The inhibition of monocarboxylate transporter 2 (MCT2) by AR-C155858 is modulated by the associated ancillary protein

Abstract

In mammalian cells, MCTs (monocarboxylate transporters) require association with an ancillary protein to enable plasma membrane expression of the active transporter. Basigin is the preferred binding partner for MCT1, MCT3 and MCT4, and embigin for MCT2. In rat and rabbit erythrocytes, MCT1 is associated with embigin and basigin respectively, but its sensitivity to inhibition by AR-C155858 was found to be identical. Using RT (reverse transcription)–PCR, we have shown that Xenopus laevis oocytes contain endogenous basigin, but not embigin. Co-expression of exogenous embigin was without effect on either the expression of MCT1 or its inhibition by AR-C155858. In contrast, expression of active MCT2 at the plasma membrane of oocytes was significantly enhanced by co-expression of exogenous embigin. This additional transport activity was insensitive to inhibition by AR-C155858 unlike that by MCT2 expressed with endogenous basigin that was potently inhibited by AR-C155858. Chimaeras and C-terminal truncations of MCT1 and MCT2 were also expressed in oocytes in the presence and absence of exogenous embigin. L-Lactate Km values for these constructs were determined and revealed that the TM (transmembrane) domains of an MCT, most probably TM7–TM12, but not the C-terminus, are the major determinants of L-lactate affinity, whereas the associated ancillary protein has little or no effect. Inhibitor titrations of lactate transport by these constructs indicated that embigin modulates MCT2 sensitivity to AR-C155858 through interactions with both the intracellular C-terminus and TMs 3 and 6 of MCT2. The C-terminus of MCT2 was found to be essential for its expression with endogenous basigin.

Transport Activity of the High-affinity Monocarboxylate Transporter MCT2 Is Enhanced by Extracellular Carbonic Anhydrase IV but Not by Intracellular Carbonic Anhydrase II

“…Furthermore, studies indicate that these chaperones, both glycoproteins containing a single transmembrane domain with a short C terminus located in the cytosol and immunoglobulin-like domains in the extracellular region (43), remain tightly associated with the transporter in the membrane and are also involved in regulation/modulation of inhibitor sensitivity (9,10,41,42,44). In X. laevis oocytes, CD147 is endogenously expressed, whereas GP70, the preferred ancillary protein of MCT2, is not (9). These observations are confirmed by our experiments.…”

“…Oocytes-It has been shown that functional expression of MCT2 requires the ancillary protein GP70, which is not endogenously expressed in Xenopus oocytes (9,10). To examine the need of GP70 for proper expression of MCT2, we either expressed MCT2 alone or together with GP70 in Xenopus oocytes.…”

“…Experiments using heterologous protein expression in Xenopus oocytes revealed that MCTs require an ancillary protein, either CD147 (basigin, extracellular matrix metalloproteinase inducer) or GP70, for proper expression in the plasma membrane and, hence, transport activity. Although MCT1, MCT3, and MCT4 are normally associated with CD147, which is intrinsically expressed in Xenopus oocytes, MCT2 prefers GP70, which is not found in frog oocytes (9,10).…”

Targeting lactate metabolism for cancer therapeutics

“…A notable, and exploitable, feature of MCT transporters is that cochaperone immunoglobulin-family single-membrane pass proteins are required for their transport to the surface of the cell membrane. Specifically, MCT1, MCT3, and MCT4 bind to CD147 (also known as basigin, EMMRIN, and OX-47), which is required for their expression on the cell surface, whereas MCT2 binds and requires embigin for cell surface expression (60,61). Notably, the expression of CD147 on the cell surface also depends on co-expression with an MCT protein, and this interaction stabilizes both binding partners (62).…”

In Vitro and In Vivo Evidence for Active Brain Uptake of the GHB Analog HOCPCA by the Monocarboxylate Transporter Subtype 1

“…Oocytes were injected with 20 ng of the relevant cRNA. Oocytes to express MCT2 were injected with a mixture of 10 ng cRNA encoding MCT2 and 10 ng cRNA encoding the ancillary protein embigin (Ovens et al, 2010b). Control oocytes were injected with the equivalent volume of water (36.8 nl).…”