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Alteration of cell cycle kinase complexes in human papillomavirus E6- and E7-expressing fibroblasts precedes
1Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill 27599, USA.
Abstract:
Expression of viral oncoproteins results in the loss of cell cycle checkpoint control and the accumulation of chromosomal abnormalities. Expression of both human papillomavirus type 16 oncoproteins, E6 and E7, in normal human fibroblasts completely dissociates p21 and proliferating cell nuclear antigen from the quarternary cyclin-cyclin-dependent kinase (CDK) complexes present in normal cells, causes disruption of the cyclin D-CDK4 complex and replacement with a CDK4-p16 complex, and leaves binary complexes of cyclin B1-CDC2 and cyclin A-CDK2 intact. These results are identical to those observed in fully transformed cells. The expression of the individual oncoproteins dramatically affects the association of proliferating cell nuclear antigen into the complexes while leaving the total cellular levels unaltered. Expression of low-risk human papillomavirus has no effect on cyclin complexes. These findings provide evidence for the gross alteration of cyclin-CDK complexes in preneoplastic cells and links this alteration to the loss of genomic stability.
Insights
Human papillomavirus oncoproteins disrupt cell cycle control by altering cyclin-cyclin-dependent kinase complexes, leading to genomic instability. This impacts cell cycle regulation and is linked to cancer development.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Viral oncoproteins, such as those from human papillomavirus (HPV), are known to disrupt normal cellular functions.
- Cell cycle checkpoint control is crucial for maintaining genomic stability.
- Dysregulation of cyclin-cyclin-dependent kinase (CDK) complexes is implicated in cancer development.
Purpose of the Study:
- To investigate the effects of HPV type 16 oncoproteins (E6 and E7) on cell cycle regulatory complexes in normal human fibroblasts.
- To determine how these oncoproteins alter the composition and function of cyclin-CDK complexes.
- To link these alterations to the loss of genomic stability observed in preneoplastic cells.
Main Methods:
- Expression of HPV type 16 E6 and E7 oncoproteins in normal human fibroblasts.
- Analysis of cyclin-CDK complexes using co-immunoprecipitation and Western blotting.
- Assessment of proliferating cell nuclear antigen (PCNA) association with cyclin-CDK complexes.
- Comparison of alterations in normal fibroblasts with those in fully transformed cells and cells expressing low-risk HPV.
Main Results:
- HPV 16 E6 and E7 expression dissociated p21 and PCNA from normal quaternary cyclin-CDK complexes.
- The cyclin D-CDK4 complex was disrupted and replaced by a CDK4-p16 complex.
- Binary complexes of cyclin B1-CDC2 and cyclin A-CDK2 remained intact.
- Individual oncoproteins differentially affected PCNA association without altering total cellular levels.
- Low-risk HPV expression had no significant effect on cyclin complexes.
Conclusions:
- HPV type 16 oncoproteins cause gross alterations in cyclin-CDK complexes in preneoplastic cells.
- These alterations in cell cycle regulation are directly linked to the observed loss of genomic stability.
- The findings provide a molecular mechanism connecting HPV infection to the development of cervical cancer and other HPV-associated malignancies.