Internal ribosome initiation of translation and the control of cell death

The majority of cellular stresses lead to the inhibition of cap-dependent t ranslation, Some mRNAs, however, are translated by a cap-independent mechan ism, mediated by ribosome binding to internal ribosome entry site (IRES) el ements located in the 5' untranslated region. Interestingly, IRES elements are found in the mRNAs of several survival factors, oncogenes and proteins crucially involved in the control of apoptosis, These mRNAs are translated under a variety of stress conditions, including hypoxia, serum deprivation, irradiation and apoptosis. Thus, IRES-mediated translational control might have evolved to regulate cellular responses in acute but transient stress conditions that would otherwise lead to cell death.