Site-specific phosphorylation of ZYG-1 regulates ZYG-1 stability and centrosome number

Spindle bipolarity is critical for genomic integrity. As centrosome number often dictates bipolarity, tight control of centrosome assembly is vital for faithful cell division. The master centrosome regulator ZYG-1/Plk4 plays a pivotal role in this process. In C. elegans, casein kinase II (CK2) negatively regulates centrosome duplication by controlling centrosome-associated ZYG-1 levels. Here, we investigated CK2 as a regulator of ZYG-1 and its impact on centrosome assembly. We show that CK2 phosphorylates ZYG-1 in vitro and physically interacts with ZYG-1 in vivo. Depleting CK2 or blocking ZYG-1 phosphorylation at CK2 target sites leads to centrosome amplification. Non-phosphorylatable ZYG-1 mutants exhibit elevated ZYG-1 levels, leading to increased ZYG-1 and downstream factors at centrosomes, thus driving centrosome amplification. Moreover, inhibiting the 26S proteasome prevents degradation of the phospho-mimetic ZYG-1. Our findings suggest that CK2-dependent phosphorylation of ZYG-1 controls ZYG-1 levels via proteasomal degradation to limit centrosome number.

Structure of a 10-23 Deoxyribozyme Exhibiting a Homodimer Conformation

Deoxyribozymes (DNAzymes) are in vitro evolved DNA sequences capable of catalyzing chemical reactions. The RNA cleaving 10-23 DNAzyme was the first DNAzyme to be evolved and possesses clinical and biotechnical applications as a biosensor and a knockdown agent. DNAzymes do not require the recruitment of other components to cleave RNA and can turnover, thus they have a distinct advantage over other knockdown methods (siRNA, CRISPR, morpholinos). Despite this, a lack of structural and mechanistic information has hindered the optimization and application of the 10-23 DNAzyme. Here, we report a 2.7 Å crystal structure of the RNA cleaving 10-23 DNAzyme in a homodimer conformation. Although proper coordination of the DNAzyme to substrate is observed along with intriguing patterns of bound magnesium ions, the dimer conformation likely does not capture the true catalytic form of the 10-23 DNAzyme.

Site-Specific Phosphorylation of ZYG-1 Regulates ZYG-1 Stability and Centrosome Number

Spindle bipolarity is critical for genomic integrity. Given that centrosome number often dictates mitotic bipolarity, tight control of centrosome assembly is vital for the fidelity of cell division. The kinase ZYG-1/Plk4 is a master centrosome factor that is integral for controlling centrosome number and is modulated by protein phosphorylation. While autophosphorylation of Plk4 has been extensively studied in other systems, the mechanism of ZYG-1 phosphorylation in C. elegans remains largely unexplored. In C. elegans, Casein Kinase II (CK2) negatively regulates centrosome duplication by controlling centrosome-associated ZYG-1 levels. In this study, we investigated ZYG-1 as a potential substrate of CK2 and the functional impact of ZYG-1 phosphorylation on centrosome assembly. First, we show that CK2 directly phosphorylates ZYG-1 in vitro and physically interacts with ZYG-1 in vivo. Intriguingly, depleting CK2 or blocking ZYG-1 phosphorylation at putative CK2 target sites leads to centrosome amplification. In the non-phosphorylatable (NP)-ZYG-1 mutant embryo, the overall levels of ZYG-1 are elevated, leading to an increase in centrosomal ZYG-1 and downstream factors, providing a possible mechanism of the NP-ZYG-1 mutation to drive centrosome amplification. Moreover, inhibiting the 26S proteasome blocks degradation of the phospho-mimetic (PM)-ZYG-1, while the NP-ZYG-1 mutant shows partial resistance to proteasomal degradation. Our findings suggest that site-specific phosphorylation of ZYG-1, partly mediated by CK2, controls ZYG-1 levels via proteasomal degradation, limiting centrosome number. We provide a mechanism linking CK2 kinase activity to centrosome duplication through direct phosphorylation of ZYG-1, which is critical for the integrity of centrosome number.

Influence of selection bias on the test decision. A simulation study

BACKGROUND

Selection bias arises in clinical trials by reason of selective assignment of patients to treatment groups. Even in randomized clinical trials with allocation concealment this phenomenon can occur if future assignments can be predicted due to knowledge of former allocations.

OBJECTIVES

Considering unmasked randomized clinical trials with allocation concealment the impact of selection bias on type I error rate under permuted block randomization is investigated. We aimed to extend the existing research into this topic by including practical assumptions concerning misclassification of patient characteristics to get an estimate of type I error close to clinical routine. To establish an upper bound for the type I error rate different biasing strategies of the investigator are compared first. In addition, the aspect of patient availability is considered.

METHODS

To evaluate the influence of selection bias on type I error rate under several practical situations, different block sizes, selection effects, biasing strategies and success rates of patient classification were simulated using SAS.

RESULTS

Type I error rate exceeds 5 percent significance level; it reaches values up to 21 percent. More cautious biasing strategies and misclassification of patient characteristics may diminish but cannot eliminate selection bias. The number of screened patients is about three times larger than the needed number for the trial.

CONCLUSIONS

Even in unmasked randomized clinical trials using permuted block randomization with allocation concealment the influence of selection bias must not be disregarded evaluating the test decision. It should be incorporated when designing and reporting a clinical trial.

Recombinant hirudin for cardiopulmonary bypass anticoagulation: a randomized, prospective, and heparin-controlled pilot study

BACKGROUND

Lepirudin, a recombinant hirudin, is a direct acting thrombin inhibitor that has been used as a heparin alternative in patients with heparin-induced thrombocytopenia requiring on-pump cardiac surgery. To evaluate the efficacy, safety, and clinical utility of lepirudin as a cardiopulmonary bypass (CPB) anticoagulant, we compared lepirudin with heparin in a routine CPB setting.

METHODS

Twenty patients were randomly assigned to receive lepirudin (0.25 mg/kg b. w. bolus and 0.2 mg/kg b. w. added to the CPB priming) or heparin (400 U/kg b. w. bolus) with protamine reversal. Lepirudin and heparin anticoagulation during CPB was monitored using the ecarin clotting time or ACT, respectively and additional lepirudin (5 mg) or heparin (5000 U) boluses were administered.

RESULTS

The CPB circuit was performed in both groups without thromboembolic complications. Median blood loss during the first 36 hours was statistically higher ( P = 0.007) in the lepirudin group (1.226 +/- 316 ml) compared to the heparin group (869 +/- 189 ml). One patient of the lepirudin group developed pulmonary embolism 24 hours after surgery. This patient was tested homozygous for the FV-Leiden mutation.

CONCLUSION

Lepirudin provides effective CPB anticoagulation but induces a higher postoperative blood loss than heparin. Lepirudin should be restricted to patients undergoing CPB who cannot be exposed to heparin.

A phase II study of low-dose prolonged infusional gemcitabine combined with oral treosulfan in patients with platinum- and taxane-resistant ovarian cancer or other Mullerian tract carcinomas

15004

The prognosis of patients (pts) with epthelial ovarian cancer (EOC) and other Mullerian tract carcinomas such as papillary-serous peritoneal carcinoma (PSPC), fallopian tube cancer (FTC), and uterine papillary-serous carcinoma (UPSC) resistant to both platinum and taxanes is particularly poor. Recently, we have reported preliminary results of modified GeT - gemcitabine (dFdC) and treosulfan (TREO) (Kurbacher et al, Proc ASCO 2005). Now, mature results of this phase II trial are available. A total of 35 patients (pts) were included (EOC, 29; FTC, 4; PSPC, 1; UPSC, 1). Patients had failed a median of 2 prior chemotherapies (1, n = 10; 2, n = 11; 3, n = 7; 4, n = 3; 5, n = 3; 7, n = 1) including platinum and paclitaxel in all, anthracyclines in 16, dFdC in either 6, and topotecan in 5 pts. GeT was administered at a q2w schedule with dFdC at 450 mg/m2 (3 h infusion), day 1, and oral TREO at 1,000 mg/m2/d, day 1–4. A total of 192 cycles were given with a median of 6 (range: 2–10). All pts had measurable or evaluable disease according to RECIST and Rustin criteria, repectively. All treatments were evaluable for both toxicity and response. Myelosuppression was frequent but exceeded NCI-CTC grade 2 in only 17/192 cycles (9%). G 3–4 neutropenia was observed during 5/192 cycles (3%), G 3–4 thrombocytopenia did not occur. Interval prolongation due to febrile urinary tract infection or subileus was necessary in two pts. In another patient, treatment was terminated due to non-fatal pulmonary embolism. Other toxicities did not exceed NCI-CTC grade 2 nor did any other patient require hospitalization due to therapy-related complications. A total of 11 CR, 7 PR, 9 SD, and 8 PD were recorded accounting for an objective response rate of 51% with 27 pts (77%) benefiting from GeT. The median progression-free survival was 27 weeks. Until now, 15 pts are still alive, the median overall survival is 76.5 weeks. Regarding the intensive pre-treatment of the pts, the modified GeT treatment was easy to tolerate and produced a promising clinical efficacy in EOC and other Mullerian tract carcinomas resistant to both platinum and taxanes. Large-scaled clinical trials are now warrented to confirm these encouraging results.

No significant financial relationships to disclose.

Neoadjuvant, biweekly, dose-dense chemotherapy with epirubicin (E) and cyclophosphamide (C) followed by docetaxel (T) in primary breast cancer (BC)

10656

Background: Primary chemotherapy is established in the treatment of local advanced BC. Two important advances are the chance to detect the clinical responders during the chemotherapy and an increasing rate of breast conserving surgery (BCS). According to the promissing results of dose-dense chemotherapy schedules in the adjuvant setting we tested the benefit of this approach in a primary chemotherapy protocol. Methods: This clinical trial (01/2003–11/2005) enrolled 93 females with advanced (cT2-cT4), non metastatic BC. The pts received four courses of E (90 mg/m2) and C (600 mg/m2) q2w, followed by four courses of T (100/75 mg/m2) q2w. The severe hand-foot-skin reaction NCI-CTG grade 3 during the T courses of the first pts (G1: n = 19) lead to a dose reduction of T to 75 mg/m2 for the following pts (G2: n = 73). During the first four cycles Pegfilgrastim was applied to prevent neutropenic complications. After every two cycles the actual tumor size was measured by clinical and sonographical examination. The clinical and pathological response, the toxicity and the rate of BCS were evaluated. Results: Pathological complete remission (pCR) of the invasive tumors was observed in 7/19 pts (G1) and 17/73 (G2), pathological partial remission (pPR) in 7/19 pts (G1) and 28/73 (G2), minimal response (pMR) in 3/19 pts (G1) and 14/73 (G2), a stable disease in 2/19 pts (G1) and 11/73 (G2). Two pts in group two showed a progressive disease (pPD). Three pts developed neutropenic fever and stopped the chemotherapy after the 5th and 6th cycle, respectively. One patient died after the 8th cycle in neutropenic sepsis. During this trial the main side effect of T was a hand-foot-skin reaction. Conclusions: This neoadjuvant dose-dense chemotherapy is a potent schedule for the treatment of primary BC. Using T with 75 mg/m2 instead of 100 g/m2 is generally better tolerated. The first group of pts treated with T 100 mg/m2 exhibited a higher frequency of pCR (36.8%) compared to the pts treated with 75 mg/m2 (pCR 23.3%), (p = 0.23). But the increased rate of severe side effects lead to an early dose reduction to 75 mg/m2 in this clinical trial.These first promissing results will be improved in an enlarged number of pts.

No significant financial relationships to disclose.

The expression of prion protein (PrP(C)) in the megakaryocyte lineage

BACKGROUND

Cellular prion protein (PrP(C)) is a naturally occurring protein in normal individuals which adopts an abnormal conformation, termed scrapie prion protein (PrP(Sc)) that is associated with disease. There is great concern that clinically asymptomatic variant Creutzfeldt-Jacob disease (vCJD) may transmit PrP(Sc) in blood transfusion products. PrP(C) is widely expressed and has been found in human blood. The majority of cellular borne PrP(C) is associated with platelets (84%). Although PrP(C) mRNA has been demonstrated in platelets, the quantity is unknown and may not reflect the total PrP(C) present.

OBJECTIVE

To investigate the expression of PrP(C) in the megakaryocyte lineage.

METHODS

The expression of PrP(C) was studied in CD34+ cells, cultured megakaryocytes and platelets using electron microscopy, flow cytometry, semi-quantitative RT-PCR and immunofluorescence confocal microscopy.

RESULTS AND CONCLUSIONS

The expression of PrP(C) appeared to increase with differentiation and polyploidization in the megakaryocyte lineage. PrP(C) was located within platelet alpha-granules and its source is likely to be from megakaryocyte precursors. If PrP(Sc) has a similar distribution, these results have implications for the selection of blood donors and preparation of cell-depleted blood products.

Identification of CD146 as a component of the endothelial junction involved in the control of cell-cell cohesion

CD146 is a cell-surface molecule belonging to the immunoglobulin superfamily and expressed in all types of human endothelial cells. Confocal and electron microscopic analysis of confluent human umbilical vein endothelial cells (HUVECs) were used to demonstrate that CD146 is a component of the endothelial junction. Double immunolabeling with vascular endothelial cadherin showed that CD146 is localized outside the adherens junction. Moreover, CD146 expression is not restricted to the junction, since part of the labeling was detectable at the apical side of the HUVECs. Interestingly, cell-surface expression of CD146 increased when HUVECs reached confluence. In addition, the paracellular permeability of CD146-transfected fibroblast cells was decreased compared with that of control cells. Finally, CD146 colocalized with actin, was partly resistant to Triton X-100 extraction, and had its expression altered by actin-disrupting agents, indicating that CD146 is associated with the actin cytoskeleton. These results show the regulated expression of CD146 at areas of cell-cell junction and strongly suggest involvement of CD146 as a mediator of cell-cell interaction.

Compared effects of Mpl ligand and other cytokines on human MK differentiation

The discovery of the Mpl ligand (Mpl-L), also called thrombopoietin (TPO), has facilitated in vitro investigation of human megakaryocytopoiesis. By confocal microscopy, endomitosis appeared as abortive mitosis skipping late stages of mitosis. No telophase and cytokinesis were observed. A spherical multipolar spindle which limits chromatid segregation was observed. The nuclear envelope subsequently reformed isolating all chromatids in a single nucleus. Platelet shedding was ultrastructurally studied. Platelet release occurred after formation of long cytoplasmic extensions (proplatelet formation), constriction areas delineating platelet territories. Heterogeneity in platelet size may be determined by the length of these extensions. Pegylated-recombinant human megakaryocyte growth and development factor, a truncated form of Mpl-L, was the most efficient cytokine to produce proplatelet-bearing megakaryocytes (MKs) and platelets in vitro. However, functional platelets with a normal ultrastructure could be produced in the presence of a combination of other cytokines. Finally, we investigated whether the induction of MK differentiation by the MS-5 stromal cell lines is due to Mpl-L. MS-5 cells synthesized Mpl-L transcripts and a biologically active protein. When human CD34+ cells were grown in contact or noncontact cultures with MS-5 cells, MK differentiation was observed. Soluble Mpl receptor (sMpl-Fc) addition inhibited MK growth, suggesting that the MK-promoting activity was due to Mpl-L production. Marrow stromal cell lines derived from TPO-/- mice were also able to sustain MK growth. Despite the absence of any production of Mpl-L, the sMpl-Fc continued to inhibit MK differentiation. This result suggests that the sMpl has a direct inhibitory effect and may explain the divergent results in the literature concerning the precise role of Mpl-L on the MK terminal differentiation.

Transforming growth factor inhibits erythropoiesis by blocking proliferation and accelerating differentiation of erythroid progenitors

Erythropoiesis is positively regulated by stem cell factor, interleukin 3, and erythropoietin, which synergize to allow the production of hemoglobinized red blood cells from erythroid progenitors. In contrast, interferon gamma, tumor necrosis factor alpha, and transforming growth factor B(1), (TGF-beta(1)) are powerful inhibitors of erythropoiesis. Interferon gamma and alpha act principally by inducing apoptosis. The aim of this study was to elucidate the mechanisms by which TGF-beta(1) inhibits erythropoiesis. We used an in vitro serum-free system of human red blood cell production. From a virtually pure population of CD36(+) erythroid progenitors, stem cell factor, interleukin 3, and erythropoietin allowed massive proliferation (x300) and promoted terminal red blood cell differentiation. We show here that TGF-beta(1) (2 ng/mL) inhibited the growth of CD36(+) cells by 15-fold. TGF-beta(1) markedly accelerated and increased erythroid differentiation as assessed by hemoglobin and glycophorin expression. Furthermore, May-Grünwald-Giemsa staining and ultrastructural analysis revealed that TGF-beta(1) induced full differentiation toward normal enucleated red cells even in the absence of macrophages. This acceleration of erythroid differentiation did not modify the pattern of hemoglobin chains expression from adult or fetal erythroid progenitors. Analysis of apoptosis, cell cycle and Ki-67 expression showed that TGF-beta(1) inhibited cell proliferation by decreasing the cycle of immature erythroid cells and accelerating maturation toward orthochromatic normoblasts that are not in cycle. We showed that TGF-beta(1) is a paradoxical inhibitor of erythropoiesis that acts by blocking proliferation and accelerating differentiation of erythroid progenitors.

Acquired delta-storage pool deficiency associated with idiopathic myelofibrosis

A 73-year-old woman complained of easy bruising, as a consequence of prolonged bleeding time despite normal platelet counts. Platelet aggregation profile, mepacrine fluorescence test, flow cytometry and transmission electron microscopy studies led to the diagnosis of delta-storage pool deficiency (SPD) A few months later, she developed hyperleucocytosis with immature granulocytes and erythroblasts. The presence of bone marrow fibrosis and clonal cytogenetic abnormalities led to the diagnosis of idiopathic myelofibrosis (IM). Association between SPD and IM has never been reported. The pathogenesis of this unusual association remains unclear and may involve proliferation of abnormal monoclonal stem cells with differentiation into activated megakaryocytes associated with impaired dense granule development and increased cytokines release which may be. involved in myelofibrosis.

Hematologic involvement in mitochondrial cytopathies in childhood: a retrospective study of bone marrow smears

We retrospectively analyzed the bone marrow (BM) smears of 10 children with mitochondrial cytopathies. Light microscopic examination showed large and coalescent cytoplasmic vacuolization of some BM precursors in nine cases, including two children with normal peripheral blood counts and four with sideroblastic anemia. BM ultrastructural study showed abnormal mitochondria in the erythroid lineage in all three children studied. Ultrastructural studies in two cases revealed a population of giant mitochondria with abnormal ultrastructure coexisting with a population of normal mitochondria in proerythroblasts, basophil erythroblasts, and less commonly in more mature erythroblasts. In a third child, mitochondria were normal in size with cristae either absent or exhibiting abnormal longitudinal orientation. Heteroplasmic segregation of mitochondria during cell division could account for the finding of a double population of cells on ultrastructural examination. These features suggest that cytologic and ultrastructural BM examination could be useful for the diagnosis of mitochondrial disorders. That is, when large and coalescent cytoplasmic vacuoles of BM precursor cells are present, the clinician should search for mitochondrial cytopathy in a child with unexplained cytopenia(s).