Monocarboxylate Transporter 13 (MCT13/SLC16A13) Functions as a Novel Plasma Membrane Oligopeptide Transporter

Luciferase-based bioluminescence revealed the facilitated diffusion of D-luciferin mediated by SLC17A3

SLC17A3 localized to the apical membrane of the renal proximal tubules has been implicated in the urinary excretion of drugs and endogenous/exogenous metabolites transported into the tubules by OAT1 and OAT3. Because SLC17A3 mediates the facilitated diffusion of organic anions, which requires a sensitive and rapid assay, no system has been established to evaluate its transport activity in mammalian cells. In this study, we demonstrated that the exposure of cells expressing click beetle luciferase (bLuc) and SLC17A3 to D-luciferin produces marked bioluminescence, which enables the evaluation of SLC17A3 function. The bioluminescence intensity increased under depolarized membrane potential conditions, consistent with the unique feature of SLC17A3 as a voltage-dependent organic anion transporter. SLC17A3-mediated bioluminescence was saturable with an apparent Michaelis-Menten constant (Km) of 8.1 μM. The inhibitory effects of various compounds including OAT1/OAT3 substrates and inhibitors on bioluminescence were in good agreement with those reported in SLC17A3-expressing Xenopus oocytes using radio-labeled substrates. Interestingly, we found that sulfinpyrazone and lesinurad, uricosuric drugs that inhibit SLC22A12/URAT1, are potent SLC17A3 inhibitors, suggesting the possibility that they alter the pharmacokinetics of OAT1/OAT3-substrate drugs and urate. Taken together, the bioluminescence-based SLC17A3 functional assay is robust and reliable. This strategy enables the study of its transport activity and the identification of potential SLC17A3-mediated drug-drug interactions. This approach also provides an opportunity to elucidate the molecular mechanisms involved in the urinary excretion of organic anions.

Embryonic temperature influences transcriptomic and methylation profiles in the liver of juvenile largemouth bass

Understanding the impacts of environmental conditions at early life stages on phenotypes and physiological responses to thermal variability at later stages is crucial for elucidating adaptive strategies in fish species. This study investigated the lasting effects of embryonic temperature on the growth performance, transcriptomic profiles, and CpG methylation status of juvenile largemouth bass (Micropterus salmoides) under normal and heat stress (HS) conditions. Embryos were incubated at three temperatures (22 °C, 25 °C, and 28 °C), reared at a constant 25 °C for three months, and subjected to acute HS at 37 °C. Liver samples were collected before and after HS for mRNA sequencing and reduced representation bisulfite sequencing. Significant differences in body size, body weight, condition factor, and hepatosomatic index were observed among groups. Fish hatched at 28 °C displayed a significantly higher standard length and body weight and lower hepatosomatic index than those hatched at lower temperatures. PCA analysis and Venn diagrams based on transcriptomes revealed transcriptomic response to HS differed at 28 °C while 22 and 25 °C were similar. Heat shock protein genes followed a similar trend. Epigenetic analyses revealed distinct CpG methylation patterns across incubation groups, while DNA methylation barely contributes to transcriptional differences. Under HS, different incubation groups exhibit various DNA methylation alterations. The "Neuroactive ligand-receptor interaction" pathway appeared to play an important role in the response to HS, suggesting a potential involvement of epigenetic regulation. Additionally, the atrnl1 gene may be involved in a DNA methylation-mediated regulatory mechanism in response to HS.

The Use of Carboxyfluorescein Reveals the Transport Function of MCT6/SLC16A5 Associated with CD147 as a Chloride-Sensitive Organic Anion Transporter in Mammalian Cells

Oral drug absorption involves drug permeation across the apical and basolateral membranes of enterocytes. Although transporters mediating the influx of anionic drugs in the apical membranes have been identified, transporters responsible for efflux in the basolateral membranes remain unclear. Monocarboxylate transporter 6 (MCT6/SLC16A5) has been reported to localize to the apical and basolateral membranes of human enterocytes and to transport organic anions such as bumetanide and nateglinide in the Xenopus oocyte expression system; however, its transport functions have not been elucidated in detail. In this study, we characterized the function of MCT6 expressed in HEK293T cells and explored fluorescent probes to more easily evaluate MCT6 function. The results illustrated that MCT6 interacts with CD147 to localize at the plasma membrane. When the uptake of various fluorescein derivatives was examined in NaCl-free uptake buffer (pH 5.5), the uptake of 5-carboxyfluorescein (5-CF) was significantly greater in MCT6 and CD147-expressing cells. MCT6-mediated 5-CF uptake was saturable with a Km of 1.07 mM and inhibited by several substrates/inhibitors of organic anion transporters and extracellular Cl ion with an IC50 of 53.7 mM. These results suggest that MCT6 is a chloride-sensitive organic anion transporter that can be characterized using 5-CF as a fluorescent probe.