Differential subcellular localization of functionally divergent survivin splice variants

Abstract

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.

Characterisation of the anti-apoptotic function of survivin-ΔEx3 during TNFα−mediated cell death

“…These data confirm our hypothesis that survivinDEx3 is an anti-apoptotic factor, functioning like vIAP (Wang et al, 2002). It is known that survivin-DEx3 is overexpressed in a number of tumours, and may contribute to tumourigenesis by protecting malignant cells from apoptosis by undefined mechanisms (Mahotka et al, 1999(Mahotka et al, , 2002a(Mahotka et al, , 2002b. Our data provide further insights into these mechanisms.…”

“…A nuclear localisation signal (NLS) is embedded in its unique C terminus (Mahotka et al, 2002b). Survivin-DEx3 is also distributed in the cytosol, with a fraction located at the mitochondria in HeLa and Daoy cells (Rodriguez et al, 2002;Mahotka et al, 2002b;Caldas et al, 2005;You et al, 2006). Survivin and survivin-DEx3 form heterodimers, thereby regulating the balance between proliferation and cell death .…”

The effects of knockdown of wild-type survivin, survivin-2B or survivin-Δ3 on the radiosensitization in a soft tissue sarcoma cells in vitro under different oxygen conditions

“…Because of the different subcellular localization of splice variant survivin-D3 (nucleus) and survivin-2B (cytoplasm), it was suggested that they may play different roles in cell cycle and apoptosis. 34,35 Thus, one mechanism for survivin-2B-related induction of apoptosis is to block mitochondrial-localized survivin delivery into the cytosol by their physical interaction. 10,29 Therefore, the knockdown of survivin-2B may release wild-type survivin and inhibit apoptosis after a stimulus like irradiation.…”

“…33 It has been suggested that survivin-D3 has antiapoptotic activity similar to survivin, whereas survivin-2B might have a pro-apoptotic function. 30,34 A model proposed that survivin-2B or survivin-D3 may heterodimerize with survivin to modulate the role of survivin in control of mitosis and/or apoptosis and change the normal localization of the survivin isoforms. 33,34 Recently, an inhibitory function of survivin and survivin-D3 for mitochondrial-dependent apoptosis was determined.…”

“…30,34 A model proposed that survivin-2B or survivin-D3 may heterodimerize with survivin to modulate the role of survivin in control of mitosis and/or apoptosis and change the normal localization of the survivin isoforms. 33,34 Recently, an inhibitory function of survivin and survivin-D3 for mitochondrial-dependent apoptosis was determined. 35 Noton et al 36 demonstrated that neither survivin-2B nor survivin-D3 has an essential function during mitosis or can rescue cell growth restrictions caused by wild-type survivin depletion.…”