Voss Oliver H, Kim Sunghan, Wewers Mark D, Doseff Andrea I
Heart and Lung Research Institute and Division of Pulmonary and Critical Care, Department of Molecular Genetics, the Ohio State University, Columbus, Ohio 43210, USA.
J Biol Chem. 2005 Apr 29;280(17):17371-9. doi: 10.1074/jbc.M412449200. Epub 2005 Feb 16.
Monocytes are central components of the innate immune response and normally circulate for a short period of time before undergoing spontaneous apoptosis. During inflammation, differentiation, or oncogenic transformation, the life span of monocytes is prolonged by preventing the activation of the apoptotic program. Here we showed that caspase-3, a cysteine protease required for monocyte apoptosis, is a phosphoprotein. We identified protein kinase Cdelta (PKCdelta) as a member of the protein kinase C family that associates with and phosphorylates caspase-3. The PKCdelta-dependent phosphorylation of caspase-3 resulted in an increase in the activity of caspase-3. This effect of PKCdelta is specific to caspase-3, as evidenced by the absence of similar effects on caspase-9. The activity of PKCdelta precedes the activation of caspase-3 during spontaneous monocyte apoptosis and in monocyte-induced apoptosis. We found that the overexpression of PKCdelta resulted in an increase of apoptosis, whereas its inhibition blocked caspase-3 activity and decreased apoptosis. Our results provided evidence that the PKCdelta-dependent phosphorylation of caspase-3 provided a novel pro-apoptotic mechanism involved in the regulation of monocyte life span.
单核细胞是固有免疫反应的核心组成部分，通常在自发凋亡前短时间内循环。在炎症、分化或致癌转化过程中，单核细胞的寿命通过阻止凋亡程序的激活而延长。在这里，我们表明半胱天冬酶-3（一种单核细胞凋亡所需的半胱氨酸蛋白酶）是一种磷蛋白。我们鉴定出蛋白激酶Cδ（PKCδ）是蛋白激酶C家族的成员，它与半胱天冬酶-3结合并使其磷酸化。PKCδ依赖性的半胱天冬酶-3磷酸化导致半胱天冬酶-3活性增加。PKCδ的这种作用对半胱天冬酶-3具有特异性，这在对半胱天冬酶-9没有类似作用中得到证明。在自发单核细胞凋亡和单核细胞诱导的凋亡过程中，PKCδ的活性先于半胱天冬酶-3的激活。我们发现PKCδ的过表达导致凋亡增加，而其抑制则阻断半胱天冬酶-3活性并减少凋亡。我们的结果提供了证据，表明PKCδ依赖性的半胱天冬酶-3磷酸化提供了一种涉及单核细胞寿命调节的新的促凋亡机制。
