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Three differentially expressed survivin cDNA variants encode proteins with distinct antiapoptotic functions
E M Conway1, S Pollefeyt, J Cornelissen
1Departments of Medicine and the Institute of Medical Science, University of Toronto, Toronto, Canada. ed.conway@med.kuleuven.ac.be
Abstract:
Survivin is a member of the inhibitor of apoptosis protein (IAP) family that is believed to play a role in oncogenesis. To elucidate further its physiologic role(s), we have characterized the murine survivin gene and complementary DNA (cDNA). The structural organization of the survivin gene, located on chromosome 11E2, is similar to that of its human counterpart, both containing 4 exons. Surprisingly, 3 full-length murine survivin cDNA clones were isolated, predicting the existence of 3 distinct survivin proteins. The longest open reading frame, derived from all 4 exons, predicts a 140-amino acid residue protein, survivin(140), similar to human survivin, which contains a single IAP repeat and a COOH-terminal coiled-coil domain that links its function to the cell cycle. A second cDNA, which retains intron 3, predicts the existence of a 121-amino acid protein, survivin(121) that lacks the coiled-coil domain. Removal of exon 2-derived sequences by alternative pre-messenger RNA (mRNA) splicing results in a third 40-amino acid residue protein, survivin(40), lacking the IAP repeat and coiled-coil structure. Predictably, only recombinant survivin(140) and survivin(121) inhibited caspase-3 activity. All 3 mRNA species were variably expressed during development from 7.5 days postcoitum. Of the adult tissues surveyed, thymus and testis accumulated high levels of survivin(140) mRNA, whereas survivin(121)-specific transcripts were detected in all tissues, while those representing survivin(40) were absent. Human counterparts to the 3 survivin mRNA transcripts were identified in a study of human cells and tissues. The presence of distinct isoforms of survivin that are expressed differentially suggests that survivin plays a complex role in regulating apoptosis. (Blood. 2000;95:1435-1442)
Insights
Murine survivin gene characterization revealed three distinct survivin proteins (isoforms) with varying roles in apoptosis regulation. These survivin isoforms are differentially expressed during development and in adult tissues.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Survivin, an inhibitor of apoptosis protein (IAP) family member, is implicated in oncogenesis.
- Understanding the physiological roles of survivin requires detailed characterization of its gene and protein products.
Purpose of the Study:
- To characterize the murine survivin gene and its complementary DNA (cDNA).
- To identify and describe distinct survivin protein isoforms and their functional properties.
Main Methods:
- Gene and cDNA characterization of murine survivin.
- Analysis of survivin gene structure, including exon-intron organization.
- Isolation and sequencing of survivin cDNA clones.
- Expression analysis of survivin mRNA species during development and in adult tissues.
- Functional assays to assess caspase-3 inhibition by recombinant survivin proteins.
Main Results:
- The murine survivin gene, located on chromosome 11E2, comprises 4 exons, similar to its human counterpart.
- Three distinct survivin cDNA clones were identified, predicting three protein isoforms: survivin(140), survivin(121), and survivin(40).
- Survivin(140) contains an IAP repeat and coiled-coil domain; survivin(121) lacks the coiled-coil domain; survivin(40) lacks both.
- Only survivin(140) and survivin(121) inhibited caspase-3 activity.
- All three mRNA species were expressed during development, with survivin(140) abundant in adult thymus and testis, survivin(121) detected in all tissues, and survivin(40) absent.
- Human counterparts to these survivin transcripts were identified.
Conclusions:
- The murine survivin gene generates at least three distinct protein isoforms through alternative splicing and intron retention.
- Differential expression patterns of survivin isoforms suggest complex roles in regulating apoptosis during development and in adult tissues.
- These findings highlight the intricate mechanisms of survivin function and its potential involvement in oncogenesis.