The invention provides a method of modulating Wnt signalling comprising modulating Trabid activity. Preferably modulating Trabid activity comprises inhibiting; Trabid activity. The invention also provides a method of reducing TCF transcription, said method comprising reducing Trabid activity. A method for identifying a-modulator of Trabid said method comprising; providing a Trabid substrate comprising a detectable moiety coupled to a tag moiety by ubiquitin; immobilizing first and second portions of said substrate; adding a candidate modulator to the first said portion; contacting first and second portions with Trabid; incubating to allow Trabid action, assaying cleavage of ubiquitin by separation of tag from detectable moiety, wherein separation of an amount of detectable moiety from said first portion which is different from the amount of detectable moiety separated from said second portion identifies said candidate as a modulator of Trabid. The invention provides uses of Trabid and of Trabid inhibitors as-medicaments.