Justa-Schuch, DanielaSilva-Garcia, MariaPilla, EstherEngelke, MichaelKilisch, MarkusLenz, ChristofMöller, UlrikeNakamura, FumihikoUrlaub, HenningGeiss-Friedlander, Ruth2016-11-182016Justa-Schuch, Daniela, Maria Silva-Garcia, Esther Pilla, Michael Engelke, Markus Kilisch, Christof Lenz, Ulrike Möller, Fumihiko Nakamura, Henning Urlaub, and Ruth Geiss-Friedlander. 2016. “DPP9 is a novel component of the N-end rule pathway targeting the tyrosine kinase Syk.” eLife 5 (1): e16370. doi:10.7554/eLife.16370. http://dx.doi.org/10.7554/eLife.16370.2050-084Xhttp://nrs.harvard.edu/urn-3:HUL.InstRepos:29407611The aminopeptidase DPP9 removes dipeptides from N-termini of substrates having a proline or alanine in second position. Although linked to several pathways including cell survival and metabolism, the molecular mechanisms underlying these outcomes are poorly understood. We identified a novel interaction of DPP9 with Filamin A, which recruits DPP9 to Syk, a central kinase in B-cell signalling. Syk signalling can be terminated by degradation, requiring the ubiquitin E3 ligase Cbl. We show that DPP9 cleaves Syk to produce a neo N-terminus with serine in position 1. Pulse-chases combined with mutagenesis studies reveal that Ser1 strongly influences Syk stability. Furthermore, DPP9 silencing reduces Cbl interaction with Syk, suggesting that DPP9 processing is a prerequisite for Syk ubiquitination. Consistently, DPP9 inhibition stabilizes Syk, thereby modulating Syk signalling. Taken together, we demonstrate DPP9 as a negative regulator of Syk and conclude that DPP9 is a novel integral aminopeptidase of the N-end rule pathway. DOI: http://dx.doi.org/10.7554/eLife.16370.001en-USSykDPP9N-end ruleprotein half-lifeCblB cell signallingHumanJournal Article2016-11-1810.7554/eLife.16370