MRNA stability and translation

Kedersha, N., and Anderson, P. (2002). Stress granules Sites of mRNA triage that regulate mRNA stability and translatability. Biochem. Soc. Trans. 30, 963—969. 

Hitti, E., Iakovleva, T., Brook, M., Deppenmeier, S., Gruber, A. D., Radzioch, D., Clark, A. R., Blackshear, P. J., Kotlyarov, A., and Gaestel, M. (2006). Mitogen-activated protein kinase-activated protein kinase 2 regulates tumor necrosis factor mRNA stability and translation mainly by altering tristetraprolin expression, stability, and binding to adenine/uridine-rich element. Mol. Cell Biol. 26, 2399—2407. 

Mechanism and Genetics of Induction in Mammals. Many different mechanisms may be involved in CYP induction. These include increased transcription of DNA, increased mRNA translation to protein, mRNA stabilization, and protein stabilization. Induction can only occur in intact cells and cannot be achieved by the addition of inducers directly to cell fractions such as microsomes. It has been known for some time that in most cases of increase in monooxygenase activity there is a true induction involving synthesis of new enzyme, and not the activation of enzyme already synthesized, since induction is generally prevented by inhibitors of protein synthesis. For example, the protein synthesis inhibitors such as puromycin, ethionine, and cyclo-heximide inhibit aryl hydrocarbon hydroxylase activity. A simplified scheme for gene expression and protein synthesis is shown in Figure 9.7. 

Riboswitch-mediated gene regulation occurs after transcription initiation, as the regulatory element is part of the regulated transcript. In bacteria, preferred modes of regulation are at the levels of premature termination of transcription (referred to as transcriptional attenuation) and translation initiation. Rare examples identified so far in eukaryotic cells affect mRNA stability and splicing. 

Evidence for control at the level of mRNA stability and enhanced translation efficiency has been presented by Novak -. The 3 -region of the gene appears to be important in stability. The relevance of this rat model to human P450 2E1 is still unknown. 

Although most mRNAs in mammalian cells are very stable (half-lives measured in hours), some mrn over very rapidly (half-lives of 10-30 minutes). In certain instances, mRNA stability is subject to regulation. This has important implications since there is usually a direct relationship between mRNA amount and the translation of that mRNA into its cognate protein. Changes in the stability of a specific mRNA can therefore have major effects on biologic processes. 

Synthesis of the transferrin receptor (TfR) and that of ferritin are reciprocally linked to cellular iron content. Specific untranslated sequences of the mRNAs for both proteins (named iron response elements) interact with a cytosolic protein sensitive to variations in levels of cellular iron (iron-responsive element-binding protein). When iron levels are high, cells use stored ferritin mRNA to synthesize ferritin, and the TfR mRNA is degraded. In contrast, when iron levels are low, the TfR mRNA is stabilized and increased synthesis of receptors occurs, while ferritin mRNA is apparently stored in an inactive form. This is an important example of control of expression of proteins at the translational level. 

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