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Published on: October 21, 2012
Interactions between cell growth-regulating domains in the products of the adenovirus E1A oncogene
Abstract:
Among the various biological activities expressed by the products of the adenovirus E1A gene are the abilities to induce cellular DNA synthesis and proliferation in quiescent primary baby rat kidney cells. The functional sites for these activities lie principally within two regions of the E1A proteins: an N-terminal region and a small second region of approximately 20 amino acids further downstream. To study the biological functions of the first domain, we constructed an in-frame deletion of amino acid positions 23 through 107 of the E1A products. This deletion did not impede the ability of the E1A products to transactivate the adenovirus early region 3 promoter in a transient-expression assay in HeLa cells. The ability to induce DNA synthesis in quiescent baby rat kidney cells was, however, lost in the absence of these sequences. Deletion of the small second region induced a form of S phase in which DNA synthesis occurred in the apparent absence of controls required for the cessation of DNA synthesis and progression through the remainder of the cell cycle. These cells did not appear to accumulate in or before G2, and many appeared to have a DNA content greater than that in G2. The functions of both domains are required for production of transformed foci in a ras cooperation assay. Focus formation occurred, however, even when the two domains were introduced on two separate plasmids. This complementation effect appeared to require expression of both of the mutant proteins and did not appear to result merely from recombination at the DNA level.
Insights
Adenovirus E1A gene products stimulate cell DNA synthesis and proliferation. Specific regions within E1A control these functions, with deletions impacting cell cycle progression and transformation.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Adenovirus E1A proteins are known to induce cellular DNA synthesis and proliferation.
- These biological activities are primarily mediated by two distinct functional regions within the E1A proteins.
Purpose of the Study:
- To investigate the specific roles of the two functional domains of adenovirus E1A proteins in inducing cellular DNA synthesis and proliferation.
- To analyze the impact of deletions in these domains on cell cycle regulation and oncogenic transformation.
Main Methods:
- Constructed an in-frame deletion mutant of E1A proteins, removing amino acid positions 23 through 107.
- Assessed the ability of E1A mutants to transactivate the adenovirus early region 3 promoter in HeLa cells.
- Evaluated the induction of DNA synthesis in quiescent baby rat kidney cells.
- Examined cell cycle progression and DNA content in cells expressing E1A deletion mutants.
- Utilized a ras cooperation assay to assess focus formation and cellular transformation.
Main Results:
- Deletion of the N-terminal region (amino acids 23-107) abolished the ability to induce DNA synthesis in quiescent cells, but retained promoter transactivation.
- Deletion of the second small region resulted in uncontrolled S phase, with cells exhibiting abnormal DNA content and progression.
- Both E1A functional domains are necessary for ras-mediated cellular transformation, but can be complemented in trans.
Conclusions:
- The N-terminal domain of adenovirus E1A is crucial for initiating DNA synthesis and cell proliferation.
- The second E1A domain regulates the cessation of DNA synthesis and normal cell cycle progression.
- Coordinated function of both E1A domains is essential for transformation, with functional complementation possible between separate mutant proteins.
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