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C M Chiang

Publications and source records attributed to C M Chiang.

At least 37 records · Page 2Linked to original sources
PubMed1996

A histone octamer-like structure within TFIID.

The general transcription factor TFIID nucleates initiation complex formation through direct core promoter binding, commits promoters within chromatin to transcription, and mediates the action of transcriptional activators, a phenomenon that may correlate with enhanced TFIID recruitment or conformational changes in TFIID-promoter complexes. Molecular studies of the multiprotein TFIID complex have identified a primary TATA binding subunit (TBP), TBP-associated factors (TAFs) that interact with and mediate the function of activators and intersubunit interactions but have yielded relatively little insight into the structural organization of the complex or the actual mechanism of transcriptional activation. Here we present biochemical evidence for the structural relevance of histone homologies in the human TFIID subunits hTAF80, hTAF31 and hTAF20/15. Together with analyses of native TFIID complexes and accompanying crystallographic studies, the results suggest that there is a histone octamer-like TAF complex within TFIID.

Amino Acid Sequence↗
PubMed1996

Augmented two-channel arrhythmia detection: an efficient diagnostic method for implantable devices.

ICDs are highly effective in preventing sudden cardiac death. However, inappropriate device shocks caused by false-positive diagnoses are estimated to happen in 20% of all patients. The need for implantable electrical devices to detect with precision arrhythmias requiring therapy has spawned a variety of proposals for better means of tachycardia identification. To address this problem, the augmented two-channel arrhythmia detection (A2CAD) algorithm, a real-time scheme utilizing timing and morphology from both the atrial and ventricular channels, is introduced. The algorithm uses rate detection as a first stage and augments this with morphological signal analysis in rhythms that confound the rate only diagnoses. The software executes in real-time (online), and has been tested on 60 passages of two-channel intracardiac signals. The following arrhythmias constituted the test set: 10 AF and/or atrial flutter; 15 SVT; 16 VT; 10 ventricular flutter or VF; 5 sinus tachycardia; and 4 cases of AF concurrent with VF. Results from 60 patient cases indicate 57 (95%) of 60 success rate for A2CAD, validating its potential for implementation in future implantable devices.

Algorithms↗
PubMed1996

Establishment of stable cell lines expressing potentially toxic proteins by tetracycline-regulated and epitope-tagging methods.

A tetracycline-regulated expression system is combined with the FLAG-epitope tagging method for conditional expression of potentially toxic proteins in mammalian cells. This strategy allows a controlled expression of exogenous gene products and also provides a unique way of protein purification. Two mammalian expression plasmids containing the FLAG sequence and flanking multiple cloning sites were created for conditional protein expression. The cDNAs encoding human basal transcription factors TBP, TAFII55 and the p62 subunit of TFIIH were individually cloned into these vectors and introduced into a HeLa-derived cell line that constitutively expresses a tetracycline-regulated transactivator (tTA). The established clonal human cell lines express FLAG-tagged basal transcription factors in a manner modulated by the amount of tetracycline in the growth medium. In the absence of tetracycline, tTA binds to the DNA recognition sites of the expression plasmid and induces the expression of tagged proteins. When tetracycline is added back to the growth medium, the induced protein starts to decay. This provides us with an estimation of the in vivo half-lives of TBP and TAFII55, which were assessed to be less than 20 and 6 hours, respectively, in HeLa cells. The level of induced proteins in the absence of tetracycline could be further enhanced by including the antibiotic G418 to presumably boost the production of tTA which in turn activates the expression of tagged proteins.

Base Sequence↗
PubMed1995

Cloning of an intrinsic human TFIID subunit that interacts with multiple transcriptional activators.

TFIID is a multisubunit protein complex comprised of the TATA-binding protein (TBP) and multiple TBP-associated factors (TAFs). The TAFs in TFIID are essential for activator-dependent transcription. The cloning of a complementary DNA encoding a human TFIID TAF, TAFII55, that has no known homolog in Drosophila TFIID is now described. TAFII55 is shown to interact with the largest subunit (TAFII230) of human TFIID through its central region and with multiple activators--including Sp1, YY1, USF, CTF, adenoviral E1A, and human immunodeficiency virus-type 1 Tat proteins--through a distinct amino-terminal domain. The TAFII55-interacting region of Sp1 was localized to its DNA-binding domain, which is distinct from the glutamine-rich activation domains previously shown to interact with Drosophila TAFII110. Thus, this human TFIID TAF may be a co-activator that mediates a response to multiple activators through a distinct mechanism.

Adenovirus E1A Proteins↗
PubMed1994

TATA-binding protein-associated factor(s) in TFIID function through the initiator to direct basal transcription from a TATA-less class II promoter.

The RNA polymerase II (Pol II) basal transcription factor TFIID is composed of the TATA box-binding protein (TBP) and several TBP-associated factors (TAFs). TBP is required for Pol II transcription from TATA-containing and TATA-less promoters. TATA-less promoters of mRNA-encoding genes often contain an initiator element at the transcription start site that is sufficient to direct accurate Pol II transcription. Here we address the mechanisms of functional TBP recruitment to the TATA-less initiator-dependent promoter of the mouse terminal deoxynucleotidyl transferase (TdT) gene. We show that the natural TATA-less TdT initiator region is sufficient to promote low levels of specific transcription in vitro and to direct the assembly of a stable preinitiation complex. In contrast to what is observed for several other promoters lacking a consensus TATA element, the TATA-binding activity of TBP is not required for the functional recruitment of TFIID to the natural TATA-less TdT and beta-polymerase promoters. Moreover, a comparison of TBP and highly purified epitope-tagged TFIID reveals that one or several TAFs function independently of distal regulatory elements to mediate initiator-directed (basal) transcription from the natural TATA-less TdT core promoter in crude nuclear extracts. Furthermore, by using a transcription system reconstituted with purified components, we present the first evidence for a basal transcription function of TAFs through the TdT initiator element. Altogether, our results suggest an alternative pathway for TFIID recruitment to initiator-dependent TATA-less class II promoters in which TAF(s) recruit TBP by interacting either directly or indirectly with the initiator region.

Base Sequence↗
PubMed1994

Two distinct types of cardiotoxin as revealed by the structure and activity relationship of their interaction with zwitterionic phospholipid dispersions.

Cardiotoxins (CTXs) are a group of homologous proteins found in cobra snake venom and consist of 60-62 amino acid residues. Although CTXs are known to consist of three extended beta-sheet loops similar to neurotoxins, the target and interaction of CTXs with membranes unlike those of neurotoxins are not well understood. Herein, we report comparative studies of 10 CTXs purified from Taiwan cobra (Naja naja atra) and Mozambique spitting cobra (Naja mossambica mossambica) snake venoms with respect to their interactions with zwitterionic phospholipids. Based on the CTX-induced mixing of sphingomyelin vesicles and the binding of CTX to lysophosphatidylcholine micelles, two distinct types of CTX, i.e. P- and S-type CTX, are identified. P-type CTXs are characterized by the presence of Pro-31 within a putative phospholipid binding site near the tip of loop 2; whereas S-type CTXs are characterized by the presence of Ser-29 within the same but more hydrophilic region. Although binding of all CTXs to phospholipid membranes involves a phospholipid binding site at loop 1, P-type CTXs exhibit higher fusion and binding activity than S-type CTXs, presumably due to the additional phospholipid binding site at loop 2. The binding modes of P- and S-type CTX are thus different. Analysis of the primary structures of 46 CTXs from the genus Naja indicates that these two types of CTXs exist in all species examined. Reasonable structure/activity correlation can be detected for the effects of CTXs on muscle and red blood cells, although notable exceptions are also found. S-type CTXs are generally found to exhibit higher muscle cell depolarization activity, whereas P-type CTXs are found to possess a higher hemolytic activity. Thus the mechanism of action of CTXs seems to involve CTX-membrane interactions and depends on the type of the cell membrane and CTX molecules under study. The two lipid binding sites in P-type CTXs and one lipid binding site in S-type CTXs show large variation in their amino acid residues, but they do display some common distribution of residue type. Analogous to the signal sequences for protein import, these regions are characterized by the coexistence of an exposed hydrophobic surface flanked on either side by a cationic residue. A hypothesis is proposed to explain the general cytotoxic and specific cardiotoxic effect of CTXs based on the two CTX subtypes in snake venom.

Amino Acid Sequence↗
PubMed1994

Direct interaction of human TFIID with the HIV-1 transactivator tat.

The tat gene of the human immunodeficiency virus (HIV) plays a central role in the activation and life cycle of HIV. The tat protein (Tat) specifically transactivates HIV transcription in vivo and in vitro, exerting its effects at the level of transcriptional initiation and elongation. Here we report that Tat binds directly to the basal transcription factor TFIID. The transcriptional activity of HeLa extracts was depleted after chromatography on a Tat affinity column, which specifically retained the polymerase II-specific factor TFIID. Direct interaction of Tat with holo-TFIID, composed of TATA-binding protein (TBP) and associated factors (TAFs), was observed. Tat binds, through amino acids 36-50, directly to the TBP subunit of TFIID. Our results suggest that Tat may transduce upstream or downstream regulatory signals by direct interaction with the basal transcription factor TFIID.

Base Sequence↗
PubMed1994

Discrimination of ventricular tachycardia from sinus tachycardia by antitachycardia devices: value of median filtering.

Rate and rate variation algorithms used by implantable devices designed for management of life-threatening arrhythmias have major limitations in separating physiologic sinus tachycardia (ST) from pathologic ventricular tachycardia (VT) requiring therapy. These algorithms presently utilize criteria such as simple heart rate, stability of rate, or derivative of rate (sudden onset) which assumes a gradual onset for ST and an abrupt onset for VT. An alternative method employing median filtering was designed, tested, and compared to a previously published sudden onset rate algorithm using the same data set for analysis of performance. In 50 patients, the onset of ST during exercise and onset of VT were analysed. To accommodate occasional outlying intervals which might affect rate derived by averaging, a five-cycle median filter was used to smooth heart rate. Results from using a 'fixed-interval' or a 'percent' change in the median gave better discrimination of ST and VT than previously published 'fixed-interval' or 'percent' change algorithms. The superiority of median filtering performance was validated by statistical measures.

Algorithms↗
PubMed1994

Automated analysis of spontaneously occurring arrhythmias by implantable devices. Limitations of using rate and timing features alone.

Real-time automated systems for arrhythmia analysis by implantable antitachycardia devices have been designed to incorporate two-channel rate criteria with intracavitary atrial and ventricular electrogram morphology. Because the power requirements for morphologic analysis substantially limit antitachycardia device longevity, the authors sought to develop an alternative algorithm that relies solely on rate and three newly developed timing features: onset (median ventricular rate filtering to detect abrupt onset), loss of atrioventricular (AV) sequency (premature ventricular depolarizations), and regularity-multiplicity (minimal median cycle length variation concurrent with integral [n:1] AV periodicity). This system was assessed using spontaneously occurring arrhythmias in patients undergoing electrophysiology studies. Electrograms were captured on FM tape (1-500 Hz) using biopolar catheters in the high right atrium and the left ventricular apex. In 11 patients, 25 distinct arrhythmias were analyzed, which included sinus tachycardia (ST) (1 passage), supraventricular tachycardia (SVT) (6 passages), ventricular tachycardia (VT) with concurrent sinus rhythm (16 passages), VT with concurrent atrial flutter (VT/AFl) (2 passages), and ventricular fibrillation (VF) (1 passage). The algorithm correctly diagnosed 1 of 1 episode of ST, 4 of 6 episodes of SVT, 15 of 16 episodes of VT with concurrent sinus rhythm, 0 of 2 episodes of VT/AFl, and 1 of 1 episode of VF. Ventricular tachycardia episodes were misdiagnosed as SVT because of absence of loss of AV sequency in VT onset (1 episode), presence of multiplicity between VT and AFl (1 episode), and absence of VT regularity during AFl (1 episode).(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1994

The value of rate regularity and multiplicity measures to detect ventricular tachycardia in the presence of atrial fibrillation or flutter.

The predominant cause of inappropriate therapy by implantable antitachycardia devices with pacing and nonpacing cardioverter defibrillators, is mistaking a fast ventricular response during atrial fibrillation or flutter with true ventricular tachycardia (VT). The distinction between these arrhythmias is an important consideration in addressing the problem of reducing false-positives in detection mechanisms for implantable devices. Dual chamber analysis that examines atrial and ventricular event ratios has been proposed as a solution to this problem, but would still fail in distinguishing paroxysmal VT requiring treatment from a fast but otherwise benign ventricular response during atrial fibrillation or flutter. In this study, two methods for discriminating these tachyarrhythmias were evaluated. Method 1 examined ventricular rate and rate regularity as a method for VT detection. Method 2 combined rate and regularity as well as an additional multiplicity criterion for recognition of atrial flutter with a fast ventricular response. In 20 patients, Method 1 had 100% sensitivity of VT detection and 80% specificity for detection of atrial fibrillation or flutter. Method 2 had 90% sensitivity and 90% specificity. These results suggest that use of these algorithms in future implantable devices would result in a decrease in false-positive device therapies.

Algorithms↗
PubMed1994

Digital signal processing chip implementation for detection and analysis of intracardiac electrograms.

The adoption of digital signal processing (DSP) microchips for detection and analysis of electrocardiographic signals offers a means for increased computational speed and the opportunity for design of customized architecture to address real-time requirements. A system using the Motorola 56001 DSP chip has been designed to realize cycle-by-cycle detection (triggering) and waveform analysis using a time-domain template matching technique, correlation waveform analysis (CWA). The system digitally samples an electrocardiographic signal at 1000 Hz, incorporates an adaptive trigger for detection of cardiac events, and classifies each waveform as normal or abnormal. Ten paired sets of single-chamber bipolar intracardiac electrograms (1-500 Hz) were processed with each pair containing a sinus rhythm (SR) passage and a corresponding arrhythmia segment from the same patient. Four of ten paired sets contained intraatrial electrograms that exhibited retrograde atrial conduction during ventricular pacing; the remaining six paired sets of intraventricular electrograms consisted of either ventricular tachycardia (4) or paced ventricular rhythm (2). Of 2,978 depolarizations in the test set, the adaptive trigger failed to detect 6 (99.8% detection sensitivity) and had 11 false triggers (99.6% specificity). Using patient dependent thresholds for CWA to classify waveforms, the program correctly identified 1,175 of 1,197 (98.2% specificity) sinus rhythm depolarizations and 1,771 of 1,781 (99.4% sensitivity) abnormal depolarizations. From the results, the algorithm appears to hold potential for applications such as real-time monitoring of electrophysiology studies or detection and classification of tachycardias in implantable antitachycardia devices.

Algorithms↗
PubMed1994

A rate responsive pacemaker that physiologically reduces pacing rates at rest.

Current rate responsive pacemakers incorporate sensors such as minute ventilation (MV) for adapting to changing patient conditions during exercise and periods of exertion. However, for sleep and/or rest periods, the only pacemakers currently on the market that slow the pacing rate utilize an internal timer to determine a decrease in pacing rate. It would be advantageous if the pacing rate could be automatically lowered during periods of sleep or rest. This study utilized a rate responsive sensor, MV, to track the patient's sleeping and resting periods and to decrease the pacing rate at such times. A total of eight patients implanted with Sentri 1210 single chamber MV sensor pacemakers were studied. A sleep rate (SR) of 45 beats/min was selected. A sleep rate response function, which indicated the relationship between changes in MV and corresponding heart rate, was initially set at a value of 16 and continually and automatically updated in a 3-month study. Adaptation was based on the premise that 3 hours per day should be spent at the SR. The average decrease in pacing rates from onset to 3 month for the eight patients was 12.4% +/- 5.3%. Correspondingly, the histograms of the lowest datalog histogram (40-59 beats/min) increased from 0% to 15.4% +/- 0.9% of paced beats. Correlation between the patients' 24-hour diary and Holter recordings showed that the pacing rates during sleep were consistently lower than when the patients were awake and active. This was also the case with a patient whose nocturnal and daily routine was intentionally altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

MR imaging evaluation of bone marrow signal change in post-irradiation patients with nasopharyngeal carcinoma.

BACKGROUND: The normal distribution of red and yellow marrow can be altered by therapeutic irradiation, which causes a well-documented sequence of bone marrow changes. This study measured the T1 signal intensity of the clivus and cervical vertebral bodies of NPC patients who had received a complete course of radiation therapy. METHODS: There were 3 categories of patients: Group I: NPC patients who had radiation myelitis; 14 persons which a total 20 times of MRI. Group II: NPC patients, without radiation myelitis; 6 patients, which a total 6 times of MRI. Group III (control group): patients who received MRI of the cervical spine because of cervical spondylosis or HIVD, were total of 45 patients. In the sagittal section of T1WI, the signal intensity of the bone marrow of clivus and C2 to T1 vertebral bodies was measured. RESULTS: 1). There were homogeneous increases of signal intensity of the bone marrow of clivus and C2 to T1 in Groups I and II. 2). There was no statistical difference between Groups I and II. 3). The increased signal intensity of bone marrow after radiation showed no difference in short and long duration between radiation therapy and MR examinations, indicating that bone marrow signal intensities were increased in NPC patients whether or not they had radiation myelitis. CONCLUSIONS: Signal change in bone marrow may have occurred soon after radiation therapy, and may have persisted for several years. The radiation myelitis always involved the low medulla oblongata to C5 level; however, the bone marrow signal change always extended downward to the T1 level, so bone marrow is more sensitive than the spinal cord and is prone to be affected by irradiation.

Adult↗
PubMed1993

Unique TATA-binding protein-containing complexes and cofactors involved in transcription by RNA polymerases II and III.

Two multisubunit complexes containing the TATA-binding protein (TBP) were isolated from HeLa cells constitutively expressing the FLAG epitope-tagged TBP using antibody affinity and peptide elution methods. One of the complexes (f:TFIID), isolated from the P11 0.85 M KCl fraction, contains at least 13 specific TBP-associated factors (TAFs) and can mediate activator-dependent transcription by RNA polymerase II. Importantly, activator function through the highly purified f:TFIID complex still requires a general cofactor fraction containing upstream factor stimulatory activity (USA). As previously observed with partially purified activator-competent natural TFIID, f:TFIID generates extended TATA-dependent footprints on the intrinsically strong adenovirus major late promoter (MLP) but only restricted footprints on the weak adenovirus E1b and E4 and HIV (core) promoters. Along with previous demonstrations of activator-induced downstream TFIID interactions on the E4 promoter, these results argue for a relationship between downstream interactions and overall promoter strength. Initiator-like sequences appear not to be essential for downstream interactions since they have no effect on downstream MLP interactions when mutated, do not effect downstream interactions on the HIV promoter and are not present on the inducible E4 promoter. The other multisubunit complex (f:TFIIIB), isolated from the P11 0.30 M KCl fraction, contains four specific TAFs and can substitute for one of the fractions (TFIIIB) required for RNA polymerase III (pol III) transcription. Neither f:TFIID nor TBP could substitute for this pol III TBP-containing fraction. This plus the fact that f:TFIIIB failed to generate a footprint on the MLP underscores the importance of TAFs in determining promoter specificity by different RNA polymerases.

Adenovirus E1B Proteins↗
PubMed1993

Real-time arrhythmia identification from automated analysis of intraatrial and intraventricular electrograms.

Implantable cardioverter defibrillators have dramatically improved survival rates for patients at risk of sudden cardiac death, but the occurrence of inappropriate shocks remains an unresolved problem. Various means for better tachycardia detection, chiefly morphological analysis, have been proposed to address this problem. A new computerized scheme entitled Two-Channel Rate-Morphology (2CRM) was introduced. It is a real-time arrhythmia detection algorithm that combines timing and morphology information from intraatrial and intraventricular electrograms for arrhythmia diagnosis. The program 2CRM applies an initial cycle-by-cycle coding scheme followed by contextual diagnosis of underlying rhythm. The program was tested on 36 distinct passages of two-channel intracardiac signals from 30 patients. The distribution of the arrhythmias are as follows: 4 atrial fibrillation, 6 atrial flutter, 6 supraventricular tachycardia, 10 ventricular tachycardia, and 10 ventricular flutter-fibrillation. Of the analyzed 3,417 individual cardiac cycles 3,135 (91.7%) were correctly identified. Contextual diagnosis reversed 123 single-cycle errors to obtain a performance of 3,258 correct out of 3,417 (95.3%). Utilizing an uninterrupted continuous correct contextual diagnosis as indicator of successful arrhythmia detection, 2CRM obtained an accuracy of 34 out of 36 passages (94.4%).

Algorithms↗