Expression of Organic Cation Transporter SLC22A16 in Human Endometria

Bacterial over-expression of functionally active human CT2 (SLC22A16) carnitine transporter

BACKGROUND

Escherichia coli is a widely used tool for the over-expression of human proteins for studying structure and function. The toxicity of human proteins for E. coli often hampers the expression. This study aims to find conditions for the expression of a membrane transporter known as the carnitine transporter CT2. The knowledge on this transporter is scarce, thus obtaining the recombinant protein is very important for further studies.

METHODS AND RESULTS

The cDNAs coding for human CT2 (hCT2) was cloned in the pH6EX3 vector and different transformed E. coli strains were cultured in absence or in presence of glucose. hCT2 expression was obtained. The protein was purified and reconstituted into proteoliposomes in a functionally active state.

CONCLUSIONS

Using the appropriate IPTG concentration, together with the addition of glucose, hCT2 has been expressed in E. coli. The protein is active and shows capacity to transport carnitine in proteoliposomes. The results have a great interest in basic biochemistry of membrane transporters and applications to human health since hCT2 is involved in human pathology.

Organic Cation Transporters in Human Physiology, Pharmacology, and Toxicology

Individual cells and epithelia control the chemical exchange with the surrounding environment by the fine-tuned expression, localization, and function of an array of transmembrane proteins that dictate the selective permeability of the lipid bilayer to small molecules, as actual gatekeepers to the interface with the extracellular space. Among the variety of channels, transporters, and pumps that localize to cell membrane, organic cation transporters (OCTs) are considered to be extremely relevant in the transport across the plasma membrane of the majority of the endogenous substances and drugs that are positively charged near or at physiological pH. In humans, the following six organic cation transporters have been characterized in regards to their respective substrates, all belonging to the solute carrier 22 (SLC22) family: the organic cation transporters 1, 2, and 3 (OCT1–3); the organic cation/carnitine transporter novel 1 and 2 (OCTN1 and N2); and the organic cation transporter 6 (OCT6). OCTs are highly expressed on the plasma membrane of polarized epithelia, thus, playing a key role in intestinal absorption and renal reabsorption of nutrients (e.g., choline and carnitine), in the elimination of waste products (e.g., trimethylamine and trimethylamine N-oxide), and in the kinetic profile and therapeutic index of several drugs (e.g., metformin and platinum derivatives). As part of the Special Issue Physiology, Biochemistry, and Pharmacology of Transporters for Organic Cations, this article critically presents the physio-pathological, pharmacological, and toxicological roles of OCTs in the tissues in which they are primarily expressed.

Carnitine Traffic in Cells. Link With Cancer

Metabolic flexibility is a peculiar hallmark of cancer cells. A growing number of observations reveal that tumors can utilize a wide range of substrates to sustain cell survival and proliferation. The diversity of carbon sources is indicative of metabolic heterogeneity not only across different types of cancer but also within those sharing a common origin. Apart from the well-assessed alteration in glucose and amino acid metabolisms, there are pieces of evidence that cancer cells display alterations of lipid metabolism as well; indeed, some tumors use fatty acid oxidation (FAO) as the main source of energy and express high levels of FAO enzymes. In this metabolic pathway, the cofactor carnitine is crucial since it serves as a “shuttle-molecule” to allow fatty acid acyl moieties entering the mitochondrial matrix where these molecules are oxidized via the β-oxidation pathway. This role, together with others played by carnitine in cell metabolism, underlies the fine regulation of carnitine traffic among different tissues and, within a cell, among different subcellular compartments. Specific membrane transporters mediate carnitine and carnitine derivatives flux across the cell membranes. Among the SLCs, the plasma membrane transporters OCTN2 (Organic cation transport novel 2 or SLC22A5), CT2 (Carnitine transporter 2 or SLC22A16), MCT9 (Monocarboxylate transporter 9 or SLC16A9) and ATB^{0, +} [Sodium- and chloride-dependent neutral and basic amino acid transporter B(0+) or SLC6A14] together with the mitochondrial membrane transporter CAC (Mitochondrial carnitine/acylcarnitine carrier or SLC25A20) are the most acknowledged to mediate the flux of carnitine. The concerted action of these proteins creates a carnitine network that becomes relevant in the context of cancer metabolic rewiring. Therefore, molecular mechanisms underlying modulation of function and expression of carnitine transporters are dealt with furnishing some perspective for cancer treatment.

Route-specific association of progestin therapy and concurrent metformin use in obese women with complex atypical hyperplasia

INTRODUCTION

Previous studies have suggested that metformin use may enhance the therapeutic effect of progestin therapy for endometrial hyperplasia or malignancy. However, it is not known how the impact of concurrent metformin may be altered by route of progestin therapy, either locally via an intrauterine device or systemically. This study examined the effectiveness of concurrent metformin use and progestin therapy for women with complex atypical hyperplasia stratified by progestin route (systemic vs local).

METHODS

This single-institution retrospective study examined consecutive women with complex atypical hyperplasia who received progestin therapy from 2003 to 2018. Time-dependent analyses for complete response rate were performed comparing concurrent metformin users versus non-users in the oral progestin group and in the levonorgestrel-releasing intrauterine device group.

RESULTS

Across the study cohort (n=245), there were 137 (55.9%) women who responded to progestin therapy. In the oral progestin group (n=176), the median age and body mass index were 36 years and 37.7 kg/m2, respectively. 36 (20.5%) of women on oral progestins also took metformin. After controlling for diabetes status, women taking both oral progestins and metformin had a complete response rate similar to those not taking metformin (6 month cumulative rates, 23.1% vs 27.8%, adjusted hazard ratio (aHR) 0.71, 95% confidence interval (95% CI) 0.36 to 1.41). In the levonorgestrel-releasing intrauterine device group (n=69), the median age and body mass index were 35 years and 39.9 kg/m2, respectively. There were 15 (21.7%) women who took metformin in addition to the levonorgestrel-releasing intrauterine device. After controlling for diabetes status, women who had the levonorgestrel-releasing intrauterine device and took metformin had a significantly higher complete response rate compared with those not taking metformin (6 month cumulative rates, 86.7% vs 58.9%, aHR 2.31, 95% CI 1.09 to 4.89).

CONCLUSION

In a predominantly obese population, concurrent metformin may possibly offer treatment benefit when used with the levonorgestrel-releasing intrauterine device.

The human organic cation transporter OCT1 mediates high affinity uptake of the anticancer drug daunorubicin

Anthracyclines such as daunorubicin are anticancer agents that are transported into cells, and exert cytotoxicity by blocking DNA metabolism. Although there is evidence for active uptake of anthracyclines into cells, the specific transporter involved in this process has not been identified. Using the high-grade serous ovarian cancer cell line TOV2223G, we show that OCT1 mediated the high affinity (K_m ~ 5 μM) uptake of daunorubicin into the cells, and that micromolar amounts of choline completely abolished the drug entry. OCT1 downregulation by shRNA impaired daunorubicin uptake into the TOV2223G cells, and these cells were significantly more resistant to the drug in comparison to the control shRNA. Transfection of HEK293T cells, which accommodated the ectopic expression of OCT1, with a plasmid expressing OCT1-EYFP showed that the transporter was predominantly localized to the plasma membrane. These transfected cells exhibited an increase in the uptake of daunorubicin in comparison to control cells transfected with an empty EYFP vector. Furthermore, a variant of OCT1, OCT1-D474C-EYFP, failed to enhance daunorubicin uptake. This is the first report demonstrating that human OCT1 is involved in the high affinity transport of anthracyclines. We postulate that OCT1 defects may contribute to the resistance of cancer cells treated with anthracyclines.

The SLC22 family with transporters of organic cations, anions and zwitterions

The SLC22 family contains 13 functionally characterized human plasma membrane proteins each with 12 predicted α-helical transmembrane domains. The family comprises organic cation transporters (OCTs), organic zwitterion/cation transporters (OCTNs), and organic anion transporters (OATs). The transporters operate as (1) uniporters which mediate facilitated diffusion (OCTs, OCTNs), (2) anion exchangers (OATs), and (3) Na(+)/zwitterion cotransporters (OCTNs). They participate in small intestinal absorption and hepatic and renal excretion of drugs, xenobiotics and endogenous compounds and perform homeostatic functions in brain and heart. Important endogeneous substrates include monoamine neurotransmitters, l-carnitine, α-ketoglutarate, cAMP, cGMP, prostaglandins, and urate. It has been shown that mutations of the SLC22 genes encoding these transporters cause specific diseases like primary systemic carnitine deficiency and idiopathic renal hypouricemia and are correlated with diseases such as Crohn's disease and gout. Drug-drug interactions at individual transporters may change pharmacokinetics and toxicities of drugs.

Cellular pharmacokinetic mechanisms of adriamycin resistance and its modulation by 20(S)-ginsenoside Rh2 in MCF-7/Adr cells

BACKGROUND AND PURPOSE

Intracellular pharmacokinetics of anticancer drugs in multi-drug resistance (MDR) cancer cells is hugely important in the evaluation and improvement of drug efficacy. By using adriamycin as a probe drug in MDR cancer cells, we developed a cellular pharmacokinetic-pharmacodynamic (PK-PD) model to reveal the correlation between cellular pharmacokinetic properties and drug resistance. In addition, the ability of 20(S)-ginsenoside Rh2 (20(S)-Rh2) to reverse MDR was further investigated.

EXPERIMENTAL APPROACH

The cellular pharmacokinetics of adriamycin were analysed visually and quantitatively in human breast cancer cells MCF-7 and in adriamycin-resistant MCF-7 (MCF-7/Adr) cells. Mitochondria membrane potential was assayed to evaluate the apoptotic effect of adriamycin. Subsequently, a PK-PD model was developed via MATLAB.

KEY RESULTS

Visual and quantitative data of the dynamic subcellular distribution of adriamycin revealed that it accumulated in cells, especially nuclei, to a lesser and slower extent in MCF-7/Adr than in MCF-7 cells. 20(S)-Rh2 increased the rate and amount of adriamycin entering cellular/subcellular compartments in MCF-7/Adr cells through inhibition of P-glycoprotein (P-gp) activity, in turn augmenting adriamycin-induced apoptosis. The integrated PK-PD model mathematically revealed the pharmacokinetic mechanisms of adriamycin resistance in MCF-7/Adr cells and its reversal by 20(S)-Rh2.

CONCLUSIONS AND IMPLICATIONS

P-gp, which is overexpressed and functionally active at cellular/subcellular membranes, influences the cellular pharmacokinetic and pharmacological properties of adriamycin in MCF-7/Adr cells. Inhibition of P-gp activity represents a key mechanism by which 20(S)-Rh2 attenuates adriamycin resistance. Even more importantly, our findings provide a new strategy to explore the in-depth mechanisms of MDR and evaluate the efficacy of MDR modulators.

The human carnitine transporter SLC22A16 mediates high affinity uptake of the anticancer polyamine analogue bleomycin-A5

Bleomycin is used in combination with other antineoplastic agents to effectively treat lymphomas, testicular carcinomas, and squamous cell carcinomas of the cervix, head, and neck. However, resistance to bleomycin remains a persistent limitation in exploiting the full therapeutic benefit of the drug with other types of cancers. Previously, we documented that the Saccharomyces cerevisiae L-carnitine transporter Agp2 is responsible for the high affinity uptake of polyamines and of the polyamine analogue bleomycin-A5. Herein, we document that the human L-carnitine transporter hCT2 encoded by the SLC22A16 gene is involved in bleomycin-A5 uptake, as well as polyamines. We show that NT2/D1 human testicular cancer cells, which highly express hCT2, are extremely sensitive to bleomycin-A5, whereas HCT116 human colon carcinoma cells devoid of detectable hCT2 expression or MCF-7 human breast cancer cells that only weakly express the permease showed striking resistance to the drug. NT2/D1 cells accumulated fluorescein-labeled bleomycin-A5 to substantially higher levels than HCT116 cells. Moreover, L-carnitine protected NT2/D1 cells from the lethal effects of bleomycin-A5 by preventing its influx, and siRNA targeted to hCT2 induced resistance to bleomycin-A5-dependent genotoxicity. Furthermore, hCT2 overexpression induced by transient transfection of a functional hCT2-GFP fusion protein sensitized HCT116 cells to bleomycin-A5. Collectively, our data strongly suggest that hCT2 can mediate bleomycin-A5 and polyamine uptake, and that the rate of bleomycin-A5 accumulation may account for the differential response to the drug in patients.

Biological roles of estrogen and progesterone in human endometrial carcinoma--new developments in potential endocrine therapy for endometrial cancer

Endometrial carcinoma is one of the most common female pelvic malignancies. It is well known that uterine endometrial cell proliferation is under the control of both estrogen and progesterone. In this review, results of the recent studies on the biosynthesis and action of estrogen and progestin in normal endometrium and its disorders will be summarized and the new aspects of hormonal therapies in the patients with endometrial carcinoma will be discussed including its future prospectives. We reported that the enzymes responsible for intratumoral estrogen metabolism and biosynthesis are markedly different between human breast and endometrial carcinoma, although both of them are considered "estrogen-dependent malignancies". In addition, the biological significance of Progesterone receptor (PR) isoforms is considered to differ between endometrial and breast carcinomas. Clinical data concerning Hormone replacement therapy (HRT) and estrogen-dependent cancer risk also support these findings. These basic and clinical findings help to understand the biology and provide the new knowledge for prevention, diagnosis and treatment of human endomerial carcinoma. Specific endocrine treatment of endometrial carcinoma should be explored in future, although aromatase inhibitors are the most effective endocrine treatments of estrogen-responsive breast carcinoma. Retinoid, metabolities of vitamin A, and synthetic peroxisome proliferator-activated receptor (PPAR) gamma ligands, which have been used for the treatment of insulin resistance in type II diabetes mellitus, may be the important candidates as drugs not only for prevention but also for possible endocrine treatment of endometrial carcinoma.

Expression of Organic Cation Transporter SLC22A16 in Human Epithelial Ovarian Cancer

The SLC22A16 is one of the newly isolated organic cation transporters, which is responsible for uptake and transport of adriamycin into cells. Adriamycin is considered to be an active agent for ovarian cancer. Recently, the benefit of adding adriamycin to the current standard regimen, paclitaxel and platinum, is evaluated to improve the outcome of patients with ovarian cancer. Therefore, we examined the expression of SLC22A16 in ovarian cancers. Twelve ovarian carcinoma cell lines were used for immunoblotting and reverse transcription-polymerase chain reaction to confirm the expression of SLC22A16 mRNA and protein. Five normal ovaries, 12 ovarian adenomas, and 94 ovarian cancer cases were obtained from patients after surgical therapy. The specimens were used for immunohistochemistry. The median value of relative SLC22A16 gene expression in cell lines derived from clear-cell adenocarcinoma was significantly higher than that in cell lines from other histologies (P < 0.001). Expression of SLC22A16 protein was also detected in cell lines derived from clear-cell adenocarcinoma. The SLC22A16 immunoreactivity was detected in 15 (16%) of 94 epithelial ovarian cancer, 1 (8.3%) of 12 benign adenomas, but 0 (0%) of 5 normal ovary cases. In ovarian cancer tissues, SLC22A16 immunoreactivity was detected in 2 (5%) of 38 serous adenocarcinoma, 1 (6.7%) of 15 endometrioid adenocarcinoma, 0 (0%) of 14 mucinous adenocarcinoma, and 12 (46.2%) of 26 clear-cell adenocarcinoma (P < 0.0001, clear-cell vs other histologies). In conclusion, SLC22A16 was abundantly expressed in clear-cell adenocarcinoma. Our results suggest that adriamycin-related chemicals that are taken up via SLC22A16 may have the potential to be effective against clear-cell adenocarcinoma.