Analysis of the transcriptional response to retinoic acid in T47D breast cancer cells with impaired RARA function

It has been shown that retinoic acid (RA) can both inhibit and promote cancer cell growth, but the basis of this “paradox” is still not clear. The action of RA is mainly mediated by RA receptors (RARs), which classically function as ligand-activated transcription factors. Upon binding to the RA receptor alpha (RARA), RA modulates the transcription of several RA-target genes involved in multiple cellular processes, including cell proliferation. We have found that functional inhibition of RARA transcriptional function by stable expression of a RARA dominant negative (RARA403) converts T47D breast cancer cells from growth-inhibited to growth-promoted by supraphysiological RA (Ren et al., MCB, 2005, PMID:16287870; Somenzi et al., PloS ONE, 2007, PMID:17786207). We hypothesized that RA-induced cell growth requires both the activation of RA-responsive tumor-promoting signalings and lack of activation of RA-responsive tumor suppressor signalings. To identify these signalings, we analyzed the transcriptional response to RA in our model of the “RA paradox” by using gene expression microarrays. To impair RARA transcriptional function, T47D breast cancer cells were stably transfected with the RARA403 mutant (DNC8 clone). In parallel, T47D were stably transfected with the empty vector to obtain a control clone (LXC5 clone, also called T47D-Ctrl). The two clones were grown with or without RA (1 uM) for 72h, and analyzed on gene expression microarrays to identify genes with differential response to RA in presence or absence of functional RARA transcriptional function. A total of 8 samples were analyzed: LXC5 minus RA, LXC5 plus RA, DNC8 minus RA, DNC8 plus RA, in duplicate.