The cationic amino acid transporter (CAT) family is comprised of four homologous membrane proteins: CAT-1, CAT-2, CAT-3 and CAT-4, encoded by the SLC7A1−4 genes, respectively. The major difference between these transporters is at the level of tissue specificity and regulation of their expression^1,2.

The CAT family is included in the Na⁺-independent transport system, (named system y⁺) that mediate L-arginine uptake in most tissues and cells³.

CAT-2 (SLC7A2) is known to transport cationic amino acids such as L-arginine, L-ornithine, and L-lysine. It is considered to be the major arginine transporter in most cells and tissues. It can be expressed in two spliced variants, CAT-2A and CAT-2B. CAT-2A, is a low-affinity transporter, constitutively expressed in liver and muscle cells, whereas CAT-2B, is a high-affinity transporter, abundantly expressed in macrophages³.

Macrophages isolated from mice deficient in CAT-2 show impaired ability to transport arginine intracellularly and to produce nitric oxide in response to endotoxin, thus CAT2 may also be important in regulating immune cell function in inflammation⁴.

Studies have identified CAT2 as a regulator of fibrotic responses in the lung⁵.