Regulated Binding of Importin-α to Protein Kinase Cδ in Response to Apoptotic Signals Facilitates Nuclear Import
Regulated Binding of Importin-α to Protein Kinase Cδ in Response to Apoptotic Signals Facilitates Nuclear Import
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DOI：
10.1074/jbc.m111.255950
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发表时间：
2011-10-14
影响因子：
4.8
通讯作者：
Reyland, Mary E.
中科院分区：
文献类型：
--
作者：
Adwan, Tariq S.;Ohm, Angela M.;Reyland, Mary E.
PKC δ在细胞凋亡剂的作用下转位到细胞核中，并作为一种有效的细胞死亡信号发挥作用。PKC δ的胞质滞留及其向细胞核的转运对于细胞内稳态是必不可少的，但这些过程是如何调节的知之甚少。我们发现，PKC δ驻留在细胞质中的构象，排除了结合的importin-alpha。非活性状态下PKC δ的结构模型表明，通过C2和催化结构域之间的分子内接触，阻止核定位序列（NLS）与importin-α结合。我们以前已经表明，PKC δ是磷酸化的特定酪氨酸残基在响应凋亡剂。在这里，我们表明，磷酸化的PKC δ在Tyr-64和Tyr-155的结果在构象变化，允许暴露的NLS和结合的importin-alpha。此外，Hsp 90与PKC δ结合的动力学与输入素-α相似，并且是输入素-α与NLS相互作用所必需的。最后，我们阐明了一个保守的PPxxP基序，重叠的NLS，在PKC δ的核排斥的作用。保守的脯氨酸突变为丙氨酸增强了importin-alpha与PKC δ的结合，并诱导其在静息细胞中的核输入。因此，PPxxP基序对于维持有利于PKC δ的细胞飞溅保留的构象是重要的。总之，这项研究建立了一种新的机制，保留在静息细胞的细胞质中的PKC δ和调节其核输入响应凋亡刺激。
PKC delta translocates into the nucleus in response to apoptotic agents and functions as a potent cell death signal. Cytoplasmic retention of PKC delta and its transport into the nucleus are essential for cell homeostasis, but how these processes are regulated is poorly understood. We show that PKC delta resides in the cytoplasm in a conformation that precludes binding of importin-alpha. A structural model of PKC delta in the inactive state suggests that the nuclear localization sequence (NLS) is prevented from binding to importin-alpha through intramolecular contacts between the C2 and catalytic domains. We have previously shown that PKC delta is phosphorylated on specific tyrosine residues in response to apoptotic agents. Here, we show that phosphorylation of PKC delta at Tyr-64 and Tyr-155 results in a conformational change that allows exposure of the NLS and binding of importin-alpha. In addition, Hsp90 binds to PKC delta with similar kinetics as importin-alpha and is required for the interaction of importin-alpha with the NLS. Finally, we elucidate a role for a conserved PPxxP motif, which overlaps the NLS, in nuclear exclusion of PKC delta. Mutagenesis of the conserved prolines to alanines enhanced importin-alpha binding to PKC delta and induced its nuclear import in resting cells. Thus, the PPxxP motif is important for maintaining a conformation that facilitates cytosplasmic retention of PKC delta. Taken together, this study establishes a novel mechanism that retains PKC delta in the cytoplasm of resting cells and regulates its nuclear import in response to apoptotic stimuli.