The Stability and Expression Level of Bok Are Governed by Binding to Inositol 1,4,5-Trisphosphate Receptors
The Stability and Expression Level of Bok Are Governed by Binding to Inositol 1,4,5-Trisphosphate Receptors
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DOI：
10.1074/jbc.m115.711242
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发表时间：
2016-05-27
影响因子：
4.8
通讯作者：
Wojcikiewicz, Richard J. H.
中科院分区：
文献类型：
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作者：
Schulman, Jacqualyn J.;Wright, Forrest A.;Wojcikiewicz, Richard J. H.
Bok是Bcl-2蛋白家族的一员，该家族控制内在凋亡途径，尽管Bok在该途径中所起的作用尚不清楚。我们以前在培养的细胞系中已经表明，博克与肌醇1，4，5-三磷酸受体（IP（3）Rs）强烈相互作用，这表明它可能有助于IP 3R四聚体的结构完整性或稳定性。在这里，我们报道了Bok在小鼠组织中类似地与IP 3 R相关，基本上所有细胞Bok都与IP 3 R结合，是Bok BH 4结构域的螺旋性质而不是特定氨基酸介导与IP 3 R的结合，Bok通过与IP 3 R结合而显着稳定，未结合的Bok被蛋白酶体泛素化和降解，并且与IP（3）Rs的结合限制了过表达的Bok的促凋亡作用。刺激IP 3R活性、细胞凋亡、磷酸化和内质网应激的药物并没有触发成熟的Bok从IP（3）Rs或Bok降解中解离，表明蛋白酶体介导的Bok降解的作用是破坏新合成的与IP 3R无关的Bok。这种意想不到的蛋白水解机制的存在是为了将Bok限制在与IP（3）Rs结合的范围内，这意味着未结合的Bok对细胞活力有害，并有助于解释目前关于Bok细胞作用的不确定性。
Bok is a member of the Bcl-2 protein family that governs the intrinsic apoptosis pathway, although the role that Bok plays in this pathway is unclear. We have shown previously in cultured cell lines that Bok interacts strongly with inositol 1,4,5-trisphosphate receptors (IP(3)Rs), suggesting that it may contribute to the structural integrity or stability of IP3R tetramers. Here we report that Bok is similarly IP3R-assocated in mouse tissues, that essentially all cellular Bok is IP3R bound, that it is the helical nature of the Bok BH4 domain, rather than specific amino acids, that mediates binding to IP(3)Rs, that Bok is dramatically stabilized by binding to IP(3)Rs, that unbound Bok is ubiquitinated and degraded by the proteasome, and that binding to IP(3)Rs limits the pro-apoptotic effect of overexpressed Bok. Agents that stimulate IP3R activity, apoptosis, phosphorylation, and endoplasmic reticulum stress did not trigger the dissociation of mature Bok from IP(3)Rs or Bok degradation, indicating that the role of proteasome-mediated Bok degradation is to destroy newly synthesized Bok that is not IP3R associated. The existence of this unexpected proteolytic mechanism that is geared toward restricting Bok to that which is bound to IP(3)Rs, implies that unbound Bok is deleterious to cell viability and helps explain the current uncertainty regarding the cellular role of Bok.