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A small nuclear RNA, hdm365, is the major processing product of the human mdm2 gene
1Children's Cancer Research Institute, St Anna Kinderspital, Kinderspitalgasse 6, Vienna A-1090, Austria.
Abstract:
mdm2 encodes for an E3 ubiquitin ligase targeting constitutively expressed p53 for proteasomal degradation. Several protein isoforms have been described for human MDM2 (HDM2), some of which may correspond to splicing variants detectable by RT-PCR in many tumors. Upon cellular stress, p53 becomes resistant to MDM2 and, in a feedback loop, up-regulates mdm2 transcription. The physiological relevance of stress-induced mdm2 gene activity is not well understood. We describe a small nuclear RNA of 365 bases comprised of the first five hdm2 exons and lacking polyadenylation. hdm365 precedes full-length hdm2 RNA expression after induction by p53 and accumulates to significant levels in the nucleus, detectable at the site of hdm2 transcription and processing only. Considering a 10-fold lower stability and high steady-state levels of the novel RNA species, hdm365 appears to be the major processing product of hdm2 transcripts. hdm365 induction was observed after ectopic expression of p53 and after DNA damaging treatment of tumor cell lines, primary fibroblasts and lymphocytes, and was not related to apoptosis. Corresponding truncated transcripts were observed in hdm2 amplified cells. High stress-inducible expression levels, absence of a corresponding protein, and nuclear localisation of hdm365 suggest a novel RNA-based function for hdm2.
Insights
A novel nuclear RNA, hdm365, is a major product of MDM2 (mouse double minute 2 homolog) transcripts. Stress induces hdm365, suggesting a new RNA-based function for MDM2 in cellular responses.
Area of Science:
- Molecular Biology
- Cancer Biology
- RNA Biology
Background:
- MDM2 (mouse double minute 2 homolog) is an E3 ubiquitin ligase that targets p53 for degradation.
- Stress conditions induce p53 resistance to MDM2 and upregulate MDM2 transcription.
- The function of stress-induced MDM2 gene activity remains unclear.
Purpose of the Study:
- To investigate the role and nature of stress-induced MDM2 gene activity.
- To characterize a novel RNA species associated with MDM2 transcription.
Main Methods:
- Reverse transcription polymerase chain reaction (RT-PCR) to detect RNA splicing variants.
- Analysis of nuclear RNA accumulation and localization.
- Assessment of RNA stability and expression levels under various cellular conditions.
Main Results:
- A 365-base nuclear RNA (hdm365) was identified, comprising the first five exons of hdm2 and lacking polyadenylation.
- hdm365 precedes full-length hdm2 RNA expression and accumulates in the nucleus at the transcription site.
- hdm365 exhibits lower stability but high steady-state levels, indicating it's a major processing product of hdm2 transcripts.
- hdm365 is induced by p53 expression and DNA damage in various cell types, independent of apoptosis.
- Truncated transcripts similar to hdm365 were observed in MDM2-amplified cells.
Conclusions:
- hdm365 represents a significant, stress-inducible, non-coding RNA product of the hdm2 gene.
- Its nuclear localization and high expression levels suggest a novel RNA-based function for MDM2.
- Further research is needed to elucidate the specific role of hdm365 in cellular stress responses.