Abstract 2242: Correlation between the overexpression of the metastasis-inducer transcription factors Snail and Yin Yang 1 and BRAF mutations in a large panel of melanoma cell lines

Abstract

Abstract Over 90% of melanoma express oncogenic mutations in BRAF at the V600E position. Most of the transforming activity of the BRAF V600E is thought to result through the activation of the mitogen-activated protein kinase (MAPK) pathway. The discovery of BRAF mutations has alluded to targeted therapy. The role of BRAF mutations in the regulation of oncogenes involved in metastasis has not been fully explored. The metastasis-inducer gene product Snail regulates the EMT phenotype in the metastasis cascade. Snail is under the transcription regulation of NF-κB and is constitutively activated in tumors. Noteworthy, Snail negatively regulates the expression of the metastasis suppressor gene product, RKIP. Likewise, Yin-Yang 1 (YY1) regulates Snail and is downstream of NF-κB. The regulation of the YY1, Snail and RKIP expressions by BRAF mutations has been investigated. We hypothesized that the expression levels of YY1 will be correlated with the expression levels of Snail and inversely correlated with the expression levels of RKIP in melanoma and that the BRAF mutations may enhance these relationships due to its activation of the NF-κB pathway. In this study, we have analyzed a panel of 32 melanoma cell lines with BRAF mutations using a tissue microarray technology. The gene products YY1, Snail and RKIP were examined and, in addition, the inactive phosphorylated form of RKIP was also evaluated. Protein expressions were assessed by immunohistochemistry and were then analyzed by blinded observers under light microscopy. The mean intensities for the expression of each gene product were determined by using the software Image-ProPlus 6.3. The data revealed the following: (1) There was a correlation between the levels of YY1 and Snail expressions in the cell lines and (2) There was an inverse correlation between the levels of RKIP and both Snail and YY1 levels. The relationship between active RKIP and inactive phospho-RKIP demonstrated that the majority was in the inactivated phosphorylated form. These findings demonstrate that melanoma with BRAF mutations, which activate the NF-κB pathway, resulted in the upregulation of the metastasis inducer gene products YY1 and Snail and, consequently, inhibition and/or inactivation of the metastasis-suppressor RKIP. Thus, these studies revealed that BRAF mutations regulate the EMT metastatic phenotype through the activation of NF-κB, Snail, and YY1, while inhibiting and/or inhibiting the metastasis suppressor RKIP. We suggest that Snail, YY1, and RKIP are potential targets for therapeutic intervention in the inhibition of metastasis. In addition, we have shown that these same gene products regulate tumor cell resistance to cytotoxic therapeutics and, thereby, targeted therapeutic interventions may exert dual roles in the inhibition of metastasis and reversal of resistance. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2242.