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Transformation-defective adenovirus 5 E1A mutants exhibit antioncogenic properties in human BLM melanoma cells
1Institute for Molecular Biology (Cancer Research), University of Essen Medical School, Germany.
Abstract:
Adenoviral E1 A proteins exhibit a strong tumor-suppressive activity in human tumor cells. However, E1 A is capable of transforming rodent and human cells in cooperation with other oncoproteins, such as activated RAS. Thus, the therapeutic use of wild-type E1A harbors the principal risk of enhancing tumor malignancy. This prompted us to construct E1A 13S cDNA-derived mutants that were unable to transform baby mouse kidney cells in cooperation with E1B and to test their tumor-suppressive activity in BLM human melanoma cells. Anchorage-independent growth in soft agar was reduced for those cell lines expressing the E1AdelCR2 mutant, which lacks the entire conserved region 2 (CR2) sequences, or for cells expressing the E1AcR3Ex2 mutant, which contains CR3 plus exon 2 sequences. In contrast, cell lines expressing the entire E1A wild-type (E1AWT) or only the exon 2 sequences (E1AEx2) grew like the parental BLM cells. Moreover, inoculation of nude mice with BLM cells or cells expressing E1AEx2 revealed large tumors after 2 weeks. In contrast, tumors derived from E1AdelCR2- or E1ACR3Ex2-expressing cells exhibited a substantial delay in tumor growth accompanied by a loss of E1A expression in the outgrown tumors. Cell lines expressing E1AWT showed an intermediate phenotype. Thus, expression of CR3 plus exon 2 sequences is sufficient to enhance both the antioncogenic properties and the therapeutic safety of E1A in our system.
Insights
Modified adenoviral E1A proteins show reduced tumor-promoting activity. Specific E1A mutants, E1AdelCR2 and E1ACR3Ex2, demonstrate enhanced tumor suppression and therapeutic safety in melanoma cells.
Area of Science:
- Oncology
- Virology
- Molecular Biology
Background:
- Adenoviral E1A proteins possess tumor-suppressive properties in human cells.
- However, wild-type E1A can promote tumor malignancy when cooperating with oncoproteins like RAS.
- This duality necessitates the development of safer E1A variants for therapeutic applications.
Purpose of the Study:
- To engineer E1A mutants with reduced oncogenic potential.
- To evaluate the tumor-suppressive activity and therapeutic safety of these mutants in human melanoma cells.
Main Methods:
- Construction of E1A 13S cDNA-derived mutants, including E1AdelCR2 (lacking conserved region 2) and E1ACR3Ex2 (containing CR3 plus exon 2).
- Assessment of anchorage-independent growth in soft agar for cell lines expressing different E1A variants.
- Tumorigenicity assays in nude mice using BLM melanoma cells expressing E1A mutants.
Main Results:
- E1AdelCR2 and E1ACR3Ex2 mutants significantly reduced anchorage-independent growth compared to wild-type E1A or E1AEx2.
- Tumor growth was substantially delayed in nude mice inoculated with E1AdelCR2- or E1ACR3Ex2-expressing cells.
- Loss of E1A expression was observed in outgrown tumors from E1AdelCR2 and E1ACR3Ex2 groups, suggesting adaptation.
Conclusions:
- The E1AdelCR2 and E1ACR3Ex2 mutants exhibit potent tumor-suppressive activity in human melanoma cells.
- Expression of CR3 plus exon 2 sequences is sufficient to enhance both antioncogenic properties and therapeutic safety of E1A.
- These findings support the potential of modified E1A proteins as safer oncoterapeutic agents.