Objective: To study the effect of phytoestrogenic components of betulin and the addition of receptor blocker (ICI182780) on melanin synthesis and its mechanism on A375 cells.Method: 1 μmol·L-1 betulin was applied to A375 melanocytes and then the experimental cells were divided into blank group (DMEM complete culture fluid)

estradiol group (1×10-3 μmol·L-1)

betulin group (1 μmol·L-1)

and betulin + ICI182780 group (1 μmol·L-1 + 1 μmol·L-1). Melanin content was determined by NaOH lysis; Western blot

and real-time fluorescent quantitative polymerase chain reaction(Real-time PCR) were used to determine the protein content and mRNA expression of key protein kinase mitogen activated protein kinase(MAPK) p38 in estrogen receptor(ER)/mitogen activated protein kinase(MAPK) pathway

c-Jun N-terminal kinase(JNK)

extracellular signal-regulated kinase 2(ERK2) and micrometamorphic-related transcription factor(MITF)

dopa oxidation assay for tyrosinase (TYR)

tyrosinase-related protein-1(TRP-1)

and tyrosinase-related protein-2(TRP-2).Result: As compared with the blank group

betulin group and betulin + ICI182780 group had significant inhibition on melanin synthesis in A375 cells (P<0.01); 1 μmol·L-1 betulin had different inhibitory effects on expression of the above proteins in A375 cells (P<0.05

P<0.01)

as well as on ERK2

MITF

and TRP-1(P<0.05

P<0.01) mRNA expression (P<0.05

P<0.01). As compared with the betulin group

ICI182780 can reverse the inhibitory effect of betulin on melanin synthesis of A375 cells(P<0.01); ICI182780 can reverse the inhibitory effect of betulin on the above protein expression in A375 cells as well as mRNA expression of ERK2

MITF

and TRP-1(P<0.05

P<0.01).Conclusion: Betulin can down-regulate the expression levels of MITF

TYR

TRP-1 and TRP-2 proteins through ER-MAPK signaling pathway

thus reducing melanin synthesis.