In vitro effects of melanocyte-stimulating hormone, adrenocorticotropic hormone, 17 beta-estradiol, or testosterone propionate on Cloudman S91 mouse melanoma cells

17beta-estradiol, progesterone, and dihydrotestosterone suppress the growth of human melanoma by inhibiting interleukin-8 production

We studied the effects of 17beta-estradiol, progesterone, and dihydrotestosterone on in vitro growth of human metastatic melanoma. Each sex hormone inhibited the growth of melanoma receptor-dependently; 17beta-estradiol inhibited 3H-thymidine uptake of estrogen receptor-positive WM266-4 and NM26, but not that of the receptor-negative HS15. Progesterone inhibited 3H-thymidine uptake of progesterone receptor-positive WM266-4 and HS15, but not that of the receptor-negative NM26. Dihydrotestosterone inhibited 3H-thymidine uptake of androgen receptor-positive HS15 and NM26, but not that of the receptor-negative WM266-4. The growth inhibition by each hormone was counteracted by the respective hormone receptor antagonist. The combination of more than two hormones neither gave additive nor synergistic growth inhibition. The growth inhibition by each sex hormone was counteracted by interleukin-8 but not by the other growth factors. Each sex hormone reduced the constitutive interleukin-8 secretion and mRNA levels in the respective receptor-positive melanoma but not in the receptor-negative melanoma. Transient transfection showed that each sex hormone inhibited the constitutive chloramphenicol acetyltransferase expression driven by interleukin-8 promoter in the respective receptor-positive melanoma but not in the receptor-negative melanoma. Transfection with a series of 5'-deleted interleukin-8 promoter/chloramphenicol acetyltransferase reporter constructs demonstrated that the sequences between -98 and -63 bp on interleukin-8 promoter may be involved in the transcriptional repression. These data suggest that 17beta-estradiol, progesterone, and dihydrotestosterone suppress the growth of melanoma by inhibiting interleukin-8 production in a receptor-dependent manner.

The relationship between tyrosinase activity and skin color in human foreskins

Tyrosinase activity was assayed in black and white human foreskin samples by measuring both the hydroxylation of tyrosine to dopa (tyrosine hydroxylase activity) and the conversion of [14C]tyrosine to [14C]melanin (melanin synthesis assay). Enzyme activity was found both in the particulate (75%) and soluble (25%) fractions of the cell. Membrane-bound tyrosinase was readily solubilized by either zwitter-ionic or nonionic detergents. The anionic detergent, sodium cholate, inhibited enzyme activity. Tyrosinase activity in black foreskin homogenates averaged almost three times that in white skin samples (33.8 pmols 3H2O/h/mg skin in black and 12.71 pmoles 3H2O/h/mg skin in white skin), although considerable overlap in activities existed among the two groups. Tyrosinase activities measured with two separate assays, tyrosine hydroxylase and [14C]melanin assays, were similar, suggesting that tyrosine hydroxylase activity is tightly coupled to melanin synthesis. Tyrosinase activity determined by either assay method generally correlated with skin melanin content. Kinetic analysis of tyrosinase from black and white foreskin revealed a Km for tyrosine of 2.5 X 10(-4) M in both skin types. Immunotitration experiments suggested that the difference in tyrosinase activities between white and black skin may be due, not only to different amounts of enzyme present in the melanocytes, but also possibly to differences in the catalytic activities of the enzyme found in melanocytes of black and white skin.

Human melanoma cells: functional modulation by calciotropic hormones

Four human melanoma cell lines were examined for their responsiveness to the hormones 1,25-dihydroxyvitamin D3 (1,25[OH]2D3), calcitonin, and parathyroid hormone (1-34). Cells from each of the 4 lines contained high affinity binding sites for 1,25(OH)2D3. At high cell densities, binding of 1,25(OH)2D3 was diminished due to a decrease in receptor number with no apparent change in affinity. Preincubation with 1,25(OH)2D3 (10(-10) to 10(-8) M) increased tyrosinase activity 1.3- to 3.2-fold and 25-hydroxyvitamin D3-24-hydroxylase activity 1.4- to 10-fold. Human calcitonin (0.82 to 82.5 ng/well) raised the intracellular concentration of cyclic adenosine monophosphate 1.4- to 9.4-fold. Tyrosinase activity increased in response to calcitonin in 2 of the cell lines, decreased in the third, and showed no change in the fourth. Human parathyroid hormone (1-34) in concentrations of 1 to 10 ng/ml produced no significant changes in cyclic adenosine monophosphate accumulation, cell numbers, or tyrosinase activity in any of the cell lines. This study indicates that the phenotype of human melanoma cells can be modulated by the calciotropic hormones 1,25(OH)2D3 and calcitonin.

Inhibition of clonogenic growth of melanoma cells by combination of melanocyte stimulating hormone and theophylline

The combination of MSH and theophylline is synergistic in inhibiting the growth as well as stimulating the differentiation of pigmented melanoma cells. In order to determine if a permanent alteration in the proliferative potential of these cells was achieved, we examined the effect of MSH and theophylline alone and in combination upon the plating efficiency and tumorigenicity of S-91 Cloudman melanoma cells. Following treatment with the combination of MSH and theophylline, the cells became deeply pigmented and had their colony forming ability reduced to 28% of control. Neither MSH or theophylline alone, although effective in reducing the growth rate of the cells, caused a significant reduction in clonogenic growth. When cells were pretreated with MSH and theophylline alone or in combination and reinjected into mice, the combination of MSH and theophylline caused a significant reduction in percentage of animals developing tumor (reduced to 14% of control). Cells treated with either MSH or theophylline alone were similar in their tumorigenic potential to control cells. These effects were selective since the nonmelanocytic control cells, mouse fibroblast L929 and Chinese hamster ovary when treated similarly did not exhibit any alteration in their clonogenic potential. The treatment of responsive cells with the combination of MSH and theophylline is capable of causing permanent decrease in the proliferative potential of murine melanoma cells and may have relevance to the treatment of this disease in man.

Effect of ACTH and corticosterone on melanogenesis and cyclic nucleotide levels in the B-16 melanoma

The acute in vitro action of ACTH and corticosterone individually and in combination were determined in the B-16 melanoma grown in vivo. ACTH elevated levels 10-fold while tyrosinase activity generally was depressed. Corticosterone depressed cAMP levels and tyrosinase activity. ACTH in the presence of corticosterone produced a coincident peak in tyrosinase activity and cAMP levels followed by a depression of enzymatic activity. The results demonstrate that cAMP is not the sole modulator of tyrosinase activity and that ACTH, corticosterone and cAMP interact in the regulation of B-16 melanoma tyrosinase activity.

Interaction of ACTH, corticosterone and cyclic nucleotides in Harding-Passey melanoma melanogenesis

The acute in vitro action of adrenocorticotropin (ACTH) and corticosterone alone and in combination were determined in the Harding-Passey (HP) melanoma grown in vivo. Hormone treated melanoma dice (5--240 min) were analyzed for tyrosinase activity, cyclic AMP (cAMP) and cyclic GMP (cGMP). ACTH elevated cAMP and cGMP levels 20- and 13-fold, respectively, in the HP melanoma. However, these large increases in cyclic nucleotide levels were accompanied by only a 49% increase in tyrosinase activity. Corticosterone elicited a similar response. ACTH plus corticosterone produced an early cAMP and cGMP peak followed by depression. ACTH plus corticosterone stimulated tyrosinase activity coincident with the early cyclic nucleotide peak followed by a drop in tyrosinase activity which was subsequently elevated. The results indicate that neither cAMP nor cGMP are the sole modulators of tyrosinase activity and suggest the interaction of ACTH, corticosterone and cyclic nucleotides in the regulation of melanoma tyrosinase activity.

Melanin in the rat brain

Melanin was measured in various parts of the rat brain by a spectrophotofluorometric assay. This method could detect natural, Sepia melanin as well as melanin synthesized from L-DOPA. Contrary to published expectations of other investigators, measurable amounts of melanin were found in the brain of albino as well as pigmented rats. The highest concentrations of melanin occurred in the pons-medulla and midbrain, but all regions within the blood-brain barrier contained greater concentrations than samples from many other tissues in the body. No significant change in the melanin content was found after various endocrine manipulations such as removal of the pituitary, pineal, adrenals, thyroid, testes, or ovaries, exposure to constant illumination or darkness, and daily injection for 5 weeks of alpha-MSH, Pro-Leu-Gly-NH2 (MIF-I) or melatonin. As expected, retinal tissue from black-hooded rats contained extremely high levels of melanin whereas that from albino rats contained no melanin. It is thought that the presence of melanin in the brain of albino and pigmented rats may have a function which is still unknown.