Bcl-2 delays cell cycle through mitochondrial ATP and ROS

Abstract

Bcl-2 inhibits cell proliferation by delaying G/G to S phase entry. We tested the hypothesis that Bcl-2 regulates S phase entry through mitochondrial pathways. Existing evidence indicates mitochondrial adenosine tri-phosphate (ATP) and reactive oxygen species (ROS) are important signals in cell survival and cell death, however, the molecular details of how these 2 processes are linked remain unknown. In this study, 2 cell lines stably expressing Bcl-2, 3T3Bcl-2 and C3HBcl-2, and vector-alone PB controls were arrested in G/G phase by serum starvation and contact inhibition, and ATP and ROS were measured during re-stimulation of cell cycle entry. Both ATP and ROS levels were decreased in G/G arrested cells compared with normal growing cells. In addition, ROS levels were significant lower in synchronized Bcl-2 cells than those in PB controls. After re-stimulation, ATP levels increased with time, reaching peak value 1-3 hours ahead of S phase entry for both Bcl-2 cells and PB controls. Consistent with 2 hours of S phase delay, Bcl-2 cells reached ATP peaks 2 hours later than PB control, which suggests a rise in ATP levels is required for S phase entry. To examine the role of ATP and ROS in cell cycle regulation, ATP and ROS level were changed. We observed that elevation of ATP accelerated cell cycle progression in both PB and Bcl-2 cells, and decrease of ATP and ROS to the level equivalent to Bcl-2 cells delayed S phase entry in PB cells. Our results support the hypothesis that Bcl-2 protein regulates mitochondrial metabolism to produce less ATP and ROS, which contributes to S phase entry delay in Bcl-2 cells. These findings reveal a novel mechanistic basis for understanding the link between mitochondrial metabolism and tumor-suppressive function of Bcl-2.

Downregulation of cyclooxygenase‑1 stimulates mitochondrial apoptosis through the NF‑κB signaling pathway in colorectal cancer cells

“…COX-1 knockdown in the present study induced caspase-dependent apoptosis with upregulation of cytosolic cytochrome c, caspase-9 and -3 activation, and PARP cleavage, along with downregulation of mitochondria cytochrome c, which indicated that cytochrome c leaks from the mitochondria to the cytosol. In addition, Bcl-2 family members are key factors in mitochondrial function, cell cycle and apoptosis (23,24). In the present study, it was also revealed that downregulation of COX-1 in CRC cells significantly decreased anti-apoptotic Bcl-2 expression and increased pro-apoptotic Bax expression, with deleterious mitochondrial function.…”

<p>Polyphyllin VI Induces Apoptosis and Autophagy via Reactive Oxygen Species Mediated JNK and P38 Activation in Glioma</p>

“…38,39 Consequently, targeting ROS has been considered a promising strategy for anti-tumor therapy, since it can stimulate or inhibit different cell signaling pathways to induce apoptosis and autophagy thereby inhibit tumor growth. 40,41 Additionally, high levels of ROS can induce cell cycle arrest. In the present study, PPVI-induced cell death paralleled the levels of ROS.…”

PGC-1α coordinates with Bcl-2 to control cell cycle in U251 cells through reducing ROS

“…This is consistent with the fact that Bcl-2’s anti-tumor function was activated only in G 0 /G 1 stage after serum starvation but not in normal growing status (Janumyan et al, 2008). Taken together, these results strongly indicate that ROS might play a role in Bcl-2’s cell cycle function (Du et al, 2017). Mitochondrial OXPHOS impinges on many cellular functions, including energy allocation and programmed cell death.…”

“…Cells transfected with the empty vector served as the control (referred to as 3T3PB in this paper). We have reported that PGC-1α inhibits the cell cycle progress, and Bcl-2 exerts its anti-tumor function by delay cell cycle progress only at the G 0 /G 1 stage (Fu et al, 2016; Du et al, 2017; Janumyan et al, 2008). Therefore, here, we first synchronize cells at the G0/G1 stage by serum starvation, then compare PGC-1α expression in 3T3Bcl-2 cells with 3T3PB cells.…”