Difference in Activation of Signaling Pathways in A431 Cells with Confluence-Dependent and Confluence-Independent TRAIL Resistance

The mechanisms underlying cancer cell resistance to TRAIL-induced apoptosis are highly diverse and are of scientific and practical interest. We have demonstrated earlier that the human skin cancer A431 cell line sensitive to TRAIL-induced apoptosis in low-density culture (3 × 104 cells/cm2) acquired transient TRAIL resistance in dense, confluent cultures (3 × 105 cells/cm2). We have derived two cell lines, TRAILresistant (A431-R) and TRAIL-sensitive (A431-S), regardless of cell culture density, from parental A431 cell line using selection and clonal technique. We have obtained the genome-wide transcriptome data for these cell lines in low and high (confluent) density cultures and analyzed signaling pathway changes in these cells with respect to confluence-dependent and confluence-independent resistance to TRAIL-induced apoptosis. Signaling pathways were assayed using GSEA, which provides an entire cell transcriptome analysis and takes into account even small significant changes in the genes belonging to different signaling pathways that may be more important than a significant increase in a single gene. It is found that the confluence-dependent TRAIL resistance of cells A431 is associated with activation of a vast number of signaling pathways linked with the protective effects of RAS and interferon signaling, a change in the cytokine microenvironment, and suppression of the antitumor immune response. In contrast, the confluence-independent resistance of the A431- R cells is associated with activation of Nuclear factor erythroid 2-related factor 2 (NFE2L2) and Peroxisome proliferator-activated receptor alpha (PPARA) transcription factors. The TRAIL sensitivity of A431-S cells in confluent culture correlates with a decrease of the RAS and PPARA signaling pathways activity.