After engaging writers, publisher says what it thinks (5,2)
I believe the answer is:
opens up
'says what it thinks' is the definition.
(to open up is to speak honestly)
'after engaging writers publisher' is the wordplay.
'after engaging' is an insertion indicator.
'writers' becomes 'pens' (writing implements).
'publisher' becomes 'OUP' (abbreviation for Oxford University Press).
'pens' inserted inside 'oup' is 'OPENS UP'.
(Other definitions for opens up that I've seen before include "starts shooting" , "talks without inhibitions" , "talks freely" , "Becomes more communicative" .)