Uveal melanocytes express high constitutive levels of MMP-8 which can be upregulated by TNF-α via the MAPK pathway

Matrix metalloproteinase (MMP)-8 is the most potent MMP for degrading collagen type-1 and plays an important role in inflammatory reactions and tissue remolding processes. MMP-8 is expressed mainly by polymorphonuclear leukocytes and is not expressed constitutively by most non-leukocytes. We studied the constitutive and TNF-α-induced expression of MMP-8 in cultured human uveal melanocytes (UM) and the relevant signal pathways involved. Conditioned media and cells were collected from UM and other cell types. MMP-8 proteins and mRNA were measured using ELISA kit, western blot and real time RT-PCR, respectively. Phosphorylated p38 MAPK, ERK1/2, and JNK1/2 were measured by ELISA kit and western blot. Very high levels of MMP-8 proteins and mRNA were detected in the conditioned media and cell lysates in 11 UM cell lines and three uveal melanoma cell lines cultured without serum, but not in media and cell lysates from other ocular resident cells or 12 malignant cell lines from other tissues, with exception of cutaneous melanoma cells. TNF-α moderately increased MMP-8 mRNA and protein levels in a dose- and time-dependent manner, accompanied by a significant increase of phosphorylated JNK1/2 and ERK1/2 in cell lysates. ERK1/2 (U0126) and JNK1/2 (SP600125) inhibitors significantly blocked TNF-α-induced and constitutive expression of MMP-8 in UM. This is the first report on the expression and secretion of MMP-8 by UM and uveal melanoma cells. The data suggest that UM may play a role in the remolding process and pathogenesis of inflammatory-related diseases in the eye via secretion of MMP-8.