Translational regulation of gene expression during conditions of cell stress

A number of stresses, including nutrient stress, temperature shock, DNA damage, and hypoxia, can lead to changes in gene expression patterns caused by a general shutdown and reprogramming of protein synthesis. Each of these stress conditions results in selective recruitment of ribosomes to mRNAs whose protein products are required for responding to stress. This recruitment is regulated by elements within the 5' and 3' untranslated regions of mRNAs, including internal ribosome entry segments, upstream open reading frames, and microRNA target sites. These elements can act singly or in combination and are themselves regulated by trans-acting factors. Translational reprogramming can result in increased life span, and conversely, deregulation of these translation pathways is associated with disease including cancer and diabetes.     

Translational regulation of light-induced ribulose 1,5-bisphosphate carboxylase gene expression in amaranth.

The regulation of the genes encoding the large and small subunits of ribulose 1,5-bisphosphate carboxylase was examined in amaranth cotyledons in response to changes in illumination. When dark-grown cotyledons were transferred into light, synthesis of the large- and small-subunit polypeptides was initiated very rapidly, before any increase in the levels of their corresponding mRNAs. Similarly, when light-grown cotyledons were transferred to total darkness, synthesis of the large- and small-subunit proteins was rapidly depressed without changes in mRNA levels for either subunit. In vitro translation or in vivo pulse-chase experiments indicated that these apparent changes in protein synthesis were not due to alterations in the functionality of the mRNAs or to protein turnover, respectively. These results, in combination with our previous studies, suggest that the expression of ribulose 1,5-bisphosphate carboxylase genes can be adjusted rapidly at the translational level and over a longer period through changes in mRNA accumulation.     

Translational control of gene expression and disease

In the past decade, translational control has been shown to be crucial in the regulation of gene expression. Research in this field has progressed rapidly, revealing new control mechanisms and adding constantly to the list of translationally regulated genes. There is accumulating evidence that translational control plays a primary role in cell-cycle progression and cell differentiation, as well as in the induction of specific cellular functions. Recently, the aetiologies of several human diseases have been linked with mutations in genes of the translational control machinery, highlighting the significance of this regulatory mechanism. In addition, deregulation of translation is associated with a wide range of cancers. Current research focuses on novel therapeutic strategies that target translational control, a promising concept in the treatment of human diseases.     

Translational control of alpha-amylase gene expression in Aspergillus awamori

Regulation of alpha-amylase gene expression in Aspergillus awamori was studied by analyzing the enzyme activity levels, rate of protein synthesis, and alpha-amylase-specific mRNA levels under various conditions of growth. alpha-Amylase synthesis was sensitive to catabolite repression as glucose repressed its synthesis by about fourfold. The stimulation of alpha-amylase synthesis in the presence of its substrate starch was shown to be due to derepression rather than induction as the enzyme was synthesized at similar rates in both starch and starvation media. Repression and derepression of enzyme synthesis was found to be mediated at the translational level. The cellular levels of alpha-amylase-specific mRNA as measured by an in vitro translation assay system, were almost identical under all conditions of enzyme synthesis. Relative in vivo and in vitro alpha-amylase mRNA template activities suggest that alpha-amylase mRNA is translated much more efficiently during the derepression than under the conditions of repressed synthesis.     

Translational regulation of nuclear gene COX4 expression by mitochondrial content of phosphatidylglycerol and cardiolipin in Saccharomyces cerevisiae

Previous results indicated that translation of four mitochondrion-encoded genes and one nucleus-encoded gene (COX4) is repressed in mutants (pgs1Delta) of Saccharomyces cerevisiae lacking phosphatidylglycerol and cardiolipin. COX4 translation was studied here using a mitochondrially targeted green fluorescence protein (mtGFP) fused to the COX4 promoter and its 5' and 3' untranslated regions (UTRs). Lack of mtGFP expression independent of carbon source and strain background was established to be at the translational level. The translational defect was not due to deficiency of mitochondrial respiratory function but was rather caused directly by the lack of phosphatidylglycerol and cardiolipin in mitochondrial membranes. Reintroduction of a functional PGS1 gene under control of the ADH1 promoter restored phosphatidylglycerol synthesis and expression of mtGFP. Deletion analysis of the 5' UTR(COX4) revealed the presence of a 50-nucleotide fragment with two stem-loops as a cis-element inhibiting COX4 translation. Binding of a protein factor(s) specifically to this sequence was observed with cytoplasm from pgs1Delta but not PGS1 cells. Using HIS3 and lacZ as reporters, extragenic spontaneous recessive mutations that allowed expression of His3p and beta-galactosidase were isolated, which appeared to be loss-of-function mutations, suggesting that the genes mutated may encode the trans factors that bind to the cis element in pgs1Delta cells.     

Hormonal regulation of gene expression

The involvement of plant hormones in the regulation of gene expression is well-recognized. Current research using molecular approaches has resulted in the isolation and characterization of a number of hormone-responsive genes and cDNAs. These genes are proving to be valuable molecular probes to study the mode of action of plant hormones. This review will briefly describe some recent molecular data from selected hormone-responsive plant systems. Results of these studies indicate potential complexity in the regulation of these genes. These results and future challenges are discussed.     

Nutritional regulation of gene expression

Summary The human genome has now been mapped with a complete sequence to follow shortly. The race is on to apply the vast amount of information contained in the billions of base-pairs. Concurrently, there is an increased demand from the public for perceived natural products. The nutritional supplement and pharmaceutical industries are broadening their product lines to meet this ever-increasing demand. As the genetic basis of disease becomes more evident, it is clear that the two industries will be forced to turn their attention to nutrients affecting gene expression. Such nutritional regulators of gene expression, or genomeceuticals (Brudnak, 2001), have enormous potential for therapeutic and prophylactic applications in both industries by affecting the integrity and expression of genes. However, there are caveats to this application, which if unheeded, may have disastrous results. This paper explores the idea behind the burgeoning area of genomeceuticals as well as some potential pit-falls that this novel area harbors. Representative examples are presented with a subsequent discussion focusing on the specifics of the application. Calculations based on: mw of GlcNAc · HCl=215.64, mw GlcNAc=179.18. Given: an infusion rate of 15 μM/Kg/min, 15 μM of GlcNAc=2.68 mg, and GHCl (glucosamine hydrochloride) is 83% GlcNAc.     

Temporal regulation of gene expression

Molecular biology gives a static--not a dynamic--vision of the mechanisms regulating gene expression. Genetics already gave to time a limited place in the explanation of living phenomena. Such a static vision is supported by the techniques--such as X-ray crystallography--used by the biologists. However time is an important parameter in the control of gene expression during the cellular response to external signals, during life and aging of organisms or even in the succession of living forms which takes place in evolution. Models are slowly moving, due to the eruption of new technologies giving access to the fast events which occur inside living cells. A new dynamic vision is progressively replacing the old one. The consequences of these changes on the form of the future biology remain still unknown.