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Two posttranscriptional pathways that regulate p21(Cip1/Waf1/Sdi1) are identified by HPV16-E6 interaction and
B A Burkhart1, D A Alcorta, C Chiao
1Laboratory of Molecular Carcinogenesis, National Institute of Environmental Health Science, Research Triangle Park, North Carolina, 27709, USA.
Abstract:
The p21((Cip1/Waf1/Sdi1)) protein is a cyclin-dependent kinase inhibitor that is induced in normal human fibroblasts (NHF) following DNA damage, following serum stimulation, and at cellular senescence. Expression of the human papilloma virus 16 E6 oncoprotein in NHF cells results in the loss of the p21 protein, independent of mRNA level under most conditions. The p21 protein levels in NHF-E6 cells remained low following DNA damage or serum stimulation even though mRNA levels increased. In contrast, the p21 protein was transiently induced in NHF-E6 cells at the onset of cellular senescence. Expression of the E6 oncoprotein in transformed cells had no effect on p21 protein levels. This demonstrates that two posttranscriptional pathways regulate expression of p21 protein in NHF cells under different conditions. Disruption of posttranscriptional regulation is correlated with extension of life span, altered cell fate, and transformation.
Insights
The human papillomavirus E6 oncoprotein disrupts p21 protein regulation in normal human fibroblasts, affecting cell fate. This study reveals posttranscriptional control of p21 protein levels under various cellular conditions.
Area of Science:
- Molecular Biology
- Cell Biology
- Virology
Background:
- The p21 protein (also known as Cip1/Waf1/Sdi1) is a key cyclin-dependent kinase inhibitor.
- p21 expression is typically induced in normal human fibroblasts (NHF) by DNA damage, serum stimulation, and cellular senescence.
- The human papillomavirus (HPV) 16 E6 oncoprotein is known to affect cellular processes.
Purpose of the Study:
- To investigate the effect of HPV 16 E6 oncoprotein expression on p21 protein levels in NHF cells.
- To elucidate the regulatory mechanisms of p21 protein expression under different conditions in the presence of E6.
- To determine if E6 affects p21 at the transcriptional or posttranscriptional level.
Main Methods:
- Culturing normal human fibroblasts (NHF) and NHF cells expressing HPV 16 E6 oncoprotein.
- Inducing DNA damage and serum stimulation in cultured cells.
- Monitoring p21 protein and mRNA levels under various conditions, including cellular senescence.
- Comparing p21 regulation in NHF-E6 cells with control NHF cells and transformed cells.
Main Results:
- HPV 16 E6 expression in NHF cells led to a loss of p21 protein, largely independent of mRNA levels.
- In NHF-E6 cells, p21 protein levels remained low after DNA damage or serum stimulation, despite increased mRNA.
- p21 protein was transiently induced during cellular senescence in NHF-E6 cells.
- E6 oncoprotein expression had no impact on p21 protein levels in transformed cells.
Conclusions:
- Two distinct posttranscriptional pathways regulate p21 protein expression in NHF cells under different stimuli.
- Disruption of p21 posttranscriptional regulation by E6 is linked to extended cellular lifespan, altered cell fate, and potentially transformation.
- These findings highlight the critical role of posttranscriptional control in maintaining normal cellular processes and preventing oncogenesis.