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Src-homology domain 2 is responsible for transcriptional suppression induced by expression of Lck
1Virology Division, National Cancer Center Research Institute, Tokyo, Japan.
Abstract:
Overexpression of Lck was shown, by our previous study, to suppress gene transcription from various viral and cellular promoters. The suppression of transcription from human T-cell leukemia virus promoter by Lck was independent of the presence of the enhancer core sequences within the long terminal repeat. The suppression of transcription was observed with Lck mutants that had either diminished or enhanced tyrosine-kinase activity. A mutant lacking the myristylation site also suppressed transcription. From the analysis with various deletion mutants of Lck, it was suggested that Src-homology domain 2 (SH2) is both necessary and sufficient for the suppression of transcription. A similar effect was also observed with the SH2 domain of the v-src gene. Thus, overexpression of Lck could suppress gene expression through a unique function of the SH2 domain.
Insights
Overexpression of Lck kinase suppresses gene transcription. This effect is mediated by the Src-homology domain 2 (SH2), independent of kinase activity.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Previous studies demonstrated that Lck kinase overexpression suppresses gene transcription from viral and cellular promoters.
- The mechanism of this transcriptional suppression by Lck was not fully understood.
Purpose of the Study:
- To investigate the mechanism by which Lck overexpression suppresses gene transcription.
- To identify the specific domains of Lck responsible for transcriptional suppression.
Main Methods:
- Utilized various viral and cellular promoters to assess Lck's effect on transcription.
- Employed deletion mutants and site-specific mutants of Lck to analyze domain function.
- Examined the role of tyrosine-kinase activity and the myristylation site in Lck-mediated suppression.
- Assessed the function of the Src-homology domain 2 (SH2) in transcriptional suppression.
Main Results:
- Lck overexpression suppressed transcription from the human T-cell leukemia virus promoter, irrespective of enhancer sequences.
- Transcriptional suppression occurred even with Lck mutants possessing altered tyrosine-kinase activity or lacking the myristylation site.
- Deletion mutant analysis indicated that the SH2 domain of Lck is both necessary and sufficient for transcriptional suppression.
- The SH2 domain of the v-src gene also exhibited a similar suppressive effect.
Conclusions:
- Lck kinase overexpression suppresses gene expression through a mechanism involving its SH2 domain.
- The SH2 domain plays a critical role in Lck-mediated transcriptional repression, independent of its kinase activity.