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PubMedDate not supplied

Effect of mixed (RB 38A) and selective (RB 38B) inhibitors of enkephalin degrading enzymes on a model of depression in the rat.

This is a study of the effects of the endogenous opioid peptides, enkephalins, on learned helplessness, an experimental model of depression in rats. For this purpose, the responses induced by RB 38A, a mixed inhibitor of enkephalin catabolism, and RB 38B, a selective inhibitor of neutral endopeptidase EC 3.4.24.11, were compared with the antidepressive effect induced by imipramine. RB 38A and RB 38B induced an imipramine-like effect in reducing helpless behavior, as illustrated by the decrease in the number of escape failures. According to the different pharmacological potential of both inhibitors to reduce enkephalin metabolism, complete inhibition of enkephalins (RB 38A) produced a higher response than that obtained with a partial inhibitor (RB 38B). On the other hand, naloxone (NLX) was found to facilitate the induction of learned helplessness, and to antagonize the effect of both enkephalin-degrading enzyme inhibitors. These results suggest that modifications in the activity of the endogenous opioid system could take place in this model of depression. The antidepressant-like effects induced by RB 38B, and especially by RB 38A, in the learned helplessness paradigm suggest that new mixed enkephalinase inhibitors, able to cross the blood-brain barrier, could provide a new strategy in the treatment of affective disorders.

Animals↗
PubMed2001

New layered materials: syntheses, structures, and optical properties of K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiaAg(2)S(4), Cs(2)TiAg(2)sS(4), and Cs(2)TiCu(2)Se(4).

The new compounds K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiAg(2)S(4), Cs(2)TiAg(2)S(4), and Cs(2)TiCu(2)Se(4) have been synthesized by the reactions of A(2)Q(3) (A = K, Rb, Cs; Q = S, Se) with Ti, M (M = Cu or Ag), and Q at 823 K. The compounds Rb(2)TiCu(2)S(4), Cs(2)TiAg(2)S(4), and Cs(2)TiCu(2)Se(4) are isostructural. They crystallize with two formula units in space group P4(2)/mcm of the tetragonal system in cells of dimensions a = 5.6046(4) A, c = 13.154(1) A for Rb(2)TiCu(2)S(4), a =6.024(1) A, c = 13.566(4) A for Cs(2)TiAg(2)S(4), and a =5.852(2) A, c =14.234(5) A for Cs(2)TiCu(2)Se(4) at 153 K. Their structure is closely related to that of Cs(2)ZrAg(2)Te(4) and comprises [TiM(2)Q(4)(2)(-)] layers, which are separated by alkali metal atoms. The [TiM(2)Q(4)(2)(-)] layer is anti-fluorite-like with both Ti and M atoms tetrahedrally coordinated to Q atoms. Tetrahedral coordination of Ti(4+) is rare in the solid state. On the basis of unit cell and space group determinations, the compounds K(2)TiCu(2)S(4) and Rb(2)TiAg(2)S(4) are isostructural with the above compounds. The band gaps of K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiAg(2)S(4), and Cs(2)TiAg(2)S(4) are 2.04, 2.19, 2.33, and 2.44 eV, respectively, as derived from optical measurements. From band-structure calculations, the optical absorption for an A(2)TiM(2)Q(4) compound is assigned to a transition from an M d and Q p valence band (HOMO) to a Ti 3d conduction band.

Journal Article↗
PubMed1992

Identification of a 60-kilodalton Rb-binding protein, RBP60, that allows the Rb-E2F complex to bind DNA.

Several reports have indicated that the product of the retinoblastoma gene (Rb) complexes with the transcription factor E2F. We present evidence that the DNA-binding of the Rb-E2F complex involves another cellular factor. Addition of Rb to purified preparations of E2F does not generate an Rb-E2F complex that can bind DNA, and in fact, we see an inhibition of the DNA-binding ability of E2F. On the other hand, addition of Rb to cruder preparations of E2F results in the formation of an Rb-E2F complex (E2Fr) that can bind DNA and produces a distinct complex in gel retardation assays. We have identified and purified a 60-kDa protein that allows the Rb-E2F complex to bind DNA, and we show that this 60-kDa protein exerts its effect by directly interacting with Rb.

Animals↗
PubMed1989

K+ and Rb+ transport by the rabbit CCD: Rb+ reduces K+ conductance and Na+ transport.

We compared transport of K+ and Rb+ across the rabbit cortical collecting duct to gain insight into the mechanisms of K+ secretion. Passive tracer fluxes, active secretory rates, electrophysiological behavior, and the ability of each ion to support Na+-K+-ATPase activity were determined. When active transport was inhibited by amiloride, K+ permeability was twice the Rb+ permeability. Transepithelial conductance (GT) was half as great in solutions where 5 mM Rb+ replaced 5 mM K+. When 4 mM Ba2+ was added to the lumen, both Rb+ and K+ permeability fell to values not different from that expected for paracellular diffusion. The relationship between Ba2+-induced changes in the K+ and Rb+ permeabilities and in the simultaneously measured GT provides strong evidence that K+ transport across the apical membrane is largely, if not exclusively, conductive. We also determined that net K+ secretion is greater than net Rb+ secretion (when each is the abundant ion). The reasons for this difference probably involve several steps in the K+ secretory process and include the following: 1) reduced ATPase activity in the presence of Rb+ (approximately 80%) compared with K+, 2) reduction of Na+ absorption, and 3) partial blockade of the apical (and perhaps basolateral) K+ conductance. Although there were quantitative differences between K+ and Rb+ transport, we found no evidence suggesting that these ions are transported by different mechanisms.

Absorption↗
PubMedDate not supplied

Infrequent alternations of RB pathway (Rb-p16INK4A-cyclinD1) in adenoid cystic carcinoma of salivary glands.

Retinoblastoma (Rb) tumor suppressor genes' products and of the proteins regulating its phosphorylation and function in G1 arrest, p16INK4A and cyclin D1, play important roles in the regulation of the cell cycle. Rb gene inactivation, reflected by the absence of Rb protein expression, has been reported in oral squamous cell carcinomas. p16INK4A is frequently deleted, methylated, or mutated, and cyclin D1 gene amplification in many malignancies including oral squamous cell carcinomas (SCC). These findings suggested that Rb pathway of G1 arrest are the most commonly affected genes in Oral SCC. However, alternation of Rb pathway in salivary gland tumors was not clear. In this study, the expressions of Rb, p16INK4A, and cyclin D1 alternations were analyzed by immunohistochemical assay in 5 specimens of normal salivary glands and twenty-two cases of adenoid cystic carcinomas (ACC). Proliferating cell nuclear antigen (PCNA) labelling index (P.I.) was used for the evaluation of cell proliferation. Rb was consistently expressed in normal salivary glands and ACC. Loss of p16INK4A expression was observed in three cases (13.6%) of ACC. And overexpression of cyclin D1 was observed in four cases (18.2%). The three p16INK4A absent cases were the tumors with predominantly solid pattern and those cases were overexpressed cyclin D1. The cell proliferation activities of p16INK4A absent tumors (P.I. = 24.2 +/- 2.1%) were significantly higher than those of p16INK4A present tumors (P.I. = 10.4 +/- 3.5%) (P < 0.05). Cyclin D1 expression was also related to cell proliferation (P.I. of cyclin D1 negative cases vs. cyclin D1 positive: 10.1 +/- 3.0% vs. 22.6 +/- 3.4%) (P < 0.05). These findings suggested, however, alternations of Rb pathway were infrequent events in ACC of salivary glands and inactivation of p16INK4A, cyclin D1 overexpression may be related to the high cell proliferating activity of ACC.

Adult↗
PubMedDate not supplied

Interaction of the Rb tumor suppressor protein with the c-fos promoter in c-fos transfected cells overexpressing c-fos and Rb.

The Rb tumor suppressor protein is overexpressed in HeLa cell lines permanently transfected with a constitutively expressed c-fos gene. CP17-14 cell overexpression of Rb may be due to a balancing response to overexpression of the stimulatory effects of c-fos overexpression on transcription. The cis-acting retinoblastoma control element (RCE, -97 to -86 bp) in the human c-fos promoter is thought to allow regulation of c-fos by Rb. Gel-shift assays were performed with a 168 bp fragment encoding the c-fos RCE. Competition assays with increasing mass of unlabeled probe or dose-dependence assays using increasing mass of nuclear proteins, demonstrated sequence-specific complex formation. Indistinguishable complexes were formed between the c-fos RCE fragment in transfected cells, but at higher levels (> 50%), compared to proteins from parental cells. Supershift analysis utilizing epitope-specific Rb-monoclonal antibodies indicated the presence of Rb protein bound to the RCE-containing DNA fragment. In contrast, polyclonal anti-Rb antibodies enhanced the amounts of nuclear protein-DNA complexes detected but did not result in a supershift. These results suggested the presence of Rb and/or Rb-like peptides involved in complex formation and the presence of multiple variants of RCE-binding complexes in response to c-fos over-expression.

DNA-Binding Proteins↗
PubMed2001

Trimerization of alkali dicyanamides M[N(CN)2] and formation of tricyanomelaminates M3[C6N9] (M = K, Rb) in the melt: crystal structure determination of three polymorphs of K[N(CN)2], two of Rb[N(CN)2], and one of K3[C6N9] and Rb3[C6N9] from X-ray powder diffractometry.

The alkali dicyanamides M[N(CN)2] (M=K, Rb) were synthesized through ion exchange, and the corresponding tricyanomelaminates M3[C6N9] were obtained by heating the respective dicyanamides. The thermal behavior of the dicyanamides and their reaction to form the tricyanomelaminates were investigated by temperature-dependent X-ray powder diffractometry and thermoanalytical measurements. Potassium dicyanamide K[N(CN)2] was found to undergo four phase transitions: At 136 degrees C the low-temperature modification alpha-K[N(CN)2] transforms to beta-K[N(CN)2], and at 187degrees C the latter transforms to the high-temperature modification gamma-K[N(CN)2], which melts at 232 degrees C. Above 310 degrees C the dicyanamide ions [N(CN)2]- trimerize and the resulting tricyanomelaminate K3[C6N9] solidifies. Two modifications of rubidium dicyanamide have been identified: Even at -25 degrees C, the a form slowly transforms to beta-Rb[N(CN)2] within weeks. Rb[N(CN)2] has a melting point of 190 degrees C. Above 260 degrees C the dicyanamide ions [N(CN)2]- of the rubidium salt trimerize in the melt and the tricyanomelaminate Rb3[C6N9] solidifies. The crystal structures of all phases were determined by powder diffraction methods and were refined by the Rietveld method. alpha-K[N(CN)2] (Pbcm, a = 836.52(1), b = 46.90(1), c =7 21.27(1) pm, Z = 4), gamma-K[N(CN)2] (Pnma, a = 855.40(3), b = 387.80(1), 1252.73(4) pm, Z = 4), and Rb[N(CN)2] (C2/c, a = 1381.56(2), b = 1000.02(1), c = 1443.28(2) pm, 116.8963(6) degrees, Z = 16) represent new structure types. The crystal structure of beta-K[N(CN)2] (P2(1/n), a = -726.92(1), b 1596.34(2), c = 387.037(5) pm, 111.8782(6) degrees, Z = 4) is similar but not isotypic to the structure of alpha Na[N(CN)2]. alpha-Rb[N(CN)2] (Pbcm, a = 856.09(1), b = 661.711(7), c = 765.067(9) pm, Z = 4) is isotypic with alpha-K[N(CN)2]. The alkali dicyanamides contain the bent planar anion [N(CN)2]- of approximate symmetry C2, (average bond lengths: C-N(bridge) 133, C-N(term) 113 pm; average angles N-C-N 170 degrees, C-N-C 120 degrees). K3[C6N9] (P2(1/c), a = 373.82(1), b = 1192.48(5), c = 2500.4(1) pm, beta = 101.406(3) degrees, Z = 4) and Rb,[C6N9] (P2(1/c), a = 389.93(2), b = 1226.06(6), c = 2547.5(1) pm, 98.741(5) degrees, Z=4) are isotypic and they contain the planar cyclic anion [C6N9]3-. Although structurally related, Na3[C6N9] is not isotypic with the tricyanomelaminates M3[C6N9] (M = K, Rb).

Journal Article↗
PubMed2004

Overexpression of E2F1 associated with LOH at RB locus and hyperphosphorylation of RB in non-small cell lung carcinoma.

PURPOSE: E2F1 plays a critical role in cell proliferation, and its function is controlled by the retinoblastoma (RB) protein. We examined the expression of E2F1 and the aberration of RB gene and protein to elucidate what factors contribute to the overexpression of E2F1 in non-small cell lung carcinomas. METHODS: The expression level of E2F1 in tissues of non-small cell lung carcinomas was measured by means of quantitative reverse transcription-polymerase chain reaction and immunohistochemistry. For RB, we examined loss of heterozygosity (LOH) by PCR-restriction fragment length polymorphism and a variable number of tandem repeats, and protein expression by immunohistochemistry. RESULTS: Fifteen cases of carcinoma (46%) showed high transcription levels of E2F1 gene. Immunohistochemically, almost all (14 of 15) cases overexpressing E2F1 mRNA were positive for E2F1 protein. LOH at the RB locus was found in 13 of 30 informative cases. In 13 cases with LOH, ten showed overexpression of E2F1 mRNA and protein. Immunohistochemical positivity for phosphorylated RB protein was also closely correlated with overexpression of E2F1. CONCLUSIONS: Our results suggest that overexpression of E2F1, induced both by LOH at the RB locus and anomalous phosphorylation of the RB protein, is involved in the development of non-small cell lung carcinoma.

Adenocarcinoma↗
PubMed2005

Caspase-9 can antagonize p53-induced apoptosis by generating a p76(Rb) truncated form of Rb.

The tumor suppressor Rb (retinoblastoma protein) is known to regulate p53-dependent apoptosis, but the mechanisms involved are unclear. In a rat fibroblast model, we previously observed that caspase inhibition potentiates p53-dependent apoptosis and prevents the Rb cleavage associated with p53 activation. These results suggested that a caspase(s) can antagonize p53-mediated apoptosis via the production of a protective Rb truncated form. Here, we identify caspase-9 as the caspase that interferes, upstream of the mitochondrion, with p53-induced apoptosis in both immortalized and primary fibroblasts. This caspase can be detected as a p38 processed form in living cells, in the absence of apoptosome formation and apoptotic signal. We also provide evidence that the involvement of caspase-9 in a pre-mitochondrial protective pathway results from the previously undescribed cleavage of Rb, at a LExD site, into a p76(Rb) form, which antagonizes p53-induced apoptosis. These results establish that a truncated form of Rb can display an antiapoptotic activity, rather than just being a by-product of Rb degradation.

Animals↗
PubMed2004

Rb+ flux through hERG channels affects the potency of channel blocking drugs: correlation with data obtained using a high-throughput Rb+ efflux assay.

The nonradioactive Rb+ efflux assay has become a reliable and efficient high-throughput hERG screening method, but it is limited by its low sensitivity for potent hERG blockers. Using the patch clamp technique, the authors found that the low sensitivity is due in part to the use of Rb+ as the permeating cation in the assay. The affinities of the drugs measured by patch clamp technique in the presence of Rb+ were 3- to 10-fold lower than when measured by the same method in the presence of K+ ions. The apparent affinity of the drugs decreased even further when monitored by the Rb+ efflux assay. It was also observed that Rb+ had minimal effects on the activation properties of channels while there was a significant change in the half-inactivation potential. This voltage shift reduces hERG channel inactivation at efflux assay potentials, and will reduce the affinity of hERG-blocking drugs that bind to inactivated states of the channel. In combination with the effects of elevated extracellular ion concentrations, it is likely that Rb+ modulation of hERG channel inactivation is largely responsible for the reduced drug potencies observed in the Rb+ efflux assay.

Biological Assay↗
PubMedDate not supplied

A mathematical model of the regulation of the G1 phase of Rb+/+ and Rb-/- mouse embryonic fibroblasts and an osteosarcoma cell line.

A mathematical model integrating the roles of cyclin D, cdk4, cyclin E, cdk2, E2F and RB in control of the G1 phase of the cell cycle is described. Experimental results described with murine embryo fibroblasts (MEFs), either Rb+/+ or Rb-/-, and with the RB-deficient osteosarcoma cell line, Saos-2, served as the basis for the formulation of this mathematical model. A model employing the known interactions of these six proteins does not reproduce the experimental observations described in the MEFs. The appropriate modelling of G1 requires the inclusion of a sensing mechanism which adjusts the activity of cyclin E/cdk2 in response to both RB concentration and growth factors. Incorporation of this sensing mechanism into the model allows it to reproduce most of the experimental results observed in Saos-2 cells, Rb-/- MEFS, and Rb+/+ MEFs. The model also makes specific predictions which have not been tested experimentally.

Animals↗
PubMedDate not supplied

Na,K-ATPase characterized in artificial membranes. 2. Successive measurement of ATP-driven Rb-accumulation, ouabain-blocked Rb-flux and palytoxin-induced Rb-efflux.

The Na,K-ATPase is a multifunctional system anchored in the membrane of eukaryotic cells; it is responsible for the establishment and regulation of the Na/K balance of cell and organism by a stoichiometric mechanism linking Na extrusion to K uptake and ATP hydrolysis. The receptor for cardioactive steroids such as digoxin and ouabain is located at the extracellular surface of the system. Conversely, palytoxin, the most potent animal toxin, exerts its toxic effect by creating nonspecific leaks in the cell membrane leading to K-efflux and influx of Na and Ca ions. Ouabain prevents the pore-forming action of palytoxin in cells and therefore Na,K-ATPase is suspected to be the common receptor of ouabain and palytoxin. We have developed an artificial membrane system to determine structure-function relationships and ligand interactions of purified Na,K-ATPase: two-sided, bi-directional ATP-filled liposomes. In this system, ATP-driven 86Rb accumulation, arrest of 86Rb-uptake by ouabain, and palytoxin-induced 86Rb-leak were measured successively in the same preparation. Ouabain prevented the leak when the enzyme was ouabain-sensitive (rabbit kidney) but not when it was ouabain-resistant (rat kidney). On the basis of these data in conjunction with conformational analyses, allosteric conformational competition for the ouabain-palytoxin antagonism is proposed.

Acrylamides↗
PubMed2005

Sperm dysfunction in the Rb(6.16)- and Rb(6.15)-bearing mice revisited: involvement of Hyalp1 and Hyal5.

Earlier we showed that Sperm adhesion molecule1 (Spam1), the best studied sperm hyaluronidase, is involved in the sperm dysfunction associated with Robertsonian translocations (Rb). The dysfunction results in reduced fertility in mice homozygous for the Rb(6.16) or the Rb(6.15) translocation and transmission ratio distortion (TRD) in heterozygous males. This conclusion was based on the finding that Spam1 in the Rbs harbors multiple point mutations and a genomic alteration at the locus [in the case of Rb(6.16)]; and is accompanied by reduced steady-state levels of the RNA and protein. Here we show that closely linked family members in the hyaluronidase gene cluster on mouse chromosome 6, Hyalp1 and Hyal5, also harbor point mutations in these Rbs, leading to nonconservative substitutions in both the encoded proteins. To test if Spam1 by itself is capable of producing TRD we analyzed the transmission of wild-type and null alleles of the gene in the progeny of carriers and show that there is no significant TRD. This lack of TRD in null carriers argues for only a contributory role of Spam1 in the TRD seen in the Rb-bearing mice, and supports the involvement of Hyalp1 and/or Hyal5 in the sperm dysfunction and the resulting TRD. It is proposed that the clustering of point mutations in all three genes results from the cumulative effect of spontaneous mutations that do not disperse in the population due to suppression of recombination that occurs at Rb junctions.

Amino Acid Sequence↗
PubMed1993

Dibutyryl cyclic AMP enhances the down-regulation of RB protein during G1 phase in the proliferating primary rat hepatocytes, but inhibits their entries into S phase and RB's phosphorylation.

To elucidate the cAMP's bi-directional dual effect on hepatic regeneration with a special reference to RB protein, we studied the serial change of RB protein in the proliferating primary rat hepatocytes and the effect of dibutyryl cAMP (DBcAMP) on it. RB protein in the hepatocytes was down-regulated during the G1 phase, and the highly phosphorylated/the underphosphorylated ratio of RB protein increased at the S phase. DBcAMP (1 mM) addition, inhibitory on the DNA synthesis, enhanced this down-regulation, but did not increase the phosphorylated form of RB protein at the S phase. High dose of cAMP at the late G1-G1/S phase could block some essential events for G1/S transition including phosphorylation of RB protein.

Animals↗
PubMedDate not supplied

The effect of idebenone on the passive K+ and Rb+ permeability of the brain cell membranes of CFY rats as revealed by the Rb+-discrimination ratio.

Rubidium (Rb(+)) uptake and release of brain cortical neurons of adult (12-15 month old), normal, female CFY rats were studied in placebo- and idebenone-treated animals. Treatment period was up to 5 weeks, with 50 mg/kg bw/day idebenone (oxidized form) suspended in 5% gum arabic (verum-group), or only with the latter solvent (placebo-group). Rb(+) can replace up to 60% of the intracellular K(+), and can be used as a tracer of the K(+) movement across the cell membrane. Loading with RbCI was performed from the 3rd week of the idebenone treatment by daily intraperitoneal injections of a dose of 300 mg/kg bw, for 14 days. During the subsequent Rb(+)-release period, the so-called Rb(+)/K(+) discrimination ratio (DR) (Relman et al., 1957, J. Clin. Invest., 36, 1249) was determined on the 3rd and 8th days. Rb(+) and K(+) contents were measured by means of bulk specimen X-ray microanalysis in the intracellular water of brain cells and by atomic absorption spectrophotometry in the serum, in 3-4 animals per group, whereas these concentrations in the cerebrospinal fluid were calculated on the basis of known serum/liquor distribution factors. Normal aging causes a marked increase of DR in brain and liver cells. The values of DR obtained in both placebo and verum groups were identical with those of the age-matched, completely untreated controls. It is important to stress that the subacute idebenone treatment did not cause any deterioration of this parameter, i.e., under the given conditions idebenone does not affect the cell membrane passive Rb(+) and K(+) permeability characteristics in the neurons of adult, normal, female CFY rats.

Journal Article↗
PubMed2000

Rb and p130 regulate RNA polymerase I transcription: Rb disrupts the interaction between UBF and SL-1.

We have previously demonstrated that the protein encoded by the retinoblastoma susceptibility gene (Rb) functions as a regulator of transcription by RNA polymerase I (rDNA transcription) by inhibiting UBF-mediated transcription. In the present study, we have examined the mechanism by which Rb represses UBF-dependent rDNA transcription and determined if other Rb-like proteins have similar effects. We demonstrate that authentic or recombinant UBF and Rb interact directly and this requires a functional A/B pocket. DNase footprinting and band-shift assays demonstrated that the interaction between Rb and UBF does not inhibit the binding of UBF to DNA. However, the formation of an UBF/Rb complex does block the interaction of UBF with SL-1, as indicated by using the 48 kDa subunit as a marker for SL-1. Additional evidence is presented that another pocket protein, p130 but not p107, can be found in a complex with UBF. Interestingly, the cellular content of p130 inversely correlated with the rate of rDNA transcription in two physiological systems, and overexpression of p130 inhibited rDNA transcription. These results suggest that p130 may regulate rDNA transcription in a similar manner to Rb.

Animals↗
PubMed1993

The activation domain of transcription factor PU.1 binds the retinoblastoma (RB) protein and the transcription factor TFIID in vitro: RB shows sequence similarity to TFIID and TFIIB.

The retinoblastoma (RB) tumor suppressor protein and the TATA-box-binding protein TFIID form contacts with a number of viral transactivator proteins. One of these, the adenovirus E1A protein, can bind to both proteins. Here we present evidence that the cellular transcription factor PU.1 can bind to both RB and TFIID. Like E1A, PU.1 binds to the conserved C-terminal domain of TFIID and to the RB "pocket" domain. The PU.1 sequences required to bind either protein lie within a 75-amino acid region which functions as an independent activation domain in vivo. The ability of PU.1 to contact directly both RB and TFIID through the same 75-residue domain prompted us to look for sequence similarity between these two proteins. We find that the previously defined domain A of the RB pocket shows sequence similarity to the conserved C terminus of TFIID, whereas domain B shows sequence similarity to a second general transcription factor, TFIIB. The potential for RB to influence transcription by using TFIID- and TFIIB-related functions is discussed.

Amino Acid Sequence↗