Related Experiment Videos
T-cell receptor sequences that elicit strong down-regulation of premature termination codon-bearing transcripts
Jayanthi P Gudikote1, Miles F Wilkinson
1Department of Immunology, The University of Texas M.D.Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
Abstract:
The nonsense-mediated decay (NMD) RNA surveillance pathway detects and degrades mRNAs containing premature termination codons (PTCs). T-cell receptor (TCR) and immunoglobulin transcripts, which commonly harbor PTCs as a result of programmed DNA rearrangement during normal development, are down-regulated much more than other known mammalian gene transcripts in response to nonsense codons. Here, we demonstrate that this is not because of promoter or cell type but instead is directed by regulatory sequences within the rearranging VDJ exon and immediately flanking intron sequences of a Vbeta8.1 TCR-beta gene. Insertion of these sequences into a heterologous gene elicited strong down-regulation (>30-fold) in response to PTCs, indicating that this region is sufficient to trigger robust down-regulation. The rearranging Vbeta5.1 exon and the flanking intron sequences from another member of the TCR-beta family also triggered strong down-regulation, suggesting that down-regulatory-promoting elements are a conserved feature of TCR genes. Importantly, we found that the Vbeta8.1 down-regulatory-promoting element was position dependent, such that it failed to function when positioned downstream of a PTC. To our knowledge, this is the first class of down-regulatory elements identified that act upstream of nonsense codons.
Insights
Regulatory sequences in T-cell receptor genes trigger nonsense-mediated decay (NMD) of transcripts with premature stop codons. These elements are conserved and function upstream of the nonsense codon, offering new insights into RNA surveillance.
Area of Science:
- Molecular Biology
- RNA Biology
- Immunology
Background:
- Nonsense-mediated decay (NMD) is an RNA surveillance pathway that degrades mRNAs with premature termination codons (PTCs).
- T-cell receptor (TCR) and immunoglobulin transcripts are unusually sensitive to NMD due to PTCs arising from DNA rearrangement.
- Previous understanding did not fully explain this heightened sensitivity.
Purpose of the Study:
- To identify the regulatory elements responsible for the enhanced NMD of TCR transcripts.
- To determine if these elements are sufficient to confer NMD sensitivity to other genes.
- To investigate the mechanism and conservation of these regulatory elements.
Main Methods:
- Gene insertion experiments: TCR gene sequences (VDJ exon and flanking introns) were inserted into a reporter gene.
- NMD assays: The effect of PTCs on the expression of the reporter gene with inserted TCR sequences was measured.
- Comparative analysis: Sequences from different TCR-beta genes were tested.
Main Results:
- Specific regulatory sequences within the rearranging VDJ exon and flanking introns of a Vbeta8.1 TCR-beta gene were identified as sufficient to trigger robust NMD (>30-fold down-regulation) in response to PTCs.
- Similar down-regulatory elements were found in other TCR-beta genes, indicating conservation.
- The Vbeta8.1 down-regulatory element's function was position-dependent, failing when located downstream of a PTC.
Conclusions:
- Regulatory sequences within TCR genes, specifically VDJ exons and flanking introns, are responsible for enhanced NMD.
- These elements represent a newly identified class of upstream-acting down-regulatory elements in RNA surveillance.
- The findings provide a mechanistic explanation for the NMD sensitivity of TCR transcripts and highlight conserved regulatory features in immune gene development.