Profane sentence newspaperman holds up (6)
I believe the answer is:
defile
'profane' is the definition.
(thesaurus)
'sentence newspaperman holds up' is the wordplay.
'sentence' becomes 'life' (I have seen 'Longest sentence' mean 'life' so perhaps 'sentence' could also mean 'life').
'newspaperman' becomes 'ed'.
'holds' is an insertion indicator.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'life' placed inside 'ed' is 'elifed'.
'elifed' back-to-front is 'DEFILE'.
(Other definitions for defile that I've seen before include "Soil" , "Corrupt or violate" , "Spoil; narrow gorge" , "Desecrate" , "Pollute in narrow gorge" .)