Modulation of the cancer cell transcriptome by culture media formulations and cell density

We investigated how varying the composition of cell culture formulations and growing cancer cells at different densities might affect tumor cell genotype. Specifically, we compared gene expression profiles generated by human MDA‑MB‑231 breast cancer cells cultured in different media [minimum essential medium (MEM), Dulbecco's modified Eagle's medium (DMEM), or Roswell Park Memorial Institute (RPMI)‑1640 medium] containing different concentrations of fetal bovine serum (FBS) or different sera (equine or bovine) that were grown at different cell densities. More than 2,000 genes were differentially modulated by at least a 2‑fold difference when MDA‑MB‑231 cancer cells were 90% confluent and compared with cultures that were 50% confluent. Altering the concentration of serum produced an even more pronounced effect on MDA‑MB‑231 cancer cell gene expression in that 2,981 genes were differentially expressed in a comparison between cells cultured in 0.1% FBS and same cell density cultures that were maintained in 10% FBS. A comparison between MDA‑MB‑231 cancer cells that were 90% confluent in MEM, DMEM, or RPMI‑1640 media, all containing 10% FBS, resulted in 8,925 differentially expressed genes. Moreover, one‑quarter (25.6%) of genes from our genome‑wide expression analysis were expressed at significantly different levels by cells grown in MEM, DMEM, or RPMI‑1640 media. Genes associated with epithelial‑mes-enchymal transition (EMT) were among the genes that were differentially modulated by cells grown in different cell culture formulations and these genes were verified at the protein level. Collectively, these results underscore the importance of accurate reporting and maintenance of uniform culture conditions to ensure reproducible results.