Abstract
The extracellular-signal-regulated kinases ERK1 and ERK2 (hereafter ERK1/2) represent the foremost mitogenic pathway in mammalian cells, and their dysregulation drives tumorigenesis and confers therapeutic resistance. ERK1/2 are known to be activated by MAPK/ERK kinase (MEK)-mediated phosphorylation. Here, we show that ERK1/2 are also modified by lysine-63 (K63)-linked polyubiquitin chains. We identify the tripartite motif-containing protein TRIM15 as a ubiquitin ligase and the tumour suppressor CYLD as a deubiquitinase of ERK1/2. TRIM15 and CYLD regulate ERK ubiquitination at defined lysine residues through mutually exclusive interactions as well as opposing activities. K63-linked polyubiquitination enhances ERK interaction with and activation by MEK. Downregulation of TRIM15 inhibits the growth of both drug-responsive and drug-resistant melanomas. Moreover, high TRIM15 expression and low CYLD expression are associated with poor prognosis of patients with melanoma. These findings define a role of K63-linked polyubiquitination in the ERK signalling pathway and suggest a potential target for cancer therapy.