The effects and mechanisms of SLC34A2 in tumorigenesis and progression of human non-small cell lung cancer

Mechanosensitive channels TMEM63A and TMEM63B mediate lung inflation-induced surfactant secretion

Pulmonary surfactant is a lipoprotein complex lining the alveolar surface to decrease the surface tension and facilitate inspiration. Surfactant deficiency is often seen in premature infants and in children and adults with respiratory distress syndrome. Mechanical stretch of alveolar type 2 epithelial (AT2) cells during lung expansion is the primary physiological factor that stimulates surfactant secretion; however, it is unclear whether there is a mechanosensor dedicated to this process. Here, we show that loss of the mechanosensitive channels TMEM63A and TMEM63B (TMEM63A/B) resulted in atelectasis and respiratory failure in mice due to a deficit of surfactant secretion. TMEM63A/B were predominantly localized at the limiting membrane of the lamellar body (LB), a lysosome-related organelle that stores pulmonary surfactant and ATP in AT2 cells. Activation of TMEM63A/B channels during cell stretch facilitated the release of surfactant and ATP from LBs fused with the plasma membrane. The released ATP evoked Ca2+ signaling in AT2 cells and potentiated exocytic fusion of more LBs. Our study uncovered a vital physiological function of TMEM63 mechanosensitive channels in preparing the lungs for the first breath at birth and maintaining respiration throughout life.

SLC34A2 promotes cell proliferation by activating STX17-mediated autophagy in esophageal squamous cell carcinoma

BACKGROUND

Solute carrier family 34 member 2 (SLC34A2) has been implicated in the development of various malignancies. However, the clinical significance and underlying molecular mechanisms of SLC34A2 in esophageal squamous cell carcinoma (ESCC) remain elusive.

METHODS

Western blotting, quantitative real-time PCR and immunohistochemistry were utilized to evaluate the expression levels of SLC34A2 mRNA/protein in ESCC cell lines or tissues. Kaplan-Meier curves were employed for survival analysis. CCK-8, colony formation, EdU and xenograft tumor model assays were conducted to determine the impact of SLC34A2 on ESCC cell proliferation. Cell cycle was examined using flow cytometry. RNA-sequencing and enrichment analysis were carried out to explore the potential signaling pathways. The autophagic flux was evaluated by western blotting, mRFP-GFP-LC3 reporter system and transmission electron microscopy. Immunoprecipitation and mass spectrometry were utilized for identification of potential SLC34A2-interacting proteins. Cycloheximide (CHX) chase and ubiquitination assays were conducted to test the protein stability.

RESULTS

The expression of SLC34A2 was significantly upregulated in ESCC and correlated with unfavorable clinicopathologic characteristics particularly the Ki-67 labeling index and poor prognosis of ESCC patients. Overexpression of SLC34A2 promoted ESCC cell proliferation, while silencing SLC34A2 had the opposite effect. Moreover, SLC34A2 induced autophagy to promote ESCC cell proliferation, whereas inhibition of autophagy suppressed the proliferation of ESCC cells. Further studies showed that SLC34A2 interacted with an autophagy-related protein STX17 to promote autophagy and proliferation of ESCC cells by inhibiting the ubiquitination and degradation of STX17.

CONCLUSIONS

These findings indicate that SLC34A2 may serve as a prognostic biomarker for ESCC.

SLC34A2 Targets in Calcium/Phosphorus Homeostasis of Mammary Gland and Involvement in Development of Clinical Mastitis in Dairy Cows

The type II Na/Pi co-transporter (NaPi2b), encoded by the solute carrier (SLC) transporter 34A2 (SLC34A2), is responsible for calcium (Ca) and phosphorus (P) homeostasis. Unbalanced Ca/P metabolism induces mastitis in dairy cows. However, the specific role of SLC34A2 in regulating this imbalance in Holstein cows with clinical mastitis (CM) remains unclear. The aim of this study was to investigate the role of SLC34A2 and identify differentially expressed proteins (DEPs) that interact with SLC34A2 and are associated with Ca/P metabolism in dairy cows with CM. Immunohistochemical and immunofluorescence staining results showed that SLC34A2 was located primarily in the mammary epithelial cells of the mammary alveoli in both the control (healthy cows, Con/C) and CM groups. Compared to the Con/C group, the relative expression of the SLC34A2 gene and protein were significantly downregulated in the CM group. We identified 12 important DEPs included in 11 GO terms and two pathways interacting with SLC34A2 using data-independent acquisition proteomics. The PPI (protein-and-protein interaction) network results suggested that these DEPs were associated with ion metabolism and homeostasis, especially SLC34A2. These results demonstrate that SLC34A2 downregulation is negatively correlated with the occurrence and development of CM in Holstein cows, providing a basis for exploring the function and regulatory mechanism of SLC34A2 in Ca/P metabolism and homeostasis in Holstein cows with CM.

Evolution of chromosome-arm aberrations in breast cancer through genetic network rewiring

The basal breast cancer subtype is enriched for triple-negative breast cancer (TNBC) and displays consistent large chromosomal deletions. Here, we characterize evolution and maintenance of chromosome 4p (chr4p) loss in basal breast cancer. Analysis of The Cancer Genome Atlas data shows recurrent deletion of chr4p in basal breast cancer. Phylogenetic analysis of a panel of 23 primary tumor/patient-derived xenograft basal breast cancers reveals early evolution of chr4p deletion. Mechanistically we show that chr4p loss is associated with enhanced proliferation. Gene function studies identify an unknown gene, C4orf19, within chr4p, which suppresses proliferation when overexpressed-a member of the PDCD10-GCKIII kinase module we name PGCKA1. Genome-wide pooled overexpression screens using a barcoded library of human open reading frames identify chromosomal regions, including chr4p, that suppress proliferation when overexpressed in a context-dependent manner, implicating network interactions. Together, these results shed light on the early emergence of complex aneuploid karyotypes involving chr4p and adaptive landscapes shaping breast cancer genomes.

A single-cell atlas of West African lungfish respiratory system reveals evolutionary adaptations to terrestrialization

The six species of lungfish possess both lungs and gills and are the closest extant relatives of tetrapods. Here, we report a single-cell transcriptome atlas of the West African lungfish (Protopterus annectens). This species manifests the most extreme form of terrestrialization, a life history strategy to survive dry periods that can last for years, characterized by dormancy and reversible adaptive changes of the gills and lungs. Our atlas highlights the cell type diversity of the West African lungfish, including gene expression consistent with phenotype changes of terrestrialization. Comparison with terrestrial tetrapods and ray-finned fishes reveals broad homology between the swim bladder and lung cell types as well as shared and idiosyncratic changes of the external gills of the West African lungfish and the internal gills of Atlantic salmon. The single-cell atlas presented here provides a valuable resource for further exploration of the respiratory system evolution in vertebrates and the diversity of lungfish terrestrialization.

Molecular Impact of Conventional and Electronic Cigarettes on Pulmonary Surfactant

The alveolar epithelium is covered by a non-cellular layer consisting of an aqueous hypophase topped by pulmonary surfactant, a lipo-protein mixture with surface-active properties. Exposure to cigarette smoke (CS) affects lung physiology and is linked to the development of several diseases. The macroscopic effects of CS are determined by several types of cell and molecular dysfunction, which, among other consequences, lead to surfactant alterations. The purpose of this review is to summarize the published studies aimed at uncovering the effects of CS on both the lipid and protein constituents of surfactant, discussing the molecular mechanisms involved in surfactant homeostasis that are altered by CS. Although surfactant homeostasis has been the topic of several studies and some molecular pathways can be deduced from an analysis of the literature, it remains evident that many aspects of the mechanisms of action of CS on surfactant homeostasis deserve further investigation.

In silico analysis of the solute carrier (SLC) family in cancer indicates a link among DNA methylation, metabolic adaptation, drug response, and immune reactivity

Introduction: The oncogenic transformation is driven by genetic and epigenetic alterations influencing cancer cell fate. These alterations also result in metabolic reprogramming by modulating the expression of membrane Solute Carrier (SLC) transporters involved in biomolecules trafficking. SLCs act as tumor suppressors or promoters influencing cancer methylome, tumor growth, immune-escape, and chemoresistance. Methods: This in silico study aimed to identify the deregulated SLCs in various tumor types compared to normal tissues by analyzing the TCGA Target GTEx dataset. Furthermore, the relationship between SLCs expression and the most relevant tumor features was tackled along with their genetic regulation mediated by DNA methylation. Results: We identified 62 differentially expressed SLCs, including the downregulated SLC25A27 and SLC17A7, as well as the upregulated SLC27A2 and SLC12A8. Notably, SLC4A4 and SLC7A11 expression was associated with favorable and unfavorable outcome, respectively. Moreover, SLC6A14, SLC34A2, and SLC1A2 were linked to tumor immune responsiveness. Interestingly, SLC24A5 and SLC45A2 positively correlated with anti-MEK and anti-RAF sensitivity. The expression of relevant SLCs was correlated with hypo- and hyper-methylation of promoter and body region, showing an established DNA methylation pattern. Noteworthy, the positive association of cg06690548 (SLC7A11) methylation with cancer outcome suggests the independent predictive role of DNA methylation at a single nucleotide resolution. Discussion: Although our in silico overview revealed a wide heterogeneity depending on different SLCs functions and tumor types, we identified key SLCs and pointed out the role of DNA methylation as regulatory mechanism of their expression. Overall, these findings deserve further studies to identify novel cancer biomarkers and promising therapeutic targets.

Heterogeneous pattern of gene expression driven by TTN mutation is involved in the construction of a prognosis model of lung squamous cell carcinoma

Objective

To investigate the impact that TTN mutation had on the gene heterogeneity expression and prognosis in patients with lung adenocarcinoma.

Methods

In this study, the Cancer Genome Atlas (TCGA) dataset was used to analyze the TTN mutations in lung adenocarcinoma. Lung adenocarcinoma data was collected from the TCGA database, clinical information of patients was analyzed, and bioinformatics statistical methods were applied for mutation analysis and prognosis survival analysis. The results were verified using the GEO dataset.

Results

The incidence of TTN mutations in lung adenocarcinoma was found to be 73%, and it was related to the prognosis of lung adenocarcinoma. Ten genes were screened with significant contributions to prognosis. A prognosis model was constructed and verified by LASSO COX analysis in the TCGA and GEO datasets based on these ten beneficial factors. The independent prognostic factor H2BC9 for TTN mutation-driven gene heterogeneity expression was screened through multi-factor COX regression analysis.

Conclusion

Our data showed that the gene heterogeneity expression, which was driven by TTN mutations, prolonged the survival of lung adenocarcinoma patients and provided valuable clues for the prognosis of TTN gene mutations in lung adenocarcinoma.

Antibody Drug Conjugates in Lung Cancer: State of the Current Therapeutic Landscape and Future Developments

While both targeted therapy and immunotherapy-based strategies have emerged as frontline standard-of-care for patients with advanced lung cancer, acquired resistance and disease progression remain inevitable in most cases. Chemotherapy is a common salvage option in this scenario, but is limited by a relatively narrow therapeutic index. The emergence of antibody-drug conjugates (ADCs) offer an appealing alternative. ADCs couple the specificity of a monoclonal antibody with the cytotoxic effects of chemotherapy to facilitate the targeted delivery of cytotoxic payloads directly to cancer cells. Here, we review the general structure and function of ADCs, followed by a discussion of emerging ADCs in lung cancer and the future applications of this increasingly relevant class of novel agents.

Evaluation of the Prognostic Value of Solute Carrier Family 34 Member 2 "SLC34A2" in Papillary Thyroid Carcinoma: An Immunohistochemical Study

Background

Papillary thyroid carcinoma (PTC) usually has an indolent clinical course, yet a subset of patients might show an aggressive course. Thus, better stratification of at-risk patients is mandatory for proper management. Solute carrier family 34 member 2 (SLC34A2) is an independent prognostic indicator in several cancers. However, only a few studies have been conducted to evaluate the prognostic value of SLC34A2 in PTC, with none of them assessing its immunohistochemical (IHC) expression in a large cohort of patients with PTC or exploring its possible relationship with tumor progression. Aim of the Study. We aimed to evaluate the IHC expression of SLC34A2 in a large series of PTC patients, correlate its expression with established clinicopathological factors, and find any possible relationship between this marker and patient prognosis. Material and Methods. A total of 476 samples (including 238 samples of PTC and 238 samples of normal thyroid tissue) collected between 2002 and 2005 were extracted from the archives of the Pathology Lab, Ain Shams University Hospitals. IHC analysis was performed using an anti-SLC34A2 antibody. Follow-up data were obtained.

Results

High SLC34A2 expression significantly correlated with important adverse clinicopathological parameters of PTC—i.e., late tumor stage, positive extrathyroid extension, tumor size  >  4 cm, and age  ≥  55 years (p ≤ 0.001 for each). Kaplan–Meier analysis revealed that high SLC34A2 expression significantly correlated with shorter disease-free survival (DFS; p = 0.005), but not with overall survival (p = 0.111). Multivariate analysis showed SLC34A2 to be an independent prognostic factor affecting DFS.

Conclusions

High SLC34A2 IHC expression correlated with adverse clinicopathological prognostic parameters. Furthermore, SLC34A2 was identified as an independent factor for DFS that could serve to improve risk stratification of PTC patients for better management.

Long Non-Coding RNA MEG3 in Cellular Stemness

Long non-coding RNAs (lncRNAs) regulate a diverse array of cellular processes at the transcriptional, post-transcriptional, translational, and post-translational levels. Accumulating evidence suggests that lncRNA MEG3 exerts a large repertoire of regulatory functions in cellular stemness. This review focuses on the molecular mechanisms by which lncRNA MEG3 functions as a signal, scaffold, guide, and decoy for multi-lineage differentiation and even cancer progression. The role of MEG3 in various types of stem cells and cancer stem cells is discussed. Here, we provide an overview of the functional versatility of lncRNA MEG3 in modulating pluripotency, differentiation, and cancer stemness.

A guide to plasma membrane solute carrier proteins

This review aims to serve as an introduction to the solute carrier proteins (SLC) superfamily of transporter proteins and their roles in human cells. The SLC superfamily currently includes 458 transport proteins in 65 families that carry a wide variety of substances across cellular membranes. While members of this superfamily are found throughout cellular organelles, this review focuses on transporters expressed at the plasma membrane. At the cell surface, SLC proteins may be viewed as gatekeepers of the cellular milieu, dynamically responding to different metabolic states. With altered metabolism being one of the hallmarks of cancer, we also briefly review the roles that surface SLC proteins play in the development and progression of cancer through their influence on regulating metabolism and environmental conditions.

Use of four genes in exosomes as biomarkers for the identification of lung adenocarcinoma and lung squamous cell carcinoma

The determination of biomarkers in the blood specific for lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) is crucial for the selection of effective treatment strategies and the prediction of prognosis. The purpose of the present study was to analyze the differentially expressed genes (DEGs) in LUSC and LUAD from The Cancer Genome Atlas (TCGA) database. In order to identify the potential biomarkers for non-small cell lung cancer (NSCLC) for clinical diagnosis, bioinformatics was used to analyze the DEGs of two subtypes of NSCLC, LUAD and LUSC. Exosomes were isolated from the serum of patients with LUAD or LUSC and identified using transmission electron microscopy, nanoparticle tracking analysis and western blot analysis. A total of four differential exosomal mRNAs were selected for validation with serum samples from 70 patients with NSCLC via reverse transcription-quantitative polymerase chain reaction. Receiver operating characteristic curves were established to evaluate the clinical diagnostic value of four DEGs for patients with LUAD and LUSC. The analysis based on TCGA data revealed the DEGs in LUSC and LUAD: A total of 1,619 genes were differentially expressed in patients with LUSC and LUAD. DEGs analyzed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that inflammation-related signaling pathways, such as complement pathways, and multiple autoimmune diseases, such as systemic lupus erythematosus and asthma were mainly enriched in LUAD. The cell cycle, Hippo signaling pathway, Rap1 signaling pathway and Wnt signaling pathway were the main signaling pathways enriched in LUSC. The combination of tumor protein P63 (TP63), keratin 5 (KRT5), CEA cell adhesion molecule 6 (CEACAM6) and surfactant protein B (SFTPB) improved the specificity and sensitivity in the diagnosis of different lung cancer subtypes. Exosomal TP63, KRT5, CEACAM6 and SFTPB mRNAs can thus be used as biomarkers to differentiate between LUSC and LUAD, and may provide a novel strategy for their differential diagnosis and treatment.

Identification of Potential BRAF Inhibitor Joint Therapy Targets in PTC based on WGCAN and DCGA

As the most common mutation in papillary thyroid cancer (PTC), B-type Raf kinase V600E mutation (BRAFV600E ) has become an important target for the clinical treatment of PTC. However, the clinical application still faces the problem of resistance to BRAF inhibitors (BRAFi). Therefore, exploring BRAFV600E-associated prognostic factors to providing potential joint targets is important for combined targeted therapy with BRAFi. In this study, we combined transcript data and clinical information from 199 BRAF wild-type (BRAFWT ) patients and 283 BRAFV600E mutant patients collected from The Cancer Genome Atlas (TCGA), and screened 455 BRAFV600E- associated genes through differential analysis and weighted gene co-expression network analysis. Based on these BRAFV600E -associated genes, we performed functional enrichment analysis and co-expression differential analysis and constructed a core co-expression network. Next, genes in the differential co-expression network were used to predict drugs for therapy in the crowd extracted expression of differential signatures (CREEDS) database, and the key genes were selected based on the hub co-expression network through survival analyses and receiver operating characteristic (ROC) curve analyses. Finally, we obtained eight BRAFV600E -associated biomarkers with both prognostic and diagnostic values as potential BRAFi joint targets, including FN1, MET, SLC34A2, NGEF, TBC1D2, PLCD3, PROS1, and NECTIN4. Among these genes, FN1, MET, PROS1, and TBC1D2 were validated through GEO database. Two novel biomarkers, PROS1 and TBC1D2, were further validated by qRT-PCR experiment. Besides, we obtained four potential targeted drugs that could be used in combination with BRAFi to treat PTC, including MET inhibitor, ERBB3 inhibitor, anti-NaPi2b antibody-drug conjugate, and carboplatin through literature review. The study provided potential drug targets for combination therapy with BRAFi for PTC to overcome the drug resistance for BRAFi.

Circulating tumor cell characterization of lung cancer brain metastases in the cerebrospinal fluid through single-cell transcriptome analysis

BACKGROUND

Brain metastases explain the majority of mortality associated with lung cancer, which is the leading cause of cancer death. Cytology analysis of the cerebrospinal fluid (CSF) remains the diagnostic gold standard, however, the circulating tumor cells (CTCs) in CSF (CSF-CTCs) are not well defined at the molecular and transcriptome levels.

METHODS

We established an effective CSF-CTCs collection procedure and isolated individual CSF cells from five lung adenocarcinoma leptomeningeal metastases (LUAD-LM) patients and three controls. Three thousand seven hundred ninety-two single-cell transcriptomes were sequenced, and single-cell RNA sequencing (scRNA-seq) gene expression analysis was used to perform a comprehensive characterization of CSF cells.

RESULTS

Through clustering and expression analysis, we defined CSF-CTCs at the transcriptome level based on epithelial markers, proliferation markers, and genes with lung origin. The metastatic-CTC signature genes are enriched for metabolic pathway and cell adhesion molecule categories, which are crucial for the survival and metastases of tumor cells. We discovered substantial heterogeneity in patient CSF-CTCs. We quantified the degree of heterogeneity and found significantly greater among-patient heterogeneity compared to among-cell heterogeneity within a patient. This observation could be explained by spatial heterogeneity of metastatic sites, cell-cycle gene, and cancer-testis antigen (CTA) expression profiles as well as the proportion of CTCs displaying mesenchymal and cancer stem cell properties. In addition, our CSF-CTCs transcriptome profiling allowed us to determine the biomarkers during the progression of an LM patient with cancer of unknown primary site (CUP).

CONCLUSIONS

Our results will provide candidate genes for an RNA-based digital detection of CSF-CTCs from LUAD-LM and CUP-LM cases, and shed light on the therapy and mechanism of LUAD-LM.

Characterizing heterogeneity of non-small cell lung tumour microenvironment to identify signature prognostic genes

Growing evidence has highlighted the immune response as an important feature of carcinogenesis and therapeutic efficacy in non‐small cell lung cancer (NSCLC). This study focused on the characterization of immune infiltration profiling in patients with NSCLC and its correlation with survival outcome. All TCGA samples were divided into three heterogeneous clusters based on immune cell profiles: cluster 1 ('low infiltration' cluster), cluster 2 ('heterogeneous infiltration' cluster) and cluster 3 ('high infiltration' cluster). The immune cells were responsible for a significantly favourable prognosis for the 'high infiltration' community. Cluster 1 had the lowest cytotoxic activity, tumour‐infiltrating lymphocytes and interferon‐gamma (IFN‐γ), as well as immune checkpoint molecules expressions. In addition, MHC‐I and immune co‐stimulator were also found to have lower cluster 1 expressions, indicating a possible immune escape mechanism. A total of 43 differentially expressed genes (DEGs) that overlapped among the groups were determined based on three clusters. Finally, based on a univariate Cox regression model, prognostic immune‐related genes were identified and combined to construct a risk score model able to predict overall survival (OS) rates in the validation datasets.

SLC34A2 simultaneously promotes papillary thyroid carcinoma growth and invasion through distinct mechanisms

Thyroid cancer is the fastest growing cancer among all solid tumors in recent decades. Papillary thyroid carcinoma (PTC) is the most predominant type of thyroid cancer. Around 30% of PTC patients with distant metastases and local invasion receive poor prognosis. Thus, the identification of new druggable biological targets is of great importance. Accumulating evidence indicates that solute carrier family numbers have emerged as obligate effectors during the progression of multiple malignancies. Here, we uncovered the functional significance, molecular mechanisms, and clinical impact of solute carrier family 34 member A2 (SLC34A2) in PTC. SLC34A2 was markedly overexpressed in PTC tissues at both mRNA and protein levels compared with matched adjacent normal tissues due to promoter hypomethylation mediated by the DNA methyltransferase 3 beta (DNMT3B). Furthermore, a series of in vivo and in vitro gain- or loss-of-functional assays elucidated the role of SLC34A2 in boosting cell proliferation, cell cycle progression, migration, invasion, and adhesion of PTC cells. Using immunoprecipitation and mass spectrometry, we discovered that SLC34A2 bound to the actin-binding repeats domain of Cortactin (CTTN), thereby inducing the invadopodia formation of PTC cells to promote the metastasis potential of PTC cells. Besides, our mechanistic studies, as well as gene set enrichment analysis (GSEA), have pinpointed the PTEN/AKT/FOXO3a pathway as a major signaling functioning downstream of SLC34A2 regulated cell growth. Taken together, our results highlighted that SLC34A2 plays a pivotal oncogenic role during carcinogenesis and metastasis through distinct mechanisms in PTC.

Antibody-drug conjugates for lung cancer in the era of personalized oncology

With 9.6 million deaths in 2018, cancer represents one of the most common causes of death, both in men and women. Despite recent advances in the understanding of molecular mechanisms involved in cancer development and progression, treatment options are still limited. Limitations of traditional chemotherapy include the lack of selectivity and the unfavorable safety profile. The efficacy of targeted therapies (e.g., tyrosine kinase inhibitors) is also limited by their cytostatic action, which inhibits tumor cell proliferation without inducing tumor cell death, and by the risk of acquired resistance. Antibody-drug conjugates (ADCs), a newly developed class of engineered anticancer drugs, consist of recombinant monoclonal antibodies against tumor-specific antigens that are covalently bound to cytotoxic agents. They have been designed to overcome the limitations of traditional chemotherapy and targeted therapies by combining the target selectivity of monoclonal antibodies with the high potency of cytotoxic drugs. Currently, ADCs that have received regulatory approval include brentuximab vedotin for CD30-positive Hodgkin lymphoma and trastuzumab emtansine for human epidermal growth factor receptor 2-positive breast cancer. However, over 80 novel ADCs are actively being investigated in preclinical studies and early-phase clinical trials. In this review, we will provide a comprehensive overview of the biological rational, efficacy and safety of ADCs as therapeutic agents against non-small cell lung cancer and small cell lung cancer.

Expression of C-terminal ALK, RET, or ROS1 in lung cancer cells with or without fusion

Background

Genetic alterations, including mutation of epidermal growth factor receptor or v-Ki-ras2 kirsten rat sarcoma viral oncogene homolog and fusion of anaplastic lymphoma kinase (ALK), RET proto-oncogene (RET), or v-ros UR2 sarcoma virus oncogene homolog 1 (ROS1), occur in non-small cell lung cancers, and these oncogenic drivers are important biomarkers for targeted therapies. A useful technique to screen for these fusions is the detection of native carboxy-terminal (C-terminal) protein by immunohistochemistry; however, the effects of other genetic alterations on C-terminal expression is not fully understood. In this study, we evaluated whether C-terminal expression is specifically elevated by fusion with or without typical genetic alterations of lung cancer.

Methods

In 37 human lung cancer cell lines and four tissue specimens, protein and mRNA levels were measured by capillary western blotting and reverse transcription–PCR, respectively.

Results

Compared with the median of all 37 cell lines, mRNA levels at the C-terminus of all five of the fusion-positive cell lines tested (three ALK, one RET, and one ROS1) were elevated at least 2000-, 300-, or 2000-fold, respectively, and high C-terminal protein expression was detected. In an ALK fusion–positive tissue specimen, the mRNA and protein levels of C-terminal ALK were also markedly elevated. Meanwhile, in one of 36 RET fusion–negative cell lines, RET mRNA levels at the C-terminus were elevated at least 500-fold compared with the median of all 37 cell lines, and high C-terminal protein expression was detected despite the absence of RET fusion.

Conclusions

This study of 37 cell lines and four tissue specimens shows the detection of C-terminal ALK or ROS1 proteins could be a comprehensive method to determine ALK or ROS1 fusion, whereas not only the detection of C-terminal RET protein but also other methods would be needed to determine RET fusion.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5527-2) contains supplementary material, which is available to authorized users.

Correction to: The effects and mechanisms of SLC34A2 in tumorigenesis and progression of human non-small cell lung cancer

AbstractAfter the publication of this article [1] it came to our attention that there were some errors in two of the figures.

SLC34A2 promotes neuroblastoma cell stemness via enhancement of miR-25/Gsk3β-mediated activation of Wnt/β-catenin signaling

Cancer stem cells contribute to cancer progression, but the mechanisms underlying neuroblastoma stem cell development are unclear. Here, we examined the roles of the transcription factor SLC34A2 in regulating the stemness of neuroblastoma cells. We found that SLC34A2 expression was negatively correlated with the overall survival and relapse‐free survival probability of neuroblastoma patients. Additionally, SLC34A2 expression was observed to be remarkably increased in spheroids derived from neuroblastoma cells. Knockdown of SLC34A2 attenuated the expression of stemness markers and spheroid formation capacity of neuroblastoma cell‐derived spheroids, and overexpression of SLC34A2 exerted the opposite effects in neuroblastoma cells. Mechanistically, SLC34A2 was found to directly bind to the promoter of MIR25, which targets glycogen synthesis kinase 3β (Gsk3β), an antagonist of Wnt signaling. Transfection of miR‐25 inhibitor or a Gsk3β overexpression plasmid attenuated the effects of SLC34A2 overexpression on the stemness of neuroblastoma cells. Our results demonstrate that miR‐25/Gsk3β‐mediated activation of Wnt signaling is responsible for SLC34A2‐induced enhancement of neuroblastoma cell stemness.

Identifying primary site of lung-limited Cancer of unknown primary based on relative gene expression orderings

Background

Precise diagnosis of the tissue origin for metastatic cancer of unknown primary (CUP) is essential for deciding the treatment scheme to improve patients’ prognoses, since the treatment for the metastases is the same as their primary counterparts. The purpose of this study is to identify a robust gene signature that can predict the origin for CUPs.

Methods

The within-sample relative gene expression orderings (REOs) of gene pairs within individual samples, which are insensitive to experimental batch effects and data normalizations, were exploited for identifying the prediction signature.

Results

Using gene expression profiles of the lung-limited metastatic colorectal cancer (LmCRC), we firstly showed that the within-sample REOs in lung metastases of colorectal cancer (CRC) samples were concordant with the REOs in primary CRC samples rather than with the REOs in primary lung cancer. Based on this phenomenon, we selected five gene pairs with consistent REOs in 498 primary CRC and reversely consistent REOs in 509 lung cancer samples, which were used as a signature for predicting primary sites of metastatic CRC based on the majority voting rule. Applying the signature to 654 primary CRC and 204 primary lung cancer samples collected from multiple datasets, the prediction accuracy reached 99.36%. This signature was also applied to 24 LmCRC samples collected from three datasets produced by different laboratories and the accuracy reached 100%, suggesting that the within-sample REOs in the primary site could reveal the original tissue of metastatic cancers.

Conclusions

The result demonstrated that the signature based on within-sample REOs of five gene pairs could exactly and robustly identify the primary sites of CUPs.

Knockdown of SLC34A2 inhibits cell proliferation, metastasis, and elevates chemosensitivity in glioma

Solute carrier 34 A2 (SLC34A2) is a member of SLC34 family that is a group of phosphate transporters. SLC34A2 has been reported to play critical roles in tumorigenesis and progression. However, the researches about the biological roles of SLC34A2 in glioma have not yet been reported. In this study, we analyzed the expression patterns of SLC34A2 in clinical glioma tumor tissues and cell lines. The results demonstrated that SLC34A2 was generally overexpressed in both glioma tissues and cell lines. To further investigate the roles of SLC34A2 in glioma, lentivirus containing specific SLC34A2 short hairpin RNA (sh-SLC34A2) was used to infect glioma cell lines U251 and U87 for the knockdown of SLC34A2. The following studies proved that SLC34A2 knockdown exhibited suppressive effects on cell proliferation and migration/invasion. SLC34A2 knockdown also inhibited epithelial-mesenchymal transition (EMT) phenotype, as evidenced by the increased E-cadherin expression, and the decreased N-cadherin and fibronectin expressions. Besides, knockdown of SLC34A2 enhanced the temozolomide (TMZ) sensitivity of U251 and U87 cells. In vivo tumorigenicity assay demonstrated that SLC34A2 knockdown inhibited tumor growth. Moreover, SLC34A2 knockdown suppressed the activation of epidermal growth factor receptor (EGFR)/PI3K/AKT signaling pathway in U87 cells. GW2974 (EGFR inhibitor) increased SLC34A2 knockdown-inhibited cell proliferation, migration/invasion, as well as enhanced SLC34A2 knockdown-increased the TMZ sensitivity of glioma cells. These findings suggested that SLC34A2 might be a new potential therapeutic target for the therapy of glioma patients.

The role of SLC34A2 in intestinal phosphate absorption and phosphate homeostasis

There has recently been significant interest in the concept of directly targeting intestinal phosphate transport to control hyperphosphatemia in patients with chronic kidney disease. However, we do not have a complete understanding of the cellular mechanisms that govern dietary phosphate absorption. Studies in the 1970s documented both active and passive pathways for intestinal phosphate absorption. However, following the cloning of the intestinal SLC34 cotransporter, NaPi-IIb, much of the research focused on the role of this protein in active transcellular phosphate absorption and the factors involved in its regulation. Generation of a conditional NaPi-IIb knockout mouse has demonstrated that this protein is critical for the maintenance of skeletal integrity during periods of phosphate restriction and that under normal physiological conditions, the passive sodium-independent pathway is likely be the more dominant pathway for intestinal phosphate absorption. The review aims to summarise the most recent developments in our understanding of the role of the intestine in phosphate homeostasis, including the acute and chronic renal adaptations that occur in response to dietary phosphate intake. Evidence regarding the overall contribution of the transcellular and paracellular pathways for phosphate absorption will be discussed, together with the clinical benefit of inhibiting these pathways for the treatment of hyperphosphatemia in chronic kidney disease.

Inorganic phosphate transporters in cancer: Functions, molecular mechanisms and possible clinical applications

Inorganic phosphate is one of the most essential nutrients for the maintenance of cell life. Because of its essential role in nutrient supplementation, the study of plasma membrane inorganic phosphate transporters in cancer biology has received much attention in recent years. Several studies suggest that these transporters are up-regulated in tumor cells and thus have been considered to be important promoters of tumor progression. Altered expression levels of inorganic phosphate transporters, such as NaPi-IIb (SLC34A2) and PiT-1 (SLC20A1), have been demonstrated. The purpose of this review article was to gather the relevant experimental records on inorganic phosphate transporters in tumors and to demonstrate the importance of these proteins in clinical applications. In this work, we demonstrate that for decades, the potential use of the inorganic phosphate transporter as an antigen for the diagnosis of tumor subtypes remained unknown. With the advancement in molecular biology techniques, phosphate transporters have been identified as being associated with cancer. In addition to their altered expression in cancer, several studies have demonstrated other functions of inorganic phosphate transporters, such as transceptors, rearrangements with oncogenes and modifications in the expression of ABC transporters, aiding in the process of proliferation and drug resistance.

Solute carrier family 34 member 2 overexpression contributes to tumor growth and poor patient survival in colorectal cancer

Solute carrier family 34 member 2 (SLC34A2) is a well-known sodium-dependent phosphate transporter that has recently been linked to cancer development. However, its specific oncogenic role remains controversial in numerous human malignancies, and is currently unknown in colorectal cancer (CRC). Therefore, in this study we firstly used Oncomine database to determine its expression in cancer tissues and found it is overexpressed in thyroid, ovarian and renal cancer, while it is opposite in lung, breast and pancreas cancer. Using qRT-PCR and western blot, we then demonstrated its overexpression in CRC tissues as compared with adjacent normal tissues (n = 20). In a retrospective cohort enrolling 190 CRC patients, we proved its expression was significantly correlated with N stage. Furthermore, high SLC34A2 expression is associated with higher postoperative metastasis rate and serves as an independent adverse factor affecting patient prognosis. In subgroup analysis, SLC34A2 expression could stratify the patient prognosis in stage II and III CRC, but failed in stage IV CRC. In cellular assays in vitro, knockdown of SLC34A2 dramatically inhibited the proliferation and colony formation, induced the apoptosis and arrests the cell cycle progression of HCT-116 CRC cells. In cellular assays in vivo, knockdown of SLC34A2 significantly inhibited the growth of xenografts, decreasing Ki-67 and proliferating cell nuclear antigen (PCNA) expression and increasing apoptosis rate. Taken together, our study indicates SLC34A2 plays a crucial promoting role in CRC development and therefore has great potential to be further developed as a reliable biomarker for CRC diagnosis and treatment.

High expression of SLC34A2 is a favorable prognostic marker in lung adenocarcinoma patients

Dysregulation of SLC34A2 (NaPi2b) in tumors has attracted wide attention, but its expression and function in non-small cell lung cancer remains unclear. By examining its expression in lung adenocarcinoma and correlation to patient outcome, we aimed to explore its prognostic and therapeutic values in this deadly disease. Overall, 175 cases of lung adenocarcinoma sample were included in this study. Histological subtyping of them was diagnosed according to standards of the International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society in 2011. Protein expression of SLC34A2 and anaplastic lymphoma kinase in these samples was determined by immunohistochemistry. Epidermal growth factor receptor mutations were examined using amplification refractory mutation system. Statistical analysis was performed using software of Pearson's correlation coefficient. High expression of SLC34A2 was identified in about 2/3 patients and correlated with significantly better patient's overall survival. Epidermal growth factor receptor mutations were detected in about 53% of patients with no statistically significant difference to patient's overall survival. Anaplastic lymphoma kinase rearrangement was found in 8 out of 175 patients, harboring this abnormality leads to shorter overall survival. No correlation has been found between SLC34A2 expression and epidermal growth factor receptor mutation or anaplastic lymphoma kinase rearrangements in lung adenocarcinoma. High expression of SLC34A2 is present in about 3/4 lung adenocarcinoma samples and predicts better outcome. Since it is a membrane protein, antibody-based drugs targeting this marker might bring new resolution to this deadly disease.

Quantifying critical states of complex diseases using single-sample dynamic network biomarkers

Dynamic network biomarkers (DNB) can identify the critical state or tipping point of a disease, thereby predicting rather than diagnosing the disease. However, it is difficult to apply the DNB theory to clinical practice because evaluating DNB at the critical state required the data of multiple samples on each individual, which are generally not available, and thus limit the applicability of DNB. In this study, we developed a novel method, i.e., single-sample DNB (sDNB), to detect early-warning signals or critical states of diseases in individual patients with only a single sample for each patient, thus opening a new way to predict diseases in a personalized way. In contrast to the information of differential expressions used in traditional biomarkers to “diagnose disease”, sDNB is based on the information of differential associations, thereby having the ability to “predict disease” or “diagnose near-future disease”. Applying this method to datasets for influenza virus infection and cancer metastasis led to accurate identification of the critical states or correct prediction of the immediate diseases based on individual samples. We successfully identified the critical states or tipping points just before the appearance of disease symptoms for influenza virus infection and the onset of distant metastasis for individual patients with cancer, thereby demonstrating the effectiveness and efficiency of our method for quantifying critical states at the single-sample level.

The concept of dynamic network biomarkers (DNB) was proposed for detecting the critical state or tipping point of a complex disease (a pre-disease state immediately preceding the disease state), and has been applied to study the mechanism of cell fate decision and immune checkpoint blockade. But DNB cannot be used to identify the critical state or tipping point for a single patient because evaluating DNB for critical state required the data of multiple samples. The proposed method can identify the critical state of a complex disease for a single patient by implementing the concept of DNB. This method not only can be applied to detect the critical state or tipping point of a single sample, but also can be used to study the mechanism of complex disease at a single sample level. The ability of accurately and efficiently identifying the critical state for a single sample can benefit the development of personalized medicine.

Knockdown of SLC34A2 Inhibits Hepatocellular Carcinoma Cell Proliferation and Invasion

The gene solute carrier family 34 (sodium phosphate), member 2 (SLC34A2), is a member of the SLC34 family. Increasing evidence suggests that SLC34A2 is involved in the development of many human carcinomas. However, its role in hepatocellular carcinoma (HCC) is still unclear. Therefore, in this study we investigated the role of SLC34A2 in HCC and explored the underlying mechanism. We found that the expression of SLC34A2 is upregulated in HCC cell lines. Knockdown of SLC34A2 obviously inhibited HCC cell proliferation, migration/invasion, and the epithelial–mesenchymal transition (EMT) phenotype. Furthermore, knockdown of SLC34A2 significantly inhibited the expression of phosphorylated PI3K and AKT in HCC cells. Taken together, these results suggest that knockdown of SLC34A2 inhibits proliferation and migration by suppressing activation of the PI3K/AKT signaling pathway in HCC cells, and SLC34A2 may be a potential therapeutic target for the treatment of HCC.

Overexpression of SLC34A2 is an independent prognostic indicator in bladder cancer and its depletion suppresses tumor growth via decreasing c-Myc expression and transcriptional activity

Solute carrier family 34 member 2 (SLC34A2), a pH-sensitive sodium-dependent phosphate transporter, is associated with several human cancers. In this study, we investigate the clinical significance of SLC34A2 and its function in human bladder cancer (BC). The expression dynamics of SLC34A2 were examined in two independent cohorts of BC samples by quantitative PCR, western blotting and immunohistochemical staining. In the training cohort (156 cases), we applied the X-tile program software to assess the optimal cutoff points for biomarkers in order to accurately classify patients according to clinical outcome. In the validation cohort (130 cases), the cutoff score derived from X-title analysis was investigated to determine the association of SLC34A2 expression with survival outcome. A series of in vitro and in vivo assays were then performed to elucidate the function of SLC34A2 in BC and its underlying mechanisms. Results showed that SLC34A2 was significantly upregulated in BC cell lines and clinical samples. In both two cohorts of BC samples, high expression of SLC34A2 was associated with large tumor size, advanced T status and poor patients' survival. The depletion of SLC34A2 in BC suppressed cellular viability, colony formation and anchorage-independent growth in vitro, and inhibited xenograft tumor growth in vivo, whereas overexpression of SLC34A2 had the converse effect. Simultaneously, downregulation of SLC34A2 decreased the transcriptional activity and protein expression level of c-Myc in BC cells, whereas restoration of c-Myc expression could compromise the anti-proliferation effect of SLC34A2 depletion. Furthermore, miR-214 was proved as a negative regulator of SLC34A2. Our present study illustrated that SLC34A2 has an important role in promoting proliferation and tumorigenicity of BC, and may represent a novel therapeutic target for this disease.

Decreased expression of miR-939 contributes to chemoresistance and metastasis of gastric cancer via dysregulation of SLC34A2 and Raf/MEK/ERK pathway

BACKGROUND

The development of chemoresistance and metastasis are the leading causes of death for gastric cancer (GC) patients, however, the molecular mechanisms involved remain unclear. Dysregulation of miRNAs is associated with a variety of disease, including GC. Recently, microarray profiling analysis revealed that miR-939 was dysregulated in human GC samples, but the role of miR-939 in GC has not been intensively investigated.

METHODS

In the present study, we firstly examined the expression pattern of miR-939 in two independent cohorts of clinical GC samples: one cohort of 112 GC patients with stage I-III disease who underwent surgery followed by adjuvant chemotherapy; and another cohort of 110 GC patients with stage IV disease who received palliative chemotherapy. A series of in vivo and in vitro assays were then performed to investigate the function of miR-939 in GC.

RESULTS

We detected that reduced expression of miR-939 was associated with chemoresistance and increased risk of tumor recurrence in GC patients. Further function study demonstrated that overexpression of miR-939 suppressed GC cell growth, and enhanced 5-fluorouracil-induced chemosensitivity by compromising cellular growth and inducing apoptosis in vitro and in vivo. Moreover, miR-939 repressed the migration and invasion of GC cells in vitro, and diminished the occurrence of lung metastasis in vivo. We further identified solute carrier family 34 member 2 (SLC34A2) was a novel target of miR-939. Mechanistically, we elucidated that miR-939 exerted its function mainly through inhibiting SLC34A2/Raf/MEK/ERK pathway, which is activated in GC. Multivariate analysis identified miR-939, SLC34A2, and their combination as independent indicators for poor prognosis and tumor recurrence in GC patients.

CONCLUSION

Our data indicate that miR-939 acts as a tumor suppressor miRNA in GC, and miR-939/SLC34A2 axis represents a novel therapeutic strategy for future GC treatment.

MicroRNA-410 acts as oncogene in NSCLC through downregulating SLC34A2 via activating Wnt/β-catenin pathway

SLC34A2 had been reported to be down-regulated in human NSCLC cells and patient tissues, and played a significant role in lung cancer. However, the mechanism of its unusual expressionin NSCLC has not been fully elucidated. In present study, we identified SLC34A2 was a direct target of miR-410 and could be inhibited by miR-410 transcriptionally and post-transcriptionally. MiR-410 promoted the growth, invasion and migration of NSCLC cells in vitro. An orthotopic xenograft nude mouse model further affirmed that miR-410 promoted NSCLC cell growth and metastasis in vivo. Moreover, restoring SLC34A2 expression effectively reversed the miR-410-mediated promotion of cell growth, invasion and migration in NSCLC cells. In addition, miR-410high /SLC34A2low expression signature frequently existed in NSCLC cells and tumor tissues. MiR-410 significantly increased the expression of DVL2 and β-catenin protein while decreased that of Gsk3β protein of Wnt/β-catenin signaling pathway, while SLC34A2 partly blocked the effects of miR-410 on those protein expressions. Hence, our data for the first time delineated that unusual expression of SLC34A2 was modulated by miR-410, and miR-410 might positivelycontribute to the tumorigenesis and development of NSCLC by down-regulating SLC34A2 and activating Wnt/β-catenin signaling pathway. MiR-410 might be a new potential therapeutic target for NSCLC.