Resolving mechanisms of apoptosis in response to WNT3A in Melanoma

Abstract

Wnt/β-catenin and ERK/MAPK signaling regulate the balance of differentiation and proliferation in melanoma. Aberrant activation of ERK/MAPK signaling results from the BRAFV600E or NRASQ61X mutations in greater than 70% of primary melanoma samples. Previous data have shown that BRAF inhibition in combination with Wnt/β-catenin activation promotes robust melanoma apoptosis in a subset of melanomas. This finding raised the question of what factors predict sensitivity to apoptosis in response to WNT3A and how Wnt/β-catenin signaling is regulated in melanoma. My thesis research addresses this question by testing if Wnt/β-catenin signaling can promote apoptosis in BRAF and NRAS-mutant backgrounds, and it addresses how Wnt/β-catenin signaling is regulated in melanoma using combinatorial screening techniques. Here, I present evidence that combined ERK/MAPK pathway inhibition and Wnt/β-catenin activation leads to apoptosis in NRAS-mutant melanomas. Additional experiments demonstrate that the stability AXIN1 protein, a negative regulator of Wnt/β-catenin signaling, is required for resistance to apoptosis. Finally, I use high throughput screening to discover FAM129B as a novel positive regulator of Wnt/β-catenin signal transduction and the apoptotic response to WNT3A in melanoma. Collectively, these data expand the genetic contexts melanomas undergo apoptosis following WNT3A treatment and MEK inhibition, and further resolves Wnt/β-catenin pathway regulation in melanoma. The findings presented here highlight the importance of AXIN1 depletion across multiple mutational backgrounds, and identify numerous putative regulators of Wnt/β-catenin signaling which may ultimately regulate apoptosis in melanoma.