Biomedical subjects

Mei Li

Publications and source records attributed to Mei Li.

At least 127 records · Page 7Linked to original sources

PubMed2003

LRH-1/hB1F and HNF1 synergistically up-regulate hepatitis B virus gene transcription and DNA replication.

Enhancer II (ENII) is one of the critical cis-elements in the Hepatitis B Virus (HBV) genome for the hepatic viral gene transcription and DNA replication. The liver-specific activity of ENII is regulated by multiple liver-enriched transcription factors, including LRH-1/hB1F, HNF1, HNF3b, HNF4 and C/EBP. Knowledge on the interplay of these important factors is still limited. In this study, we demonstrate a functional synergism between the orphan nuclear receptor LRH-1/hB1F and the homeoprotein HNF1 in up-regulating the liver-specific activity of ENII. This synergism is sufficient for initiating the viral gene transcription and DNA replication in non-hepatic cells. We have defined the activation domains in hB1F and HNF1 that contribute to the synergism. We further show that hB1F and HNF1 can interact directly in vitro and have mapped the domains required for this interaction.

Base Sequence↗

PubMed2003

A novel, non-prostanoid EP2 receptor-selective prostaglandin E2 agonist stimulates local bone formation and enhances fracture healing.

UNLABELLED: CP-533,536, a newly discovered, non-prostanoid EP2 receptor-selective PGE2 agonist, stimulates local bone formation and enhances fracture healing in rat models. INTRODUCTION: There is a significant medical need for agents that can stimulate local bone formation and enhance fracture healing. We tested the effects of CP-533,536, a newly discovered, non-prostanoid EP2 receptor-selective prostaglandin E2 (PGE2) agonist, in stimulating local bone formation and enhancing fracture healing in rat models. MATERIALS AND METHODS: In the first model, a single injection of CP-533,536 at doses of 0.3, 1, or 3 mg/kg to the proximal tibial metaphysis of 6-week-old male rats was given on day 1, and the local bone anabolic effect was determined on day 7. We then tested the effects of this compound in inducing bone formation on rat periosteum of the femur. A single dose of 0.3 mg of CP-533,536 incorporated in a poly-(D,L-lactide-co-glycolide) (PLGH) matrix was injected onto the periosteum of the femur in 3-week-old male rats, and local bone formation was determined on day 14. Finally, the ability of CP-533,536 in PLGH matrix in enhancing fracture healing was tested using the rat femoral fracture model. CP-533,536 in PLGH matrix at doses of 0.05, 0.5, or 5 mg was delivered to the local fracture site on the same day of fracture, and its efficacy was evaluated on day 21. RESULTS AND CONCLUSIONS: A single injection of CP-533,536 at doses of 0.3, 1, or 3 mg/kg to the proximal tibial metaphysis dose-dependently stimulated local lamellar bone formation on trabecular, endocortical, and periosteal surfaces, and thus increased bone mineral content and bone strength at the injected site. Similarly, a single injection of 0.3 mg of CP-533,536 incorporated in PLGH matrix onto the periosteum of the femur induced significantly local bone formation. In the rat femoral fracture model, CP-533,536 in PLGH matrix at doses of 0.05, 0.5, and 5 mg dose-dependently increased callus size, density, and strength compared with PLGH matrix alone. These results show that CP-533,536 stimulates new bone formation on trabecular, endocortical, and periosteal surfaces and enhances fracture healing. These data reveal that EP2 receptor-selective agonists provide therapeutic potential for local bone augmentation, bone repair, and bone healing in humans.

Animals↗

PubMed2003

Expression of ORF2 partial gene of hepatitis E virus in tomatoes and immunoactivity of expression products.

AIM: To transfer hepatitis E virus (HEV) ORF2 partial gene to tomato plants, to investigate its expression in transformants and the immunoactivity of expression products, and to explore the feasibility of developing a new type of plant-derived HEV oral vaccine. METHODS: Plant binary expression vector p1301E2, carrying a fragment of HEV open reading frame-2 (named HEV-E2), was constructed by linking the fragment to a constitutive CaMV35s promoter and nos terminator, then directly introduced into Agrobacterium tumefaciens EHA105. With leaf-disc method, tomato plants medicated by EHA105 were transformed and hygromycin-resistant plantlets were obtained in selective medium containing hygromycin. The presence and integration of foreign DNA in transgenic tomato genome were confirmed by Gus gene expression, PCR amplification and Southern dot blotting. The immunoactivity of recombinant protein extracted from transformed plants was examined by enzyme-linked immunosorbant assay (ELISA) using a monoclonal antibody specifically against HEV. ELISA was also used to estimate the recombinant protein content in leaves and fruits of the transformants. RESULTS: Seven positive lines of HEV-E2-transgenic tomato plants confirmed by PCR and Southern blotting were obtained and the immunoactivity of recombinant protein could be detected in extracts of transformants. The expression levels of recombinant protein were 61.22 ng/g fresh weight in fruits and 6.37-47.9 ng/g fresh weight in leaves of the transformants. CONCLUSION: HEV-E2 gene was correctly expressed in transgenic tomatoes and the recombinant antigen derived from them has normal immunoactivity. Transgenic tomatoes may hold a good promise for producing a new type of low-cost oral vaccine for hepatitis E virus.

Administration, Oral↗

PubMed2003

Glycylproline dipeptidyl aminopeptidase isoenzyme in diagnosis of primary hepatocellular carcinoma.

AIM: To investigate the role of glycylproline dipeptidyl aminopeptidase (GPDA) isoenzyme in the diagnosis of primary hepatocellular carcinoma (PHC), especially in patients with negative alpha-fetoprotein (AFP). METHODS: A stage gradient polyacrylamide gel discontinuous electrophoresis system was developed to separate serum GPDA isoenzymes, which were determined in 102 patients with PHC, 45 cases with liver cirrhosis, 24 cases with chronic hepatitis, 35 cases with benign liver space-occupying lesions, 20 cases with metastatic liver cancer and 50 cases with extra-hepatic cancer, as well as 80 healthy subjects. The relationships between GPDA isoenzymes and AFP, the sizes of tumors, as well as alanine aminotransferase (ALT) were also analyzed. RESULTS: Serum GPDA was separated into two isoenzymes, GPDA-S and GPDA-F. The former was positive in all subjects, while the latter was found mainly in majority of PHC (85.3 %) and a few cases with liver cirrhosis (11.1 %), chronic hepatitis (33.3 %), metastatic liver cancer (15.0 %) and non-hepatic cancer (16.0 %). GPDA-F was negative in all healthy subjects and patients with benign liver space-occupying lesions, including abscess, cysts and angioma. There was no correlation between GPDA-F and AFP concentration or tumor size. GPDA-F was consistently positive and not correlated with ALT in PHC, but GPDA-F often converted to negative as decline of ALT in benign liver diseases. The electrophoretic migration of GPDA-F became sluggish after the treatment of neuraminidase. CONCLUSION: GPDA-F is a new useful serum marker for PHC. Measurement of serum GPDA-F is helpful in diagnosis of PHC, especially in patients with negative AFP. GPDA-F is one kind of glycoproteins rich in sialic acid.

Aminopeptidases↗

PubMed2003

Oral immunization of animals with transgenic cherry tomatillo expressing HBsAg.

AIM: To investigate the expression of recombinant HBsAg (rHBsAg) in transgenic cherry tomatillo in order to explore the feasibility of producing HBV oral vaccine with cherry tomatillo by animal immune tests. METHODS: The recombinant plant expression vector containing HBsAg gene was constructed. Mediated with Agrobacterium tumefaciens, HBsAg gene was transferred into cotyledons of cherry tomatillo. Transformed cherry tomatillos were obtained through hygromycin delay-selection. Integrated DNA in transgenic cherry tomatillo was confirmed by hygromycin resistance selection, Gus detection, polymerase chain reaction (PCR) and dot blotting analysis. Antigenicity of rHBsAg was examined by ELISA and the immunogenicity of rHBsAg derived from transgenic cherry tomatillo tissues was confirmed by oral feed of transformed tissues to BALB/c mice primed with commercial HBV vaccines. Specific antibody titers in mice's serum were examined by ELISA every week. RESULTS: By far, 10 positive lines of transgenic cherry tomatillos containing HBsAg gene were obtained. Among different organs of the same transgenic cherry tomatillo, level of rHBsAg expressed in leaves was the highest with the yield up to 300ng/g fresh weight. And the rHBsAg expression level in fruits was about 10 ng/g fresh weight. In animal immune tests, oral delivery with transgenic tissues to mice primed with commercial vaccine instead of naive mice resulted in significant immune response. CONCLUSION: The result of this animal immune test indicated the rHBsAg derived from transgenic cherry tomatillo possessed normal immunogenicity. This work demonstrated the feasibility to generate oral immunogenic rHBsAg in transgenic cherry tomatillo, and would provide some experimental approach for the production of low-cost oral vaccines using transgenic cherry tomatillo in large scale.

Administration, Oral↗

PubMed2003

[A study on the expression of VEGF in the blunt injury of rat's skin].

OBJECTIVE: To evaluate changes of VEGF in skin after blunt injury. METHODS: The rats of injury groups were subjected to skin blunt injury by free-falling iron hammer. The samples taken at 1 h, 3 h, 6 h, 12 h, 1 d, 3 d, 5 d, 7 d, 9 d after injury were studied by immunohistochemistry and MIAS image analysis system. RESULTS: In the skin of normal control group the expression level of VEGF was low. The increase of VEGF could be observed at 1 day after injury, reached peak at 7 days and declined at 9 days. CONCLUSION: Blunt injury in the skin could induce the expression of the VEGF. Moreover, the change pattern of VEGF level was quite regular with time and could be used to estimate the time after skin injury.

Animals↗

PubMed2003

[The effects of continuous stimulation with different doses of parathyroid hormone 1-34 fragment on human SaoS-2 cells].

OBJECTIVE: To observe the effects of different doses of human parathyroid hormone fragment (hPTH)1-34 on SaoS cells and to explore the signal pathway and mechanism. METHODS: 5 x 10(4) cells/ml SaoS cells were seeded. Doses of 5, 50, 500 and 5 000 micro g/L hPTH1-34 were supplemented respectively. Total RNA was extracted by Trizol kit. Alkaline phosphatase (ALP), osteocalcin (BGP) and cAMP concentrations were measured by chemical, radioimmunoassay and competitive protein binding methods. c-fos gene expression level was semi-quantified by reverse transcriptase (RT)-PCR. RESULTS: ALP activity was higher in 500 micro g/L dose (P < 0.05 vs. control). BGP level was inhibited in 5 000 micro g/L dose (P < 0.05 vs. control and pretreatment). 50 and 500 micro g/L hPTH1-34 enhanced cAMP level significantly (P < 0.05 vs. control). No obvious increase of cAMP level was found in 5 000 micro g/L and 5 micro g/L dose groups (P > 0.05 vs. control and pretreatment). c-fos expression was higher in 50 and 500 micro g/L group. CONCLUSION: Different doses of hPTH1-34 exert distinct effects on osteoblasts. hPTH1-34 affects ALP and c-fos depending on protein kinase A signal pathway. hPTH1-34 exerts its action via regulation of osteoblasts by c-fos.

Alkaline Phosphatase↗

PubMed2003

Preliminary clinical observation of arteriovenous sheathotomy for treatment of branch retinal vein occlusion.

PURPOSE: To document the anatomic and functional improvement of six patients with branch retinal vein occlusion (BRVO) following successful arteriovenous adventitial sheathotomy (AAS). METHODS: Retrospective study of 6 patients (6 eyes) with BRVO treated with AAS. All patients were not eligible for laser photocoagulation and had both macular edema and intraretinal hemorrhage. The visual acuity was in the range of 0.4 to 0.02. All patients underwent pars plana vitrectomy and AAS. The clinical improvement was determined by fundus photograph, fluorescein angiography (FAG), optical coherence tomography (OCT) and multifocal electroretinography (ERG). All patients were followed postoperatively for an average of 20 months ranging from 12 to 24 months. RESULTS: Sheathotomy and decompression of the arteriole/venule (A/V) crossing were achieved in all 6 patients. 5 patients have improved their best-corrected visual acuity 4 lines or more. The best one could reach to 1.0. One month after the operation, fundus photograph and FAG demonstrated the resolution of intraretinal hemorrhage, reduction of non-perfusion area and apparent resolution of retinal venous dilation and tortuosity. OCT confirmed remarkable reduction of retinal thickness. The microcysts at the fovea diminished. Multifocal ERG showed the recovery of the central peak at the macular and the peripheral response density. However, capillary nonperfusion area and microaneurysm were found out by FAG in four patients at the points distal to the sheathotomy three months after the operation. CONCLUSIONS: Anatomic and functional improvement of retina can be achieved in patients with BRVO through AAS. However, the capillary nonperfusion and microaneurysm may follow this surgical procedure in some cases that need further treatment with laser photocoagulation. The better visual improvement may be expected in the patients with earlier surgical intervention.

Aged↗

PubMed2003

[Assessment of preoperative localization techniques for patients with primary hyperparathyroidism].

OBJECTIVE: To evaluate the sensitivity and usefulness of 99mTc-sestamibi scintigraphy (SS) and neck ultrasonography (US) as preoperative localization procedures in patients with primary hyperparathyroidism (pHPT). METHODS: 160 patients with proved pHPT in Peking Union Medical College Hospital from June 1983 to June 2002 were studied. There were 107 women(66.9%) and 53 men (33.1%), with a mean age of 38.9 years (10-73 years). 100 patients were underwent SS and 148 patients were underwent US prior to surgery, and the results were compared with operative and histological findings. RESULTS: The sensitivity of SS and US in localization of the enlarged parathyroid glands was 94.0% and 85.1% respectively, and the positive predictive value of SS and US was 100% and 89.1% respectively, the overall sensitivity was 98.9% by combination of SS and US. In solitary parathyroid adenomas group (n = 145), the sensitivity of SS and US was 93.3% and 84.7% respectively; There was no significant difference (P = 0.428) in sensitivity of SS between the parathyroid glands correctly identified and undetected in classical neck location as compared with ectopic parathyroid glands, whereas significantly (P = 0.026) influenced by the US sensitivity. CONCLUSIONS: Different sensitivity exit between SS and VS in preoperative localization in patients with pHPT undergoing parathyroidectomy. The combined use of SS and US could increase the sensitivity of localization technique. Ectopic parathyroid had no influence on the sensitivity of 99mTc-MIBI scanning, but decreased the sensitivity of ultrasonography. The size of parathyroid tumors had effects on the sensitivity of ultrasonography. Otherwise, various conditions causing SS false negative were observed. Some interfere factors should be excluded when SS negative results were encountered in clinical practice.

Adolescent↗

PubMed2003

[Nitrogen removal from the sewage containing seawater via nitrite pathway].

With control of the concentration of free ammonia (FA), shortened nitrification-denitrification was accomplished in SBR to achieve enhanced nitrogen removal from the sewage containing seawater. Several parameters which included salinity, temperature, pH and NH4(+)-N load were studied to evaluate their effects. The results of experiences indicated that shortened nitrification-denitrification can be accomplished in sewage containing seawater with relatively high salinity. With various salinity, the nitrogen removal efficiency had relationship with the NH4(+)-N load, there should be a lower NH4(+)-N load when the salinity was high. The nitrogen removal efficiency reached above 90% when the NH4(+)-N load was not exceed 0.15 kg/(kg.d). Elevation of the temperature availed to higher nitrogen removal efficiency, this efficiency doubled when the reaction temperature was changed from 20 degrees C to 30 degrees C. Relatively high value of pH, in the range of 7.5 and 8.5 had advantage to achieve effective shortened nitrification-denitrification which caused by the selective inhibition of free ammonia(FA).

Nitrites↗

PubMed2003

[Experimental study on the disinfection of wastewater by swept pulsed electromagnetic field].

In this paper, an applicable swept pulsed equipment was developed to treat the domestic wastewater and the effect of swept pulsed electromagnetic field on disinfection was studied. It was found that the effect was obvious and the disinfection performance of electromagnetic field was increased with the increasing of the pH, the temperature, the treatment time and the bactericidal concentration. The experimental results showed that the amounts of total bacterium and coliform per milliliter were decreased from 7.2 x 10(6) to 2.2 x 10(4) and from 9.2 x 10(5) to 3.5 x 10(4) respectively after the treatment period of 4 h when the temperature was 25 degrees C and pH 9.0. Corresponding, the removal efficiency of total bacterium were 99.7% and 96.2%.

Bacteria↗

PubMed2003

[Role of free radicals in brain edema induced by endotoxin in infant rats and the therapeutic effect of dexamethasone and IVIG].

OBJECTIVE: Glucocorticoid is considered as an effective drug for prevention and treatment of brain edema and reducing the blood-brain barrier (BBB) permeability. Intravenous immunoglobulin (IVIG) is frequently used to treat neurological diseases with immune abnormality, its function and potential mechanism on brain edema have not been reported. In this study, the roles of the total hydrosulfide group (TSH), non-protein hydrosulfide group (NPSH) and malondialdehyde (MDA) in etiology of the endotoxin brain edema in infant rats and the interfering effects of dexamethasone (DEX) and IVIG were investigated. METHODS: In 35 infant rats, 10 mg/kg lipopolysaccharide (LPS) was intraperitoneally injected. The same volume of normal saline was injected to 24 control rats. Ten mg/kg DEX and 400 mg/kg IVIG were intravenously injected respectively to 36 and 24 infant rats instantly following LPS injection. The TSH, NPSH and MDA concentrations and the brain Evans blue contents were detected at different time in the brain tissue. The brain water content was measured by drying method. RESULTS: The brain water, EB and MDA contents after endotoxin injection were significantly higher than those of control group, while the brain TSH, NPSH content were significantly lower than those of control group (P < 0.05 or P < 0.01); After treatment with DEX or IVIG, the brain EB, MDA and water content significantly decreased with the peak at 6 h (P < 0.05 or P < 0.01), TSH and NPSH significantly increased compared with LPS group. However, the NPSH content in IVIG treatment group did not change significantly (P > 0.05). CONCLUSION: Free radicals play a role in the brain edema induced by LPS in infant rats. The primary results suggested that DEX and IVIG have therapeutic effect for the endotoxin-induced brain edema by affecting the free radicals.

Animals↗

PubMed2003

[The effect of treating obstructive disease of lacrimal passage by lacrimal plastic operation with Nd:YAG laser].

OBJECTIVE: To study the therapeutic effects of Nd:YAG laser on obstructive diseases of the lacrimal passage. METHODS: 693 eyes in 603 cases with obstructive diseases of lacrimal passage, including obstruction of lacrimal puncta (23 eyes), lacrimal duct (192 eyes), nasolacrimal duct (227 eyes), chronic dacryocystitis (231 eyes), and traumatic laceration of lacrimal canaliculus (20 eyes), were treated by lacrimal plastic operation with Nd:YAG laser and the therapeutic effects were compared among the groups. RESULTS: The cure rates and effective rates of the five diseases were 86.9% and 95.7%, 89.1% and 93.8%, 93.0% and 96.0%, 78.4% and 82.7%, 40.0% and 65.0%, respectively. By Ridit analysis, R +/- S(R) values for each group were 0.921 +/- 0.023, 0.914 +/- 0.009, 0.927 +/- 0.007, 0.856 +/- 0.013, 0.749 +/- 0.055. CONCLUSIONS: The therapeutic effect on chronic dacryocystitis is less than those of obstruction of nasolacrimal duct and lacrimal duct (P < 0.05). The therapeutic effect on traumatic laceration of lacrimal canaliculus is less than that of the other four groups (P < 0.05). Therefore, it should be restricted on indication for the cases of chronic dacryocystitis and traumatic laceration of lacrimal canaliculus.

Adolescent↗

PubMed2002

[Alendronate in postmenopausal women with osteopenia and osteoporosis: effects on bone mineral density during treatment and after withdrawal].

OBJECTIVE: To determine the efficacy of alendronate (Fosamax) administration and withdrawal on the bone mineral density (BMD) in postmenopausal women with osteopenia and osteoporosis. METHODS: Alendronate (10 mg) and calcium carbonate (containing calcium 500 mg) were administered daily to 25 Chinese menopausal women with osteopenia and osteoporosis for 6 months and to 15 women for 12 months. After the withdrawal of alendronate, calcium carbonate was administered continuously. Follow-up was made three times for the 6-month group: before treatment, 6 months after treatment, and 13 +/- 4 months (6 - 24 months) after aldoronate withdrawal, and was made four times for the 12-month group: before treatment, 6 months and 12 months after treatment, and 23 +/- 7 months (14 - 36 months) after alendronate withdrawal to determine the BMD of lumbar spine 2 approximately 4, neck of femur, Wards triangle, and greater trochanter and blood alkaline phosphatase (ALP). RESULTS: Compared to the baseline value, the BMD in lumbar spine and hip increased significantly 6 months after treatment in 6-month group, with the BMD in lumbar spine 2 - 4 increased by 5.3% (P < 0.001). In the 6 month group, no significant decline was found in the BMD in lumbar spine and hip 13 +/- 4 months after alendronate withdrawal, the BMD in greater trochanter even increased further compared with that 6 months after treatment. In the 12-month group, the BMD significantly increased except in the Wards triangle after 6 months' treatment with an increase by 4.2% in lumbar spine 2 - 4 (P < 0.001). After 12 months' treatment the increment of BMD in lumbar spine 2 - 4 was 6.1% (P < 0.001) and the BMD of the hip remained unchanged. 23 +/- 7 months after the alendronte withdrawal the values of BMD in lumbar spine and hip were almost the same as that 12 months after treatment. CONCLUSION: Alendronate increases the BMD in spine and hip, especially in lumbar spine. The skeletal benefits are maintained for at least 13 - 23 months in spine and hip after withdrawal of alendrenate.

Aged↗

PubMed2002

Crystal structure studies on rubrerythrin: enzymatic activity in relation to the zinc movement.

Rubrerythrin (Rr) is a non-heme iron protein isolated from anaerobic sulfate-reducing bacteria. Rr is a dimeric molecule, each monomer contains a Fe(SCys)(4) center in the C-terminal domain and a binuclear metal center in the N-terminal domain. Rr structures with different protein sources and/or preparation procedures have been studied. Two Rr crystal structures have been solved with significant differences in their binuclear metal centers. The first structure, which was obtained from expressed protein under aerobic conditions, has a diiron-oxo center. The second structure, which was obtained from native protein of Desulfovibrio vulgaris under aerobic conditions, has an Fe-Zn center with the zinc position differing from the corresponding iron position in the former structure by approximately 2 A. The crystal structures of Rr isolated from D. vulgaris (Hildenborough, NCIB 8303), the same as the second structured but prepared under anaerobic conditions, are reported in this paper. The binuclear metal center in these structures is an Fe-Zn center. When the crystal was exposed to air, the zinc atom moved gradually, approximately 2 A, accompanied by the entrance of a water molecule (or hydroxyl group) and changes in the binuclear metal center microenvironment. This finding can explain the differences between the two different structures. The results suggest that the zinc movement may be related to the enzymatic activity of Rr.

Bacterial Proteins↗

PubMed2002

Testosterone reduction prevents phenotypic expression in a transgenic mouse model of spinal and bulbar muscular atrophy.

Spinal and bulbar muscular atrophy (SBMA) is a polyglutamine disease caused by the expansion of a CAG repeat in the androgen receptor (AR) gene. We generated a transgenic mouse model carrying a full-length AR containing 97 CAGs. Three of the five lines showed progressive muscular atrophy and weakness as well as diffuse nuclear staining and nuclear inclusions consisting of the mutant AR. These phenotypes were markedly pronounced in male transgenic mice, and dramatically rescued by castration. Female transgenic mice showed only a few manifestations that markedly deteriorated with testosterone administration. Nuclear translocation of the mutant AR by testosterone contributed to the phenotypic difference with gender and the effects of hormonal interventions. These results suggest the therapeutic potential of hormonal intervention for SBMA.

Animals↗

PubMed2002

Distinct roles of two Mg2+ binding sites in regulation of murine flap endonuclease-1 activities.

Removal of flap DNA intermediates in DNA replication and repair by flap endonuclease-1 (FEN-1) is essential for mammalian genome integrity. Divalent metal ions, Mg(2+) or Mn(2+), are required for the active center of FEN-1 nucleases. However, it remains unclear as to how Mg(2+) stimulates enzymatic activity. In the present study, we systemically characterize the interaction between Mg(2+) and murine FEN-1 (mFEN-1). We demonstrate that Mg(2+) stimulates mFEN-1 activity at physiological levels but inhibits the activity at concentrations higher than 20 mM. Our data suggest that mFEN-1 exists as a metalloenzyme in physiological conditions and that each enzyme molecule binds two Mg(2+) ions. Binding of Mg(2+) to the M1 binding site coordinated by the D86 residue cluster enhances mFEN-1's capability of substrate binding, while binding of the metal to the M2 binding site coordinated by the D181 residue cluster induces conformational changes. Both of these steps are needed for catalysis. Weak, nonspecific Mg(2+) binding is likely responsible for the enzyme inhibition at high concentrations of the cation. Taken together, our results suggest distinct roles for two Mg(2+) binding sites in the regulation of mFEN-1 nuclease activities in a mode different from the "two-metal mechanism".

Amino Acid Substitution↗

PubMed2002

Physiological and retinoid-induced proliferations of epidermis basal keratinocytes are differently controlled.

To investigate the roles of retinoic acid (RA) receptors (RARs) in the physiology of epidermis that does not express RAR beta, conditional spatio-temporally controlled somatic mutagenesis was used to selectively ablate RAR alpha in keratinocytes of RAR gamma-null mice. Keratinocyte proliferation was maintained in adult mouse epidermis lacking both RAR alpha and RAR gamma, as well as in RAR beta-null mice. All RAR-mediated signalling pathways are therefore dispensable in epidermis for homeostatic keratinocyte renewal. However, topical treatment of mouse skin with selective retinoids indicated that RXR/RAR gamma heterodimers, in which RXR transcriptional activity was subordinated to that of its RAR gamma partner, were required for retinoid-induced epidermal hyperplasia, whereas RXR homodimers and RXR/RAR alpha heterodimers were not involved. RA-induced keratinocyte proliferation was studied in mutant mice in which RXR alpha, RXR alpha and RAR alpha, RAR gamma, or RXR alpha and RAR gamma genes were specifically disrupted in either basal or suprabasal keratinocytes. We demonstrate that the topical retinoid signal is transduced by RXR alpha/RAR gamma heterodimers in suprabasal keratinocytes, which, in turn, stimulate proliferation of basal keratinocytes via a paracrine signal that may be heparin-binding EGF-like growth factor.

Alleles↗