Abstract
Epigenetic mechanisms participate in melanoma development and progression. The effect of histone modifications and their catalysing enzymes over euchromatic promoter DNA methylation in melanoma remains unclear. This study investigated the potential association of p16(INK) (4A) promoter methylation with histone methyltransferase SETDB1 expression in Greek patients with sporadic melanoma and their correlation with clinicopathological characteristics. Promoter methylation was detected by methylation-specific PCR in 100 peripheral blood samples and 58 melanoma tissues from the same patients. Cell proliferation (Ki-67 index), p16(INK) (4A) and SETDB1 expression were evaluated by immunohistochemistry. High-frequency promoter methylation (25.86%) was observed in tissue samples and correlated with increased cell proliferation (P=0.0514). p16(INK) (4A) promoter methylation was higher in vertical growth-phase (60%) melanomas than in radial (40%, P=0.063) and those displaying epidermal involvement (P=0.046). Importantly, p16(INK) (4A) methylation correlated with increased melanoma thickness according to Breslow index (P=0.0495) and marginally with increased Clark level (I/II vs III/IV/V, P=0.070). Low (1-30%) p16(INK) (4A) expression was detected at the majority (19 of 54) of melanoma cases (35.19%), being marginally correlated with tumor lymphocytic infiltration (P=0.078). SETDB1 nuclear immunoreactivity was observed in 47 of 57 (82.46%) cases, whereas 27 of 57 (47.37%) showed cytoplasmic immunoexpression. Cytoplasmic SETDB1 expression correlated with higher frequency of p16(INK) (4A) methylation and p16(INK) (4A) expression (P=0.033, P=0.011, respectively). Increased nuclear SETDB1 levels were associated with higher mitotic count (0-5/mm(2) vs >5/mm(2) , P=0.0869), advanced Clark level (III-V, P=0.0380), epidermal involvement (P=0.0331) and the non-chronic sun exposure-associated melanoma type (P=0.0664). Our data demonstrate for the first time the association of histone methyltransferase SETDB1 with frequent methylation of the euchromatic p16(INK) (4A) promoter and several prognostic parameters in melanomas.
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