ERK/p90RSK/14-3-3 signalling has an impact on expression of PEA3 Ets transcription factors via the transcriptional repressor capicua

Compounds that inhibit signalling upstream of ERK (extracellular-signal-regulated kinase) are promising anticancer therapies, motivating research to define how this pathway promotes cancers. In the present study, we show that human capicua represses mRNA expression for PEA3 (polyoma enhancer activator 3) Ets transcription factors ETV1, ETV4 and ETV5 (ETV is Ets translocation variant), and this repression is relieved by multisite controls of capicua by ERK, p90(RSK) (p90 ribosomal S6 kinase) and 14-3-3 proteins. Specifically, 14-3-3 binds to p90(RSK)-phosphorylated Ser(173) of capicua thereby modulating DNA binding to its HMG (high-mobility group) box, whereas ERK phosphorylations prevent binding of a C-terminal NLS (nuclear localization sequence) to importin alpha 4 (KPNA3). ETV1. ETV4 and ETV5 mRNA levels in melanoma cells are elevated by siRNA (small interfering RNA) knockdown of capicua, and decreased by inhibiting ERK and/or expressing a form of capicua that cannot bind to 14-3-3 proteins. Capicua knockdown also enhances cell migration. The findings of the present study give further mechanistic insights into why ETV1 is highly expressed in certain cancers, indicate that loss of capicua can desensitize cells to the effects of ERK pathway inhibitors, and highlight interconnections among growth factor signalling, spinocerebellar ataxias and cancers.