Figure 4.

ATRA increases COX-2 expression at the transcriptional level of regulation. (a) 10 μM ATRA increases the mesangial expression of COX-2 mRNA, analysed by semiquantitative RT-PCR, after a 24 h incubation. Equal mRNA loading was confirmed by coamplification of 18S mRNA. Normalized density ratio of COX-2 over 18 S RNA is indicated for each band. The photograph represents at least three repeated experiments. (b) ATRA-treated cells do not show a decreased decay rate of COX-2 mRNA as compared to controls. The time course of the decay of COX-2 mRNA was analysed by Northern blot, in MC treated for 24 h with ATRA vehicle or with 10 μM ATRA and then with 2 μg ml⁻¹ actinomycin D for 0–8 h. Equal mRNA loading was confirmed by probing with GAPDH. The graph is the densitometric analysis of the COX-2 mRNA level normalized to the level of GAPDH mRNA. Results are the mean±s.d. of four separate experiments (c) ATRA (10 μM/24 h) increases the activity in MC of the human COX-2 gene promoter, determined in triplicate in four separate experiments, by transient transfection assay. ^*P<0.01 vs control.