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R H Kennett

Publications and source records attributed to R H Kennett.

At least 19 recordsLinked to original sources
PubMed2001

Inhibition of N-myc expression and induction of apoptosis by iron chelation in human neuroblastoma cells.

Neuroblastoma is the second most common solid malignancy of childhood. Enhanced expression of the amplified N-myc gene in the tumor cells may be associated with poor patient prognosis and may contribute to tumor development and progression. The use of deferoxamine mesylate (DFO), an iron chelator, to treat neuroblastoma is being investigated in national clinical studies. We show here by TUNEL assay and DNA laddering that DFO induces apoptosis in cultured human neuroblastoma cells, which is preceded by a decrease in the expression of N-myc and the altered expression of some other oncogenes (up-regulating c-fos and down-regulating c-myb) but not housekeeping genes. The decrease in N-myc expression is iron-specific but does not result from inhibition of ribonucleotide reductase, because specific inhibition of this iron-containing enzyme by hydroxyurea does not affect N-myc protein levels. Nuclear run-on and transient reporter gene expression experiments show that the decrease in N-myc expression occurs at the level of initiation of transcription and by inhibiting N-myc promoter activity. Comparison across neuroblastoma cell lines of the amount of residual cellular N-myc protein with the extent of apoptosis measured as pan-caspase activity after 48 h of iron chelation reveals no correlation, suggesting that the decrease in N-myc expression is unlikely to mediate apoptosis. In conclusion, chelation of cellular iron by DFO may alter the expression of multiple genes affecting the malignant phenotype by multiple pathways. Given the clinical importance of N-myc overexpression in neuroblastoma malignancy, decreasing N-myc expression by DFO might be useful as an adjunct to current

Aphidicolin↗
PubMed1996

Identification of epitope recognized by an anti-c-myc monoclonal antibody that cross-reacts with E. coli sigma factor using phage display libraries.

BACKGROUND: During the epitope mapping of monoclonal antibodies specific for myc proteins, two E. coli proteins cross-reactive with an anti-c-myc monoclonal antibody (MYC-X-5/1) were identified. One of the proteins is approximately 90 kDa and the other is over 150 kDa in apparent molecular mass. The molecular masses of these cross-reactive proteins suggested that they may be subunits of E. coli RNA polymerase. OBJECTIVES: We have investigated whether or not the proteins cross-reactive with MYC-X-5/1 are subunits of E. coli RNA polymerase. In addition, we have attempted to determine the epitope of MYC-X-5/1. STUDY DESIGN: The reactivity of MYC-X-5/1 antibody was tested against highly purified E. coli RNA polymerase holo-enzyme preparations and the cell lysate made from E. coli carrying a multi-copy plasmid with an insert of the rpoD gene, the structural gene for the E. coli sigma subunit. The epitope of MYC-X-5/1 was determined by use of phage display of random peptide libraries. RESULTS: On immunoblotting assays, MYC-X-5/1 reacted with the 90-kDa protein in the E. coli RNA polymerase preparations and with the 90-kDa protein over-expressed in E. coli carrying the plasmid with the rpoD insert. In addition, we have deduced the epitope of the MYC-X-5/1 antibody to be residues 235-245 of the human c-myc protein. A highly similar sequence to this was also identified in residues 62-72 of the sigma subunit of E. coli RNA polymerase. CONCLUSION: These data demonstrated that the 90-kDa protein cross-reactive with MYC-X-5/1 is the sigma subunit of E. coli RNA polymerase. Furthermore, this study shows that random peptide libraries displayed on filamentous phage are useful tools for epitope mapping and defining cross-reactivities of monoclonal antibodies.

Amino Acid Sequence↗
PubMed1994

Cloning, analysis, and chromosomal localization of myoxin (MYH12), the human homologue to the mouse dilute gene.

The mouse dilute gene encodes a novel type of non-muscle myosin that structurally combines elements from both nonmuscle myosin type I and nonmuscle myosin type II. Phenotypically, mutations in the mouse dilute gene result not only in the lightening of coat color, but also in the onset of severe neurological defects shortly after birth. This may indicate that the mouse dilute gene is important in maintaining the normal neuronal function in the mouse. We report the isolation and sequencing of "myoxin" (MYH12), the human homologue of the mouse dilute gene, and its assignment to human chromosome 15.

Amino Acid Sequence↗
PubMed1994

3,4-dihydroxyphenylalanine (dopa) metabolism and retinoic acid induced differentiation in human neuroblastoma.

In mature cells of the sympathetic nervous system and the adrenal gland, the activity of dihydroxyphenylalanine decarboxylase (DDC) is higher than that of tyrosine hydroxylase and 3,4-dihydroxyphenylalanine (dopa) does not accumulate in the cells. On the other hand, it is known that in some neuroblastoma cells there is a relative deficiency of DDC, resulting in accumulation and secretion of dopa. Such a relative deficiency of DDC is a characteristic of neural cells at an early stage of neural crest development, suggesting the neuroblastoma are cells arrested in early neural crest development. If this were the case, it is possible that agents such as retinoic acid (RA) could induce neuroblastoma to differentiate into mature cells with respect to their metabolism of catecholamines. We have measured the effect of RA on the metabolism of dopa and expression of tyrosine hydroxylase and DDC in human neuroblastoma cell lines, CHP-126, CHP-134, IMR-32, NB-69, and LA-N-5. When the cell cultures were treated with RA, they showed wide variations in response as measured by morphological change, growth inhibition, enzyme activities and enzyme expressions. The RA treatment modulated the activities of tyrosine hydroxylase and DDC, but does not increase DDC relative to tyrosine hydroxylase. It is concluded that RA does not induce biochemical differentiation of the neuroblastoma into mature cells even when there are extensive morphological changes and suppression of growth rate.

Cell Differentiation↗
PubMed1990

Antisense inhibition of single copy N-myc expression results in decreased cell growth without reduction of c-myc protein in a neuroepithelioma cell line.

The N-myc gene is transiently expressed during normal embryonic development and abnormally expressed in several tumors of neuroendocrine origin. Little is known of the function of the N-myc gene product in either normal or neoplastic tissue. We utilized synthetic antisense oligodeoxynucleotides to specifically inhibit N-myc gene expression in the neuroepithelioma cell line CHP100. These cells contain single copy N-myc alleles but overexpress c-myc. N-myc antisense oligomer treatment was found to be growth inhibitory without affecting levels of c-myc protein. N-myc antisense oligomer-treated cells also lost the characteristic cellular heterogeneity displayed by CHP100 in vitro.

Cell Division↗
PubMed1990

Molecular genetic characterization of epitope-specific monoclonal antibodies against the myc family proteins.

The myc family proteins were used to produce monoclonal antibodies with defined specificities. The pattern of mosaic homology among the myc family proteins facilitated the efficient identification of monoclonal antibodies specific to myc homology box sequences. Sequential epitopes for pan-myc reactive monoclonal antibodies produced against N-myc/c-myc fusion protein were further defined by use of truncated myc proteins made in E. coli and synthetic oligopeptides corresponding to myc box sequences. One class of antibodies was found to be specific to the first myc box sequence, whereas the other was found to be reactive with the third myc box sequence. Further development of anti-myc monoclonal antibodies, especially those antibodies specific to each myc box sequence, would be likely to facilitate analysis of the possible biological functions of the myc proteins in vivo and in vitro.

Amino Acid Sequence↗
PubMed1990

Prolonged N-myc protein half-life in a neuroblastoma cell line lacking N-myc amplification.

Genomic amplification of the oncogene N-myc is associated with rapid tumor progression and poor prognosis in patients with neuroblastoma (NB). However, 40% of NBs which lack N-myc amplification are also clinically aggressive. Factors other than N-myc copy number must therefore play a role in determining tumor progression in these NBs. We have established an unusual human NB cell line (NBL-S) from the primary tumor of a patient with rapidly progressive disease which lacks N-myc amplification. The doubling time in vitro (48 h) and the time from injection of 2 x 10(7) cells to detectable tumors in nude mice (46 days) in similar to NB cell lines with amplified N-myc. However, karyotype analysis reveals no evidence of double minutes (DMs), homogeneously staining regions (HSRs), or chromosome 1p deletions, features commonly seen in NB cell lines. The cells have the cell surface phenotype typical of N-myc amplified NB (HLA-A,B,C negative and HSAN 1.2 positive), and similar to other NB cell lines, N-myc RNA and protein are expressed. Interestingly, the half-life of the N-myc protein in NBL-S is prolonged (approximately 100 min) compared to the short N-myc protein half-life previously described in N-myc amplified NB cell lines (approximately 30 min). Because N-myc protein is thought to have a regulatory role, prolongation of the half-life of this protein may be an important factor in the regulation of growth in NBs which lack N-myc amplification and rapidly progress.

Animals↗
PubMed1989

Glutaraldehyde fixation of the primary antibody-antigen complex on nitrocellulose paper increases the overall sensitivity of immunoblot assay.

A simple method to increase the overall sensitivity of immunoblot assays is described. The method is based on fixation of the primary monoclonal antibody-antigen complex on nitrocellulose paper by a divalent crosslinker, glutaraldehyde. The fixation of the antibody-antigen complex significantly increases the sensitivity of the assay. Unexpectedly, the glutaraldehyde treatment also improves the signal/noise ratio by decreasing non-specific binding of secondary antibodies and/or tertiary reagents. Thus, a significant overall improvement of immunoblot assays is achieved by this method.

Aldehydes↗
PubMed1989

The human L-myc gene is expressed as two forms of protein in small cell lung carcinoma cell lines: detection by monoclonal antibodies specific to two myc homology box sequences.

The L-myc gene is the third member of the myc family of proto-oncogenes. Amplification and elevated expression of the L-myc gene has been detected in a subset of small cell lung carcinoma (SCLC) cell lines. The biological properties and functions of the L-myc gene and its product have not yet been elucidated. Monoclonal antibodies against two myc homology boxes were used to characterize the L-myc gene product. These antibodies react with two groups of polypeptides of apparent masses of 60, 61 and 66 kd (the long forms), and 34 and 37 kd (the short forms) in SCLC cells expressing L-myc transcripts. The long form L-myc proteins are associated with the nuclear fraction of the cells. The short form L-myc proteins are present in the cytoplasmic fraction, though diffusion of the short forms from the nucleus during cell fractionation cannot be ruled out. The half-life of the long form polypeptides is approximately 45-90 min. The short form polypeptides have a half-life of approximately 120-180 min. The L-myc protein is not detectable in the mitotic cells, suggesting that the L-myc protein expression is tightly regulated during the cell cycle.

Amino Acid Sequence↗
PubMed1987

Simple and rapid purification of monoclonal antibodies from cell culture supernatants and ascites fluids by hydroxylapatite chromatography on analytical and preparative scales.

A simple and rapid method for the purification of murine and human monoclonal antibodies from ascites fluids and cell culture supernatants is described. The method, based on the use of hydroxylapatite (HAP) column chromatography, is applicable on both analytical and preparative scales. In our work on purification of monoclonal antibodies, we have found that the combination of a single step elution of impurities followed by linear gradient elution of antibody provides an excellent purification of the antibody from cell culture and ascites fluids. The procedure provides very good resolution at high flow rates. The cell culture supernatant can be pumped on the preparative column at the rate of 2-3 ml/min without any measureable back pressure. The binding is independent of the flow rate. This method has been successfully used to purify several monoclonal antibodies of different subtypes from cell culture supernatants.

Animals↗
PubMed1986

The use of conventional antisera in the production of specific monoclonal antibodies.

We have shown here that conventionally produced antisera aids in the production of specific monoclonal antibodies. The complex of immunoglobulin plus antigen acted as an effective immunogen in both rats and mice. Stable cell lines producing anit-human alpha 2M monoclonal antibodies to numerous antigenic sites on the alpha 2M molecule have been generated by this method. This method has also been used to produce monoclonal antibodies to human complement components. This procedure of immunizing mice with an immunoprecipitated product derived from conventionally produced antisera is a unique approach in that the antigen is conveniently enriched without tedious and time-consuming biochemical purification. In addition, the use of the immunoprecipitated product in conjunction with the immunoprecipitating antisera allows for rapid screening of the hybridomas in the initial stages when cell growth and maintenance is critical. This method thus further simplifies the task of obtaining a specific monoclonal antibody from a complex mixture. A final consideration is the wide availability of conventionally produced antisera to numerous proteins and other biological substances that could be used in the production of monoclonal antibodies, and consequently these antibodies could be used in more detailed studies of these same molecules.

Animals↗
PubMed1986

Identification and characterization of the NMYC gene product in human neuroblastoma cells by monoclonal antibodies with defined specificities.

Increased N-myc (now designated NMYC in human gene nomenclature) gene expression has been detected at the transcriptional level in certain types of neoplasms. As yet, the N-myc gene product has not been identified. To detect and characterize the N-myc gene product, we have developed monoclonal antibodies against the putative N-myc gene product made in Escherichia coli as a fusion protein. The antibodies that recognize the N-myc-specific regions were selected on the basis of their reactivities to different portions of the fusion protein. These monoclonal antibodies detect a pair of closely migrating polypeptides of 60 and 63 kDa in nuclear fractions of human neuroblastoma cells. The relative levels of the polypeptides are roughly proportional to the level of N-myc transcripts present in a panel of neuroblastoma lines. These two polypeptides have a half-life of approximately equal to 35 min, and they are indistinguishable from each other by their epitopic profiles.

Antibodies, Monoclonal↗
PubMed1985

Detection of E. coli colonies expressing the v-sis oncogene product with monoclonal antibodies made against synthetic peptides.

A method for immunodetection of individual epitopes on eukaryotic proteins synthesized in E. coli colonies is described. The system is developed using monoclonal antibodies produced against the Ha-ras protein produced in E. coli JM103. Monoclonal antibodies made against a synthetic peptide from the v-sis oncogene sequence are then used to identify bacterial colonies in which the v-sis protein is being produced. Production of the v-sis protein by these E. coli colonies was confirmed by immunoblot analysis. The assay utilizes peroxidase conjugated anti-mouse immunoglobulin and 4-chloro-1-naphthol to detect the positive colonies and can detect on the order of 200 pg antigen per E. coli colony.

Antibodies, Monoclonal↗
PubMed1985

Selection of variant neuroblastoma cell line which has lost cell surface expression of antigen detected by monoclonal antibody PI153/3.

A variant of the human neuroblastoma cell line, IMR-5, was selected by a series of treatments with the monoclonal antibody PI153/3 and complement. The variant, M-1, was not reactive by either cytotoxicity or binding assays with the PI153/3 antibody or with two other monoclonal antibodies that were selected on the basis of their inhibition of PI153/3 binding. Although no antigen could be detected on the cell surface or in the supernatant of the variant cell line, a reduced level of binding could be detected in M1 cell extracts compared to extracts of IMR5. The variant cell line did not differ from IMR5 in its sensitivity in lysis by other antibodies, in its lack of expression of HLA antigens, or in its capacity to form tumors in nude mice.

Animals↗