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Translation of the placenta growth factor mRNA is severely affected by a small open reading frame localized in the 5'
D Maglione1, V Guerriero, M Rambaldi
1International Institute of Genetics and Biophysics, CNR, Naples, Italy.
Abstract:
The recently identified placenta growth factor gene (PIGF) code for a protein related to the vascular permeability factor (VPF). We present evidence indicating that expressing of this gene could be regulated at the post-transcriptional level. The region upstream to the coding region of PIGF mRNA contains a small open reading frame (ORF), potentially coding for a peptide of 15 amino acids. The translation of different constructs in reticulocyte and wheat germ lysates as well as in COS-1 and CV-1 cells indicates that this short region is a translational inhibitory element since mutations in its two potential initiator codons increase PIGF synthesis in vivo. Using RNAse protection assay, we demonstrate that the PIGF mRNAs obtained from human term placenta and JEG choriocarcinoma cell line have a complete 5' untranslated region and, consequently, also the above mentioned small ORF. Finally, the analysis of a bovine PIGF genomic clone reveals that this small ORF is strongly conserved with respect to both putative peptide sequences and distance from the PIGF coding region.
Insights
Placenta growth factor (PIGF) gene expression is regulated post-transcriptionally. A small open reading frame (ORF) in the PIGF mRNA 5' untranslated region acts as a translational inhibitor, impacting PIGF synthesis.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The placenta growth factor (PIGF) gene encodes a protein related to vascular permeability factor (VPF).
- Gene expression regulation can occur at post-transcriptional levels, including translational control.
Purpose of the Study:
- To investigate the post-transcriptional regulation of PIGF gene expression.
- To identify regulatory elements within the PIGF mRNA sequence.
- To determine the functional role of a small open reading frame (ORF) in the PIGF 5' untranslated region (UTR).
Main Methods:
- In vitro translation assays using reticulocyte and wheat germ lysates.
- Expression studies in COS-1 and CV-1 cells with mutated PIGF constructs.
- RNAse protection assays to analyze PIGF mRNA structure.
- Analysis of a conserved bovine PIGF genomic clone.
Main Results:
- A small ORF within the PIGF mRNA 5' UTR functions as a translational inhibitory element.
- Mutations in the initiator codons of this ORF significantly increase PIGF synthesis in vivo.
- PIGF mRNAs from human placenta and choriocarcinoma cells contain a complete 5' UTR with the inhibitory ORF.
- The inhibitory ORF and its position relative to the PIGF coding region are conserved in bovine PIGF.
Conclusions:
- PIGF gene expression is regulated at the translational level by a conserved inhibitory element in its 5' UTR.
- This translational control mechanism plays a significant role in modulating PIGF protein synthesis.
- The findings provide insights into the complex regulation of angiogenic factors.