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Biomedical subjects

F Y Chen

Publications and source records attributed to F Y Chen.

At least 19 recordsLinked to original sources
PubMed1998

Mitral valve repair in cardiomyopathy.

BACKGROUND: Volume overload secondary to mitral regurgitation (MR) in cardiomyopathy is considered critical in the pathogenesis of subsequent ventricular dysfunction. Open mitral valve repair (OMVP) is hypothesized to improve symptomatology and ventricular function by reducing the volume overload of the left ventricle. METHODS AND RESULTS: All patients who underwent OMVP with a left ventricular ejection fraction (EF) of < 0.30 (n = 81) from 1984 through 1997 were reviewed (1 patient was lost to follow-up). Fifteen operations (18.5%) were repeat operations after previous coronary artery bypass graft surgery. Preoperative and postoperative EFs and NYHA class were compared. Survival probabilities were calculated, and multivariate analysis was performed. The average age of all patients was 67.1 years (range, 41 to 83 years). Mean follow-up was 1.7 years (range, 2 months to 8.5 years). The most common mitral repair was ring annuloplasty. Sixty-two patients (77%) had concomitant coronary artery bypass graft surgery. The surgery mortality rate was 11% (9 of 81); 6 of these 9 patients were > 70 years old. The overall Kaplan-Meier survival probability rate at 1, 2, 3, 4, and 5 years was 0.73, 0.68, 0.58, 0.50, and 0.38, respectively. EF improved significantly (0.24 to 0.32; P < 0.0001), as did the NYHA class (3.2 to 1.6; P < 0.0001), at follow-up. There was no difference in late survival between patients with an EF of < 0.20 (21 patients) and those with an EF between 0.20 and 0.30 (P = NS). Risk factors for death included heart failure and old age. CONCLUSIONS: OMVP for MR in the setting of ischemic cardiomyopathy and low EF appear to improve ventricular function, medium-term patient symptomatology, and survival.

Adult↗
PubMed1997

Cytoplasmic sequestration of an O6-methylguanine-DNA methyltransferase enhancer binding protein in DNA repair-deficient human cells.

O6-Methylguanine-DNA methyltransferase (MGMT), an enzyme that repairs adducts at O6 of guanine in DNA, is a major determinant of susceptibility to simple methylating carcinogens or of tumor response to anticancer chloroethylating drugs. To investigate the mechanisms underlying cellular expression of this DNA repair enzyme, we focused on the role of a 59-bp enhancer of the human MGMT gene in the regulation of its expression. By using chloramphenicol acetyltransferase reporter assays, we found that the enhancer activity, which was present in both MGMT-expressing (Mer+) and -deficient (Mer-) cells, correlated with the endogenous MGMT activity in Mer+ cell lines. Band-shift assays and deletion analysis of the 59-bp sequence defined a minimal 9-mer cis element (5'-CTGGGTCGC-3') for specific trans factor binding. The MGMT enhancer binding protein (MEBP), 45 kDa by Southwestern blot analysis, was present in the nuclei of all Mer+ cells tested but was apparently restricted to the cytoplasm of Mer- cells. We conclude that the MEBP-enhancer interaction plays an important role in regulating constitutive MGMT expression in Mer+ cells and that MEBP exclusion from the nucleus may account for the down-regulation of MGMT in Mer- cells.

Base Sequence↗
PubMed1997

Issues involved in assessing competency.

A psychiatric competency assessment entails more than merely conducting a few clinical tests to diagnose the cause of a cognitive impairment. The psychiatrist may need to explore other aspects of the patient's life, including his or her interpersonal relationships and functional abilities. To provide a truly useful consult for other physicians, legal professional, family members, and the patient, the psychiatrist must be able to integrate the medical findings along with all relevant personal information and apply this information to the legal standards of the particular jurisdiction. By being able to apply both medical and legal knowledge of proxy decision making, the psychiatrist will be better prepared to make recommendations that will facilitate the proper care and services for the cognitively impaired patient.

Aged↗
PubMed1997

Thoracoscopic transmyocardial laser revascularization.

BACKGROUND: Transmyocardial laser revascularization is a promising surgical technique used to treat nonreconstructable ischemic heart disease. Recent clinical data show that this technique improves the regional perfusion of ischemic myocardium and reduces angina. Presently, transmyocardial laser revascularization requires an open, lateral thoracotomy. We report here the use of thoracoscopic techniques to perform transmyocardial laser revascularization in a closed chest fashion. METHODS: Five Yorkshire farm pigs underwent left chest thoracoscopic exploration and pericardiotomy. A specialized laser handpiece then was introduced into the chest and thoracoscopic transmyocardial laser revascularization was performed (one channel per square centimeter) using an 800-W CO2 laser. RESULTS: Video analysis and gross pathology revealed that the anatomic area accessible to thoracoscopic transmyocardial laser revascularization included the entire left ventricular free wall distributions of the left anterior descending, left circumflex, and posterior descending arteries, from base to apex. Standard hematoxylin and eosin staining confirmed the creation of complete and patent 1-mm-diameter transmural channels throughout these distributions. CONCLUSION: We have shown that transmyocardial laser revascularization can be performed effectively and safely by thoracoscopy, and that this less invasive technique may reduce morbidity and provide a more cost-effective alternative therapy for nonreconstructable ischemic heart disease.

Animals↗
PubMed1997

Right latissimus dorsi cardiomyoplasty improves left ventricular energetics.

BACKGROUND: The mechanism by which cardiomyoplasty appears to enhance left ventricular (LV) function is not well understood. We applied the time-varying elastance model to study the effect of cardiomyoplasty on LV function, ventriculovascular coupling, and LV energetics in an acute canine model. METHODS: Right latissimus dorsi cardiomyoplasty was performed in 5 dogs. The end-systolic pressure-volume relation was generated by using brief caval occlusions. End-systolic elastance, effective arterial elastance, stroke work, internal work, total mechanical work, and stroke work efficiency (stroke work/total mechanical work) were calculated from these pressure-volume data. Myocardial oxygen consumption and overall mechanical efficiency (stroke work/myocardial oxygen consumption) were predicted using the myocardial oxygen consumption-total mechanical work relation. RESULTS: Skeletal muscle contraction significantly increased end-systolic elastance, an index of contractility. Although stroke work did not change significantly, the increase in end-systolic elastance led to a 29% decrease in total mechanical work, a 50% decrease in internal work, and an increase in stroke work efficiency from 53% to 66%. This was consistent with the observed 29% decrease in effective arterial elastance/end-systolic elastance, an indicator of ventriculovascular coupling that is related inversely to stroke work efficiency. Predicted myocardial oxygen consumption decreased by at least 22%, and predicted overall mechanical efficiency increased at a minimum from 16.1% to 18.4%. CONCLUSIONS: These results support the theory that cardiomyoplasty unloads the LV by decreasing LV volumes and increasing contractility. These effects appear to improve LV energetics by decreasing total mechanical work without significantly affecting stroke work, resulting in improved stroke work efficiency. The decrease in total mechanical work strongly suggests a decrease in myocardial oxygen consumption and an increase in overall mechanical efficiency.

Animals↗
PubMed1996

Decreased myocardial oxygen consumption indices in dynamic cardiomyoplasty.

BACKGROUND: To investigate the theory of decreased myocardial oxygen consumption (MVo2) in dynamic cardiomyoplasty (DCM), previous studies have calculated indices of MVo2 in DCM. These previous studies, however, used left ventricular pressure in formulas that assumed the assumed the heart to be in its native state, with the reference pressure at the epicardium assumed to be atmospheric. In DCM, however, the reference pressure at the epicardium is no longer atmospheric but rather is the compressive pressure generated by the latissimus dorsi (LD). We therefore used the transmural myocardial pressure, Pt, to calculate indices of MVo2 in DCM. METHODS AND RESULTS: A half-ellipsoidal, fluid-filled balloon was interposed between the LD and myocardium in a balloon-mediated cardiomyoplasty procedure in five goats. With commonly used LD stimulation parameters, Pt was calculated as left ventricular pressure minus balloon luminal pressure. Using Pt, the transmural tension time index (TtTI) and transmural pressure volume area (PtVA) were calculated. In another series of four goats, LD stimulation parameters were optimized and the TtTI and PtVA recalculated. With standard LD stimulation parameters, the TtTI decreased by 48%, from 15.8 to 8.2 mm Hg.s, and the PtVA by 21%, from 775 to 612 mm Hg.mL, as the LD was stimulated to contract. When the optimized parameters were used, the TtTI decreased by 45%, from 11.2 to 6.2 mm Hg.s, and the PtVA by 33%, from 1984 to 1371 mm Hg.mL. CONCLUSIONS: Our results suggest that DCM with a fluid-filled balloon decreases MVo2 as the LD contracts and that LD stimulation parameters have a determining effect on this benefit.

Animals↗
PubMed1996

Inhibition of cerebral neurogenic vasodilation by L-glutamine and nitric oxide synthase inhibitors and its reversal by L-citrulline.

The possibility that L-citrulline is able to reverse inhibition of neurogenic vasodilation in isolated porcine cerebral arteries produced by nitric oxide synthase (NOS) inhibitors and Gln was examined by using in vitro tissue bath techniques. The results indicated that transmural nerve stimulation elicited a frequency-dependent and tetrodotoxin-sensitive vasodilation in isolated ring segments of arteries with or without endothelial cells. The dilation was abolished by L-N-omega-nitro-L-Arg and L-N-omega-L-Arg methyl ester and was completely reversed by L-citrulline, but not by D-citrulline. In parallel studies, the transmural nerve stimulation-induced relaxation was blocked in part by Gln. The blockade was completely reversed by L-citrulline and L-Arg, but not by their D-enantiomers. The time courses of relaxation after L-citrulline reversal of inhibition of vasodilation produced by Gln and NOS inhibitors were identical to that of relaxation in the control. The residual relaxation after L-citrulline reversal was abolished by L-NNA and L-N-omega-nitro-L-Arg. At 1 mM, L-glutamate, tau-aminobutyric acid or NH4Cl did not block transmural nerve stimulation-induced relaxation, nor did Gln inhibit sodium nitroprusside-induced relaxation or neuronal NOS activity. These results provide pharmacological evidence that cerebral perivascular nerves can recycle L-citrulline to L-Arg for synthesizing nitric oxide to induce neurogenic vasodilation. Although the exact mechanism of action of Gln in inhibiting nitric oxidergic neurovascular transmission remains undetermined, Gln does not seem to act by releasing ammonium ions, inhibiting NOS or modifying the nitric oxide-cyclic GMP pathway. Cerebral metabolism of Gln may play an important role in regulating nitric oxidergic neurogenic vasodilation.

Animals↗
PubMed1996

Photosensitization of bilirubin on proliferation and DNA synthesis in ascitic hepatoma cells.

AIM: To observe the effects and its mechanism of photosensitization of bilirubin on ascitic hepatoma (Hep A) cells. METHODS: After the cells were illuminated under the light (1.0 x 10(5) lx) for 10 min, deoxy[3H]thymidine was added for DNA synthesis assay. The cells were dyed with 0.5% trypan blue and were counted. RESULTS: The cell mortality of illuminated groups were much higher than that of dark groups (P < 0.01). The inhibitions of DNA synthesis of illuminated groups were stronger than that of dark groups (P < 0.01). The cell mortality and inhibition of DNA synthesis of illuminated groups were positively dependent upon the concentrations of bilirubin and illuminating time. No difference of DNA synthesis between room light illumination groups and dark groups (P < 0.05). CONCLUSION: The photosensitization of bilirubin killed Hep A cells obviously. Bilirubin under room light had no effect on inhibition of DNA synthesis. The photosensitization of bilirubin was closely related to 1O2 and H2O2 and not to OH. and O2-. Bilirubin, the end product of heme catabolism in mammals, is a potentially cytotoxic, lipid soluble waste product that needs to be excreted. However, bilirubin at micromolar concentration in vitro, efficiently scavenges peroxyl radicals. In liposomes, bilirubin suppresses the antioxidation more than alpha-tocopherol, which is regarded as the best antioxidant of lipid peroxidation. Thus bilirubin is a physiological, chain-breaking antioxidant. Bilirubin exhibited antitumor activity and acted as a photosensitizer with four pyrrole rings. Many photosensitizers have been used to treat cancer due to their photosensitization. In this paper, the photosensitization of bilirubin on DNA synthesis in ascitic hepatoma (Hep A) cells and on cell mortality were studied.

Animals↗
PubMed1995

Defining a novel cis element in the 3'-untranslated region of mammalian ribonucleotide reductase component R2 mRNA: role in transforming growth factor-beta 1 induced mRNA stabilization.

Ribonucleotide reductase R2 gene expression is elevated in BALB/c 3T3 fibroblasts treated with transforming growth factor beta 1. We investigated the possibility that the 3'-UTR of ribonucleotide reductase R2 mRNA contains regulatory information for TGF-beta 1 induced message stability. Using end-labeled RNA fragments in gel shift assays and UV cross-linking analyses, we detected in the 3'-UTR a novel 9 nucleotide (nt) cis element, 5'-GAGUUUGAG-3' site, which interacted specifically with a cytosolic protease sensitive factor to form a 75 kDa complex. The cis element protein binding activity was inducible and markedly up-regulated cross-link 4 h after TGF-beta 1 treatment of mouse BALB/c 3T3 cells. Other 3'-UTRs [IRE, GM-CSF, c-myc and homopolymer (U)] were poor competitors to the cis element with regard to forming the TGF-beta 1 dependent RNA-protein complex. However, the cis element effectively competed out the formation of the R2 3'-UTR protein complex. Cytosolic extracts from a variety of mammalian cell lines (monkey Cos7, several mouse fibrosarcomas and human HeLa S3) demonstrated similar TGF-beta 1 dependent RNA-protein band shifts as cell extract from BALB/c 3T3 mouse fibroblasts. Binding was completely prevented by several different mutations within the cis element, and by substitution mutagenesis, we were able to predict the consensus sequences, 5'-GAGUUUNNN-3' and 5'-NNNUUUGAG-3' for optimal protein binding. These results support a model in which the 9 nt region functions in cis to destabilize R2 mRNA in cells; and upon activation, a TGF-beta 1 responsive protein is induced and interacts with the 9 nt cis element in a mechanism that leads to stabilization of the mRNA. This appears to be the first example of a mRNA binding site that is involved in TGF-beta 1-mediated effects.

3T3 Cells↗
PubMed1995

New technique measures decreased transmural myocardial pressure in cardiomyoplasty.

BACKGROUND: We introduce the use of a fluid-filled balloon, interposed between myocardium and latissimus dorsi (LD), as a new technique to measure transmural myocardial pressure in an acute goat model of dynamic cardiomyoplasty. METHODS: A half-ellipsoidal balloon, composed of polychloryl vinyl layers, was sutured to the atrioventricular groove in 5 goats, thereby completely enveloping both ventricles. Left LD dynamic cardiomyoplasty was then performed, anchoring the LD to the felt sewing skirt of the balloon so that the LD completely covered the balloon. Left ventricular pressure and balloon pressure were measured with the stimulator in the 1:2 mode as balloon volume was varied. RESULTS: Average transmural myocardial pressure, defined as left ventricular pressure minus balloon pressure, decreased from 34.4 mm Hg to 15.6 mm Hg during stimulator-on beats (p < 0.05). CONCLUSION: These results support the conclusion that dynamic cardiomyoplasty unloads the left ventricle by decreasing wall stress. Furthermore, transmural myocardial pressure decreased more when balloon volume was increased, implying that the LD sarcomere length has an effect on wall stress. A balloon may therefore allow optimization of LD sarcomere length and thus assisted cardiac performance.

Animals↗
PubMed1995

Arginine synthesis from citrulline in perivascular nerves of cerebral artery.

Cerebral neurogenic vasodilation is mediated predominantly by nitric oxide (NO). Thus, NO was suggested to be a vasodilator transmitter. In the present study, the possibility that cerebral perivascular nerves can convert citrulline to arginine was examined to ascertain that NO is derived directly from these perivascular nerves. To investigate the uptake of citrulline and its conversion to arginine, both fresh and cold storage-denervated porcine cerebral arteries with or without endothelial cells were incubated at 37 degrees C for 2 hr in Krebs-Ringer bicarbonate buffer containing 0.5 mM purified [14C]ureido-citrulline. The formation of [14C]arginine was measured as 14CO2 by a coupled enzymatic assay involving arginase and urease. The abolishment of nitric oxidergic nerves was verified by NADPH-diaphorase (constitutive NO synthases) histochemical staining method. The results indicated that there was an active conversion of [14C]arginine from [14C]citrulline in nerve-intact arteries denuded of endothelial cells. The conversion was significantly decreased in denervated arteries, accompanied by a significantly reduced citrulline uptake into these denervated arteries. L-Glutamine, but not L-glutamate, gamma-aminobutyric acid, or nitro-L-arginine significantly inhibited the uptake of [14C]citrulline into cerebral perivascular nerves. These data suggest that porcine cerebral vasodilator nerves are nitric oxidergic in nature and citrulline, co-produced with NO by NO synthases from arginine, can be recycled to form arginine in these nerves. The existence of a functional arginine-citrulline cycle may contribute to a constant supply of L-arginine and suggests a neuronal source of NO for inducing cerebral vasodilation.

Animals↗
PubMed1994

Defining a novel ribonucleotide reductase r1 mRNA cis element that binds to an unique cytoplasmic trans-acting protein.

Ribonucleotide reductase is a highly regulated rate-limiting enzyme activity in DNA synthesis, responsible for reducing ribonucleotides to their deoxyribonucleotide forms. Using 3'-end labeled RNA and band-shift and UV cross-linking analyses, we have identified a cis-element, 5'-CAAACUUC-3', within the 3'-untranslated region of the mammalian ribonucleotide reductase R1 mRNA, which binds a cytoplasmic protein in BALB/c 3T3 mouse cells, to form a 57 kDa RNA-protein complex. Sequence-specific binding was observed, and binding was prevented by several different mutations within the cis-element. We suggest that this cis-trans interaction plays a role in R1 mRNA stability.

3T3 Cells↗
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↗