Jan 13, 1998

Activation of the cyclic AMP pathway by alpha-melanotropin mediates the response of human melanocytes to ultraviolet B radiation

Cancer Research
S ImZ Abdel-Malek

Abstract

A hallmark of sun exposure is increased melanin synthesis by cutaneous melanocytes which protects against photodamage and photocarcinogenesis. Irradiation of human keratinocytes or melanocytes with ultraviolet (UV) rays stimulates the synthesis and release of alpha-melanotropin (alpha-MSH) and adrenocorticotropic hormone (ACTH), which induce cyclic AMP (cAMP) formation and increase the proliferation and melanogenesis of human melanocytes. We report that stimulation of cAMP formation is obligatory for the melanogenic response of cultured normal human melanocytes to UVB radiation. In the absence of cAMP inducers, UVB radiation inhibited, rather than stimulated, melanogenesis. UVB radiation (28 mJ/cm2) arrested melanocytes in the G1 phase of the cell cycle, and concomitant treatment with 0.1 microM alpha-MSH enhanced their proliferation but did not increase the surviving fraction. Irradiation with UVB, with or without alpha-MSH, caused prolonged expression of p53 and p21(waf-1, cip-1), maintained pRB in a hypophosphorylated state, and reduced the expression of Bcl2. However, alpha-MSH allowed UVB-irradiated melanocytes to enter S phase, suggesting that alpha-MSH acts as a mitogen rather than a survival factor, and that overexpress...Continue Reading

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Mentioned in this Paper

Melanocyte
Tyrosinase related protein-1
ACTH (1-13)NH2
Oncoprotein p21
Phenoloxidase B
Oxidase
TYRP1 protein, human
Cyclins
Protein p53
Cyclic AMP, (R)-Isomer

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