Overexpression of SLC1a5 in lymph node metastases outperforms assessment in the primary as a negative prognosticator in non-small cell lung cancer

Amino acid transporters within the solute carrier superfamily: Underappreciated proteins and novel opportunities for cancer therapy

BACKGROUND

Solute carrier (SLC) transporters, a diverse family of membrane proteins, are instrumental in orchestrating the intake and efflux of nutrients including amino acids, vitamins, ions, nutrients, etc, across cell membranes. This dynamic process is critical for sustaining the metabolic demands of cancer cells, promoting their survival, proliferation, and adaptation to the tumor microenvironment (TME). Amino acids are fundamental building blocks of cells and play essential roles in protein synthesis, nutrient sensing, and oncogenic signaling pathways. As key transporters of amino acids, SLCs have emerged as crucial players in maintaining cellular amino acid homeostasis, and their dysregulation is implicated in various cancer types. Thus, understanding the intricate connections between amino acids, SLCs, and cancer is pivotal for unraveling novel therapeutic targets and strategies.

SCOPE OF REVIEW

In this review, we delve into the significant impact of amino acid carriers of the SLCs family on the growth and progression of cancer and explore the current state of knowledge in this field, shedding light on the molecular mechanisms that underlie these relationships and highlighting potential avenues for future research and clinical interventions.

MAJOR CONCLUSIONS

Amino acids transportation by SLCs plays a critical role in tumor progression. However, some studies revealed the tumor suppressor function of SLCs. Although several studies evaluated the function of SLC7A11 and SLC1A5, the role of some SLC proteins in cancer is not studied well. To exert their functions, SLCs mediate metabolic rewiring, regulate the maintenance of redox balance, affect main oncogenic pathways, regulate amino acids bioavailability within the TME, and alter the sensitivity of cancer cells to therapeutics. However, different therapeutic methods that prevent the function of SLCs were able to inhibit tumor progression. This comprehensive review provides insights into a rapidly evolving area of cancer biology by focusing on amino acids and their transporters within the SLC superfamily.

Sijunzi Tang improves gefitinib resistance by regulating glutamine metabolism

Lung cancer is a major health concern and significant barrier to human well-being and social development. Although targeted therapy has shown remarkable progress in the treatment of lung cancer, the emergence of drug resistance has limited its clinical efficacy. Sijunzi Tang (SJZ) is a classical Chinese herbal formula known for tonifying qi and nourishing the lungs, has been recognized for its potential in lung cancer management. However, the underlying mechanism of its combined use with anti-cancer drugs remains unclear. Here, we investigated the anti-lung cancer efficacy and underlying mechanisms of the combination of gefitinib and SJZ in gefitinib-resistant human lung adenocarcinoma cells (PC-9/GR). We conducted in vitro and in vivo experiments using histopathology and targeted metabolomics approaches. Our results demonstrated that the combination of SJZ and gefitinib exhibited synergistic effects on tumor growth inhibition in PC-9/GR-bearing nude mice. Notably, the co-administration of SJZ and gefitinib synergistically promoted tumor cell apoptosis, potentially through the regulation of BAX and BCL-2 expression. Immunohistochemistry and western blot analysis found down-regulation of GLS, GS, and SLC1A5 expression in the co-administration group compared to the control and the individual treatment groups. Targeted metabolomics revealed significant alterations in the plasma glutamine metabolic markers glutamine, alanine, succinate, glutamate, and pyruvate. Of the glutamine metabolism markers measured in tumor tissues, glutamine and pyruvate demonstrated significant differences across the treatment groups. These findings suggest that administration of SJZ improves gefitinib resistance in the treatment of lung cancer without toxic effects. Moreover, SJZ may affect glutamine metabolism by regulating key targets involved in glutamine metabolism (SLC1A5, GLS, and GS) and modulating the levels of related metabolic markers, ultimately reducing gefitinib resistance.

Glutamine metabolism in tumor metastasis: Genes, mechanisms and the therapeutic targets

Cancer cells frequently change their metabolism from aerobic glycolysis to lipid metabolism and amino acid metabolism to adapt to the malignant biological behaviours of infinite proliferation and distant metastasis. The significance of metabolic substances and patterns in tumour cell metastasis is becoming increasingly prominent. Tumour metastasis involves a series of significant steps such as the shedding of cancer cells from a primary tumour, resistance to apoptosis, and colonisation of metastatic sites. However, the role of glutamine in these processes remains unclear. This review summarises the key enzymes and transporters involved in glutamine metabolism that are related to the pathogenesis of malignant tumour metastasis. We also list the roles of glutamine in resisting oxidative stress and promoting immune escape. Finally, the significance of targeting glutamine metabolism in inhibiting tumour metastasis was proposed, research in this field improving our understanding of amino acid metabolism rewiring and simultaneously bringing about new and exciting therapeutic prospects.

Therapeutic Potential of Glutamine Pathway in Lung Cancer

Cancer cells tend to obtain the substances needed for their development depending on altering metabolic characteristics. Among the reorganized metabolic pathways, Glutamine pathway, reprogrammed to be involved in the physiological process including energy supply, biosynthesis and redox homeostasis, occupies an irreplaceable role in tumor cells and has become a hot topic in recent years. Lung cancer currently maintains a high morbidity and mortality rate among all types of tumors and has been a health challenge that researchers have longed to overcome. Therefore, this study aimed to clarify the essential role of glutamine pathway played in the metabolism of lung cancer and its potential therapeutic value in the interventions of lung cancer.

Comprehensive Analysis of Potential Correlation Between Solute Carrier 1A (SLC1A) Family and Lung Adenocarcinoma

Background

Lung adenocarcinoma (LUAD) is the most common dangerous malignant tumor and the leading cause of global cancer incidence and mortality. The Solute Carrier 1A (SLC1A) family play a significant part in cellular biological process, inflammation, and immunity. Specific functions of the SLC1A family in lung cancer are still not systematically described.

Objective

This study aimed to explore the best biological understanding of SLC1A family in lung cancer.

Methods

To study the expression and role of the SLC1A family in lung cancer, researchers used a variety of bioinformatics databases and tools.

Results

Aberrant expression of SLC1A family genes were demonstrated and analyzed the association with gender, tumor grade, cancer stages, and nodal metastasis status. The ectopic expression of SLC1A family genes has prognostic value for LUAD patients. Immune infiltration revealed a significant correlation between SLC1A family genes expression in LUAD. SLC1A family genes were involved in manifold biological processes and have different levels of DNA methylation and genetic alteration.

Conclusions

These findings suggested that members of the SLC1A family could be a potential target for the development of LUAD therapeutics as well as a reliable indicator of LUAD prognostic value.

Discoidin domain receptor 1 promotes hepatocellular carcinoma progression through modulation of SLC1A5 and the mTORC1 signaling pathway

PURPOSE

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world with a high mortality rate. Receptor tyrosine kinases play important roles in the occurrence and development of various cancers. Discoid protein domain receptor 1 (DDR1) is a special type of transmembrane receptor tyrosine kinase. Here, we show that the expression of DDR1 is significantly increased in HCC and is related to a poor clinical prognosis.

METHODS

The expression of DDR1 in HCC cell lines and primary HCC specimens was evaluated using Western blotting and immunohistochemistry. A correlation between DDR1 and SLC1A5 expression was also investigated in primary HCC specimens. Cell proliferation was evaluated using in vitro CCK8 and colony formation assays. Gene knock-down and overexpression assays, CHX, NH₄CL and Mg132 interference tests and immunoprecipitation, as well as nude mouse xenograft models were used to assess the mechanism by which DDR1 promotes tumorigenesis in vitro and in vivo.

RESULTS

We found that DDR1 promotes the proliferation of HCC cells and accelerates the growth of HCC tumor xenografts, while DDR1 downregulation had the opposite effect. We also found that loss or gain of DDR1 expression affected HCC cell cycle progression. Mechanistically, we found that DDR1 interacts with SLC1A5, which belongs to the solute carrier (SLC) family of transporters, and regulates its stability, thereby affecting the mTORC1 signaling pathway. In addition, we found that SLC1A5 regulation by DDR1 can be restored by lysosome inhibitors. We also found that DDR1 is highly expressed in HCC tissues and that increased DDR1 expression predicts a shorter overall survival (OS) time. We additionally found that the expression of SLC1A5 was positively correlated with that of DDR1. Together, our data indicate that DDR1 acts as a tumor-promoting factor that can control HCC cell proliferation and cell cycle progression by stabilizing SLC1A5 in a lysosome-dependent way.

CONCLUSIONS

Our study reveals a new mechanism by which DDR1 plays a liver cancer-promoting role. We also found that DDR1 expression serves as an independent prognostic marker, and that DDR1 and SLC1A5 expression levels are positively correlated in clinical samples. Our findings provide a new perspective for understanding HCC development and offers new targets for the treatment and management of HCC.

Glutamine-Derived Aspartate Biosynthesis in Cancer Cells: Role of Mitochondrial Transporters and New Therapeutic Perspectives

Simple Summary

In recent years, aspartate has been increasingly acknowledged as a critical player in the metabolism of cancer cells which use this metabolite for nucleotide and protein synthesis and for redox homeostasis. Most intracellular aspartate derives from the mitochondrial catabolism of glutamine. To date at least four mitochondrial transporters have been involved in this metabolic pathway. Their involvement appears to be cancer type-specific and dependent on glutamine availability. Targeting these mitochondrial transporters may represent a new attractive strategy to fight cancer. The aim of this review is to dissect the role of each of these transporters in relation to the type of cancer and the availability of nutrients in the tumoral microenvironment.

Abstract

Aspartate has a central role in cancer cell metabolism. Aspartate cytosolic availability is crucial for protein and nucleotide biosynthesis as well as for redox homeostasis. Since tumor cells display poor aspartate uptake from the external environment, most of the cellular pool of aspartate derives from mitochondrial catabolism of glutamine. At least four transporters are involved in this metabolic pathway: the glutamine (SLC1A5_var), the aspartate/glutamate (AGC), the aspartate/phosphate (uncoupling protein 2, UCP2), and the glutamate (GC) carriers, the last three belonging to the mitochondrial carrier family (MCF). The loss of one of these transporters causes a paucity of cytosolic aspartate and an arrest of cell proliferation in many different cancer types. The aim of this review is to clarify why different cancers have varying dependencies on metabolite transporters to support cytosolic glutamine-derived aspartate availability. Dissecting the precise metabolic routes that glutamine undergoes in specific tumor types is of upmost importance as it promises to unveil the best metabolic target for therapeutic intervention.

Identification of ubiquitinated substrate proteins and their gene expression patterns in lung adenocarcinoma

Background

Lung cancer is a malignant disease with the highest cancer-related mortality rate. In lung adenocarcinoma (LUAD), protein ubiquitination can regulate multiple biological processes. A LUAD ubiquitylome analysis has not yet been reported.

Methods

We used for the first time ion mobility into liquid chromatography-mass spectrometry to perform accurate and reliable ubiquitylome and proteomic analysis of clinical LUAD and normal tissues and combined it with transcriptome data obtained from public databases. Ubiquitinated protein substrates and their gene expression pattern landscapes in LUAD were identified using bioinformatics methods.

Results

Our data revealed a ubiquitination landscape in LUAD and identified characteristic protein ubiquitination motifs. We found that the ubiquitinated peptide motifs in LUAD were completely different from those of previously published lung squamous cell carcinoma (LUSC). Moreover, we identified two gene expression patterns of ubiquitinated proteins and revealed that survival differences between these patterns may be correlated with the tumor immune infiltrating microenvironment. Finally, we constructed a prognostic predictive model to quantify the relationship between expression patterns and survival. We found a relationship between the patient-applied model score and multiple drug sensitivity. Therefore, our model can serve as a guide for LUAD clinical treatment.

Conclusions

Our work addresses the lack of ubiquitylome studies in LUAD and provides new perspectives for subsequent research and clinical treatment.

Circular RNA circ-LDLRAD3 serves as an oncogene to promote non-small cell lung cancer progression by upregulating SLC1A5 through sponging miR-137

Circular RNAs (circRNAs) are closely associated with the development of non-small cell lung cancer (NSCLC); however, it is still unclear whether circular RNA circ-LDLRAD3 participated in the regulation of NSCLC progression. In this study, we found that circ-LDLRAD3 was high-expressed and miR-137 was low-expressed in NSCLC tissues and cells compared to their normal counterparts, which showed negative correlations in NSCLC tissues. Further experiments validated that miR-137 could be sponged and inhibited by circ-LDLRAD3 in NSCLC cells. In addition, knock-down of circ-LDLRAD3 and miR-137 overexpression promoted NSCLC cell apoptosis, and inhibited cell proliferation and invasion. Similarly, upregulation of circ-LDLRAD3 or miR-137 ablation had opposite effects on the above cell functions. Besides, the glutamine transporter SLC1A5 was validated to be the downstream target of circ-LDLRAD3 and miR-137, and upregulated circ-LDLRAD3 increased SLC1A5 expression levels by downregulating miR-137. Furthermore, the effects of downregulated circ-LDLRAD3 on cell proliferation, apoptosis and mobility were all reversed by knocking down miR-137 and overexpressing SLC1A5. Taken together, this in vitro study found that knock-down of circ-LDLRAD3 inhibited the development of NSCLC by regulating miR-137/SLC1A5 axis.

Glucose and glutamine metabolism in relation to mutational status in NSCLC histological subtypes

BACKGROUND

Both hypoxia and oncogenic mutations rewire tumor metabolism. In this study, glucose and glutamine metabolism-related markers were examined in stage I - resectable stage IIIA non-small cell lung cancer (NSCLC). Furthermore, expression of metabolism-related markers was correlated with mutational status to examine mutations associated with rewired tumor metabolism.

METHODS

Mutation analysis was performed for 97 tumors. Glucose and glutamine metabolism-related marker expression was measured by immunofluorescent staining (protein) and qPCR (mRNA) (n = 81).

RESULTS

Glutamine metabolism-related markers were significantly higher in adeno- than squamous cell NSCLCs. Glucose transporter 1 (GLUT1) protein expression was higher in solid compared to lepidic adenocarcinomas (P < 0.01). In adenocarcinomas, mRNA expression of glutamine transporter SLC1A5 correlated with tumor size (r(p) = 0.41, P = 0.005). Furthermore, SLC1A5 protein expression was significantly higher in adenocarcinomas with worse pTNM stage (r(s) = 0.39, P = 0.009). EGFR-mutated tumors showed lower GLUT1 protein (P = 0.017), higher glutaminase 2 (GLS2) protein (P = 0.025) and higher GLS2 mRNA expression (P = 0.004), compared to EGFR wild-type tumors. GLS mRNA expression was higher in KRAS-mutated tumors (P = 0.019). TP53-mutated tumors showed higher GLUT1 expression (P = 0.009).

CONCLUSIONS

NSCLC is a heterogeneous disease, with differences in mutational status and metabolism-related marker expression between adeno- and squamous cell NSCLCs, and also within adenocarcinoma subtypes. GLUT1 and SLC1A5 expression correlate with aggressive tumor behavior in adenocarcinomas but not in squamous cell NSCLCs. Therefore, these markers could steer treatment modification for subgroups of adenocarcinoma patients. TP53, EGFR and KRAS mutations are associated with expression of glucose and glutamine metabolism-related markers in NSCLC.

Glutamine addiction activates polyglutamine-based nanocarriers delivering therapeutic siRNAs to orthotopic lung tumor mediated by glutamine transporter SLC1A5

Many human cancer cells exhibit an oncogenetic-driven addiction to glutamine (Gln) as rapidly proliferating cancer cells consume Gln at a dramatically increased rate compared to normal cells. Tumor cells, therefore, compete with host cells for Gln, which causes Gln to flux from normal tissues to the tumor. We have developed and characterized a Gln macromolecular analog polyglutamine (PGS) for the delivery of gene regulators, such as siRNAs, in our previous works. Here, we hypothesize that PGS can utilize the Gln transporter SLC1A5 to specifically deliver therapeutic compounds to Gln-addicted cancer cells. Compared to human lung fibroblast HLF cells, cisplatin-resistant human lung adenocarcinoma A549/DDP cells significantly overexpress SLC1A5, which has a high binding affinity to PGS, as confirmed through molecular docking analysis. Due to the differences in Gln metabolism between malignant and normal cells, PGS/siRNA complexes were remarkably increased in cancer cells, especially when cells were deprived of Gln, which mirrors the conditions that are commonly found in a tumor microenvironment. Furthermore, we identified that chemical and genetic inhibition of Gln transporter SLC1A5 reduced the cellular internalization of PGS/siRNA complexes, suggesting a critical role for SLC1A5 in PGS uptake in cells. In turn, PGS upregulated SLC1A5 expression. Increased uptake of PGS complexes profoundly decreased intracellular Gln levels. Decreased Gln caused a moderate reduction in cell growth. To restore drug sensitivity and further enhance anti-tumor effects, the hybrid siRNAs anti-Survivin and anti-MDR1 (siSM), as model therapeutics, were administered through the PGS delivery system, which resulted in knockdown of Survivin and MDR1 and further sensitized cancer cells to the drug cisplatin (DDP). Since PGS complexes administered i.v. mostly accumulated in the lung parenchyma, a lung orthotopic tumor model was established to evaluate their inhibitory effects on tumors in the lungs. PGS/siSM comparably decreased the rate of tumor growth, while concurrent administration of PGS/siSM and DDP enhanced this effect and insignificantly improved life span. Consistent with our hypothesis, this study demonstrated that PGS mimicked Gln in the SLC1A5 pathway and selectively ferried therapeutics to Gln-addicted cancer cells. Our findings identified a new lung cancer targeting strategy based on Gln metabolism and can be used as a drug/gene delivery system.