Tamura Yuki, Simizu Siro, Osada Hiroyuki
Antibiotics Laboratory, Discovery Research Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
FEBS Lett. 2004 Jul 2;569(1-3):249-55. doi: 10.1016/j.febslet.2004.06.003.
Bcl-2 protein play important roles in the regulation of apoptosis. We previously reported that the phosphorylation of Bcl-2 was augmented by treatment with protein phosphatase 2A (PP2A) inhibitor; however, the kinase responsible for Bcl-2 phosphorylation had not yet been identified. In this study, we identified extracellular-signal-regulated kinase (ERK) as the responsible kinase for the phosphorylation of Bcl-2. We also found that the transmembrane region (TM) deleted form of Bcl-2 (Bcl-2DeltaTM), which was unable to localize on the mitochondria was constitutively phosphorylated, whereas wild-type Bcl-2 that localized on the mitochondria, was present in its hypophosphorylated form. The phosphorylation of Bcl-2DeltaTM was retarded by treatment with MAP kinase ERK kinase (MEK) inhibitor and PP2A did not bind to Bcl-2DeltaTM. These observations suggest that Bcl-2DeltaTM is constitutively phosphorylated by ERK, but is not dephosphorylated by PP2A in human tumor cell lines. The phosphorylation of Bcl-2 resulted in a reduction in anti-apoptotic function, implying that dephosphorylation promoted the anti-apoptotic activity of Bcl-2 protein in human tumor cell lines. Thus, the present findings suggest that ERK and PP2A are physiological regulators of Bcl-2 phosphorylation, and these enzymes exert an influence on the anti-apoptotic function of Bcl-2.
Bcl-2蛋白在细胞凋亡调控中发挥重要作用。我们之前报道过，用蛋白磷酸酶2A（PP2A）抑制剂处理可增强Bcl-2的磷酸化；然而，负责Bcl-2磷酸化的激酶尚未确定。在本研究中，我们确定细胞外信号调节激酶（ERK）是负责Bcl-2磷酸化的激酶。我们还发现，无法定位于线粒体的Bcl-2跨膜区（TM）缺失形式（Bcl-2DeltaTM）持续被磷酸化，而定位于线粒体的野生型Bcl-2则以低磷酸化形式存在。用丝裂原活化蛋白激酶ERK激酶（MEK）抑制剂处理可抑制Bcl-2DeltaTM的磷酸化，且PP2A不与Bcl-2DeltaTM结合。这些观察结果表明，在人肿瘤细胞系中，Bcl-2DeltaTM持续被ERK磷酸化，但不被PP2A去磷酸化。Bcl-2的磷酸化导致抗凋亡功能降低，这意味着去磷酸化促进了人肿瘤细胞系中Bcl-2蛋白的抗凋亡活性。因此，本研究结果表明，ERK和PP2A是Bcl-2磷酸化的生理调节因子，这些酶对Bcl-2的抗凋亡功能产生影响。
