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AAC-11, a novel cDNA that inhibits apoptosis after growth factor withdrawal
1Department of Pathology, Anatomy, and Cell Biology, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
Abstract:
Many growth factors and cytokines act as cellular survival factors by preventing programmed cell death (apoptosis). However, the specific genes and corresponding proteins that mediate survival are poorly defined. To identify potential survival genes, a cDNA library was prepared from murine fibroblasts and screened by a functional expression cloning approach. A 1023-bp cDNA, AAC-11, was identified that encodes a protein of approximately 25 kDa. The AAC-11 gene shows strong species conservation and is ubiquitously expressed in embryonic and adult tissues with multiple transcripts, as well as in various human tumor cell lines. The predicted protein contains a leucine zipper domain but lacks a DNA-binding domain. BALB/c3T3 fibroblasts that were stably transfected with AAC-11 cDNA were viable in serum-free medium for up to 12 weeks. The protective action of AAC-11 was abolished by mutation of leucines to arginines within the leucine zipper domain. We also isolated a longer AAC-11 cDNA that codes for up to an additional 290 amino-terminal amino acids but did not protect against apoptosis. The cDNA for human AAC-11 was identified and exhibits strong homology with the murine species and retains the leucine zipper domain. Western immunoblots of BALB/c3T3 cells using rabbit anti-AAC-11 polyclonal serum revealed a major native 55-kDa AAC-11 protein and a minor 25-kDa protein corresponding to the long and short forms of AAC-11 cDNA, respectively. In summary, we report a cDNA whose expression supports cell viability after withdrawal of growth factors. The corresponding native protein may function as a novel inhibitor of apoptosis.
Insights
Researchers identified a novel gene, AAC-11, that promotes cell survival by inhibiting apoptosis. This discovery offers potential new strategies for preventing programmed cell death in various tissues and cancer cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Growth factors and cytokines prevent programmed cell death (apoptosis), but the specific genes involved are not well understood.
- Identifying these survival genes is crucial for understanding cell viability and developing therapeutic strategies.
Purpose of the Study:
- To identify novel genes that function as cellular survival factors.
- To characterize the function and properties of a newly identified survival gene, AAC-11.
Main Methods:
- Functional expression cloning of a murine fibroblast cDNA library.
- Stable transfection of BALB/c3T3 fibroblasts with AAC-11 cDNA.
- Site-directed mutagenesis to investigate the role of the leucine zipper domain.
- Isolation and characterization of human AAC-11 cDNA.
- Western immunoblot analysis to detect AAC-11 protein forms.
Main Results:
- A 1023-bp cDNA, AAC-11, was identified, encoding a ~25 kDa protein with a leucine zipper domain.
- AAC-11 expression conferred resistance to apoptosis in serum-free medium.
- The protective effect was dependent on the leucine zipper domain.
- Both murine and human AAC-11 genes were identified, showing conservation and ubiquitous expression.
- Native AAC-11 proteins of 55 kDa and 25 kDa were detected, corresponding to different cDNA forms.
Conclusions:
- AAC-11 is a novel gene that supports cell viability by inhibiting apoptosis.
- The AAC-11 protein, particularly its leucine zipper domain, plays a critical role in cell survival.
- AAC-11 represents a potential therapeutic target for conditions involving excessive cell death.