Predictive value of the SLC22A18 protein expression in glioblastoma patients receiving temozolomide therapy

Identification of miRNA signature associated with BMP2 and chemosensitivity of TMZ in glioblastoma stem-like cells

Glioblastoma multiform (GBM) is the most lethal intracranial tumor in adults. Glioblastoma stem-like cells (GSCs) are responsible for tumorigenesis and chemotherapy resistance. BMPs are known to increase temozolomide (TMZ) response in GSCs, however, the intracellular molecular mechanism remains largely unknown. In this study, we built a GSC cell model called U87S, and performed RNA sequencing to identify differentially expressed (DE) miRNA profiles in U87S cells treated with BMP2, TMZ or combined BMP2 and TMZ respectively. Bioinformatics analysis revealed that most DE miRNAs were involved in the cancer pathways, suggesting their crucial roles in gliomagenesis. Eight miRNAs from RNA-seq were validated. Four out of these miRNAs (has-miR-199a-3p, hsa-miR-374b-5p, hsa-miR-320d, and hsa-miR-339-5p) were found significantly up-regulated in GBM tumor tissues. One of them, hsa-miR-199a-3p, was significantly correlated with the survival of GBM patients, and differentially expressed in U87S cells. Expression of hsa-miR-199a-3p was up-regulated by BMP. Overexpression of hsa-miR-199a-3p in U87S cells inhibited cell viability and enhanced the cytotoxicity of TMZ. And activation of BMP boosted the effect of hsa-miR-199a-3p on cell viability and TMZ-mediated cytotoxicity. Besides, expressions of five predicted targets of hsa-miR-199a-3p were evaluated. Four of them were differentially expressed in GBM tumors. And one of them, SLC22A18, was associated with the survival of GBM patients. In the end, a hsa-miR-199a-3p-mediated ceRNA network was constructed for the convenience of future study. Together, our data provided DE miRNA expression profiles associated with BMP2 and TMZ in GSCs, which might lead to finding out miRNA-based target therapies that specially target GSCs.

Knockdown of Orphan Transporter SLC22A18 Impairs Lipid Metabolism and Increases Invasiveness of HepG2 Cells

PURPOSE

The aim of this work is to investigate the roles of solute carrier family 22 member 18 (SLC22A18) in lipid metabolism and in establishing the tumor phenotype of HepG2 cells.

METHODS

SLC22A18-knockdown HepG2 cells were established by stable transfection with shRNA. Protein expression levels were measured by quantitative proteomics and Western blot analysis. Cell growth was examined by cell counting kit. Accumulation of triglyceride-rich lipid droplets was measured by Oil-Red O staining. Cell migration and invasion were examined by Transwell assays.

RESULTS

SLC22A18-knockdown HepG2 cells accumulated triglyceride-rich lipid droplets and showed decreased expression levels of lysosomal/autophagic proteins, suggesting that lipid degradation is suppressed. Growth of HepG2 cells was decreased by SLC22A18 knockdown, but was restored by free fatty acid supplementation. In addition, SLC22A18 knockdown decreased the expression of insulin-like growth factor-binding protein 1 (IGFBP-1) and increased the invasion ability of HepG2 cells. Exogenous IGFBP-1 blocked the increase of invasion activity induced by SLC22A18 knockdown.

CONCLUSION

Our results suggest that suppression of SLC22A18 decreased the supply of intracellular free fatty acids from triglyceride-rich lipid droplets by impairing the lysosomal/autophagy degradation pathway and reduced the invasive activity of HepG2 cells by decreasing IGFBP-1 expression.

Silencing SATB1 overcomes temozolomide resistance by downregulating MGMT expression and upregulating SLC22A18 expression in human glioblastoma cells

Glioblastoma multiforme (GBM) is the most common malignant tumor of the central nervous system and has a very poor prognosis. Currently, patients were treated by resection followed by radiotherapy plus concurrent temozolomide (TMZ) chemotherapy. However, many patients are resistant to TMZ-induced DNA damage because of upregulated expression of the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT). In this study, upregulation of SATB1 and MGMT, and downregulation of SLC22A18 resulted in acquisition of TMZ resistance in GBM U87 cells. Inactivation of special AT-rich sequence-binding protein 1 (SATB1) using short hairpin RNA (shRNA) downregulated MGMT expression and upregulated solute carrier family 22 member 18 (SLC22A18) expression in GBM cells. This suggested SATB1-mediated posttranscriptional regulation of the MGMT and SLC22A18 protein levels. Immunohistochemical analysis of malignant glioma specimens demonstrated a significant positive correlation between the levels of MGMT and SATB1, and a negative correlation between the levels of SLC22A18 and SATB1. Importantly, in recurrent, compared with the primary, lesions in 15 paired identical tumors, the SATB1 and MGMT protein levels were increased and the SLC22A18 levels were decreased. Finally, in TMZ-resistant GBM, SATB1 knockdown enhanced TMZ efficacy. Consequently, SATB1 inhibition might be a promising strategy combined with TMZ chemotherapy to treat TMZ-resistant GBM.

SLC transporters as a novel class of tumour suppressors: identity, function and molecular mechanisms

The role of plasma membrane transporters in cancer is receiving increasing attention in recent years. Several transporters for essential nutrients are up-regulated in cancer and serve as tumour promoters. Transporters could also function as tumour suppressors. To date, four transporters belonging to the SLC gene family have been identified as tumour suppressors. SLC5A8 is a Na(+)-coupled transporter for monocarboxylates. Among its substrates are the bacterial fermentation products butyrate and propionate and the ubiquitous metabolite pyruvate. The tumour-suppressive function of this transporter relates to the ability of butyrate, propionate and pyruvate to inhibit histone deacetylases (HDAC). SLC5A8 functions as a tumour suppressor in most tissues studied thus far, and provides a molecular link to Warburg effect, a characteristic feature in most cancers. It also links colonic bacteria and dietary fibre to the host. SLC26A3 as a tumour suppressor is restricted to colon; it is a Cl(-)/HCO(-) 3 exchanger, facilitating the efflux of HCO(-) 3 The likely mechanism for the tumour-suppressive function of SLC26A3 is related to intracellular pH regulation. SLC39A1 is a Zn(2+) transporter and its role in tumour suppression has been shown in prostate. Zn(2+) is present at high concentrations in normal prostate where it elicits its tumour-suppressive function. SLC22A18 is possibly an organic cation transporter, but the identity of its physiological substrates is unknown. As such, there is no information on molecular pathways responsible for the tumour-suppressive function of this transporter. It is likely that additional SLC transporters will be discovered as tumour suppressors in the future.

microRNA-137 functions as a tumor suppressor in human non-small cell lung cancer by targeting SLC22A18

Our previous study demonstrated that the overexpression of solute carrier family 22 member 18 (SLC22A18) in human non-small cell lung cancer (NSCLC) tissues might be associated with tumor progression and patients' prognosis. The aim of this study was to investigate the molecular mechanisms underlying its roles in NSCLC. As a result, bioinformatics analysis and luciferase reporter assay showed that microRNA (miRNA)-137 directly targeted SLC22A18 in NSCLC cells. Then, functional studies indicated that the ectopic expression of miR-137 significantly inhibited NSCLC cell proliferation, invasion and migration by targeting SLC22A18. More importantly, the decreased expression of miR-137 in clinical NSCLC tissues was correlated with advanced TNM stage, positive metastasis and poor prognosis of patients with this malignancy. In conclusion, these findings offer the convincing evidence that the roles of SLC22A18 in NSCLC progression may be partially caused by the regulatory effects of miR-137, which may function as a tumor suppressor. Our clinical data further indicated that miR-137 may be an independent favorable prognostic factor in NSCLC patients.

In vitro and in vivo radiosensitization of human glioma U251 cells induced by upregulated expression of SLC22A18

Our previous study showed that solute carrier family 22 (organic cation transporter) member 18 (SLC22A18) downregulation via promoter methylation was associated with the development and progression of glioma, and the elevated expression of SLC22A18 was found to increase the sensitivity of glioma U251 cells to the anticancer drug 1,3-bis(2-chloroethyl)-1-nitrosourea. In this study, we investigated the possible upregulated expression of SLC22A18-induced enhancement of radiosensitivity of human glioma U251 cells in order to provide evidence in support of further clinical investigations. Stably overexpressing SLC22A18 human glioma U251 cells were generated to investigate the effect of SLC22A18 on the sensitivity of cells to irradiation in vitro using clonogenic survival assay. The apoptosis of U251 cells was examined with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. DNA damage and repair were measured using γH2AX foci. The effect of SLC22A18 on the in vivo tumor radiosensitivity was investigated in the orthotopic mice model. Upregulated expression of SLC22A18 enhanced the radiosensitivity of glioma U251 cells and also enhanced irradiation-induced apoptosis of U251 cells, but irradiation-induced apoptosis did not correlate with radiosensitizing effect of upregulated expression of SLC22A18. The repair of irradiation-induced double-strand-breaks was retarded in stably overexpressing SLC22A18 U251 cells. In the orthotopic mice model, the upregulated expression of SLC22A18 in U251 cells enhanced the effect of irradiation treatment and increased the survival time of mice. These results show that upregulated expression of SLC22A18 radiosensitizes human glioma U251 cells by suppressing DNA repair capacity.

The association between the expression of solute carrier transporters and the prognosis of pancreatic cancer

OBJECTIVES

The aim of this study was to investigate the prognostic significance of fourteen anticancer drug-relevant solute carrier transporters (SLCs) in pancreatic cancer in the context of clinical-pathological characteristics and the KRAS mutation status of tumors.

METHODS

Tumors and non-neoplastic pancreatic tissues were obtained from 32 histologically verified patients with pancreatic ductal adenocarcinoma. The transcript profile of SLCs was assessed using quantitative real-time PCR. KRAS mutations in exon 2 were assessed by high-resolution melting analysis and confirmed by sequencing.

RESULTS

SLC22A3 and SLC22A18 were upregulated and SLC22A1, SLC22A2, SLC22A11, SLC28A1, SLC28A3 and SLC29A1 were downregulated when compared with non-neoplastic pancreatic tissues. Moreover, significantly lower levels of SLC22A1, SLC22A11 and SLC29A1 were found in tumors with angioinvasion. There was also a significantly higher transcript level of SLC28A1 in tumors with regional lymph nodes affected by metastasis. The study found that a high expression of SLC28A1 was significantly associated with poor overall survival in unselected patients. In contrast, a high expression of SLC22A3 or SLC29A3 was significantly associated with longer overall survival in patients treated with nucleoside analogs. Protein expression of SLC22A1, SLC22A3 and SLC29A3 in tumor tissues of patients with pancreatic carcinoma was observed by immunoblotting for the first time. Finally, SLC levels were not found to be associated with KRAS mutation status in exon 2.

CONCLUSIONS

This study identified a number of associations of transcript levels of SLCs with prognosis of pancreatic cancer patients.