer cells modulate their metabolic networks to support cell proliferation and a higher demand of building blocks. These changes may restrict the availability of certain amino acids for protein synthesis, which can be utilized for cancer therapy. However, little is known about the amino acid demand changes occurring during aggressive and invasive stages of cancer. Recently, we developed diricore, an approach based on ribosome profiling that can uncover amino acid limitations. Here, we applied diricore to a cellular model in which epithelial breast cells respond rapidly to TGFβ1, a cytokine essential for cancer progression and metastasis, and uncovered shortage of leucine. Further analyses indicated that TGFβ1 treatment of human breast epithelial cells reduces the expression of SLC3A2, a subunit of the leucine transporter, which diminishes leucine uptake and inhibits cell proliferation. Thus, we identified a specific amino acid limitation associated with the TGFβ1 response, a vulnerability that might be associated with aggressiveness in cancer.

CD98 regulates vascular smooth muscle cell proliferation in atherosclerosis

BACKGROUND AND AIMS

Vascular smooth muscle cells (VSMC) migrate and proliferate to form a stabilizing fibrous cap that encapsulates atherosclerotic plaques. CD98 is a transmembrane protein made of two subunits, CD98 heavy chain (CD98hc) and one of six light chains, and is known to be involved in cell proliferation and survival. Because the influence of CD98hc on atherosclerosis development is unknown, our aim was to determine if CD98hc expressed on VSMC plays a role in shaping the morphology of atherosclerotic plaques by regulating VSMC function.

METHODS

In addition to determining the role of CD98hc in VSMC proliferation and apoptosis, we utilized mice with SMC-specific deletion of CD98hc (CD98hcfl/flSM22αCre+) to determine the effects of CD98hc deficiency on VSMC function in atherosclerotic plaque.

RESULTS

After culturing for 5 days in vitro, CD98hc-/- VSMC displayed dramatically reduced cell counts, reduced proliferation, as well as reduced migration compared to control VSMC. Analysis of aortic VSCM after 8 weeks of HFD showed a reduction in CD98hc-/- VSMC proliferation as well as increased apoptosis compared to controls. A long-term atherosclerosis study using SMC-CD98hc-/-/ldlr-/- mice was performed. Although total plaque area was unchanged, CD98hc-/- mice showed reduced presence of VSMC within the plaque (2.1 ± 0.4% vs. 4.3 ± 0.4% SM22α-positive area per plaque area, p < 0.05), decreased collagen content, as well as increased necrotic core area (25.8 ± 1.9% vs. 10.9 ± 1.6%, p < 0.05) compared to control ldlr-/- mice.

CONCLUSIONS

We conclude that CD98hc is required for VSMC proliferation, and that its deficiency leads to significantly reduced presence of VSMC in the neointima. Thus, CD98hc expression in VSMC contributes to the formation of plaques that are morphologically more stable, and thereby protects against atherothrombosis.

Role of CD98 in invasion and metastasis of hepatocellular carcinoma cells

AIM

To knock down CD98 expression in human hepatocellular carcinoma (HCC) cells by RNA interference (RNAi) to explore the role of CD98 in HCC progression.

METHODS

Down-regulation of CD98 expression in human HCC cell line (FHCC-98) was performed by RNAi and verified by Western blot analysis. The role of CD98 in the invasion and metastasis of FHCC-98 cells was investigated using cell adhesion assay, transwell invasion assay, and monolayer wound healing assay.

RESULTS

After transient transfection with siRNA targeting CD98 for 48 h, the protein expression of CD98 in human HCC cells was significantly knocked down. Moreover, the numbers of attached cells and invaded cells, and wound closure rate were significantly decreased compared to cells transfected with the negative control siRNA.

CONCLUSION

CD98 may promote tumor invasion and metastasis in HCC via enhancement of the abilities of tumor cells to adhere, invade and migrate. CD98 may be a novel therapeutic target for the treatment of HCC.

Integrins in the Spotlight of Cancer

Integrins are heterodimeric cell surface receptors that bind to different extracellular ligands depending on their composition and regulate all processes which enable multicellular life. In cancer, integrins trigger and play key roles in all the features that were once described as the Hallmarks of Cancer. In this review, we will discuss the contribution of integrins to these hallmarks, including uncontrolled and limitless proliferation, invasion of tumor cells, promotion of tumor angiogenesis and evasion of apoptosis and resistance to growth suppressors, by highlighting the latest findings. Further on, given the paramount role of integrins in cancer, we will present novel strategies for integrin inhibition that are starting to emerge, promising a hopeful future regarding cancer treatment.

Dominant Suppression of β1 Integrin by Ectopic CD98-ICD Inhibits Hepatocellular Carcinoma Progression

Hepatocellular carcinoma (HCC) is currently the third most common cause of cancer-related death in the Asia-Pacific region. Our previous work showed that knockdown of CD98 significantly inhibits malignant HCC cell phenotypes in vitro and in vivo. The level of CD98 in the membrane is tightly regulated to mediate complex processes associated with cell–cell communication and intracellular signaling. In addition, the intracellular domain of CD98 (CD98-ICD) seems to be of vital importance for recycling CD98 to the membrane after it is endocytosed. The intracellular and transmembrane domains of CD98 associate with β-integrins (primarily β1 but also β3), and this association is essential for CD98 mediation of integrin-like signaling and complements dominant suppression of β1-integrin. We speculated that isolated CD98-ICD would similarly suppress β1-integrin activation and inhibit the malignant behaviors of cancer cells. In particular, the exact role of CD98-ICD has not been studied independently in HCC. In this study, we found that ectopic expression of CD98-ICD inhibited the malignant phenotypes of HCC cells, and the mechanism possibly involves β1-integrin suppression. Moreover, the expression levels of CD98, β1-integrin-A (the activated form of β1-integrin) and Ki-67 were significantly increased in HCC tissues relative to those of normal liver tissues. Therefore, our preliminary study indicates that ectopic CD98-ICD has an inhibitory role in the malignant development of HCC, and shows that CD98-ICD acts as a dominant negative mutant of CD98 that attenuates β1-integrin activation. CD98-ICD may emerge as a promising candidate for antitumor treatment.

Conditional deletion of CD98hc inhibits osteoclast development

The CD98 heavy chain (CD98hc) regulates virus-induced cell fusion and monocyte fusion, and is involved in amino acid transportation. Here, we examined the role that CD98hc plays in the formation of osteoclasts using CD98hc^flox/floxLysM-cre peritoneal macrophages (CD98hc-defect macrophages). Peritoneal macrophages were stimulated with co-cultured with osteoblasts in the presence of 1,25(OH)² vitamin D₃, and thereafter stained with tartrate-resistant acid phosphatase staining solution. The multinucleated osteoclast formation was severely impaired in the peritoneal macrophages isolated from the CD98hc^-defect mice compared with those from wild-type mice. CD98hc mediates integrin signaling and amino acid transport through the CD98 light chain (CD98lc). In integrin signaling, suppression of the M-CSF-RANKL-induced phosphorylation of ERK, Akt, JNK and p130Cas were observed at the triggering phase in the CD98h-defect peritoneal macrophages. Moreover, we showed that the general control non-derepressible (GCN) pathway, which was activated by amino acid starvation, was induced by the CD98hc-defect peritoneal macrophages stimulated with RANKL. These results indicate that CD98 plays two important roles in osteoclast formation through integrin signaling and amino acid transport.

•

The osteoclastogenesis was severely impaired in the CD98hc-defect macrophages.

•

CD98hc-defect peritoneal macrophages fall into amino acid starvation, resulting in inducing the general control non-derepressible (GCN) pathway in the osteoclastogenesis.

Basigin-mediated redistribution of CD98 promotes cell spreading and tumorigenicity in hepatocellular carcinoma

Background

Dysregulated endocytosis of membrane proteins contributes significantly to several hallmarks of cancer. Basigin can enhance cancer progression, but its precise mechanism remains unclear. CD98 promotes cell spreading and tumorigenicity by triggering integrin clustering and enhancing cell adhesion to the extracellular matrix. The endocytosis and recyle of basigin and CD98 might play critical roles in cancer.

Methods

The role of CD98 was confirmed in liver cancer cells by cell spreading in vitro and tumorigenicity by nude mice xenograft tumor assay in vivo; membrane expression of basigin and CD98 in SMMC-7721 was measured by FCAS; pull down and SPR analysis were uses to reveal the direct association between basigin and CD98; DsRed1 tagged CD98 was blocked in the cytoplasm in K7721 (whose basigin was knockn out) and had a well colocalization with ER and Rab5a positive recycling endosomes under co-focal; finally, by FRET imaging and FCAS we observed the internalization of basigin and CD98 was flotillin-1-regulated, and their recycle at early steps was Arf6-mediated.

Results

Basigin and CD98 were highly expressed and co-localized on the human hepatocellular carcinoma (HCC) cell membrane; basigin can directly bind to CD98, mediating CD98 redistribution on the HCC cell membrane and activating the downstream integrin signaling pathway. Internalization of basigin and CD98 was flotillin-1 regulated the and their recycling was mediated by Arf6. This recycling process for basigin and CD98 promotes cell spreading and tumor growth in liver cancer xenografts.

Conclusion

Basigin, as a redistribution chaperone of CD98, plays a critical role in promoting cell spreading and the progression of hepatocellular carcinoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-015-0226-6) contains supplementary material, which is available to authorized users.

CD99 inhibits CD98-mediated β1 integrin signaling through SHP2-mediated FAK dephosphorylation

The human CD99 protein is a 32-kDa type I transmembrane glycoprotein, while CD98 is a disulfide-linked 125-kDa heterodimeric type II transmembrane glycoprotein. It has been previously shown that CD99 and CD98 oppositely regulate β1 integrin signaling, though the mechanisms by which this regulation occurs are not known. Our results revealed that antibody-mediated crosslinking of CD98 induced FAK phosphorylation at Y397 and facilitated the formation of the protein kinase Cα (PKCα)-syntenin-focal adhesion kinase (FAK), focal adhesions (FAs), and IPP-Akt1-syntenin complex, which mediates β1 integrin signaling. In contrast, crosslinking of CD99 disrupted the formation of the PKCα-syntenin-FAK complex as well as FA via FAK dephosphorylation. The CD99-induced dephosphorylation of FAK was apparently mediated by the recruitment of Src homology region 2 domain-containing phosphatase-2 (SHP2) to the plasma membrane and subsequent activation of its phosphatase activity. Further consequences of the activation of SHP2 included the disruption of FAK-talin and talin-β1 integrin interactions and attenuation in the formation of the IPP-Akt1-syntenin complex at the plasma membrane, which resulted in reduced cell-ECM adhesion. This report uncovers the molecular mechanisms underlying the inverse regulation of β1 integrin signaling by CD99 and CD98 and may provide a novel therapeutic approach to treat inflammation and cancer.

Retinoblastoma binding protein 2 (RBP2) promotes HIF-1α-VEGF-induced angiogenesis of non-small cell lung cancer via the Akt pathway

Background

Pathological angiogenesis plays an essential role in tumor aggressiveness and leads to unfavorable prognosis. The aim of this study is to detect the potential role of Retinoblastoma binding protein 2 (RBP2) in the tumor angiogenesis of non-small cell lung cancer (NSCLC).

Methods

Immunohistochemical staining was used to detect the expression of RBP2, hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and CD34. Two pairs of siRNA sequences and pcDNA3-HA-RBP2 were used to down-regulate and up-regulate RBP2 expression in H1975 and SK-MES-1 cells. An endothelial cell tube formation assay, VEGF enzyme-linked immunosorbent assay, real-time PCR and western blotting were performed to detect the potential mechanisms mediated by RBP2 in tumor angiogenesis.

Results

Of the 102 stage I NSCLC specimens analyzed, high RBP2 protein expression is closely associated with tumor size (P = 0.030), high HIF-1α expression (P = 0.028), high VEGF expression (P = 0.048), increased tumor angiogenesis (P = 0.033) and poor prognosis (P = 0.037); high MVD was associated with high HIF-1α expression (P = 0.034), high VEGF expression (P = 0.001) and poor prognosis (P = 0.040). Multivariate analysis indicated that RBP2 had an independent influence on the survival of patients with stage I NSCLC (P = 0.044). By modulating the expression of RBP2, our findings suggested that RBP2 protein depletion decreased HUVECs tube formation by down-regulating VEGF in a conditioned medium. RBP2 stimulated the up-regulation of VEGF, which was dependent on HIF-1α, and activated the HIF-1α via phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Moreover, VEGF increased the activation of Akt regulated by RBP2.

Conclusions

The RBP2 protein may stimulate HIF-1α expression via the activation of the PI3K/Akt signaling pathway under normoxia and then stimulate VEGF expression. These findings indicate that RBP2 may play a critical role in tumor angiogenesis and serve as an attractive therapeutic target against tumor aggressiveness for early-stage NSCLC patients.