Functional genomic analysis reveals cross-talk between peroxisome proliferator-activated receptor γ and calcium signaling in human colorectal cancer cells

Activation of PPAR gamma in MOSER cells inhibits anchorage-dependent and anchorage-independent growth and invasion through Matrigel-coated transwell membranes. We carried out a longitudinal two-class microarray analysis in which mRNA abundance was measured as a function of time in cells treated with a thiazolidinedione PPAR gamma agonist or vehicle. A statistical machine learning algorithm that employs an empirical Bayesian implementation of the multivariate HotellingT2 score was used to identify differentially regulated genes. HotellingT2 scores, MB statistics, and maximum median differences were used as figures of merit to interrogate genomic ontology of these targets. Three major cohorts of genes were regulated: those involved in metabolism, DNA replication, and migration/motility, reflecting the cellular phenotype that attends activation of PPAR gamma. The bioinformatic analysis also inferred that PPAR gamma regulates calcium signaling. This response was unanticipated, because calcium signaling has not previously been associated with PPAR gamma activation. Ingenuity pathway analysis inferred that the nodal point in this cross-talk was Down syndrome critical region 1 (DSCR1). DSCR1 is an endogenous calcineurin inhibitor that blocks dephosphorylation and activation of members of the cytoplasmic component of nuclear factor of activated T cells transcription factors. Lentiviral short hairpin RNA-mediated knockdown of DSCR1 blocks PPAR gamma inhibition of proliferation and invasion, indicating that DSCR1 is required for suppression of transformed properties of early stage colorectal cancer cells by PPAR gamma. These data reveal a novel, heretofore unappreciated link between PPAR gamma and calcium signaling and indicate that DSCR1, which has previously been thought to function by suppression of the angiogenic response in endothelial cells, may also play a direct role in transformation of epithelial cells.