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N H Colburn

Publications and source records attributed to N H Colburn.

14 recordsLinked to original sources
PubMed1992

The presence in a mouse T cell line of a 97-kDa protein kinase C (PKC) with characteristics similar to known members of the novel PKC subgroup and its possible role in lymphocyte gene expression.

The receptor for tumor-promoting phorbol esters has been shown to be the Ca+2/phospholipid dependent enzyme protein kinase C (PKC). There are two major groups of PKC, the conventional PKC isotypes alpha, beta I, beta II, gamma) and the novel Ca+2-independent PKC (delta, epsilon, zeta, eta). Phorbol esters previously have been demonstrated to increase human IFN-gamma gene expression after treatment of a murine T cell line (Cl 9) that has been transfected with human IFN-gamma genomic DNA. In contrast, treatment with Ca+2 ionophore alone or in combination with phorbol ester did not enhance IFN-gamma production in a synergistic manner above the level obtained with phorbol ester treatment alone. To determine whether the lack of effect of Ca+2 ionophore is due to a defect in PKC, we compared the level of PKC autophosphorylation in the mouse T cell line (Cl 9), a mouse epidermal cell line (JB6), and purified rat brain PKC by in vitro kinase assays. The results demonstrate that instead of the expected 80-kDa autophosphorylated PKC band seen in purified rat brain PKC or mouse JB6 cell lysates, only a novel 97-kDa Ca+2-independent phosphoprotein was observed in Cl 9 cells. To ascertain if there was any nucleic acid sequence similarity to PKC epsilon, we hybridized Cl 9 poly(A+) RNA with a cloned fragment of the PKC epsilon gene and observed two hybridizing RNA bands (4.4 and 4.0 kb). Our results suggest that the 97-kDa phosphoprotein is similar to, but not identical with, PKC epsilon and is the major PKC expressed in the Cl 9 murine T cell line. These data suggested that the 97-kDa PKC may be responsible for the induction of both the transfected human IFN-gamma gene and the endogenous murine IL-2R alpha-chain.

Animals↗
PubMed1992

An infrequent point mutation of the p53 gene in human nasopharyngeal carcinoma.

Point mutations in the p53 gene have been detected in a variety of human cancers; the mutations are clustered in four "hot-spots" located in the coding region of exons 5, 7, and 8, which coincide with the four most highly conserved regions of the gene. We report the finding of a heterozygous G----C mutation at codon 280 (exon 8), position 2, of the p53 gene in a nasopharyngeal carcinoma (NPC) cell line, originating from Guangdong, a province in the People's Republic of China that leads the world in NPC incidence. A survey of nasopharyngeal tissues and NPC biopsies revealed that 1 out of 12 NPC samples from Hunan, another province in the People's Republic of China with high NPC incidence, had the same heterozygous mutation at codon 280 of p53, and none of 10 biopsies from Taiwan showed a mutation within exons 5-8 of the p53 gene. No other alteration of gene structure, including gross rearrangement or loss of heterozygosity or abnormality of gene expression was detected in NPC cell lines or NPC biopsies. We conclude from this study that mutational or other alterations of the p53 gene are not common in nasopharyngeal carcinogenesis and that a codon-280 mutation of p53 may be involved in less than 10% of NPC cases. This result contrasts with the relatively high frequency of p53 mutations associated with several other human carcinomas and suggests the importance of other genes in NPC genesis.

Base Sequence↗
PubMed1992

Acquisition of a growth-inhibitory response to phorbol ester involves DNA damage.

TPA (12-O-tetradecanoylphorbol-13-acetate), a potent tumor promoter, has been shown to stimulate or inhibit cell growth depending on the cell type investigated. We recently found that RT101 cells, a transformed mouse JB6 epidermal cell line, acquired a greater growth inhibition response to TPA during conventional subcultivation. The growth of low-passage RT101 cells was slightly inhibited by TPA in monolayer culture but stimulated in soft agar. In contrast, the growth of high-passage cells was greatly inhibited by TPA in both monolayer culture and in soft agar. Inhibition was dose dependent, directly correlated with protein kinase C-activating activities of tumor promoters, and was found to be reversible. TPA-treated high-passage cells were greatly reduced in volume, showed extensive abnormal mitoses, and were more susceptible to detachment. High-passage cells were also found to be less tumorigenic as indicated by in vivo tumorigenicity assay in nude mice. TPA treatment rendered cells still less tumorigenic in the case of both cell lines. The mechanism for acquisition of increased sensitivity to TPA of RT101 cells during subculture was investigated; it involved nonrandom DNA damage and detachment of nonviable cells. The results suggest the possibility that early-passage RT101 cells contained two subpopulations, one TPA-sensitive and one TPA-resistant population. Conventional subcultivation may have selected for the former subpopulation. The sensitive subpopulation may have been irreversibly inhibited as a result of TPA-induced cell killing, possibly apoptosis.

Animals↗
PubMed1992

Differential c-jun expression in response to tumor promoters in JB6 cells sensitive or resistant to neoplastic transformation.

The activity of AP-1, a trans-acting transcription factor, is stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA) and epidermal growth factor (EGF) in promotion-sensitive (P+) but not in promotion-resistant (P-) JB6 mouse epidermal cell lines. TPA and EGF also promote neoplastic transformation only in P+ cells. Thus, it has been proposed that AP-1-dependent gene expression is involved in determining sensitivity to tumor promotion. This paper explores the possible basis for the differential inducibility of AP-1 activity in P+ and P- JB6 cells, focusing in particular on the regulation of expression of the components of the AP-1 complex at the mRNA level. The expression of jun and fos gene family members, which make up the AP-1 complex, can be stimulated by serum and a number of growth factors, including EGF, and by TPA. Therefore, the possibility that differential expression of one or more forms of jun or fos contributes to the differential AP-1 activity was considered. The data presented here demonstrate both similarities and differences in the basal and TPA- or EGF-induced levels of fos and jun family members between P+ and P- cells. The most striking observation was that the overall TPA- and EGF-induced levels of jun but not fos expression were higher in P+ cells. This suggests that tumor promoter-regulated c-jun expression may contribute to the differential AP-1 activation observed in these cells and may be important in determining sensitivity to promotion of neoplastic transformation.

Animals↗
PubMed1992

12-O-tetradecanoylphorbol-13-acetate--induced levels of AP-1 proteins: a 46-kDa protein immunoprecipitated by anti-fra-1 and induced in promotion-resistant but not promotion-sensitive JB6 cells.

Neoplastic transformation and transcriptional activation by activator protein-1 (AP-1) complex are stimulated by tumor-promoting agents in promotion-sensitive (P+) but not promotion-resistant (P-) mouse epidermal JB6 cells in culture. This implicates AP-1 as a specific regulator of signal transduction pathways in the promotion phase of neoplastic transformation. We therefore hypothesized that the defective P- responsiveness may be due to limiting levels of AP-1 protein components in those cells. In this investigation, steady-state levels of AP-1 protein components were measured by immunoprecipitating proteins from 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated P+ and P- cells to discern what may limit the AP-1 response. Whereas the AP-1 proteins junB, junD, and fosB did not show differential basal or TPA-inducible levels in P+ and P- cells, a 46-kDa species precipitated by anti-fra-1 antibody was TPA-inducible in P- cells but not in P+ cells, and c-jun protein was present at higher levels in TPA-treated and untreated P+ cells than in P- cells. These data raise the possibility that the 46-kDa fra-1-related protein may be a negative modulator of AP-1 activity and suggest that elevated levels of this 46-kDa species and limiting levels of c-jun may significantly impair AP-1 function or transformation response in P- cells or both.

Amino Acid Sequence↗
PubMed1992

A simple method using PCR for direct sequencing of genomic DNA from frozen tumor tissue embedded in optimal cutting temperature compound.

Described here is a three-day protocol that directly yields DNA sequence after isolating and PCR amplifying genomic DNA from a small sample of frozen nasopharyngeal carcinoma tissue embedded in optimal cutting temperature (OCT) compound. The method is consistently successful, reproducible and will facilitate the rapid analysis of DNA sequence from very small samples.

Base Sequence↗
PubMed1992

Differential induction of 15 and 16 kDa nuclear proteins in promotion sensitive and promotion resistant mouse JB6 cells.

Gene expression relevant to promotion of neoplastic transformation was investigated by measuring proteins differentially synthesized in two mouse epidermal JB6 cell lines sensitive (P+) or resistant (P-) to tumor promoter induced transformation. One dimensional polyacrylamide gel electrophoresis of proteins from cells that had been pulse labeled with 35S-methionine after various times of exposure to the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) revealed two protein bands whose intensity increased after 20-24 hr exposure to TPA. Cell fractionation showed that these proteins of 15 and 16 kDa were localized in the nuclear, not the cytosolic, fraction. Parallel studies with 32P-labeled cells showed no evidence for phosphorylation of these proteins. Comparison of P- with P+ cells showed that the observed induction of p15/16 synthesis at 20 hr was specific for P+ cells, with little evidence for stimulated synthesis in P- cells during a 48 hr period. We thus conclude that the tumor promoter produces a late stimulation in the rate of synthesis of 15 and 16 kDa nuclear proteins preferentially in promotion sensitive cells.

Animals↗
PubMed1991

Synergistic inhibition of phorbol ester-induced transformation of JB6 cells by transforming growth factor-beta and retinoic acid.

Transforming growth factor-beta (TGF-beta) plays a complex role as a regulator of proliferation and differentiation of many cell types, including cells of epithelial origin. In this study, we examined whether TGF-beta, alone or in combination with retinoic acid, was able to inhibit the transformation of the murine epidermal cell line JB6. When treated with phorbol myristate acetate (PMA) and other tumor promoters, the nontumorigenic and anchorage-dependent JB6 cells acquired a tumor phenotype, as shown by the acquisition of tumorigenicity and anchorage independence. We found that TGB-beta inhibited the PMA-induced transformation of a subclone of JB6 cells. The effect of TGF-beta was due to an anti-transformation promoting activity, rather than to generalized growth inhibition, since TGF-beta neither inhibited the growth of monolayer cultures of JB6 cells, nor affected the colony-forming efficiency in agar of the JB6-derived permanently transformed RT101 cell line. TGF-beta was synergistic with retinoic acid, a known anti-tumor promoter, in inhibiting the PMA-induced transformation of JB6 cells. Examination of TGF-beta receptor expression on JB6 cells, by both binding and affinity labeling, showed that treatment with PMA significantly decreased TGF-beta receptor expression while retinoic acid counteracted this effect of PMA, thus suggesting that the synergy between retinoic acid and TGF-beta may be due, at least in part, to modulation of TGF-beta receptor expression. TGF-beta, therefore, appears to function as an incomplete antipromoter whose action can be permitted and/or complemented by retinoic acid. Our data demonstrating that TGF-beta has anti-transformation promoting activity suggest that TGF-beta plays a role in maintaining homeostasis of epithelial cells, not only by regulating cell proliferation and differentiation, but also by counteracting events that lead to malignant transformation.

Animals↗
PubMed1991

Isolation and partial characterization of a transformation-associated sequence from human nasopharyngeal carcinoma.

A transforming activity associated with Chinese nasopharyngeal carcinoma (NPC) cell line CNE2 DNA has been identified by transfer into nontransformed promotion-sensitive mouse JB6(P+) C141 cells. To clone this transformation-associated sequence, we carried out three cycles of transfection, followed by cloning of anchorage-independent transformants in soft agar. A tertiary CNE/JB6 clonal transfectant cell line 625 whose DNA showed transforming activity, as indicated in both soft-agar assay and nude-mice implantation, was used to make a genomic library in the vector lambda dash. Using the human repeated sequence Blur 8 to screen the library, we obtained 10 human Alu-positive clones. A cloned Alu-positive insert of 16 kbp, CNE 323, was characterized in detail. CNE 323 transferred moderate transforming activity when introduced into JB6 P+ cells and showed no homology to Ha-, Ki-, or N-ras genes; human promotion sensitivity genes; src, myb, jun, myc, fos, raf, or int-2 oncogenes; or epidermal growth factor receptor. The isolated CNE 323 DNA sequence appeared to preserve the genomic structure of the original sequence found in CNE2 cells and in nude mouse tumors induced by CNE2 cells or by CNE/JB6 transfectant cells, indicating that the cloned NPC sequence was activated during NPC carcinogenesis and not during transfection or construction of the library, and that the cloned sequence or a larger sequence of which it was part played a role in tumor formation. Finally, we identified a 1.3-kb mRNA that hybridizes to a subclone of the 16-kb NPC sequence in CNE2 cell poly (A)+ RNA.

Animals↗
PubMed1991

Gene regulation and genetic susceptibility to neoplastic transformation: AP-1 and p80 expression in JB6 cells.

The mouse epidermal JB6 cell system consists of clonal genetic variants that are sensitive (P+) or resistant (P-) to the promotion of neoplastic transformation by phorbol esters and other tumor-promoting agents. P+ cells display AP-1-dependent phorbol-ester-inducible transactivation of gene expression, whereas P- cells have a defect in transactivation. Transfection of promotion sensitivity gene pro-1 into P- cells reconstituted both P+ phenotype and AP-1-dependent phorbol-ester-inducible transactivation. P- and P+ cells exhibited induction of c-jun and c-fos messenger RNA levels by phorbol ester, but P- cells had significantly lower basal and induced levels of jun mRNA than P+ cells. Basal and induced levels of c-jun protein were significantly lower in P- cells as well. Differences in levels the 80-kDa pI 4.5 protein p80 were also observed in JB6 cells as a function of preneoplastic progression; high levels of p80 protein and mRNA were observed in P- cells, intermediate levels in P+ cells, and negligible levels were observed in transformed derivatives of JB6 cells. Phorbol ester treatment induced phosphorylation but not synthesis of p80. These data are consistent with the hypotheses that AP-1 is required in the signal transduction pathway for promotion of neoplastic transformation by tumor promoter, that pro genes may control AP-1 activity, that threshold levels of Jun mRNA and protein may play a role in transactivation and promotion sensitivity, and that the p80 protein in JB6 cells may behave in vivo as a suppressor of cellular transformation.

Amino Acid Sequence↗
PubMed1990

Deletion mapping of tumor promotion-susceptibility gene pro1 implicates an RNA polymerase III transcription unit.

The murine gene pro1 has been cloned from JB6 epidermal cell lines that are sensitive to neoplastic transformation by tumor promoters. Insensitive JB6 variants acquire susceptibility to neoplastic transformation by tumor promoters when transfected with pro1. The repetitive nature of pro1 was indicated by sequence and Southern analysis. In contrast, northern analysis of RNA from promotion-sensitive cells revealed the presence of a small pro1-hybridizing transcript. Strand-specific RNA probes implicated an RNA polymerase III (RNAPIII) coding domain in pro1 as the source of this hybridization signal. Ribonuclease protection of gel-purified pro1 RNA from JB6 variant cell lines identified a 130-nucleotide transcript. The size of this transcript is compatible with in vitro RNAPIII transcription of pro1. Deletion mapping of pro1 by exonuclease III demonstrated that the biologically active domain included the RNAPIII transcription unit. RNA probes map pro1 RNA within the activity domain. These results delineate an activity domain of 597 nucleotides and suggest that a small RNA is the product of promotion-sensitivity gene pro1.

Alleles↗
PubMed1975

Decrease of epidermal histidase activity by tumor-promoting phorbol esters.

The potent skin tumor promoter (12-O-tetradecanoyl phorbol-13-acetate (TPA) stimulates epidermal macromolecular synthesis as well as proliferation, but little is known of specific functional aberrations produced by TPA. This report presents results of a study on the effects of TPA on epidermal histidase (L-histidine ammonia lyase), an enzyme found in normal epidermis but not in dermis or in mouse squamous cell carcinomas. Histidase activity was assayed on postmitochondrial supernatants obtained from hairless mouse epidermis after removal by keratotome. Topical TPA treatment at doses active in tumor promotion (1.7 to 17.0 nmoles/application) produced dose-dependent decreases in epidermal histidase specific activity at 19 hr posttreatment. The onset of the decrease occurred at 12 hr with recovery to control level specific activity by 5 days, showing kinetics similar to those obtained for stimulation of DNA synthesis. This decrease in histidase could not be attributed to a general inhibition of soluble protein synthesis or to the appearance of an inhibitor of histidase activity. The strong promoter TPA produced a greater histidase decrease than did the moderate promoter and mitogen 12,13-didecanoyl phorbol at equimolar dose, while phorbol, a nonpromoter and nonmitogen, produced no effects on histidase. The relationship of this histidase depression to tumor promotion and not initiation is further indicated by the finding that (a) Tween 60, a structurally unrelated tumor promotor, also produced a decrease in histidase; and (b) the tumor initiator urethan and an initiating dose of 9,10-dimethybenz(a)anthracene showed no effects on histadase activity.

Ammonia-Lyases↗