Human Embryonic Stem Cells Have Constitutively Active Bax at the Golgi and Are Primed to Undergo Rapid Apoptosis

Abstract

Human embryonic stem (hES) cells activate a rapid apoptotic response after DNA damage but the underlying mechanisms are unknown. A critical mediator of apoptosis is Bax, which is reported to become active and translocate to the mitochondria only after apoptotic stimuli. Here we show that undifferentiated hES cells constitutively maintain Bax in its active conformation. Surprisingly, active Bax was maintained at the Golgi rather than at the mitochondria, thus allowing hES cells to effectively minimize the risks associated with having pre-activated Bax. After DNA damage, active Bax rapidly translocated to the mitochondria by a p53-dependent mechanism. Interestingly, upon differentiation, Bax was no longer active and cells were not acutely sensitive to DNA damage. Thus, maintenance of Bax in its active form is a unique mechanism that can prime hES cells for rapid death, likely to prevent the propagation of mutations during the early critical stages of embryonic development.

Innate Immunity in Pluripotent Human Cells

“…More importantly, several lines of evidence suggest that STAT1 signaling plays a pro-apoptotic role by upregulating the expression of caspases (43)(44)(45) or by repressing pro-survival NF-B signaling (46). Interestingly, hESCs are primed to undergo rapid apoptosis (47). It is thus possible that human pluripotent cells naturally suppress STAT1 phosphorylation to attenuate pro-apoptotic signals.…”

“…As a result, cellular responses to dsRNA and the subsequent response to type I IFNs would be disadvantageous to them. Last, human embryonic stem cells are primed to undergo rapid apoptosis (47). Because there is a well established association between STAT1 activation and apoptosis, it would make sense for human pluripotent cells to down-regulate STAT1 signaling by expressing a high level of SOCS1.…”

Tonic Activation of Bax Primes Neural Progenitors for Rapid Apoptosis through a Mechanism Preserved in Medulloblastoma

“…However, CGNPs responded to ABT 737 with extremely rapid induction of apoptosis, while we previously found that ABT 737 did not induce death in human ES cells (Dumitru et al, 2012). This differential sensitivity highlights key differences in the regulation of Bax in ES cells and CGNPs.…”

“…We have recently demonstrated that embryonic stem (ES) cells regulate apoptosis through a specialized mechanism in which proapoptotic Bax is constitutively activated and sequestered in the Golgi compartment (Dumitru et al, 2012). This mechanism eliminates stem cells with DNA damage.…”

Src Acts as an Effector for Ku70-dependent Suppression of Apoptosis through Phosphorylation of Ku70 at Tyr-530

“…Involvement of Src and Ku70 in Suppression of ApoptosisPrevious studies reported that Ku70 plays a role in suppression of apoptosis (43)(44)(45)(46)(47)(48). To understand the regulation of the ability of Ku70 to suppress apoptosis, we attempted to establish stable Ku70-knockdown cell lines.…”