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F Y Chen

Publications and source records attributed to F Y Chen.

31 records · Page 2Linked to original sources
PubMed1994

Regulation of mammalian ribonucleotide reductase R1 mRNA stability is mediated by a ribonucleotide reductase R1 mRNA 3'-untranslated region cis-trans interaction through a protein kinase C-controlled pathway.

Ribonucleotide reductase catalyses the reaction that eventually provides the four deoxyribonucleotides required for the synthesis and repair of DNA. U.v.-cross-linking and band-shift experiments have identified in COS 7 monkey cells an approx. 57 kDa ribonucleotide reductase R1 mRNA-binding protein called R1BP, which binds specifically to a 49-nt region of the R1 mRNA 3'-untranslated region (3'UTR). The R1BP-RNA binding activity was down-regulated by the tumour promoters phorbol 12-myristate 13-acetate (PMA; 'TPA') and okadaic acid, and up-regulated by the protein kinase C inhibitor staurosporine, in a dose-dependent fashion. Furthermore, staurosporine treatment decreased the stability of R1 and CAT (chloramphenicol acetyltransferase)/R1 hybrid mRNAs, whereas PMA and okadaic acid increased the stability of these messages, in a dose-dependent manner. In contrast, treatment of cells with forskolin, a protein kinase A inhibitor, did not alter either R1BP-RNA binding or R1 mRNA-stability characteristics. Transfectants containing R1 or CAT/R1 cDNA constructs with a deletion of the 49-nt 3'UTR sequence failed to respond in message-stability studies to the effects of PMA, staurosporine or okadaic acid. These observations indicate that a protein kinase C signal pathway regulates ribonucleotide reductase R1 gene expression post-transcriptionally, through a mechanism involving a specific cis-trans interaction at a 49-nt region within the R1 mRNA 3'UTR.

3T3 Cells↗
PubMed1994

Phorbol ester modulation of a novel cytoplasmic protein binding activity at the 3'-untranslated region of mammalian ribonucleotide reductase R2 mRNA and role in message stability.

The R2 gene of ribonucleotide reductase is elevated in BALB/c 3T3 fibroblasts treated with the tumor promotor, 12-O-tetradecanoylphorbol-13-acetate (TPA). TPA treatment increased the half-life of the R2 message by 3-fold, showing that TPA regulates R2 gene expression by a post-transcriptional mechanism(s). A 20-nucleotide (nt) TPA-responsive region was found within the R2 mRNA 3'-untranslated region (3'UTR). Ultraviolet cross-linking detected a novel 45-kDa protein-R2 mRNA complex migration band that bound selectively to the 20-nt fragment and did not bind to the 5'UTR or the coding region of the R2 message, or to the 3'UTRs of mRNA from several other genes, or to the homopolymer poly(A) sequence. The-45 kDa protein-R2 mRNA binding activity observed in unstimulated cells was markedly down-regulated after TPA treatment. Deletion of a 201-nt region, containing the 20-nt sequence, from the 3'UTR caused stabilization of hybrid chloramphenicol acetyltransferase mRNA in the absence of TPA treatment. Furthermore, in vitro decay reaction mixtures supplemented with the 20-nt sense RNA transcript resulted in stabilization of R2 message. A model is presented of R2 message regulation in which a cis-element within the 20-nt sequence of the 3'UTR interacts with a cytosolic protein to form a 45-kDa protein-mRNA binding complex. The TPA-induced alteration of R2 message stability is at least in part due to the down-regulation of the 45-kDa protein-mRNA binding activity which is linked to a reduction in the rate of R2 mRNA degradation.

3T3 Cells↗
PubMed1994

Right latissimus dorsi cardiomyoplasty improves left ventricular function by increasing peak systolic elastance (Emax).

BACKGROUND: Dynamic cardiomyoplasty remains a promising but poorly understood surgical modality for selected patients with dilated cardiomyopathy. Despite encouraging clinical results, objective evidence of enhanced ventricular function using traditional indexes (cardiac output, ejection fraction, and dP/dt) has been difficult to document after cardiomyoplasty. Several investigators have suggested that cardiomyoplasty acts partly by unloading the left ventricle. These indexes all depend somewhat on loading conditions, however, and might not detect such an interaction. The time-varying elastance model provides an index of contractility, Emax, that is relatively insensitive to changes in loading conditions. We applied this model to study the effect of right latissimus dorsi cardiomyoplasty on left ventricular function in an acute canine model. METHODS AND RESULTS: Five dogs underwent acute cardiomyoplasty using untrained right latissimus dorsi muscle. Instrumentation included Millar pressure transducers in the left ventricle and aortic root, an electromagnetic flow probe around the ascending aorta, and a volume conductance catheter in the left ventricle. A cuffed nerve electrode around the thoracodorsal nerve and a right ventricular sensing lead were connected to a Medtronic Cardiomyostimulator (5 V, 30 Hz, 1:1 synchronization). Transient caval occlusions were performed with the stimulator both off and on to calculate Emax and the slope of the end-systolic pressure-volume relationship (Ees). Turning the stimulator on significantly increased peak systolic elastance (Emax) and end-systolic elastance (Ees) in all five dogs by an average of 56% and 78%, respectively (P < .05). End-diastolic volume and end-systolic volume decreased by 18% and 28%, respectively (P < .05). All other measured hemodynamic parameters, including peak left ventricular pressure, mean arterial pressure, cardiac output, stroke volume, stroke work, ejection fraction, preload-recruitable stroke work, and dP/dt, did not change significantly. CONCLUSIONS: These results show that, in this acute canine model, right latissimus dorsi cardiomyoplasty significantly improves left ventricular function while decreasing left ventricular volumes. The results are consistent with the theory that cardiomyoplasty increases contractility while unloading the ventricle by decreasing end-diastolic volume. This increase in Emax despite inconsistent changes in other indexes underlies the importance of using load-insensitive indexes of ventricular function when studying cardiomyoplasty.

Animals↗
PubMed1993

A novel transforming growth factor-beta 1 responsive cytoplasmic trans-acting factor binds selectively to the 3'-untranslated region of mammalian ribonucleotide reductase R2 mRNA: role in message stability.

Ribonucleotide reductase is a highly regulated enzyme that provides the four deoxyribonucleotides required for DNA synthesis. Our studies showed that TGF-beta 1 treatment of BALB/c 3T3 mouse fibroblasts markedly elevated ribonucleotide reductase R2 mRNA levels, and also increased the half-life of R2 message by 4-fold from 1.5 h in untreated cells to 6 h in treated cells. We describe a novel 75 Kd sequence-specific cytoplasmic factor (p75) that binds selectively to a 83-nucleotide 3'-untranslated region of R2 mRNA and did not bind to the 5'UTR, the coding region of the R2 message or to the 3'UTRs of other mRNAs (from c-myc, GM-CSF and the iron responsive element from the transferrin receptor mRNA), or to the homopolymer poly(A) sequence. p75-RNA binding activity, which requires new protein synthesis, is not present in untreated cells, but is induced following TGF-beta 1 stimulation. The in vivo kinetics of appearance of p75 binding activity paralleled the accumulation of R2 mRNA. Insertion of the 3'-untranslated region into the chloramphenicol acetyltransferase (CAT) message confers TGF-beta 1 induced stability of RNA in stably transfected cells, while the same insert carrying a deletion of the 83-nucleotide fragment had little affect on RNA levels. Furthermore, in vitro decay reactions that contained the 83-nucleotide RNA or deletion of this fragment caused a significant decrease in TGF-beta 1 stabilization of R2 message. A model is presented of R2 message regulation in which TGF-beta 1 mediated stabilization of R2 message involves a specific interaction of a p75-trans-acting factor with a cis-element(s) stability determinant within the 83-nucleotide sequence which is linked to a reduction in the rate of R2 mRNA degradation.

3T3 Cells↗
PubMed1993

Mammalian ribonucleotide reductase R1 mRNA stability under normal and phorbol ester stimulating conditions: involvement of a cis-trans interaction at the 3' untranslated region.

Ribonucleotide reductase R1 gene expression is elevated in BALB/c 3T3 fibroblasts treated with the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA). We show that TPA treatment increased the half-life of R1 mRNA by 5-fold, indicating that TPA regulates R1 gene expression by a post-transcriptional mechanism. We investigated the possibility that the 3' untranslated region (3'UTR) of R1 mRNA contains regulatory information for TPA-mediated message stability. Our studies demonstrated that a 49 nucleotide (nt) TPA-responsive region existed within the R1 mRNA 3'UTR. Deletion of the 49 nt region led to the abolishment of TPA-induced stability of R1 and hybrid CAT mRNAs. Further deletions of the 3'UTR did not significantly affect mRNA turnover rates. In addition, we detected by cross-linking a novel 52-57 kDa R1 mRNA-binding protein (R1BP) that bound selectively to the 49 nt region of the R1 mRNA 3'UTR and did not bind to the 5'UTR, the coding region or other mRNA 3'UTRs. The R1BP-RNA binding activity observed in unstimulated cells was rapidly and markedly down-regulated after TPA treatment, suggesting a role for R1BP in mRNA metabolism, and in the mechanism of action of TPA-induced R1 message stabilization. These results support a novel model of R1 gene regulation in which a cis-element(s) within the 49 nt region of the R1 mRNA 3'UTR interacts with R1BP in a mechanism that regulates R1 message stability. We propose that this model accounts for the TPA-mediated stability alteration of R1 message, through down-regulation of R1BP-RNA binding activity linked to a reduction in the rate of R1 mRNA degradation.

3T3 Cells↗
PubMed1993

Role of nitric oxide in neurogenic vasodilation of porcine cerebral artery.

A superfusion bioassay cascade, with porcine pial arteries as donor tissues and rabbit aortic rings as detector tissues, was used to examine the role of nitric oxide (NO) in cerebral nonadrenergic, noncholinergic neurogenic vasodilation. All arteries were mechanically denuded of endothelium. In the presence of atropine (1 microM) and guanethedine (0.3 microM), transmural nerve stimulation (TNS) of cerebral arteries (CA) resulted in a frequency-dependent relaxation of phenylephrine-precontracted aortic rings. Relaxation was abolished by tetrodotoxin (2 microM) superfused onto and by cold-storage denervation of CA, suggesting that a vasodilating factor (VF) of neuronal origin in CA was released upon TNS. The VF-induced relaxation was inhibited by NW-nitro-L-arginine (0.3 mM) superfused onto CA. This inhibition was reversed by L-arginine (0.3 mM) but not D-arginine (0.3 mM). Exogenously applied NO onto CA also induced dilations of aortic rings in a concentration-dependent manner. The VF- and NO-induced dilations, which were abolished by hemoglobin (0.3 microM), and enhanced by superoxide dismutase (30 U/ml), declined to the same extent with similar time courses from the first to the second aortic ring. These findings indicate that VF and NO possess a similar labile nature and half-life, suggesting that VF is NO or a related substance. Identical frequency-response curves of TNS (2-16 Hz) and concentration-response curves of NO (10-1000 nM) further suggest that < 1000 nM of NO was released from CA upon TNS at the maximal frequency used.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Protein kinase A-dependent binding of a nuclear factor to the 21-base-pair repeat of the human T-cell leukemia virus type I long terminal repeat.

The long terminal repeat (LTR) of the human T-cell leukemia virus type I (HTLV-I) contains an imperfect repeat of 21 nucleotides which governs the response to the virus trans-activator protein tax and to cyclic AMP. In a murine thymocyte cell line defective in the catalytic subunit of protein kinase A, the response of the HTLV-I LTR to cyclic AMP is abolished and the response to tax is substantially diminished. This report shows that a factor present in nuclear extracts of wild-type cells binds to the HTLV-I 21-nucleotide sequence and that this binding activity is missing from the extracts of protein kinase A-defective cells. Treatment of nuclear extracts of protein kinase A-defective cells with the bovine protein kinase A catalytic subunit restores the binding activity, whereas treatment of wild-type nuclear extracts with a protein phosphatase destroys the binding activity. The binding factor is referred to as protein kinase A-dependent factor (PKAF). These results indicate that in murine thymocytes the response of the HTLV-I LTR to cyclic AMP depends upon the binding of a phosphorylated protein to the 21-nucleotide repeat sequence and that the response to tax is partially dependent upon binding of the phosphorylated protein. The results suggest a model in which the phosphorylation of a transcription factor by protein kinase A regulates HTLV-I gene expression.

Animals↗
PubMed1989

Suppression of experimental uveitis in rats by anti-I-A antibodies.

I-region-associated (Ia) class II major histocompatibility complex (MHC) products are known to play a major role in autoimmunity. Effects of anti-I-A and anti-I-E monoclonal antibodies on development of experimental autoimmune uveitis (EAU) were investigated in Lewis rats. Prior to sensitization with S-antigen, seven groups of rats, six in each group, were injected intraperitoneally with one of the following agents. Groups 1, 2, and 3 (controls) received saline, RPMI and mouse immunoglobulin G (IgG), respectively. Groups 4 and 5 were injected with anti-I-E antibodies, 80 micrograms and 1000 micrograms, respectively. Similarly, groups 6 and 7 received anti-I-A, 100 micrograms and 750 micrograms, respectively. The treatments were repeated on days 1, 2, 5, 8, and 11 after S-antigen injection. All these animals were killed on day 18. In addition, two groups of rats sensitized with S-antigen were treated with 750 micrograms anti-I-A antibodies on days 5, 6, and 7 (group 8) and on days 7, 8 and 9 (group 9). An additional group (group 10) of Lewis rats was treated with 750 micrograms anti-I-A 1 day prior to and on days 1 and 2 after S-antigen injection. These group-10 animals were killed on day 31. Histopathologically, the enucleated globes of animals treated with high dose anti-I-A revealed marked suppression or inhibition of uveitis development. Such inhibition was virtually complete when the antibody was administered within a week of S-antigen injection, and the inhibitory effect lasted for at least 31 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

An engineering model of dynamic cardiomyoplasty. II. Clinical applications.

Previously, a modification to the Sunagawa engineering model for the isolated left ventricle and arterial system was proposed and validated for dynamic cardiomyoplasty in an acute goat preparation. To test the hypothesis that this model may be applied to the clinical scenario in cardiomyoplasty patients, we predicted human stroke volume using the model with human clinical data from the literature. Predicted stroke volume correlated well with published stroke volume in patients who have had the dynamic cardiomyoplasty procedure. These results suggest that the modest hemodynamic improvement commonly reported after the procedure is performed may be due to diminished latissimus dorsi strength after transformation. The validity of both the original Sunagawa model and the previously proposed modification for dynamic cardiomyoplasty is further supported with these results. A nomogram methodology for predicting stroke volume after dynamic cardiomyoplasty for any particular patient is presented.

Biomechanical Phenomena↗
PubMedDate not supplied

An engineering model of dynamic cardiomyoplasty. I.

Dynamic cardiomyoplasty (DCM) is an emerging surgical procedure for heart failure in which the patient's latissimus dorsi (LD) muscle is wrapped around the heart and stimulated to contract in synchrony with the heartbeat as a cardiac assist measure. A 6 week training protocol of progressive electrical stimulation renders the normally fatigueable skeletal muscle fatigue-resistant and suitable for chronic stimulation. To date, over 500 procedures have been performed in worldwide clinical trials. Investigators typically report symptomatic improvement and modest hemodynamic improvement in patients. Controversy exists regarding the exact mechanism of DCM. To test the hypothesis that DCM augments cardiac stroke volume through improvement in systolic function, we formulated an engineering model of dynamic cardiomyoplasty to predict stroke volume. The heart and the LD were modeled as nested (series) elastance chambers, and the vasculature was represented by a two-element Windkessel model. Using five healthy goats, we verified model predictions of stroke volume for both stimulator ON beats (y = 1.00x-0.08, r = 0.87, p < 0.0001) and OFF beats (y = 1.01x+1.06, r = 0.91, p < 0.0001), where x and y are the measured and predicted stroke volumes, respectively. The model confirms that using untrained latissimus dorsi applied to the normal myocardium produces only moderate increases in stroke volume and suggests that future research should focus on increasing LD strength after training.

Cardiomyoplasty↗
PubMedDate not supplied

Posttranscriptional regulation of ribonucleotide reductase R1 gene expression is linked to a protein kinase C pathway in mammalian cells.

A rate-limiting reaction in DNA synthesis is catalyzed by ribonucleotide reductase, the enzyme responsible for reducing ribonucleotides to provide the deoxyribonucleotide precursors of DNA. In this study, we have tested the hypothesis that posttranscriptional regulation of ribonucleotide reductase R1 gene expression is controlled by a protein kinase C signal pathway. We show that mouse BALB/c 3T3 fibroblasts treated with the potent and highly specific protein kinase C inhibitor bisindolylmaleimide GF 109203X contain significantly reduced steady-state levels of R1 mRNA and protein. Message half-life studies demonstrate that this is due, at least in part, to a marked decrease in R1 message stability in cells treated with the protein kinase C inhibitor. Furthermore, the protein kinase C signal pathway appears to be specifically involved in this regulation since 8-bromo-cAMP, a modulator of the protein kinase A pathway, had no effect on R1 mRNA levels or stability properties. Cross-linking assays revealed that the binding activity of a R1 mRNA 3'-untranslated region binding protein (R1BP), which was previously shown to be involved in the regulation of R1 mRNA stability, was significantly elevated after treatment of the cells with GF 109203X, in a dose-dependent manner. However, treatment with 8-bromo-cAMP at concentrations up to 2.5 mM did not obviously affect the basic level of the R1BP-RNA interaction. These observations provide a better understanding of the biochemical signals that are critical for the cis-trans interaction-mediated posttranscriptional regulation of ribonucleotide reductase R1 gene expression.

8-Bromo Cyclic Adenosine Monophosphate↗