Celebrity blows whistle, turns (4)
I believe the answer is:
star
'celebrity' is the definition.
(I've seen this before)
'blows whistle turns' is the wordplay.
'blows whistle' becomes 'rats'.
'turns' says the letters should be written in reverse.
'rats' written backwards gives 'STAR'.
(Other definitions for star that I've seen before include "Public figure" , "Astronomer - dreamer" , "It twinkles" , "Twinkling celestial body" , "Eg, Betelgeuse" .)