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Two human FLT4 receptor tyrosine kinase isoforms with distinct carboxy terminal tails are produced by alternative
K Pajusola1, O Aprelikova, E Armstrong
1Department of Pathology, University of Helsinki, Finland.
Abstract:
FLT4 is a recently cloned gene encoding a transmembrane tyrosine kinase related to the FLT1 and KDR/FLK1 vascular endothelial growth factor receptors. We have previously shown that FLT4 is expressed as transcripts of 4.5 and 5.8 kb in several human fetal and adult tissues. Here we show that these transcripts encode two polypeptides, FLT4s (short) and FLT41 (long), which are proteolytically processed in transfected cells and leukemia cells and which have different carboxy terminal tails. The 3' coding region of the 5.8 kb mRNA was found to be 65 codons longer than that of the the 4.5 kb mRNA. Analysis of the genomic structure of the region encoding the two carboxy termini revealed that the two transcripts are generated by alternative polyadenylation and subsequent alternative splicing during RNA processing. Our findings thus show regulation of FLT4 structure in the carboxy terminal tail considered important for receptor function. The significance of the two forms may relate to the role of additional potential autophosphorylation sites in the FLT4 long form.
Insights
The FLT4 gene produces two distinct protein forms, short (FLT4s) and long (FLT4l), through alternative RNA processing. These variants, differing in their C-terminal tails, may impact vascular endothelial growth factor receptor signaling.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- FLT4 is a gene encoding a transmembrane tyrosine kinase, part of the vascular endothelial growth factor receptor family.
- Previous studies identified FLT4 transcripts of 4.5 and 5.8 kb in human tissues.
Purpose of the Study:
- To investigate the molecular basis for the two FLT4 transcripts.
- To determine the structural differences between the polypeptides encoded by these transcripts.
- To elucidate the regulatory mechanisms generating FLT4 variants.
Main Methods:
- Analysis of gene expression in transfected and leukemia cells.
- Comparison of 3' coding regions of 4.5 kb and 5.8 kb FLT4 mRNA.
- Genomic structure analysis of the carboxy-terminal encoding region.
Main Results:
- The 4.5 kb and 5.8 kb transcripts encode short (FLT4s) and long (FLT4l) polypeptides, respectively.
- FLT4s and FLT4l possess distinct carboxy-terminal tails.
- Alternative polyadenylation and splicing generate the two FLT4 transcript variants.
- The FLT4 long form contains additional potential autophosphorylation sites.
Conclusions:
- FLT4 protein structure is regulated at the post-transcriptional level via alternative polyadenylation and splicing.
- The distinct C-terminal tails of FLT4s and FLT4l may confer differential functions.
- The presence of extra autophosphorylation sites in FLT4l could influence receptor signaling pathways.