Metastatic cancer cells increase glucose consumption and metabolism via glycolysis, producing large quantities of lactate. Recent work has shown that lactate efflux is mediated by monocarboxylate transporters (MCT), which are composed of a catalytic unit (MCT) and an accessory subunit (CD147), comprising the functional lactate transporter. CD147, an extracellular matrix metalloproteinase (MMP) inducer, is highly expressed in metastatic cancer cells. Because aerobic glycolysis is a hallmark of metastatic cancer, we examined whether increases in CD147 expression were linked to MCT expression in MDA-MB-231, a highly metastatic breast cancer cell line. MCT4 mRNA and protein expression were increased in MDA-MB-231 cells compared with cells derived from normal mammary tissue. MCT4 colocalized with CD147 in the plasma membrane and in membrane blebs shed from the cell surface. Small interfering RNA-mediated silencing of MCT4 impaired the maturation and trafficking of CD147 to the cell surface, resulting in accumulation of CD147 in the endoplasmic reticulum. Silencing MCT4 also resulted in fewer membrane blebs and decreased migration of MDA-MB-231 cells in vitro. Knockdown of CD147 resulted in loss of MCT4 in the plasma membrane and accumulation of the transporter in endolysosomes. These studies establish for the first time that increased expression of CD147 in metastatic cancer cells is coupled to the up-regulation of MCT4. The synergistic activities of the MCT/CD147 complex could facilitate migration of tumor cells by CD147-mediated MMP induction and lactate-stimulated angiogenesis and hyaluronan production. These data provide a molecular link between two hallmarks of metastatic cancer: the glycolytic switch and increased expression of CD147. [Cancer Res 2007;67(9):4182-9]

Many morphological, molecular, and electrophysiological features of the Nrl(-/-) photoreceptors are cone-like, and strongly distinguish these cells from rods. This retina provides a model for the investigation of cone function and cone-specific genetic disease.

In Bsg(-/-) mice, there is a severe reduction in accumulation of the MCT1 and -3 proteins in the RPE and a concomitant reduction in MCT1 and -4 in the neural retina supporting a role for 5A11/basigin in the targeting of these transporters to the plasma membrane. Decreased expression of MCT1 and -4 on the surfaces of Müller and photoreceptor cells may compromise energy metabolism in the outer retina, leading to abnormal photoreceptor cell function and degeneration.

The properties of TSH-dependent iodide (I-) uptake are defined for a cloned, continuously growing, functioning rat thyroid cell line (FRTL-5 cells). Since these cells grow without a lumen and are therefore restricted in their ability to iodinate thyroglobulin, the FRTL-5 cells offer the opportunity to directly study transport processes across the membrane into the cell as well as the process whereby I- moves from the cell. FRTL-5 cells concentrate I- approximately 30-fold and exhibit many of the properties of I- uptake seen in thyroid tissue slice and primary cell culture systems. In these cells, accumulation of I- is consistent with a Na+-dependent carrier model for I- uptake, and effects on the influx and efflux processes can be dissociated. Because FRTL-5 cells can be maintained in culture indefinitely and can provide large quantities of a homogeneous functional thyroid cell preparation for study, these cells offer the unique opportunity to further define the mechanism and kinetics of I- transport in a less complex system.

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Glucose is a key metabolite used by cancer cells to generate ATP, maintain redox state and create biomass. Glucose can be catabolized to lactate in the cytoplasm, which is termed glycolysis or alternatively can be catabolized to carbon dioxide and water in the mitochondria via oxidative phosphorylation (OXPHOS). Metabolic heterogeneity exists in a subset of human tumors, with some cells maintaining a glycolytic phenotype while others predominantly utilize OXPHOS. Cells within tumors interact metabolically with transfer of catabolites from supporting stromal cells to adjacent cancer cells. The Reverse Warburg Effect describes when glycolysis in the cancer-associated stroma metabolically supports adjacent cancer cells. This catabolite transfer, which induces stromal-cancer metabolic coupling, allows cancer cells to generate ATP, increase proliferation and reduce cell death. Catabolites implicated in metabolic coupling include the monocarboxylates lactate, pyruvate and ketone bodies. Monocarboxylate transporters (MCT) are critically necessary for release and uptake of these catabolites. MCT4 is involved in the release of monocarboxylates from cells, is regulated by catabolic transcription factors such as hypoxia inducible factor 1 alpha (HIF1A) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and is highly expressed in cancer-associated fibroblasts. Conversely, MCT1 is predominantly involved in the uptake of these catabolites and is highly expressed in a subgroup of cancer cells. MYC and TIGAR, which are genes involved in cellular proliferation and anabolism are inducers of MCT1. Profiling human tumors on the basis of an altered redox balance and intra-tumoral metabolic interactions may have important biomarker and therapeutic implications. Alterations in the redox state and mitochondrial function of cells can induce metabolic coupling. Hence, there is interest in redox and metabolic modulators as anticancer agents. Also, markers of metabolic coupling have been associated with poor outcomes in numerous human malignancies and may be useful prognostic and predictive biomarkers.

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