Translational control of ornithine aminotransferase. Modulation by initiation factor eIF-4E

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Ornithine aminotransferase (OAT) is a key mitochondrial enzyme with high expression in liver, kidney, and retina.
• Previous studies showed similar OAT mRNA levels but differing protein levels and activity in retinoblastoma cell lines RB355 and Y79.

Purpose of the Study:

• To investigate the regulatory mechanisms of OAT synthesis in RB355 and Y79 retinoblastoma cell lines.
• To determine the role of translational control in differential OAT protein expression.

Main Methods:

• Nuclear runoff assays to assess OAT gene transcription rates.
• Polysome profiling to analyze OAT mRNA distribution and translation status.
• Cycloheximide treatment to evaluate translation initiation and elongation.
• Overexpression of wild-type and mutant eukaryotic initiation factor eIF-4E.

Main Results:

• No significant differences in OAT gene transcription were observed between RB355 and Y79 cells.
• OAT mRNA in RB355 cells was found in lighter polysome fractions, indicating reduced translation initiation.
• RB355 cells exhibited lower levels of eukaryotic initiation factor eIF-4E mRNA and protein.
• Overexpression of wild-type eIF-4E in RB355 cells increased OAT protein levels to match those in Y79 cells.

Conclusions:

• Translational control, specifically the availability of eukaryotic initiation factor eIF-4E, is a key determinant of OAT protein levels in retinoblastoma cells.
• Reduced eIF-4E levels in RB355 cells limit OAT translation, explaining the lower OAT protein expression compared to Y79 cells.
• An alternatively spliced OAT mRNA variant was identified but was not affected by eIF-4E levels.