34 results on '"X Shawn Liu"'
Search Results
2. Supplementary Figure 3 from Plk1 Phosphorylation of Orc2 and Hbo1 Contributes to Gemcitabine Resistance in Pancreatic Cancer
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Xiaoqi Liu, Elena G. Chiorean, Tony Hazbun, Timothy L. Ratliff, Stephen F. Konieczny, Bennett D. Elzey, Shihuan Kuang, Steven J. Rice, X. Shawn Liu, and Bing Song
- Abstract
PDF file - 67K, Orc2-A and Hbo1-A mutant cells are sensitive to gemcitabine treatment
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- 2023
3. Data from Plk1 Phosphorylation of Orc2 and Hbo1 Contributes to Gemcitabine Resistance in Pancreatic Cancer
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Xiaoqi Liu, Elena G. Chiorean, Tony Hazbun, Timothy L. Ratliff, Stephen F. Konieczny, Bennett D. Elzey, Shihuan Kuang, Steven J. Rice, X. Shawn Liu, and Bing Song
- Abstract
Although gemcitabine is the standard chemotherapeutic drug for treatment of pancreatic cancer, almost all patients eventually develop resistance to this agent. Previous studies identified Polo-like kinase 1 (Plk1) as the mediator of gemcitabine resistance, but the molecular mechanism remains unknown. In this study, we show that Plk1 phosphorylation of Orc2 and Hbo1 mediates the resistance to gemcitabine. We show that the level of Plk1 expression positively correlates with gemcitabine resistance, both in pancreatic cancer cells and xenograft tumors. Overexpression of Plk1 increases gemcitabine resistance, while inhibition of Plk1 sensitizes pancreatic cancer cells to gemcitabine treatment. To validate our findings, we show that inhibition of Plk1 sensitizes tumors to gemcitabine treatment in a mouse xenograft study. Mechanistically, we find that Plk1 phosphorylation of Orc2 maintains DNA replication on gemcitabine treatment. Furthermore, Plk1 phosphorylation of Hbo1 transcriptionally increases cFos expression and consequently elevates its target multidrug resistance 1 (MDR1), which was previously reported to confer chemotherapeutic drug resistance. Knockdown of cFos or MDR1 sensitizes gemcitabine-resistant cells to gemcitabine treatment. Finally, pancreatic cancer cells expressing Plk1-unphosphorylatable mutants of Orc2 or Hbo1 are more sensitive to gemcitabine than cells expressing wild-type Orc2 or Hbo1. In short, our study provides a mechanism for Plk1-mediated gemcitabine resistance, suggesting that Plk1 is a promising target for treatment of gemcitabine-resistant pancreatic cancer. Mol Cancer Ther; 12(1); 58–68. ©2012 AACR.
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- 2023
4. Supplementary Figure 2 from Plk1 Phosphorylation of Orc2 and Hbo1 Contributes to Gemcitabine Resistance in Pancreatic Cancer
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Xiaoqi Liu, Elena G. Chiorean, Tony Hazbun, Timothy L. Ratliff, Stephen F. Konieczny, Bennett D. Elzey, Shihuan Kuang, Steven J. Rice, X. Shawn Liu, and Bing Song
- Abstract
PDF file - 102K, Gemcitabine-resistant tumors are sensitive to inhibition of Plk1
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- 2023
5. Supplementary Table 1 from Plk1 Phosphorylation of Orc2 and Hbo1 Contributes to Gemcitabine Resistance in Pancreatic Cancer
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Xiaoqi Liu, Elena G. Chiorean, Tony Hazbun, Timothy L. Ratliff, Stephen F. Konieczny, Bennett D. Elzey, Shihuan Kuang, Steven J. Rice, X. Shawn Liu, and Bing Song
- Abstract
PDF file - 17K, The IC50 values of Gemcitabine in Pancreatic cell lines
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- 2023
6. Supplementary Figure 1 from Plk1 Phosphorylation of Orc2 and Hbo1 Contributes to Gemcitabine Resistance in Pancreatic Cancer
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Xiaoqi Liu, Elena G. Chiorean, Tony Hazbun, Timothy L. Ratliff, Stephen F. Konieczny, Bennett D. Elzey, Shihuan Kuang, Steven J. Rice, X. Shawn Liu, and Bing Song
- Abstract
PDF file - 44K, Inhibition of Plk1 sensitizes cells to gemcitabine
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- 2023
7. Supplementary Methods and Figure Legends from Plk1 Phosphorylation of Orc2 and Hbo1 Contributes to Gemcitabine Resistance in Pancreatic Cancer
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Xiaoqi Liu, Elena G. Chiorean, Tony Hazbun, Timothy L. Ratliff, Stephen F. Konieczny, Bennett D. Elzey, Shihuan Kuang, Steven J. Rice, X. Shawn Liu, and Bing Song
- Abstract
PDF file - 88K
- Published
- 2023
8. Rett Syndrome astrocytes disrupt neuronal activity and cerebral organoid development through transfer of dysfunctional mitochondria
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Danielle L Tomasello, M. Inmaculada Barrasa, David Mankus, Katia I Alarcon, Abigail KR Lytton-Jean, X. Shawn Liu, and Rudolf Jaenisch
- Abstract
Studies on the function of Methyl CpG binding protein 2 (MECP2) and the consequence ofMECP2deficiency and duplication have largely focused on neurons. The function of MECP2 in human glia, along with the comprehensive understanding of glial function in neurodevelopmental disorders, is much less understood. Using female and male human embryonic stem cell (hESC) lines to modelMECP2loss-of-function (LOF) in Rett Syndrome (RTT) in the developing brain, we investigated the molecular underpinnings of astrocyte (AST) development and dysfunction, and the mechanisms by which AST contribute to neuronal activity. Here we show that hESC-derived RTT ASTs have fewer mitochondria yet similar levels of reactive oxygen species compared to isogenic controls (CTR). We identified significantly diminished mitochondrial respiration that was compensated by increased glycolysis, and that the molecular mechanism behind mitochondrial dysfunction were reduced key proteins around the tricarboxylic acid (TCA) cycle and electron transport chain (ETC). We found an increased abundance of cytosolic amino acids in RTT ASTs under basal conditions that was readily depleted when energy demands were increased. We determined that RTT AST can donate their mitochondria to hESC-derived cortical neurons, and that isolated mitochondria from RTT ASTs are sufficient to cause significant changes to neuronal activity, increasing local field potentials to a hyperexcitable state. To examine mitochondrial health in the developing brain, we derived cerebral organoids. Ultrastructural analysis indicated that mitochondria from RTT hESC-derived organoids were significantly smaller compared to mitochondria from CTR organoids, indicating decreased connectivity and function, and this phenotype was stronger in glia compared to neurons. Using a multiomics epigenetics approach, we found hallmarks of RTT developmental delay and glial specific gene expression changes that corroborate altered energy metabolism and mitochondrial dysfunction. Based on these results, we propose that release of dysfunctional mitochondria from RTT ASTs to neurons furthers pathophysiology of the syndrome.
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- 2023
9. Multiplex epigenome editing of MECP2 to rescue Rett syndrome neurons
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Junming Qian, Xiaonan Guan, Bing Xie, Chuanyun Xu, Jacqueline Niu, Xin Tang, Charles H. Li, Henry M. Colecraft, Rudolf Jaenisch, and X. Shawn Liu
- Subjects
General Medicine - Abstract
Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by loss-of-function heterozygous mutations of methyl CpG-binding protein 2 ( MECP2 ) on the X chromosome in young females. Reactivation of the silent wild-type MECP2 allele from the inactive X chromosome (Xi) represents a promising therapeutic opportunity for female patients with RTT. Here, we applied a multiplex epigenome editing approach to reactivate MECP2 from Xi in RTT human embryonic stem cells (hESCs) and derived neurons. Demethylation of the MECP2 promoter by dCas9-Tet1 with target single-guide RNA reactivated MECP2 from Xi in RTT hESCs without detectable off-target effects at the transcriptional level. Neurons derived from methylation-edited RTT hESCs maintained MECP2 reactivation and reversed the smaller soma size and electrophysiological abnormalities, two hallmarks of RTT. In RTT neurons, insulation of the methylation-edited MECP2 locus by dCpf1-CTCF (a catalytically dead Cpf1 fused with CCCTC-binding factor) with target CRISPR RNA enhanced MECP2 reactivation and rescued RTT-related neuronal defects, providing a proof-of-concept study for epigenome editing to treat RTT and potentially other dominant X-linked diseases.
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- 2023
10. Contributors
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Taqveema Ali, Nafisa H. Balasinor, Taylor S. Campbell, Akin Cayir, Keran Chen, Laura R. Cortes, Chloe M. Farrell, Nancy G. Forger, Zhengying He, Lauren E. Hood, Jiachun Jiang, Kirtan Kaur, Jyotdeep Kaur, Shagufta Khan, Jonna M. Leyrer-Jackson, Simeiyun Liu, X. Shawn Liu, Steven J. Millership, Rakesh K. Mishra, Kumari Nishi, M. Foster Olive, Beenish Rahat, Valerie Jane Robert, Tania L. Roth, Guy A. Rutter, Joshua F. Shaffer, Renuka Sharma, Upasna Sharma, Surabhi Srivastava, Zoe Stamoulis, Minglu Wang, and Vanessa Yu
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- 2023
11. The Emerging field of epigenetic editing: implication for translational purposes for diseases with developmental origin
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Minglu Wang and X. Shawn Liu
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- 2023
12. Multiplex Epigenome Editing ofMECP2to Rescue Rett Syndrome Neurons
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Junming Qian, Xiaonan Guan, Bing Xie, Chuanyun Xu, Jacqueline Niu, Xin Tang, Charles H. Li, Henry M. Colecraft, Rudolf Jaenisch, and X. Shawn Liu
- Abstract
Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by loss-of-function heterozygous mutations of Methyl CpG-binding Protein 2 (MECP2) on the X chromosome in girls. Reactivation of the silent wild-typeMECP2allele from the inactive X chromosome (Xi) represents a promising therapeutic opportunity for female patients with RTT. Here, we applied a multiplex epigenome editing approach to reactivate MECP2 from Xi in RTT human embryonic stem cells (hESCs) and derived neurons. Demethylation of theMECP2promoter by dCas9-Tet1 with target sgRNA reactivated MECP2 from Xi in RTT hESCs without detectable off-target effects at the transcriptional level. Neurons derived from methylation-edited RTT hESCs maintained MECP2 reactivation and reversed the smaller soma size and electrophysiological abnormalities, two hallmarks of RTT. In RTT neurons, insulation of the methylation editedMECP2locus by dCpf1-CTCF with target CRISPR RNA enhanced MECP2 reactivation and rescued RTT-related neuronal defects, providing a proof-of-concept study for epigenome editing to treat RTT and potentially other dominant X-linked diseases.One-Sentence SummaryReactivation ofMECP2from the inactive X chromosome by multiplex epigenome editing rescues Rett syndrome neurons in vitro.
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- 2022
13. Hippocampal cells segregate positive and negative engrams
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Monika Shpokayte, Olivia McKissick, Xiaonan Guan, Bingbing Yuan, Bahar Rahsepar, Fernando R. Fernandez, Evan Ruesch, Stephanie L. Grella, John A. White, X. Shawn Liu, and Steve Ramirez
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Optogenetics ,Memory ,Medicine (miscellaneous) ,Prefrontal Cortex ,General Agricultural and Biological Sciences ,Amygdala ,Hippocampus ,General Biochemistry, Genetics and Molecular Biology - Abstract
The hippocampus is involved in processing a variety of mnemonic computations specifically the spatiotemporal components and emotional dimensions of contextual memory. Recent studies have demonstrated cellular heterogeneity along the hippocampal axis. The ventral hippocampus has been shown to be important in the processing of emotion and valence. Here, we combine transgenic and all-virus based activity-dependent tagging strategies to visualize multiple valence-specific engrams in the vHPC and demonstrate two partially segregated cell populations and projections that respond to appetitive and aversive experiences. Next, using RNA sequencing and DNA methylation sequencing approaches, we find that vHPC appetitive and aversive engram cells display different transcriptional programs and DNA methylation landscapes compared to a neutral engram population. Additionally, optogenetic manipulation of tagged cell bodies in vHPC is not sufficient to drive appetitive or aversive behavior in real-time place preference, stimulation of tagged vHPC terminals projecting to the amygdala and nucleus accumbens (NAc), but not the prefrontal cortex (PFC), showed the capacity drive preference and avoidance. These terminals also were able to change their capacity to drive behavior. We conclude that the vHPC contains genetically, cellularly, and behaviorally segregated populations of cells processing appetitive and aversive memory engrams.
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- 2022
14. MeCP2 links heterochromatin condensates and neurodevelopmental disease
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Xin Tang, Gary LeRoy, Alicia V. Zamudio, Alessandra Dall’Agnese, Richard A. Young, Emile Wogram, Jurian Schuijers, Nancy M. Hannett, Jonathan E. Henninger, Tenzin Lungjangwa, Tong Ihn Lee, Jesse M. Platt, Eliot L. Coffey, Ozgur Oksuz, X. Shawn Liu, Styliani Markoulaki, Charles H. Li, Lena K. Afeyan, Rudolf Jaenisch, and Devon S. Svoboda
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congenital, hereditary, and neonatal diseases and abnormalities ,Euchromatin ,Methyl-CpG-Binding Protein 2 ,Heterochromatin ,Rett syndrome ,Adaptive Immunity ,medicine.disease_cause ,Article ,MECP2 ,Mice ,03 medical and health sciences ,0302 clinical medicine ,Neurodevelopmental disorder ,Intellectual Disability ,mental disorders ,Rett Syndrome ,medicine ,Animals ,Constitutive heterochromatin ,Epigenetics ,030304 developmental biology ,Neurons ,0303 health sciences ,Mutation ,Multidisciplinary ,Chemistry ,medicine.disease ,Immunity, Innate ,nervous system diseases ,Cell biology ,Phenotype ,Female ,030217 neurology & neurosurgery - Abstract
Methyl CpG binding protein 2 (MeCP2) is a key component of constitutive heterochromatin, which is crucial for chromosome maintenance and transcriptional silencing1–3. Mutations in the MECP2 gene cause the progressive neurodevelopmental disorder Rett syndrome3–5, which is associated with severe mental disability and autism-like symptoms that affect girls during early childhood. Although previously thought to be a dense and relatively static structure1,2, heterochromatin is now understood to exhibit properties consistent with a liquid-like condensate6,7. Here we show that MeCP2 is a dynamic component of heterochromatin condensates in cells, and is stimulated by DNA to form liquid-like condensates. MeCP2 contains several domains that contribute to the formation of condensates, and mutations in MECP2 that lead to Rett syndrome disrupt the ability of MeCP2 to form condensates. Condensates formed by MeCP2 selectively incorporate and concentrate heterochromatin cofactors rather than components of euchromatic transcriptionally active condensates. We propose that MeCP2 enhances the separation of heterochromatin and euchromatin through its condensate partitioning properties, and that disruption of condensates may be a common consequence of mutations in MeCP2 that cause Rett syndrome. The chromatin protein MeCP2 is a component of dynamic, liquid-like heterochromatin condensates, and the ability of MeCP2 to form condensates is disrupted by mutations in the MECP2 gene that occur in the neurodevelopmental disorder Rett syndrome.
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- 2020
15. Fragile X Syndrome Patient-Derived Neurons Developing in the Mouse Brain Show FMR1-Dependent Phenotypes
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Marine A. Krzisch, Hao Wu, Bingbing Yuan, Troy W. Whitfield, X. Shawn Liu, Dongdong Fu, Carrie M. Garrett-Engele, Andrew S. Khalil, Tenzin Lungjangwa, Jennifer Shih, Aaron N. Chang, Stephen Warren, Angela Cacace, Kristin R. Andrykovich, Rosalie G.J. Rietjens, Owen Wallace, Mriganka Sur, Bhav Jain, and Rudolf Jaenisch
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Neurons ,Mice, Knockout ,Mice ,Fragile X Mental Retardation Protein ,Phenotype ,Neural Stem Cells ,Fragile X Syndrome ,Humans ,Animals ,Brain ,Biological Psychiatry - Abstract
Fragile X syndrome (FXS) is characterized by physical abnormalities, anxiety, intellectual disability, hyperactivity, autistic behaviors, and seizures. Abnormal neuronal development in FXS is poorly understood. Data on patients with FXS remain scarce, and FXS animal models have failed to yield successful therapies. In vitro models do not fully recapitulate the morphology and function of human neurons.To mimic human neuron development in vivo, we coinjected neural precursor cells derived from FXS patient-derived induced pluripotent stem cells and neural precursor cells derived from corrected isogenic control induced pluripotent stem cells into the brain of neonatal immune-deprived mice.The transplanted cells populated the brain and a proportion differentiated into neurons and glial cells. Immunofluorescence and single and bulk RNA sequencing analyses showed accelerated maturation of FXS neurons after an initial delay. Additionally, we found increased percentages of Arc- and Egr-1-positive FXS neurons and wider dendritic protrusions of mature FXS striatal medium spiny neurons.This transplantation approach provides new insights into the alterations of neuronal development in FXS by facilitating physiological development of cells in a 3-dimensional context.
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- 2021
16. Fragile X syndrome patient-derived neurons developing in the mouse brain show FMR1 -dependent phenotypes
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Mriganka Sur, Angela Cacace, Dongdong Fu, Aaron N. Chang, Rudolf Jaenisch, Jennifer Shih, Bingbing Yuan, Carrie M. Garrett-Engele, X. Shawn Liu, Kristin R. Andrykovich, Bhav Jain, Hao Wu, Troy W. Whitfield, Marine Krzisch, Rosalie G. J. Rietjens, Stephen T. Warren, and Wallace Owen Brendan
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congenital, hereditary, and neonatal diseases and abnormalities ,Arc (protein) ,Context (language use) ,Biology ,Medium spiny neuron ,medicine.disease ,FMR1 ,Transplantation ,Fragile X syndrome ,nervous system ,Precursor cell ,medicine ,Induced pluripotent stem cell ,Neuroscience - Abstract
Abnormal neuronal development in Fragile X syndrome (FXS) is poorly understood. Data on FXS patients remain scarce and FXS animal models have failed to yield successful therapies. In vitro models do not fully recapitulate the morphology and function of human neurons. Here, we co-injected neural precursor cells (NPCs) from FXS patient-derived and corrected isogenic control induced pluripotent stem cells into the brain of neonatal immune-deprived mice. The transplanted cells populated the brain and a proportion differentiated into neurons and glial cells. Single-cell RNA sequencing of transplanted cells revealed upregulated excitatory synaptic transmission and neuronal differentiation pathways in FXS neurons. Immunofluorescence analyses showed accelerated maturation of FXS neurons after an initial delay. Additionally, increased percentages of Arc- and Egr1-positive FXS neurons and wider dendritic protrusions of mature FXS striatal medium spiny neurons pointed to an increase in synaptic activity and synaptic strength as compared to control. This transplantation approach provides new insights into the alterations of neuronal development in FXS by facilitating physiological development of cells in a 3D context, and could be used to test new therapeutic compounds correcting neuronal development defects in FXS.
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- 2021
17. Hippocampal cells multiplex positive and negative engrams
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Monika Shpokayte, Olivia McKissick, Xiaonan Guan, Bingbing Yuan, Bahar Rahsepar, Fernando R. Fernandez, Evan Ruesch, Stephanie L. Grella, John A. White, X. Shawn Liu, and Steve Ramirez
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medicine.anatomical_structure ,Transgene ,medicine ,Hippocampus ,Engram ,Optogenetics ,Hippocampal formation ,Biology ,Nucleus accumbens ,Prefrontal cortex ,Neuroscience ,Amygdala - Abstract
The hippocampus is involved in processing a variety of mnemonic computations specifically the spatiotemporal components and emotional dimensions of contextual memory.1–3 Recent studies have demonstrated vast structural and functional heterogeneity along the dorsal-ventral axis1, 5 of the hippocampus. The ventral hippocampus has been shown to be important in the processing of emotion and valence.6–9 Here, we combine transgenic and all-virus based activity-dependent tagging strategies to visualize multiple valence-specific engrams in the vHPC and demonstrate two partially segregated cell populations and projections that respond to appetitive and aversive experiences. Next, using RNA sequencing and DNA methylation sequencing approaches, we find that vHPC appetitive and aversive engram cells display distinct transcriptional programs and DNA methylation landscapes compared to a neutral engram population. Additionally, while optogenetic manipulation of tagged cell bodies in vHPC is not sufficient to drive appetitive or aversive behavior in real-time place preference, stimulation of tagged vHPC terminals projecting to the amygdala and nucleus accumbens (NAc), but not the prefrontal cortex (PFC), had the capacity drive preference and avoidance. These terminals can also undergo a “switch” or “reset” in their capacity to drive either, thereby demonstrating their adaptable contributions to behavior. We conclude that the vHPC contains genetically, cellularly, and behaviorally distinct populations of cells processing appetitive and aversive memory engrams. Together, our findings provide a novel means by which to visualize multiple engrams within the same brain and point to their unique genetic signatures as reference maps for the future development of new therapeutic strategies.One sentence summaryThe hippocampus contains neurons that correspond to positive and negative engrams, which are segregated by their molecular, cellular, and projection-specific features.
- Published
- 2020
18. Patient Loss to Follow-up After Upper Extremity Surgery: A Review of 2563 Cases
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X Shawn Liu, Kanu S. Goyal, Alex C. DiBartola, Joseph A Rosenbaum, Hannah K. Fox, and Yoni M Blau
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Adult ,Male ,medicine.medical_specialty ,Insurance type ,030230 surgery ,Medicare ,Logistic regression ,Postoperative management ,Upper Extremity ,03 medical and health sciences ,0302 clinical medicine ,Humans ,Medicine ,Orthopedic Procedures ,Orthopedics and Sports Medicine ,Private insurance ,Lost to follow-up ,Aged ,Retrospective Studies ,Surgery Articles ,030222 orthopedics ,Insurance, Health ,Medicaid ,business.industry ,Incidence (epidemiology) ,Upper extremity surgery ,Middle Aged ,United States ,Surgery ,Logistic Models ,Workers' Compensation ,Female ,Lost to Follow-Up ,business - Abstract
Background: Postoperative care is essential to optimizing patient outcome. We sought to determine the incidence and associated demographic and surgical factors of postoperative patient loss to follow-up following hand and upper extremity surgery. Methods: In all, 2834 surgical cases (2467 patients) were retrospectively reviewed. All surgical cases from July 2014 to June 2015 at a single practice with five surgeons were assessed. Charts were reviewed for compliance with postoperative follow-up. Variables were described with proportions and compared using logistic regression analysis. Results: In total, 2563 cases (2388 patients) met the inclusion criteria. Overall loss to follow-up rate was 26%. Patients lost to follow-up based on insurance type were 13% for worker’s compensation, 22% for private insurance, 21% for Medicare, 38% for Medicaid, and 44% for self-pay. Patients with expected short-term follow-up were lost at a 23% rate. Expected mid- and long-term follow-up patients were lost at 34% and 20% rates, respectively. Patients below 30 years old were lost to follow-up at a 42% rate compared to patients 30 to 64 years old (26%) and greater than or equal to 65 years (13%). Males had a higher rate of loss to follow-up, 32%, compared with females (22%). Patients living greater than 50 miles from our surgery center were lost to follow-up at a rate of 31%, compared with those who lived less than 50 miles (25%). Conclusions: We have identified demographic variables associated with patients being lost to follow-up after hand and upper extremity surgery. With this knowledge, we hope to develop methods of either improving in-office follow-up rates or discover new avenues to deliver postoperative care.
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- 2018
19. Prognostic value of microRNA expression levels in pancreatic adenocarcinoma: a review of the literature
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X Shawn Liu, Cory Pettit, Mary Dillhoff, Andrei Manilchuk, Carl Schmidt, Patrick Wald, Wei Chen, Evan Wuthrick, and Terence M. Williams
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0301 basic medicine ,Oncology ,medicine.medical_specialty ,pancreatic cancer ,non-coding RNA ,Review ,chemotherapy ,03 medical and health sciences ,0302 clinical medicine ,Text mining ,Internal medicine ,Pancreatic cancer ,microRNA ,Adjuvant therapy ,Medicine ,prognostic biomarker ,miRNA ,Patterns of failure ,business.industry ,Non-coding RNA ,medicine.disease ,3. Good health ,030104 developmental biology ,030220 oncology & carcinogenesis ,Adenocarcinoma ,business ,Microrna profiling - Abstract
Background Clinical and pathologic markers of prognosis and patterns of failure help guide clinicians in selecting patients for adjuvant therapy after surgical resection for pancreatic adenocarcinoma (PDAC). Recent studies have reported the prognostic utility of microRNA profiling in numerous malignancies. Here, we review and summarize the current literature regarding associations between microRNA expression and overall survival in PDAC patients. Materials and methods We conducted a systematic search in the PubMed database to identify all primary research studies reporting prognostic associations between tumor and/or serum microRNA expression and overall survival in PDAC patients. Eligible articles were reviewed by the authors and relevant findings are summarized below. Results We found 53 publications that fit our search criteria. In total, 23 up-regulated and 49 down-regulated miRNAs have been associated with worse overall survival. MiR-21 is the most commonly reported miRNA, appearing in 19 publications, all of which report aberrant over-expression and association with shorter survival in PDAC. Other miRNAs that appear in multiple publications include miR-10b, -21, -34a, -155, -196a, -198, -200c, -203, -210, -218, -222, and -328. We summarize the preclinical and clinical data implicating these miRNAs in various molecular signaling pathways and cellular functions. Conclusions There is growing evidence that miRNA expression profiles have the potential to provide tumor-specific prognostic information to assist clinicians in more appropriately selecting patients for adjuvant therapy. These molecules are often aberrantly expressed and exhibit oncogenic and/or tumor suppressor functions in PDAC. Additional efforts to develop prognostic and predictive molecular signatures, and further elucidate miRNA mechanisms of action, are warranted.
- Published
- 2017
20. Editing the Epigenome to Tackle Brain Disorders
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Rudolf Jaenisch and X. Shawn Liu
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0301 basic medicine ,Histone Acetyltransferases ,Epigenomics ,Gene Editing ,Brain Diseases ,Brain development ,Methyltransferase ,Disease outcome ,General Neuroscience ,Computational biology ,Epigenome ,Biology ,DNA Methylation ,Epigenesis, Genetic ,03 medical and health sciences ,030104 developmental biology ,0302 clinical medicine ,Epigenome editing ,CRISPR ,Animals ,Humans ,Epigenetics ,CRISPR-Cas Systems ,030217 neurology & neurosurgery - Abstract
Genetic studies of epigenetic modifiers such as DNA methyltransferases and histone acetyltransferases have revealed a critical role for epigenetic regulation during brain development and function. Alteration of epigenetic modifications have been documented in a variety of brain disorders, including neurodevelopmental, psychiatric, and neurodegenerative diseases. Development of epigenome editing tools enables a functional dissection of the link between altered epigenetic changes and disease outcomes. Here, we review the development of epigenome editing tools, summarize proof of concept applications focusing on brain disease-associated genes, and discuss the promising application and challenges of epigenome editing to tackle brain disorders.
- Published
- 2019
21. Plk1 Phosphorylation of Orc2 and Hbo1 Contributes to Gemcitabine Resistance in Pancreatic Cancer
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Bennett D. Elzey, Bing Song, Steven J Rice, Elena G. Chiorean, Tony R. Hazbun, Stephen F. Konieczny, Xiaoqi Liu, Timoty L Ratliff, Shihuan Kuang, and X. Shawn Liu
- Subjects
DNA Replication ,Antimetabolites, Antineoplastic ,Cancer Research ,Mutant ,Origin Recognition Complex ,Mice, Nude ,Cell Cycle Proteins ,Protein Serine-Threonine Kinases ,Biology ,Deoxycytidine ,PLK1 ,Article ,Inhibitory Concentration 50 ,Mice ,chemistry.chemical_compound ,Mediator ,Cell Line, Tumor ,Proto-Oncogene Proteins ,Pancreatic cancer ,medicine ,Animals ,Humans ,Phosphorylation ,Histone Acetyltransferases ,Kinase ,Pteridines ,medicine.disease ,Xenograft Model Antitumor Assays ,Gemcitabine ,Pancreatic Neoplasms ,Oncology ,chemistry ,Drug Resistance, Neoplasm ,Tissue Array Analysis ,Cancer research ,Female ,Protein Processing, Post-Translational ,Proto-Oncogene Proteins c-fos ,Carcinoma, Pancreatic Ductal ,medicine.drug - Abstract
Although gemcitabine is the standard chemotherapeutic drug for treatment of pancreatic cancer, almost all patients eventually develop resistance to this agent. Previous studies identified Polo-like kinase 1 (Plk1) as the mediator of gemcitabine resistance, but the molecular mechanism remains unknown. In this study, we show that Plk1 phosphorylation of Orc2 and Hbo1 mediates the resistance to gemcitabine. We show that the level of Plk1 expression positively correlates with gemcitabine resistance, both in pancreatic cancer cells and xenograft tumors. Overexpression of Plk1 increases gemcitabine resistance, while inhibition of Plk1 sensitizes pancreatic cancer cells to gemcitabine treatment. To validate our findings, we show that inhibition of Plk1 sensitizes tumors to gemcitabine treatment in a mouse xenograft study. Mechanistically, we find that Plk1 phosphorylation of Orc2 maintains DNA replication on gemcitabine treatment. Furthermore, Plk1 phosphorylation of Hbo1 transcriptionally increases cFos expression and consequently elevates its target multidrug resistance 1 (MDR1), which was previously reported to confer chemotherapeutic drug resistance. Knockdown of cFos or MDR1 sensitizes gemcitabine-resistant cells to gemcitabine treatment. Finally, pancreatic cancer cells expressing Plk1-unphosphorylatable mutants of Orc2 or Hbo1 are more sensitive to gemcitabine than cells expressing wild-type Orc2 or Hbo1. In short, our study provides a mechanism for Plk1-mediated gemcitabine resistance, suggesting that Plk1 is a promising target for treatment of gemcitabine-resistant pancreatic cancer. Mol Cancer Ther; 12(1); 58–68. ©2012 AACR.
- Published
- 2013
22. Chemical Visualization of Phosphoproteomes on Membrane
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X. Shawn Liu, Liang Xue, Xiaoqi Liu, Anton Iliuk, and W. Andy Tao
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Proteomics ,inorganic chemicals ,Proteome ,Blotting, Western ,Cell Cycle Proteins ,Protein Serine-Threonine Kinases ,Biology ,Biochemistry ,Antibodies ,Cell Line ,Analytical Chemistry ,Proto-Oncogene Proteins ,Humans ,Protein phosphorylation ,Phosphorylation ,Molecular Biology ,Protein-Serine-Threonine Kinases ,Kinase ,Research ,Phosphoproteomics ,Membrane Proteins ,Phosphoproteins ,Nanostructures ,Cell biology ,enzymes and coenzymes (carbohydrates) ,HEK293 Cells ,Membrane protein ,HeLa Cells - Abstract
With new discoveries of important roles of phosphorylation on a daily basis, phospho-specific antibodies, as the primary tool for on-membrane detection of phosphoproteins, face enormous challenges. To address an urgent need for convenient and reliable analysis of phosphorylation events, we report a novel strategy for sensitive phosphorylation analysis in the Western blotting format. The chemical reagent, which we termed pIMAGO, is based on a multifunctionalized soluble nanopolymer and is capable of selectively binding to phosphorylated residues independent of amino acid microenvironment, thus offering great promise as a universal tool in biological analyses where the site of phosphorylation is not known or its specific antibody is not available. The specificity and sensitivity of the approach was first examined using a mixture of standard proteins. The method was then applied to monitor phosphorylation changes in in vitro kinase and phosphatase assays. Finally, to demonstrate the unique ability of pIMAGO to measure endogenous phosphorylation, we used it to visualize and determine the differences in phosphorylated proteins that interact with wild-type and kinase dead mutant of Polo-like kinase 1 during mitosis, the results of which were further confirmed by a quantitative phosphoproteomics experiment.
- Published
- 2012
23. Hypoxia promotes satellite cell self-renewal and enhances the efficiency of myoblast transplantation
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Xinsheng Lai, Pengpeng Bi, Weiyi Liu, Xiaoqi Liu, Shihuan Kuang, Yefei Wen, and X. Shawn Liu
- Subjects
Satellite Cells, Skeletal Muscle ,Myoblasts, Skeletal ,Notch signaling pathway ,Mice, Transgenic ,Biology ,MyoD ,Resting Phase, Cell Cycle ,Mice ,Animals ,Myocyte ,Stem Cell Niche ,Molecular Biology ,Cells, Cultured ,Myogenin ,Cell Proliferation ,MyoD Protein ,Receptors, Notch ,Cell growth ,PAX7 Transcription Factor ,Development and Stem Cells ,musculoskeletal system ,Cell Hypoxia ,Cell biology ,Transplantation ,MicroRNAs ,Mice, Inbred mdx ,Stem cell ,Myoblast division ,Signal Transduction ,Developmental Biology - Abstract
Microenvironmental oxygen (O2) regulates stem cell activity, and a hypoxic niche with low oxygen levels has been reported in multiple stem cell types. Satellite cells are muscle-resident stem cells that maintain the homeostasis and mediate the regeneration of skeletal muscles. We demonstrate here that hypoxic culture conditions favor the quiescence of satellite cell-derived primary myoblasts by upregulating Pax7, a key regulator of satellite cell self-renewal, and downregulating MyoD and myogenin. During myoblast division, hypoxia promotes asymmetric self-renewal divisions and inhibits asymmetric differentiation divisions without affecting the overall rate of proliferation. Mechanistic studies reveal that hypoxia activates the Notch signaling pathway, which subsequently represses the expression of miR-1 and miR-206 through canonical Hes/Hey proteins, leading to increased levels of Pax7. More importantly, hypoxia conditioning enhances the efficiency of myoblast transplantation and the self-renewal of implanted cells. Given the robust effects of hypoxia on maintaining the quiescence and promoting the self-renewal of cultured myoblasts, we predict that oxygen levels in the satellite cell niche play a central role in precisely balancing quiescence versus activation, and self-renewal versus differentiation, in muscle stem cells in vivo.
- Published
- 2012
24. Phosphorylation of CLIP-170 by Plk1 and CK2 promotes timely formation of kinetochore–microtubule attachments
- Author
-
Xiaoming Yang, X. Shawn Liu, Xiaoqi Liu, Jerrold R. Turner, Yingmin Wang, Hongchang Li, and Yun Wang
- Subjects
education ,Dynein ,Mitosis ,Cell Cycle Proteins ,macromolecular substances ,Protein Serine-Threonine Kinases ,Biology ,Microtubules ,PLK1 ,Article ,General Biochemistry, Genetics and Molecular Biology ,Kinetochore microtubule ,Microtubule ,Proto-Oncogene Proteins ,Serine ,Humans ,cardiovascular diseases ,Phosphorylation ,Prometaphase ,Casein Kinase II ,Kinetochores ,Molecular Biology ,General Immunology and Microbiology ,Kinetochore ,General Neuroscience ,fungi ,Dynactin Complex ,Neoplasm Proteins ,Cell biology ,surgical procedures, operative ,Dynactin ,Microtubule-Associated Proteins ,HeLa Cells ,Protein Binding - Abstract
CLIP-170 is implicated in the formation of kinetochore-microtubule attachments through direct interaction with the dynein/dynactin complex. However, whether this important function of CLIP-170 is regulated by phosphorylation is unknown. Herein, we have identified polo-like kinase 1 (Plk1) and casein kinase 2 (CK2) as two kinases of CLIP-170 and mapped S195 and S1318 as their respective phosphorylation sites. We showed that a CK2 unphosphorylatable mutant lost its ability to bind to dynactin and to localize to kinetochores during prometaphase, indicating that the CK2 phosphorylation of CLIP-170 is involved in its dynactin-mediated kinetochore localization. Furthermore, we provide evidence that Plk1 phosphorylation of CLIP-170 at S195 enhances its association with CK2. Finally, we detected defects in the formation of kinetochore fibres in cells expressing the CLIP-S195A and -S1318A, but not the CLIP-S195E and -S1318D, confirming that Plk1- and CK2-associated phosphorylations of CLIP-170 are involved in the timely formation of kinetochore-microtubule attachments in mitosis.
- Published
- 2010
25. A serotonin receptor antagonist induces oocyte maturation in both frogs and mice: Evidence that the same G protein-coupled receptor is responsible for maintaining meiosis arrest in both species
- Author
-
X. Shawn Liu, Mario Tiberi, X. Johné Liu, Véronique Montplaisir, Ling Wang, Jay M. Baltz, and Yinglun Sheng
- Subjects
medicine.medical_specialty ,Ranidae ,Physiology ,Clinical Biochemistry ,Ritanserin ,Biology ,Serotonergic ,Cell Line ,Receptors, G-Protein-Coupled ,Mice ,chemistry.chemical_compound ,Internal medicine ,Cyclic AMP ,medicine ,Animals ,Humans ,Serotonin receptor antagonist ,5-HT receptor ,Mesulergine ,Colforsin ,Cell Biology ,Oligonucleotides, Antisense ,Oocyte ,Meiosis ,Endocrinology ,medicine.anatomical_structure ,chemistry ,Receptors, Serotonin ,Metitepine ,Oocytes ,Female ,Serotonin Antagonists ,Serotonin ,Mitogen-Activated Protein Kinases ,medicine.drug - Abstract
Accumulating evidence has indicated that vertebrate oocytes are arrested at late prophase (G2 arrest) by a G protein coupled receptor (GpCR) that activates adenylyl cyclases. However, the identity of this GpCR or its regulation in G2 oocytes is unknown. We demonstrated that ritanserin (RIT), a potent antagonist of serotonin receptors 5-HT2R and 5-HT7R, released G2 arrest in denuded frog oocytes, as well as in follicle-enclosed mouse oocytes. In contrast to RIT, several other serotonin receptor antagonists (mesulergine, methiothepine, and risperidone) had no effect on oocyte maturation. The unique ability of RIT, among serotonergic antagonists, to induce GVBD did not match the antagonist profile of any known serotonin receptors including Xenopus 5-HT7R, the only known Gs-coupled serotonin receptor cloned so far in this species. Unexpectedly, injection of x5-HT7R mRNA in frog oocytes resulted in hormone-independent frog oocyte maturation. The addition of exogenous serotonin abolished x5-HT7R-induced oocyte maturation. Furthermore, the combination of x5-HT7R and exogenous serotonin potently inhibited progesterone-induced oocyte maturation. These results provide the first evidence that a G-protein coupled receptor related to 5-HT7R may play a pivotal role in maintaining G2 arrest in vertebrate oocytes. © 2004 Wiley-Liss, Inc.
- Published
- 2004
26. Stromal response to Hedgehog signaling restrains pancreatic cancer progression
- Author
-
Phillip D. Jones, Sally Kawano, Huaijun Wang, Julien Fitamant, Dai Chen Wu, X. Shawn Liu, Yves Boucher, Vikram Deshpande, Krishna S. Ghanta, Tomoyo Sakata Kato, Philip A. Beachy, Jürgen K. Willmann, John J. Lee, Nabeel Bardeesy, Shiwei Han, Julia M. Nagle, Rushika M. Perera, and James K. Chen
- Subjects
Pathology ,medicine.medical_specialty ,Stromal cell ,Knockout ,cerulein ,Proto-Oncogene Proteins p21(ras) ,Paracrine signalling ,Mice ,hedgehog agonist ,Pancreatic Cancer ,Rare Diseases ,Pancreatic cancer ,medicine ,Animals ,Humans ,2.1 Biological and endogenous factors ,Hedgehog Proteins ,Sonic hedgehog ,Aetiology ,Hedgehog ,Cancer ,Mice, Knockout ,Multidisciplinary ,biology ,Carcinoma ,tumor stroma ,medicine.disease ,Hedgehog signaling pathway ,Desmoplasia ,Pancreatic Neoplasms ,Orphan Drug ,PNAS Plus ,Pancreatic Ductal ,5.1 Pharmaceuticals ,biology.protein ,Cancer research ,cancer therapy ,medicine.symptom ,Signal transduction ,Development of treatments and therapeutic interventions ,Digestive Diseases ,Carcinoma, Pancreatic Ductal ,Signal Transduction - Abstract
Pancreatic ductal adenocarcinoma (PDA) is the most lethal of common human malignancies, with no truly effective therapies for advanced disease. Preclinical studies have suggested a therapeutic benefit of targeting the Hedgehog (Hh) signaling pathway, which is activated throughout the course of PDA progression by expression of Hh ligands in the neoplastic epithelium and paracrine response in the stromal fibroblasts. Clinical trials to test this possibility, however, have yielded disappointing results. To further investigate the role of Hh signaling in the formation of PDA and its precursor lesion, pancreatic intraepithelial neoplasia (PanIN), we examined the effects of genetic or pharmacologic inhibition of Hh pathway activity in three distinct genetically engineered mouse models and found that Hh pathway inhibition accelerates rather than delays progression of oncogenic Kras-driven disease. Notably, pharmacologic inhibition of Hh pathway activity affected the balance between epithelial and stromal elements, suppressing stromal desmoplasia but also causing accelerated growth of the PanIN epithelium. In striking contrast, pathway activation using a small molecule agonist caused stromal hyperplasia and reduced epithelial proliferation. These results indicate that stromal response to Hh signaling is protective against PDA and that pharmacologic activation of pathway response can slow tumorigenesis. Our results provide evidence for a restraining role of stroma in PDA progression, suggesting an explanation for the failure of Hh inhibitors in clinical trials and pointing to the possibility of a novel type of therapeutic intervention.
- Published
- 2014
27. Plk1 phosphorylation of Orc2 promotes DNA replication under conditions of stress
- Author
-
Xiaoqi Liu, X. Shawn Liu, Korbin Davis, and Bing Song
- Subjects
DNA Replication ,Chromatin Immunoprecipitation ,Amino Acid Motifs ,Origin Recognition Complex ,Eukaryotic DNA replication ,Cell Cycle Proteins ,Protein Serine-Threonine Kinases ,Pre-replication complex ,Genomic Instability ,Cell Line ,S Phase ,DNA replication factor CDT1 ,Replication factor C ,Control of chromosome duplication ,Stress, Physiological ,Proto-Oncogene Proteins ,Humans ,Protein Interaction Domains and Motifs ,Phosphorylation ,Molecular Biology ,Protein Kinase Inhibitors ,biology ,Cell Biology ,Articles ,Molecular biology ,DNA replication origin ,Cell biology ,Licensing factor ,S Phase Cell Cycle Checkpoints ,biology.protein ,Origin recognition complex ,Protein Binding - Abstract
Polo-like kinase 1 (Plk1) plays pivotal roles in mitosis; however, little is known about its function in S phase. In this study, we show that inhibition of Plk1 impairs DNA replication and results in slow S-phase progression in cultured cancer cells. We have identified origin recognition complex 2 (Orc2), a member of the DNA replication machinery, as a Plk1 substrate and have shown that Plk1 phosphorylates Orc2 at Ser188 in vitro and in vivo. Furthermore, Orc2-S188 phosphorylation is enhanced when DNA replication is under challenge induced by ultraviolet, hydroxyurea, gemcitabine, or aphidicolin treatment. Cells expressing the unphosphorylatable mutant (S188A) of Orc2 had defects in DNA synthesis under stress, suggesting that this phosphorylation event is critical to maintain DNA replication under stress. To dissect the mechanism pertinent to this observation, we showed that Orc2-S188 phosphorylation associates with DNA replication origin and that cells expressing Orc2-S188A mutant fail to maintain the functional pre-replicative complex (pre-RC) under DNA replication stress. Furthermore, the intra-S-phase checkpoint is activated in Orc2-S188A-expressing cells to cause delay of S-phase progress. Our study suggests a novel role of Plk1 in facilitating DNA replication under conditions of stress to maintain genomic integrity.
- Published
- 2011
28. The substrates of Plk1, beyond the functions in mitosis
- Author
-
Xiaoqi Liu, Bing Song, and X. Shawn Liu
- Subjects
DNA Replication ,Cell division ,Mitosis ,Eukaryotic DNA replication ,Cell Cycle Proteins ,Review ,Biology ,Protein Serine-Threonine Kinases ,Biochemistry ,PLK1 ,Microtubules ,Chromosomes ,Microtubule ,Proto-Oncogene Proteins ,Drug Discovery ,Animals ,Humans ,Cell Cycle ,DNA replication ,Cell Biology ,G2-M DNA damage checkpoint ,Cell cycle ,Cell biology ,Tumor Suppressor Protein p53 ,Biotechnology - Abstract
Polo-like kinase 1 (Plk1) is a key regulator of cell division in eukaryotic cells. In this short review, we briefly summarized the well-established functions modulated by Plk1 during mitosis. Beyond mitosis, we focused mainly on the unexpected processes in which Plk1 emerges as a critical player, including microtubule dynamics, DNA replication, chromosome dynamics, p53 regulation, and recovery from the G2 DNA-damage checkpoint. Our discussion is mainly based on the critical substrates targeted by Plk1 during these cellular events and the functional significance associated with each phosphorylation event.
- Published
- 2010
29. Polo-like kinase 1 phosphorylation of p150Glued facilitates nuclear envelope breakdown during prophase
- Author
-
Xiaoming Yang, Hongchang Li, Bing Song, Xiaoqi Liu, X. Shawn Liu, and Yun Wang
- Subjects
Time Factors ,Nuclear Envelope ,Dynein ,Blotting, Western ,Green Fluorescent Proteins ,Cyclin B ,Fluorescent Antibody Technique ,Cell Cycle Proteins ,Polo-like kinase ,Biology ,Protein Serine-Threonine Kinases ,PLK1 ,Microtubules ,Prophase ,Cell Line ,Substrate Specificity ,Microtubule ,Cell Line, Tumor ,Proto-Oncogene Proteins ,Humans ,Amino Acid Sequence ,Phosphorylation ,Mitosis ,Multidisciplinary ,Sequence Homology, Amino Acid ,Dynactin Complex ,Biological Sciences ,Immunohistochemistry ,Cell biology ,Amino Acid Substitution ,Mutation ,biology.protein ,Dynactin ,RNA Interference ,Microtubule-Associated Proteins ,HeLa Cells ,Protein Binding - Abstract
Nuclear envelope breakdown (NEBD) is an essential step during the G2/M transition in higher eukaryotic cells. Increasing evidence supports the notion that both microtubules and microtubule-associated motor proteins are critical regulators of NEBD. Although it has been described that p150 Glued , the major component of the dynein/dynactin complex, localizes in the nuclear envelope during prophase, the exact role of p150 Glued and its regulation during NEBD are largely elusive. Polo-like kinase 1 (Plk1), the best characterized Ser/Thr kinase, is involved in mitotic entry in several systems; however, the targets of Plk1 during NEBD are unknown. Herein, we show that in mammalian cells both Plk1 and p150 Glued regulate NEBD and that Plk1 interacts with and phosphoryates p150 Glued during NEBD at prophase. Using various approaches, we showed that Plk1 phosphorylates p150 Glued at Ser-179 and that the pS179 epitope is generated at the nuclear envelope of prophase cells. Significantly, Plk1-mediated phosphorylation of p150 Glued at Ser-179 positively regulates its accumulation at the nuclear envelope during prophase. Finally, we found that cells expressing the Plk1-unphosphorylatable mutant (p150 Glued -S179A) arrest at G2, as indicated by reduced NEBD, increased levels of cyclin B and phospho-H3, but a decreased level of Cdc2 kinase activity. Taking these data together, we conclude that Plk1 phosphorylation of p150 Glued might be one major pathway of NEBD regulation.
- Published
- 2010
30. Polo-like kinase 1 phosphorylation of G2 and S-phase-expressed 1 protein is essential for p53 inactivation during G2 checkpoint recovery
- Author
-
X. Shawn Liu, Xiaoqi Liu, Bing Song, and Hongchang Li
- Subjects
G2 Phase ,DNA damage ,Recombinant Fusion Proteins ,Cell Cycle Proteins ,Polo-like kinase ,Biology ,Protein Serine-Threonine Kinases ,Biochemistry ,PLK1 ,Cell Line ,Proto-Oncogene Proteins ,Genetics ,Humans ,Phosphorylation ,Cell Cycle Protein ,Molecular Biology ,Kinase ,Scientific Reports ,G2-M DNA damage checkpoint ,Cell biology ,RNA Interference ,Tumor Suppressor Protein p53 ,Microtubule-Associated Proteins ,Nuclear localization sequence ,DNA Damage - Abstract
In response to G2 DNA damage, the p53 pathway is activated to lead to cell-cycle arrest, but how p53 is eliminated during the subsequent recovery process is poorly understood. It has been established that Polo-like kinase 1 (Plk1) controls G2 DNA-damage recovery. However, whether Plk1 activity contributes to p53 inactivation during this process is unknown. In this study, we show that G2 and S-phase-expressed 1 (GTSE1) protein, a negative regulator of p53, is required for G2 checkpoint recovery and that Plk1 phosphorylation of GTSE1 at Ser 435 promotes its nuclear localization, and thus shuttles p53 out of the nucleus to lead to its degradation during the recovery.
- Published
- 2010
31. Oocyte isolation and enucleation
- Author
-
X Shawn, Liu and X Johné, Liu
- Subjects
Cell Nucleus ,Solutions ,Xenopus laevis ,Oocytes ,Animals ,Female ,Cell Separation ,Collagenases ,Microdissection - Abstract
Xenopus laevis oocytes are popular cells in experimental biology. Fully grown oocytes are large (approximately 1.3-mm diameter) with an enormous nucleus (approximately 300-microm diameter). Oocytes are generally isolated by either manual dissection (manual defolliculation) or enzymatic (mainly with collagenase preparations) digestion of the extracellular connective tissues. In this chapter, we describe both procedures, which are routinely used in our laboratory. However, manual defolliculation does not actually remove the innermost layer of follicle cells, which are anchored to the vitelline membrane. To remove these follicle cells, further mechanical or enzymatic treatment is required. On the other hand, many have experienced nonspecific effects with collagenase-treated oocytes, including spontaneous oocyte maturation and reduced oocyte health. We discuss possible explanations and solutions to these problems. Finally, we also describe procedures we employ routinely to isolate oocyte nuclei and enucleated oocytes.
- Published
- 2006
32. Oocyte Isolation and Enucleation
- Author
-
X. Shawn Liu and X. Johné Liu
- Subjects
biology ,Chemistry ,Enucleation ,Xenopus ,Vitelline membrane ,Oocyte ,biology.organism_classification ,Cell biology ,Follicle ,Cell nucleus ,medicine.anatomical_structure ,Collagenase ,medicine ,Extracellular ,medicine.drug - Abstract
Xenopus laevis oocytes are popular cells in experimental biology. Fully grown oocytes are large (approximately 1.3-mm diameter) with an enormous nucleus (approximately 300-microm diameter). Oocytes are generally isolated by either manual dissection (manual defolliculation) or enzymatic (mainly with collagenase preparations) digestion of the extracellular connective tissues. In this chapter, we describe both procedures, which are routinely used in our laboratory. However, manual defolliculation does not actually remove the innermost layer of follicle cells, which are anchored to the vitelline membrane. To remove these follicle cells, further mechanical or enzymatic treatment is required. On the other hand, many have experienced nonspecific effects with collagenase-treated oocytes, including spontaneous oocyte maturation and reduced oocyte health. We discuss possible explanations and solutions to these problems. Finally, we also describe procedures we employ routinely to isolate oocyte nuclei and enucleated oocytes.
- Published
- 2006
33. Abstract 2050: Plk1 phosphorylation of Orc2 promotes DNA replication under conditions of stress
- Author
-
X. Shawn Liu, Korbin Davis, Xiaoqi Liu, and Bing Song
- Subjects
DNA replication factor CDT1 ,DNA re-replication ,Cancer Research ,Replication factor C ,Oncology ,biology ,Control of chromosome duplication ,biology.protein ,DNA replication ,Origin recognition complex ,Eukaryotic DNA replication ,Molecular biology ,DNA replication origin - Abstract
Polo-like kinase 1 (Plk1) plays pivotal roles in mitosis, however, little is known about its function in S phase. In this study, we show that inhibition of Plk1 impairs DNA replication and results in slow S-phase progression in cultured cancer cells. We have identified Origin Recognition Complex 2 (Orc2), a member of the DNA replication machinery, as a Plk1 substrate and have shown that Plk1 phosphorylates Orc2 at Ser188 in vitro and in vivo. Furthermore, Orc2-S188 phosphorylation is enhanced when DNA replication is under challenge induced by UV, hydroxyurea, gemcitabine, or aphidicolin treatment; cells expressing the unphosphorylatable mutant (S188A) of Orc2 had defects in DNA synthesis under stress, suggesting that this phosphorylation event is critical to maintain DNA replication under stress. To dissect the mechanism pertinent to this observation, we showed that Orc2-S188 phosphorylation associates with DNA replication origin and that cells expressing Orc2-S188A mutant fail to maintain the functional pre-replicative complex (pre-RC) under DNA replication stress. Furthermore, the intra-S phase checkpoint is activated in Orc2-S188A-expressing cells to cause delay of S-phase progress. Our study suggests a novel role of Plk1 in facilitating DNA replication under conditions of stress to maintain genomic integrity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2050. doi:1538-7445.AM2012-2050
- Published
- 2012
34. Targeting Plk1 in cutaneous T-cell lymphomas (CTCLs)
- Author
-
X. Shawn Liu and Xiaoqi Liu
- Subjects
medicine.anatomical_structure ,T cell ,medicine ,Cancer research ,Cell Biology ,Biology ,Molecular Biology ,PLK1 ,Developmental Biology - Published
- 2011
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