Primary cultured cells were transfected with dominant negative STAT3(S727A), constitutively active STAT3(S727E), dominant negative STAT3(Y705F) or wild type STAT3 as control (kind gift of Dr Too, National University of Singapore, Singapore (32 (link))). Transfection was achieved using X-treme transfection reagent (Roche, MA) in serum free medium for 24 hours.