Oligopeptide transporter Slc15A modulates macropinocytosis in Dictyostelium by maintaining intracellular nutrient status

Leep2A and Leep2B function as a RasGAP complex to regulate macropinosome formation

Macropinocytosis mediates the non-selective bulk uptake of extracellular fluid, enabling cells to survey the environment and obtain nutrients. A conserved set of signaling proteins orchestrates the actin dynamics that lead to membrane ruffling and macropinosome formation across various eukaryotic organisms. At the center of this signaling network are Ras GTPases, whose activation potently stimulates macropinocytosis. However, how Ras signaling is initiated and spatiotemporally regulated during macropinocytosis is not well understood. By using the model system Dictyostelium and a proteomics-based approach to identify regulators of macropinocytosis, we uncovered Leep2, consisting of Leep2A and Leep2B, as a RasGAP complex. The Leep2 complex specifically localizes to emerging macropinocytic cups and nascent macropinosomes, where it modulates macropinosome formation by regulating the activities of three Ras family small GTPases. Deletion or overexpression of the complex, as well as disruption or sustained activation of the target Ras GTPases, impairs macropinocytic activity. Our data reveal the critical role of fine-tuning Ras activity in directing macropinosome formation.

A transcription factor complex in Dictyostelium enables adaptive changes in macropinocytosis during the growth-to-development transition

Macropinocytosis, an evolutionarily conserved endocytic pathway, mediates nonselective bulk uptake of extracellular fluid. It is the primary route for axenic Dictyostelium cells to obtain nutrients and has also emerged as a nutrient-scavenging pathway for mammalian cells. How cells adjust macropinocytic activity in various physiological or developmental contexts remains to be elucidated. We discovered that, in Dictyostelium cells, the transcription factors Hbx5 and MybG form a functional complex in the nucleus to maintain macropinocytic activity during the growth stage. In contrast, during starvation-induced multicellular development, the transcription factor complex undergoes nucleocytoplasmic shuttling in response to oscillatory cyclic adenosine 3',5'-monophosphate (cAMP) signals, which leads to increased cytoplasmic retention of the complex and progressive downregulation of macropinocytosis. Therefore, by coupling macropinocytosis-related gene expression to the cAMP oscillation system, which facilitates long-range cell-cell communication, the dynamic translocation of the Hbx5-MybG complex orchestrates a population-level adjustment of macropinocytic activity to adapt to changing environmental conditions.

Proton-Coupled Oligopeptide Transport (Slc15) in the Brain: Past and Future Research

This mini-review describes the role of the solute carrier (SLC)15 family of proton-coupled oligopeptide transporters (POTs) and particularly Pept2 (Slc15A2) and PhT1 (Slc15A4) in the brain. That family transports endogenous di- and tripeptides and peptidomimetics but also a number of drugs. The review focuses on the pioneering work of David E. Smith in the field in identifying the impact of PepT2 at the choroid plexus (the blood-CSF barrier) as well as PepT2 and PhT1 in brain parenchymal cells. It also discusses recent findings and future directions in relation to brain POTs including cellular and subcellular localization, regulatory pathways, transporter structure, species differences and disease states.

Gum Arabic-Stabilized Ferric Oxyhydroxide Nanoparticles for Efficient and Targeted Intestinal Delivery of Bioavailable Iron

Nanostructured iron(III) compounds are promising food fortificants with desirable iron bioavailability and food compatibility. Here, gum arabic (GA) solubilized 252 mg of iron(III) per g at neutral pH in the form of GA-stabilized ferric oxyhydroxide nanoparticles (GA-FeONPs) with Z-average size of 142.7 ± 5.9 nm and ζ-potential of -20.50 ± 1.25 mV. Calcein-fluorescence-quenching assay revealed well-absorbed iron from GA-FeONPs by polarized Caco-2 cells due to efficient macropinocytic internalization and asialoglycoprotein receptor-mediated specific endocytosis facilitated by the polypeptide and arabinogalactan fractions of GA, respectively, with endocytosed GA-FeONPs being in part basolaterally transcytosed and in another part degraded into cellular labile iron pool. GA-FeONPs showed good colloidal stability under varied pH, gastrointestinal, thermal processing, and spray/freeze drying conditions and displayed remarkably weaker pro-oxidant activity than FeSO₄ in glyceryl trilinoleate emulsion (P < 0.05). Oral pharmacokinetics unveiled desirable iron bioavailability of GA-FeONPs relative to FeSO₄, i.e., 124.27 ± 5.91% in aqueous solution and 161.64 ± 5.01% in milk. Overall, GA-FeONPs are a promising novel iron fortificant with food-compatible, efficient, and targeted intestinal iron delivery and sustained iron-release properties.

First person – Yiwei Zhang and Hui Tu

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Yiwei Zhang and Hui Tu are co-first authors on ‘ Oligopeptide transporter Slc15A modulates macropinocytosis in Dictyostelium by maintaining intracellular nutrient status’, published in JCS. Yiwei is a PhD student in the lab of Huaqing Cai at Institute of Biophysics, Chinese Academy of Sciences, Beijing, China, where she is interested in understanding the interrelationship between cellular nutrient status and macropinocytic activity, and lipid transport. Hui is a PhD student in the same lab, investigating the mechanisms of macropinocytosis, cell migration and lipid transport.