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C C Howe

Publications and source records attributed to C C Howe.

31 records · Page 2Linked to original sources
PubMed1986

Expression of the intracisternal A-particle is elevated during differentiation of embryonal carcinoma cells.

Three cDNA clones coding for the 3' region of the intracisternal A-particle (IAP), a mouse endogenous retrovirus, were isolated during screening of a library for genes whose expression was modulated during the retinoic acid-induced differentiation of the embryonal carcinoma cell line F9 into parietal endoderm-like (PE-like) cells. In contrast to previously reported results, no IAP transcripts were detected in either F9 cells or two pluripotent cell lines tested. Instead, IAP transcripts as well as IAPs were abundant in the PE-like cells PYS-2 and F9AcCl 9 and in retinoic acid-induced F9 cells but not in the other differentiated cell types of teratocarcinoma origin which were examined. A comparison of the nucleotide sequences of the three IAP cDNA clones with a genomically integrated proviral sequence (MIA14) demonstrated heterogeneity in both length and sequence among the clones. The position of the poly(A) addition site was determined to be 15 nucleotides from the proposed poly(A) addition signal and to occur after the sequence CAGA, not CA, as previously proposed. Length heterogeneity was greatest in a region of TC repeats 80 base pairs 5' to the poly(A) addition site. Additionally, the putative TATAA box found in MIA14 was deleted in the cDNA clones and in the long terminal repeat regions from two other genomic clones examined. The heterogeneity evident among the cDNA clones further demonstrated that at least two distinct IAP genes are activated during differentiation. An analysis of the rate of transcription in isolated nuclei indicated that the activation of expression of IAP genes in PE-like cells is the result of transcriptional regulation. Together, these observations suggest that the modulation of IAP transcription is regulated autonomously rather than by the fortuitous integration of an IAP sequence adjacent to a developmentally regulated cellular gene.

Animals↗
PubMed1984

Functional role of laminin carbohydrate.

Previous work showed that tunicamycin suppresses glycosylation of laminin. In the present work, the role of glycosylation in the secretion of laminin and in the disulfide bonding of laminin subunits was studied, using tunicamycin to inhibit glycosylation. Tunicamycin inhibited extensively the secretion of laminin into culture medium and extracellular matrix even though the treated cells contained higher concentrations of laminin than the control cells. The laminin subunits synthesized in the presence of tunicamycin were disulfide bonded. Thus, suppression of glycosylation did not adversely affect disulfide bonding of the subunits, but did decrease the secretion of laminin. Glycosidases were also used to remove the carbohydrate of laminin to study the role of carbohydrate in the stability of laminin and in its interaction with another extracellular matrix component, heparin. The glycosidases removed about 73% of [3H]glucosamine. Both glycosidase-treated and untreated laminin were stable when incubated with cell lysate or culture medium. The glycosidase-treated laminin bound as efficiently as the untreated laminin to heparin. These results suggest that the presence of a carbohydrate moiety, at least at the level found in untreated laminin, is not essential in binding to heparin or in protecting laminin from proteolytic degradation in the cell or culture medium.

Animals↗
PubMed1984

Post-transcriptional regulation of the abundance of mRNAs encoding alpha-tubulin and a 94,000-dalton protein in teratocarcinoma-derived stem cells versus differentiated cells.

Changes in the expression of the genes encoding alpha-tubulin and a 94,000-dalton protein (p94) specified by a cDNA clone, p4-30, were examined in a differentiated teratocarcinoma-derived parietal endoderm cell line, PYS-2, and an undifferentiated teratocarcinoma stem cell line, F9. Relative to other proteins or mRNA species, the synthesis rate of the alpha-tubulins and of p94, as well as the levels of their corresponding cytoplasmic mRNAs, were lower in PYS-2 than in F9 cells. The decrease was greater for the relative abundance of cytoplasmic alpha-tubulin mRNA than for p94 mRNA. Similarly, induction of differentiation of F9 cells by simultaneous exposure to retinoic acid (RA) and dibutyryl cyclic AMP resulted in reduced relative levels of the cytoplasmic mRNAs for these proteins. The reduction in abundance of the two RNA species was not due to a decrease in growth rate since the differentiated cells, PYS-2, RA-treated F9, and RA plus dibutyryl cyclic AMP-treated F9 cells, grew at a rate similar to that of undifferentiated F9 cells. However, induction of differentiation of F9 cells by treatment with RA alone did not cause down-regulation of the two RNA species. The relative levels of total cellular RNA encoding alpha-tubulin and p94 in PYS-2 cells were also lower than those in F9 cells to an extent comparable to the decrease in the cytoplasmic RNAs. Since the apparent relative rates of RNA transcription were similar in both cell types, we conclude that the reduction in relative levels of the alpha-tubulin and p94 RNAs in the cell depends largely on the relative stability of the two RNAs and not on the relative rates of transcription. The faster disappearance of the two RNA species relative to other cellular RNAs from actinomycin D-treated PYS-2 compared with F9 cells is consistent with this interpretation.

Animals↗
PubMed1983

Structural analysis of three subunits of laminin from teratocarcinoma-derived parietal endoderm cells.

The structure of the three polypeptide chains of the laminin subunits and the number of glycosylation sites in each polypeptide chain were determined using peptide mapping by high-performance liquid chromatography. Analysis of the [35S]methionine-labeled underglycosylated laminin isolated from tunicamycin (TM)-treated cells revealed that the three subunits of laminin contain unique polypeptide chains. Analysis of [3H]glucosamine-labeled glycosylated laminin subunits showed that they are sialylated and that each subunit has 11-14 glycosylation sites.

Animals↗
PubMed1980

Human hepatocellular carcinoma cell lines secrete the major plasma proteins and hepatitis B surface antigen.

Analysis of the cell culture fluid from two new human hepatoma-derived cell lines reveals that 17 of the major human plasma proteins are synthesized and secreted by these cells. One of these cell lines, Hep 3B, also produces the two major polypeptides of the hepatitis B virus surface antigen. When Hep 3B in injected into athymic mice, metastatic hepatocellular carcinomas appear. These cell lines provide experimental models for investigation of plasma protein biosynthesis and the relation of the hepatitis B viru genome to tumorigenicity.

Blood Proteins↗
PubMed1979

Cytoplasmic and nuclear protein synthesis in preimplantation mouse embryos.

Cytoplasmic and nuclear proteins synthesized by mouse embryos at different stages of preimplantation development were analyzed by two-dimensional polyacrylamide gel electrophoresis. Several nuclear-specific proteins (i.e. proteins more abundant in the nucleus than in the cytoplasm) and numerous cytoplasmic-specific proteins were observed. The trends of changes in the nuclear and cytoplasmic protein synthesis are similar. Moderate changes occur between the unfertilized egg and the zygote. Striking changes characterized by the disappearance of numerous major oocyte-specific proteins and the appearance of a large number of new, stage-specific proteins occur between the zygote and the 4- to 8-cell stages. In contrast, between the 4- and 8-cell and early blastocyst periods, only a few new proteins appear, and a small number of oocyte-specific or other stage-specific proteins disappear. Minor differences in protein synthesis were observed between the trophoblast and inner cell mass.

Animals↗
PubMed1977

Studies on viral DNA protein complexes isolated at different times after infection of monkey kidney cells with simian virus 40.

The major protein components of the DNA complex, isolated from SV40-infected monkey cells, are the major viral structural polypeptide VP1 and cellular histones. At early times (24 h) after infection, VP1 is present in large amounts relative to histones, whereas at late times (48 h), the complex contains mostly histones. The amount of VP1 in the complex can be correlated to the amount of "free" VP1 present in the cells, i.e. VP1 not yet incorporated into virus particles. At early times about 40% of VP1 is "free" VP1; at late times, most of the VP1 is incorporated into virus particles. In contrast, viral DNA is produced in huge excess and only about 13% is incorporated into virions. In agreement with the above result, we find that only about 16% of the DNA in the DNA complex can be chased into virions. There is, apparently, no turnover of newly synthesized VP1 that is associated with the DNA complex at late times after infection.

Animals↗
PubMed1975

Fate of parental simian virus 40 DNA in permissive monkey kidney cells.

The fate of parental SV40 DNA in monkey kidney cells was investigated by infecting the cells with purified virus labelled with [3-H]-thymidine. 5-Bromodeoxyuridine (200 mug/ml) was added to the cells at 2 h after infection to label virus progeny DNA. At 72 h post-infection the cells were harvested and virus DNA was extracted and fractionated by isopycnic sedimentation in CsCL solution. The following DNAs with characteristic densities were found: light (LL), 1.70 g/ml; hybrid (HL), 1-75 g/ml and heavy DNA (HH), 1-80 g/ml. Of the total cell-associated [3-H]-radioactivity (derived from parental virus), more than 90% was recovered in unreplicated parental DNA(LL DNA), about 2% was recovered in the HL DNA and about 1-7% was associated with the HH DNA. The unreplicated parental DNA was present as uncoated intact DNA complexed with proteins present in the infected cell. The HL DNA contains one light parental and one heavy progeny DNA strand. The nature of the radioactivity present in the HH DNA remains to be determined.

Adenine↗
PubMed1973

Multiple and specific initiation of T4 DNA replication.

Partially replicated T4 DNA molecules (PRM) whose parental or progeny DNA was labeled with bromodeoxyuridine BUdR was analyzed by gradual shearing followed by CsCl banding of the sheared product. Analysis of PRM containing 18-mum replicated DNA showed that each replicated region was 3- to 6-mum long, indicating three to 6 replicative sites per molecule. Analysis of PRM containing 9-mum replicated DNA similarly indicated two to three replicated regions per molecule. DNA from the replicated regions of PRM containing 10-mum replicated DNA ("donor") was hybridized to DNA from mature phage ("recipient"), and the resulting hybrid was subjected to digestion with exonuclease I. The extent of protection of the recipient and more efficient self-annealing of progeny fragments from PRM indicated that the replicated regions represented 8 to 10 nonrandom locations of the genome. Possible significance of multiple sites for initiation of DNA replication is discussed.

Bromodeoxyuridine↗