Expression of L-type amino acid transporter 1 (LAT1) in esophageal carcinoma

BACKGROUND AND OBJECTIVES: It has been reported that amino acid transport systems play an important role in cell proliferation. Their activity is increased in malignant cells compared to benign cells. In this study, we investigated whether L-type amino acid transporter 1 (LAT1) is expressed in human non-cancerous esophageal mucosa and esophageal squamous cell carcinoma. We also examined whether LAT1 expression is correlated with histopathological features. METHODS: From January 1999 to December 2001, sections of formalin-fixed, paraffin-embedded tissue from 11 cases of early esophageal carcinoma (T1) and 19 cases of advanced esophageal carcinoma (T2, T3) were entered in the study. Histopathologically, all 30 cases were squamous cell carcinoma. Immunohistochemical staining was performed using rabbit anti-LAT1 IgG, with the standard avidin-streptavidin immuno-peroxidase method. Measurement was performed by means of computer-assisted image analysis. The ratio of cells with LAT1 expression in esophageal squamous cell carcinoma and non-cancerous esophageal mucosa was used for analysis in this study. RESULTS: Non-cancerous esophageal mucosa expressed LAT1 only in the basal layer of the esophageal wall. Esophageal squamous cell carcinoma expressed LAT1 throughout the tumor. LAT1 expression in esophageal squamous cell carcinoma was significantly higher than that in non-cancerous esophageal mucosa. LAT1 expression in esophageal squamous cell carcinoma increased as the depth of invasion progressed (T1 < T2 (P = 0.0477), T2 < T3 (P = 0.0415), T1 < T3 (P = 0.0044)), and as the tumor size increased. Also, high LAT1 expression was significantly associated with well-differentiated carcinoma. CONCLUSION: These results suggest that LAT1 plays a significant role in cell proliferation, differentiation, and invasion in esophageal squamous cell carcinoma.     

L-type amino acid transporter 1 (LAT1) expression in malignant pleural mesothelioma

L-Type amino acid transporter 1 (LAT1) is known to be highly expressed in various human neoplasms. However, little is known about how LAT1 is expressed in malignant pleural mesothelioma (MPM). Twenty-one patients were included in this study. Tumor sections were stained by immunohistochemistry for LAT1, glucose transporter 1 (GLUT1), GLUT3, hypoxia inducible factor-1α (HIF-1α), hexokinase I, vascular endothelial growth factor (VEGF), microvessel density (MVD) by determination of CD34, epidermal growth factor receptor (EGFR), phosphatase and tensin analog (PTEN), p-AKT, p-manmalian target of rapamycin (mTOR), p-S6K, p53 and BCL-2. LAT1 was overexpressed in approximately 50% of the patients with MPM. LAT1 expression was closely correlated with CD98, hypoxic markers, the mTOR pathway, Ki-67 and p53. The overexpression of LAT1 was closely associated with poor outcome in patients with MPM. LAT1 is closely associated with tumor development and progression in patients with MPM.     

Prognostic significance of L-type amino acid transporter 1 (LAT1) and 4F2 heavy chain (CD98) expression in early stage squamous cell carcinoma of the lung

The purpose of this study was to evaluate the prognostic value of L-type amino acid transporter 1 (LAT 1) and 4F2 heavy chain (CD98) in patients with stage I squamous cell carcinoma of the lung. A total of 84 consecutive patients with completely resected pathologic stage I squamous cell carcinoma of the lung were retrospectively reviewed. All patients underwent resection of the tumor and the immunohistochemical analysis was done to determine the expression of LAT 1, CD98, Ki-67 labeling index, vascular endothelial growth factor, and microvessel density. These pathological parameters were correlated with the prognosis of patients after complete resection of the tumor. A positive rate of LAT 1 expression (87%; 73/84) was significantly higher than that of CD98 expression (65%; 55/84) ( P =  0.0018). Cooperative expression of LAT 1 and CD98 was recognized in 62% (52/84). LAT 1 expression was significantly correlated with CD98, Ki-67 labeling index, vascular endothelial growth factor, and microvessel density. The 5-year survival rates of the LAT 1-positive and LAT1-negative patients were 59% and 88%, respectively ( P =  0.2186). Tumor cell proliferation and angiogenesis were not also (a) prognostic factor. However, the 5-year survival rate of patients with both LAT 1 and CD98-positivity (57%) was significantly worse than that of other patients (88%; P  = 0.0136). Multivariate analysis confirmed that positive cooperative expression of LAT 1 and CD98 was an independent factor for predicting a poor prognosis. A cooperative expression of LAT 1 and CD98 is a significant pathological factor for predicting the poor prognosis in patients with resectable stage I squamous cell carcinoma of the lung. ( Cancer Sci 2009; 100: 249–254)     

L-type amino acid transporter 1 as a potential molecular target in human astrocytic tumors

L-type amino acid transporter 1 (LAT1) is a Na+-independent neutral amino acid transport agency and essential for the transport of large neutral amino acids. LAT1 has been identified as a light chain of the CD98 heterodimer from C6 glioma cells. LAT1 also corresponds to TA1, an oncofetal antigen that is expressed primarily in fetal tissues and cancer cells. We have investigated for the first time, the expression of the transporter in the human primary astrocytic tumor tissue from 60 patients. LAT1 is unique because it requires an additional single membrane spanning protein, the heavy chain of 4F2 cell surface antigen (4F2hc), for its functional expression. 4F2hc expression was also determined by immunohistochemistry. Kaplan-Meier analyses demonstrated that high LAT1 expression correlated with poor survival for the study group as a whole (p<0.0001) and for those with glioblastoma multiforme in particular (p=0.0001). Cox regression analyses demonstrated that LAT1 expression was one of significant predictors of outcome, independent of all other variables. On the basis of these findings, we also investigated the effect of the specific inhibitor to LAT1, 2-aminobicyclo-2 (2,2,1)-heptane-2-carboxylic acid (BCH), on the survival of C6 glioma cells in vitro and in vivo using a rat C6 glioma model. BCH inhibited the growth of C6 glioma cells in vitro and in vivo in a dose-dependent manner. Kaplan-Meier survival data of rats treated with BCH were significant. These findings suggest that LAT1 could be one of the molecular targets in glioma therapy.     

Expression of L-type amino acid transporter 1 (LAT1) and 4F2 heavy chain (4F2hc) in liver tumor lesions of rat models.

BACKGROUND AND OBJECTIVES: It has been said that amino acid transporters play an important role in supplying nutrition to cells and for cell proliferation. In this study, we examined whether LAT1 and 4F2hc are closely related to tumor growth. METHODS: Rat colon cancer cells (RCN-9) were injected into the spleen of 12 male rats (inbred F344/DuCrj). In each rat, liver samples including tumor lesions were immunostained with anti-LAT1 and anti-4F2hc antibodies. The staining area of LAT1 and 4F2hc tumor lesions was calculated by computer analysis. RESULTS: Sixty-eight tumor nodules were observed in 12 livers. Out of the 68 tumor nodules, 36 nodules (52.9%) indicated a positive staining of LAT1 and 32 (47.1%) had a negative staining of LAT1. However, the LAT1 expression was scarcely detected in non-tumor areas. In terms of the 4F2hc expression, there were 56 nodules (82.4%) with 4F2hc positive and 12 (17.6) with 4F2hc negative. In addition, the expression of 4F2hc in non-tumor areas was almost the same as the expression of 4F2hc in tumor lesions. The average tumor size of the group with LAT1 positive and 4F2hc positive (n = 31) was 0.845 +/- 0.232 mm(2), which was significantly larger than that of the group with LAT1 negative and 4F2hc negative group (n = 7) (0.090 +/- 0.028 mm(2)) or the group with LAT1 positive and 4F2hc negative (n = 5) (0.097 +/- 0.025 mm(2)), respectively (P = 0.0017, P = 0.007). CONCLUSION: LAT1 was related to tumor growth. We think that LAT1 can possibly enhance its ability to promote tumor growth in cooperation with 4F2hc.     

High expression of L-type amino acid transporter 1 in infiltrating glioma cells

L-type amino acid transporter 1 (LAT1), a neutral amino acid transport agent, is essential for the transport of large neutral amino acids. LAT1 also corresponds to tumor-associated gene-1 (TA1), an oncofetal antigen that is expressed primarily in fetal tissues and cancer cells such as glioma cells. We have investigated the expression of the transporter in the human primary glioma tissue from 68 patients. Among these patients, we could see the border zone between tumors and normal bain tissues in 10 patients. By WHO criteria, two of the specimens were diagnosed as grade 2, three as grade 3, and five as grade 4 [glioblastoma multiforme (GBM)]. In 9 of 10 cases, we could identify the infiltrating glioma cells associated with stronger immunoreactivity for LAT1. These tumor cells aggregated around the neurons in the border zone and were often found in the perivascular space. In one GBM case, the tumors seemed to develop expansively and separated from the normal brain with a border of arachnoid membrane. The expression of LAT1 was always higher in infiltrating glioma cells than in cells located in the center of the tumor. These findings suggest that LAT1 is one of the molecular targets for glioma therapy.     

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.     

Expression of L‐type amino acid transporter 1 (LAT1) as a prognostic and therapeutic indicator in multiple myeloma

L‐type amino‐acid transporter 1 (LAT1) plays a key role in cell growth and survival. To determine the prognostic significance of LAT1 in multiple myeloma (MM), we investigated the expression of LAT1 and its functional subunit, 4Fc heavy chain (CD98), on myeloma cells by immunohistochemistry in 100 newly diagnosed MM patients. High expression (moderate or strong staining intensity) of LAT1 and CD98 was detected in 56% and 45% of patients, respectively. The LAT1 expression score was positively correlated with Ki‐67 index (r = 0.631, P < 0.001), and there was a statistically significant difference in Durie–Salmon stage between patients with high and low LAT1 expression (P = 0.03). In 43 patients treated with melphalan and prednisolone, the overall response rate was significantly higher in the high LAT1 expression group (60.0%) than in the low LAT1 expression group (17.6%) (P = 0.03). Multivariate analysis confirmed that high expression of LAT1 was a significant prognostic factor for predicting poor overall survival independently from the International Staging System (both P = 0.01). Here, we show that the overexpression of LAT1 is significantly associated with high proliferation and poor prognosis in newly diagnosed MM patients. Thus, LAT1 may be a promising pathological marker for identifying high‐risk MM.     

氨基酸转运蛋白LAT4调控髓系白血病细胞自噬的机制探讨

目的:探究氨基酸转运蛋白LAT4调控髓系白血病细胞自噬的机制。方法:通过RNAi技术敲低HL-60细胞中LAT4的表达，CCK-8检测细胞体外增殖能力的变化，免疫荧光检测自噬标志物LC3Ⅱ的表达变化。Western Blot检测给予LAT4抑制剂BCH梯度浓度抑制后细胞内自噬相关蛋白的表达差异。谷氨酰胺剥夺诱导自噬后加入最适剂量BCH抑制LAT4，采用液滴计数仪检测细胞对3H-Leucine摄取率的变化。结果:干扰LAT4表达能显著降低HL-60细胞体外增殖能力并促进自噬蛋白LC3Ⅱ的表达。BCH梯度抑制LAT4活性后LAT4和pS6K蛋白表达受到显著抑制，LC3Ⅱ蛋白表达量增加，50 μmol/L BCH的LAT4活性抑制效果最佳。3H-Leucine摄取率随BCH抑制LAT4时间增加而降低，BCH作用8 h后3H-Leucine摄取率分别较0 h、4 h降低47.64%和27.05%（P＜0.001）。结论:LAT4通过转运亮氨酸激活HL-60细胞内pS6K表达，抑制自噬发生。     

Proteomics and phosphoproteomics reveal key regulators associated with cytostatic effect of amino acid transporter LAT1 inhibitor

L‐type amino acid transporter 1 (LAT1) is highly expressed in various cancers and plays important roles not only in the amino acid uptake necessary for cancer growth but also in cellular signaling. Recent research studies have reported anticancer effects of LAT1 inhibitors and demonstrated their potential for cancer therapy. Here, we characterized the proteome and phosphoproteome in LAT1‐inhibited cancer cells. We used JPH203, a selective LAT1 inhibitor, and performed tandem mass tag–based quantitative proteomics and phosphoproteomics on four biliary tract cancer cell lines sensitive to JPH203. Our analysis identified hundreds to thousands of differentially expressed proteins and phosphorylated sites, demonstrating the broad influence of LAT1 inhibition. Our findings showed various functional pathways altered by LAT1 inhibition, and provided possible regulators and key kinases in LAT1‐inhibited cells. Comparison of these changes among cell lines provides insights into general pathways and regulators associated with LAT1 inhibition and particularly suggests the importance of cell cycle–related pathways and kinases. Moreover, we evaluated the anticancer effects of the combinations of JPH203 with cell cycle–related kinase inhibitors and demonstrated their potential for cancer therapy. This is the first study providing the proteome‐wide scope of both protein expression and phosphorylation signaling perturbed by LAT1 inhibition in cancer cells.     

Activation of a system A amino acid transporter, ATA1/SLC38A1, in human hepatocellular carcinoma and preneoplastic liver tissues

The expression of amino acid transporter (AT) mRNAs including A system (ATA1/SNAT1/SLC38A1, ATA2/SNAT2/SLC38A2 and ATA3/SNAT3/SLC38A4), L system (LAT1/SLC7A5 and LAT2/SLC7A8), and y+ (CAT2/SLC7A2) genes, were compared among hepatocellular carcinoma (HCC) and non-cancerous liver cells. Among them the ATA1 mRNA expression was significantly elevated in all HCC cell lines (HepG2, HLF, HuH7 and JHH4) examined compared with normal liver tissue. We further discovered that the expression of ATA1 mRNA was significantly activated in HCC tissues and also elevated in pre-malignant cirrhotic livers from HCC patients, compared with normal livers from non-HCC patients. The ATA1 protein was extensively accumulated in the cytoplasm of pre-malignant liver and most HCCs, while being weak or undetectably low in normal liver tissues. SiRNA-mediated suppression of endogenous ATA1 lowered the viability of HepG2 cells. Thus, the activation of ATA1 confers growth and survival advantages in pre-malignant and malignant liver lesions.     

Prognostic significance of L-type amino acid transporter 1 expression in resectable stage I-III nonsmall cell lung cancer

The clinical significance of L-type amino acid transporter 1 (LAT1) expression remains unclear, whereas many experimental studies have demonstrated that LAT1 is associated with the proliferation of cancer cells. The purpose of this study was to evaluate the prognostic value of LAT1 in patients with nonsmall cell lung cancer (NSCLC). A total of 321 consecutive patients with completely resected pathologic stage I-III NSCLC were retrospectively reviewed. Expression of LAT1 and proliferative activity, as determined by the Ki-67 labelling index, was also evaluated immunohistochemically and correlated with the prognosis of patients who underwent complete resection of the tumour. Expression of LAT1 was positive in 163 patients (51%) (29% of adenocaricnoma (58 of 200 patients), 91% of squamous cell carcinoma (91 of 100 patients), and 67% of large cell carcinoma (14 of 21 patients)). The 5-year survival rate of LAT1-positive patients (51.8%) was significantly worse than that of LAT1-negative patients (87.8%; P<0.001). L-type amino acid transporter 1 expression was significantly associated with lymph node metastasis and disease stage. Multivariate analysis confirmed that positive expression of LAT1 was an independent factor for predicting a poor prognosis. There was a significant correlation between LAT1 expression and Ki-67 labelling index. LAT1 expression is a promising pathological factor to predict the prognosis in patients with resectable stage I-III NSCLC.     

氨基酸转运载体ＬＡＴ１在肿瘤中的研究进展

氨基酸是构成蛋白质的基本元件,同时参与细胞内许多重要的代谢途径。氨基酸的跨膜运输依赖氨基酸转运载体（氨基酸跨膜转运蛋白）的介导。Ｌ型氨基酸转运载体１（ＬＡＴ１）是Ｌ型氨基酸转运载体中的重要成员,主要负责转运大的、支链的、芳香族的中性氨基酸,包括一些必需氨基酸,如亮氨酸。ＬＡＴ１在恶性肿瘤中呈过表达,可以促进肿瘤细胞的增殖、侵袭和迁移。ＬＡＴ１在医学、营养等生命科学领域有着重要的研究意义。本文就ＬＡＴ１在肿瘤研究中的进展作一综述。     

Correlation of L-type amino acid transporter 1 and CD98 expression with triple negative breast cancer prognosis

Triple negative breast cancer (TNBC) is a heterogeneous, aggressive cancer for which there is no effective chemotherapy or targeted therapy. We aimed to evaluate L-type amino acid transporter (LAT) 1 and CD98 expression immunohistochemically in patients with breast cancer, especially TNBC. Out of 129 patients, LAT1 was positive in 56 patients (43.4%), and CD98 was positive in 41 patients (31.8%). The positive ratio of LAT1 expression in luminal A cases was 7.9%, 30.0% in luminal B cases, 71.4% in HER2 cases and 64.0% in TN cases. HER2 and TN subtypes expressed LAT1 and CD98 at higher levels than luminal A and B subtypes (both P < 0.001). LAT1 and CD98 expression correlated with tumor size (LAT1, P = 0.010; CD98, P = 0.007), nuclear grade (LAT1, P < 0.001; CD98, P < 0.001) and Ki67 labeling index (LAT1, P < 0.001; CD98, P = 0.001). LAT1 and CD98 expression was negatively associated with ER and PgR (both P < 0.001). In TNBC, the 5-year disease-free rate of CD98+ (63.6%) or LAT1+/CD98+ (61.9%) patients was significantly worse than that of CD98- (89.3%) patients or those with no co-expression of LAT1 and CD98 (89.7%), respectively (P = 0.014, P = 0.009). The 5-year survival rates of CD98 positive/negative patients were 77.3% and 100% (P = 0.050), respectively, whereas that of patients with LAT1+/CD98+ (76.2%) was significantly worse (100%) (P = 0.040). Multivariate analysis confirmed that CD98+ or LAT1+/CD98+ expression were risk factors for relapse in TNBC (P = 0.023, P = 0.019). Thus, in the present study we show that LAT1 and CD98 expression are prognostic factors. Inhibition of these proteins might provide a new therapeutic strategy in TNBC.     

Serum amino acid levels in patients with hepatocellular carcinoma

Serum amino acid concentrations in cirrhotic patients with and without hepatocellular carcinoma (HCC) were investigated. Elevation of serum aromatic amino acids (AAA) and methionine levels observed in cirrhotic patients without malignancy was not apparent in cirrhotic cases with HCC, and thus the ratio of branched chain amino acids (BCAA) to AAA was not so diminished in the latter cases. Development of hepatic encephalopathy in cirrhotic patients with HCC led to only a slight change in the serum aminogram characteristic of hepatic failure. In patients who underwent operations, tissue amino acid compositions of hepatocellular, gastric, and colon cancers were compared with each other and their respective surrounding epithelia. Amino acid contents in the tumor tissue were generally higher than those in the respective nontumorous parts, especially in the case of HCC. The methionine, tyrosine, and phenylalanine contents in HCC were much higher than in cirrhotic or normal liver. Serum aminograms in rats with ethionine-induced HCC were similar to those in cirrhotic patients with HCC. Amino acid contents in HCC were much higher than those in the surrounding cirrhotic liver tissue of rats. Serum and liver tyrosine and isoleucine contents rose significantly in rats 5 to 6 weeks after the initiation of a 0.25% ethionine-containing diet. After the 20th week of the experiment, by which time well-differentiated HCC had developed, liver tyrosine and isoleucine contents increased whereas serum isoleucine concentrations decreased. The results suggest that the serum amino acid patterns characteristic of cirrhotic patients with HCC may result from the increased consumption of amino acids by HCC. Determinations of the amino acid levels are also useful for estimating the prognosis and discovering imminent hepatic encephalopathy in cirrhotic patients with HCC.     

Clinicopathological Significance of L-type Amino Acid Transporter 1 (LAT1) Expression in Patients with Adenoid Cystic Carcinoma

The expression of L-type amino acid transporter 1 (LAT1) is correlated with tumor cell growth and survival. However, the clinicopathological significance of LAT1 expression in adenoid cystic carcinoma (ACC) remains to be elucidated. The aim of this study is to investigate the clinicopathological significance of LAT1 expression in ACC. A total of 30 patients with ACC were retrospectively reviewed. Tumor sections were stained by immunohistochemistry for LAT1, p53, and CD98, and cell proliferation and microvessel density (MVD) were determined by Ki-67 and CD34, respectively. High LAT1 and CD98 expression were observed in 27 % (8/30) and 23 % (7/30) of samples, respectively (p?>?0.999). The high expression of LAT1 was significantly correlated with cell proliferation (Ki-67) and the cell cycle regulator p53. By univariate analysis, solid histological pattern, maxillary tumor site, LAT1, CD98, Ki-67 and p53 were significantly associated with poor prognosis. Multivariate analysis demonstrated that the high expression of LAT1 was an independent prognostic factor for predicting poor prognosis after surgical resection. LAT1 is a promising clinical marker to predict the outcome after surgery in patients with ACC.