Assuntos
Amidas/farmacologia , Melaninas/agonistas , Melanócitos/efeitos dos fármacos , Melanoma/prevenção & controle , Fenetilaminas/farmacologia , Quinolinas/farmacologia , Protetores Solares/farmacologia , Amidas/química , Amidas/isolamento & purificação , Animais , Linhagem Celular , Avaliação Pré-Clínica de Medicamentos , Humanos , Melaninas/biossíntese , Melanócitos/enzimologia , Melanoma/enzimologia , Camundongos , Monofenol Mono-Oxigenase/metabolismo , Oxirredução , Fenetilaminas/química , Fenetilaminas/isolamento & purificação , Quinolinas/química , Quinolinas/isolamento & purificação , Bibliotecas de Moléculas Pequenas , Relação Estrutura-Atividade , Protetores Solares/química , Protetores Solares/isolamento & purificação , Tirosina/metabolismo , Raios Ultravioleta/efeitos adversosRESUMO
Melanocytes photoprotect the skin through transfer of melanin-containing melanosomes to keratinocytes. Factors that increase melanocyte dendricity increase melanosome transfer, and are important for prevention of skin cancer. Secretory phospholipase-A2 type X (sPLA2-X) is released by epidermal keratinocytes and we have shown that lysophosphatidylcholine (LPC), the main lysophospholipid released in response to sPLA2-X activity, stimulates melanocyte dendricity. LPC activates protein kinase C (PKC) and increases cAMP in other cells. Treatment of melanocytes with sPLA2-X or LPC induced phosphorylation of the zeta isoform of PKC, and inhibition of protein kinase C zeta (PKCzeta) activity abrogated LPC-dependent dendricity. We have shown previously that the guanosine triphosphate-binding proteins Rac and Rho link hormone signaling and dendricity in melanocytes. Treatment of melanocytes with LPC induced rapid activation of Rac that peaked at 30 minutes; Rho was also activated, but peaked earlier and declined faster. Through the use of constitutively active mutants of Rac, we show that PKCzeta activation is downstream of Rac. We conclude that the primary signaling pathway for LPC-dependent dendrite formation in human melanocytes involves the activation of PKCzeta and that PKCzeta phosphorylation is Rac dependent. Downstream mediators of LPC-dependent dendricity include Rac and Rho.
Assuntos
Células Dendríticas/citologia , Ativação Enzimática , Lisofosfatidilcolinas/metabolismo , Melanócitos/enzimologia , Melanócitos/metabolismo , Proteína Quinase C/metabolismo , Proteínas rac de Ligação ao GTP/metabolismo , Animais , Humanos , Lisofosfolipídeos/metabolismo , Melanócitos/citologia , Camundongos , Fosfolipases A/metabolismo , Fosfolipases A2 , Fosforilação , Isoformas de Proteínas , Proteínas Recombinantes/química , Transdução de SinaisRESUMO
Photoprotection of the skin is provided by melanocytes, neural crest derived cells that synthesize melanin in specialized organelles that are transferred to keratinocytes. Secretory phospholipases comprise a large family of Ca2+-dependent enzymes that liberate arachidonic acid (AA), a precursor of prostaglandins, as well as lysophospholipids. The predominant secretory phospholipase expressed by keratinocytes is group X secretory phospholipase A2 (sPLA2), which liberates large amounts of AA and the lysophospholipid lysophosphatidylcholine (LPC), from membrane preparations. Recent work by our laboratory has shown that melanocytes express receptors for prostaglandins that upon activation stimulate melanocyte dendricity and activity of tyrosinase, a key enzyme in melanin biosynthesis. In the present study, we have treated human melanocytes with recombinant sPLA2-X and show that low levels of sPLA2-X stimulate both tyrosinase activity and melanocyte dendricity. We found that the effects of sPLA2-X are mediated predominantly by LPC, not AA, and we have demonstrated expression of the phospholipase A2 receptor and two G-protein-coupled receptors for LPC (G2A and GPR119) in human melanocytes. Because secretory phospholipases are released during inflammation and are regulated by UV irradiation, our data suggest an important role for sPLA2-X in cutaneous pigmentation through the release of LPC.
