Education & Certifications
Ph.D., Institute of Biochemistry and Cell Biology, Chinese Academy of Science, Molecular and Cell Biology (2007)
In mammalian embryos, embryonic stem cells (ESCs) and induced pluripotent cells, a shortened G1 phase is correlated with the pluripotent state. To molecularly define this phase, we compared transcripts from the shortened G1 of human ESCs (hESCs) with those from the longer G1 of derived endoderm. We identified JMJD5, a JmjC (Jumonji C) domain containing protein that, when depleted in hESCs, causes the accumulation of cells in G1 phase, loss of pluripotency, and subsequent differentiation into multiple lineages, most prominently ectoderm and trophectoderm. Furthermore, we demonstrate that the JMJD5 phenotype is caused by the upregulation of CDKN1A (p21), as depleting both JMJD5 and CDKN1A (p21) in hESCs restores the rapid G1 phase and rescues the pluripotent state. Overall, we provide genetic and biochemical evidence that the JMJD5/CDKN1A (p21) axis is essential to maintaining the short G1 phase which is critical for pluripotency in hESCs. Stem Cells 2014;32:2098-2110.
View details for DOI 10.1002/stem.1724
View details for PubMedID 24740926
We previously showed that FAM29A, a spindle-associated protein, promotes microtubule-dependent microtubule amplification through its interaction with and recruitment of NEDD1, the targeting subunit of the gamma-tubulin ring complex. We report here that FAM29A is regulated by Plk1, a kinase essential for spindle assembly and its bipolarity. Plk1, FAM29A and NEDD1 form three separate complexes in vivo, not one single complex. Plk1 recruits FAM29A to spindle microtubules, which, in turn, targets NEDD1 to the spindle. Plk1 also recruits NEDD1 to the centrosomes, probably through a Plk1-NEDD1 interaction, but this interaction does not contribute to targeting NEDD1 to the spindle. Altering intracellular levels of FAM29A changes the distribution of NEDD1 between the centrosomes and the spindle, indicating that FAM29A controls the partition of NEDD1 between these two mitotic structures. Thus, Plk1 promotes microtubule nucleation from the centrosomes through a FAM29A-independent pathway and from the spindle through a FAM29A-dependent pathway. FAM29A controls the relative contributions of these two pathways to microtubule polymerization during mitosis.
View details for DOI 10.1242/jcs.048223
View details for Web of Science ID 000268179400019
View details for PubMedID 19596795
View details for PubMedCentralID PMC2909321
Efficient assembly of a mitotic spindle and stable attachment of microtubules (k-fibers) to kinetochores are essential for the high fidelity of chromosome segregation. Both spindle assembly and k-fiber formation require robust nucleation and polymerization of microtubules mediated by the gamma-tubulin ring complex (gammaTuRC). It has been well established that centrosomes and chromatin are the two centers for microtubule nucleation. We recently demonstrate a third mechanism for microtubule nucleation and polymerization, in which the existing microtubules in the spindle act as templates to promote the formation of new microtubules. We showed that a novel spindle-associated protein, FAM29A, plays a critical role in this microtubule-dependent microtubule amplification. FAM29A associates with spindle microtubules and directly interacts with and recruits NEDD1, the targeting subunit of gammaTuRC. Spindle-associated gammaTuRC then promotes microtubule nucleation required for spindle assembly and k-fiber formation. This novel microtubule amplification pathway provides a powerful mechanism to control the local cytoskeleton structures independent of centrosomes and chromatin. We speculate that microtubule amplification not only functions in mitosis, but may also act in other physiological processes to re-enforce existing cytoskeleton structures.
View details for PubMedID 19641730
View details for PubMedCentralID PMC2717520
Mitotic spindle mediates the segregation of chromosomes in the cell cycle and the proper function of the spindle is crucial to the high fidelity of chromosome segregation and to the stability of the genome. Nucleation of microtubules (MTs) from centrosomes and chromatin represents two well-characterized pathways essential for the assembly of a dynamic spindle in mitosis. Recently, we identified a third MT nucleation pathway, in which existing MTs in the spindle act as a template to promote the nucleation and polymerization of MTs, thereby efficiently amplifying MTs in the spindle. We will review here our current understanding on the molecular mechanism, the physiological function and the cell-cycle regulation of MT amplification.
View details for DOI 10.1007/s10059-009-0014-2
View details for Web of Science ID 000263383200001
View details for PubMedID 19214428
Microtubules (MTs) are nucleated from centrosomes and chromatin. In addition, MTs can be generated from preexiting MTs in a gamma-tubulin-dependent manner in yeast, plant, and Drosophila cells, although the underlying mechanism remains unknown. Here we show the spindle-associated protein FAM29A promotes MT-dependent MT amplification and is required for efficient chromosome congression and segregation in mammalian cells. Depletion of FAM29A reduces spindle MT density. FAM29A is not involved in the nucleation of MTs from centrosomes and chromatin, but is required for a subsequent increase in MT mass in cells released from nocodazole. FAM29A interacts with the NEDD1-gamma-tubulin complex and recruits this complex to the spindle, which, in turn, promotes MT polymerization. FAM29A preferentially associates with kinetochore MTs and knockdown of FAM29A reduces the number of MTs in a kinetochore fiber, activates the spindle checkpoint, and delays the mitotic progression. Our study provides a biochemical mechanism for MT-dependent MT amplification and for the maturation of kinetochore fibers in mammalian cells.
View details for DOI 10.1083/jcb.200807046
View details for Web of Science ID 000261232000010
View details for PubMedID 19029337
View details for PubMedCentralID PMC2592839
Recently, acetylcholinesterase (AChE) has been studied as an important apoptosis regulator. We previously showed that cellular calcium mobilization upregulated AChE expression by modulating promoter activity and mRNA stability. In this study, we have identified a potential Smad3/4 binding element, TGCCAGACA, located within the -601 to -571 bp fragment of the AChE promoter, as an important calcium response motif. Smad2/3 and Smad4 were shown to bind this element. Overexpression of human Smad3 increased AChE transcription activity in a dose-dependent manner in HeLa cells, whereas dominant-negative Smad3 blocked this activation. Upon A23187 and thapsigargin treatment, nuclear Smad3 accumulation was observed, an effect that was blocked by the intracellular Ca(2+) chelator BAPTA-AM. Calcium-induced AChE transcriptional activation was significantly blocked when the nuclear localization signal of Smad3 was destroyed. Taken together, our data suggest Smad3 can regulate AChE transcriptional activation following calcium-induced nuclear accumulation.
View details for DOI 10.1007/s00018-009-0037-z
View details for Web of Science ID 000267680500014
View details for PubMedID 19468687
We previously reported that the expression of acetylcholinesterase during A23187-induced apoptosis of HeLa cells is regulated by Ca(2+) mobilization through the modulation of mRNA stability and acetylcholinesterase promoter activity. Transactivation of the human acetylcholinesterase promoter by A23187 was partially mediated by the distal CCAAT motif within the -1270 to -1248 fragment of the human acetylcholinesterase promoter, which was bound by the CCAAT binding factor (CBF/NF-Y). In the present study, we investigated the molecular mechanisms by which CBF/NF-Y regulates A23187-induced activation of the human acetylcholinesterase promoter. The results indicate that CBF/NF-Y binding to the distal CCAAT motif suppresses the promoter activity. Electrophoretic mobility shift assays (EMSAs) demonstrated that binding of CBF/NF-Y to the distal CCAAT motif decreased after A23187 treatment. Our results suggest that acetylcholinesterase promoter activation during A23187-induced HeLa cell apoptosis may result partly from the dissociation of CBF/NF-Y from the distal CCAAT motif in the acetylcholinesterase promoter, reversing this suppression.
View details for DOI 10.1016/j.bbagen.2007.07.007
View details for Web of Science ID 000250187600006
View details for PubMedID 17728068
We previously reported that acetylcholinesterase plays a critical role in apoptosis and its expression is regulated by Ca(2+) mobilization. In the present study, we show that activated calpain, a cytosolic calcium-activated cysteine protease, and calcineurin, a calcium-dependent protein phosphatase, regulate acetylcholinesterase expression during A23187-induced apoptosis. The calpain inhibitor, calpeptin, and the calcineurin inhibitors, FK506 and cyclosporine A, inhibited acetylcholinesterase expression at both mRNA and protein levels and suppressed the activity of the human acetylcholinesterase promoter. In contrast, overexpression of constitutively active calcineurin significantly activated the acetylcholinesterase promoter. Furthermore, we identify a role for the transcription factor NFAT (nuclear factor of activated T cells), a calcineurin target, in regulating the acetylcholinesterase promoter during ionophore-induced apoptosis. Overexpression of human NFATc3 and NFATc4 greatly increased the acetylcholinesterase promoter activity in HeLa cells treated with A23187. Overexpression of constitutive nuclear NFATc4 activated the acetylcholinesterase promoter independent of A23187, whereas overexpression of dominant-negative NFAT blocked A23187-induced acetylcholinesterase promoter activation. These results indicate that calcineurin mediates acetylcholinesterase expression during apoptosis.
View details for DOI 10.1016/j.bbamcr.2007.01.008
View details for Web of Science ID 000245784700014
View details for PubMedID 17320203
Acetylcholinesterase (AChE) is thought to play an important role during apoptosis. Our results showed that H2O2 induced AChE activity, a functional marker in apoptosis, increases in neuronal-like PC12 cells. Glutathione, which is involved in cellular redox homeostasis, inhibited the increase of AChE activity, suggesting that reactive oxygen species (ROS) play a key role in this process. Further investigation showed that the elevation of AChE was observed after the degradation of Akt, release of cytochrome c from mitochondria into the cytosol, and activation of caspase family members. When nerve growth factor (NGF) was present, with the maintenance of Akt level, the elevation of AChE, the cytochrome c diffusion, as well as apoptosis were markedly attenuated in H2O2-treated PC12 cells. However, wortmannin, an inhibitor of the PI3K/Akt pathway, accelerated the apoptosis and increased the AChE activity. The overexpression of constitutively activated Akt, which is a downstream signalling element of the NGF receptor TrkA, delayed mitochondrial collapse and inhibited elevation of AChE activity. Thus, NGF prevented apoptosis and elevation of AChE activity by activating the Akt pathway and stabilizing the function of mitochondria.
View details for DOI 10.1111/j.1745-7270.2007.00247.x
View details for Web of Science ID 000243881000007
View details for PubMedID 17213958
We have recently reported that acetylcholinesterase expression was induced during apoptosis in various cell types. In the current study we provide evidence to suggest that the induction of acetylcholinesterase expression during apoptosis is regulated by the mobilization of intracellular Ca(2+). During apoptosis, treatment of HeLa and MDA-MB-435s cells with the calcium ionophore A23187 resulted in a significant increase in acetylcholinesterase mRNA and protein levels. Chelation of intracellular Ca(2+) by BAPTA-AM (1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester), an intracellular Ca(2+) chelator, inhibited acetylcholinesterase expression. A23187 also enhanced the stability of acetylcholinesterase mRNA and increased the activity of acetylcholinesterase promoter, effects that were blocked by BAPTA-AM. Perturbations of cellular Ca(2+) homeostasis by thapsigargin resulted in the increase of acetylcholinesterase expression as well as acetylcholinesterase promoter activity during thapsigargin induced apoptosis in HeLa and MDA-MB-435s cells, effects that were also inhibited by BAPTA-AM. We further demonstrated that the transactivation of the human acetylcholinesterase promoter by A23187 and thapsigargin was partially mediated by a CCAAT motif within the -1270 to -1248 fragment of the human acetylcholinesterase promoter. This motif was able to bind to CCAAT binding factor (CBF/NF-Y). These results strongly suggest that cytosolic Ca(2+) plays a key role in acetylcholinesterase regulation during apoptosis induced by A23187 and thapsigargin.
View details for DOI 10.1016/j.biocel.2006.06.012
View details for Web of Science ID 000241963000009
View details for PubMedID 17000130