PKC phosphorylates HEXIM1 and regulates P-TEFb activity
PKC phosphorylates HEXIM1 and regulates P-TEFb activity
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PKC 磷酸化 HEXIM1 并调节 P-TEFb 活性
DOI：
10.1093/nar/gks682
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发表时间：
2012-10-01
影响因子：
14.9
通讯作者：
Peterlin, B. Matija
中科院分区：
文献类型：
--
作者：
Fujinaga, Koh;Barboric, Matjaz;Peterlin, B. Matija
正转录延伸因子 b (P-TEFb) 调节 RNA 聚合酶 II 延伸。在细胞中，P-TEFb 在较小的活性状态和较大的非活性状态之间划分。在后者中，HEXIM1 与 7SK snRNA 结合，招募并灭活 7SK snRNP 中的 P-TEFb。多种刺激可以影响这种 P-TEFb 平衡。在本研究中，我们证明蛋白激酶 C (PKC) 磷酸化 HEXIM1 中 158 位 (S158) 的丝氨酸。这种磷酸化的 HEXIM1 蛋白既不结合 7SK snRNA，也不抑制 P-TEFb。佛波酯或 T 细胞抗原受体的结合会激活 PKC 和 T 细胞中发现的组成型活性 (CA) PKCθ 蛋白的表达，从而抑制 7SK snRNP 的形成。所有这些刺激都会增加 P-TEFb 依赖性转录。相反，激酶阴性 PKCθ 和突变型 HEXIM1 (S158A) 蛋白会阻断这些 PKC 激活刺激的作用。这些结果表明 PKC 对 HEXIM1 的磷酸化代表了细胞中 P-TEFb 活性的主要调节步骤。
The positive transcription elongation factor b (P-TEFb) regulates RNA polymerase II elongation. In cells, P-TEFb partitions between small active and larger inactive states. In the latter, HEXIM1 binds to 7SK snRNA and recruits as well as inactivates P-TEFb in the 7SK snRNP. Several stimuli can affect this P-TEFb equilibrium. In this study, we demonstrate that protein kinase C (PKC) phosphorylates the serine at position158 (S158) in HEXIM1. This phosphorylated HEXIM1 protein neither binds to 7SK snRNA nor inhibits P-TEFb. Phorbol esters or the engagement of the T cell antigen receptor, which activate PKC and the expression of the constitutively active (CA) PKCθ protein, which is found in T cells, inhibit the formation of the 7SK snRNP. All these stimuli increase P-TEFb-dependent transcription. In contrast, the kinase-negative PKCθ and the mutant HEXIM1 (S158A) proteins block effects of these PKC-activating stimuli. These results indicate that the phosphorylation of HEXIM1 by PKC represents a major regulatory step of P-TEFb activity in cells.