Expression of TRB3 mRNA Correlates to the Temporal Phosphorylation of eIF2‐α by Nutrient Limitation in PC‐3 Human Prostate Cancer Cells

Nutrient limitation affects the apoptosis and/or cell survival of tumor cells. The process of how nutrient limitation regulates TRB3 (a tribbles homolog) expression in human prostatic tumor PC‐3 cells was studied. PC‐3 cells were incubated in MEM, MEM free of amino acids or glucose. Samples were then collected at the following time points: 0, 4, 8, 12, 16 hours. Real‐Time qRT‐PCR was used to quantify mRNA expression of TRB3 and Western Blot was used to compare protein expression levels. PC‐3 cells showed a temporal response to amino acid and glucose starvation through differential expression of the TRB3 gene. While both starvation conditions led to an increase in TRB3 transcription, this increase occurred approximately 4 hours later in glucose starvation compared to amino acid starvation. This may point to the importance of TRB3 in both amino acid and glucose starvation pathways. Nutrient starvation is also known to lead to the increased phosphorylation of the α subunit of Eukaryotic Initiation Factor 2 (eIF2‐α), which decreases general translation, and increases specific translation and transcription of certain genes, including those containing the Amino Acid Response Element (AARE). Our experiment showed a temporal phosphorylation difference of eIF2‐α between the two starvation conditions, matching the data obtained from TRB3 mRNA analysis. We conclude that TRB3, a gene whose transcription increases significantly with nutrient deprivation, is directly correlated to the phosphorylation of eIF2‐α.