Activation of c-jun N-terminal kinase is associated with cell proliferation and shorter relapse-free period in superficial spreading malignant melanoma

Signaling pathways regulating cell proliferation and survival have become attractive targets for anticancer strategies. In the present study, we analyzed by immunohistochemistry, a panel of benign nevi, superficial spreading and nodular primary melanomas and metastases for expression of activated p38/mitogen-activated protein kinase (p-p38) and c-jun N-terminal kinase (JNK) (p-JNK) and correlated the findings with known prognostic variables. Twenty-five and 35% of the primaries and 9 and 25% of the metastases expressed variable levels of p-p38 and p-JNK, respectively. In benign nevi, 73.5% expressed p-JNK and 7% expressed p-p38. For patients with superficial spreading melanomas, high level of cytoplasmic p-JNK was associated with thicker tumors (P = 0.017) and shorter disease- free survival (P = 0.003) as well as with markers of cell proliferation (cyclin A (P = 0.017) and p21 (P = 0.021)). In nodular melanomas, nuclear p-p38 was associated with Ki-67 (P = 0.012), but neither cytoplasmic nor nuclear localized p-p38 was associated with disease outcome. Of note, in superficial spreading melanomas, a positive correlation between cytoplasmic p- JNK and cytoplasmic p-extracellular signal-regulated kinase ERK1/2 (P = 0.005) and p-p38 (P = 0.003) was observed. Likewise, p-p38 in cytoplasm was positively associated with cytoplasmic p-ERK1/2 (P < 0.0005) and p-Akt (P = 0.047). In contrast, except for a positive correlation between nuclear p-p38 and membranous p-TrkA (P = 0.02), no correlation between the activation status of the different signaling pathways was observed in nodular melanomas. In conclusion, our results suggest that in benign nevi activated JNK may have a role in restricting uncontrolled cell proliferation or survival. However, during tumor progression, activation of JNK is associated with cell proliferation and shorter relapse-free period for patients with superficial spreading melanomas, suggesting that the JNK activation status could be a marker for clinical outcome in at least a subgroup of malignant melanoma. In contrast, activation of p38 seems to play a less important role in development and progression of malignant melanomas.