Papas K K, Sun L, Roos E S, Gounarides J S, Shapiro M, Nalin C M
Core Technologies/Analytics and Bio-NMR US, Novartis Institute for Biomedical Research, Novartis Pharmaceuticals Corporation, Summit, NJ 07901, USA.
FEBS Lett. 1999 Mar 12;446(2-3):338-42. doi: 10.1016/s0014-5793(99)00240-9.
As a result of Myc-dependent transcription of the LDH-A gene, Myc-transformed cells (Rat1-Myc) exhibit increased lactate production rates (LPR) even under aerobic conditions (the Warburg effect). Recently, the increased susceptibility to stress-induced apoptosis associated with Myc transfection has been linked to the overexpression of the LDH-A gene. In this report we demonstrate that the overexpression of the anti-apoptotic protein Bcl-2 in Rat1-Myc cells (Rat1-Myc-Bcl-2) reduces the molar ratio of lactate production to glucose consumption (Y(L/G)). The Bcl-2 induced reduction in Y(L/G) may be associated with reduced expression of the LDH-A gene, or a decrease in LDH-A activity. Stimulation of apoptosis by staurosporine, a protein kinase C inhibitor, reduces the LPR in Rat1-Myc cells in a dose-dependent manner. The staurosporine effect on the LPR is rapid and precedes the execution phase of apoptosis as defined by caspase activation and PARP cleavage. This effect on LPR is completely blocked by Bcl-2 overexpression. Serum starvation alone does not affect the LPR of Rat1-Myc or Rat1-Myc-Bcl-2 cells; however, the effect of staurosporine on the LPR of Rat1-Myc cells is potentiated by serum starvation. These data demonstrate that Bcl-2 overexpression reduces the Y(L/G) in Rat1-Myc cells, perhaps via a reduction in the activity or expression of the LDH-A gene, and this reduction may desensitize cells to some pro-apoptotic stimuli. The reduction in LPR in response to staurosporine may be an early step in the induction of apoptosis in Rat1-Myc cells. By abolishing the reduction in LPR, Bcl-2 may protect Rat1-Myc cells from staurosporine-induced apoptosis. Moreover, the lack of effect by serum starvation on the LPR supports a model in which serum starvation induces apoptosis through a pathway distinct from that of the staurosporine and glucose-dependent apoptotic pathway(s) in Myc-transformed cells.
由于乳酸脱氢酶A（LDH-A）基因的Myc依赖性转录，即使在有氧条件下（瓦伯格效应），Myc转化的细胞（Rat1-Myc）也表现出乳酸产生率（LPR）增加。最近，与Myc转染相关的应激诱导凋亡易感性增加与LDH-A基因的过表达有关。在本报告中，我们证明抗凋亡蛋白Bcl-2在Rat1-Myc细胞（Rat1-Myc-Bcl-2）中的过表达降低了乳酸产生与葡萄糖消耗的摩尔比（Y(L/G)）。Bcl-2诱导的Y(L/G)降低可能与LDH-A基因表达降低或LDH-A活性降低有关。蛋白激酶C抑制剂星形孢菌素刺激凋亡以剂量依赖性方式降低Rat1-Myc细胞中的LPR。星形孢菌素对LPR的作用迅速，且先于由半胱天冬酶激活和聚（ADP-核糖）聚合酶（PARP）裂解所定义的凋亡执行阶段。这种对LPR的作用被Bcl-2过表达完全阻断。单独的血清饥饿不影响Rat1-Myc或Rat1-Myc-Bcl-2细胞的LPR；然而，血清饥饿增强了星形孢菌素对Rat1-Myc细胞LPR的作用。这些数据表明，Bcl-2过表达降低了Rat1-Myc细胞中的Y(L/G)，可能是通过降低LDH-A基因的活性或表达，并且这种降低可能使细胞对某些促凋亡刺激不敏感。响应星形孢菌素的LPR降低可能是Rat1-Myc细胞凋亡诱导的早期步骤。通过消除LPR的降低，Bcl-2可能保护Rat1-Myc细胞免受星形孢菌素诱导的凋亡。此外，血清饥饿对LPR缺乏影响支持了一种模型，即血清饥饿通过与Myc转化细胞中星形孢菌素和葡萄糖依赖性凋亡途径不同的途径诱导凋亡。
