Survivin is an inhibitor of apoptosis protein that also plays critical roles in regulating the cell cycle and mitosis. Its prominent expression in essentially all human malignancies, and low or absent expression in most normal tissues, suggests that it would be an ideal target for cancerdirected therapy. Impeding development of safe and effective survivin antagonists for clinical use is a lack of understanding of the molecular mechanisms by which survivin differentially affects apoptosis and cell division, in normal and malignant cells. We show that the diverse functional roles of survivin can be explained, in part, by its heterodimerization with survivin splice variants in tumor cells. Survivin and survivin-DEx3 interact within the mitochondria where they may inhibit mitochondrialdependent apoptosis. If the expression of all survivin forms is eliminated by siRNA transfections, cells undergo both apoptosis and defective cell division. Overall, we provide new insights suggesting that targeting specific survivin isoforms, rather than survivin alone, may selectively and effectively destroy tumor cells. These findings are likely to have a significant impact in the design of biologic agents for clinical therapy.

Survivin is an inhibitor of apoptosis protein (IAP) that is markedly overexpressed in most cancers. We identified two novel functionally divergent splice variants, i.e. non-antiapoptotic survivin-2B and antiapoptotic survivin-deltaEx3. Because survivin-2B might be a naturally occurring antagonist of antiapoptotic survivin variants, we analyzed the subcellular distribution of these proteins. PSORT II analysis predicted a preferential cytoplasmic localization of survivin and survivin-2B, but a preferential nuclear localization of survivin-deltaEx3. GFP-tagged survivin variants confirmed the predicted subcellular localization and additionally revealed a cell cycle-dependent nuclear accumulation of survivin-deltaEx3. Moreover, a bipartite nuclear localization signal found exclusively in survivin-deltaEx3 may support cytoplasmic clearance of survivin-deltaEx3. In contrast to the known association between survivin and microtubules or centromeres during mitosis, no corresponding co-localization became evident for survivin-deltaEx3 or survivin-2B. In conclusion, our study provided data on a differential subcellular localization of functionally divergent survivin variants, suggesting that survivin isoforms may perform different functions in distinct subcellular compartments and distinct phases of the cell cycle.

Survivin, a novel member of the inhibitor of apoptosis protein (IAP) family, reduces the susceptibility of tumor cells to proapoptotic stimuli, thereby promoting tumor cell survival during tumor progression and treatment with anticancer drugs. Recently, we identified 2 novel alternative splice variants of survivin, survivin-2B and survivin-⌬Ex3, which differ in their antiapoptotic properties. Survivin-2B has lost its antiapoptotic potential and may act as a naturally occurring antagonist of antiapoptotic survivin and survivin-⌬Ex3. Because the in vivo expression of these splice variants in human cancer has not been analyzed so far, 57 renal cell carcinomas (RCCs) were explored using quantitative reverse transcriptase polymerase chain reaction. We found that all RCCs express survivin-⌬Ex3, survivin-2B and survivin, the latter being the dominant transcript. When we compared early and intermediate stages with late stages of clear cell RCCs, no significant changes in the expression levels of survivin and survivin-⌬Ex3 became evident. However, a significant decrease was observed for the mRNA ratio between survivin-2B and survivin in late tumor stages (p ‫؍‬ 0.036). Chromophilic/papillary RCCs, which are known to be less aggressive than clear cell RCCs, did not show significantly lower expression levels of antiapoptotic survivin and survivin⌬Ex3, compared with stage-adjusted clear cell RCCs. Our study demonstrates for the first time in vivo expression of functionally different survivin variants and suggests a role of these survivin splice variants in the progression and clinical behavior of human RCCs.

Survivin is a novel member of the inhibitor of apoptosis family and determines the susceptibility of tumour cells to proapoptotic stimuli. Recently, we identified two novel alternative splice variants of survivin, differing in their anti-apoptotic properties: whereas the anti-apoptotic potential of survivin-DEx3 is preserved, survivin-2B has lost its anti-apoptotic potential and may act as a naturally occurring antagonist of survivin. Because the in vivo expression of these alternative splice variants has not been explored so far, we analysed gastric carcinomas of different histological subtypes, grades and stages. Since no antibodies are currently available to determine the novel splice variants, quantitative reverse transcriptase polymerase chain reaction was performed, using RNA samples obtained from 30 different gastric carcinomas. Polymerase chain reactions products were quantified by densitometric evaluation. We found that all gastric carcinomas, irrespective of their histological types, grades or stages, express survivin-DEx3, survivin-2B and survivin, the latter being the dominant transcript. Comparing the disease stages I+II with III+IV, expression of survivin and survivin-DEx3 remained unchanged. In contrast, a significant (P=0.033) stage-dependent decrease in the expression of survivin-2B became evident. Our study demonstrates for the first time the expression of alternative splice variants in gastric carcinomas and provides a first clue to a role of survivin-2B in tumour progression.

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