Tissue-specific processing of cocaine- and amphetamine-regulated transcript peptides in the rat

Cocaine- and amphetamine-regulated transcript (CART) is a recently discovered hypothalamic peptide regulated by leptin and with a potent appetite-suppressing activity. In the rat, the CART gene encodes a peptide of 116 amino acid residues (or a splice variant 13 residues longer). The predicted signal sequence is 27 amino acid residues, resulting in a prohormone of 89 residues. The CART prohormone contains several potential posttranslational processing sites in the form of mono- and dibasic sequences. In the present study we have purified CART peptides from extracts of adrenal gland, hypothalamus, nucleus accumbens, and pituitary gland (anterior and neurointermediate lobe) of the rat and determined the peptide structures by using microsequencing and mass spectrometry. In none of the tissues examined the long splice variant was found. From the adrenal gland, the CART(1–89) and CART(10–89) peptides were isolated, in contrast to the hypothalamus and nucleus accumbens, from which the shorter form peptides CART(42–89) and CART(49–89) were purified. From the anterior lobe of the pituitary gland, CART(42–89) was isolated, in contrast to the neurointermediate lobe, which contains only CART(49–89). This tissue-specific processing indicates that CART peptides may have different biological functions in the periphery and in the central nervous system.