Translocation from nuclei to cytoplasm is necessary for anti A-PCD activity and turnover of the Type II IAP BcBir1

Summary: Type II inhibitors of apoptosis (IAPs) belong to a subgroup of IAP-related proteins. While IAPs are restricted to animals, Type II IAPs are found in other phyla, including fungi. BcBir1, a Type II IAP from Botrytis cinerea has anti apoptotic-like programmed cell death (A-PCD) activity, which is important for pathogenicity of this fungus. Here we report on the role of sub-cellular localization of BcBir1 in protein turnover and anti A-PCD activity. Expression of BcBir1 in Saccharomyces cerevisiae had no effect on sensitivity of the yeast cells to A-PCD-inducing conditions, whereas expression of a truncated N' part reduced sensitivity of the cells to these conditions. The full-length BcBir1 protein was detected only in the yeast nucleus, whereas the N' part was observed both in the nucleus and cytoplasm. In B. cinerea, BcBir1 was mainly nuclear under optimal conditions, whereas under A-PCD-inducing conditions it shuttled to the cytoplasm and then it was completely degraded. Collectively, our results show that anti A-PCD activity of BcBir1 occurs in the cytoplasm, the C′ end mediates regulation of steady state level of BcBir1 in the nucleus, and the N' end mediates anti A-PCD activity as well as fast degradation of BcBir1 in the cytoplasm. Typ II IAP are part of the chromosomal passenger complex (CPC), and have anti-apoptotic function. Cytoplasmic localization is necessary for anti apoptotic activity of BcBir1, a Type II IAP from the fungus Botrytis cinerea. Under non-stress conditions, BcBir1 is mainly nuclear, the C′ part mediates cell cycle and is tightly regulated. Under apoptotic like programmed cell death (A-PCD) conditions, BcBir1 moves to cytoplasm, and the BIR domains function in A-PCD and protein turn over.