Chou M M, Hou W, Johnson J, Graham L K, Lee M H, Chen C S, Newton A C, Schaffhausen B S, Toker A
University of Pennsylvania School of Medicine, Department of Cell and Developmental Biology, Philadelphia 19104, USA.
Curr Biol. 1998 Sep 24;8(19):1069-77. doi: 10.1016/s0960-9822(98)70444-0.
Protein kinase C zeta (PKC zeta) is a member of the PKC family of enzymes and is involved in a wide range of physiological processes including mitogenesis, protein synthesis, cell survival and transcriptional regulation. PKC zeta has received considerable attention recently as a target of phosphoinositide 3-kinase (PI 3-kinase), although the mechanism of PKC zeta activation is, as yet, unknown. Recent reports have also shown that the phosphoinositide-dependent protein kinase-1 (PDK-1), which binds with high affinity to the PI 3-kinase lipid product phosphatidylinositol-3,4,5-trisphosphate (Ptdins-3,4,5-P3), phosphorylates and potently activates two other PI 3-kinase targets, the protein kinases Akt/PKB and p70S6K. We therefore investigated whether PDK-1 is the kinase that activates PKC zeta.
In vivo, PI 3-kinase is both necessary and sufficient to activate PKC zeta. PDK-1 phosphorylates and activates PKC zeta in vivo, and we have shown that this is due to phosphorylation of threonine 410 in the PKC zeta activation loop. In vitro, PDK-1 phosphorylates and activates PKC zeta in a Ptdins-3,4,5-P3-enhanced manner. PKC zeta and PDK-1 are associated in vivo, and membrane targeting of PKC zeta renders it constitutively active in cells.
Our results have identified PDK-1 as the kinase that phosphorylates and activates PKC zeta in the PI 3-kinase signaling pathway. This phosphorylation and activation of PKC zeta by PDK-1 is enhanced in the presence of Ptdins-3,4-5-P3. Consistent with the notion that PKCs are enzymes that are regulated at the plasma membrane, a membrane-targeted PKC zeta is constitutively active in the absence of agonist stimulation. The association between PKC zeta and PDK-1 reveals extensive cross-talk between enzymes in the PI 3-kinase signaling pathway.
蛋白激酶Cζ（PKCζ）是蛋白激酶C家族的成员，参与多种生理过程，包括有丝分裂原生成、蛋白质合成、细胞存活和转录调控。PKCζ作为磷酸肌醇3激酶（PI 3激酶）的作用靶点，近来受到了广泛关注，但其激活机制尚不清楚。最近的报道还显示，磷酸肌醇依赖性蛋白激酶-1（PDK-1）与PI 3激酶的脂质产物磷脂酰肌醇-3,4,5-三磷酸（Ptdins-3,4,5-P3）具有高亲和力结合，可磷酸化并有效激活另外两个PI 3激酶作用靶点，即蛋白激酶Akt/PKB和p70S6K。因此，我们研究了PDK-1是否是激活PKCζ的激酶。
在体内，PI 3激酶对于激活PKCζ既是必需的也是充分的。PDK-1在体内可磷酸化并激活PKCζ，我们已证明这是由于PKCζ激活环中的苏氨酸410发生磷酸化所致。在体外，PDK-1以Ptdins-3,4,5-P3增强的方式磷酸化并激活PKCζ。PKCζ与PDK-1在体内相关联，并且PKCζ定位于细胞膜使其在细胞中组成性激活。
我们的结果已确定PDK-1是在PI 3激酶信号通路中磷酸化并激活PKCζ的激酶。在Ptdins-3,4,5-P3存在的情况下，PDK-1对PKCζ的这种磷酸化和激活作用增强。与PKC是在质膜上受到调控的酶这一观点一致，靶向细胞膜的PKCζ在没有激动剂刺激的情况下组成性激活。PKCζ与PDK-1之间的关联揭示了PI 3激酶信号通路中酶之间广泛的相互作用。
