Protein biosynthesis (translation) is fundamental to the sustenance of cellular life. A rate-limiting enzyme for the initiation of this biosynthesis is the Eukaryotic Initiation Factor Two (eIF-2). This protein consists of three subunits (eIF-2alpha, eIF-2beta and eIF-2gamma). The transcription factor, alpha- Pal, apparently coordinates the basal transcription of these housekeeping genes to ensure adequate levels of the mRNAs. Because protein biosynthesis is fundamentally critical to the full expression of any gene, one expects its regulation to be linked to those of major physiological pathways which rely on efficient synthesis of needed proteins. In this respect, alpha-Pal appears to link the transcription of key metabolic genes to cellular growth and development; processes which rely on timely and efficient synthesis of needed proteins. In support of this, we observe that: 1) Potential targets for alpha-Pal are genes involved in cellular proliferation, or the growth-responsive metabolic pathways, energy transduction, translation and DNA replication/repair; suggesting that alpha-Pal functions to modulate the transcription of metabolic genes required for cellular growth. 2) Both the protein sequence and the DNA-recognition site of alpha-Pal are strongly homologous to those of two evolutionarily-distant developmental transcription factors; sea Urchin's P3A2 and Drosophila's ewg. This suggests that alpha-Pal transcriptionally regulates developmental functions during human embryogenesis, possibly growth. A regulatory link between a cell's translation and cycle pathways may point to mechanisms for efficient expression of genes in response to the cell's metabolic and growth state. Understanding such mechanisms may facilitate the development of technologies for efficient expression of transgenes in vivo. In this respect cells stably overexpressing alpha-Pal overexpress eIF-2, and become slow-growing due to an arrest at the S-phase of cycle. In contrast, TF-1 cells underexpressing alpha-Pal become fast-growing and exhibit increased rate of apoptosis. The observed changes in growth rate, S-phase blockade and increase in apoptosis rate, indicated a perturbation in the activity of E2F1; a transcription factor which is critical to cell cycle S-phase transition. In tandem with this cells overexpressing alpha-Pal have decreased levels of E2F1 mRNA and protein, whereas, cells underexpressing alpha-Pal have increased levels of E2F1 mRNA and protein. In addition, alpha- Pal binds to and protects multiple sites in the promoter of E2F1 in vitro. Therefore, it appears that alpha-Pal transactivates the transcription of eIF2 genes but suppresses the transcription of E2F1 gene. This is the first example of a direct regulatory link between the cycle and translation pathways of a cell.
