When HIF-1α expression is increased, MUC5AC expression is induced; conversely, when HIF-1α expression is decreased, MUC5AC expression is reduced accordingly. (A) Gain-of-function study with mammalian HIF-1α expression vector in NCI-H292 cells. DNA of the pCMV vector encoding HIF-1α, or empty pCMV vector without HIF-1α, was transiently transfected. The expression of both HIF-1α and MUC5AC gene was increased when transfected with pCMV-HIF-1α vector, compared to transfection of empty control vectors under normoxic conditions (n = 3, *p<0.05). (B) Loss-of-function study with transfected HIF-1α siRNA in NCI-H292 cells. The expression of both HIF-1α and MUC5AC gene was suppressed when transfected with siRNA of HIF-1α, compared to transfection of siRNA negative control under hypoxic conditions for 6 h (n = 3, *p<0.05). Data is shown as mean ± standard deviation. (N; normoxia, C; control).