The SV40 large T antigen-p53 complexes bind and activate the insulin-like growth factor-I promoter stimulating cell...

Area of Science:

• Oncology
• Molecular Biology
• Virology

Background:

• Cellular p53 protein is a critical tumor suppressor inactivated in most human cancers.
• In DNA tumor virus infections, viral tumor antigens (Tag) bind to p53, forming complexes.
• The prevailing view considers Tag-p53 complexes solely as a mechanism for p53 inactivation.

Purpose of the Study:

• To investigate the functional role of Tag-p53 complexes beyond p53 inactivation.
• To elucidate the mechanism by which Tag-p53 complexes contribute to malignant cell growth.
• To explore the regulation of gene transcription by Tag-p53 complexes in human cells.

Main Methods:

• Experiments using primary human cells and SV40-transformed human cells.
• Analysis of Tag-p53 complex formation and its effect on p53 tumor suppressor activities.
• Investigation of Tag-p53 complex binding to the insulin-like growth factor I (IGF-I) promoter with pRb and p300.
• Assessment of transcriptional changes and cell growth following p53 depletion.

Main Results:

• Tag-p53 complexes possess growth-stimulatory activities essential for malignant cell proliferation.
• These complexes regulate IGF-I gene transcription by binding to its promoter with pRb and p300.
• Depletion of p53 causes structural changes in the complex, leading to IGF-I promoter repression and growth arrest.
• p53 acts as an active partner in the Tag-p53 complex, not a passive one.

Conclusions:

• Tag-p53 complexes actively promote malignant cell growth by activating the IGF-I signaling pathway.
• This provides a novel interpretation of DNA tumor virus transformation, highlighting p53's active role.
• The findings challenge the dogma of p53 being merely sequestered and inactivated by viral tumor antigens.