miR-125b promotes cell death by targeting spindle assembly checkpoint gene MAD1 and modulating mitotic progression

The spindle assembly checkpoint (SAC) is a 'wait-anaphase' mechanism that has evolved in eukaryotic cells in response to the stochastic nature of chromosome-spindle attachments. In the recent past, different aspects of the SAC regulation have been described. However, the role of microRNAs in the SAC is vaguely understood. We report here that Mad1, a core SAC protein, is repressed by human miR-125b. Mad1 serves as an adaptor protein for Mad2 - which functions to inhibit anaphase entry till the chromosomal defects in metaphase are corrected. We show that exogenous expression of miR-125b, through downregulation of Mad1, delays cells at metaphase. As a result of this delay, cells proceed towards apoptotic death, which follows from elevated chromosomal abnormalities upon ectopic expression of miR-125b. Moreover, expressions of Mad1 and miR-125b are inversely correlated in a variety of cancer cell lines, as well as in primary head and neck tumour tissues. We conclude that increased expression of miR-125b inhibits cell proliferation by suppressing Mad1 and activating the SAC transiently. We hypothesize an optimum Mad1 level and thus, a properly scheduled SAC is maintained partly by miR-125b.

MUC1 regulates PDGFA expression during pancreatic cancer progression

Pancreatic Ductal Adenocarcinoma (PDA) has one of the worst prognoses of all cancers. Mucin 1 (MUC1), a transmembrane mucin glycoprotein, is a key modulator of several signaling pathways that affect oncogenesis, motility, and metastasis. Its expression is known to be associated with poor prognosis in patients. However, the precise mechanism remains elusive. We report a novel association of MUC1 with Platelet-Derived Growth Factor-A (PDGFA). PDGFA is one of the many drivers of tumor growth, angiogenesis, and metastasis in PDA. Using mouse PDA models as well as human samples, we show clear evidence that MUC1 regulates the expression and secretion of PDGFA. This, in turn, influences proliferation and invasion of pancreatic cancer cells leading to higher tumor burden in vivo. In addition, we reveal that MUC1 over expressing cells are heavily dependent on PDGFA both for proliferation and invasion while MUC1-null cells are not. Moreover, PDGFA and MUC1 are critical for translocation of βcatenin to the nucleus for oncogenesis to ensue. Finally, we elucidate the underlying mechanism by which MUC1 regulates PDGFA expression and secretion in pancreatic cancer cells. We show that MUC1 associates with Hif1-α, a known transcription factor involved in controlling PDGFA expression. Furthermore, MUC1 facilitates Hif1-α translocation to the nucleus. In summary, we have demonstrated that MUC1-induced invasion and proliferation occurs via increased exogenous production of PDGFA. Thus, impeding MUC1 regulation of PDGFA signaling may be therapeutically beneficial for patients with PDA.

Identification of fluorescent compounds with non-specific binding property via high throughput live cell microscopy

INTRODUCTION

Compounds exhibiting low non-specific intracellular binding or non-stickiness are concomitant with rapid clearing and in high demand for live-cell imaging assays because they allow for intracellular receptor localization with a high signal/noise ratio. The non-stickiness property is particularly important for imaging intracellular receptors due to the equilibria involved.

METHOD

Three mammalian cell lines with diverse genetic backgrounds were used to screen a combinatorial fluorescence library via high throughput live cell microscopy for potential ligands with high in- and out-flux properties. The binding properties of ligands identified from the first screen were subsequently validated on plant root hair. A correlative analysis was then performed between each ligand and its corresponding physiochemical and structural properties.

RESULTS

The non-stickiness property of each ligand was quantified as a function of the temporal uptake and retention on a cell-by-cell basis. Our data shows that (i) mammalian systems can serve as a pre-screening tool for complex plant species that are not amenable to high-throughput imaging; (ii) retention and spatial localization of chemical compounds vary within and between each cell line; and (iii) the structural similarities of compounds can infer their non-specific binding properties.

CONCLUSION

We have validated a protocol for identifying chemical compounds with non-specific binding properties that is testable across diverse species. Further analysis reveals an overlap between the non-stickiness property and the structural similarity of compounds. The net result is a more robust screening assay for identifying desirable ligands that can be used to monitor intracellular localization. Several new applications of the screening protocol and results are also presented.

Fluorescence correlation spectroscopy to determine the diffusion coefficient of α-synuclein and follow early oligomer formation

Fluorescence correlation spectroscopy (FCS) can be used to determine the diffusion coefficient of fluorescently labeled α-synuclein. It is a technique based on the use of a confocal microscope. By applying FCS in a combination of short sampling times and repeated measurements, the disappearance of individual α-synuclein molecules (called monomers) and the formation of oligomers can be characterized during the early aggregation process.

Delusional parasitosis: Worms of the mind

Delusional parasitosis is an uncommon psychotic illness. Patients often report to dermatologists and physicians for treatment and are brought to psychiatric attention only for associated psychological distress. One such case is discussed in this report.

Raised calcium promotes α-synuclein aggregate formation

Parkinson's and Parkinson's-plus diseases are associated with abnormal, aggregated forms of the protein, α-synuclein. We have investigated the effects of calcium on α-synuclein aggregation in vitro and in vivo. We treated monomeric α-synuclein with calcium in vitro and used fluorescence imaging, fluorescence correlation and scanning electron microscopy to investigate protein aggregation. Incubation of fluorescent-labelled monomeric α-synuclein (24h) at low concentration (10 μM) with calcium resulted in surface aggregates (1.5±0.7 μm(2)) detected by fluorescence microscopy saturating at a half-maximum calcium concentration of 80 μM, whilst incubations without calcium showed few protein aggregates. Scanning electron microscopy revealed that α-synuclein surface plaques (0.5-1 μm) form in the presence of calcium and comprise 10-20 nm globular particles. Incubation of α-synuclein at high concentration (75 μM; 6h) resulted in soluble oligomeric aggregates detected by fluorescence correlation spectroscopy in a calcium dependent process, saturating at a half maximum calcium concentration of 180 μM. In cell culture experiments, we used thapsigargin or calcium ionophore A23187 to induce transient increases of intracellular free calcium in human 1321N1 cells expressing an α-synuclein-GFP construct and observed calcium flux and α-synuclein aggregation by fluorescence microscopy. The cell culture data shows that a transient increase in intracellular free calcium significantly increased the proportion of cells bearing cytoplasmic α-synuclein aggregates 6 and 12h post-treatment (P, 0.01). Our data indicates that calcium accelerates α-synuclein aggregation on surfaces, in free solution and in cultured cells and suggests that surface adsorption may play an important role in the calcium-dependent aggregation mechanism.

MUC1 enhances invasiveness of pancreatic cancer cells by inducing epithelial to mesenchymal transition

Increased motility and invasiveness of pancreatic cancer cells are associated with epithelial to mesenchymal transition (EMT). Snai1 and Slug are zinc-finger transcription factors that trigger this process by repressing E-cadherin and enhancing vimentin and N-cadherin protein expression. However, the mechanisms that regulate this activation in pancreatic tumors remain elusive. MUC1, a transmembrane mucin glycoprotein, is associated with the most invasive forms of pancreatic ductal adenocarcinomas (PDA). In this study, we show that over expression of MUC1 in pancreatic cancer cells triggers the molecular process of EMT, which translates to increased invasiveness and metastasis. EMT was significantly reduced when MUC1 was genetically deleted in a mouse model of PDA or when all seven tyrosines in the cytoplasmic tail of MUC1 were mutated to phenylalanine (mutated MUC1 CT). Using proteomics, RT-PCR and western blotting, we revealed a significant increase in vimentin, Slug and Snail expression with repression of E-Cadherin in MUC1-expressing cells compared with cells expressing the mutated MUC1 CT. In the cells that carried the mutated MUC1 CT, MUC1 failed to co-immunoprecipitate with β-catenin and translocate to the nucleus, thereby blocking transcription of the genes associated with EMT and metastasis. Thus, functional tyrosines are critical in stimulating the interactions between MUC1 and β-catenin and their nuclear translocation to initiate the process of EMT. This study signifies the oncogenic role of MUC1 CT and is the first to identify a direct role of the MUC1 in initiating EMT during pancreatic cancer. The data may have implications in future design of MUC1-targeted therapies for pancreatic cancer.

Early aggregation steps in alpha-synuclein as measured by FCS and FRET: evidence for a contagious conformational change

The kinetics of aggregation of alpha-synuclein are usually studied by turbidity or Thio-T fluorescence. Here we follow the disappearance of monomers and the formation of early oligomers using fluorescence correlation spectroscopy. Alexa488-labeled A140C-synuclein was used as a fluorescent probe in trace amounts in the presence of excess unlabeled alpha-synuclein. Repeated short measurements produce a distribution of diffusion coefficients. Initially, a sharp peak is obtained corresponding to monomers, followed by a distinct transient population and the gradual formation of broader-sized distributions of higher oligomers. The kinetics of aggregation can be followed by the decreasing number of fast-diffusing species. Both the disappearance of fast-diffusing species and the appearance of turbidity can be fitted to the Finke-Watzky equation, but the apparent rate constants obtained are different. This reflects the fact that the disappearance of fast species occurs largely during the lag phase of turbidity development, due to the limited sensitivity of turbidity to the early aggregation process. The nucleation of the early oligomers is concentration-dependent and accompanied by a conformational change that precedes beta-structure formation, and can be visualized using fluorescence resonance energy transfer between the donor-labeled N-terminus and the acceptor-labeled cysteine in the mutant A140C.

The intravenous adenosine test: a new test for the identification of bradycardia pacing indications? A pilot study in subjects with bradycardia pacing indications, vasovagal syncope and controls

BACKGROUND

Intravenous adenosine has recently been used in the diagnosis of unexplained syncope, but there is no consensus as to the meaning of a 'positive' test. The objective is to determine the sensitivity and specificity of intravenous adenosine testing in the diagnosis of bradycardia-pacing indications [sinus node dysfunction(SND), atrio-ventricular block (AVB) and cardio-inhibitory carotid sinus syndrome (CSS)].

DESIGN

Pilot cohort study.

METHODS

Patients-(i) Bradycardia-pacing group: Consecutive patients referred for pacing for SND, AVB and CSS; (ii) Consecutive head-up tilt (HUT)-positive VVS patients. Controls-(i) Simple controls (S-Con: normal examination/ECG) and (ii) Electrophysiology controls (EP-Con: consecutive subjects referred for accessory pathway ablation). Pacing referrals and EP-Con had electrophysiology studies to confirm referral diagnosis and exclude others. All subjects had bolus injection of 20 mg intravenous adenosine during continuous ECG and blood pressure monitoring (positive test: >or=6 s asystole, >or=10 s high-degree AVB post-injection). Sensitivity, specificity, safety and tolerability of the test were measured.

RESULTS

Of 264 potential participants (4 SND, 8 AVB, 7 CSS, 10 VVS, 10 EP-Con and 11 S-Con) 50 were studied. All (100%) of the bradycardia-pacing group were adenosine test-positive, as were 6 (60%) VVS. None (0%) and 3 (27%) of the EP- and S-Con groups were positive. Adenosine testing was 100% sensitive and 86% specific for bradycardia-pacing indications, and 100% specific using the diagnostically 'clean' EP-Con results. There were no significant adverse or side effects.

CONCLUSION

Adenosine testing reliably identified patients with definitive bradycardia-pacing indications in whom alternative diagnoses were excluded. Further work is needed to evaluate the role of this test in the diagnosis of unexplained syncope.

Predictive value of novel and existing activating EGFR mutations for improved survival in malignant peritoneal mesothelioma (MPM) and response to EGFR-TK inhibitors (EGFR-TKI)

11030

Background: MPMs are highly aggressive tumors with most patients diagnosed surviving 8–12 months. Currently there is a paucity of information about the molecular/biological perturbations involved in tumor formation. Previously we presented (at ASCO 2007) that novel EGFR-TK mutations occurred in these tumors predictive of optimal surgical cytoreduction; but the EGFR activity of these mutations was being investigated. Here we present the EGFR activity of these mutations as well as matured outcome data. Methods: Twenty-nine MPM patients were evaluated at a single tertiary center and tumors were probed for mutations in the TK domain of EGF receptor (mut+). All specimens were examined for somatic mutations by PCR amplification and confirmed by multiple independent PCRs. Twenty-five patients were treated with cytoreductive surgery (CRS) ± IPHC and clinical data including age, sex, cytoreductive score, histology, mutation, and survival was available for comparison of the mut+ and mut- groups. A COS-7 cell expression model was used to determine the time dependent activating profile of these mutations, as well as response to EGFR-TKI-inhibitor. Results: Mutations were found in 31% (9/29) of the tumors; 7 of these mutations were novel. All 7 novel mutations and L858R mutation identified were activating mutations with similar activation profiles. All mutations were responsive to EGFR-TKI treatment. Of the 25 patients managed surgically there were 7 mut+ and 18 mut-. Two of 7 (29%) mut+ have progressed and died of disease with a MFT of 22 months; while 13/18 (72%) mut- had progressive disease and 10/18 (56%) died with median TTP and survival of 12 months and14 months respectively. Estimated 3-year PFS was 70% mut+ and 25% mut- on log rank analysis p=0.099. Conclusions: This is the first report that MPM-EGFR mutations are activating mutations and responsive to EGFR-TKI-therapy. The mut+ subset has a “relative” improved outcome compared to wild type, but still developed progressive disease. TKIs may be a promising therapy in mut+ MPMs patients. Further elucidation of other molecular and pathway perturbations in this disease is necessary, as well as, validation of these results in a larger cohort.

No significant financial relationships to disclose.

Enzymatic investigation of the Staphylococcus aureus type I signal peptidase SpsB - implications for the search for novel antibiotics

Staphylococcus aureus has one essential type I signal peptidase (SPase), SpsB, which has emerged as a potential target in the search for antibiotics with a new mode of action. In this framework, the biochemical properties of SpsB are described and compared with other previously characterized SPases. Two different substrates have been used to assess the in vitro processing activity of SpsB: (a) a native preprotein substrate immunodominant staphylococcal antigen A and (b) an intramolecularly quenched fluorogenic synthetic peptide based on the sequence of the SceD preprotein of Staphylococcus epidermidis for fluorescence resonance energy transfer-based analysis. Activity testing at different pH showed that the enzyme has an optimum pH of approximately 8. The pH-rate profile revealed apparent pK(a) values of 6.6 and 8.7. Similar to the other SPases, SpsB undergoes self-cleavage and, although the catalytic serine is retained in the self-cleavage product, a very low residual enzymatic activity remained. In contrast, a truncated derivative of SpsB, which was nine amino acids longer at the N-terminus compared to the self-cleavage product, retained activity. The specificity constants (k(cat)/K(m)) of the full-length and the truncated derivative were 1.85 +/- 0.13 x 10(3) m(-1).s(-1) and 59.4 +/- 6.4 m(-1).s(-1), respectively, as determined using the fluorogenic synthetic peptide substrate. These observations highlight the importance of the amino acids in the transmembrane segment and also those preceding the catalytic serine in the sequence of SpsB. Interestingly, we also found that the activity of the truncated SpsB increased in the presence of a non-ionic detergent.