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

L-Type Amino Acid Transporter 1 (LAT1) Promotes PMA-Induced Cell Migration through mTORC2 Activation at the Lysosome

The mTOR signaling pathway integrates signaling inputs from nutrients, including glucose and amino acids, which are precisely regulated by transporters depending on nutrient levels. The L-type amino acid transporter 1 (LAT1) affects the activity of mTORC1 through upstream regulators that sense intracellular amino acid levels. While mTORC1 activation by LAT1 has been thoroughly investigated in cultured cells, the effects of LAT1 expression on the activity of mTORC2 has scarcely been studied. Here, we provide evidence that LAT1 recruits and activates mTORC2 on the lysosome for PMA-induced cell migration. LAT1 is translocated to the lysosomes in cells treated with PMA in a dose- and time-dependent manner. Lysosomal LAT1 interacted with mTORC2 through a direct interaction with Rictor, leading to the lysosomal localization of mTORC2. Furthermore, the depletion of LAT1 reduced PMA-induced cell migration in a wound-healing assay. Consistent with these results, the LAT1 N3KR mutant, which is defective in PMA-induced endocytosis and lysosomal localization, did not induce mTORC2 recruitment to the lysosome, with the activation of mTORC2 determined via Akt phosphorylation or the LAT1-mediated promotion of cell migration. Taken together, lysosomal LAT1 recruits and activates the mTORC2 complex and downstream Akt for PMA-mediated cell migration. These results provide insights into the development of therapeutic drugs targeting the LAT1 amino acid transporter to block metastasis, as well as disease progression in various types of cancer.

The Epigenesis of Salivary Glands Carcinoma: From Field Cancerization to Carcinogenesis

Salivary gland carcinomas (SGCs) are a diverse collection of malignant tumors with marked differences in biological activity, clinical presentation and microscopic appearance. Although the etiology is varied, secondary radiation, oncogenic viruses as well as chromosomal rearrangements have all been linked to the formation of SGCs. Epigenetic modifications may also contribute to the genesis and progression of SGCs. Epigenetic modifications are any heritable changes in gene expression that are not caused by changes in DNA sequence. It is now widely accepted that epigenetics plays an important role in SGCs development. A basic epigenetic process that has been linked to a variety of pathological as well as physiological conditions including cancer formation, is DNA methylation. Transcriptional repression is caused by CpG islands hypermethylation at gene promoters, whereas hypomethylation causes overexpression of a gene. Epigenetic changes in SGCs have been identified, and they have been linked to the genesis, progression as well as prognosis of these neoplasms. Thus, we conduct a thorough evaluation of the currently known evidence on the involvement of epigenetic processes in SGCs.

ZNF24 regulates the progression of KRAS mutant lung adenocarcinoma by promoting SLC7A5 translation

Background

Clinical treatment of RAS mutant cancers is challenging because of the complexity of the Ras signaling pathway. SLC7A5 is a newly discovered downstream gene of the Ras signaling pathway, but the regulatory mechanism is unclear. We aimed to explore the molecular mechanism and role in KRAS mutant lung adenocarcinoma progression.

Methods

Key gene that regulated SLC7A5 in KRAS mutant lung adenocarcinoma was screened by RNA sequencing and bioinformatics analysis. The effect of this gene on the expression of SLC7A5 was studied by RNAi. The regulatory mechanism between the two genes was investigated by immunofluorescence, CoIP, pulldown and yeast two-hybrid assays. The location of the two genes was determined by inhibiting Ras and the downstream pathways PI3K-AKT and MEK-ERK. By in vivo and in vitro experiments, the effects of the key gene on the biological functions of KRAS mutant lung adenocarcinoma were explored.

Results

We found a novel gene, ZNF24, which upregulated SLC7A5 protein expression rather than mRNA expression in KRAS mutant lung adenocarcinoma. Endogenous protein interactions occurred between ZNF24 and SLC7A5. Ras inhibition reduced the expression of ZNF24 and SLC7A5. ZNF24 and SLC7A5 are located downstream of the MEK-ERK and PI3K-AKT pathways. In vivo and in vitro functional experiments confirmed that the ZNF24-SLC7A5 signaling axis promoted the proliferation, invasion and migration of KRAS mutant lung adenocarcinoma.

Conclusions

ZNF24 promoted the growth of KRAS mutant lung adenocarcinoma by upregulating SLC7A5 protein expression, which suggested that ZNF24 is a new biomarker of KRAS mutant tumors and could be a new potential therapeutic target for Ras-driven tumors.

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

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

Impact of tumor site on the prognosis of salivary gland neoplasms: A systematic review and meta-analysis

In numerous types of cancer, the primary tumor site can show a correlation with disease behavior and survival outcomes. In salivary gland tumors (SGTs) this association remains controversial. This study assessed the association between primary sites of SGTs and prognosis. Studies from five databases were assessed and a meta-analysis was performed using studies that presented 95 % confidence interval (95 % CI), hazard ratio (HR) and survival analysis. Gathered information from 46,361 patients showed that site had a prognostic impact on SGTs. Tumors involving minor salivary glands showed worse overall survival (HR = 1.60; 95 % CI = 1.17-2.19; p = 0.003), disease-specific survival (HR=1.63; 95 % CI = 1.12-2.37; p = 0.01), and cause-specific survival (HR=2.10; 95 % CI = 1.72-2.55; p = 0.00001). Tumors from major salivary glands showed better recurrence-free survival (HR=2.31; 95 % CI = 1.77-3.02; p = 0.00001), and locoregional control of disease (HR=2.66; 95 % CI = 1.20-5.91; p = 0.02). Our results showed that the primary site of SGTs has an impact on patient prognosis.

Review of the Correlation of LAT1 With Diseases: Mechanism and Treatment

LAT1 is a member of the system L transporter family. The main role of the LAT1 is to transport specific amino acids through cell membranes to provide nutrients to cells and participate in several metabolic pathways. It also contributes to the transport of hormones and some drugs, which are essential for the development and treatment of some diseases. In recent years, many studies have shown that LAT1 is related to cancer, obesity, diabetes, and other diseases. However, the specific mechanism underlying the influence of LAT1 on such conditions remains unclear. Through the increasing number of studies on LAT1, we have obtained a preliminary understanding on the function of LAT1 in diseases. These studies also provide a theoretical basis for finding treatments for LAT1-related diseases, such as cancer. This review summarizes the function and mechanism of LAT1 in different diseases and the treatment of LAT1-related diseases. It also provides support for the development of novel and reliable disease treatments.

Prognostic value of LAT-1 status in solid cancer: A systematic review and meta-analysis

Background

The expression of the L-type amino acid transporter 1 (LAT1) plays a significant role in tumor progression. However, it remains unclear whether high LAT1 expression correlates with poor prognosis of solid tumor patients. Here, we conducted a meta-analysis to assess the potential of LAT1 in predicting the prognosis of tumor patients.

Methods and findings

A total of 4,579 cases were analyzed from 35 qualified studies. In patients with solid tumors, elevated expression of LAT1 is associated with poor prognosis (overall survival [OS]: pooled hazard ratio (HR) = 1.848, 95% confidence interval (CI) = 1.620–2.108, P < 0.001; disease free survival [DFS]: pooled HR = 1.923, 95% CI = 1.585–2.333, P < 0.001; progression free survival [PFS]: pooled HR = 1.345, 95% CI = 1.133–1.597, P = 0.001). Furthermore, in subgroup analysis, we found an association between high LAT1 expression and poor OS in non-small cell lung cancer (HR = 1.554, 95% CI = 1.345–1.794, P < 0.001), pancreatic cancer (HR = 2.052, 95% CI = 1.613–2.724, P < 0.001) and biliary tract cancer (HR = 2.253, 95% CI = 1.562–3.227, P < 0.001).

Conclusion

The results of this meta-analysis indicate the reliability and potential of using LAT1 expression as a predictive biomarker in solid cancers prior to treatment. However, further studies with larger sample sizes would be beneficial for fully evaluating the predictive value of LAT1 expression for clinical applications.

Epigenetic alterations in salivary gland tumors

Salivary gland tumors (SGTs) comprise a heterogeneous group of benign and malignant neoplasms that exhibit significant variability in their microscopic appearance, clinical presentation, and biological behavior. The etiologic factors are unknown; however, chromosomic translocation, secondary radiation, and chemotherapy can be associated with the development of SGT. It has been indicated that epigenetic alterations can be responsible for the development and progress of these neoplasms. The epigenetic mechanisms are defined as a set of DNA changes that do not alter the sequence of nucleotide bases but alter the expression of the proteins. These alterations have been studied in the SGT, and they were associated with the development and progress of these neoplasms and may influence on SGT prognosis. Hence, we critically review the currently available data on the participation of epigenetic events on salivary gland tumors.

Prognostic significance of p53 immunohistochemical expression in adenoid cystic carcinoma of the salivary glands: a meta-analysis

Adenoid cystic carcinoma of salivary glands is a rare adenocarcinoma and has been placed in “high-risk” category as poor long-term prognosis. The purpose of this study was to investigate p53 protein expression in adenoid cystic carcinoma of salivary glands and its correlation with clinicopathological parameters and prognosis. Literatures were searched from PubMed, Embase, Cochrane Library and Web of Science, which investigated the relationships between p53 expression and pathological type, clinical stage, local recurrence, metastasis, nerve infiltration and overall survival. A total of 1,608 patients from 36 studies were included in the analysis. The results showed that p53-postive expression rate was 49% in adenoid cystic carcinoma of salivary glands (OR=10.34, 95%CI: 4.93-21.71, P < 0.0001). The p53-postive expression was closely related to tumor types (OR=0.30, 95%CI: 0.14-0.65, P < 0.0001). The tumor with solid histological subtype had a strong positive correlation with p53 expression. The combined analysis revealed that the p53-positive expression rate among patients in T1and T2 stage was 41.4%, compared to 53.2% among those in T3 and T4 stage. However, there was no significant correlation between tumor stage and p53 expression (OR=0.47, 95% CI: 0.17-1.29, P = 0.14). Besides, compared to patients with p53-negative expression, those with p53-positive expression had a greater chance of developing metastasis, local recurrence and nerve infiltration as well as poorer 5-year overall survival (P < 0.01). In conclusion, the p53 expression is related to the survival of adenoid cystic carcinoma of salivary glands. It can be considered as the auxiliary detection index in treatment and prognosis of adenoid cystic carcinoma of salivary glands.

Clinicopathological significance of LAT1 and ASCT2 in patients with surgically resected esophageal squamous cell carcinoma

BACKGROUND

Amino acid transporters are highly expressed in various human cancers. L-type amino acid transporter 1 (LAT1) and system alanine-serine-cysteine amino acid transporter-2 (ASCT2) play a crucial role in tumor progression and survival. However, the clinicopathological significance of these transporters in patients with esophageal squamous cell carcinoma (ESCC) remains unclear.

METHODS

One hundred and fifty-seven patients with surgically resected ESCC were evaluated. Immunohistochemical analysis was performed for LAT1, ASCT2, CD98, Ki-67, and micro-vessel density (MVD), as determined by CD34 expression.

RESULTS

LAT1 and ASCT2 were positively expressed in 59% (93/157) and 48% (76/157) of tumors respectively. LAT1 and ASCT2 expression significantly correlated with T factor, N factor, lymphatic permeation, vascular invasion, and CD98 expression. The 5-year survival rates of LAT1-high and -low and ASCT2-high and -low expressing patients were 62.0% and 69.6% (P < 0.05) and 59.6% and 70.1% (P = 0.068), respectively. The combined positive expression of LAT1 and ASCT2 was a significant prognostic factor in univariate analysis.

CONCLUSION

High expression of LAT1 and ASCT2 correlates with metastasis and invasion. Accordingly, these proteins could serve as prognostic biomarkers and therapeutic targets for treating patients with surgically resectable ESCC. J. Surg. Oncol. 2016;113:381-389. © 2016 Wiley Periodicals, Inc.

Expression of ER stress markers (GRP78/BiP and PERK) in adenoid cystic carcinoma

CONCLUSION

A high GRP78/BiP expression was proved to be a significant marker for predicting poor outcome after surgery. GRP78/BiP may be a promising molecular target for treatment of ACC.

BACKGROUND

The glucose-regulated protein GRP78/BiP plays a crucial role in the endoplasmic reticulum (ER) stress. The level of GRP78 is highly elevated in various human cancers, but the clinicopathological significance of GRP78/BiP remains controversial in patients with adenoid cystic carcinoma (ACC).

METHODS

A total of 26 ACC patients were analyzed, and tumor specimens were stained by immunohistochemistry for GRP78/BiP, PERK, Ki-67, and microvessel density (MVD) determined by CD34.

RESULTS

GRP78/BiP and PERK were highly expressed in 58% (15/26) and 35% (9/26), respectively. The high expression of GRP78/BiP was significantly associated with PERK, cell proliferation and angiogenesis.

miR-34a is an intracellular and exosomal predictive biomarker for response to docetaxel with clinical relevance to prostate cancer progression

BACKGROUND

Docetaxel-resistance limits successful treatment of castration resistant prostate cancer. We previously demonstrated that extracellular vesicles (exosomes) may play a role in regulating docetaxel resistance. Here, we investigated intracellular and extracellular (exosomal) miRNAs related to docetaxel resistance.

METHODS

Following global miRNA profiling of cell line models of docetaxel-resistance and their corresponding exosomes, we investigated the clinical relevance of four selected miRNAs (miR-598, miR-34a, miR-146a, miR-148a) in four publically available clinical cohorts representing both primary and advanced disease in tissue and urine specimens. One of these miRNAs, miR-34a was selected for functional evaluation by miRNA inhibition and over-expression in vitro. We further assessed the panel of miRNAs for their combined clinical relevance as a biomarker signature by examining their common predicted targets.

RESULTS

A strong correlation was found between the detection of miRNAs in exosomes and their corresponding cells of origin. Of the miRNAs chosen for further validation and clinical assessment, decreased miR-34a levels showed substantial clinical relevance and so was chosen for further analysis. Manipulating miR-34a in prostate cancer cells confirms that this miRNA regulates BCL-2 and may, in part, regulate response to docetaxel. When combined, these miRNAs are predicted to regulate a range of common mRNA targets, two of which (e.g., SNCA, SCL7A5) demonstrate a strong relationship with prostate cancer progression and poor prognosis.

CONCLUSIONS

This study supports the extracellular environment as an important source of minimally invasive predictive biomarkers representing their cellular origin. Using miR-34a as example, we showed that biomarkers identified in this manner may also hold functional relevance.