Activation of the MAPK pathway is a common event in uveal melanomas although it rarely occurs through mutation of BRAF or RAS

Abstract

In contrast to cutaneous melanoma, there is no evidence that BRAF mutations are involved in the activation of the mitogen-activated protein kinase (MAPK) pathway in uveal melanoma, although there is increasing evidence that this pathway is activated frequently in the latter tumours. In this study, we performed mutation analysis of the RAS and BRAF genes in a panel of 11 uveal melanoma cell lines and 19 primary uveal melanoma tumours. In addition, Western blot and immunohistochemical analyses were performed on downstream members of the MAPK pathway in order to assess the contribution of each of these components. No mutations were found in any of the three RAS gene family members and only one cell line carried a BRAF mutation (V599E). Despite this, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK), ERK and ELK were constitutively activated in all samples. These data suggest that activation of the MAPK pathway is commonly involved in the development of uveal melanoma, but occurs through a mechanism different to that of cutaneous melanoma.

Figure 1

Expression levels of members of the MAPK pathway downstream of RAS and BRAF in 11 uveal melanoma cell lines. Actin levels were assessed as a loading control.

Figure 2

ERK1/2 and phospho-ERK1/2 expression in uveal melanoma cell lines (Mel 202, Ocm 1, Mel 285, Mel 290) cultured with (+) and without (−) serum (24 h). A similar lack of effect of serum on influencing the level of phospho-ERK1/2 was seen for each of the other uveal melanoma cell lines (data not shown).