Turn up distrustful and self-assertive (5)
I believe the answer is:
pushy
'self-assertive' is the definition.
(thesaurus)
'turn up distrustful' is the wordplay.
'turn' shows that the letters should be reversed in order.
'distrustful' becomes 'shy' ('shy' can be a synonym of 'distrustful').
'up' reversed gives 'pu'.
'pu'+'shy'='PUSHY'
'and' is the link.
(Other definitions for pushy that I've seen before include "Socially aggressive" , "Overly assertive" , "Aggressive; overbearing" , "Informally aggressive, not patient" , "Forward" .)