Characterization of high-power and very-high-power short-duration radiofrequency lesions performed with a new-generation catheter and a temperature-control ablation mode

Funding Acknowledgements

Type of funding sources: None.

Introduction

High-power short-duration (HP-SD) and very high-power short-duration (VHP-SD) has recently emerged as an alternative ablation strategy to shorten application times while maintaining or improving the effectiveness and safety of atrial fibrillation ablation (1 - 2). Although usually performed with standard irrigated-tip catheters in a power-controlled mode, a novel dedicated catheter with a multi-thermocouple system capable of real-time temperature monitoring and optimized for temperature-controlled ablation by power and irrigation rate modulation has been developed for this scenario (3 - 4).

Purpose

We conducted an experimental ex-vivo study to analyse the differences between radiofrequency lesions obtained with this novel catheter (QDOT MICRO®) using HP-SD and VHP-SD. Besides, we also aim to compare them to HP-SD lesions obtained with a standard non-dedicated catheter (THERMOCOOL SMARTTOUCH®) and to conventional-powered lesions performed with either catheter.

Methods

280 epicardial radiofrequency applications were performed on porcine left ventricle submerged in 37ºC saline: 40 VHP-SD (90W) with QDOT MICRO (4 sets of 10 using a contact force (CF) of 10 and 20 grams and an application time of 3 and 4 seconds); 80 HP-SD lesions (50W), 40 of them with QDOT MICRO and 40 of them with THERMOCOOL SMARTTOUCH (4 sets of 10 lesions using a CF of 10 and 20 and an ablation index (AI) of 400 and 550 with each catheter) and 160 conventional-power lesions (35 and 40W), 80 of them with QDOT MICRO and 80 of them with THERMOCOOL SMARTTOUCH (4 sets of 10 lesions using a CF of 10 and 20 and an AI of 400 and 550 for each catheter and power setting). After each application, lesions were cross-sectioned and measured. Volume vas calculated using a validated formula (5).

Results

In an intracatheter analysis, HP-SD lesions were bigger than VHP-SD ones, both when using parameters intended for posterior wall ablation (AI 400 in HP-SD or 3 seconds in VHP-SD), 98.1±11.7 vs 36.8±8.5 mm3, p<0.0001 with 10g CF, and 106.7±8.1 vs 52.3±9.8 mm3, p<0.0001 with 20g CF; and when using parameters intended for anterior wall ablation (AI 550 in HP-SD or 4 seconds in VHP-SD), 227.6±25.1 vs 61.0±7.8 mm3, p<0.0001 with 10g CF, and 186.6±23.3 vs 72.2±5.0 mm3, p<0.0001 with 20g CF (see figure).

In an intercatheter analysis, conventional as well as HP-SD lesions were generally smaller with THERMOCOOL SMARTTOUCH than with QDOT MICRO, although less difference could be found when applying a CF of 20g instead of 10g (see figure and table).

Conclusions

VHP-SD lesions are smaller than HP-SD ones, which would allow for a safer and faster ablation. However, a HP-SD strategy would be preferable over VHP-SD if greater lesion volume is desirable.

Subjective identification and ablation of drivers in persistent atrial fibrillation (CHAOS-AF study): results of the first 50 patients

Funding Acknowledgements

Type of funding sources: None.

Background

Ablation of drivers in persistent atrial fibrillation (AF) has shown controversial results [1-5].

Purpose

To test the efficacy of a tailored approach for persistent AF ablation which includes pulmonary vein isolation (PVI) plus ‘subjective’ identification and ablation of drivers.

Methods

From May 2017, selected patients with persistent AF and ongoing AF at the beginning of the ablation procedure were included. Conventional high-density mapping catheters were used. Drivers were subjectively identified as: a) fractionated continuous (or quasi-continuous) electrograms on 1-2 adjacent bipoles, without dedicated software (Figure, A, dashed line; PR = PentaRay NAV); and b) sites with spatiotemporal dispersion (i.e. all the cycle length comprised within the mapping catheter) plus non-continuous fractionation on single bipoles (Figure, B, arrows; in panels A and B: paper speed 200 mm/s; ORB = 24-pole ORBITER Woven catheter, blue bipoles around tricuspid annulus and green bipoles into the coronary sinus). Ablation included PVI + focal or linear ablation targeting sites with drivers. Ablation success was defined as conversion to sinus rhythm or atrial flutter during ablation. Follow-up included visits with 24h Holter ECG at 3-6-12 months. The primary endpoint was one-year survival free from atrial arrhythmias lasting >30 seconds. We present the results of the first 50 patients included, comparing them with all consecutive patients with persistent AF treated with a PVI-only strategy.

Results

173 Patients received ablation: 50 with the tailored approach (61,2±9,6 years; 24% females) and 123 with only PVI (62,5±9,6 years; 25% females; 89% cryoablation). Basal characteristics were similar (Table), but more patients with long-standing persistent AF were ablated witth the tailored-approach group. In the tailored-approach group, 21 patients (42%) presented 40 detectable sites with continuous fractionated electrograms, 38 on the left atrium and 2 on the right atrium, which was only mapped if ablation of drivers in the left atrium was not successful; 18 (45%) were located within the pulmonary vein antra. 41 patients (82%) showed 143 sites with spatiotemporal dispersion (4 [3 – 4] per patient). Ablation success was achieved in 21 patients (42%; conversion to sinus rhythm, n=7; conversion to atrial flutter, n=14) in the tailored-approach group and 1 patient (0,8%, sinus rhythm) in the PVI-only group. Excluding a 3-month blanking period, the tailored approach, compared to only PVI, improved one-year freedom from atrial arrhythmias (70% Vs 52%, p=0,032) (Figure, C), at the cost of a longer median procedural time (244 [187–275] Vs 108 [81–143] min, p<0,001) and fluoroscopy time (41 [28–65] Vs 33 [21–45] min, p<0,001).

Conclusion

Subjective identification and ablation of drivers, added to PVI, improved one-year survival free from atrial arrhythmias.

Subjective identification and ablation of drivers in persistent atrial fibrillation

Background

Ablation of drivers in persistent atrial fibrillation (AF) has shown controversial results.

Purpose

To test the efficacy of a tailored approach for persistent AF ablation which includes pulmonary vein isolation (PVI) plus “subjective” identification and ablation of drivers.

Methods

From May 2017 to December 2019, selected patients with persistent AF and ongoing AF at the beginning of the ablation procedure were included. Conventional high-density mapping catheters (PentaRay NAV, IntellaMap Orion or Advisor HD Grid) were used. Drivers were subjectively identified as: a) fractionated continuous (or quasi-continuous) electrograms on 1–2 adjacent bipoles, without dedicated software (Figure 1A, dashed line; PR = PentaRay NAV); and b) sites with spatiotemporal dispersion (i.e. all the cycle length comprised within the mapping catheter) plus non-continuous fractionation on single bipoles (Figure 1B, arrows; in panels A and B: paper speed 200 mm/s; ORB = 24-pole ORBITER Woven catheter, blue bipoles around tricuspid annulus and green bipoles into the coronary sinus). Ablation included PVI + focal or linear ablation targeting sites with drivers. Ablation success was defined as conversion to sinus rhythm or atrial flutter during ablation. Follow-up included visits with 24h Holter ECG at 3–6–12 months. Survival free from atrial arrhythmias lasting >30 seconds was compared between patients ablated with this tailored approach, and all consecutive patients with persistent AF treated with a PVI-only strategy during the same period.

Results

158 Patients received ablation: 35 with the tailored approach (61,7±10,2 years; 29% females) and 123 with only PVI (62,5±9,6 years; 25% females; 89% cryoablation). Basal characteristics were similar (Table 1). In the tailored-approach group, 14 patients (40%) presented 28 detectable sites with continuous fractionated electrograms, 26 on the left atrium and 2 on the right atrium, which was only mapped if ablation of drivers in the left atrium was not successful; 12 (43%) were located within the pulmonary vein antra. 27 patients (77%) showed 103 sites with spatiotemporal dispersion (4 [3–5] per patient). Ablation success was achieved in 17 patients (48%; conversion to sinus rhythm, n=7; conversion to atrial flutter, n=10) in the tailored-approach group and 1 patient (0,8%, sinus rhythm) in the PVI-only group. Excluding a 3-month blanking period, the tailored approach, compared to only PVI, improved one-year freedom from atrial arrhythmias (71% Vs 51%, p=0,05) and mean survival free from atrial arrhythmias (26±3 months; 95% CI 21–32 months Vs 18±2 months; 95% CI 15–22 months) (Figure 1C), at the cost of a longer median procedural time (246 [212–277] vs 108 [81–143] min, p<0,001) and fluoroscopy time (51 [36–76] vs 33 [21–45] min, p<0,001).

Conclusion

Subjective identification and ablation of drivers, added to PVI, improved freedom from atrial arrhythmias.

Funding Acknowledgement

Type of funding sources: None. Table 1. Basal characteristicsFigure 1

Stabilization of unstable reentrant atrial tachycardias via fractionated continuous electrical activity ablation (CHAOS study)

Funding Acknowledgements

Type of funding sources: None.

Background. Unstable reentrant atrial tachycardias (ATs) (i.e. those with frequent circuit modification or conversion to atrial fibrillation) are challenging to ablate. 

Purpose. We have tested a strategy to convert unstable reentrant ATs into mappable stable ATs based on the detection and ablation of rotors.

Methods. From May 2017 to December 2019, we included all consecutive patients scheduled for ablation of reentrant AT, excluding CTI-dependent atrial flutter, in which the tachycardia circuit was unstable. Operators subjectively identified rotors as sites with fractionated continuous (or quasi-continuous) electrical signals on 1-2 adjacent bipoles of conventional high-density mapping catheters, without dedicated software (Figure, A). Focal ablation of these sites was performed in order to stabilize the AT or convert it into sinus rhythm. In patients without rotors or failed rotor ablation, sites with spatiotemporal dispersion (i.e. all the cycle length comprised within the mapping catheter) plus non-continuous fractionation on single bipoles were targeted (Figure, B). Procedural success was defined as the successful ablation of all inducible ATs, without need of cardioversion, final sinus rhythm and non-inducibility. Follow-up included visits with ECG and 24h Holter-ECG at 3, 6 and 12 months.

Results. From May 2017 to December 2019, 97 patients were scheduled for reentrant AT ablation, excluding CTI-dependent atrial flutter. Of these, 18 patients (18.6%; 72.1 ± 8.9 years of age, 9 females) presented unstable circuits and were included. 9 patients (50%) had structural cardiomyopathy, 11 patients (61%) prior atrial arrhythmias ablations, and 4 patients (22%) previous cardiac surgery. 13 patients (72%) had detectable rotors (26 rotors; median 2 [1–3] rotors per patient); focal ablation achieved conversion into stable AT or sinus rhythm in 12 (92%). In the other patient, and the 5 patients without detectable rotors, 17 sites with spatiotemporal dispersion were detected and focally ablated, with success to achieve arrhythmia stabilization in 5 patients (83%). Globally, and excluding one patient with spontaneous AT stabilization, ablation success to stabilize the AT was achieved in 16/17 patients (94.1%). Procedural success was achieved in 16/18 patients (88.9%). Rate of one-year freedom from atrial arrhythmias was 66.7%. In the 9 patients with stable ATs ablated during the same period, procedural success (92.4%) and one-year freedom from atrial arrhythmias (65.8%) were similar (Figure, C).

Conclusion. Most unstable reentrant ATs show detectable rotors, identified as sites with single-bipole fractionated quasi-continuous signals, or spatiotemporal dispersion plus non-continuous fractionation. Ablation of these sites is highly effective to stabilize the AT or convert it into sinus rhythm. Abstract FIGURE

MAPping with fragmentation analysis in patients with atypical atrial FLUtter using the RHYthmia navigation system (MAP-FLURHY study)

Background

Atypical atrial flutter (AAFL) circuits use areas of slow conduction which can be visualized as fragmented electrograms (fEGMs).

Purpose

To test an ablation strategy based on the identification and ablation of spots with fEGMs in AAFL.

Methods

The MAP-FLURHY study prospectively included all AAFL ablations with Rhythmia in our Center from June 2016 to June 2019. Patients with non-mappable AAFL, frequent conversion to atrial fibrillation, or cavotricuspid isthmus-dependent flutters were excluded from analysis. The IntellaMap ORION catheter was used to detect fragmentation areas, arbitrarily defined as fEGMs >70ms. Entrainment was used to check if these areas belonged to the AAFL circuit. Ablation targeted the longest fEGM within the circuit (return cycle <30ms): focal ablation for microreentries, and lines including the fEGMs for macroreentries. Ablation success was defined as conversion to sinus rhythm or another flutter. Procedural success was defined as successful ablation of all inducible flutters. Follow-up included visits with 24h Holter ECG at 3–6-12 months.

Results

50 Patients received ablation (Figure). 27 Patients (70.6±13.1 years; 10 females; LVEF 57%±13%) with 44 mappable AAFLs were included in the analysis (Table). All AAFLs showed areas with fEGMs (106 areas; 2.4 areas per flutter). 42/44 AAFLs had fEGMs within the circuit, which were target of ablation. Ablation success: 34/36 AAFLs (94%); success could not be assessed in 6 circuits, due to mechanical conversion to sinus rhythm onto the target fEGM. Fragmented areas within the AAFL circuits (n=51) were longer (110±30 vs 90±15 ms, p<0.001) but had similar voltage (0.34±0.25 vs 0.36±0.26 mV) than areas outside the circuits (n=45). A fEGM duration >100ms/>40% of the cycle length predicted to be a successful site for ablation with 72.3%/73.8% specificity. Procedural success was achieved in 24/27 patients (89%). Excluding a 2-month blanking period, mean survival free from atrial arrhythmias was 19 (95% CI: 12.6–25.5) months. 57% of the patients were free from atrial arrhythmias at 1 year.

Conclusions

Most AAFLs had detectable fEGMs which could be target of ablation with high efficacy.

Figure 1

Funding Acknowledgement

Type of funding source: None

Targeting MAD2 modulates stemness and tumorigenesis in human Gastric Cancer cell lines

Rationale: Gastric cancer (GC) is a solid tumor that contains subpopulations of cancer stem cells (CSCs), which are considered drivers of tumor initiation and metastasis; responsible for therapeutic resistance; and promoters of tumor relapse. The balance between symmetric and asymmetric division is crucial for stem cell maintenance. The objective of this study is to evaluate the role of MAD2, a key protein for proper mitotic checkpoint activity, in the tumorigenesis of GC.

Methods: Gastric cancer stem cells (GCSCs) were obtained from MKN45, SNU638 and ST2957 cell lines. Pluripotency and stemness markers were evaluated by RT-qPCR and autofluorescence and membrane markers by flow cytometry. Relevant signal transduction pathways were studied by WB. We analysed cell cycle progression, migration and invasion after modulation of MAD2 activity or protein expression levels in these in vitro models. In vivo assays were performed in a nude mouse subcutaneous xenograft model.

Results: We found that NANOG, CXCR4 and autofluorescence are common and consistent markers for the GCSCs analysed, with other markers showing more variability. The three main signalling pathways (Wnt/β-catenin; Hedgehog and Notch) were activated in GCSCs. Downregulation of MAD2 in MKN45^CSCs decreased the expression of markers CXCR4, CD133, CD90, LGR5 and VIM, without affecting cell cycle profile or therapy resistance. Moreover, migration, invasion and tumor growth were clearly reduced, and accordingly, we found that metalloprotease expression decreased. These results were accompanied by a reduction in the levels of transcription factors related with epithelial-to-mesenchymal transition.

Conclusions: We can conclude that MAD2 is important for GCSCs stemness and its downregulation in MKN45^CSCs plays a central role in GC tumorigenesis, likely through CXCR4-SNAI2-MMP1. Thus, its potential use in the clinical setting should be studied as its functions appear to extend beyond mitosis.

P2839The golden age of ablation: results for atypical flutter ablation in the very elderly

Introduction

Atypical flutter ablation (AFL) is a challenging procedure with limited long-term benefits and not exempt from significant risks.

Purpose

To compare the efficacy and safety of this procedure in a population of octogenarian patients over a population of younger patients.

Methods

From 2015 to 2018, all patients in which AFL ablation was attempted were included. Activation and voltage mapping were used to define AFL circuit. Radiofrequency lesions were performed to operator's discretion until AFL termination. Programmed atrial stimulation was repeated to test inducibility, and any sustained induced arrhythmia was ablated. Follow-up included visits with ECG and/or 24h Holter-ECG at 3 and 12 months.

Results

107 patients (55 females) were included, 26 (24%) aged 80 or older (table). Successful ablation of the original circuit was achieved in 96% in both groups (acute success rate, p=0.973), with induction of other AFL circuits in 43% (46% octogenarians, 42% younger, p=0.708), successfully ablated in 88% in both groups (total success rate, p=0.952). No significant difference was detected in the rate of adverse events (8% in octogenarians versus 7% in younger, p=0.962), with a case of cardiac tamponade in the former, successfully resolved. After a mean follow-up of 11±12 months, 52 patients (49%) were free from recurrence, 13 (50%) in the octogenarian group and 39 (48%) in the younger, with an estimated median survival free from atrial arrhythmias of 26 months (95% CI: 4–48) in the octogenarian group and 18 months (95% CI: 5–32) in the younger group (p=0.716). After multivariate analysis, history of prior AF and indexed left atrial volume, but not age, predicted recurrence.

Demographical and clinical variables All patients (n=107) Octogenarians (n=26) No octogenarians (n=81) p-value Age (years) 69±13 83±3 65±11 <0.0001* Cardiomyopathy (%) 54 (50%) 13 (26%) 41 (51%) 0.956 Left ventricular ejection fraction (%) 60±13 57±17 61±11 0.24 Indexed left atrial volume (ml/m2) 45±19 48±14 43±19 0.55 Prior AF history 49 (46%) 7 (27%) 42 (52%) 0.026* Prior ablation procedures 53 (50%) 8 (31%) 45 (56%) 0.028* Prior cardiac surgery 30 (28%) 2 (8%) 28 (35%) 0.008* Left AFL origin (%) 87 (81%) 24 (92%) 63 (78%) 0.098 *Statistically significant difference.

Survival function

Conclusion

AFL ablation was as effective and safe in octogenarian as in younger ones, with a median survival time free from atrial arrhythmias of more than 2 years.

XPA, XPC, and XPD Modulate Sensitivity in Gastric Cisplatin Resistance Cancer Cells

Cisplatin is an election drug widely used in clinic for the treatment of advanced gastric cancer. However, the heterogeneity of the gastric tumors and its resistance to the drugs, make in some cases the response very low and the prognosis unpredictable. In this manuscript we aim to find the molecular processes involved in cisplatin-induced apoptosis in two gastric cancer cell lines with different sensitivity to the treatment: AGS and MKN45. The apoptosis induction is higher in MKN45 than in AGS cells in response to CDDP. The intrinsic apoptotic pathway study revealed that MKN45 cells undergo degradation of Mcl-1 together with an increase of Bid and Bad levels, which results in sensitivity to CDDP. In addition, DNA repair NER pathway is impair in MKN45 cells due to low levels of XPC and the absence of translocation of XPA and XPD to the nucleus after stimuli. Altogether, these results suggest that NER and Bcl-2 protein family proteins are potential targets to improve the response to cisplatin treatment.

Targeting Chk2 improves gastric cancer chemotherapy by impairing DNA damage repair

Our results demonstrate that the addition of cisplatin after paclitaxel-induced mitotic arrest was more effective than individual treatment on gastric adenocarcinoma cells (MKN45). However, the treatment did not induce benefits in cells derived from lymph node metastasis (ST2957). Time-lapse microscopy revealed that cell death was caused by mitotic catastrophe and apoptosis induction, as the use of the caspase inhibitor z-VAD-fmk decreased cell death. We propose that the molecular mechanism mediating this cell fate is a slippage suffered by these cells, given that our Western blot (WB) analysis revealed premature cyclin B degradation. This resulted in the cell exiting from mitosis without undergoing DNA damage repair, as demonstrated by the strong phosphorylation of H2AX. A comet assay indicated that DNA repair was impaired, and Western blotting showed that the Chk2 protein was degraded after sequential treatment (paclitaxel-cisplatin). Based on these results, the modulation of cell death during mitosis may be an effective strategy for gastric cancer therapy.

Abstract 2366: Role of MKP1 in skin carcinogenesis

Dual-specificity phosphatase type 1 (DUSP1/MKP1), is a member of the dual-specific family of phosphatases that can dephosphorylate and inactivate all three major Mitogen-Activated Protein Kinases (MAPKs), including Extracellular Regulated Kinase (ERK1/2), c-Jun N-Terminal Kinase (JNK1/2), and p38. MKP1 is a nuclear protein whose expression is regulated by mitogenic, inflammatory and DNA-damage stimuli. Basal levels of MKP1 are usually low in normal cells, however high levels of the protein have been found in several human tumours such as ovarian, breast, prostate and lung. Amplification and mutation of Ha-Ras correlates with the malignancy of tumours that appears in chemically-induced mouse skin and additionally, an increase in Ha-Ras levels induces JNK1/2 and ERK1/2 activity, known substrates of MKP1, however, there is no evidence in the literature of a relationship between MKP1 and skin cancer. The objective of this study was to investigate the role of MKP1 in carcinogenesis and tumor development in carcinogen-induced skin cancer. MKP1 wild-type (mkp1+/+) and MKP1 knock-out (mkp1-/-) mice were subjected to the standard two-stage skin carcinogenesis protocol using 7, 12-dimethylbenz(a)anthraacene (DMBA) as the initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as the promoter. We observed a significant decrease in both papilloma incidence and papilloma multiplicity in mkp1+/+ mice undergoing two-stage skin carcinogenesis relative to mkp1-/- littermates. Morphological evaluation of skin lesions from mkp1+/+ and mkp1-/- mice revealed a significant reduction in both tumour incidence and tumour multiplicity in mkp1+/+ mice relative to mkp1-/- littermates. No differences were found between mkp1+/+ and mkp1-/- skin hyperplasia following TPA challenge, but we observed reduced bromodeoxyuridine (BrdUrd) incorporation in mkp1+/+ epidermis compared with mkp1-/- epidermis. Targeted disruption of MKP1 gene led to a slight increase in ERK1/2 protein in mkp1-/- mice, whereas p38 and JNK1/2 proteins were expressed at similar levels in the epidermis of mkp1+/+ and mkp1-/- mice. We examined the effect of MKP1 deficiency on ERK1/2 activation and we observed that TPA-mediated activation of ERK1/2 was diminished in mkp1+/+ epidermis compared with mkp1-/- epidermis. Finally, we have also observed a marked reduction in MKP1 expression levels in human basal (BCC) and squamous cell carcinoma (SCC) in relation to normal skin. In contrast to the results found in other tumor types as lung cancer, our data provide a strong evidence for MKP1 having a role in the tumorogenesis and development of skin cancer by attenuating epidermal response to tumour promotion, and ultimately, two-stage skin carcinogenesis, very likely by impairing the activation of the ERK1/2 pathway, critically linked to control of cell proliferation and skin tumorigenesis. Supported by PI081485 and P09/1988 and by an unrestricted educational grant from Fundación Mutua Madrileña 2007-0444

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 2366. doi:1538-7445.AM2012-2366

Human recombinant erythropoietin does not promote cancer growth in presence of functional receptors expressed in cancer cells

Human recombinant erythropoietin (hrEPO) therapy might be associated with tumor progression and death. This effect has been suggested to be secondary to rhEPO binding to its receptor (EPOR) expressed on cancer cells. However, there are several concerns about EPOR functionality when expressed on cancer cells. In this paper we have provided evidence that EPOR expressed in cancer cells could be implicated in proliferation events because a transfection of EPOR siRNA to EPOR-expressing bladder cancer cells resulted in a marked reduction in cell growth. However, these cell lines do not grow in the presence of hrEPO. Furthermore, bladder cancer patients that expressed EPOR in tumor samples had a reduced survival in absence of rhEPO treatment. Therefore, EPOR is implicated in bladder cancer growth but this effect appears to be independent from rhEPO supplementation. Reports which suggest that rhEPO promotes cancer growth due to the expression of EPOR in cancer cells must be observed with caution since in the presence of functional EPOR rhEPO does not promote growth.

The DASH complex and Klp5/Klp6 kinesin coordinate bipolar chromosome attachment in fission yeast

We identified a truncated allele of dam1 as a multicopy suppressor of the sensitivity of cdc13-117 (cyclin B) and mal3-1 (EB-1) cells to thiabendazole, a microtubule poison. We find that Dam1 binds to the plus end of spindle microtubules and kinetochores as cells enter mitosis and this is dependent on other components of the fission yeast DASH complex, including Ask1, Duo1, Spc34 and Dad1. By contrast, Dad1 remains bound to kinetochores throughout the cell cycle and its association is dependent on the Mis6 and Mal2, but not Mis12, Nuf2 or Cnp1, kinetochore proteins. In cells lacking Dam1, or other components of the DASH complex, anaphase is delayed due to activation of the spindle assembly checkpoint and lagging sister chromatids are frequently observed and occasionally sister chromatid pairs segregate to the same spindle pole. We find that the mitotic centromere-associated Klp5/Klp6 kinesin complex is essential in cells lacking components of the DASH complex. Cells lacking both Dam1 and Klp5 undergo a first cell cycle arrest in mitosis due to a failure to establish bipolar chromosome attachment.

FK506 sensitizes mammalian cells to high osmolarity by modulating p38 MAP kinase activation

The immunosuppressants tacrolimus (FK506) and cyclosporin A (CsA) have increased the survival rates in organ transplantation. Both drugs inhibit the protein phosphatase calcineurin (CaN) in activated T cells, exhibiting similar side-effects. Diabetes is observed more often in FK506 than CsA therapy, probably due to inhibition of new molecular targets other than CaN. We studied FK506 toxicity in mammalian cells. FK506, but not CsA, regulated p38 activation by osmotic stress, and decreased viability in osmostressed cells. In addition, FK506 treatment strongly increased the phosphorylation of the eukaryotic initiation factor-2alpha (eIF-2alpha) subunit. eIF-2alpha phosphorylation, p38 inhibition and cell lethality were relieved by addition of excess amino acids to the medium, suggesting that amino acid availability mediated FK506 toxicity. Therefore, these FK506-dependent responses could be relevant to the non-therapeutic effects of FK506 therapy.

The antidiabetic agent sodium tungstate activates glycogen synthesis through an insulin receptor-independent pathway

Sodium tungstate is a powerful antidiabetic agent when administered orally. In primary cultured hepatocytes, tungstate showed insulin-like actions, which led to an increase in glycogen synthesis and accumulation. However, this compound did not significantly alter the insulin receptor activation state or dephosphorylation rate in cultured cells (CHO-R) or in primary hepatocytes, in either short or long term treatments. In contrast, at low concentrations, tungstate induced a transient strong activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) after 5-10 min of treatment, in a similar way to insulin. Moreover, this compound did not significantly delay or inhibit the dephosphorylation of ERK1/2. ERK1/2 activation triggered a cascade of downstream events, which included the phosphorylation of p90rsk and glycogen synthase-kinase 3beta. Experiments with a specific inhibitor of ERK1/2 activation and kinase assays indicate that these proteins were directly involved in the stimulation of glycogen synthase and glycogen synthesis induced by tungstate without a direct involvement of protein kinase B (PKB/Akt). These results show a direct involvement of ERK1/2 in the mechanism of action of tungstate at the hepatic level.

The immunosuppressant FK506 uncovers a positive regulatory cross-talk between the Hog1p and Gcn2p pathways

The immunosuppressant Tacrolimus (FK506) has increased the survival rates of organ transplantation. FK506 exerts its immunosuppressive effect by inhibition of the protein phosphatase calcineurin in activated T-cells. Unfortunately, FK506 therapy is associated with undesired non-therapeutic effects involving targets other than calcineurin. To identify these targets we have addressed FK506 cellular toxicity in budding yeast. We show that FK506 increased cell sensitivity upon osmotic challenge independently of calcineurin and the FK506-binding proteins Fpr1p, -2p, -3p, and -4p. FK506 also induced strong amino acid starvation and activation of the general control (GCN) pathway. Tryptophan prototrophy or excess tryptophan overcame FK506 toxicity, showing that tryptophan deprivation mediated this effect. Mutation of the GCN3 and -4 genes partially alleviated FK506 toxicity, suggesting that activation of the GCN pathway by FK506 was also involved in osmotic tolerance. FK506 enhanced osmotic stress-dependent Hog1p kinase phosphorylation that was not accompanied by induction of a Hog1p-dependent reporter. Interestingly, deletion of the GCN2 gene suppressed FK506-dependent Hog1p hyperphosphorylation and restored Hog1p-dependent reporter activity. Conversely, deletion of the HOG1 gene impaired FK506-dependent activation of Gcn2p kinase and translation of a GCN4-LacZ reporter, highlighting functional cross-talk between the Gcn2p and Hog1p protein kinases. Taken together, these data demonstrate that both FK506-induced amino acid starvation and activation of the GCN pathway contribute to cell sensitivity to osmotic stress and reveal a positive regulatory loop between the Hog1p and Gcn2p pathways. Given the conserved nature of Gcn2p and Hog1p pathways, this mechanism of FK506 toxicity could be relevant to the non-therapeutic effects of FK506 therapy.

Schizosaccharomyces pombe essential genes: a pilot study

After completion of the Schizosaccharomyces pombe genome sequence, we have carried out a pilot gene deletion project to assess the feasibility of a genome-wide deletion project and to estimate the percentage of essential genes. Using a PCR-based gene deletion procedure, we investigated 100 genes within a 253-kb region of chromosome II. Eight of nine genes located within a region of 18 kb could not be deleted, suggesting that systematic deletion of all fission yeast genes may be difficult to achieve using this PCR approach. The percentage of essential genes was found to be 17.5%. Further deletion of selected S. pombe genes revealed that whether a gene is essential or not is correlated with the timing of its appearance on the tree of life and its conservation within all branches of the tree. None of the investigated ancient genes in fission yeast that have been lost in the Saccharomyces cerevisiae lineage are essential. In agreement with S. cerevisiae and Caenorhabditis elegans genome analyses, our data suggest that natural selection has preferentially kept the genes required for vital functions. We propose that many of the essential eukaryotic genes appeared with the first eukaryotic cell and have remained conserved in all species.

Growth hormone protects against radiotherapy-induced cell death

BACKGROUND

In vivo treatment with growth hormone reduces radiation-associated mortality. The molecular mechanisms underlying this effect are unknown. It has been described that increased sensitivity to ionising radiation can be due to defects in machinery involved in detection and/or repair of DNA double-strand breaks.

OBJECTIVE

To study the mechanisms involved in growth hormone action on the increased survival in irradiated cells.

MATERIALS AND METHODS

CHO-4 cells stably expressing the growth hormone receptor were used. A cell viability assay was carried out to analyse the increase in survival induced by growth hormone in irradiated cells. To investigate whether the DNA repair mechanism could be implicated in this effect we performed DNA reactivation assays using pHIV-LUC and pCMV-betagal plasmids as control. Identical studies were also conducted using the radiomimetic drug, bleomycin.

RESULTS

Growth hormone protects CHO-4 cells from bleomycin- and radiation-induced cell death. In pHIV-LUC transfected cells, a time-dependent decrease in luciferase activity was observed after irradiation in the absence of growth hormone. However, cells pretreated with this hormone maintained reporter activity. When cells were transfected with irradiated pHIV-LUC plasmid, only the hormone-treated cells recovered the transcriptional activity.

CONCLUSIONS

Growth hormone exerts a radioprotective effect in CHO-4 cells stably transfected with the complementary DNA for the rat growth hormone receptor. The radioprotection is triggered directly by the hormone and it is also observed with bleomycin. The increased survival in response to radiation and bleomycin treatment induced by growth hormone correlates with an enhanced ability of the cells to repair damaged DNA.