Multiple elements in the 5' untranslated region down-regulate c-sis messenger RNA translation

Area of Science:

• Molecular Biology
• Cell Signaling
• Oncogenes

Background:

• Platelet-derived growth factor (PDGF) B-chain synthesis is regulated transcriptionally and translationally.
• The 5' untranslated region (UTR) of c-sis mRNA is known to inhibit PDGF-B chain synthesis.
• Previous studies indicated ambiguity regarding specific down-regulatory regions within the 5' UTR.

Purpose of the Study:

• To elucidate the complex mechanisms of translational regulation of PDGF-B chain synthesis.
• To identify specific regions within the c-sis mRNA 5' UTR responsible for translational inhibition.
• To investigate the role of upstream open reading frames and secondary structures in regulating PDGF-B chain expression.

Main Methods:

• Site-directed mutagenesis of the c-sis mRNA 5' UTR, including point and deletion mutants.
• Expression analysis of c-sis mRNA mutants in COS1 cells.
• Assessment of PDGF-B chain synthesis following mutant expression.

Main Results:

• Mutating upstream AUGs did not affect PDGF-B chain synthesis.
• Two distinct, partially overlapping regions (nucleotides 1-651 and 475-1022) within the 5' UTR independently inhibited translation.
• Each inhibitory region contains potential stem-loop structures and GC-rich elements that may interact to block translation.

Conclusions:

• PDGF-B chain translational inhibition by the c-sis mRNA 5' UTR is more complex than previously understood.
• The identified regulatory regions can independently inhibit translation, suggesting a multi-faceted regulatory mechanism.
• Inhibition is not solely attributable to specific secondary structures or GC-rich elements within the 5' UTR.