Biomedical subjects

H Cheng

Publications and source records attributed to H Cheng.

At least 91 records · Page 5Linked to original sources

PubMed2000

Involvement of multiple intracellular release channels in calcium sparks of skeletal muscle.

In many types of muscle, intracellular Ca(2+) release for contraction consists of brief Ca(2+) sparks. Whether these result from the opening of one or many channels in the sarcoplasmic reticulum is not known. Examining massive numbers of sparks from frog skeletal muscle and evaluating their Ca(2+) release current, we provide evidence that they are generated by multiple channels. A mode is demonstrated in the distribution of spark rise times in the presence of the channel activator caffeine. This finding contradicts expectations for single channels evolving reversibly, but not for channels in a group, which collectively could give rise to a stereotyped spark. The release channel agonists imperatoxin A, ryanodine, and bastadin 10 elicit fluorescence events that start with a spark, then decay to steady levels roughly proportional to the unitary conductances of 35%, 50%, and 100% that the agonists, respectively, promote in bilayer experiments. This correspondence indicates that the steady phase is produced by one open channel. Calculated Ca(2+) release current decays 10- to 20-fold from spark to steady phase, which requires that six or more channels be open during the spark.

Animals↗

PubMed2000

Evidence that ThiI, an enzyme shared between thiamin and 4-thiouridine biosynthesis, may be a sulfurtransferase that proceeds through a persulfide intermediate.

ThiI is an enzyme common to the biosynthetic pathways leading to both thiamin and 4-thiouridine in tRNA. Comparison of the ThiI sequence with protein sequences in the data bases revealed that the Escherichia coli enzyme contains a C-terminal extension displaying sequence similarity to the sulfurtransferase rhodanese. Cys-456 of ThiI aligns with the active site cysteine residue of rhodanese that transiently forms a persulfide during catalysis. We investigated the functional importance of this sequence similarity and discovered that, like rhodanese, ThiI catalyzes the transfer of sulfur from thiosulfate to cyanide. Mutation of Cys-456 to alanine impairs this sulfurtransferase activity, and the C456A ThiI is incapable of supporting generation of 4-thiouridine in tRNA both in vitro and in vivo. We therefore conclude that Cys-456 of ThiI is critical for activity and propose that Cys-456 transiently forms a persulfide during catalysis. To accommodate this hypothesis, we propose a general mechanism for sulfur transfer in which the terminal sulfur of the persulfide first acts as a nucleophile and is then transferred as an equivalent of S(2-) rather than S(0).

Amino Acid Sequence↗

PubMed2000

Perceived parental behaviour, self-esteem and happiness.

BACKGROUND: This study set out to determine to what extent recalled parental rearing styles (authoritarian, authoritativeness, permissiveness), personality (extraversion, neuroticism, psychoticism, lie), and self-esteem predicted self-rated happiness in a normal, nonclinical, population of young people in their late teens and early 20s. METHODS: Each participant completed a few questionnaires: the Eysenck Personality Questionnaire (revised), the Rosenberg Self-Esteem Scale, the Parental Authority Questionnaire and the Oxford Happiness Inventory. It was predicted that sex, extraversion, neuroticism, self-esteem and both maternal and paternal authoritativeness would be significant predictors of happiness. RESULTS: Regressional and path analysis showed self-esteem to be the most dominant and powerful predictor of happiness. The effect of sex on happiness was moderated by neuroticism, which related to self-esteem, which directly influenced happiness. Stability, extraversion and maternal authoritativeness were significant predictors of self-esteem accounting for one-third of the variance. CONCLUSION: The results are considered in terms of the distinct literature on the relation between personality and happiness and on the relation between parental styles and self-esteem. Self-esteem was both a direct and a moderator variable for young people's self-reported happiness. Extraversion had both direct and indirect predictive power of happiness, whereas neuroticism predicted happiness mediating through self-esteem. Maternal authoritativeness was the only direct predictor of happiness when paternal and maternal rearing styles were examined together, suggesting that a reasonable discipline exercised by mothers towards their children was particularly beneficial in enhancing the offsprings' self-esteem.

Adolescent↗

PubMed2000

Connexin 43 expression is downregulated in raft cultures of human keratinocytes expressing the human papillomavirus type 16 E5 protein.

A decrease in gap junction-mediated cell-to-cell communication has previously been observed in monolayer cultures of human keratinocytes (HaCaT cells) expressing the human papillomavirus type 16 E5 (HPV16 E5) gene and attributed to the reduced phosphorylation of connexin 43, the most abundant connexin in HaCaT cells. In line with this observation, we have now analyzed the effect of HPV16 E5 on connexin 43 expression in raft cultures produced by transfected HaCaT cells. These keratinocytes transcribe HPV16 E5 under the control of a dexamethasone-inducible promoter. Our results show that treatment with dexamethasone leads to an almost complete disappearance of connexin 43 in rafts expressing the E5 gene but not in control rafts. In our study we discuss the possible effects of this downregulation on cell-cell communication and cellular malignant transformation.

Cell Culture Techniques↗

PubMed2000

G(i)-dependent localization of beta(2)-adrenergic receptor signaling to L-type Ca(2+) channels.

A plausible determinant of the specificity of receptor signaling is the cellular compartment over which the signal is broadcast. In rat heart, stimulation of beta(1)-adrenergic receptor (beta(1)-AR), coupled to G(s)-protein, or beta(2)-AR, coupled to G(s)- and G(i)-proteins, both increase L-type Ca(2+) current, causing enhanced contractile strength. But only beta(1)-AR stimulation increases the phosphorylation of phospholamban, troponin-I, and C-protein, causing accelerated muscle relaxation and reduced myofilament sensitivity to Ca(2+). beta(2)-AR stimulation does not affect any of these intracellular proteins. We hypothesized that beta(2)-AR signaling might be localized to the cell membrane. Thus we examined the spatial range and characteristics of beta(1)-AR and beta(2)-AR signaling on their common effector, L-type Ca(2+) channels. Using the cell-attached patch-clamp technique, we show that stimulation of beta(1)-AR or beta(2)-AR in the patch membrane, by adding agonist into patch pipette, both activated the channels in the patch. But when the agonist was applied to the membrane outside the patch pipette, only beta(1)-AR stimulation activated the channels. Thus, beta(1)-AR signaling to the channels is diffusive through cytosol, whereas beta(2)-AR signaling is localized to the cell membrane. Furthermore, activation of G(i) is essential to the localization of beta(2)-AR signaling because in pertussis toxin-treated cells, beta(2)-AR signaling becomes diffusive. Our results suggest that the dual coupling of beta(2)-AR to both G(s)- and G(i)-proteins leads to a highly localized beta(2)-AR signaling pathway to modulate sarcolemmal L-type Ca(2+) channels in rat ventricular myocytes.

Animals↗

PubMed2000

Birth control method choice and use of barrier methods for sexually transmitted disease prevention among low-income African-American women.

In a prospective study of 1122 women attending a sexually transmitted disease (STD) clinic in Alabama, consistent use of the male condom and vaginal microbicide/spermicides was promoted to reduce STD risk. This analysis evaluated: 1) baseline characteristics that may influence birth control method choice; and 2) the association of birth control method and other baseline characteristics with consistency of barrier use during follow up. Birth control method was associated with sociodemographic variables, sexual, and reproductive history. Women who adopted user-independent methods (tubal ligation, implants, injectable hormones) appear to have completed their family plan. Oral contraceptive users were of higher socioeconomic status and at lower STD risk. Barrier method users and women who used no method were young and at higher STD risk. Consistency of condom/spermicide use increased in all groups. Barrier method users were more likely than other women to use condoms and spermicides during the study. Women who used no birth control method at baseline experienced the largest increase in barrier use during follow up, although their barrier use rates were lower than in other groups. The synergism between the intention to prevent pregnancy and the intention to prevent STD should be considered in the design of interventions promoting condom use.

Adolescent↗

PubMed2000

The South Asian cataract management study: complications, vision outcomes, and corneal endothelial cell loss in a randomized multicenter clinical trial comparing intracapsular cataract extraction with and without anterior chamber intraocular lens implantation.

OBJECTIVE: To determine clinical outcomes of primary intracapsular cataract surgery with and without implantation of anterior chamber lenses. DESIGN: A multicenter randomized clinical trial. PARTICIPANTS: One thousand two hundred twenty-nine male and female patients 40-75 years of age with senile cataract. METHODS: Study patients were recruited from screening eye camps and outpatient clinics. Randomization to the two treatment groups was performed after screening for predetermined inclusion and exclusion criteria. Demographics, visual acuity, intraocular pressures, and corneal endothelial cell data were recorded before surgery and at 6 weeks, 12 months, and 24 months after surgery. Monitoring of the study was secured by a standardized image documentation procedure on all patients using the IMAGEnet digital imaging system. Analysis of corneal endothelial cell images was performed with the Cell Soft software (Topcon Corporation, Japan). MAIN OUTCOME MEASURES: Visual acuity and central corneal endothelial cell loss. RESULTS: The patients were randomized to intraocular lens (IOL; n = 616) and no IOL (n = 613) implantation. Surgical complications were reported in 177 (14.4%) patients (IOL = 14.8%; no IOL = 14.0%). The most frequent complication observed was vitreous loss which occurred in 10.3% of eyes (IOL = 11.2%; no IOL = 9.5%). At the final examination (2 years after surgery), 88% of the operated eyes had a best corrected vision of 6/18 or better (IOL = 88.8%; no IOL = 86.6%). Analysis of corneal endothelial cell data showed a small but significantly greater cell loss 6 weeks after surgery in eyes with IOL compared with those without IOL, but no overall difference was found between the treatment groups in the long term follow-up. CONCLUSIONS: The findings indicate that there is a rationale for the use of anterior chamber intraocular lenses in primary intracapsular cataract surgery.

Adult↗

PubMed2000

Validity and coverage of estimates of relative accuracy.

PURPOSE: Studies comparing test accuracy often restrict the confirmation procedure to subjects classified as positive by either test. Relative sensitivity (RSN) and relative false-positive rate (RFP) are two estimable comparative measures of accuracy. This article evaluates the influence of sample size, disease prevalence, and test accuracy on the validity of point estimates of RSN and RFP, and on the coverage of their confidence intervals (CI). METHODS: For each combination of sample size, disease prevalence, test accuracy, and interdependence between tests 1,000 samples were generated using computer simulations. The percent bias in the RSN and RFP estimates was measured by comparing the means of the 1,000 values computed in each simulation (log-transformed) with their theoretical values. Coverage of the estimated CI was measured by computing the proportion that actually included the theoretical values. Application of these methods was illustrated with data from a study comparing mammography and physical examination in screening for breast cancer. RESULTS: RSN estimates were valid if the true number of diseased cases exceeded 30, and RFP estimates were valid if the number of nondiseased subjects exceeded 200. When the numbers of diseased and nondiseased subjects exceeded 150 each, the 95% CI of RSN and RFP provided adequate coverage of the parameters (95 +/- 2%). CONCLUSION: Sample size is the most important variable for the validity and coverage of RSN and RFP estimates. For small samples, validity and coverage of RSN and RFP also depend on the accuracy of each test and on the degree of interdependence between the tests.

Adult↗

PubMed2000

Cyclic core dendrimer as a new kind of vector for gene transfer into mammalian cells.

Cyclic core dendritic polymer is a new type of synthetic polymers. The ability of generation 4 of the dendrimer with a core of 1,4,7,10-tetraazacyclododecane to function as an effective gene delivery vector was investigated. Results from fluorescence in situ hybridization (FISH) show that the pCH 110 plasmid DNA was transferred into human small intestine cancer metastatic ascites (HICMA) cells induced by this kind of dendrimer as a vector. The transferred LacZ, GFP and luciferase genes were highly expressed in the transfected HICMA, COS-7 and 293 cells. These studies demonstrate that the dendrimer can transfect mammalian cells in vitro which offers an alternatively efficient method for mammalian gene transfer.

Animals↗

PubMed2000

Effects of Ca2+ on the activity and stability of methanol dehydrogenase.

The effects of exogenously added Ca2+ on the enzymatic activity and structural stability of methanol dehydrogenase were studied for various Ca2+ concentrations. Methanol dehydrogenase activity increased significantly with increasing concentration of Ca2+, approaching saturation at 200 mM Ca2+. The effect of Ca2+ on the activation of MDH was time dependent and Ca2+ specific and was due to binding of the metal ions to the enzyme. Addition of increasing concentration of Ca2+ caused a decrease of the intrinsic tryptophan fluorescence intensity in a concentration-dependent manner to a minimum at 200 mM, but with no change in the fluorescence emission maximum wavelength or the CD spectra. The results revealed that the activation of methanol dehydrogenase by Ca2+ occurred concurrently with the conformational change. In addition, exogenously bound Ca2+ destabilized MDH. The potential biological significance of these results is discussed.

Alcohol Oxidoreductases↗

PubMed2000

Mechanisms of AVP-induced glucagon release in clonal alpha-cells in-R1-G9: involvement of Ca(2+)-dependent and -independent pathways.

1. The mechanisms underlying AVP-induced increase in [Ca(2+)](i) and glucagon release in clonal alpha-cells In-R1-G9 were investigated. 2. AVP increased [Ca(2+)](i) and glucagon release in a concentration-dependent manner. After the administration of AVP, glucagon was released within 30 s, quickly reached the maximum within 2 min, and maintained a steady-state concentration for at least 15 min. 3. In Ca(2+)-containing medium, AVP increased [Ca(2+)](i) in a biphasic pattern; a peak followed by a sustained plateau. In Ca(2+)-free medium, the Ca(2+) response to AVP became monophasic with lower amplitude and no plateau. Both the basal and AVP-induced glucagon releases were lower in the absence than in the presence of extracellular Ca(2+). When [Ca(2+)](i) was stringently deprived by BAPTA, a Ca(2+) chelator, AVP still significantly increased glucagon release. 4. Pretreatment with thapsigargin, a microsomal Ca(2+) ATPase inhibitor, abolished both the Ca(2+) peak and sustained plateau. 5.AVP increased intracellular concentration of IP(3). 6. U-73122 (8 microM), a phospholipase C inhibitor, abolished AVP-induced increases in [Ca(2+)](i), but only reduced AVP-induced glucagon release by 39%. 7. Pretreatment with nimodipine, an L-type Ca(2+) channel blocker failed to alter AVP-induced glucagon release or increase in [Ca(2+)](i). 8. The results suggest that AVP causes glucagon release through both Ca(2+)-dependent and -independent pathways. For the Ca(2+)-dependent pathway, the G(q) protein activates phospholipase C, which catalyzes the formation of IP(3). IP(3) induces Ca(2+) release from the endoplasmic reticulum, which, in turn, triggers Ca(2+) influx. Both Ca(2+) release and Ca(2+) influx may contribute to AVP-induced glucagon release.

Amino Acid Chloromethyl Ketones↗

PubMed2000

Electrophysiological effects of protopine in cardiac myocytes: inhibition of multiple cation channel currents.

Protopine (Pro) from Corydalis tubers has been shown to have multiple actions on cardiovascular system, including anti-arrhythmic, anti-hypertensive and negative inotropic effects. Although it was thought that Pro exerts its actions through blocking Ca(2+) currents, the electrophysiological profile of Pro is unclear. The aim of this study is to elucidate the ionic mechanisms of Pro effects in the heart. In single isolated ventricular myocytes from guinea-pig, extracellular application of Pro markedly and reversibly abbreviates action potential duration, and decreases the rate of upstroke (dV/dt)(max), amplitude and overshoot of action potential in a dose-dependent manner. Additionally, it produces a slight, but significant hyperpolarization of the resting membrane potential. Pro at 25, 50 and 100 microM reduces L-type Ca(2+) current (I(Ca,L)) amplitude to 89.1, 61.9 and 45.8% of control, respectively, and significantly slows the decay kinetics of I(Ca,L) at higher concentration. The steady state inactivation of I(Ca,L) is shifted negatively by 5.9 - 7.0 mV (at 50 - 100 microM Pro), whereas the voltage-dependent activation of I(Ca,L) remains unchanged. In contrast, Pro at 100 microM has no evident effects on T-type Ca(2+) current (I(Ca,T)). In the presence of Pro, both the inward rectifier (I(K1)) and delayed rectifier (I(K)) potassium currents are variably inhibited, depending on Pro concentrations. Sodium current (I(Na)), recorded in low [Na(+)](o) (40 mM) solution, is more potently suppressed by Pro. At 25 microM, Pro significantly attenuated I(Na) at most of the test voltages (-60 approximately +40 mV, with a 53% reduction at -30 mV. Thus, Pro is not a selective Ca(2+) channel antagonist. Rather, it acts as a promiscuous inhibitor of cation channel currents including I(Ca,L), I(K), I(K1) as well as I(Na). These findings may provide some mechanistic explanations for the therapeutic actions of Pro in the heart.

Action Potentials↗

PubMed2000

Effects of epidermal growth factor, transferrin, and insulin on lipofection efficiency in human lung carcinoma cells.

Poor transfection efficiency is the major drawback of lipofection. We showed previously that addition of transferrin (TF) to Lipofectin enhanced the expression of a reporter gene in HeLa cells by 120-fold and achieved close to 100% transfection efficiency. The purpose of this study was to determine whether TF and other ligands could improve the efficiency of lipofection in lung carcinoma cells. Confluent A549, Calu3, and H292 cells were transfected for 18 hours with a plasmid DNA (pCMVlacZ) using Lipofectin plus TF, insulin, or epidermal growth factor as the vector. The transfected cells were assessed for transfection efficiency by beta-galactosidase activity (light units/microg protein) and the percentage of blue cells following 5-bromo-4-chloro-3-indolyl beta-D-galactopyranoside staining. Lipofectin supplemented with epidermal growth factor yielded the largest enhancement of lipofection efficiency (< or =23-fold over that by Lipofectin alone) in all three cell lines. Insulin significantly enhanced the lipofection efficiency in A549 and Calu3 cells but not in H292 cells, whereas TF showed significant lipofection efficiency-enhancing effect in Calu3 and H292 cells but not in A549 cells. The transfection efficiency correlated well with the amounts of DNA delivered to the nucleus as well as the amounts of the receptor. These results indicate that the gene delivery strategy employing ligand-facilitated lipofection can achieve high transfection efficiency in human lung carcinoma cells. In addition, enhancement of the expression of the receptor may be a possible strategy for increasing the efficiency of gene targeting.

Cell Nucleus↗

PubMed2000

Interactions of the renin-angiotensin system and neuronal nitric oxide synthase in regulation of cyclooxygenase-2 in the macula densa.

Cyclooxygenase-2 (COX-2) expression in rat kidney is localized to the macula densa and the immediately proximal cTALH and increases after salt restriction. Either ACE inhibitors or AT1 receptor blockers increase COX-2 expression in both control and salt-restricted animals, suggesting that the RAS activation feedback inhibits renal cortical COX-2 expression. To determine whether increased COX-2 expression in response to ACE inhibition mediated increases in renin production, rats were treated with Captopril for 1 week with or without the specific COX-2 inhibitor, SC58236. Plasma renin activity increased significantly in the Captopril group. This increase was partially reversed by simultaneous treatment with SC58236. Kidney renin activity also increased in the Captopril group compared with control, which was also significantly inhibited by SC58236 treatment. Because of the localization of bNOS to MD and surrounding cTALH, the current study investigated the role of NO in the regulation of COX-2 expression. Rats were fed a normal diet, low salt diet or low salt diet combined with captopril and half of them were treated with the neuronal NOS inhibitor, 7-NI, and half with vehicle. After 7 days, mRNA was extracted and the microsome proteins purified from renal cortex. COX-2 mRNA expression was measured by Northern-blot and normalized with GAPDH. 7-NI treatment decreased COX-2 mRNA and immunoreactive COX-2 expression in each group. In summary, these studies indicate that COX-2 from macula densa/cTALH is a regulator of renin production and release. Angiotensin II may be a negative regulator of cTALH/macula densa COX-2 expression, and NO may mediate increased renal cortical COX-2 expression seen in volume depletion. These studies suggest important interactions between the NO and COX-2 systems in the regulation of arteriolar tone and the renin-angiotensin system by the macula densa.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2000

Modulation of the epidermal growth factor receptor by the human papillomavirus type 16 E5 protein in raft cultures of human keratinocytes.

It has been shown that the E5 protein of the human papillomavirus type 16 modulates epidermal growth factor receptor downregulation in monolayer cultures of human keratinocytes and mouse fibroblasts. We have now analysed the effect of this protein on the expression, the distribution and the activation of EGF receptors in raft cultures derived from an E5-transfected human keratinocyte cell line. The epithelia generated in these cultures were stratified and exhibited suprabasal expression of cytokeratins 1 and 10, which are known markers of early epidermal differentiation. In situ hybridization with an antisense riboprobe to the human papilloma virus type 16 E5 protein revealed a homogeneous gene expression within the entire epithelium of E5-transfected but not empty vector-transfected control cultures. Treatment of serum-starved rafts with EGF for 48 hours led to a strong decrease of suprabasal EGF receptors in control cultures, but not in rafts of E5-expressing cells. Under these conditions, no activated receptors were observed in control cultures, but activated receptors were still present in E5-raft cultures. Our results indicate that human papilloma virus type 16 E5-mediated modulation of EGF receptor expression occurs in a time- and structure-dependent manner in epithelial equivalents of human keratinocytes.

Cell Differentiation↗

PubMed2000

Salvage surgery for recurrent nasopharyngeal carcinoma.

OBJECTIVE: To evaluate the efficacy of salvage surgery in the treatment of recurrent nasopharyngeal carcinoma (NPC) at the primary site. STUDY DESIGN: A retrospective investigation of the outcome of salvage surgery for 28 patients with recurrent NPC after definite radiation therapy. METHODS: The nasopharynx was approached anteroposteriorly by the transmaxillary approach (maxillary swing, maxillectomy) or inferior approach (midline mandibulotomy or median labiomandibular glossotomy), or laterally by modified facial translocation or transpterygoid approach; intentional ligation of the internal carotid artery was performed after establishment of extracranial-intracranial (EC-IC) bypass in one patient; postoperative irradiation was given to the patients with positive pathological margins. RESULTS: Nine patients lived without disease for 20 to 93 months (mean interval, 52 mo) after surgery; among them, eight patients had T1 tumors that were resected totally by surgery via anteroposterior approaches and the other patient had postoperative irradiation to control the disease. Seven patients had local recurrence 8 to 21 months after treatment. Four patients developed distant metastases, including one patient with a T2b tumor that was totally resected through modified facial translocation approach with ligation of internal carotid artery. Eight patients died of other causes; internal carotid artery blowout was the cause of death in four of these eight patients. CONCLUSIONS: In most cases of recurrence, T1 nasopharyngeal tumors can be resected totally by anteroposterior approaches; for T2 or larger tumors, postoperative irradiation is usually necessary. Otherwise, facial translocation offers a better chance to completely resect the tumors. Internal carotid artery is better ligated if patients have received greater than 70 Gy irradiation or if the artery must be exposed during the surgery. We suggest that EC-IC bypass be used to avoid the possible complications (or cerebral ischemic stroke) caused by ligation of internal carotid artery. The transmaxillary approach is favored in the management of nasopharyngeal tumor recurrence with nasal cavity extension, and midline mandibulotomy is more suitable for resection of posterior margin of nasopharyngeal tumor recurrence. Facial translocation offers the widest operative field and is the most versatile approach for radical resection of nasopharyngeal tumor recurrence, but the surgeon should be skilled in the management of the facial nerves to reduce morbidity.

Adult↗

PubMed2000

Spontaneous activation of beta(2)- but not beta(1)-adrenoceptors expressed in cardiac myocytes from beta(1)beta(2) double knockout mice.

Although ligand-free, constitutive beta(2)-adrenergic receptor (AR) signaling has been demonstrated in naive cell lines and in transgenic mice overexpressing cardiac beta(2)-AR, it is unclear whether the dominant cardiac beta-AR subtype, beta(1)-AR, shares the ability of spontaneous activation. In the present study, we expressed human beta(1)- or beta(2)-AR via recombinant adenoviral infection in ventricular myocytes isolated from beta(1)beta(2)-AR double knockout mice, creating pure beta(1)-AR and beta(2)-AR systems with variable receptor densities. A contractile response to a nonselective beta-AR agonist, isoproterenol, was absent in double knockout mouse myocytes but was fully restored after adenoviral beta(1)-AR or adenoviral beta(2)-AR infection. Increasing the titer of adenoviral vectors (multiplicity of infection 10-1000) led to a dose-dependent expression of beta(1)- or beta(2)-AR with a maximal density of 1207 +/- 173 (36-fold over the wild-type control value) and 821+/-38 fmol/mg protein (69-fold), respectively. Using confocal immunohistochemistry, we directly visualized the cellular distribution of beta(1)-AR and beta(2)-AR and found that both subtypes were distributed on the cell surface membrane and transverse tubules, resulting in a striated pattern. In the absence of ligand, beta(2)-AR expression resulted in graded increases in baseline cAMP and contractility up to 428% and 233% of control, respectively, at the maximal beta(2)-AR density. These effects were specifically reversed by a beta(2)-AR inverse agonist, ICI 118,551 (10(-7) M). In contrast, overexpression of beta(1)-AR, even at a greater density, failed to enhance either basal cAMP or contractility; the alleged beta(1)-AR inverse agonist, CGP 20712A (10(-6) M), had no significant effect on basal contraction in these cells. Thus, we conclude that acute beta(2)-AR overexpression in cardiac myocytes elicits significant physiological responses due to spontaneous receptor activation; however, this property is beta-AR subtype specific because beta(1)-AR does not exhibit agonist-independent spontaneous activation.

Adrenergic Agonists↗

PubMed2000

HuR regulates p21 mRNA stabilization by UV light.

Expression of the cyclin-dependent kinase inhibitor p21 is highly induced by many stresses, including exposure to short-wavelength UV light (UVC), which increases p21 mRNA stability. Investigation into the mechanisms underlying this stabilization process revealed that proteins present in cytoplasmic lysates of human RKO colorectal carcinoma cells formed complexes with p21 mRNA that were inducible by treatment with UVC and other stress agents. The ubiquitous Elav-type RNA-binding protein HuR was identified within the p21 mRNA-protein complexes, as antibodies recognizing HuR supershifted these complexes and revealed HuR-immunoreactive proteins complexing with p21 mRNA on Western blots. Lowering of endogenous HuR levels through expression of antisense HuR decreased p21 RNA-protein complexes, greatly reduced the UVC inducibility and half-life of p21 mRNA, and prevented UVC-mediated induction of luciferase activity in p21 3' untranslated region-containing reporter constructs. Our findings indicate that HuR plays a major role in regulating stress-induced p21 expression by enhancing p21 mRNA stability and that these effects are coupled to HuR's elevated presence in the cytoplasm.

Antigens, Surface↗