No US city’s backing artistic gathering (5)
I believe the answer is:
salon
'artistic gathering' is the definition.
(salon can mean a gathering of artists)
'no us city's backing' is the wordplay.
'us city's' becomes 'LA's'.
'backing' is a reversal indicator.
'no'+'las'='nolas'
'nolas' backwards is 'SALON'.
(Other definitions for salon that I've seen before include "Strange loans for a hairdresser, perhaps" , "Elegant reception room" , "Elegant room - for hairdresser?" , "Establishment of, say, beauty specialist" , "Call loudly" .)