PubMed Health⌕ Search

Biomedical subjects

N Colburn

Publications and source records attributed to N Colburn.

14 recordsLinked to original sources
PubMed1999

Transgenic mice demonstrate AP-1 (activator protein-1) transactivation is required for tumor promotion.

Activator protein-1 (AP-1) is a transcription factor that consists of either a Jun-Jun homodimer or a Jun-Fos heterodimer. Transactivation of AP-1 is required for tumor promoter-induced transformation in mouse epidermal JB6 cells and for progression in mouse and human keratinocytes. Until now, the question of whether AP-1 transactivation is required for carcinogenesis in vivo has remained unanswered, as has the issue of functionally significant target genes. To address these issues we have generated a transgenic mouse in which transactivation mutant c-jun (TAM67), under the control of the human keratin-14 promoter, is expressed specifically in the basal cells of the epidermis where tumor induction is initiated. The keratin-14-TAM67 transgene was expressed in the epidermis, tongue, and cervix, with no apparent abnormalities in any tissue or organ. TAM67 expression blocked 12-O-tetradecanoylphorbol 13-acetate (TPA, phorbol 12-tetradecanoate 13-acetate) induction of the AP-1-regulated luciferase in AP-1 luciferase/TAM67 mice, but did not inhibit induction of candidate AP-1 target genes, collagenase-1 or stromelysin-3. More interestingly, TAM67 expression did not inhibit TPA-induced hyperproliferation. In two-stage skin carcinogenesis experiments, the transgenic animals showed a dramatic inhibition of papilloma induction. We conclude that transactivation of a subset of AP-1-dependent genes is required for tumor promotion and may be targeted for cancer prevention.

Animals↗
PubMed1998

Shortage of mitogen-activated protein kinase is responsible for resistance to AP-1 transactivation and transformation in mouse JB6 cells.

The JB6 mouse epidermal cell system, which includes tumor promotion-sensitive (P+) and tumor promotion-resistant (P-) cells, is a well-established and extensively used cell culture model for studying the mechanism of late-stage tumor promotion. Tumor promoters, such as 12-O-tetradecanoylphorbol 13-acetate (TPA) or epidermal growth factor (EGF), induce high levels of activator protein 1 (AP-1) activity and large, tumorigenic, anchorage-independent colonies in soft agar at a high frequency in JB6 P+ cells, but not in JB6 P- cells. We report here a molecular explanation for the defect in the AP-1 activation and promotion-resistant phenotype of P- cells. We demonstrate that the lack of AP-1 activation and cell transformation responses to TPA and EGF in P- cells appears attributable to the low level of mitogen-activated protein kinase (MAPK) (extracellular signal-regulated protein kinase, Erk) in these cells. TPA and EGF induce transactivation of AP-1 activity in P+ cells but not in P- cells. Nonphosphorylated forms and TPA- or EGF-induced phosphorylated forms of Erks (Erk1 and Erk2) in P- cells were much lower than those in P+ cells. Stable transfection of wild-type MAPK (Erk2) into P- cells restored its response to TPA and EGF for both AP-1 activation and cell transformation. These results suggest that the shortage of MAPK (Erk1 and Erk2) appears to be an important contributor to the tumor promotion-resistant phenotype in JB6 cells.

Animals↗
PubMed1996

Drug-induced reversion of progression phenotype is accompanied by reversion of AP-1 phenotype in JB6 cells.

Transformed JB6 cells can be stably reverted to nontransformed phenotype by AP-1 inhibiting gluccorticoid fluocinolone (FA) and cAMP elevator forskolin (FN), yielding stable revertants of promotion resistant (P-) and promotion sensitive (P+) phenotypes. AP-1 activity of nontransformed P- and P+ revertant clones was decreased under a variety of experimental conditions compared with their transformed counterparts. Moreover, AP-1 activity in P+ cells under anchorage-independent conditions was induced by 12-0-tetradecanoyl-phorbol-13-acetate (TPA) while AP-1 activity in the reverted P- cells was not induced, just as observed for the original P+ and P- variants. Taken together these data suggest that changes in AP-1 activity may be one key mediator not only of forward progression but also of reversion of tumor cells to nontransformed phenotype. In addition, the higher transfection efficiency of the new reverted P- and P+ cells renders them useful for studying the role of transcription factors in tumor promotion.

3T3 Cells↗
PubMed1994

p130/pRb2 has growth suppressive properties similar to yet distinctive from those of retinoblastoma family members pRb and p107.

The retinoblastoma tumor suppressor gene product, as well as its related protein p107, has been shown clearly to exert its growth suppressive effects in a cell cycle dependent manner. In this study we demonstrate that the introduction of our recently cloned Rb family member p130/pRb2 causes growth arrest in three tumor cell lines. In addition, in the nasopharyngeal carcinoma derived cell line HONE-1, we identified a low level of expression of p130/pRb2, possibly due to gene rearrangement, and a drastic reduction in proliferation upon introduction of a constitutive active p130/pRb2 complementary DNA clone. Furthermore, we were able to dissect distinct properties of the Rb family by demonstrating that p130/pRb2 inhibits proliferation of the glioblastoma cell line T98G, which is resistant to the growth suppressive effects of both pRb and p107. Our studies demonstrate that the Rb family proteins identified to date may complement each other but they are not fully functionally redundant.

Cell Division↗
PubMed1993

Progression toward tumor cell phenotype is enhanced by overexpression of a mutant p53 tumor-suppressor gene isolated from nasopharyngeal carcinoma.

We recently reported the detection of a heterozygous G-->C point mutation at codon 280 of p53 in nasopharyngeal carcinoma, which causes an Arg-->Thr substitution. To test whether this mutant p53 has gained function as an oncogene, we overexpressed the mutant p53 in nontumorigenic cells of two model systems: (i) human Saos-2 cells lacking endogenous p53 and (ii) mouse JB6 variants that bear endogenous wild-type p53. Although they have no growth advantage over the neomycin controls in monolayer culture, human Saos-2 transfectants overexpressing mutant p53 do show enhanced progression to tumor cell phenotype, as assayed by anchorage-independent growth and in vivo tumorigenicity. The enhancement is seen only in transfectants expressing higher levels of p53 protein. In the mouse JB6 system, the mutant p53 functions dominantly in the presence of endogenous wild-type p53 to enhance progression of preneoplastic promotion-sensitive cells toward anchorage-independent phenotype. Mouse JB6 transfectants of mutant p53 are, however, not tumorigenic in nude mice. We conclude from these studies that the G-->C point mutation of p53 at codon 280 is a gain-of-function mutation that appears to operate dominantly and that the mutant p53-thr280 has only moderate oncogenic activity. This mutation may cooperate with other yet-to-be isolated genes in the genesis of nasopharyngeal carcinoma.

Amino Acid Sequence↗
PubMed1993

No point mutation of Ha-ras or p53 genes expressed in preneoplastic-to-neoplastic progression as modeled in mouse JB6 cell variants.

Alterations of the p53 gene have been found in many human and animal tumors, and ras mutations have been seen somewhat less frequently. Loss of p53 tumor suppressor activity has been implicated in multistage tumor promotion/progression after initiation by Ha-ras or Ki-ras activation. Whether p53 or ras alterations occur during promotion of neoplastic transformation in JB6 cells has not been reported. Using a series of mouse JB6 variants representing different stages of progression toward the tumor-cell phenotype, we investigated whether mutational activation of Ha-ras and mutational inactivation and altered expression of the p53 gene occurred during progression. We report here that neither point mutations of the Ha-ras or p53 genes nor p53 structural alterations were involved in this process. Although there was no significant difference in steady-state levels of p53 mRNA, an elevated level of immunoprecipitable p53 protein was observed in a subset of transformed cells. We also report the detection of a second 2.2-kb p53-hybridizing transcript. This transcript was not translated into p53 protein and may be a nuclear precursor of the mature message. Both p53-hybridizing transcripts were downregulated by prolonged 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment (24 h) regardless of the stage of progression. We conclude from this study that in JB6 variants (1) mutational activation of Ha-ras and inactivation of p53 are unlikely to be involved in preneoplastic progression; (2) increased amounts of p53 protein may be involved in a subset of transformed cells, possibly reflecting a longer half-life, as demonstrated in other systems; and (3) late downregulation of p53 mRNA but not protein expression may be a secondary response in the TPA-mediated signal transduction pathway.

Animals↗
PubMed1993

Should motorcycles be operated within the legal alcohol limits for automobiles.

A motorcycle simulator was used to assess operating performance of 14 experienced motorcyclists with varying breath alcohol concentrations. Riding error scores in three defensive and evasive maneuvers plus distance traveled in a standard time period were documented at baseline and at predetermined intervals following controlled alcohol consumption. The results revealed a positive correlation between total errors and breath alcohol concentrations within a range well below the commonly accepted legal limit of intoxication of 0.10 mg/dL. There was a highly significant increase (p < 0.0055) in an operator's tendency to leave the roadway (an error that is frequently fatal for motorcyclists), as well as a reduction in ability to complete a timed course. Moreover, performance errors increased while operators were "sobering up," a dramatic finding not heretofore established in previous studies. Since the present definition of the legal limit of intoxication for motorcyclists is based on automobile studies, noted increases in reaction time and performance errors support the hypothesis that "legal alcohol levels" should be lowered for motorcycle operators.

Adult↗
PubMed1985

Community-based team approach to the management of children with cleft palate.

The child born with a cleft palate may have many associated problems in feeding, respiration, dentition, hearing, speech, language, and intellectual development as well as in psycho-social development. If the cleft is associated with a specific craniofacial syndrome, other physical problems may be present such as cardiac, kidney, digital, and visual involvement. The need for an extensive treatment program can extend from birth through adulthood. Important to the successful habilitation of these children is the early involvement of a multitude of specialists working together with the family in a team approach. The primary task of the team is to make decisions concerning timing and sequence of intervention for each individual patient. Several models for the delivery of health care services to the patient with a cleft palate are now in use. A community-based team model will be described in this article as a unique approach to the management of this population and as one that may be implemented in a cost-effective manner in communities where cleft palate teams presently do not exist.

Child↗
PubMed1984

The SESL model.

Explore the source record for details and available documents.

Communication↗
PubMed1983

Hexose uptake as an indicator of JB6 mouse epidermal cell resistance to the mitogenic activity of TPA.

JB6 mouse epidermal cells have been selected for resistance to the tumor-promoting phorbol diester TPA for (1) the plateau density mitogenic (M) response, and (2) the promotion of tumor cell phenotype (P) response. The purpose of this study was to determine the relationship of hexose uptake to the two TPA-dependent processes. Monolayers of JB6 mouse epidermal cells showing one of four different phenotypes (M+P+, M+P-, M-P+, M-P-) were exposed to 60 nM [3H(G)]2-deoxy-D-glucose (2DG) with or without TPA (10 ng/ml) stimulation. The TPA mitogen-sensitive (M+P+/-) cells, when in logarithmic growth, had a lower basal 2DG uptake rate than TPA mitogen-resistant (M-P+/-) cells. At plateau density, however, only the M+P+ cells had a significantly lower basal rate. The M+ (TPA mitogen-sensitive) cells (with low basal rates), when preincubated with TPA, exhibited a two to threefold increase in 2DG uptake, while the M- (TPA mitogen-resistant) lines, which already showed elevated rates, remained unchanged. There was also a positive association between TPA mitogen sensitivity and slower growth rate. These results suggest that low hexose sugar uptake is related to TPA mitogen sensitivity, but not to promotion sensitivity. Hence the cell's ability to increase its uptake rate may be required for the cells to respond to mitogenic stimulation by TPA.

Animals↗
PubMed1982

Developmental disfluency and emerging grammar. I. Disfluency characteristics in early syntactic utterances.

Approximately 47,200 spontaneous utterances of four nonstuttering children were analyzed for the occurrence of developmental disfluency from the time of one-word utterances through the emergence of beginning syntax. Disfluency profiles were drawn for each child at each of four mean length of utterance (MLU) levels. The frequency of total disfluency and the frequency and distribution of specified disfluency types were computed. Variations were found among the children's profiles with systematic changes in disfluency profiles for the individual child at each succeeding MLU level. The observed changes were related to the psycholinguistic features of discourse, imitation, and grammatical complexity in the children's language development.

Child↗
PubMed1982

Developmental disfluency and emerging grammar. II. Co-occurrence of disfluency with specified semantic-syntactic structures.

From a corpus of over 47,000 spontaneous utterances from four nonstuttering preschool children who were beginning to use syntax, 4,881 multiword, disfluent utterances were identified. Semantic-syntactic structures were identified among the disfluent multiword utterances and differences in frequency of structures were examined. There was variability in the developmental disfluency of the individual children, but each child's pattern of disfluency was systematic across time. Developmental disfluency shifted across structures systematically for each child and appeared to reflect a "practice effect" for those children beginning to learn syntax. The co-occurrence of disfluency with specific syntactic structures supported the premise that developmental disfluency was more strongly attached to the syntax of utterances than to the production of particular words.

Child Language↗
PubMedDate not supplied

Phosphorylation status and function of P53 are inversely related to protein kinase C activation.

The role of phosphorylation in the regulation of p53 protein function is little understood. We have addressed the role of protein kinase C (PKC) in the phosphorylation. Exposure to the protein kinase inhibitor, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7), increased the phosphorylation of wild type p53 protein, whereas exposure to the tumor promoter phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), decreased it in vivo following 3 hours incubation with mouse epidermal JB6 cells. Exposure to the c-AMP dependent protein kinase (PKA) activator, forskolin, did not decrease the phosphorylation of p53 protein. In the transient transfection/luciferase reporter transactivation assay, H7 modestly increased the mouse double minute (MDM) 2 reporter transactivation activity of p53 protein after 24 hours treatment, and TPA completely blocked it. These results suggest that the accelerated phosphorylation of wild type p53 protein is inversely related to PKC activation, and that p53 phosphorylation may have some relation to transcription factor function.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗