FKBP38 protects Bcl-2 from caspase-dependent degradation.
The cellular processes that regulate Bcl-2 at the posttranslational levels are as important as those that regulate bcl-2 synthesis. Previously we demonstrated that the suppression of FK506-binding protein 38 (FKBP38) contributes to the instability of Bcl-2 or leaves Bcl-2 unprotected from degradation in an unknown mechanism. Here, we studied the underlying molecular mechanism mediating this process. We first showed that Bcl-2 binding-defective mutants of FKBP38 fail to accumulate Bcl-2 protein. We demonstrated that the FKBP38-mediated Bcl-2 stability is specific as the levels of other anti-apoptotic proteins such as Bcl-X(L) and Mcl-1 remained unaffected. FKBP38 enhanced the Bcl-2 stability under the blockade of de novo protein synthesis, indicating it is posttranslational. We showed that the overexpression of FKBP38 attenuates reduction rate of Bcl-2, thus resulting in an increment of the intracellular Bcl-2 level, contributing to the resistance of apoptotic cell death induced by the treatment of kinetin riboside, an anticancer drug. Caspase inhibitors markedly induced the accumulation of Bcl-2. In caspase-3-activated cells, the knockdown of endogenous FKBP38 by small interfering RNA resulted in Bcl-2 down-regulation as well, which was significantly recovered by the treatment with caspase inhibitors or overexpression of FKBP38. Finally we presented that the Bcl-2 cleavage by caspase-3 is blocked when Bcl-2 binds to FKBP38 through the flexible loop. Taken together, these results suggest that FKBP38 is a key player in regulating the function of Bcl-2 by antagonizing caspase-dependent degradation through the direct interaction with the flexible loop domain of Bcl-2, which contains the caspase cleavage site.
Choi
Bo-Hwa
BH
School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551.
Feng
Lin
L
School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551.
Yoon
Ho Sup
HS
School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551. Electronic address: hsyoon@ntu.edu.sg.
D000241:Adenosine / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D018076:DNA, Complementary / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D031541:Fluorescence Resonance Energy Transfer; D015972:Gene Expression Regulation, Neoplastic; D006367:HeLa Cells; D006801:Humans; D007701:Kinetin / Q000494:pharmacology; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D022021:Tacrolimus Binding Proteins / Q000378:metabolism / Q000502:physiology*
D018076:DNA, Complementary; C471205:FKBP8 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; C527965:kinetin riboside; D053148:Caspase 3; D020169:Caspases; D022021:Tacrolimus Binding Proteins; D000241:Adenosine; D007701:Kinetin