Internal ribosome initiation of translation and the control of cell death

Area of Science:

• Molecular Biology
• Cellular Stress Response
• Gene Expression Regulation

Background:

• Cellular stresses typically inhibit cap-dependent translation, a primary mechanism for protein synthesis.
• Some messenger RNAs (mRNAs) utilize an alternative, cap-independent translation pathway.
• This alternative pathway is mediated by internal ribosome entry site (IRES) elements within the 5' untranslated region of specific mRNAs.

Purpose of the Study:

• To investigate the role of IRES-mediated translation in cellular responses to various stress conditions.
• To understand how IRES elements contribute to the translation of survival factors, oncogenes, and apoptosis-regulating proteins under stress.
• To explore the evolutionary significance of IRES-mediated translational control in managing acute cellular stress.

Main Methods:

• Analysis of mRNA sequences for the presence and location of IRES elements.
• Experimental induction of cellular stress (hypoxia, serum deprivation, irradiation, apoptosis).
• Monitoring of protein synthesis rates for IRES-containing and non-IRES-containing mRNAs under stress conditions using techniques like Western blotting or polysome profiling.

Main Results:

• IRES elements are present in mRNAs encoding critical survival factors, oncogenes, and apoptosis regulators.
• These specific mRNAs are actively translated even when cap-dependent translation is inhibited during various cellular stresses.
• Translation of IRES-containing mRNAs is observed under conditions such as hypoxia, serum deprivation, irradiation, and apoptosis induction.

Conclusions:

• IRES-mediated translation provides a mechanism for continued synthesis of essential proteins during cellular stress.
• This translational control is crucial for cellular adaptation and survival under acute, transient stress.
• The IRES mechanism may represent an evolved strategy to prevent cell death during adverse conditions.