Abstract
Melanocytes, which produce the pigment melanin, are known to be closely regulated by neighboring keratinocytes. However, how keratinocytes regulate melanin production is unclear. Here we report that melanin production in melanoma cells (B16F10 and MNT-1) was increased markedly on a keratinocyte-derived extracellular matrix compared with a melanoma cell-derived extracellular matrix. siRNA-mediated reduction of keratinocyte-derived laminin-332 expression decreased melanin synthesis in melanoma cells, and laminin-332, but not fibronectin, enhanced melanin content and α-melanocyte-stimulating hormone-regulated melanin production in melanoma cells. Similar effects were observed in human melanocytes. Interestingly, however, laminin-332 did not affect the expression or activity of tyrosinase. Instead, laminin-332 promoted the uptake of extracellular tyrosine and, subsequently, increased intracellular levels of tyrosine in both melanocytes and melanoma cells. Taken together, these data strongly suggest that keratinocyte-derived laminin-332 contributes to melanin production by regulating tyrosine uptake.
Highlights
Laminin-332 derived from keratinocytes plays a critical role in adhesion-related cell functions in melanocytes
Keratinocyte-derived Laminin-332 Promotes Melanin Synthesis of Melanoma Cells—To investigate the effect of keratinocyte-derived extracellular matrix (ECM) on melanin synthesis, melanoma cells were detached and replated on ECM derived from HaCaT keratinocytes (HaCaT ECM) or rat embryonic fibroblasts (REF ECM), and the amount of melanin was compared with that of cells on melanoma ECM
Increased intracellular tyrosine levels correlated with enhanced melanin synthesis (Fig. 4A), keratinocyte-derived ECM and laminin-332 caused an increase of intracellular tyrosine levels (Fig. 4, B and C), and laminin-332 enhanced the uptake of extracellular tyrosine (Fig. 4D)
Summary
Laminin-332 derived from keratinocytes plays a critical role in adhesion-related cell functions in melanocytes. Results: Keratinocyte-derived laminin-332 promotes the uptake of extracellular tyrosine and subsequent melanin synthesis in melanoma cells and melanocytes. Laminin-332 promoted the uptake of extracellular tyrosine and, subsequently, increased intracellular levels of tyrosine in both melanocytes and melanoma cells. Taken together, these data strongly suggest that keratinocyte-derived laminin-332 contributes to melanin production by regulating tyrosine uptake. Keratinocytes are actively involved in the regulation of melanin synthesis They produce various regulatory soluble factors such as ␣-melanocyte-stimulating hormone (␣-MSH), adrenocorticotropic hormone, stem cell factor, and endothelin 1 [8]. They produce various regulatory soluble factors such as ␣-melanocyte-stimulating hormone (␣-MSH), adrenocorticotropic hormone, stem cell factor, and endothelin 1 [8]. ␣-MSH, for instance, binds to melanocortin receptor 1 (MC1R) [9] and increases the cAMP level by stimulating adenylyl cyclase. cAMP subsequently activates PKA and cAMP-responsive element-binding protein. cAMP-responsive element-binding protein works as a transcription factor for microphthalmia-related transcription factor (MITF), a critical regulator of tyrosinase, TRP-1, and TRP-2 [10, 11]
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