FIG. 3.

RARγ₁ represses RARβ₂ gene induction in a dose-dependent manner. (A) RT-PCR determination of RNA transcripts of endogenous (lanes E) and transfected (lanes T) RARγ₁ in three selected clones compared to mock-transfected SK-N-BE2(c) cells (lanes C). The levels of transfected RARγ₁ RNA expressed relative to the amount of endogenous RNA, which was taken as 1, were 0.5, 1, and 2 in clones 1, 2, and 3, respectively. (B) Expression of endogenous and transfected RARγ₁ determined by Northern blot analysis with total RNA (20 μg) to evaluate their correct sizes. (C) Cells from clones 1, 2, and 3 were treated for 24 h in the presence of increasing RA concentrations or solvent alone. RNA was extracted, and RT-PCR was used to estimate the relative amounts of RARβ₂ gene transcripts. RNA transcripts of the β-actin gene were used to normalize the RT-PCR assays. Densitometric scanning of the gel clearly shows that a correlation exists between total RARγ₁ levels and the cell response to RA, evaluated as RARβ₂ gene induction. OD, optical density.