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R J White

Publications and source records attributed to R J White.

At least 37 records · Page 2Linked to original sources
PubMed2001

Overlapping functions of the pRb family in the regulation of rRNA synthesis.

The "pocket" proteins pRb, p107, and p130 are a family of negative growth regulators. Previous studies have demonstrated that overexpression of pRb can repress transcription by RNA polymerase (Pol) I. To assess whether pRb performs this role under physiological conditions, we have examined pre-rRNA levels in cells from mice lacking either pRb alone or combinations of the three pocket proteins. Pol I transcription was unaffected in pRb-knockout fibroblasts, but specific disruption of the entire pRb family deregulated rRNA synthesis. Further analysis showed that p130 shares with pRb the ability to repress Pol I transcription, whereas p107 is ineffective in this system. Production of rRNA is abnormally elevated in Rb(-/-) p130(-/-) fibroblasts. Furthermore, overexpression of p130 can inhibit an rRNA promoter both in vitro and in vivo. This reflects an ability of p130 to bind and inactivate the upstream binding factor, UBF. The data imply that rRNA synthesis in living cells is subject to redundant control by endogenous pRb and p130.

3T3 Cells↗
PubMed2001

Esophagitis-related esophageal shortening in opossum is associated with longitudinal muscle hyperresponsiveness.

Acute intraluminal acid perfusion induces esophageal shortening in humans and opossums. Lower esophageal sphincter (LES) hypotension and peristaltic dysfunction occur in patients and animal models of reflux esophagitis. This study examined whether similar shortening and motor dysfunction occur in anesthetized opossums after repeated esophageal acid exposure and whether this is associated with longitudinal muscle (LM) hyperresponsiveness. Manometry used before and after 3 consecutive days of 45-min perfusion with 100 mmol/l HCl or normal saline measured esophageal length and motor responses to induced swallows. LM electrical and mechanical responses were assessed using standard isometric tension and intracellular recording techniques. Compared with controls, repeated acid perfusion induced erosive esophagitis and significant esophageal shortening, associated with enhanced LM responses to carbachol, a significantly depolarized resting membrane potential, and abnormal spike patterns. LES resting pressure and swallow-induced peristalsis were unaffected. In this model of reflux esophagitis, marked persistent esophageal shortening and associated LM hyperresponsiveness occur before significant LES or peristaltic dysfunction, suggesting that esophageal shortening is the earliest motor disorder induced by acid injury.

Animals↗
PubMed2000

RNA polymerase III transcription factor TFIIIC2 is overexpressed in ovarian tumors.

Most transformed cells display abnormally high levels of RNA polymerase (pol) III transcripts. Although the full significance of this is unclear, it may be fundamental because healthy cells use two key tumor suppressors to restrain pol III activity. We present the first evidence that a pol III transcription factor is overexpressed in tumors. This factor, TFIIIC2, is a histone acetyltransferase that is required for synthesis of most pol III products, including tRNA and 5S rRNA. TFIIIC2 is a complex of five polypeptides, and mRNAs encoding each of these subunits are overexpressed in human ovarian carcinomas; this may explain the elevated TFIIIC2 activity that is found consistently in the tumors. Deregulation in these cancers is unlikely to be a secondary response to rapid proliferation, because there is little or no change in TFIIIC2 mRNA levels when actively cycling cells are compared with growth-arrested cells in culture. Using purified factors, we show that raising the level of TFIIIC2 is sufficient to stimulate pol III transcription in ovarian cell extracts. The data suggest that overexpression of TFIIIC2 contributes to the abnormal abundance of pol III transcripts in ovarian tumors.

Acetyltransferases↗
PubMed2000

Survey and summary: transcription by RNA polymerases I and III.

The task of transcribing nuclear genes is shared between three RNA polymerases in eukaryotes: RNA polymerase (pol) I synthesizes the large rRNA, pol II synthesizes mRNA and pol III synthesizes tRNA and 5S rRNA. Although pol II has received most attention, pol I and pol III are together responsible for the bulk of transcriptional activity. This survey will summarise what is known about the process of transcription by pol I and pol III, how it happens and the proteins involved. Attention will be drawn to the similarities between the three nuclear RNA polymerase systems and also to their differences.

Animals↗
PubMed2000

Actinonin, a naturally occurring antibacterial agent, is a potent deformylase inhibitor.

Peptide deformylase (PDF) is essential in prokaryotes and absent in mammalian cells, thus making it an attractive target for the discovery of novel antibiotics. We have identified actinonin, a naturally occurring antibacterial agent, as a potent PDF inhibitor. The dissociation constant for this compound was 0.3 x 10(-)(9) M against Ni-PDF from Escherichia coli; the PDF from Staphylococcus aureus gave a similar value. Microbiological evaluation revealed that actinonin is a bacteriostatic agent with activity against Gram-positive and fastidious Gram-negative microorganisms. The PDF gene, def, was placed under control of P(BAD) in E. coli tolC, permitting regulation of PDF expression levels in the cell by varying the external arabinose concentration. The susceptibility of this strain to actinonin increases with decreased levels of PDF expression, indicating that actinonin inhibits bacterial growth by targeting this enzyme. Actinonin provides an excellent starting point from which to derive a more potent PDF inhibitor that has a broader spectrum of antibacterial activity.

Amidohydrolases↗
PubMed2000

Expanded CUG repeat RNAs form hairpins that activate the double-stranded RNA-dependent protein kinase PKR.

Myotonic dystrophy is caused by an expanded CTG repeat in the 3' untranslated region of the DM protein kinase (DMPK) gene. The expanded repeat triggers the nuclear retention of mutant DMPK transcripts, but the resulting underexpression of DMPK probably does not fully account for the severe phenotype. One proposed disease mechanism is that nuclear accumulation of expanded CUG repeats may interfere with nuclear function. Here we show by thermal melting and nuclease digestion studies that CUG repeats form highly stable hairpins. Furthermore, CUG repeats bind to the dsRNA-binding domain of PKR, the dsRNA-activated protein kinase. The threshold for binding to PKR is approximately 15 CUG repeats, and the affinity increases with longer repeat lengths. Finally, CUG repeats that are pathologically expanded can activate PKR in vitro. These results raise the possibility that the disease mechanism could be, in part, a gain of function by mutant DMPK transcripts that involves sequestration or activation of dsRNA binding proteins.

Base Pairing↗
PubMed2000

Retinoblastoma protein disrupts interactions required for RNA polymerase III transcription.

The retinoblastoma protein (RB) has been shown to suppress RNA polymerase (Pol) III transcription in vivo (R. J. White, D. Trouche, K. Martin, S. P. Jackson, and T. Kouzarides, Nature 382:88-90, 1996). This regulation involves interaction with TFIIIB, a multisubunit factor that is required for the expression of all Pol III templates (C. G. C. Larminie, C. A. Cairns, R. Mital, K. Martin, T. Kouzarides, S. P. Jackson, and R. J. White, EMBO J. 16:2061-2071, 1997; W.-M. Chu, Z. Wang, R. G. Roeder, and C. W. Schmid, J. Biol. Chem. 272:14755-14761, 1997). However, it has not been established why RB binding to TFIIIB results in transcriptional repression. For several Pol II-transcribed genes, RB has been shown to inhibit expression by recruiting histone deacetylases, which are thought to decrease promoter accessibility. We present evidence that histone deacetylases exert a negative effect on Pol III activity in vivo. However, RB remains able to regulate Pol III transcription in the presence of the histone deacetylase inhibitor trichostatin A. Instead, RB represses by disrupting interactions between TFIIIB and other components of the basal Pol III transcription apparatus. Recruitment of TFIIIB to most class III genes requires its binding to TFIIIC2, but this can be blocked by RB. In addition, RB disrupts the interaction between TFIIIB and Pol III that is essential for transcription. The ability of RB to inhibit these key interactions can explain its action as a potent repressor of class III gene expression.

Animals↗
PubMed2000

Eosinophilic fasciitis with pulmonary and pleural involvement.

We report a case of eosinophilic fasciitis, with the unusual features of pulmonary and pleural involvement. Similar cases which involve the lungs have been reported after exposure to L-tryptophan, but there is no relevant drug history in this case.

Anti-Inflammatory Agents↗
PubMed2000

Large lung bullae in marijuana smokers.

The case histories are presented of four men with multiple large upper zone lung bullae but otherwise relatively preserved lung parenchyma. Each had a history of significant exposure to marijuana. In three of the four cases the tobacco smoking load had been relatively small, suggesting a possible causal role for marijuana in the pathogenesis of this unusual pattern of bullous emphysema.

Adult↗
PubMed2000

RNA polymerase III transcription: its control by tumor suppressors and its deregulation by transforming agents.

The level of RNA polymerase (pol) III transcription is tightly linked to the rate of growth; it is low in resting cells and increases following mitogenic stimulation. When mammalian cells begin to proliferate, maximal pol III activity is reached shortly before the G1/S transition; it then remains high throughout S and G2 phases. Recent data suggest that the retinoblastoma protein RB and its relatives p107 and p130 may be largely responsible for this pattern of expression. During G0 and early G1 phase, RB and p130 bind and repress the pol III-specific factor TFIIIB; shortly before S phase they dissociate from TFIIIB, allowing transcription to increase. At the end of interphase, when cells enter mitosis, pol III transcription is again suppressed; this mitotic repression is achieved through direct phosphorylation of TFIIIB. Thus, pol III transcription levels fluctuate as mammalian cells cycle, being high in S and G2 phases and low during mitosis and early G1. In addition to this cyclic regulation, TFIIIB can be bound and repressed by the tumor suppressor p53. Conversely, it is a target for activation by several viruses, including SV40, HBV, and HTLV-1. Some viruses also increase the activity of a second pol III-specific factor called TFIIIC. A large proportion of transformed and tumor cell types express abnormally high levels of pol III products. This may be explained, at least in part, by the very high frequency with which RB and p53 become inactivated during neoplastic transformation; loss of function of these cardinal tumor suppressors may release TFIIIB from key restraints that operate in normal cells.

Animals↗
PubMed2000

Quiz-o-matic: a free Web-based tool for construction of self-scoring on-line quizzes.

Increasingly, educators are using the World-Wide Web (the Web) and related technology to supplement their traditional teaching materials. In this paper, we present a free tool that has been placed on the Web to enable educators to create Web pages that present self-scoring quizzes. Such Web-based practice quizzes provide students with an opportunity for interactive assessment and review of course material. The tool, Quiz-o-Matic, uses active server pages to build the HTML and JavaScript code for each quiz, without requiring the user to edit any code. We present evidence that students judge the self-scoring quizzes to be useful and worthwhile additions to a course.

Chicago↗
PubMed1999

Resistance of small leucine-rich repeat proteoglycans to proteolytic degradation during interleukin-1-stimulated cartilage catabolism.

A bovine nasal-cartilage culture system has been utilized to analyse the catabolic events occurring in response to interleukin-1beta over a 14-day period. An early event following the start of interleukin-1 treatment was the release of glycosaminoglycan into the culture medium. This release was accompanied by the appearance in the tissue, and shortly thereafter also in the culture media, of a globular domain (G1)-containing aggrecan degradation product generated by the action of aggrecanase. Link protein was also released from the cartilage with a similar timeframe to that of the G1 fragment, although there was no evidence of its proteolytic degradation. By comparison with aggrecan, the small leucine-rich repeat proteoglycans decorin, biglycan and lumican showed a resistance to both proteolytic cleavage and release throughout the culture period. In contrast, fibromodulin exhibited a marked decrease in size after day 4, presumably due to proteolytic modification, but the major degradation product was retained throughout the culture period. Also in contrast with the early changes in the components of the proteoglycan aggregate, type II collagen did not display signs of extensive degradation until much later in the culture period. Collagen degradation products compatible with collagenase action first appeared in the medium by day 10 and increased thereafter. These data demonstrate that the leucine-rich repeat proteoglycans are resistant to proteolytic action during interleukin-1-stimulated cartilage catabolism, compared with aggrecan. This resistance and continued interaction with the surface of the collagen fibrils may help to stabilize the collagen fibrillar network and protect it from extensive proteolytic attack during the early phases of cartilage degeneration.

Aggrecans↗
PubMed1999

Regulation of RNA polymerase I transcription in response to F9 embryonal carcinoma stem cell differentiation.

Dramatic changes in the patterns of transcription are a common feature of early development. We have used F9 embryonal carcinoma cells as a model system to study gene regulation during an early stage of murine embryogenesis. We find that transcription by RNA polymerase I decreases when F9 cells differentiate into parietal endoderm. The reduced rate of transcription is associated with a down-regulation of several components of the class I transcription apparatus. The most substantial change involves the essential factor SL1, which is a multisubunit complex that contains the TATA-binding protein and three TATA-binding protein-associated factors (TAFs). The abundance of two of these TAFs, TAFI48 and TAFI95, decreases during F9 cell differentiation. Developmental regulation of a specific class of genes may therefore be achieved through changes in the availability of TAFs.

Animals↗