Targeting the function of membrane transporters in cancer stemlike cells is a potential new therapeutic approach. Cystine‐glutamate antiporter xCT expressed in CD44 variant (CD44v)‐expressing cancer ...cells contributes to the resistance to oxidative stress as well as cancer therapy through promoting glutathione (GSH)‐mediated antioxidant defense. Amino acid transport by xCT might, thus, be a promising target for cancer treatment, whereas the determination factors for cancer cell sensitivity to xCT‐targeted therapy remain unclear. Here, we demonstrate that high expression of xCT and glutamine transporter ASCT2 is correlated with undifferentiated status and diminished along with cell differentiation in head and neck squamous cell carcinoma (HNSCC). The cytotoxicity of the xCT inhibitor sulfasalazine relies on ASCT2‐dependent glutamine uptake and glutamate dehydrogenase (GLUD)‐mediated α‐ketoglutarate (α‐KG) production. Metabolome analysis revealed that sulfasalazine treatment triggers the increase of glutamate‐derived tricarboxylic acid cycle intermediate α‐KG, in addition to the decrease of cysteine and GSH content. Furthermore, ablation of GLUD markedly reduced the sulfasalazine cytotoxicity in CD44v‐expressing stemlike HNSCC cells. Thus, xCT inhibition by sulfasalazine leads to the impairment of GSH synthesis and enhancement of mitochondrial metabolism, leading to reactive oxygen species (ROS) generation and, thereby, triggers oxidative damage. Our findings establish a rationale for the use of glutamine metabolism (glutaminolysis)‐related genes, including ASCT2 and GLUD, as biomarkers to predict the efficacy of xCT‐targeted therapy for heterogeneous HNSCC tumors.
Competition exists between xCT‐mediated cystine uptake and GLUD‐mediated alpha‐KG generation.
Although cancer metastasis is associated with poor prognosis, the mechanisms of this event, especially via lymphatic vessels, remain unclear. Lymphatic vessel endothelial hyaluronan receptor 1 ...(LYVE‐1) is expressed on lymphatic vessel endothelium and is considered to be a specific marker of lymphatic vessels, but it is unknown how LYVE‐1 is involved in the growth and metastasis of cancer cells. We produced rat monoclonal antibodies (mAb) recognizing the extracellular domain of mouse LYVE‐1, and investigated the roles of LYVE‐1 in tumor formation and metastasis. The mAb 38M and 64R were selected from hybridoma clones created by cell fusion between spleen cells of rats immunized with RH7777 rat hepatoma cells expressing green fluorescent protein (GFP)‐fused mouse LYVE‐1 proteins and mouse myeloma cells. Two mAb reacted with RH7777 and HEK293F human embryonic kidney cells expressing GFP‐fused mouse LYVE‐1 proteins in a GFP expression‐dependent manner, and each recognized a distinct epitope. On immunohistology, the 38M mAb specifically stained lymphatic vessels in several mouse tissues. In the wound healing assay, the 64R mAb inhibited cell migration of HEK293F cells expressing LYVE‐1 and mouse lymphatic endothelial cells (LEC), as well as tube formation by LEC. Furthermore, this mAb inhibited primary tumor formation and metastasis to lymph nodes in metastatic MDA‐MB‐231 xenograft models. This shows that LYVE‐1 is involved in primary tumor formation and metastasis, and it may be a promising molecular target for cancer therapy.
LYVE‐1 is involved in primary tumor formation and metastasis, and may be a promising molecular target for cancer therapy with therapeutic mAb.
CD44 is an adhesion molecule expressed in cancer stem-like cells. Here, we show that a CD44 variant (CD44v) interacts with xCT, a glutamate-cystine transporter, and controls the intracellular level ...of reduced glutathione (GSH). Human gastrointestinal cancer cells with a high level of CD44 expression showed an enhanced capacity for GSH synthesis and defense against reactive oxygen species (ROS). Ablation of CD44 induced loss of xCT from the cell surface and suppressed tumor growth in a transgenic mouse model of gastric cancer. It also induced activation of p38
MAPK, a downstream target of ROS, and expression of the gene for the cell cycle inhibitor p21
CIP1/WAF1. These findings establish a function for CD44v in regulation of ROS defense and tumor growth.
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► CD44v contributes to the reduction of intracellular reactive oxygen species ► CD44v promotes GSH synthesis by interacting with glutamate-cystine transporter xCT ► Variant 8–10 region is required for CD44v-xCT interaction leading to GSH synthesis ► xCT inhibitor sulfasalazine suppresses CD44-dependent cancer cell expansion in vivo
In cancer metastasis, various environmental stressors attack the disseminating cells. The successful colonization of cancer cells in secondary sites therefore requires the ability of the cells to ...avoid the consequences of such exposure to the stressors. Here we show that orthotopic transplantation of a CD44 variant isoform-expressing (CD44v(+)) subpopulation of 4T1 breast cancer cells, but not that of a CD44v(-) subpopulation, in mice results in efficient lung metastasis accompanied by expansion of stem-like cancer cells. Such metastasis is dependent on the activity of the cystine transporter xCT, and the stability of this protein is controlled by CD44v. We find that epithelial splicing regulatory protein 1 regulates the expression of CD44v, and knockdown of epithelial splicing regulatory protein 1 in CD44v(+) cells results in an isoform switch from CD44v to CD44 standard (CD44s), leading to reduced cell surface expression of xCT and suppression of lung colonization. The epithelial splicing regulatory protein 1-CD44v-xCT axis is thus a potential therapeutic target for the prevention of metastasis.
HER1-and HER2-targeted drugs are effective in cancer therapy, especially against lung, breast and colon malignancies; however, resistance of cancer cells to HER1-and HER2-targeted therapies is ...becoming a serious problem. The avidity/affinity constant (KA) and growth inhibitory effect of anti-HER3 rat monoclonal antibodies (mAb, Ab1∼Ab6) in the presence of therapeutic mAb or low-molecular-weight inhibitors against HER family proteins were analyzed by flow cytometry-based Scatchard plots (Splot) and cell proliferation assay. The KA of Ab3 and Ab6, but not Ab1 or Ab4, split into dual (high and low) modes of KA, and Ab6 exhibited greater anti-proliferative effects against LS-174T colon cancer cells in the presence of Pertuzumab (anti-HER2 mAb). A high KA by Ab6 and Ab6-mediated increased growth inhibition were observed against NCI–H1838 lung or BT474 breast cancer cells, respectively, in the presence of Panitumumab (anti-HER1 mAb) or Perutuzumab. A high KA by Ab6 and Ab6-mediated increased anti-proliferative effects against NCI–H1838 or BT474 were also respectively observed in the presence of Erlotinib (HER1 inhibitor) or Lapatinib (HER1/HER2 inhibitor). In HER1-knockout (KO) NCI–H1838, the reactivity and KA of Ab4 increased compared with in parent NCI–H1838. In HER1-KO or HER3-KO SW1116 colon cancer cells, dual modes of KA with Pertuzumab were noted, and the combination Ab6 and Pertuzumab promoted growth inhibition of HER1-KO, but not of parent SW1116.
•Anti-proliferative effects of anti-HER3 mAb were evaluated in the presence of HER1-or HER2-targeted drugs.•Avidity constants (KA) of mAb were determined by flow cytometry (FCM)-based Scatchard plot (Splot) analysis.•High KA rather than total binding is important for the anti-proliferative capacity of mAb in combination.•Analysis of binding avidity (KA) will contribute to evaluate additional mAb aiming at therapeutic improvement over preceding anti-cancer drugs.
Copy number alterations detected by comparative genomic hybridization (CGH) can lead to the identification of novel cancer‐related genes. We analyzed chromosomal aberrations in a set of 100 human ...primary colorectal cancers (CRCs) using CGH and found a solute carrier (SLC) 7A1 gene, which encodes cationic amino acid transporter 1 (CAT1) with 14 putative transmembrane domains, in a chromosome region (13q12.3) with a high frequency of gene amplifications. SLC7A1/CAT1 is a transporter responsible for the uptake of cationic amino acids (arginine, lysine, and ornithine) essential for cellular growth. Microarray and PCR analyses have revealed that mRNA transcribed from CAT1 is overexpressed in more than 70% of human CRC samples, and RNA interference–mediated knockdown of CAT1 inhibited the cell growth of CRCs. Rats were immunized with rat hepatoma cells expressing CAT1 tagged with green fluorescent protein (GFP), and rat splenocytes were fused with mouse myeloma cells. Five rat monoclonal antibodies (mAbs) (CA1 ~ CA5) reacting with HEK293 cells expressing CAT1‐GFP in a GFP expression–dependent manner were selected from established hybridoma clones. Novel anti‐CAT1 mAbs selectively reacted with human CRC tumor tissues compared with adjacent normal tissues according to immuno‐histochemical staining and bound strongly to numerous human cancer cell lines by flow cytometry. Anti‐CAT1 mAbs exhibited internalization activity, antibody‐dependent cellular cytotoxicity, and migration inhibition activity against CRC cell lines. Furthermore, CA2 inhibited the in vivo growth of human HT29 and SW‐C4 CRC tumors in nude mice. This study suggested CAT1 to be a promising target for mAb therapy against CRCs.
Frequent gene amplification of SLC7A1/CAT1 and increased CAT1 mRNA expression in colorectal cancers (CRC) were demonstrated. Novel anti‐CAT1 monoclonal antibodies (mAbs) were developed, and higher expression of CAT1 protein in CRC and in vivo antitumor effects of mAbs on xenografted CRC cells in nude mice were confirmed. CAT1 may be a promising target for anti‐CRC therapy.
Expression of CD44, especially the variant isoforms (CD44v) of this major cancer stem cell marker, contributes to reactive oxygen species (ROS) defense through stabilizing xCT (a cystine–glutamate ...transporter) and promoting glutathione synthesis. This enhances cancer development and increases chemotherapy resistance. We investigate the role of CD44v in the regulation of the ROS defense system in cholangiocarcinoma (CCA). Immunohistochemical staining of CD44v and p38MAPK (a major ROS target) expression in Opisthorchis viverrini‐induced hamster CCA tissues (at 60, 90, 120, and 180 days) reveals a decreased phospho‐p38MAPK signal, whereas the CD44v signal was increased during bile duct transformation. Patients with CCA showed CD44v overexpression and negative‐phospho‐p38MAPK patients a significantly shorter survival rate than the low CD44v signal and positive‐phospho‐p38MAPK patients (P = 0.030). Knockdown of CD44 showed that xCT and glutathione levels were decreased, leading to a high level of ROS. We examined xCT‐targeted CD44v cancer stem cell therapy using sulfasalazine. Glutathione decreased and ROS increased after the treatment, leading to inhibition of cell proliferation and induction of cell death. Thus, the accumulation of CD44v leads to the suppression of p38MAPK in transforming bile duct cells. The redox status regulation of CCA cells depends on the expression of CD44v to contribute the xCT function and is a link to the poor prognosis of patients. Thus, an xCT inhibitor could inhibit cell growth and activate cell death. This suggests that an xCT‐targeting drug may improve CCA therapy by sensitization to the available drug (e.g. gemcitabine) by blocking the mechanism of the cell's ROS defensive system.
The redox status regulation of CCA cells depends on the expression of CD44v to contribute the xCT function and is a link to the carcinogenesis and poor prognosis of patients.
Molecular characterization of lung squamous cell carcinoma (LUSC), one of the major subtypes of lung cancer, has not sufficiently improved its nonstratified treatment strategies over decades. ...Accumulating evidence suggests that lineage-specific transcriptional regulators control differentiation states during cancer evolution and underlie their distinct biological behaviors. In this study, by investigating the super-enhancer landscape of LUSC, we identified a previously undescribed "neural" subtype defined by Sox2 and a neural lineage factor Brn2, as well as the classical LUSC subtype defined by Sox2 and its classical squamous partner p63. Robust protein-protein interaction and genomic cooccupancy of Sox2 and Brn2, in place for p63 in the classical LUSC, indicated their transcriptional cooperation imparting this unique lineage state in the "neural" LUSC. Forced expression of p63 downregulated Brn2 in the "neural" LUSC cells and invoked the classical LUSC lineage with more squamous/epithelial features, which were accompanied by increased activities of ErbB/Akt and MAPK-ERK pathways, suggesting differential dependency. Collectively, our data demonstrate heterogeneous cell lineage states of LUSC featured by Sox2 cooperation with Brn2 or p63, for which distinct therapeutic approaches may be warranted. SIGNIFICANCE: Epigenomic profiling reveals a novel subtype of lung squamous cell carcinoma with neural differentiation.
http://cancerres.aacrjournals.org/content/canres/79/24/6084/F1.large.jpg.
(Cancer Sci 2010; 101: 673–678)
Similar to normal tissue stem cells, cancer stem cells (CSCs) are thought to be quiescent or slow‐cycling and, thereby, insensitive to chemo‐ and radiotherapies. CD44, ...a cell surface component that interacts with the extracellular matrix, has been found to be highly expressed in CSCs of several solid tumors. However, the relevancy between CD44+ cells and slow‐cycling cells and the underlying mechanisms for the emergence of CD44+ CSCs during tumorigenesis have not been elucidated. Here we show that a gastric gland residing at the squamo‐columnar junction (SCJ) in normal mouse stomach contains CD44+ stem cell‐like slow‐cycling cells and that this characteristic CD44+ gland was expanded by prostaglandin E2 (PGE2) and Wnt signaling in K19‐Wnt1/C2mE mouse, a genetic mouse model for gastric tumorigenesis. The analysis of three transgenic mouse lines, K19‐Wnt1, K19‐C2mE and K19‐Wnt1/C2mE, revealed that the expansion of CD44+ SCJ cells is triggered by PGE2‐mediated signaling and is prominently enhanced by the addition of Wnt activation. Furthermore, each expanded CD44+ gland in gastric tumor of K19‐Wnt1/C2mE mouse contains a few BrdU label‐retaining quiescent or slow‐cycling cells, suggesting that the CD44+ SCJ cells in normal mouse are candidates for the cell‐of‐origin of gastric CSCs. These observations suggest that PGE2‐mediated inflammatory signaling and Wnt signaling cooperatively trigger the expansion of CD44+ slow‐cycling stem‐like cells in SCJ, leading to development of lethal gastric tumors in mice.
Human epidermal growth factor receptor (HER) family proteins are currently major targets of therapeutic monoclonal antibodies against various epithelial cancers. However, the resistance of cancer ...cells to HER family‐targeted therapies, which may be caused by cancer heterogeneity and persistent HER phosphorylation, often reduces overall therapeutic effects. We herein showed that a newly discovered molecular complex between CD98 and HER2 affected HER function and cancer cell growth. The immunoprecipitation of the HER2 or HER3 protein from lysates of SKBR3 breast cancer (BrCa) cells revealed the HER2‐CD98 or HER3‐CD98 complex. The knockdown of CD98 by small interfering RNAs inhibited the phosphorylation of HER2 in SKBR3 cells. A bispecific antibody (BsAb) that recognized the HER2 and CD98 proteins was constructed from a humanized anti‐HER2 (SER4) IgG and an anti‐CD98 (HBJ127) single chain variable fragment, and this BsAb significantly inhibited the cell growth of SKBR3 cells. Prior to the inhibition of AKT phosphorylation, BsAb inhibited the phosphorylation of HER2, however, significant inhibition of HER2 phosphorylation was not observed in anti‐HER2 pertuzumab, trastuzumab, SER4 or anti‐CD98 HBJ127 in SKBR3 cells. The dual targeting of HER2 and CD98 has potential as a new therapeutic strategy for BrCa.
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