Genetic Origins of Melanoma: Mechanism of BRAF Gene Mutation

Melanoma Background

Melanoma in the early years was described as a benign mole that continued to grow and could be recognized by an irregular shape and discoloration of the mole (Sober et al., 1979). These cancer cells were well known for their ability to spread around the body quickly and avoid the therapeutic treatment, creating a dangerous situation (Li et al., 2001). When detected early, Melanoma could be removed successfully by a surgical procedure, but when metastasized, the cancer cells were much harder to kill, and treatment with chemotherapy and radiation were not much help, leading to a poor prognosis. (Sober et al., 1979; Irie et al., 2004). This led to copious amounts of research. Researchers linked that the first step in progression of Melanoma comes from a common melanocytic nevus, whose cells lost a checkpoint in the cell cycle and began to over proliferate (Clark et al., 1984; Carson et al., 2012). Inside these melanocytic nevi, over proliferation could be caused by a mutation in a proto-oncogene that activated the MAPK pathway, inhibited tumor suppressors, and allowed melanoma characterized cells to proliferate wildly (Florenes et at., 1998; Florenes et al., 1999; Kortylewski et al., 2001). Specifically, a high percentage of melanoma cases were linked to a mutation in the proto-oncogene BRAF (Colombino et al., 2012; Davies et al., 2002). Understanding this allowed scientist to tackle new ways of therapy. For example, immunotherapy and targeted therapy in melanoma cases were shown to be more successful than the previous therapies when studied and showed great room for more research (Deken et al., 2016; Moreno et al., 2015; Koya et al., 2012; Larkin et al., Long et al., 2014; Ribas et al., 2019; Robert et al., 2015) These findings struck a lot of interest in research that focused on the BRAF gene, its mutations, and its effects that lead to melanoma. By taking this knowledge about melanoma and emphasizing the focus on targeted therapies that will inhibit the effects caused by mutated BRAF in the MAPK pathway, the prognosis of Melanoma cancer will improve tremendously.

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BRAF Gene

Characterization of the gene: BRAF

Improving the prognosis of melanoma and future treatments all starts by understanding this important gene, as it plays a lead role in a lot of actions. This proto-oncogene which encodes for serine/threonine kinase activates the MAPK signaling pathway by signaling to MEK which then sends a signal cascade down to ERK 1 and 2 (Kyriakis et al., 1992; Wajapeyee et al., 2008). The MAPK pathway is an important priority in understanding cancer cell proliferation and cancer cell survival (Kyriakis et al., 1992). Understanding the roll of activated MAPK brings hope for future therapeutics for melanoma patients (Cohen et. al., 2002). BRAF is located on chromosome 7 and is often mutated (Stagni et al., 2018). Studies have shown that when there are gains at chromosome 7 in the BRAF gene, there are high correlations of mutant melanoma diagnosis (Greshock et al., 2009; Helias-Rodzewicz et al., 2015; Stagni et al. 2018) A gene mutation in BRAF is found around 50% of the time in melanoma cells, and when this happens there is continuous activation of the kinase that starts the cascade signaling in cell proliferation (Curtin et al., 2005; Davies et al., 2002; Long et al., 2011; Si et al., 2018). With such a specific mutation linked to melanoma, there is prestigious information to be known about the BRAF mutation.

Mutations within BRAF can lead to melanoma

BRAF is most commonly mutated at the 600th amino acid, in which the amino acid Valine is switched to Glutamic Acid, giving the cell the newly mutated BRAF V600E gene (Davies et. al., 2002; Can et al, 2018). This gene may also mutate from Valine to Lysine at the 600th amino acid, which is called BRAF V600K (Wan et al., 2004). These mutations are very different from each other in ways, but both lead to big changes. As a result, these differences are best demonstrated by evaluation cohorts of Melanoma patients. For example, the proportion of melanoma cases that have a mutation in BRAF are more likely to have the V600E mutation (73%-76% of population) compared to the V600K mutation (19%-24% of population), and the V600K was mostly found in older patients compared to the younger patients with the V600E mutant gene. (Menzies et al., 2012; Ardakani et al. 2017; Bucheit et al., 2013). The mutations are also different in correlation with the prognosis and tumor characteristics, as the V600K mutant is found within patients with a short survival until stage IV and the tumor found in the neck and head area, compared to the V600E mutant found in longer survival times and in the areas such as limbs and trunk (Bucheit et al., 2013). This amino acid shift in either way (Valine to Glutamic acid or Valine to Lysine) leads to continuous signaling in the MAPK pathway, allowing cells in the pathway to have advantages when it comes to survival and making way for them to over proliferate (Can et al., 2018). This MAPK pathway being activated is an early event in the progression of melanoma (Cohen et al., 2002). Understanding this has led to therapeutic inhibition of proteins in the MAPK pathway.

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