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Biomedical subjects

A C Johnson

Publications and source records attributed to A C Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1997

Trochaic template use in early words and phrases.

The speech of twenty normally developing children whose linguistic development spanned four MLU stages was recorded. The weak syllable productions in their spontaneous and elicited words and phrases were examined. The children demonstrated more frequent use of weak syllables that occurred in trochaic (strong + weak) than iambic (weak + strong) patterns. The constraint on iambs was not absolute; even children in MLU Stage I produced weak syllables in iambs occasionally. Also, it was not a constraint on lexical representations as the same pattern was evinced for word combinations. Weakly stressed articles were omitted significantly more often from noun phrases that were iambic than from those that were trochaic. These data suggest that a pattern of the form strong syllable + optional weak syllable [S(W)] serves as a template for multisyllabic productions, whether mono- or multimorphemic. With increasing MLU, S(W) template use declined and control of timing distinctions between weak and strong syllables became more adult-like. We conclude that the trochee may function as either an optimal representational unit or as an optimal timing unit for early syllable sequences. The trochaic template is invoked when the complexity of an intended utterance exceeds the child's resources for planning and production.

Child Language↗
PubMed1997

Re-examination of 5' end of cDNA of transcription factor GCF.

N-terminal region of transcriptional factor GCF was re-examined as the published amino acid sequence is extremely basic. 5'Rapid Amplification of cDNA End (5' RACE) analysis was performed and the result revealed that sequence of the first 308 bases of published GCF cDNA does not conform to the one obtained by 5' RACE. Sequence of genomic GCF DNA is consistent with the new cDNA sequence but not with the published one. Results of ordinal RT-PCR analyses are consistent with that of 5' RACE.

Base Sequence↗
PubMed1996

Activation of epidermal growth factor receptor gene transcription by phorbol 12-myristate 13-acetate is mediated by activator protein 2.

The response of the epidermal growth factor (EGF) receptor gene to phorbol 12-myristate 13-acetate (PMA) was analyzed using nuclei and nuclear extracts prepared from PMA-treated KB cells. Transient transfection assays and nuclear run-off experiments showed that PMA increased EGF receptor gene transcription. Cell-free transcription with promoter mutants revealed that the region of the promoter containing nucleotides -150 to -16 was sufficient for PMA inducibility. A promoter fragment containing nucleotides -167 to -105 showed increased binding of a factor present in extracts prepared from PMA-treated cells. When this factor was partially purified by column chromatography, it showed specific PMA-dependent binding to an EGF receptor promoter fragment. This binding was competed by an SV40 fragment containing binding sites for Sp1, AP1, and AP2. Purified AP2 was used in DNase I footprinting experiments to show that this factor can bind to the EGF receptor promoter. Oligonucleotides corresponding to the AP2 binding sites found in the EGF receptor promoter showed the ability to bind AP2 and compete for the binding of a factor induced by PMA treatment. The addition of AP2 to nuclear extract resulted in increased transcription from the EGF receptor promoter. These results demonstrate that AP2 can activate EGF receptor gene expression and may mediate the PMA response of this gene.

Base Sequence↗
PubMed1995

Auditory and vestibular functions after single or combined exposure to toluene: a review.

Toluene is a widely used organic solvent, heavily employed in many manufacturing industries. Recently, evidence has begun to accumulate on the deleterious effect of toluene exposure has on the auditory and vestibular systems. Although little published information exists regarding these effects, the reported findings indicate a need for further investigation. The results of such investigations may dramatically affect occupational hearing conservation practices and legislation. Both human and animal studies will be summarized in discussing the effects of toluene alone or in combination with noise or other chemicals. Gaps in scientific knowledge are highlighted to assist future research.

Animals↗
PubMed1995

Function of the auditory system, the visual system, and peripheral nerve and long-term combined exposure to toluene and ethanol in rats.

Male pigmented rats (n = 36) were exposed to toluene and/or ethanol (1000 p.p.m. toluene in the inhaled air 21 hr/day, and 5.7-8.0% ethanol in the drinking water continuously) during 8 weeks. Electrophysiological recordings were made 1 week after the exposure. Auditory sensitivity (auditory brainstem response) was reduced only after exposures including toluene. At 20 kHz, ethanol antagonized toluene-induced loss of auditory sensitivity (P < 0.05). Flash evoked potentials were not affected in any group. In peripheral nerve, exposures containing ethanol were followed by increased amplitudes of nerve and muscle action potentials. Exposures including toluene were followed by an increase in liquid consumption.

Animals↗
PubMed1995

Biochemical characterization of human GCF transcription factor in tumor cells.

GCF is a transcriptional regulator that was found to repress transcription of the epidermal growth factor (EGF) receptor and several other genes and is encoded by a 3-kb mRNA (R. Kageyama and I. Pastan, Cell, 59: 815-825, 1989; A. C. Johnson et al., J. Biol. Chem., 267: 1689-1694, 1992). To identify and characterize the GCF gene product at the cellular level, we have developed antibodies against a bacterially expressed GCF fusion protein. GCF antibodies recognize GCF present in extracts from human cells and causes a "supershift" of a protein DNA complex containing a GCF oligonucleotide binding site. The major form of GCF has a molecular weight of approximately M(r) 97,000, identical to that of GCF transiently expressed in CV1 cells by the vaccinia virus system. In addition, other less abundant species with slightly higher and lower apparent molecular weight are specifically recognized, suggesting extensive posttranslational modification. GCF is highly expressed in EGF receptor-negative human cell lines (HUT102, U266, and CA46) and in lower amounts in several EGF receptor-expressing cells (KB, A431, TMK, and HeLa). Cell fractionation studies indicate that GCF is predominantly localized in the nucleus. GCF is a stable protein with a relatively long half-life. In addition, GCF is a phosphoprotein, and the phosphorylated form is found to be associated with the nuclear compartment in both HUT102 and KB cells. Phosphorylation occurs on serine and threonine residues and is stimulated by okadaic acid, phorbol myristate acetate, and cyclic AMP, but not vanadate.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗
PubMed1994

Identification of an epidermal growth factor receptor transcriptional repressor.

Identification of the factors controlling transcription of the epidermal growth factor (EGF) receptor gene is essential for understanding regulation of the EGF receptor and its overexpression in human carcinomas. In this study, we have identified a 60-base pair (bp) region (-919 to -860) relative to the AUG translation initiation codon in the EGF receptor 5' promoter that functions as a cis-acting EGF receptor transcriptional repressor (ETR). This fragment also acted as a repressor when linked to the thymidine kinase promoter. Gel mobility shift assays demonstrated that trans-acting factors bind to 60- and 19-bp fragments. Competition and chloramphenicol acetyltransferase assays with oligonucleotides containing mutations and deletions in this region indicate that the TTCGAGGG sequence (-877 to -870) is required for binding as well as repressor activity. While the ETR-protected region contains consensus sequences for the E2F binding site, no competition was observed with an E2F binding fragment. However, DNA-protein blot analysis indicates that both the 60- and 19-bp fragments specifically bind a 128-kDa polypeptide in extracts from HeLa or A431 human epidermoid carcinoma cells. These results suggest that a novel transcription factor(s) negatively regulates EGF receptor gene expression through binding to the ETR element.

Base Sequence↗
PubMed1994

Progressive hair cell loss induced by toluene exposure.

Rats were exposed to toluene by inhalation (1400 ppm, 16 h/d, 8 days) and sacrificed for morphological investigations at 3 and 5 days after the start of the exposure, and 4 days and 6 weeks after the end of the exposure. The cochleae were removed and prepared for light microscopy and scanning electron microscopy. After 3 days of toluene exposure no loss of hair cells was found. A slight loss in the third row outer hair cells was observed after 5 days of exposure. Four days after the 8-day long exposure a loss of hair cells was found in all 3 rows of outer hair cells, mainly in the middle and upper turns of the cochlea. Six weeks post-exposure the damage on the hair cells had progressed towards the basal part of the cochlea, and a 50-100% loss of outer hair cells together with some loss of inner hair cells were seen. A fairly good correlation was found between the frequency regions showing loss of hair cells and the threshold shifts previously measured by auditory brainstem responses and distortion product otoacoustic emissions in the same rats at corresponding times (Johnson and Canlon, 1994). These results indicate that the outer hair cells in the middle frequency region of the cochlea, were primarily affected by toluene exposure. However, after a long post-exposure period the damage extended basally and apically and some damage to the inner hair cells was seen.

Acoustic Stimulation↗
PubMed1994

Toluene exposure affects the functional activity of the outer hair cells.

Rats were exposed to toluene by inhalation (1400 ppm, 16 h/d, 8 days) and the auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOEs) were used as measures of the auditory sensitivity. These measurements were made before the exposure to toluene, 3 and 5 days after the start of the exposure and 4 days after the end of the exposure. To quantify the repeated DPOE data the area under the curve of the DPOE amplitudes versus the stimuli levels was calculated and used for statistical analysis. Results demonstrate that 3 days of toluene exposure tended to lower DPOE amplitudes and elevate ABR thresholds. Similarly after 5 days of exposure significantly lower DPOE amplitudes were observed at most frequencies along with elevated ABR thresholds. At 4 days post-exposure DPOE amplitudes were greatly diminished at all frequencies and the ABR thresholds were raised by about 40 dB between 1.6 and 20 kHz. These results show a parallel shift between ABR thresholds and DPOE amplitudes during toluene exposure. Furthermore, the results from the DPOE measurements indicate that mainly the outer hair cells are adversely affected by toluene exposure.

Administration, Inhalation↗
PubMed1994

Function of the auditory and visual systems, and of peripheral nerve, in rats after long-term combined exposure to n-hexane and methylated benzene derivatives. I. Toluene.

Rats were exposed to n-hexane, toluene, or toluene together with n-hexane, each solvent 1000 p.p.m. (1000 + 1000 p.p.m. in combined exposure), 21 hr/day, 7 days/week during 28 days. Neurophysiological recordings were made 2 days, 3 months, and one year after end of exposure. A reduction in auditory sensitivity, recorded by click evoked auditory brainstem response, was observed 2 days after exposure to toluene alone, or to toluene together with n-hexane, but not after exposure to n-hexane alone. The reduction lasted one year after the exposure. Three months after combined exposure, a synergistic enhancement of loss of auditory sensitivity was observed in the mixed exposure group. One amplitude in the flash evoked potentials was lowered in the n-hexane exposed group 2 days after exposure. No such reduction was seen after simultaneous exposure to toluene. Exposure to n-hexane alone caused a marked decrease in peripheral nerve conduction velocity 2 days and 3 months after exposure, while exposure to n-hexane together with toluene had only a small effect on this velocity.

Action Potentials↗
PubMed1994

Induction of epidermal growth factor receptor gene transcription by transforming growth factor beta 1: association with loss of protein binding to a negative regulatory element.

Transforming growth factor beta (TGF-beta) is a potent modulator of cell growth in many systems. In normal rat kidney fibroblasts, TGF-beta 1 increases epidermal growth factor (EGF) receptor gene transcription and synergizes with EGF to stimulate growth in soft agar, a characteristic of the transformed phenotype. In order to identify the target of TGF-beta 1 action, we have used a series of 5' deletion mutants of the EGF receptor promoter linked to a chloramphenicol acetyltransferase reporter gene (ERCAT). The TGF-beta response element(s) was localized to a cis-regulatory region which resides between positions -919 and -860 relative to the ATG translation initiation codon of the EGF receptor promoter. This 60-base pair region contains a repressor of the EGF receptor promoter and a TGF-beta inhibitory element that mediates TGF-beta 1 suppression of transin/stromelysin gene transcription through binding of a Fos-containing protein complex. Cotransfection of c-fos, c-jun, or both expression vectors with the intact or 5'-deleted ERCAT constructs identified several Fos-responsive inhibitory regions within the EGF receptor promoter, but these did not localize to the -919 to -860 promoter region. Mobility shift assays showed binding of the 60-base pair DNA fragment to proteins in extracts from untreated normal rat kidney cells; the binding was specifically competed by oligonucleotides containing a CAGATG sequence but not by oligonucleotides containing the EGF receptor repressor or the TGF-beta inhibitory element. TGF-beta 1 treatment but not anti-Fos antibody caused a decrease in specific 60-base pair DNA-protein complex formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effect of exposure to 2,5-hexanediol in light or darkness on the retina of albino and pigmented rats. I. Morphology.

Male albino (Sprague Dawley) and pigmented (Norwegian Brown) rats received 1% 2,5-hexanediol (H) in their drinking water for 5 or 8 weeks, respectively. The rats were housed either in 12 h light (average 30 cd/cm2 inside cage) and 12 h darkness (group LH) or in total darkness (group DH). Two control groups (Light only, LC; Darkness only, DC) were studied in parallel under identical conditions. The animals were sacrificed at the end of H exposure or after an ensuing 13-week period without H but under the same lighting conditions. The retinas of albino rats in the LH group showed a reduction (compared to the LC, DH and DC groups) in the number of nuclei per unit area of the outer nuclear layer (ONL; p < 0.05) and degeneration of the outer segment and the inner segment layers (photoreceptor cells). A less pronounced loss of nuclei was seen in the LC group. No decrease in the number of nuclei, or signs of degeneration, were demonstrated in the albino DH or DC groups. Thirteen weeks after exposure to H, the albino LH rats had lost about 50% of the nuclei in the ONL (p < 0.05) and the outer plexiform layer (OPL) had almost disappeared. At the corresponding time, in the pigmented rats the LH and DH groups differed from the LC and DC groups. The degenerative process resulted in no inflammatory changes in the retina. The results imply an interaction exceeding simple summation after exposure to light and H, in destroying photoreceptors and OPL (p < 0.001) in albino rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effect of exposure to 2,5-hexanediol in light or darkness on the retina of albino and pigmented rats. II. Electrophysiology.

Albino (Sprague-Dawley) and pigmented (Norwegian Brown) male rats were exposed to 2,5-hexanediol (H; 1%) in their drinking water for 5 or 8 weeks, respectively. Half of the rats of each strain were housed in light (average 30 cd/cm2 inside cage, 12 h/day); the other half was kept in constant darkness. Control groups were studied in parallel under identical conditions but without H. Electrophysiological recordings were made 2-5 days and 13 weeks after the end of the exposure to H. Alterations in the visual system, as measured by electroretinography and visual evoked response, were found in groups of albino rats exposed to H and/or light. The pupillary diameter was enlarged in the albino group exposed to both H and light. Among the pigmented rats, alterations were recorded only in the visual evoked response of the H exposed groups. The results demonstrate that simultaneous exposure to H and light can lead to alterations in visual function that are more severe than those induced by each agent alone, and may exceed a simple summation.

Animals↗
PubMed1993

The ototoxic effect of toluene and the influence of noise, acetyl salicylic acid, or genotype. A study in rats and mice.

Toluene is a widely used organic solvent causing loss of auditory sensitivity in rats and presumably in humans. Also, the hearing loss in humans occupationally exposed to noise has been reported to be aggravated by simultaneous exposure to solvents. The aim of the present investigation was to study the effects of toluene, alone or in combination with other factors, on auditory sensitivity. The influence of acoustic trauma and of acetyl salicylic acid (ASA) on toluene induced auditory sensitivity loss in the rat, as well as the influence on age-related auditory sensitivity loss in two genotypes of mice were studied. An attempt was also made to identify cochlear structures damaged by toluene. Rats or mice were exposed to toluene by inhalation during 1 or 2 weeks. Rats were exposed to noise before or after the toluene exposure, or exposed to ASA by gavage simultaneously with toluene. The effect on auditory sensitivity was measured by frequency specific auditory brainstem response (ABR) between 1.6 and 20 kHz. In the investigations concerning the site of the toluene induced impairment, distortion product otoacoustic emissions (DPOEs) and morphological techniques were used. A permanent loss of auditory sensitivity, as measured by ABR, with the maximal threshold shifts between 6.3 and 12.5 kHz, was found in rats after exposure to toluene. In addition, lowered amplitudes of the DPOEs were recorded, implying that the outer hair cells (OHCs) were affected by toluene. A morphological study confirmed that toluene mainly affects the OHCs. A potentiated loss of auditory sensitivity was seen when toluene had preceded the noise exposure. When the exposure sequence was reversed, i.e. noise preceded toluene, an additive effect was observed. ASA, itself known to cause a reversible auditory impairment, was found to enhance the loss of auditory sensitivity caused by simultaneous toluene exposure. Finally, toluene exposure accelerated the age-related hearing loss in C57BL/6J mice. In conclusion, toluene causes a characteristic mid-frequency auditory damage. The OHCs are particularly susceptible to toluene exposure. The auditory sensitivity loss induced by toluene can be enhanced by ASA and by ensuing noise exposure. Also, toluene exposure can influence the rate of progress of age-related hereditary loss of auditory sensitivity.

Analysis of Variance↗
PubMed1993

GC factor represses transcription of several growth factor/receptor genes and causes growth inhibition of human gastric carcinoma cell lines.

The GC factor (GCF) binds to specific GC-rich sequences in the epidermal growth factor receptor (EGFR) gene promoter and represses its transcription. In this study, by the use of GCF transfection, we examined whether GCF represses the gene expression of several other growth factors and receptors and causes growth inhibition of cancer cells. The transfection of GCF expression vector into gastric carcinoma cell lines (TMK-1 and MKN-28) decreased the mRNA levels of transforming growth factor (TGF) alpha, insulin-like growth factor II, and c-met. The reduction of TGF-alpha expression was confirmed at the protein level by enzyme-linked immunosorbent assay. Transfection of GCF expression vector interfered with the mRNA accumulation for EGFR and TGF-beta induced by epidermal growth factor in gastric carcinoma cell lines. The carcinoma cells transfected with GCF expression vector did not grow in a serum-free medium, whereas the control cells did grow under serum-free conditions. When the growth of the gastric carcinoma cell lines was studied in nude mice, GCF-transfected carcinoma cells showed a significantly slower growth compared to the control tumor. Transient cotransfection analysis with NIH3T3 cells revealed that GCF repressed the promoter activity of TGF-alpha in addition to EGFR. These findings indicate that GCF negatively regulates gene expression of not only the EGFR but also several other growth factor and receptor genes and can inhibit the growth of gastric carcinomas in immunodeficient mice.

Animals↗
PubMed1992

Insulin increases transcription of rat gene 33 through cis-acting elements in 5'-flanking DNA.

Gene 33 is a multihormonally-regulated rat gene whose transcription is rapidly and markedly enhanced by insulin in liver and cultured hepatoma cells. To examine the mechanism by which insulin regulates transcription, we have constructed chimeric plasmids in which expression of the bacterial cat gene, encoding chloramphenicol acetyltransferase (CAT), is governed by gene 33 promoter elements and contiguous sequences in DNA flanking the transcription start point (tsp). When transfected into H4IIE hepatoma cells, these constructs gave rise to stably transformed cell lines producing the bacterial CAT enzyme. This expression was increased by insulin treatment in a fashion resembling the effect of this hormone on transcription of the native gene. In vitro transcription assays in nuclear extracts also revealed increased transcription of the chimeric plasmids when the extracts were prepared from insulin-treated rat hepatoma cells. The results demonstrate that induction by insulin is mediated by cis-acting nucleotide sequences located between bp -480 to +27 relative to the tsp.

Animals↗