Biomedical subjects

T Ma

Publications and source records attributed to T Ma.

At least 127 records · Page 7Linked to original sources

PubMed1996

Cyclin E/Cdk2 activity is controlled by different mechanisms in the G0 and G1 phases of the cell cycle.

The experiments described in this report were undertaken to define the parameters that regulate cyclin E/cyclin-dependent kinase 2 (Cdk2) kinase activity in mitotically quiescent, serum-starved fibroblastic cells and in cells that had been stimulated to enter the cell cycle and progress through G1 into S phase. We have analyzed the expression of cyclin E and Cdk2, the extent to which these two proteins form complexes, and the enzymatic activity of cyclin E/cdk2 kinase. Particular attention was focused upon subcellular localization and the effect of compartmentalization on the association between cyclin E and Cdk2. In addition, we have examined the interaction of cyclin E/Cdk2 complexes with two well-characterized inhibitors of Cdk2 kinase activity, Cip1 and Kip1. This represents the first report in which all of these parameters have been measured simultaneously in a single, normal diploid cell line. In G0 cells, there is abundant cyclin E and Cdk2, yet there is little or no detectable Cdk2-dependent histone H1 kinase activity. After serum stimulation, there is a rapid increase in the amount of cyclin E that is bound to Cdk2, although there is no significant change in the abundance of either the cyclin or the Cdk. Immunocytochemical data indicate that cyclin E, Cip1, and Kip1 are located within the nuclei of cell in G0, but very little Cdk2 is observed within the nuclei of serum-starved cells. Cdk2 rapidly enters the nucleus upon serum stimulation. The abundance of the cyclin E/Cdk2 complex increases to the extent that the binding capacity of Cip1 is exceeded about 8-12 h after serum stimulation. The abundance of Kip1 decreases at the same time that the Cip1 threshold is exceeded, so that cyclin E/Kip1-containing complexes decrease by 90% within 8-12 h. Cyclin E/Cdk2 kinase activity begins to increase rapidly thereafter, reaching a maximum level about 16 h after serum stimulation. We have been unable to detect histone H1 kinase activity in complexes that contain cyclin E bound to Kip1 or Cip1. We conclude that compartmentalization is the predominant barrier to activation of cyclin E-dependent kinases in quiescent cells. Cip1 and Kip1 serve to prevent premature activation of cyclin E/Cdk2 complexes that form during G0 or early G1.

CDC2-CDC28 Kinases↗

PubMed1996

[The immuno-pathological damage of placenta and its types in pregnancy induced hypertension].

OBJECTIVE: To study the immuno-pathological damage to placenta and its types in pregnancy induced hypertension (PIH). METHODS: Using immunohistochemical technique (PAP method), authors studied the expression and localization of IgG, IgE, C3, C4, 5-HT on the villous vessels wall in PIH patients (n = 22) and normal pregnant women (n = 10), and observed the pathological changes of placenta with mast cell and connective tissue stain. RESULTS: The immunostaining of IgG, IgE, C3, C4, and 5-HT were seen in the wall of villous vessels in PIH patients, the strong positive rate were 100%, 90%, 100%, 100%, 90% in severe PIH patients respectively, accompanied by aggregation of mast cells and lesions of villi and villous arterioles. CONCLUSION: The immunological compound reaction and types 1, N of anaphylactic reactions took place in the placenta of PIH patients. It showed that the immunological factors were closely related to PIH.

Antigen-Antibody Complex↗

PubMed1996

[The effects of 3,4-dihydroxyacetophynone on the activity of nitric oxide synthetase in placental vascular endothelial cells and smooth muscle cells and on the level of endothelin-1 in plasma from pregnancy-induced hypertension patients].

OBJECTIVE: To observe the effects of 3,4-dihydroxyacetophynone (DHAP), one of the constituents of a traditional Chinese herbal medicine, on the activities of endothelial nitric oxide synthetase (NOS) in vascular endothelial cells (VEC) and vascular smooth muscle cells (VSMC) of placenta and the level of endothelin-1 (ET-1) in the plasma from PIH patients. METHOD: 22 nulliparous PIH patients were randomly divided into PIH group and DHAP treatment group. Each patients in DHAP group received intravenous administration of DHAP (160-240 mg/d). Blood samples were collected before the administration of DHAP and (or) before cesarean section. The placenta were assayed for nitric oxide synthase activity using histochemical analysis; the concentration of ET in plasma was measured by radioimmunoassays. 10 normal pregnant women or 10 nonpregnant women were served as controls. RESULTS: In normal pregnant controls, NOS activity was much higher than that in the PIH group; in DHAP group, there was some recovery of NOS activity after DHAP treatment. The concentration of ET was higher in PIH group than that of normal pregnant controls, but it decreased significantly after DHAP therapy (P < 0.05, vs PIH group or before DHAP therapy). CONCLUSION: This study indicates that DHAP is effective in the treatment of PIH and its mechanism of action may be due to the adjustment of NO/ET imbalance in PIH patients.

Acetophenones↗

PubMed1996

[Female idiopathic urethra tumor: clinical features diagnosis and treatment].

Female idiopathic urethra tumors are reported rarely. We treated fourteen patients patients, and described the clinical manifestations and local features of the tumors, urethra liomyoma, and fibropolypus. We found that there are close relations among tumor stage, prognosis and pathological classification. The main diagnostic methods include vaginal touch, urethroscopy, B-ultrasound exam and biopsy. The diagnostic procedure recommended is tumor location-quality-stage or a three-step method. The main treatment is operation, however, the operative mode should depend on tumor stage and patient's life quality after operation.

Adenocarcinoma↗

PubMed1995

cDNA cloning, gene organization, and chromosomal localization of a human mercurial insensitive water channel. Evidence for distinct transcriptional units.

Two distinct cDNAs encoding a human mercurial insensitive water channel (hMIWC) were cloned from a fetal brain cDNA library. The longest open reading frame of cDNA clone hMIWC1 encoded 301 amino acids with 94% identity to rat MIWC (Hasegawa, H., Ma, T., Skach, W., Matthay, M. M., and Verkman, A. S. (1994) J. Biol. Chem. 269, 5497-5500). A second cDNA (hMIWC2) had a distinct 5'-sequence upstream from base pair (bp) -34 in clone hMIWC1 and contained two additional inframe translation start codons. Expression of hMIWC cRNAs in Xenopus oocytes increased osmotic water permeability by 10-20-fold in a mercurial insensitive manner. Cell-free translation in a reticulocyte lysate/microsome system generated single protein bands at 30 kDa (hMIWC1) and 32-34 kDa (hMIWC2) without glycosylation. Northern blot and polymerase chain reaction/Southern blot analysis showed expression of mRNA encoding hMIWC in human brain - muscle >> heart, kidney, lung, and trachea. Analysis of hMIWC genomic clones indicated two distinct but overlapping transcription units from which multiple hMIWC mRNAs are transcribed. The promoter region of hMIWC1 was identified and contained TATA, CAAT, AP-1, and other regulatory elements. Primer extension revealed hMIWC1 transcription initiation at 46 bp downstream from the TATA box. There were three introns (lengths 0.9, 0.2, and 6 kilobases) in the hMIWC1 coding sequence at bp 381, 546, and 627. A distinct 5'-sequence in clone hMIWC2 suggested an alternative upstream transcription initiation site. Two alternatively spliced, nonfunctional hMIWC transcripts with exon 3 deletion and partial exon 4 deletion were identified. A poly(A)+ signal sequence was identified at 138 bp downstream of the translation stop codon. Genomic Southern blot analysis indicated the presence of a single copy hMIWC gene; chromosome-specific polymerase chain reaction and in situ hybridization localized hMIWC to human chromosome 18q22. The structural organization of the hMIWC gene represents a first step in definition of hMIWC differential expression, regulation, and possible role in human disease.

Amino Acid Sequence↗

PubMed1995

Constitutive and regulated membrane expression of aquaporin 1 and aquaporin 2 water channels in stably transfected LLC-PK1 epithelial cells.

The aquaporins (AQPs) are a family of homologous water-channel proteins that can be inserted into epithelial cell plasma membranes either constitutively (AQP1) or by regulated exocytosis following vasopressin stimulation (AQP2). LLC-PK1 porcine renal epithelial cells were stably transfected with cDNA encoding AQP2 (tagged with a C-terminal c-Myc epitope) or rat kidney AQP1 cDNA in an expression vector containing a cytomegalovirus promoter. Immunofluorescence staining revealed that AQP1 was mainly localized to the plasma membrane, whereas AQP2 was predominantly located on intracellular vesicles. After treatment with vasopressin or forskolin for 10 min, AQP2 was relocated to the plasma membrane, indicating that this relocation was induced by cAMP. The location of AQP1 did not change. The basal water permeability of AQP1-transfected cells was 2-fold greater than that of nontransfected cells, whereas the permeability of AQP2-transfected cells increased significantly only after vasopressin treatment. Endocytotic uptake of fluorescein isothiocyanate-coupled dextran was stimulated 6-fold by vasopressin in AQP2-transfected cells but was only slightly increased in wild-type or AQP1-transfected cells. This vasopressin-induced endocytosis was inhibited in low-K+ medium, which selectively affects clathrin-mediated endocytosis. These water channel-transfected cells represent an in vitro system that will allow the detailed dissection of mechanisms involved in the processing, targeting, and trafficking of proteins via constitutive versus regulated intracellular transport pathways.

Animals↗

PubMed1995

Distinct biogenesis mechanisms for the water channels MIWC and CHIP28 at the endoplasmic reticulum.

MIWC is a 32 kDa mercurial-insensitive water channel [Hasegawa et al. (1994) J. Biol. Chem. 269, 5497-5500] expressed in kidney collecting duct, brain ependymal cells, airways, and other tissues. We showed recently that the homologous water channel CHIP28 spanned the endoplasmic reticulum (ER) membrane 4 times with N- and C-termini in the cytoplasm [Skach et al., (1994) J. Cell Biol. 125, 803-815]. Hydropathy analysis of MIWC indicated up to eight hydrophobic regions (HRs) comprising potential membrane-spanning domains. To determine MIWC transmembrane topology at the ER, 10 cDNA chimeras were constructed which encoded increasing lengths of MIWC upstream from a reporter epitope (prolactin P-domain) at residues 13, 46, 73, 92, 120, 140, 164, 209, 276, and 2097, corresponding to putative polar extramembrane loops in the MIWC sequence. The chimeras were translated cell-free (rabbit reticulocyte lysate+ER-derived microsomes) and in Xenopus oocytes. Peptide chains were labeled with [35S]methionine and immunoprecipitated with a P-domain antibody. Transmembrane topology as determined by protease accessibility of the P-reporter indicated six membrane-spanning domains with N- and C-termini in the cytoplasm. The predicted topology was confirmed by demonstrating N-linked glycosylation at native residue N131 and an engineered consensus site at residue 197. Membrane integration of the nascent chain, as assayed by extractability at pH 11.5, occurred after synthesis of the first HR (residues 1-46). Translocation was terminated by a stop transfer sequence in the second HR (residues 32-73) as demonstrated by translation of the heterologous construct, [prolactin signal sequence]-[globin]-[HR2]-P.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

A kinetic analysis of hepatic microsomal activation of parathion and chlorpyrifos in control and phenobarbital-treated rats.

A kinetic analysis of cytochrome P450-mediated desulfuration (activation) or dearylation (detoxication) showed that rat hepatic microsomes have a greater capacity to detoxify and a lower capacity to activate chlorpyrifos compared to parathion. Kinetic curves for the desulfuration of both parathion and chlorpyrifos were biphasic; Kmapps of 0.23 and 71.3 microM were calculated for parathion, and 1.64 and 50.4 microM for chlorpyrifos. While phenobarbital (PB) exposure seemed to generally lower the Kmapps for desulfuration except for the low Km activity on chlorpyrifos, the results were not statistically significant. While the low Km activity contributed 44 and 60% of the control Vmax for parathion and chlorpyrifos, respectively, it contributed 50 and 17% in PB-treated rats. These studies have indicated the presence of a low Km activity capable of functioning at very low substrate concentrations. A single dearylation Kmapp was calculated, 56.0 and 9.8 microM for parathion and chlorpyrifos, respectively. Phenobarbital exposure seemed to raise the Kmapps of dearylation; however, again, the results were not statistically significant. While numerous biochemical factors contribute to the overall toxicity levels of phosphorothionate insecticides, the in vitro efficiencies of hepatic microsomal desulfuration and dearylation of parathion and chlorpyrifos correspond to the acute toxicity levels.

Analysis of Variance↗

PubMed1995

Pharmacokinetics of 1-(2-deoxy-2-fluoro-beta-L-arabinofuranosyl)-5-methyluracil (L-FMAU) in rats.

PURPOSE: The objective of this study was to characterize the pharmacokinetics of 1-(2-deoxy-2-fluoro-beta-L-arabinofuranosyl)-5-methyluracil (L-FMAU), a nucleoside analogue with potent activity against the hepatitis B virus and the Epstein-Barr virus, in rats. METHODS: Three doses of L-FMAU were administered intravenously (10, 25, and 50 mg/kg) to rats, and L-FMAU concentrations in plasma and urine were measured by HPLC. Pharmacokinetic parameters were generated by using area-moment analysis. RESULTS: There were no significant differences in the pharmacokinetic parameters between the three doses (alpha < 0.05). Thus, the disposition of L-FMAU was linear over the dosage of 10 to 50 mg/kg. Plasma concentrations of L-FMAU declined rapidly with a terminal phase half-life of 1.33 +/- 0.45 h (mean +/- SD). Total clearance of L-FMAU was moderate, averaging 1.15 +/- 0.28 L/h/kg. The fraction of compound excreted unchanged in urine was 0.59 +/- 0.13. No glucuronide metabolite was found in the urine. The steady-state volume of distribution was 1.12 +/- 0.26 L/kg indicating intracellular distribution of the compound. The fraction of L-FMAU bound to plasma proteins was approximately 15% and was independent of nucleoside concentration. CONCLUSIONS: The pharmacokinetics of L-FMAU in rats were independent of dose over the dosage range of 10 to 50 mg/kg.

Animals↗

PubMed1995

Structure and function of kidney water channels.

There is now firm evidence that water transporting proteins are expressed in renal and extrarenal tissues. In the kidney, proximal-type (CHIP28) and collecting duct (WCH-CD) water channels have been identified. We have cloned three kidney cDNAs with homology to the water channel (aquaporin) family, including a mercurial-insensitive water channel (MIWC), and a glycerol-transporting protein (GLIP) in collecting duct basolateral membrane. To elucidate water transporting mechanisms, a series of molecular and spectroscopic studies were carried out on purified CHIP28 protein and expressed chimeric and mutated CHIP28 cDNAs. The results indicate that CHIP28 transports water selectively, that CHIP28 monomers are assembled in membranes as tetramers, but that individual monomers function independently. Monomers contain multiple membrane-spanning helical domains. Based on these data and recent electron crystallography results, a model for water transport is proposed in which water moves through narrow pores located within individual CHIP28 monomers.

Amino Acid Sequence↗

PubMed1995

Use of 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil as a novel antiviral agent for hepatitis B virus and Epstein-Barr virus.

A novel anti-hepatitis B virus (anti-HBV) agent, 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil (L-FMAU), was synthesized and found to be a potent anti-HBV and anti-Epstein-Barr virus agent. Its in vitro potency was evaluated in 2.2.15 and H1 cells for anti-HBV and anti-Epstein-Barr virus activities, respectively. In vitro cytotoxicity in MT2, CEM, 2.2.15, and H1 cells was also assessed, and the results indicated high antiviral selectivities of L-FMAU in these cells.

Antiviral Agents↗

PubMed1995

Establishment and characterization of two cell lines derived from human transitional cell carcinoma.

Two continuous cell lines derived from the neoplastic urothelium had been maintained in culture for more than two years. The first cell line derived from the urothelium of a fusion papillocarcinoma on the left lateral wall of the bladder was designated as TBC-1 and grown in vitro for more than 150 generations. The second cell line derived from the urothelium of a papillocarcinoma in the left renal pelvis was designated as TPC-1 and grown in vitro for more than 100 generations. Characterization studies made on both cell lines showed that the cells had a rapid doubling time, exhibited multilayering and produced tumors in sc of BALB/c. Tumor nodules that produced sc of BALB/c kept similar cellular and pathological features to those of the primary biopsy specimens under light and electron microscopes. TPC-1 cell line exhibited a three-dimensional structure of transitional epithelium on the nylon-mesh disk which was coated with a layer of rat tail collagen. Both TBC-1 and TPC-1 cell lines formed colonies in soft agar. Their forming rates were 35% and 28%, respectively. The chromosome number of TBC-1 cells ranged from 17 to 84, with a modal number of 54; whereas that of TPC-1 cells ranged from 28 to 139, with a modal number of 49. The TBC-1 cells showed mutant p53 and ras p21 protein expression and expressed weakly ABH blood group isoantigens. Analysis of lactic dehydrogenase (LDH) isozymes showed the highest levels of LDH isozyme 4 sonicated cell lysates of TBC-1 and TPC-1 respectively.

Adult↗

PubMed1995

[Occurrence of renal cyst and tumor in patients under longterm hemodialysis].

In a period of 12 years, 887 renal failure patients were treated with hemodialysis in our research center. In 512 patients (57.7%) renal cysts were detected by ultrasonagraphy and/or CT. The cysts were apparently acquired during hemodialysis rather than congenital. More important is the fact that in 19 patients with renal cysts tumor subsequently developed. Surgical specimen confirmed that the tumor was malignant in 8 and benign in 11. The mechanism of genesis of renal cyst and tumor in patients under longterm hemodialysis is discussed. The failed kidneys become ischemic and fibrotic and the glomeruli are functionless or completely replaced by fibrotic tissue. Under the situation, the decreased washing-out effect of urinary flow in the renal tubules and tubular obstruction most likely account for cyst formation. The constant chemical and/or physical irritation by the cyst contents combined with the longterm uremia-induced immuno-suppression may contribute to the neoplastic transformation. From the sequence of events, renal cyst may be considered as a pre-cancerous manisfestation.

Adolescent↗

PubMed1995

[Determination of primaquine and hepatic targeting neoglycoalbumin-primaquine in whole blood and liver of mouse by normalphase high-performance liquid chromatography].

We have developed a method to estimate primaquine (PQ) and hepatic targeting antimalarial agent neoglycoalbumin-primaquine (NGA PQ) in whole blood and liver of mice by sensitive and selective high-performance liquid chromatography. The primaquine was extracted out with ether from the basified biological samples in the PQ diphosphate group or from the samples which were acidic hydrolyzed then basified in NGA-PQ group. The extracts were evaporated under N2 then dissolved in the mobile phase. A linear chain analogue of primaquine was used as the internal standard. The samples were injected into the normal phase silica column with chloroform: methanol:ammonia solution (86.8:12.5:0.7,V/V/V) as mobile phase and detected at 254 nm. The average recovery of the method was 100.09 +/- 3.46 (mean +/- s)%; the CV of within-day and between-day were 2.7%-6.13% (n = 5) and 8.32%-13.56% (n = 9) respectively; in PQ group and NGA-PQ group, the PQ concentrations ranged from 10-20,000 ng/ml blood or 1g. liver respectively, and they all yielded a good linear relationship with the peak height ratios. No endogeneous interference was found in chromatograms of biological samples.

Animals↗

PubMed1994

Timing of vulnerability of the brain to iodine deficiency in endemic cretinism.

BACKGROUND: Endemic cretinism, caused by severe iodine deficiency during pregnancy, is the world's most common preventable cause of mental retardation. It can be prevented by iodine treatment before conception, but whether it can be prevented or ameliorated by treatment during pregnancy or after delivery is not known. METHODS: In a severely iodine-deficient area of the Xinjiang region of China, we systematically administered iodine to groups of children from birth to three years of age (n = 689) and women at each trimester of pregnancy (n = 295); we then followed the treated children and the babies born to the treated women for two years. We used three independent measures of neural development: the results of the neurologic examination, the head circumference (which correlates with brain weight in the first postnatal year), and indexes of cognitive and motor development. Untreated children one to three years of age, who were studied when first seen, served as control subjects. RESULTS: The prevalence of moderate or severe neurologic abnormalities among the 120 infants whose mothers received iodine in the first or second trimester was 2 percent, as compared with 9 percent among the 752 infants who received iodine during the third trimester (through the treatment of their mothers) or after birth (P = 0.008). The prevalence of microcephaly (defined as a head circumference more than 3 SD below U.S. norms) decreased from 27 percent in the untreated children to 11 percent in the treated children (P = 0.006), and the mean (+/- SD) developmental quotient at two years of age increased (90 +/- 14, vs. 75 +/- 18 in the untreated children; P < 0.001). Treatment in the third trimester of pregnancy or after delivery did not improve neurologic status, but head growth and developmental quotients improved slightly. Treatment during the first trimester, which was technically problematic, improved the neurologic outcome. CONCLUSIONS: Up to the end of the second trimester, iodine treatment protects the fetal brain from the effects of iodine deficiency. Treatment later in pregnancy or after delivery may improve brain growth and developmental achievement slightly, but it does not improve neurologic status.

Brain↗

PubMed1994

Cloning of a water channel homolog expressed in brain meningeal cells and kidney collecting duct that functions as a stilbene-sensitive glycerol transporter.

In searching for a basolateral membrane water transporter in rat kidney with homology to channel forming integral protein (CHIP28), water channel-collecting duct (WCH-CD), and mercurial-insensitive water channel (MIWC), we cloned a new member of the major intrinsic protein family (GLIP, GLycerol Intrinsic Protein). GLIP cDNA had an 855-base pair open reading frame encoding a 30.5-kDa protein with 19-23% amino acid identity to the water channels and 36% identity to the bacterial glycerol facilitator GlpF. Northern blot analysis showed a 5.5-kilobase mRNA encoding GLIP in kidney, brain, and lung; RT-PCR/Southern blot analysis indicated expression of GLIP in kidney, brain, lung, eye, colon, stomach, and skeletal muscle, but not in heart, liver, and spleen. In situ hybridization in rat kidney showed GLIP mRNA expression in medullary collecting duct. Immunofluorescence with a peptide-derived polyclonal antibody showed GLIP protein expression in basolateral membrane of kidney collecting duct principal cells and brain meningeal cells. Functional measurements in Xenopus oocytes expressing GLIP cRNA showed a > 20-fold increase in [3H]glycerol uptake compared with water-injected oocytes; glycerol uptake was inhibited 88% by diisothiocyanodisulfonic stilbene (0.2 mM) and 36% by phloretin (0.25 mM). GLIP did not function as a transporter for water, urea, inositol, glucose, lactate, and monovalent ions. Glycerol uptake in oocytes expressing CHIP28 and MIWC was not different from that in water-injected controls. GLIP represents the first mammalian water channel homolog that selectively transports a solute other than water. The physiological substrate(s) and role(s) of GLIP remain to be elucidated.

Amino Acid Sequence↗

PubMed1994

Iodination of irrigation water as a method of supplying iodine to a severely iodine-deficient population in Xinjiang, China.

Severe iodine deficiency still occurs in many countries, and causes cretinism and mental impairment. In southern Xinjiang province, China, after usual methods of iodine supplementation had failed, we iodinated irrigation water to increase iodine in soil, crops, animals, and human beings. 5% potassium iodate solution, dripped into an irrigation canal for 12 or 24 days, increased soil iodine 3-fold, and crop and animal iodine 2-fold. Median urinary iodine excretion in children increased from 18 to 49 micrograms/L (two groups of similar age). The cost for iodine was US $0.05 per person per year. Soil iodine remained stable over one winter, and dripping of iodine during the second year (US $0.12 per person per year) resulted in a further 4-fold increase in soil iodine and a 1.8-fold increase in iodine in crops. We conclude that iodination of irrigation water is an advantageous and cost-effective method of supplying iodine in southern Xinjiang, and may be useful in other areas dependent on irrigation.

Agriculture↗

PubMed1994

The macromolecular state of the transcription factor E2F and glucocorticoid regulation of c-myc transcription.

Glucocorticoids inhibit transcription of the proto-oncogene c-myc in lymphoid cells of thymic origin. To determine if this effect is associated with changes in the properties of the transcription factor E2F, extracts were prepared from control and glucocorticoid-treated P1798 murine T lymphoma cells, and the macromolecular state of E2F was assessed by gel-mobility shift. Control extracts exhibit two predominant gel-mobility shift entities of which one corresponds to "free" E2F. A second entity, complex C, has properties similar to those described for the complex containing E2F, p107, cyclin A, and Cdk2. Complex C disappears after addition of dexamethasone and is replaced by complex D. The mobility of this complex and its sensitivity to SV40 T antigen suggest that complex D corresponds to an E2F-p105Rb-1 complex. Extracts from control and glucocorticoid-treated cells yield identical DNase I protection patterns on the c-myc P2 promoter. Furthermore, such extracts transcribe the c-myc P2 promoter in vitro with equal activity. The relative abundance of the E2F complexes was measured after addition of dexamethasone. Complex C disappears as cells withdraw from S phase, and complex D appears at this time. The genes encoding thymidine kinase (Tk-1) and p34cdc2 (cdc2) are regulated with kinetics similar to those observed for changes in the macromolecular state of E2F. However, regulation of c-myc expression occurs long before any change in E2F. The macromolecular state of E2F may regulate expression of genes at the G1/S boundary. However, the data are not consistent with the hypothesis that association of E2F with tumor suppressor gene products such as p107 or p105Rb-1 is relevant to glucocorticoid regulation of c-myc transcription.

Animals↗