Equilibrative nucleoside transporters

Equilibrative nucleoside transporters (ENTs) are a type of protein that facilitate the transport of nucleosides across the cell membrane. They are part of the larger family of solute carrier proteins, specifically the SLC29 family. ENTs are integral to many biological processes, including cellular metabolism, DNA synthesis, and signal transduction.

Function

ENTs function to transport nucleosides, as well as certain nucleoside analogs and nucleobases, across the cell membrane. This transport is equilibrative, meaning it occurs down a concentration gradient and does not require energy. ENTs are bidirectional, allowing for the transport of nucleosides in and out of the cell.

Types

There are four known types of ENTs in humans: ENT1, ENT2, ENT3, and ENT4. Each type has a unique tissue distribution and substrate specificity.

• ENT1 is widely expressed in various tissues and has a high affinity for both purine and pyrimidine nucleosides.
• ENT2 is also widely expressed and has a broad substrate specificity, transporting both purine and pyrimidine nucleosides as well as certain nucleobases.
• ENT3 is primarily found in intracellular membranes and has a high affinity for adenosine.
• ENT4 is a plasma membrane transporter with a high affinity for adenosine and is also known as the monoamine transporter PMAT.

Clinical significance

ENTs are of clinical significance due to their role in the uptake of nucleoside analog drugs, which are used in the treatment of various diseases including cancer and viral infections. Alterations in ENT function or expression can affect the efficacy of these drugs.

ENTs are also implicated in several diseases. For example, mutations in the gene encoding ENT3 can cause H syndrome, a rare genetic disorder.

See also

• Nucleoside
• Solute carrier family
• Cell membrane