CD98 increases renal epithelial cell proliferation by activating MAPKs

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.

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.

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.

Dermal Fibroblast SLC3A2 Deficiency Leads to Premature Aging and Loss of Epithelial Homeostasis

Skin homeostasis relies on fine-tuning of epidermis-dermis interactions and is affected by aging. While extracellular matrix (ECM) proteins, such as integrins, are involved in aging, the molecular basis of the skin changes needs to be investigated further. Here, we showed that integrin co-receptor, SLC3A2, required for cell proliferation, is expressed at the surface of resting dermal fibroblasts in young patients and is reduced drastically with aging. In vivo SLC3A2 dermal fibroblast deletion induced major skin phenotypes resembling premature aging. Knockout mice (3 months old) presented strong defects in skin elasticity due to altered ECM assembly, which impairs epidermal homeostasis. SLC3A2 dermal fibroblast loss led to an age-associated secretome profile, with 77% of identified proteins belonging to ECM and ECM-associated proteins. ECM not only contributes to skin mechanical properties, but it is also a reservoir of growth factors and bioactive molecules. We demonstrate that dermal fibroblast SLC3A2 is required for ECM to fully exert its structural and reservoir role allowing proper and efficient TGF-β localization and activation. We identified SLC3A2 as a protective controller of dermal ECM stiffness and quality required to maintain the epidermis to dermis interface as functional and dynamic.

The receptor protein tyrosine phosphatase PTPRJ negatively modulates the CD98hc oncoprotein in lung cancer cells

PTPRJ, a receptor protein tyrosine phosphatase strongly downregulated in human cancer, displays tumor suppressor activity by negatively modulating several proteins involved in proliferating signals. Here, through a proteomic-based approach, we identified a list of potential PTPRJ-interacting proteins and among them we focused on CD98hc, a type II glycosylated integral membrane protein encoded by SLC3A2, corresponding to the heavy chain of a heterodimeric transmembrane amino-acid transporter, including LAT1. CD98hc is widely overexpressed in several types of cancers and contributes to the process of tumorigenesis by interfering with cell proliferation, adhesion, and migration. We first validated PTPRJ-CD98hc interaction, then demonstrated that PTPRJ overexpression dramatically reduces CD98hc protein levels in A549 lung cancer cells. In addition, following to the treatment of PTPRJ-transduced cells with MG132, a proteasome inhibitor, CD98hc levels did not decrease compared to controls, indicating that PTPRJ is involved in the regulation of CD98hc proteasomal degradation. Moreover, PTPRJ overexpression combined with CD98hc silencing consistently reduced cell proliferation and triggered apoptosis of lung cancer cells. Interestingly, by interrogating the can Evolve database, we observed an inverse correlation between PTPRJ and SLC3A2 gene expression. Indeed, the non-small cell lung cancers (NSCLCs) of patients showing a short survival rate express the lowest and the highest levels of PTPRJ and SLC3A2, respectively. Therefore, the results reported here contribute to shed lights on PTPRJ signaling in cancer cells: moreover, our findings also support the development of a novel anticancer therapeutic approach by targeting the pathway of PTPRJ that is usually downregulated in highly malignant human neoplasias.

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.

CD98 signals controlling tumorigenesis

CD98 is implicated in a large number of cancers. CD98 regulates amino acid transport and integrin signaling, which are key drivers in tumor progression. The light chain in the CD98 heterodimer functions as an amino acid exchanger. Alongside the light chain, the heavy chain forms a heterocomplex at the plasma membrane to mediate signaling pathways. In this article, we review various approaches to blocking CD98 activity, which may lead to novel opportunities in cancer therapeutics.

Tyrosine Kinase Signaling in Clear Cell and Papillary Renal Cell Carcinoma Revealed by Mass Spectrometry-Based Phosphotyrosine Proteomics

PURPOSE

Targeted therapies in renal cell carcinoma (RCC) are limited by acquired resistance. Novel therapeutic targets are needed to combat resistance and, ideally, target the unique biology of RCC subtypes.

EXPERIMENTAL DESIGN

Tyrosine kinases provide critical oncogenic signaling and their inhibition has significantly impacted cancer care. To describe a landscape of tyrosine kinase activity in RCC that could inform novel therapeutic strategies, we performed a mass spectrometry-based system-wide survey of tyrosine phosphorylation in 10 RCC cell lines as well as 15 clear cell and 15 papillary RCC human tumors. To prioritize identified tyrosine kinases for further analysis, a 63 tyrosine kinase inhibitor (TKI) drug screen was performed.

RESULTS

Among the cell lines, 28 unique tyrosine phosphosites were identified across 19 kinases and phosphatases including EGFR, MET, JAK2, and FAK in nearly all samples. Multiple FAK TKIs decreased cell viability by at least 50% and inhibited RCC cell line adhesion, invasion, and proliferation. Among the tumors, 49 unique tyrosine phosphosites were identified across 44 kinases and phosphatases. FAK pY576/7 was found in all tumors and many cell lines, whereas DDR1 pY792/6 was preferentially enriched in the papillary RCC tumors. Both tyrosine kinases are capable of transmitting signals from the extracellular matrix and emerged as novel RCC therapeutic targets.

CONCLUSIONS

Tyrosine kinase profiling informs novel therapeutic strategies in RCC and highlights the unique biology among kidney cancer subtypes. Clin Cancer Res; 22(22); 5605-16. ©2016 AACR.

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.

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

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

Membrane protein 4F2/CD98 is a cell surface receptor involved in the internalization and trafficking of human β-Defensin 3 in epithelial cells

Human β-defensins play a pivotal role in the innate immune response. Although expressed by and acting at epithelial surfaces, little is known about their specific interaction with epithelial structures. Here, we identify the transmembrane protein CD98 as a cell surface receptor involved in the internalization of human β-defensin 3 (hBD3) in human epithelial A549 cells. CD98 and hBD3 extensively colocalize on the basolateral domain of A549. While verifying their direct binding by fluorescence resonance energy transfer and surface plasmon resonance, we mapped the interaction to CD98 residues 304-414, i.e. to the region known to interact with the proteins of intestinal bacteria during colonic invasion. Treatment of A549 cells with hBD3 dramatically reduces CD98 expression and conversely, knockdown of CD98 expression impairs hBD3 cell surface binding and internalization. Competition for bacterial binding to CD98 and downregulation of CD98 expression may represent novel mechanisms for the antibacterial activity of hBD3.

L-type amino-acid transporter 1 (LAT1): a therapeutic target supporting growth and survival of T-cell lymphoblastic lymphoma/T-cell acute lymphoblastic leukemia

The altered metabolism of cancer cells is a treasure trove to discover new antitumoral strategies. The gene (SLC7A5) encoding system L amino-acid transporter 1 (LAT1) is overexpressed in murine lymphoma cells generated via T-cell deletion of the pten tumor suppressor, and also in human T-cell acute lymphoblastic leukemia (T-ALL)/lymphoma (T-LL) cells. We show here that a potent and LAT1 selective inhibitor (JPH203) decreased leukemic cell viability and proliferation, and induced transient autophagy followed by apoptosis. JPH203 could also alter the in vivo growth of luciferase-expressing-tPTEN-/- cells xenografted into nude mice. In contrast, JPH203 was nontoxic to normal murine thymocytes and human peripheral blood lymphocytes. JPH203 interfered with constitutive activation of mTORC1 and Akt, decreased expression of c-myc and triggered an unfolded protein response mediated by the C/EBP homologous protein (CHOP) transcription factor associated with cell death. A JPH203-resistant tPTEN-/-clone appeared CHOP induction deficient. We also demonstrate that targeting LAT1 may be an efficient broad spectrum adjuvant approach to treat deadly T-cell malignancies as the molecule synergized with rapamycin, dexamethasone, doxorubicin, velcade and l-asparaginase to alter leukemic cell viability.

4F2hc-silencing impairs tumorigenicity of HeLa cells via modulation of galectin-3 and β-catenin signaling, and MMP-2 expression

4F2hc is a type-II glycoprotein whose covalent-bound association with one of several described light chains yields a heterodimer mainly involved in large neutral amino acid transport. Likewise, it is well known that the heavy chain interacts with β-integrins mediating integrin-dependent events such as survival, proliferation, migration and even transformation. 4F2hc is a ubiquitous protein whose overexpression has been related to tumor development and progression. Stable silencing of 4F2hc in HeLa cells using an artificial miRNA impairs in vivo tumorigenicity and leads to an ineffective proliferation response to mitogens. 4F2hc colocalizes with β1-integrins and CD147, but this interaction does not occur in lipid rafts in HeLa cells. Moreover, silenced cells present defects in integrin- (FAK, Akt and ERK1/2) and hypoxia-dependent signaling, and reduced expression/activity of MMP-2. These alterations seem to be dependent on the inappropriate formation of CD147/4F2hc/β1-integrin heterocomplexes on the cell surface, arising when CD147 cannot interact with 4F2hc. Although extracellular galectin-3 accumulates due to the decrease in MMP-2 activity, galectin-3 signaling events are blocked due to an impaired interaction with 4F2hc, inducing an increased degradation of β-catenin. Furthermore, cell motility is compromised after protein silencing, suggesting that 4F2hc is related to tumor invasion by facilitating cell motility. Therefore, here we propose a molecular mechanism by which 4F2hc participates in tumor progression, favoring first steps of epithelial-mesenchymal transition by inhibition of β-catenin proteasomal degradation through Akt/GSK-3β signaling and enabling cell motility.