An Activating Mutation in ERK Causes Hyperplastic Tumors in a<i>scribble</i>Mutant Tissue in<i>Drosophila</i>

Abstract

Receptor tyrosine kinase signaling plays prominent roles in tumorigenesis, and activating oncogenic point mutations in the core pathway components Ras, Raf, or MEK are prevalent in many types of cancer. Intriguingly, however, analogous oncogenic mutations in the downstream effector kinase ERK have not been described or validated <i>in vivo</i> To determine if a point mutation could render ERK intrinsically active and oncogenic, we have assayed in <i>Drosophila</i> the effects of a mutation that confers constitutive activity upon a yeast ERK ortholog and has also been identified in a few human tumors. Our analyses indicate that a fly ERK ortholog harboring this mutation alone (Rolled^R80S), and more so in conjunction with the known <i>sevenmaker</i> mutation (Rolled^R80S+D334N), suppresses multiple phenotypes caused by loss of Ras-Raf-MEK pathway activity, consistent with an intrinsic activity that is independent of upstream signaling. Moreover, expression of Rolled^R80S and Rolled^R80S+D334N induces tissue overgrowth in an established <i>Drosophila</i> cancer model. Our findings thus demonstrate that activating mutations can bestow ERK with pro-proliferative, tumorigenic capabilities and suggest that <i>Drosophila</i> represents an effective experimental system for determining the oncogenicity of ERK mutants and their response to therapy.