CD98hc (SLC3A2), a novel marker in renal cell cancer

The role of polyamine metabolism in cellular function and physiology

Polyamines are molecules with multiple amino groups that are essential for cellular function. The major polyamines are putrescine, spermidine, spermine, and cadaverine. Polyamines are important for posttranscriptional regulation, autophagy, programmed cell death, proliferation, redox homeostasis, and ion channel function. Their levels are tightly controlled. High levels of polyamines are associated with proliferative pathologies such as cancer, whereas low polyamine levels are observed in aging, and elevated polyamine turnover enhances oxidative stress. Polyamine metabolism is implicated in several pathophysiological processes in the nervous, immune, and cardiovascular systems. Currently, manipulating polyamine levels is under investigation as a potential preventive treatment for several pathologies, including aging, ischemia/reperfusion injury, pulmonary hypertension, and cancer. Although polyamines have been implicated in many intracellular mechanisms, our understanding of these processes remains incomplete and is a topic of ongoing investigation. Here, we discuss the regulation and cellular functions of polyamines, their role in physiology and pathology, and emphasize the current gaps in knowledge and potential future research directions.

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.

Hypoxia Modulates Cellular Endocytic Pathways and Organelles with Enhanced Cell Migration and 3D Cell Invasion

Hypoxia, a decrease in cellular or tissue level oxygen content, is characteristic of most tumors and has been shown to drive cancer progression by altering multiple subcellular processes. We hypothesized that the cancer cells in a hypoxic environment might have slower proliferation rates and increased invasion and migration rates with altered endocytosis compared to the cancer cells in the periphery of the tumor mass that experience normoxic conditions. We induced cellular hypoxia by exposing cells to cobalt chloride, a chemical hypoxic mimicking agent. This study measured the effect of hypoxia on cell proliferation, migration, and invasion. Uptake of fluorescently labeled transferrin, galectin3, and dextran that undergo endocytosis through major endocytic pathways (Clathrin-mediated pathway (CME), Clathrin-independent pathway (CIE), Fluid phase endocytosis (FPE)) were analyzed during hypoxia. Also, the organelle changes associated with hypoxia were studied with organelle trackers. We found that the proliferation rate decreased, and the migration and invasion rate increased in cancer cells in hypoxic conditions compared to normoxic cancer cells. A short hypoxic exposure increased galectin3 uptake in hypoxic cancer cells, but a prolonged hypoxic exposure decreased clathrin-independent endocytic uptake of galectin 3. Subcellular organelles, such as mitochondria, increased to withstand the hypoxic stress, while other organelles, such as Endoplasmic reticulum (ER), were significantly decreased. These data suggest that hypoxia modulates cellular endocytic pathways with reduced proliferation and enhanced cell migration and invasion.

An amino acid transporter subunit as an antibody-drug conjugate target in colorectal cancer

BACKGROUND

Advanced colorectal cancer (CRC) is difficult to treat. For that reason, the development of novel therapeutics is necessary. Here we describe a potentially actionable plasma membrane target, the amino acid transporter protein subunit CD98hc.

METHODS

Western blot and immunohistochemical analyses of CD98hc protein expression were carried out on paired normal and tumoral tissues from patients with CRC. Immunofluorescence and western studies were used to characterize the action of a DM1-based CD98hc-directed antibody-drug conjugate (ADC). MTT and Annexin V studies were performed to evaluate the effect of the anti-CD98hc-ADC on cell proliferation and apoptosis. CRISPR/Cas9 and shRNA were used to explore the specificity of the ADC. In vitro analyses of the antitumoral activity of the anti-CD98hc-ADC on 3D patient-derived normal as well as tumoral organoids were also carried out. Xenografted CRC cells and a PDX were used to analyze the antitumoral properties of the anti-CD98hc-ADC.

RESULTS

Genomic as well proteomic analyses of paired normal and tumoral samples showed that CD98hc expression was significantly higher in tumoral tissues as compared to levels of CD98hc present in the normal colonic tissue. In human CRC cell lines, an ADC that recognized the CD98hc ectodomain, reached the lysosomes and exerted potent antitumoral activity. The specificity of the CD98hc-directed ADC was demonstrated using CRC cells in which CD98hc was decreased by shRNA or deleted using CRISPR/Cas9. Studies in patient-derived organoids verified the antitumoral action of the anti-CD98hc-ADC, which largely spared normal tissue-derived colon organoids. In vivo studies using xenografted CRC cells or patient-derived xenografts confirmed the antitumoral activity of the anti-CD98hc-ADC.

CONCLUSIONS

The studies herewith reported indicate that CD98hc may represent a novel ADC target that, upon well-designed clinical trials, could be used to increase the therapeutic armamentarium against CRC.

MIF/SCL3A2 depletion inhibits the proliferation and metastasis of colorectal cancer cells via the AKT/GSK-3β pathway and cell iron death

This study investigated the mechanisms of migration inhibitory factor (MIF) and solute carrier family 3 member 2 (SLC3A2) in colorectal cancer progression. The levels of MIF and SLC3A2 expression in cells were measured by RT-qPCR. SW480 and SW620 cells were transfected with sh-MIF and sh-SLC3A2, respectively. MIF, SLC3A2, GPX4, E-cadherin and N-cadherin expression were detected by immunofluorescence (IF). CCK8 and Transwell assays were performed to detect cell proliferation and migration. Co-immunoprecipitation (CoIP) was used to measure the binding activity of MIF and SLC3A2. Finally, a nude mouse tumorigenicity assay was used to confirm the functions of MIF and SLC3A2 in colorectal cancer. Results showed that the levels of MIF and SLC3A2 expression were up-regulated in colorectal cancer cells. Inhibition of MIF or SLC3A2 expression prevented cell proliferation, migration, epithelial-mesenchymal transition (EMT) and invasion. In addition, knockdown of MIF and SLC3A2 promoted iron death in SW480 and SW620 cells. CoIP results showed that MIF and SLC3A2 directly interact with each other. Knockdown of both MIF and SLC3A2 inhibited tumour growth and metastasis via the AKT/GSK-3β pathway in vivo. The Akt/GSK-3β pathway was found to participate in regulating MIF and SLC3A2 both in vivo and in vitro. MIF and SLC3A2 might be potential biomarkers for monitoring the treatment of colorectal cancer.

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.

Microvascular density assessed by CD31 predicts clinical benefit upon bevacizumab treatment in metastatic colorectal cancer: results of the PassionATE study, a translational prospective Phase II study of capecitabine and irinotecan plus bevacizumab followed by capecitabine and oxaliplatin plus bevacizumab or the reverse sequence in patients in mCRC

Background

Targeted therapies offer novel opportunities to explore biomarkers based on their mode of action. Taking this into consideration, we evaluated six angiogenesis-related proteins as potential predictive biomarkers, which expression might predict the benefit of bevacizumab treatment in patients with metastatic colorectal cancer (mCRC).

Methods

This was a phase II multicenter, two-armed, randomized study, in which patients with mCRC were treated with XELIRI (capecitabine and irinotecan) plus bevacizumab followed by XELOX (capecitabine and oxaliplatin) plus bevacizumab (Arm A) or the reverse sequence (Arm B). Tissue expression level of six prespecified candidates [microvessel density assessed by CD31, PTEN, αV integrin, CD98hc, uPAR and NRP-1] was analyzed via immunohistochemistry. The prognostic impact on survival was quantified using the Cox regression model. The predictive potential for benefit from Arm A versus Arm B treatment was investigated by fitting an interaction between the biomarkers and treatment assignment within a multivariable Cox model.

Results

In total, 74 out of 126 patients were included in the analysis. The expression of PTEN, αV integrin, uPAR and NRP-1 was not associated with progression-free survival (PFS) or overall survival (OS). For the first time, we identified that patients with tumors expressing CD98hc had a longer PFS than patients without CD98hc-expression (p = 0.032). More importantly, and in accordance with previous studies, low microvessel density was found to be associated with a reduced PFS [adjusted HR per doubling of CD31-expression (p = 0.53, 95% confidence interval: 0.30-0.95, p = 0.034)].

Conclusions

These results can contribute to the development of a personalized strategy for the treatment of mCRC with bevacizumab.

Development of a high affinity Anticalin® directed against human CD98hc for theranostic applications

Enhanced amino acid supply and dysregulated integrin signaling constitute two hallmarks of cancer and are pivotal for metastatic transformation of cells. In line with its function at the crossroads of both processes, overexpression of CD98hc is clinically observed in various cancer malignancies, thus rendering it a promising tumor target.

Methods: We describe the development of Anticalin proteins based on the lipocalin 2 (Lcn2) scaffold against the human CD98hc ectodomain (hCD98hcED) using directed evolution and protein design. X-ray structural analysis was performed to identify the epitope recognized by the lead Anticalin candidate. The Anticalin - with a tuned plasma half-life using PASylation^® technology - was labeled with ⁸⁹Zr and investigated by positron emission tomography (PET) of CD98-positive tumor xenograft mice.

Results: The Anticalin P3D11 binds CD98hc with picomolar affinity and recognizes a protruding loop structure surrounded by several glycosylation sites within the solvent exposed membrane-distal part of the hCD98hcED. In vitro studies revealed specific binding activity of the Anticalin towards various CD98hc-expressing human tumor cell lines, suggesting broader applicability in cancer research. PET/CT imaging of mice bearing human prostate carcinoma xenografts using the optimized and ⁸⁹Zr-labeled Anticalin demonstrated strong and specific tracer accumulation (8.6 ± 1.1 %ID/g) as well as a favorable tumor-to-blood ratio of 11.8.

Conclusion: Our findings provide a first proof of concept to exploit CD98hc for non-invasive biomedical imaging. The novel Anticalin-based αhCD98hc radiopharmaceutical constitutes a promising tool for preclinical and, potentially, clinical applications in oncology.

SLC3A2 is a novel endoplasmic reticulum stress-related signaling protein that regulates the unfolded protein response and apoptosis

Endoplasmic reticulum (ER) stress results from imbalances in unfolded/misfolded proteins, contributing to a wide variety of human diseases. To better understand the mechanisms involved in the cellular response to ER stress in cardiomyocytes, we previously conducted a genome-wide screening in an in vitro ER stress model of rat cardiomyocytes, which highlighted amino acid transporter heavy chain, member 2 (SLC3A2) as an important factor in ER stress. In the present study, we characterized the role of SLC3A2 during the unfolded protein response (UPR), as one of the primary pathways activated during ER stress. First, we confirmed the induction of Slc3a2 mRNA expression following treatment with various ER stress inducers in rat cardiomyocytes (H9C2) and neural cells (PC12). Knockdown of Slc3a2 expression with small interfering RNA (siRNA) revealed that the encoded protein functions upstream of three important UPR proteins: ATF4, ATF6, and XBP1. siRNA-mediated knockdown of both SLC3A2 and mammalian target of rapamycin 1 (mTOR1) revealed that mTOR1 acts as a mediator between SLC3A2 and the UPR. RNA sequencing was then performed to gain a more thorough understanding of the function of SLC3A2, which identified 23 highly differentially regulated genes between the control and knockdown cell lines, which were related to the UPR and amino acid transport. Notably, flow cytometry further showed that SLC3A2 inhibition also enhanced the apoptosis of rat cardiomyocytes. Taken together, these results highlight SLC3A2 as a complex, multifunctional signaling protein that acts upstream of well-known UPR proteins with anti-apoptotic properties, suggesting its potential as a therapeutic target for ER stress-related diseases.

ZEB1 Promotes Chemoresistance to Cisplatin in Ovarian Cancer Cells by Suppressing SLC3A2

Ovarian cancer is one of the deadliest gynecological malignancies in women. Chemoresistance has been a major obstacle for ovarian cancer treatment. Zinc finger E-box-binding homeobox 1 (ZEB1) is an important regulator of tumor development in various types of cancer. Abnormal expression of SLC3A2 (CD98hc), a type 2 transmembrane cell surface molecule, has been described in several cancers. This study was designed to investigate the role of ZEB1 and SLC3A2 in the chemoresistance to cisplatin in ovarian cancer cells. We found that ZEB1 was increased in cisplatin-resistant SKOV3/DPP cells. Downregulation of ZEB1 significantly decreased cell viability in response to cisplatin, increased cis-platin-induced apoptosis, and decreased migration and invasion in the presence of cisplatin. In addition, downregulation of ZEB1 decreased the volume and weight of implanted tumors. SLC3A2 was decreased in cisplatin-resistant SKOV3/DPP cells. Upregulation of SLC3A2 significantly decreased cell viability in response to cisplatin, increased cisplatin-induced apoptosis, and decreased migration and invasion in the presence of cisplatin. Moreover, upregulation of SLC3A2 decreased the volume and weight of implanted tumors. Downregulation of ZEB1 resulted in a significant increase of SLC3A2 expression. Moreover, downregulation of SLC3A2 significantly inhibited ZEB1 knockdown-mediated inhibition of cisplatin-resistance. ZEB1-mediated regulation of SLC3A2 was involved in the chemoresistance to cisplatin in ovarian cancer cells. Overall, we provide new insights into the mechanism of chemoresistance to cisplatin in ovarian cancer cells. ZEB1/SLC3A2 may be promising therapeutic targets for enhancement of the sensitivity of ovarian cancer cells to cisplatin-mediated chemotherapy.

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.

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.

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.

SLC3A2 is upregulated in human osteosarcoma and promotes tumor growth through the PI3K/Akt signaling pathway

Growing evidence indicates that SLC3A2 (solute carrier family 3 member 2) is upregulated and correlates with tumor growth in multiple types of cancers, while the role of SLC3A2 in human osteosarcoma (OS) is rarely discussed. Thus, the aim of the present study was to demonstrate the expression of SLC3A2 in human osteosarcoma and reveal its biological function and the underlying mechanisms. RT-PCR, western blot analysis and immunohistochemistry (IHC) were used to assess the expression of SLC3A2 in OS samples and cell lines. Cell cycle, Cell Counting Kit-8 (CCK-8) and colony formation assays were used to test the cell survival capacity. To investigate the potential mechanism by which SLC3A2 regulates OS growth, we used a slide-based antibody array. We demonstrated that SLC3A2 was upregulated in OS cell lines as well as OS tissues. High expression of SLC3A2 was correlated with clinical stage and tumor size in OS. Reduced expression of SLC3A2 inhibited OS cell proliferation through G2/M phase arrest. Most importantly, we found that SLC3A2 may regulate OS growth through the PI3K/Akt signaling pathway. In conclusion, SLC3A2 is upregulated in OS and plays a crucial role in tumor growth. Targeting SLC3A2 may provide a new therapeutic strategy for OS.

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.

Comparative Tissue Proteomics of Microdissected Specimens Reveals Novel Candidate Biomarkers of Bladder Cancer

More than 380,000 new cases of bladder cancer are diagnosed worldwide, accounting for ∼150,200 deaths each year. To discover potential biomarkers of bladder cancer, we employed a strategy combining laser microdissection, isobaric tags for relative and absolute quantitation labeling, and liquid chromatography-tandem MS (LC-MS/MS) analysis to profile proteomic changes in fresh-frozen bladder tumor specimens. Cellular proteins from four pairs of surgically resected primary bladder cancer tumor and adjacent nontumorous tissue were extracted for use in two batches of isobaric tags for relative and absolute quantitation experiments, which identified a total of 3220 proteins. A DAVID (database for annotation, visualization and integrated discovery) analysis of dysregulated proteins revealed that the three top-ranking biological processes were extracellular matrix organization, extracellular structure organization, and oxidation-reduction. Biological processes including response to organic substances, response to metal ions, and response to inorganic substances were highlighted by up-expressed proteins in bladder cancer. Seven differentially expressed proteins were selected as potential bladder cancer biomarkers for further verification. Immunohistochemical analyses showed significantly elevated levels of three proteins-SLC3A2, STMN1, and TAGLN2-in tumor cells compared with noncancerous bladder epithelial cells, and suggested that TAGLN2 could be a useful tumor tissue marker for diagnosis (AUC = 0.999) and evaluating lymph node metastasis in bladder cancer patients. ELISA results revealed significantly increased urinary levels of both STMN1 and TAGLN2 in bladder cancer subgroups compared with control groups. In comparisons with age-matched hernia urine specimens, urinary TAGLN2 in bladder cancer samples showed the largest fold change (7.13-fold), with an area-under-the-curve value of 0.70 (p < 0.001, n = 205). Overall, TAGLN2 showed the most significant overexpression in individual bladder cancer tissues and urine specimens, and thus represents a potential biomarker for noninvasive screening for bladder cancer. Our findings highlight the value of bladder tissue proteome in providing valuable information for future validation studies of potential biomarkers in urothelial carcinoma.

Genetic variations in SLC3A2/CD98 gene as prognosis predictors in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is characterized by poor prognosis and only a few molecular markers may be potentially used to predict the risk of progression. This study aims to assess the effects of single nucleotide polymorphisms (SNPs) in the CD98 gene on prognosis of NSCLC patients. We genotyped three potential functional SNPs in CD98 gene using Sequenom iPLEX genotyping system in a cohort of 482 NSCLC patients. Multivariate cox proportional hazards model and Kaplan-Meier curve were used for the survival analysis. The variant-containing genotypes of rs1059292 in 5'-flanking region of CD98 gene were significantly associated with an increased risk of death in the multivariate analysis (Hazard ratio [HR], 1.49; 95% confidence interval [95% CI]: 1.04-2.14 in a dominant model). In stratified analysis, the association remained significant in patients with poor differentiation (HR=1.81, 95% CI=1.01-3.25). In addition, rs1059292 also showed a borderline significant association with T stage (OR=1.49; 95% CI: 0.96-2.35) and N stage (OR=1.53; 95% CI: 0.98-2.39). Functional analysis demonstrated that variant genotype of SNP rs1059292 significantly enhanced the transcription activity of CD98 gene promoter. Our data suggest that genetic variation of rs1059292 in CD98 gene may affect clinical outcome of NSCLC in Chinese population.

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

Background

Overexpression of CD98hc (SLC3A2) occurs in a variety of cancers and is suspected to contribute to tumor growth. CD98, a heterodimeric transmembrane protein, physically associates with certain integrin β subunit cytoplasmic domains via its heavy chain, CD98hc. CD98hc regulates adhesion-induced intracellular signal transduction via integrins, thereby, affecting cell proliferation and clonal expansion. Disruption of CD98hc led to embryonic lethality in mice (E 3.5 and E 9.5) and CD98hc −/− embryonic stem cell transplantation failed to form teratomas, while CD98hc over-expression in somatic cells resulted in anchorage-independent growth. However, it is unclear whether interference with CD98hc expression tumor cell behavior.

Methods

Renal cell cancer cell lines have been used to determine the effect of CD98hc expression on cancer cell behavior using cell adhesion, cell trans-migration and cell spreading assays. Flow cytometric analysis was performed to study the rate of apoptosis after detachment or serum starvation. shRNA-lentiviral constructs were used to stably knockdown or reconstitute full length or mutated CD98hc. The role of CD98 as a promotor of tumorigenesis was evaluated using an in in vivo tumor transplantation animal model. Immunohistochemical analysis was performed to analyze cell proliferation and CD98 expression in tumors.

Results

This report shows that CD98hc silencing in clear cell renal cancer cells reverts certain characteristics of tumorigenesis, including cell spreading, migration, proliferation and survival in vitro, and tumor growth in vivo. Acquisition of tumorigenic characteristics in clear cell renal cancer cells occurred through the integrin binding domain of CD98hc. A CD98hc/integrin interaction was required for adhesion-induced sustained FAK phosphorylation and activation of the major downstream signaling pathways PI3k/Akt and MEK/ERK, while overexpression of a constitutive active form of FAK rescued the CD98hc deficiency.

Conclusions

In this study we demonstrate that loss of CD98hc blocks tumorigenic potential in renal cell cancer.

Soluble carcinoembryonic antigen activates endothelial cells and tumor angiogenesis

Carcinoembryonic antigen (CEA, CD66e, CEACAM-5) is a cell-surface-bound glycoprotein overexpressed and released by many solid tumors that has an autocrine function in cancer cell survival and differentiation. Soluble CEA released by tumors is present in the circulation of patients with cancer, where it is used as a marker for cancer progression, but whether this form of CEA exerts any effects in the tumor microenvironment is unknown. Here, we present evidence that soluble CEA is sufficient to induce proangiogenic endothelial cell behaviors, including adhesion, spreading, proliferation, and migration in vitro and tumor microvascularization in vivo. CEA-induced activation of endothelial cells was dependent on integrin β-3 signals that activate the focal-adhesion kinase and c-Src kinase and their downstream MAP-ERK kinase/extracellular signal regulated kinase and phosphoinositide 3-kinase/Akt effector pathways. Notably, while interference with VEGF signaling had no effect on CEA-induced endothelial cell activation, downregulation with the CEA receptor in endothelial cells attenuated CEA-induced signaling and tumor angiogenesis. Corroborating these results clinically, we found that tumor microvascularization was higher in patients with colorectal cancer exhibiting higher serum levels of soluble CEA. Together, our results elucidate a novel function for soluble CEA in tumor angiogenesis.

Polyamines and membrane transporters

In recent years, our understanding of the importance of membrane transporters (MTs) in the disposition of and response to drugs has increased significantly. MTs are proteins that regulate the transport of endogenous molecules and xenobiotics across the cell membrane. In mammals, two super-families have been identified: ATP-binding cassette (ABC) and solute carrier (SLC) transporters. There is evidence that MTs might mediate polyamines (PA) transport. PA are ubiquitous polycations which are found in all living cells. In mammalian cells, three major PA are synthesised: putrescine, spermidine and spermine; whilst the decarboxylated arginine (agmatine) is not produced by mammals but is synthesised by plants and bacteria. In addition, research in the PA field suggests that PA are transported into cells via a specific transporter, the polyamine transport system(s) (PTS). Although the PTS has not been fully defined, there is evidence that some of the known MTs might be involved in PA transport. In this mini review, eight SLC transporters will be reviewed and their potential to mediate PA transport in human cells discussed. These transporters are SLC22A1, SLC22A2, SLC22A3, SLC47A1, SLC7A1, SLC3A2, SLC12A8A, and SLC22A16. Preliminary data from our laboratory have revealed that SLC22A1 might be involved in the PA uptake; in addition to one member of ABC superfamily (MDR1 protein) might also mediate the efflux of polyamine like molecules.

Downregulation of L-type amino acid transporter 1 expression inhibits the growth, migration and invasion of gastric cancer cells

Gastric cancer is the second leading cause of cancer-related mortality worldwide. Identifying the molecules that play critical roles in the development of gastric cancer, and clarifying their mechanisms, will contribute to the development of novel molecularly targeted therapeutic drugs. Recently, the large (L)-type amino acid transporter 1 (LAT1), a glycoprotein that transports amino acids through the cell membrane when associated with CD98hc, has been demonstrated to be overexpressed in various types of cancer, and to regulate multiple biological process, including cell growth, migration and invasion. However, the involvement of LAT1 in gastric cancer remains unclear. In the present study, stable gastric cancer cell lines with a LAT1 knockdown were established by transfection of constructs with inserted short (sh) RNAs, in order to clarify the role of LAT1 in gastric caner. A significant decrease in LAT1 expression was observed in the established LAT1-silenced SGC7901 cells compared with the corresponding control cells; however, the expression levels of its partner, CD98hc, were not altered. Furthermore, downregulation of LAT1 expression inhibited the proliferation, migration and invasion of gastric cancer cells. In addition, the decreased expression of LAT1 induced cell cycle arrest in the G₁/M phase. These findings suggested that LAT1 may be significant in the progression and metastasis of gastric cancer, and may be developed as a therapeutic target for cancer therapy.

Discovery of SLC3A2 cell membrane protein as a potential gastric cancer biomarker: implications in molecular imaging

Despite decreasing incidence and mortality, gastric cancer remains the second leading cause of cancer-related deaths in the world. Successful management of gastric cancer is hampered by lack of highly sensitive and specific biomarkers especially for early cancer detection. Cell surface proteins that are aberrantly expressed between normal and cancer cells are potentially useful for cancer imaging and therapy due to easy accessibility of these targets. Combining two-phase partition and isobaric tags for relative and absolute quantification methods, we compared the relative expression levels of membrane proteins between noncancer and gastric cancer cells. About 33% of the data set was found to be plasma membrane and associated proteins using this approach (compared to only 11% in whole cell analysis), several of which have never been previously implicated in gastric cancer. Upregulation of SLC3A2 in gastric cancer cells was validated by immunoblotting of a panel of 13 gastric cancer cell lines and immunohistochemistry on tissue microarrays comprising 85 matched pairs of normal and tumor tissues. Immunofluorescence and immunohistochemistry both confirmed the plasma membrane localization of SLC3A2 in gastric cancer cells. The data supported the notion that SLC3A2 is a potential biomarker that could be exploited for molecular imaging-based detection of gastric cancer.

Intestinal epithelial cell-specific CD98 expression regulates tumorigenesis in Apc(Min/+) mice

The transmembrane glycoprotein CD98 regulates integrin signaling that in turn controls cell proliferation and survival. CD98 expression is upregulated in various carcinomas, including colorectal cancer. Recently, by generating gain- and loss-of-function mouse models featuring genetic manipulation of CD98 expression specifically in intestinal epithelial cells (IECs), we have explored the crucial role of CD98 in the regulation of intestinal homeostasis and inflammation-associated tumorigenesis. In the present study, we investigated the contribution of CD98 to intestinal tumorigenesis in Apc(Min/+) mice and the underlying mechanism of action. Mice featuring IEC-specific CD98 overexpression (Tg animals) were crossed with Apc(Min/+) mice, and the characteristics of intestinal adenoma formation were assessed. Compared with Apc(Min/+) mice, Tg/Apc(Min/+) animals exhibited increases in both intestinal tumor incidence and tumor size; these parameters correlated with enhanced proliferation and decreased apoptosis of IECs. IEC-specific CD98 overexpression resulted in increased synthesis of the oncogenic proteins c-myc and cyclin-D1 in Apc(Min/+) mice, independently of the Wnt-APC-β-catenin pathway, suggesting the implication of CD98 overexpression-mediated Erk activation. IEC-specific CD98 overexpression enhanced the production of proinflammatory cytokines and chemokines that are crucial for tumorigenesis. We validated our results in mice exhibiting IEC-specific CD98 downregulation (CD98(flox/+)VillinCre animals). IEC-specific CD98 downregulation efficiently attenuated tumor incidence and growth in Apc(Min/+) mice. The reduction of intestinal tumorigenesis upon IEC-specific CD98 downregulation was caused by the attenuation of IEC proliferation and cytokine/chemokine production. In conclusion, we show that CD98 exerts an oncogenic activity in terms of intestinal tumorigenesis, via an ability to regulate tumor growth and survival.

Comparative studies on glycoproteins expressing polylactosamine-type N-glycans in cancer cells

In the series of our previous reports, we showed that some cancer cell lines specifically express polylactosamine-type N-glycans and such glycans were often modified with fucose and sulfate residues. To confirm the proteins expressing these glycans, glycopeptide mixture obtained by digestion of whole protein fractions with trypsin was captured by a polylactosamine-specific lectin, Datura strasmonium agglutinin (DSA). And the peptides and glycans of the captured glycopeptides after digestion with N-glycoamidase F were extensively analyzed by HPLC and MS techniques. We found that some glycoproteins such as CD107a and CD107b commonly contained polylactosamine-type glycans in all the examined cancer cells. But integrin-α5 (CD49e) and carcinoembryonic antigen-related cell adhesion molecule 5 (CD66e) having these glycans were specifically found in U937 (human T-lymphoma) and MKN45 (human gastric cancer) cells, respectively. These data clearly indicate that specific glycans attached to specific proteins will be promising markers for specific tumors with high accuracy.

CD98 at the crossroads of adaptive immunity and cancer

Adaptive immunity, a vertebrate specialization, adds memory and exquisite specificity to the basic innate immune responses present in invertebrates while conserving metabolic resources. In adaptive immunity, antigenic challenge requires extremely rapid proliferation of rare antigen-specific lymphocytes to produce large, clonally expanded effector populations that neutralize pathogens. Rapid proliferation and resulting clonal expansion are dependent on CD98, a protein whose well-conserved orthologs appear restricted to vertebrates. Thus, CD98 supports lymphocyte clonal expansion to enable protective adaptive immunity, an advantage that could account for the presence of CD98 in vertebrates. CD98 supports lymphocyte clonal expansion by amplifying integrin signals that enable proliferation and prevent apoptosis. These integrin-dependent signals can also provoke cancer development and invasion, anchorage-independence and the rapid proliferation of tumor cells. CD98 is highly expressed in many cancers and contributes to formation of tumors in experimental models. Strikingly, vertebrates, which possess highly conserved CD98 proteins, CD98-binding integrins and adaptive immunity, also display propensity towards invasive and metastatic tumors. In this Commentary, we review the roles of CD98 in lymphocyte biology and cancer. We suggest that the CD98 amplification of integrin signaling in adaptive immunity provides survival benefits to vertebrates, which, in turn, bear the price of increased susceptibility to cancer.

Homeostatic and innate immune responses: role of the transmembrane glycoprotein CD98

The transmembrane glycoprotein CD98 is a potential regulator of multiple functions, including integrin signaling and amino acid transport. Abnormal expression or function of CD98 and disruption of the interactions between CD98 and its binding partners result in defects in cell homeostasis and immune responses. Indeed, expression of CD98 has been correlated with diseases such as inflammation and tumor metastasis. Modulation of CD98 expression and/or function therefore represents a promising therapeutic strategy for the treatment and prevention of such pathologies. Herein, we review the role of CD98 with focus on its functional importance in homeostasis and immune responses, which could help to better understand the pathogenesis of CD98-associated diseases.

Global molecular dysfunctions in gastric cancer revealed by an integrated analysis of the phosphoproteome and transcriptome

We integrated LC-MS/MS-based and protein antibody array-based proteomics with genomics approaches to investigate the phosphoproteome and transcriptome of gastric cancer cell lines and endoscopic gastric biopsies from normal subjects and patients with benign gastritis or gastric cancer. More than 3,000 non-redundant phosphorylation sites in over 1,200 proteins were identified in gastric cancer cells. We correlated phosphoproteome data with transcriptome data sets and reported the expression of 41 protein kinases, 5 phosphatases and 65 phosphorylated mitochondrial proteins in gastric cancer cells. Transcriptional expression levels of 190 phosphorylated proteins were >2-fold higher in gastric cancer cells compared to normal stomach tissue. Pathway analysis demonstrated over-presentation of DNA damage response pathway and underscored critical roles of phosphorylated p53 in gastric cancer. This is the first study to comprehensively report the gastric cancer phosphoproteome. Integrative analysis of the phosphoproteome and transcriptome provided an expansive view of molecular signaling pathways in gastric cancer.

CD98 expression modulates intestinal homeostasis, inflammation, and colitis-associated cancer in mice

Expression of the transmembrane glycoprotein CD98 (encoded by SLC3A2) is increased in intestinal inflammatory conditions, such as inflammatory bowel disease (IBD), and in various carcinomas, yet its pathogenetic role remains unknown. By generating gain- and loss-of-function mouse models with genetically manipulated CD98 expression specifically in intestinal epithelial cells (IECs), we explored the role of CD98 in intestinal homeostasis, inflammation, and colitis-associated tumorigenesis. IEC-specific CD98 overexpression induced gut homeostatic defects and increased inflammatory responses to DSS-induced colitis, promoting colitis-associated tumorigenesis in mice. Further analysis indicated that the ability of IEC-specific CD98 overexpression to induce tumorigenesis was linked to its capacity to induce barrier dysfunction and to stimulate cell proliferation and production of proinflammatory mediators. To validate these results, we constructed mice carrying conditional floxed Slc3a2 alleles and crossed them with Villin-Cre mice such that CD98 was downregulated only in IECs. These mice exhibited attenuated inflammatory responses and resistance to both DSS-induced colitis and colitis-associated tumorigenesis. Together, our data show that intestinal CD98 expression has a crucial role in controlling homeostatic and innate immune responses in the gut. Modulation of CD98 expression in IECs therefore represents a promising therapeutic strategy for the treatment and prevention of inflammatory intestinal diseases, such as IBD and colitis-associated cancer.