Understanding the molecular and organismal function of genetic variants in non-coding regions is crucial to dissect the genetic and evolutionary basis of variation in complex traits. Combining complementary functional genomics datasets has proven a successful strategy to pinpoint the most likely causal variant and molecular mechanism supporting a genetic association. Current existing annotations only capture regulatory conditions at the baseline level. However, as we and others have shown, the effect of a genetic variant on a molecular pathway, and ultimately on the individual's phenotype, may be modulated by the cellular environmental context (gene-environment interactions, GxE). We define these genetic variants as GxE quantitative trait nucleotides (GxE-QTNs) and consider the cellular environment as a simplified but better controlled proxy of the organismal environment. Binding of TFs to specific genomic targets is defined by sequence motifs and chromatin epige- netic marks, and can be altered by the presence of GxE-QTNs. To discover genes modulated by GxE-QTNs, we have recently established a high-throughput approach to perturb the cellular environment by a panel of 50 in vitro treatments, including vitamins, metal ions, common drugs and hormones. Here we propose to use this approach to dissect these GxE-QTNs and the underlying molecular mechanism by: i) performing functional ge- nomics assays capturing chromatin accessibility; ii) analyzing the effects of naturally occurring genetic variation in regulatory elements; and iii) combining RNA-seq, ATAC-seq, MPRA and GWAS data to co-localize association signals and pinpoint complex traits causal variants.