Inactivation of p53 increases the cytotoxicity of camptothecin in human colon HCT116 and breast MCF-7 cancer cells

Camptothecin (CPT) derivatives are topoisomerase I (top1) inhibitors recently introduced as clinical agents. To explore the role of p53 in CPT-induced cytotoxicity, we examined CPT effects in two isogenic pairs of human cancer cell lines, MCF-7 breast carcinoma and HCT116 colon carcinoma cells, in which p53 function had been disrupted by transfection with the human papillomavirus type-16 E6 gene. Clonogenic survival assays showed that both MCF-7/E6 and HCT116/E6 cells were more sensitive to CPT. No differences in top1 protein levels and activity analyzed by a novel in vitro oligonucleotide assay were observed in the E6 transfectants. Also, CPT showed comparable top1 cleavable complex formation in vivo, as determined by DNA single-strand breaks and DNA protein cross-links. These results suggest that p53 can protect against CPT-induced cytotoxicity and that this protection is mediated downstream of CPT-induced DNA damage. Flow cytometry analyses showed that CPT can induce G1 arrest in cells with normal p53. This G1 arrest was markedly reduced in the p53-deficient cells. These results demonstrate a critical role of p53 as a G1 checkpoint regulator after CPT-induced DNA damage and suggest a rationale for the selectivity of CPT toward tumors with p53 mutations.     

A BAYESIAN APPROACH TO ESTIMATING AND FORECASTING ADDITIVE NONPARAMETRIC AUTOREGRESSIVE MODELS

Abstract. We present a Bayesian approach for estimating nonparametrically an additive autoregressive model with the regression curve estimates cubic smoothing splines. Our approach is robust to innovation outliers; it can handle missing observations and produce multistep ahead forecasts. The computation is carried out using Markov chain Monte Carlo and requires O( nM ) operations where n is the sample size and M is the number of Markov chain iterations. This makes it the first exact algorithm for spline smoothing of an additive autoregressive model which can handle large data sets. The properties of the estimates and forecasts are studied empirically using simulated and real data sets.     

Oesophagogastrectomy for carcinoma of the oesophagus and cardia

A retrospective review was undertaken of all oesophagectomies performed within a single unit over a 12-year period. In all, 298 patients with primary oesophageal cancer underwent resection between March 1979 and December 1991. Four patients had a three-stage oesophagogastrectomy, 27 a thoracoabdominal oesophagogastrectomy and 267 a Lewis procedure. Dysphagia was the predominant presenting symptom. The duration of symptoms was not related to the stage of disease. Before diagnosis, 52 per cent of patients tolerated symptoms for 2-4 months. Adenocarcinoma was found in 180 tumours and squamous cell carcinoma in 103. Half of the patients had evidence of metastatic spread at the time of laparotomy or thoracotomy. The 30-day mortality rate was 10 per cent and the overall actuarial 5-year survival rate of all patients 23 per cent. The actuarial 5-year survival rate of patients without lymph node involvement was 39 per cent compared with 17 per cent for those with positive nodes (P < 0.05). Five of eight patients who had anastomotic leakage died. The almost unselected nature of this series, coupled with the favourable results of oesophagectomy, support the contention that resection remains the preferred mode of treatment for carcinoma of the oesophagus of all histological types.     

FILTERING AND SMOOTHING IN STATE SPACE MODELS WITH PARTIALLY DIFFUSE INITIAL CONDITIONS

Abstract. Ansley and Kohn ( Annals of Statistics , 1985) generalized the Kalman filter to handle state space models with partially diffuse initial conditions and used this filter to compute the marginal likelihood of the observations efficiently. In this paper we simplify the algorithm and make it numerically more accurate and operationally more efficient. Based on this filtering algorithm we obtain a corresponding smoothing algorithm for the state vector.     

Use of a correlational method to estimate a listener's weighting function for speech

The purpose of this study was to determine if it is feasible to use the correlational method (Lutfi, 1995; Richards and Zhu, 1994) to estimate how listeners use or weight the information contained within various frequency bands of speech. Three naturally spoken vowel-consonant-vowel (VCV) syllables (/aba/, /aga/, and /ada/) were presented monaurally to listeners. Each of the VCV waveforms were filtered into three separate frequency bands (i.e., low, mid, and high). Each band was then independently and randomly degraded at various signal-to-noise (S/N) levels (-7, -5, -3, -1, or +1). On each trial, listeners were asked to identify the VCV that was presented to them. For each trial, the S/N level of each frequency band, the stimulus that was presented, and the listener's responses were all recorded and stored in a file. From this trial-by-trial data, a point biserial correlation was computed between the listener's response (correct or incorrect identification) and the degradation within each frequency band. The stronger the correlation, the greater influence that given frequency band had on the listener's performance on the task. From these relations it was shown that it is possible to obtain a listener's weighting function for speech. Results showed that although most listeners weighted the mid-frequency band the greatest, several of the listeners used different weighting strategies to perform the task. Several methodological issues are discussed in regard to improving the future application of the correlational method to speech.     

Casein kinase II preferentially phosphorylates human tau isoforms containing an amino-terminal insert. Identification of threonine 39 as the primary phosphate acceptor

The in vitro phosphorylation of the microtubule-associated protein tau by casein kinase II was studied. Purified human brain tau was phosphorylated by casein kinase II to a stoichiometry of 0.7 mol of 32P/mol of tau. Individual recombinant human tau isoforms were phosphorylated to stoichiometries ranging from 0.2 to 0.8 mol of 32P/mol of tau. Casein kinase II catalyzed a 4-fold greater incorporation of phosphate into the tau isoform containing a 58-amino acid insert near its amino terminus (T4L) than the isoforms without the 58-amino acid insert (T3 and T4). Phosphopeptide mapping of casein kinase II phosphorylated human tau and recombinant tau isoforms suggested that the isoforms containing an amino-terminal insert constitute the major substrates for casein kinase II within the tau family. The sites of phosphorylation on T4L were identified by digesting phosphorylated T4L with the protease Asp-N, separating the peptides by reversed phase high performance liquid chromatography, and analyzing the isolated peptides by liquid-secondary ion mass spectrometry and solid-phase amino-terminal sequencing. Thr39 was identified as the predominant phosphorylation site, which is located 5 residues from the amino-terminal insert in T4L. Phosphopeptide mapping of tau isolated from LA-N-5 neuroblastoma cells indicates that Thr39 is phosphorylated in situ. To our knowledge, this is the first demonstration of a differential phosphorylation of the human tau isoforms, with the isoforms containing the acidic amino-terminal insert being the preferred substrates of casein kinase II.