cAMP‐dependent activation of protein kinase A as a therapeutic target of skin hyperpigmentation by diphenylmethylene hydrazinecarbothioamide

Abstract

BACKGROUND AND PURPOSEcAMP as a second messenger stimulates expression of microphthalmia-associated transcription factor (MITF) or the tyrosinase gene in UVB-induced skin pigmentation. Diphenylmethylene hydrazinecarbothioamide (QNT 3-80) inhibits α-melanocytestimulating hormone (α-MSH)-induced melanin production in B16 murine melanoma cells but its molecular basis remains to be defined. Here, we investigated the mechanism underlying the amelioration of skin hyperpigmentation by QNT 3-80. EXPERIMENTAL APPROACHWe used melanocyte cultures with raised levels of cAMP and UVB-irradiated dorsal skin of guinea pigs for pigmentation assays. Immunoprecipitation, kemptide phosphorylation, fluorescence analysis and docking simulation were applied to elucidate a molecular mechanism of QNT 3-80. KEY RESULTSQNT 3-80 inhibited melanin production in melanocyte cultures with elevated levels of cAMP, including those from human foreskin. This compound also ameliorated hyperpigmentation in vivo in UVB-irradiated dorsal skin of guinea pigs. As a mechanism, QNT 3-80 directly antagonized cAMP binding to the regulatory subunit of PKA, nullified the dissociation and activation of inactive PKA holoenzyme in melanocytes and fitted into the cAMP-binding site on the crystal structure of human PKA under the most energetically favourable simulation. QNT 3-80 consequently inhibited cAMP-or UVB-induced phosphorylation (activation) of cAMP-responsive element-binding protein in vitro and in vivo, thus down-regulating expression of genes for MITF or tyrosinase in the melanogenic process. CONCLUSIONS AND IMPLICATIONSOur data suggested that QNT 3-80 could contribute significantly to the treatment of skin disorders with hyperpigmented patches with the cAMP-binding site of PKA as its molecular target.

Functional characterization of the extranasal OR2A4/7 expressed in human melanocytes

“…Melanogenesis can be induced by several complex processes via the PKC‐β, MAPK, cGMP or cAMP pathways . For example, under UV irradiation, the paracrine factor α‐MSH binds to the membrane‐bound melanocortin MC1 receptor of melanocytes, initiating a cAMP/PKA‐dependent pathway leading to enhanced expression of MITF and melanogenic enzyme tyrosinase . We prove that exposure to CHS significantly encourages cell dendricity and melanogenesis of normal human epidermal melanocytes.…”

“…In the skin, these enormous tasks are accomplished, inter alia , by the auto‐ and paracrine communication between melanocytes and keratinocytes. Melanocyte differentiation or dendricity is hypothesized to be a crucial morphological hallmark that enables the melanin transfer to keratinocytes . Melanogenesis can be induced by several complex processes via the PKC‐β, MAPK, cGMP or cAMP pathways .…”

“…Cutaneous melanogenesis is widely known to occur during sun‐induced skin tanning, thereby counteracting the photocarcinogenic effects of UV irradiation, but also constitutes pathological hyperpigmentation that emerges from melanocyte`s activity as sensory and regulatory cells . Nonetheless, melanin synthesis can also be induced in cultured human melanocytes by activating nonolfactory receptors following the exposure to distinct molecular compounds, for example α‐melanocyte‐stimulating hormone (α‐MSH) .…”

“…Nonetheless, melanin synthesis can also be induced in cultured human melanocytes by activating nonolfactory receptors following the exposure to distinct molecular compounds, for example α‐melanocyte‐stimulating hormone (α‐MSH) . Evidently, signal transduction initiated by α‐MSH relies on a cAMP/PKA‐dependent pathway leading to tyrosinase activity, a pigment biosynthetic enzyme for trafficking melanin to melanosomes . These findings imply a high degree of complexity in the regulation of melanogenesis.…”

Potential Use of Seaweed Bioactive Compounds in Skincare—A Review

“…The KIT receptor activates the cAMP pathway and MC1R activates both cAMP and ERK pathway which further phosphorylates the MITF. This leads to the expression of tyrosinase-related enzymes which further mediates the production of melanin [22][23][24][25][26]. The skin under UV generates the reactive oxygen species (ROS) that activate the α-MSH and MC1R and enhances the production of tyrosinase that leads to the excess generation of melanin [27,28].…”