ACTH4-12 is the minimal message sequence required to induce the differentiation of mouse epidermal melanocytes in serum-free primary culture

Abstract

It is well known that α-melanocyte stimulating hormone (MSH) induces the differentiation of mouse epidermal melanocytes in vivo and in vitro. Although adrenocorticotropic hormone (ACTH) possesses the same amino acid sequence as MSH does, it is not clear whether the peptide and its fragments induce the differentiation of mouse epidermal melanocytes. In this study, the differentiation-inducing potencies of human ACTH and its fragments were investigated by adding them into a culture medium (0.001-1,000 nM) from the initiation of primary culture of epidermal cell suspensions. Their potencies were compared with the potency of α-MSH. After 2-4 days of primary cultures with ACTH1-13, ACTH1-17, ACTH1-24, ACTH1-39, ACTH4-12, ACTH4-13, and α-MSH, pigment granules appeared in the cytoplasms and dendrites of melanoblasts that were in contact with the adjacent keratinocyte colonies. By 14 days, cultures contained mostly pigmented melanocytes. The order of potencies of ACTH fragments and α-MSH shown by the ED50 value was as follows: α-MSH = ACTH1-13 = ACTH1-17 = ACTH4-12 = ACTH4-13 > ACTH1-24 > ACTH1-39. The length of their peptide chains was inversely proportional to the potency. On the contrary, ACTH1-4, ACTH11-24, and ACTH18-39 failed to induce the differentiation of melanocytes. In contrast, ACTH1-10, ACTH4-10, ACTH4-11, and ACTH5-12 possessed a weak potency at high doses only (100 and 1,000 nM). These results suggest that ACTH4-12 is the minimal message sequence required to induce the differentiation of mouse epidermal melanocytes in culture completely. The amino acids of Met4 and Pro12 are suggested to be important for its potency. (C) 2000 Wiley-Liss, Inc.