Experimental Evidence for Resecretion of PGE2 across Rat Alveolar Epithelium by OATP2A1/SLCO2A1-Mediated Transcellular Transport

Cigarette smoke-induced attenuation of the prostaglandin transporter SLCO2A1 expression through aryl hydrocarbon receptor

SLCO2A1 is a prostaglandin transporter and contributes to regulating local concentration of an inflammatory mediator, PGE2. Since we previously found that cigarette smoke extracts (CSE) reduced Slco2a1 mRNA expression in rat alveolar epithelial cells, the current study aimed to investigate the effect of CSE on human SLCO2A1 mRNA expression across cell lines from organs that are susceptible to tobacco smoking-induced inflammation. 5'-Flanking regions of SLCO2A1 up to 3673 bp upstream of the transcription start site (+1) was sub-cloned into a luciferase (LUC) expression vector, and promoter activity was evaluated by a reporter assay. CSE significantly reduced SLCO2A1 mRNA expression and LUC activity driven by the construct of -3673/+4 in colon epithelial LoVo and Caco-2 and lung mucoepidermoid NCI-H292 cells, but not in liver epithelial-like HepG2 cells. Long-term exposure of LoVo cells to CSE completely suppressed SLCO2A1 protein expression. The CSE-mediated effect on LUC activity was restored by an AHR antagonist PD98059 and a known AHR ligand β-naphthoflavone significantly reduced SLCO2A1 mRNA expression in cells. Concomitantly, the CSE-mediated negative regulation of SLCO2A1 was abolished in cells transfected with the construct of -3673/+4 with mutated xenobiotic response element. Furthermore, PD98059 and an AHR inhibitor perillaldehyde diminished the negative effect of CSE on SLCO2A1 mRNA expression in Lovo, NCI-H292 and Caco-2 cells. These results demonstrate that CSE negatively modulates SLCO2A1 transcription through AHR activation, providing a toxicological implication of tobacco smoke-induced inflammation.

Modulation of prostaglandin transport activity of SLCO2A1 by annexin A2 and S100A10

Solute carrier organic anion transporter family member 2A1 (SLCO2A1) is a prostaglandin (PG) transporter and serves as the osmosensitive ATP-permeable maxi-anion channel (Maxi-Cl). Since a heterotetrameric complex of annexin A2 (ANXA2) and S100A10 is obligatory for the channel activity, the present study aimed to determine if they regulate SLCO2A1-mediated PG transport. This study examined PGE2 uptake and ATP release in Anxa2 and/or S100a10 knockout (KO) murine breast C127 cells. Deletion of Slco2a1 decreased PGE2-d4 uptake by wild-type (WT) cells in an isotonic medium (290 mosmol/kgH2O). Decreased osmolarity (135 mosmol/kgH2O) stimulated ATP release but did not affect PGE2 uptake kinetics, showing Km (1,280 nM) and Vmax (10.38 pmol/15 s/mg protein) similar to those in isotonic medium (1,227 nM and 10.65 pmol/15 s/mg protein), respectively, in WT cells. Deletion of Anxa2 associated with loss of S100a10 diminished SLCO2A1-mediated ATP release and uncompetitively inhibited PGE2 uptake with lowered Km (376 nM) and Vmax (2.59 pmol/15 s/mg protein). Moreover, the immunoprecipitation assay confirmed the physical interaction of ANXA2 with SLCO2A1 in WT cells. Enforcement of ANXA2 expression to Anxa2 KO cells partially restored PGE2 uptake and increased Km (744.3 nM) and Vmax (9.07 pmol/15 s/mg protein), whereas the uptake clearance (Vmax/Km) did not change much regardless of ANXA2 expression. These results suggest that an ANXA2/S100A10 complex modulates PG transport activity but osmolality has little effect on it; therefore, the bound form of SLCO2A1, which functions as a PG transporter and Maxi-Cl, may exist regardless of changes in the cell volume.NEW & NOTEWORTHY A previous study indicated that the ANXA2/S100A10 complex represents the regulatory component of SLCO2A1-mediated Maxi-Cl channel activity. The present study showed that apparent PGE2 uptake by C127 cells was osmoinsensitive and uncompetitively inhibited by loss of ANXA2 expression, demonstrating that ANXA2 is a regulatory factor of SLCO2A1-mediated PG transport activity.

Ceefourin-1, a MRP4/ABCC4 inhibitor, induces apoptosis in AML cells enhanced by histamine

BACKGROUND

Ceefourin-1 is a specific MRP4/ABCC4 inhibitor with potential antileukemic activity. In this study, we evaluate the ability of ceefourin-1 alone or in combination with histamine, an approved antileukemic agent, to induce cell differentiation or apoptosis in human acute myeloid leukemic cells. We also examine ceefourin-1 toxicity in mice.

METHODS

U937, HL-60, and KG1a cells were used as models for human acute myeloid leukemia. Cyclic AMP efflux was estimated by measuring intracellular and extracellular cAMP levels. Cell differentiation was assessed by levels of CD14 and CD11b by FACS, and CD88 by western blot, and by cell morphology. Apoptosis was evaluated by cleavage of caspase-3 and PARP by western blot, and by annexin V binding assay. Subacute toxicity study of ceefourin-1 was carried out in BALB/c mice.

RESULTS

Ceefourin-1 inhibits cAMP exclusion in AML cells and promotes intracellular signaling via CREB. Ceefourin-1 leads AML cells to apoptosis and histamine potentiates this effect, without evidence of cell differentiation. Intraperitoneal administration of ceefourin-1 shows no important alterations in mice blood parameters, hepatic, and renal functions, nor signs of histologic damage.

CONCLUSIONS

These results show that ceefourin-1 promotes apoptosis in AML cells that is enhanced by histamine.

GENERAL SIGNIFICANCE

This work indicates that ceefourin-1 represents a promising molecule that could be used alone or in combination with histamine for in vivo evaluation in acute myeloid leukemia malignancies.

MiR-1306-5p predicts favorable prognosis and inhibits proliferation, migration, and invasion of colorectal cancer cells via PI3K/AKT/mTOR pathway

MicroRNAs (miRNAs) play a critical role in the occurrence and progression of colorectal cancer. Our study aims to explore the role of miR-1306-5p in cell malignant phenotypes of colorectal cancer cells. RT-qPCR was performed to assess the expression of miR-1306-5p in colorectal cancer samples and cell lines. The effects of miR-1306-5p on cell proliferation, migration, and invasion were evaluated through the CCK-8 assay, wound healing assay, and transwell invasion assay, respectively. Apoptosis was detected by flow cytometry. Luciferase reporter assay was used to predict the target gene of miR-1306-5p. Western blot was used to detect the expression levels of signal pathway molecules and target proteins. We found that miR-1306-5p was low-expressed in colorectal cancer tissues and cell lines, and its expression was also associated with colorectal cancer development and prognosis. MiR-1306-5p overexpression led to a decrease in colorectal cancer cell proliferation, migration, and invasion, while promoting apoptosis. Moreover, it was discovered that SLCO2A1 was a target of miR-1306-5p. By targeting SLCO2A1, overexpression of miR-1306-5p could inhibit the PI3K/AKT/mTOR signaling pathway. Overexpression of miR-1306-5p inhibited the colorectal cancer cell malignant phenotypes via regulating PI3K/AKT/mTOR signaling pathway regulation by targeting SLCO2A1. Therefore, miR-1306-5p can be a prospective therapeutic target for treating colorectal cancer.

Recent advances in studies of SLCO2A1 as a key regulator of the delivery of prostaglandins to their sites of action

Solute carrier organic anion transporter family member 2A1 (SLCO2A1, also known as PGT, OATP2A1, PHOAR2, or SLC21A2) is a plasma membrane transporter consisting of 12 transmembrane domains. It is ubiquitously expressed in tissues, and mediates the membrane transport of prostaglandins (PGs, mainly PGE₂, PGF_2α, PGD₂) and thromboxanes (e.g., TxB₂). SLCO2A1-mediated transport is electrogenic and is facilitated by an outwardly directed gradient of lactate. PGs imported by SLCO2A1 are rapidly oxidized by cytoplasmic 15-hydroxyprostaglandin dehydrogenase (15-PGDH, encoded by HPGD). Accumulated evidence suggests that SLCO2A1 plays critical roles in many physiological processes in mammals, and it is considered a potential pharmacological target for diabetic foot ulcer treatment, antipyresis, and non-hormonal contraception. Furthermore, whole-exome analyses suggest that recessive inheritance of SLCO2A1 mutations is associated with two refractory diseases, primary hypertrophic osteoarthropathy (PHO) and chronic enteropathy associated with SLCO2A1 (CEAS). Intriguingly, SLCO2A1 is also a key component of the Maxi-Cl channel, which regulates fluxes of inorganic and organic anions, including ATP. Further study of the bimodal function of SLCO2A1 as a transporter and ion channel is expected to throw new light on the complex pathology of human diseases. Here, we review and summarize recent information on the molecular functions of SLCO2A1, and we discuss its pathophysiological significance.

Toxicological implication of prostaglandin transporter SLCO2A1 inhibition by cigarette smoke in exacerbation of lung inflammation

We reported that bleomycin (BLM)-induced pulmonary fibrosis was exacerbated in the prostaglandin transporter gene (Slco2a1)-deficient mice (Slco2a1(-/-)). Because cigarette smoke (CS) contributes to creating a profibrotic milieu in the respiratory region, the present study aimed to investigate the impact of CS on SLCO2A1-associated pathogenesis in the lungs of BLM-instilled mice. Bronchoalveolar lavage (BAL) fluid cell analysis indicated more severe inflammation in Slco2a1(-/-) on day 5 after BLM intratracheal instillation, and Slco2a1 deletion increased mRNA expression of pro-inflammatory cytokines (Tnf-α and Il-1β) and chemokine (Ccl5) in BAL cells. Male Slco2a1(-/-) exhibited significantly higher amounts of released Il-1β in BAL fluid, compared with female Slco2a1(-/-), male or female Slco2a1(+/+) group. The amount of PGE₂ collected in BAL fluid tended to increase in Slco2a1(-/-) compared with Slco2a1(+/+) group, whereas the PGE₂ concentrations in lung tissues were comparable between both groups. Besides, PGE₂ accumulated more in BAL fluid of male than that of female mice. Therefore, Slco2a1-deficient male mice were found to be more susceptible to BLM-treatment. Moreover, CS extracts (CSE) significantly reduced initial PGE₂ uptake by rat type1 alveolar epithelial cell-like (AT1-L) cells and human SLCO2A1-transfected cells. Exposure of AT1-L cells to CSE resulted in decreased mRNA expression of Slco2a1, suggesting that CS modulates SLCO2A1 function. These results indicate that exacerbated lung inflammation is attributed to an increase in Il-1β peptide and PGE₂ accumulation in the alveolar space, which exhibits a male predominance. SLCO2A1 inhibition by CSE is considered to be a new rationale for the lung toxicity of CS.

ATP-Binding Cassette Transporter C4 is a Prostaglandin D2 Exporter in HMC-1 cells

ATP-binding cassette transporter C4 (ABCC4) is associated with multidrug resistance and the regulation of cell signalling. Some prostaglandins (PGs), including: PGE₂, PGF_2α, PGE₃, and PGF_3α are known substrates of ABCC4, and are released from some types of cells to exert their biological effects. In the present study, we demonstrate that PGD₂ is a novel substrate of ABCC4 using a transport assay based on inside-out membrane vesicles prepared from ABCC4-overexpressing cells. Then, we used two types of cell lines with confirmed ABCC4 mRNA and PGD₂ release capacity (human mast cell lines HMC-1 cells and human rhabdomyosarcoma cell lines TE671 cells) to evaluate the contribution of ABCC4. The extracellular levels of PGD₂ were unchanged following addition of a selective ABCC4 inhibitor in TE671 cells. Pharmacological inhibition and knockdown of ABCC4 significantly reduced the extracellular levels of PGD₂ by at least 53% in HMC-1 cells. Moreover, the extracellular levels of PGD₂ decreased by at least 20% using the selective ABCC4 inhibitor in the other mast cell line RBL-2H3 cells. Therefore, our results suggest that ABCC4 functions as a PGD₂ exporter in HMC-1 cells.

Lipids - two sides of the same coin in lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by progressive extracellular matrix deposition in the lung parenchyma leading to the destruction of lung structure, respiratory failure and premature death. Recent studies revealed that the pathogenesis of IPF is associated with alterations in the synthesis and the activity of lipids, lipid regulating proteins and cell membrane lipid transporters and receptors in different lung cells. Furthermore, deregulated lipid metabolism was found to contribute to the profibrotic phenotypes of lung fibroblasts and alveolar epithelial cells. Consequently, several pharmacological agents, targeting lipids, lipid mediators, and lipoprotein receptors, was successfully tested in the animal models of lung fibrosis and entered early phase clinical trials. In this review, we highlight new therapeutic options to counteract disturbed lipid hemostasis in the maladaptive lung remodeling.