| MCT4 (SLC16A3) is a proton‑coupled monocarboxylate transporter of the SLC16 family that mediates efflux of lactate and other glycolytic monocarboxylates from metabolically active cells with high glycolytic rates. It is an integral plasma membrane protein with multiple transmembrane segments that requires the accessory glycoprotein CD147/Basigin for proper folding, trafficking, and surface stability, so functional MCT4 resides predominantly in CD147‑containing complexes. Its transport cycle couples outward movement of lactate anions to inward movement of protons, a mechanism that lowers cytosolic lactate and helps preserve intracellular pH while contributing to acidification of the pericellular space. In skeletal muscle, immune cells, and many solid tumors, MCT4 expression increases in parallel with glycolytic flux and hypoxia‑inducible factor‑1α activity, and high SLC16A3 transcript and protein levels align with transcriptional signatures of glycolysis, hypoxia response, and angiogenesis. In tumor tissue, MCT4‑dependent lactate export supports maintenance of an acidic microenvironment that favors matrix remodeling, stabilizes HIF‑1α, and promotes expression of pro‑angiogenic and pro‑inflammatory mediators such as IL‑8, linking transporter activity to vascular changes and inflammatory tone. High MCT4 expression correlates with increased infiltration of immunosuppressive lymphocyte populations, elevated expression of immune checkpoint molecules, and reduced overall survival across several cancer types, indicating that SLC16A3 status marks an immunometabolic state associated with immune evasion and poor prognosis. Co‑localization of MCT4 with CD147 and matrix metalloproteinase‑14 at invadopodia and other invasive structures connects lactate export to localized extracellular matrix degradation and cell migration, and experimental reduction of MCT4 expression decreases invasive behavior and enhances sensitivity to effector lymphocyte‑mediated cytotoxicity. |
