Alternative ferritin mRNA translation via internal initiation

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Ferritin is essential for intracellular iron storage and detoxification, maintaining cellular redox balance.
• Ferritin expression is regulated transcriptionally and post-transcriptionally.
• Inflammatory signals are known to induce ferritin transcription, but its translational regulation under stress is less understood.

Purpose of the Study:

• To investigate the translational control of ferritin mRNA under cellular stress conditions.
• To determine if ferritin synthesis can proceed independently of global protein synthesis inhibition.
• To identify the mechanism governing ferritin mRNA translation during stress.

Main Methods:

• Utilized HT1080 fibrosarcoma cells with inducible PKR expression to mimic stress.
• Examined ferritin synthesis in cells infected with poliovirus, a stress inducer.
• Analyzed ferritin mRNA association with polysomes under inhibited protein synthesis.
• Investigated the role of the 5' untranslated region (5' UTR) of ferritin mRNA.

Main Results:

• Ferritin mRNA translation occurred despite PKR-induced global protein synthesis shutdown.
• Iron-mediated ferritin synthesis was observed in poliovirus-infected cells with inhibited host protein synthesis.
• Ferritin mRNA was associated with heavy polysomes under global and specific translation inhibition.
• Identified an internal ribosomal entry site (IRES) within the ferritin mRNA 5' UTR.

Conclusions:

• Ferritin mRNA translation can be activated through an alternative, noncanonical mechanism.
• This IRES-mediated translation likely operates under stress conditions.
• This pathway provides a protective mechanism against oxidative stress by enabling ferritin synthesis.