Be up for depravity (4)
I believe the answer is:
evil
'depravity' is the definition.
(thesaurus)
'be up' is the wordplay.
'be' becomes 'live' (living is a kind of being).
'up' is a reversal indicator (in down clue: letters go upwards).
'live' reversed gives 'EVIL'.
'for' acts as a link.
(Other definitions for evil that I've seen before include "Vile (anag) -- really bad" , "Profoundly immoral" , "Moral depravity" , "Depraved" , "Extremely unpleasant" .)