Jim K. Wong

The checkpoint protein Chfr is a ligase that ubiquitinates Plk1 and inhibits Cdc2 at the G2 to M transition

The checkpoint protein Chfr delays entry into mitosis, in the presence of mitotic stress (Scolnick, D.M., and T.D. Halazonetis. 2000. Nature. 406:430–435). We show here that Chfr is a ubiquitin ligase, both in vitro and in vivo. When transfected into HEK293T cells, Myc–Chfr promotes the formation of high molecular weight ubiquitin conjugates. The ring finger domain in Chfr is required for the ligase activity; this domain auto-ubiquitinates, and mutations of conserved residues in this domain abolish the ligase activity. Using Xenopus cell-free extracts, we demonstrated that Chfr delays the entry into mitosis by negatively regulating the activation of the Cdc2 kinase at the G2–M transition. Specifically, the Chfr pathway prolongs the phosphorylated state of tyrosine 15 in Cdc2. The Chfr-mediated cell cycle delay requires ubiquitin-dependent protein degradation, because inactivating mutations in Chfr, interference with poly-ubiquitination, and inhibition of proteasomes all abolish this delay in mitotic entry. The direct target of the Chfr pathway is Polo-like kinase 1 (Plk1). Ubiquitination of Plk1 by Chfr delays the activation of the Cdc25C phosphatase and the inactivation of the Wee1 kinase, leading to a delay in Cdc2 activation. Thus, the Chfr pathway represents a novel checkpoint pathway that regulates the entry into mitosis by ubiquitin-dependent proteolysis.

HURP controls spindle dynamics to promote proper interkinetochore tension and efficient kinetochore capture

Through a functional genomic screen for mitotic regulators, we identified hepatoma up-regulated protein (HURP) as a protein that is required for chromosome congression and alignment. In HURP-depleted cells, the persistence of unaligned chromosomes and the reduction of tension across sister kinetochores on aligned chromosomes resulted in the activation of the spindle checkpoint. Although these defects transiently delayed mitotic progression, HeLa cells initiated anaphase without resolution of these deficiencies. This bypass of the checkpoint arrest provides a tumor-specific mechanism for chromosome missegregation and genomic instability. Mechanistically, HURP colocalized with the mitotic spindle in a concentration gradient increasing toward the chromosomes. HURP binds directly to microtubules in vitro and enhances their polymerization. In vivo, HURP stabilizes mitotic microtubules, promotes microtubule polymerization and bipolar spindle formation, and decreases the turnover rate of the mitotic spindle. Thus, HURP controls spindle stability and dynamics to achieve efficient kinetochore capture at prometaphase, timely chromosome congression to the metaphase plate, and proper interkinetochore tension for anaphase initiation.

DDA3 recruits microtubule depolymerase Kif2a to spindle poles and controls spindle dynamics and mitotic chromosome movement

Dynamic turnover of the spindle is a driving force for chromosome congression and segregation in mitosis. Through a functional genomic analysis, we identify DDA3 as a previously unknown regulator of spindle dynamics that is essential for mitotic progression. DDA3 depletion results in a high frequency of unaligned chromosomes, a substantial reduction in tension across sister kinetochores at metaphase, and a decrease in the velocity of chromosome segregation at anaphase. DDA3 associates with the mitotic spindle and controls microtubule (MT) dynamics. Mechanistically, DDA3 interacts with the MT depolymerase Kif2a in an MT-dependent manner and recruits Kif2a to the mitotic spindle and spindle poles. Depletion of DDA3 increases the steady-state levels of spindle MTs by reducing the turnover rate of the mitotic spindle and by increasing the rate of MT polymerization, which phenocopies the effects of partial knockdown of Kif2a. Thus, DDA3 represents a new class of MT-destabilizing protein that controls spindle dynamics and mitotic progression by regulating MT depolymerases.

Aurora A Regulates the Activity of HURP by Controlling the Accessibility of Its Microtubule-binding Domain

HURP is a spindle-associated protein that mediates Ran-GTP-dependent assembly of the bipolar spindle and promotes chromosome congression and interkinetochore tension during mitosis. We report here a biochemical mechanism of HURP regulation by Aurora A, a key mitotic kinase that controls the assembly and function of the spindle. We found that HURP binds to microtubules through its N-terminal domain that hyperstabilizes spindle microtubules. Ectopic expression of this domain generates defects in spindle morphology and function that reduce the level of tension across sister kinetochores and activate the spindle checkpoint. Interestingly, the microtubule binding activity of this N-terminal domain is regulated by the C-terminal region of HURP: in its hypophosphorylated state, C-terminal HURP associates with the microtubule-binding domain, abrogating its affinity for microtubules. However, when the C-terminal domain is phosphorylated by Aurora A, it no longer binds to N-terminal HURP, thereby releasing the inhibition on its microtubule binding and stabilizing activity. In fact, ectopic expression of this C-terminal domain depletes endogenous HURP from the mitotic spindle in HeLa cells in trans, suggesting the physiological importance for this mode of regulation. We concluded that phosphorylation of HURP by Aurora A provides a regulatory mechanism for the control of spindle assembly and function.

Perioperative outcomes of major noncardiac surgery in adults with congenital heart disease.

Background:An increasing number of patients with congenital heart disease are surviving to adulthood. Consensus guidelines and expert opinion suggest that noncardiac surgery is a high-risk event, but few data describe perioperative outcomes in this population. Methods:By using the Nationwide Inpatient Sample database (years 2002 through 2009), the authors compared patients with adult congenital heart disease (ACHD) who underwent noncardiac surgery with a non-ACHD comparison cohort matched on age, sex, race, year, elective or urgent or emergency procedure, van Walraven comborbidity score, and primary procedure code. Mortality and morbidity were compared between the two cohorts. Results:A study cohort consisting of 10,004 ACHD patients was compared with a matched comparison cohort of 37,581 patients. Inpatient mortality was greater in the ACHD cohort (407 of 10,004 [4.1%] vs. 1,355 of 37,581 [3.6%]; unadjusted odds ratio, 1.13; P = 0.031; adjusted odds ratio, 1.29; P < 0.001). The composite endpoint of perioperative morbidity was also more commonly observed in the ACHD cohort (2,145 of 10.004 [21.4%] vs. 6,003 of 37,581 [16.0%]; odds ratio, 1.44; P < 0.001). ACHD patients comprised an increasing proportion of all noncardiac surgical admissions over the study period (P value for trend is <0.001), and noncardiac surgery represented an increasing proportion of all ACHD admissions (P value for trend is <0.001). Conclusions:Compared with a matched control cohort, ACHD patients undergoing noncardiac surgery experienced increased perioperative morbidity and mortality. Within the limitations of a retrospective analysis of a large administrative dataset, this finding demonstrates that this is a vulnerable population and suggests that better efforts are needed to understand and improve the perioperative care they receive.

Gene expression profiling: classification of mice with left ventricle systolic dysfunction using microarray analysis.

Objective:We tested the hypothesis that a set of differentially expressed genes could be used to classify mice according to cardiovascular phenotype after prolonged catecholamine stress. Design:Prospective, randomized study. Setting:University-based research laboratory. Subjects:One hundred seventy-three male mice were studied: wild-type (WT) C57, WT FVB, WT B6129SF2/J, and &bgr;2 adrenergic receptor knockout. Interventions:Mice of each genotype were randomly assigned to 14-day infusions of isoproterenol (120 &mgr;g/g/day) or no treatment. Approximately half of the animals underwent left ventricle pressure volume loop analysis. The remaining animals were killed for extraction of messenger RNA from whole heart preparations for microarray analysis. Measurements and Main Results:We observed that WT FVB and &bgr;2 adrenergic receptor knockout mice developed systolic dysfunction in response to continuous catecholamine infusion, whereas WT C57 mice developed diastolic dysfunction. Using these mice as the derivation cohort, we identified a set of 83 genes whose differential expression correlated with left ventricle systolic dysfunction. The gene set was then used to accurately classify mice from a separate group (WT B6129SF2/J) into the cohort that developed left ventricle systolic dysfunction after catecholamine stress. Conclusions:The differential expression pattern of 83 genes can be used to accurately classify mice according to physiological phenotype after catecholamine stress.

A Thrombus in the Venous Reservoir While Using Bivalirudin in a Patient with Heparin-induced Thrombocytopenia Undergoing Heart Transplantation

Direct thrombin inhibitors are heparin alternatives for anticoagulation during cardiopulmonary bypass in patients with heparin-induced thrombocytopenia. We report a case of a large thrombus forming in the venous reservoir while using bivalirudin. We suggest that blood stasis associated with the full venous reservoir maintained in this case led to formation of a large thrombus at the top of the venous canister. Furthermore, activated clotting times may not accurately reflect the magnitude of anticoagulation when using direct thrombin inhibitors.

Heart transplantation with or without prior mechanical circulatory support in adults with congenital heart disease

OBJECTIVES Recent analyses establish that heart transplantation is increasing among adults with congenital heart disease (ACHD), but the effects of pretransplant mechanical circulatory support (MCS) on perioperative and post-transplant outcomes have not been examined in the ACHD population. METHODS Scientific Registry of Transplant Recipients data on all adult heart transplants from September 1987 to September 2012 (n = 47 160) were classified based on primary diagnosis codes as CHD or non-CHD and MCS or non-MCS. Demographic, procedural, outcome and survival variables were compared between MCS and non-MCS ACHD patient groups. RESULTS MCS was used in 83 (6.8%) ACHD patients compared with 8625 (18.8%) patients without CHD (P < 0.001). MCS as a fraction of ACHD transplants increased over time (P = 0.002). MCS patients spent more time on the wait list, had a higher baseline serum creatinine and were more likely to be male, status 1A, hospitalized, in the ICU and/or on a ventilator prior to transplant. However, MCS patients experienced equivalent short-term survival (30-day mortality = 10.8% in MCS vs 13.5% in non-MCS, P = 0.62) and overall survival by Kaplan-Meier analysis (P = 0.57). MCS patients had a longer post-transplant length of stay and were more likely to be transfused, but otherwise had no significant differences in adverse outcomes. CONCLUSIONS MCS is less commonly used in adult CHD patients compared with all patients undergoing heart transplant, but has been increasing over time. Within the ACHD population, patients with MCS have a higher risk profile, but except for increased transfusion rate and longer length of stay, do not experience less favourable post-transplant outcomes.

Obstructive Sleep Apnea Is an Independent Predictor of Postoperative Atrial Fibrillation in Cardiac Surgery

OBJECTIVE To test the hypothesis that obstructive sleep apnea (OSA) is a risk factor for development of postoperative atrial fibrillation (POAF) after cardiac surgery. DESIGN Retrospective analysis. SETTING Single-center university hospital. PARTICIPANTS Five hundred forty-five patients in sinus rhythm preoperatively undergoing coronary artery bypass grafting (CABG), aortic valve replacement, mitral valve replacement/repair, or combined valve/CABG surgery from January 2008 to April 2011. INTERVENTIONS Retrospective review of medical records. MEASUREMENTS AND MAIN RESULTS Postoperative atrial fibrillation was defined as atrial fibrillation requiring therapeutic intervention. Of 545 cardiac surgical patients, 226 (41%) patients developed POAF. The risk was higher in 72 OSA patients than 473 patients without OSA (67% v 38%, adjusted hazard ratio 1.83 [95% CI: 1.30-2.58], p<0.001). Of the 32 OSA patients who used home positive airway pressure (PAP) therapy, 18 (56%) developed POAF compared with 29 of 38 (76%) patients who did not use PAP at home (unadjusted hazard ratio 0.63 [95% CI: 0.35-1.15], p = 0.13). CONCLUSION OSA is significantly associated with POAF in cardiac surgery patients. Further investigation is needed to determine whether or not use of positive airway pressure in OSA patients reduces the risk of POAF.

P-Wave Characteristics on Routine Preoperative Electrocardiogram Improve Prediction of New-Onset Postoperative Atrial Fibrillation in Cardiac Surgery

OBJECTIVE To test the hypothesis that including preoperative electrocardiogram (ECG) characteristics with clinical variables significantly improves the new-onset postoperative atrial fibrillation prediction model. DESIGN Retrospective analysis. SETTING Single-center university hospital. PARTICIPANTS Five hundred twenty-six patients, ≥ 18 years of age, who underwent coronary artery bypass grafting, aortic valve replacement, mitral valve replacement/repair, or a combination of valve surgery and coronary artery bypass grafting requiring cardiopulmonary bypass. INTERVENTIONS Retrospective review of medical records. MEASUREMENTS AND MAIN RESULTS Baseline characteristics and cardiopulmonary bypass times were collected. Digitally-measured timing and voltages from preoperative electrocardiograms were extracted. Postoperative atrial fibrillation was defined as atrial fibrillation requiring therapeutic intervention. Two hundred eight (39.5%) patients developed postoperative atrial fibrillation. Clinical predictors were age, ejection fraction<55%, history of atrial fibrillation, history of cerebral vascular event, and valvular surgery. Three ECG parameters associated with postoperative atrial fibrillation were observed: Premature atrial contraction, p-wave index, and p-frontal axis. Adding electrocardiogram variables to the prediction model with only clinical predictors significantly improved the area under the receiver operating characteristic curve, from 0.71 to 0.78 (p<0.01). Overall net reclassification improvement was 0.059 (p = 0.09). Among those who developed postoperative atrial fibrillation, the net reclassification improvement was 0.063 (p = 0.03). CONCLUSION Several p-wave characteristics are independently associated with postoperative atrial fibrillation. Addition of these parameters improves the postoperative atrial fibrillation prediction model.