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S Strickland

Publications and source records attributed to S Strickland.

At least 91 records · Page 5Linked to original sources
PubMed1986

Studies on the hormonal regulation of plasminogen activator production in the rat ovary.

When granulosa cells are prepared from rats primed with PMSG, it is possible to induce plasminogen activator (PA) production in vitro with a variety of hormones. We have compared the effects of the gonadotropins FSH and LH on granulosa cells in culture. Although both hormones can induce enzyme secretion, the time courses of their effects are different. Whereas FSH yields a linear increase in PA production starting 2 h after the time of hormone addition, the effect of LH shows a longer lag phase, but it eventually reaches the same degree of stimulation as FSH. Experiments with an inhibitor of prostaglandin (PG) synthesis, indomethacin, and with PGs suggest the following interpretation. Granulosa cells that can produce PA can be directly stimulated by FSH, but only a small fraction of these cells can be induced by LH. However, the population that is responsive to LH begins to produce PGs after hormone treatment, and the PGs can then stimulate the entire population. Cumulus cells, which have few LH receptors, can be induced by FSH and PGs, but not LH. Experiments involving treatment of rats with indomethacin in vivo or treatment of follicles in vitro demonstrate that this compound can suppress PA secretion in the ovary, which may partially explain its ability to inhibit ovulation.

Animals↗
PubMed1986

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Adult↗
PubMed1985

Plasminogen activator in the rat ovary. Production and gonadotropin regulation of the enzyme in granulosa and thecal cells.

The production of plasminogen activator by ovarian granulosa cells has been previously reported to be temporally correlated with ovulation in the rat and to be under hormonal control of gonadotropins. We have examined the type of plasminogen activator produced by granulosa cells and also investigated other ovarian cell types for synthesis of this enzyme. Using antibodies specific for tissue-type or urokinase-type plasminogen activator, we have found that granulosa cells produce exclusively the tissue-type enzyme. However, in cultures of whole follicles isolated from the ovary, there is primarily synthesis of urokinase-type plasminogen activator. Examination of other isolated ovarian cell types has demonstrated that thecal cells secrete the urokinase-type plasminogen activator and that the production of this enzyme is also regulated by gonadotropins and temporally correlated with ovulation. These results suggest that ovulation requires both types of plasminogen activator and that the neighboring granulosa and thecal cells cooperate to ensure rupture of the follicle wall and unimpeded passage of the ovum into the oviduct.

Animals↗
PubMed1985

Two-stage hormonal control of type IV collagen mRNA levels during differentiation of F9 teratocarcinoma cells.

A cDNA clone related to mouse Type IV collagen has been prepared from F9 teratocarcinoma cells induced to differentiate with retinoic acid and dibutyryl-cAMP. This cDNA clone has been used to investigate the regulation of Type IV collagen mRNA during differentiation. The level of this mRNA is very low in untreated F9 cells, increases substantially after treatment of the cells with retinoic acid, and is further increased by addition of dibutyryl-cAMP. In contrast, dibutyryl-cAMP has no effect on the mRNA level in cells that have not been previously exposed to retinoic acid. These results demonstrate that these two compounds regulate in a sequential manner the steady-state level of Type IV collagen mRNA. This cDNA clone should allow a detailed examination of the mechanism of the two-stage regulation of collagen expression by retinoids and cyclic AMP.

Animals↗
PubMed1985

A teratocarcinoma-derived endoderm stem cell line (1H5) that can differentiate into extra-embryonic endoderm cell types.

We investigated the ability of the teratocarcinoma-derived, epithelial-type cell line 1H5 to differentiate into either of the two pathways to primary endoderm, and tested the hypothesis that 1H5 represents a state similar to primitive endoderm in the late 4th-day blastocyst. Like other endodermal cell types, 1H5 cells mixed with embryonal-carcinoma cells sort out into "embryoid bodies" or structures that resemble 4th-day mouse embryos. The epithelial line conforms morphologically and biochemically to the few known characteristics typical of primitive endoderm. The present study demonstrates that the formation in vitro of overt visceral endoderm is readily achieved. The spontaneous arrangement of the cells into a cystic form is followed by the appearance of several markers of visceral endoderm, most notably alphafetoprotein, which is detected when 1H5 cells are cultured either in the presence of retinoic acid or when the cells interact with embryonal-carcinoma cells in a specific spatial arrangement after sorting out. However, some less specific properties of visceral endoderm are not expressed. Although 1H5 differentiates histologically into parietal-like endoderm in the tumor form, parietal cells cannot yet be identified with certainty in vitro because of the paucity of parietal-specific markers. The 1H5 cell line could provide a useful system for studying the characteristics and mechanisms underlying visceral-endoderm differentiation in vitro, since it has the distinct advantage that homogeneous cultures are produced, in contrast to other teratocarcinoma cell lines such as F9 which differentiate into a mixture of cell types.

Animals↗
PubMed1984

Common control of the heat shock gene and early adenovirus genes: evidence for a cellular E1A-like activity.

We have employed an antiserum specific to the 70-kilodalton human heat shock protein and a cDNA clone specific to the mRNA for this protein to analyze the expression of the gene under noninducing conditions. Expression of the heat shock gene can be detected in the absence of heat induction, and this uninduced level of expression depends greatly on the particular cell type. For instance, the basal expression of the heat shock gene is at least 50 times higher in HeLa cells than in WI38 cells at both the mRNA and protein levels. We have previously shown that the inducer of transcription of the early adenovirus genes, the E1A gene product, also induces the heat shock gene, suggesting that these genes may be subject to the same regulation. We have, therefore, investigated the control of the adenovirus genes in relation to the cellular control of the heat shock gene. We find that human cells that allow a high level of uninduced expression of the heat shock gene (i.e., HeLa cells) also allow expression of the early adenovirus genes in the absence of the E1A inducer. The same is also true for the mouse F9 teratocarcinoma cell line. F9 stem cells, which constitutively express the heat shock protein, allow early adenovirus gene expression in the absence of E1A; upon differentiation induced by retinoic acid and cyclic AMP, the cells become restrictive and early viral gene expression requires the E1A gene product. Coordinately, upon differentiation there is also a loss of heat shock protein expression.

Adenoviruses, Human↗
PubMed1983

Infection of mouse teratocarcinoma stem cells with influenza virus: normal expression of proteins derived from spliced messenger RNAs.

Mouse teratocarcinoma stem cells before and after induction of differentiation have been infected with influenza virus. This virus is able to infect the cells irrespective of the state of differentiation. In addition, viral-encoded proteins that are known to be translated from spliced messenger RNAs are produced in normal amounts in the infected cells, and this expression is also independent of differentiation. These results indicate that both the stem cells and their differentiated progeny can efficiently splice the precursor RNAs for these influenza virus messengers.

Animals↗
PubMed1983

Structure-activity relationships of a new series of retinoidal benzoic acid derivatives as measured by induction of differentiation of murine F9 teratocarcinoma cells and human HL-60 promyelocytic leukemia cells.

A new group of retinoids, which are 3-alkyl and 3-alkoxy derivatives of (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2- naphthalenyl)-1-propenyl]-benzoic acid (TTNPB), has been synthesized. They were tested in vitro for biological activity by measuring induction of terminal differentiation in both murine F9 teratocarcinoma cells and human HL-60 promyelocytic leukemia cells. In the F9 assay, TTNPB was significantly more active (dose effective in achieving a half-maximal response, 3 X 10(-9) M) than was all-trans-retinoic acid, while the 3-methyl derivative of TTNPB was not. However, in the HL-60 assay, the 3-methyl derivative of TTNPB was more active (dose effective in achieving a half-maximal response, 2 X 10(-8) M) than was all-trans-retinoic acid, while TTNPB was less active. 3-Ethyl and 3-propyl derivatives were much less active than was all-trans-retinoic acid in both assays. These new retinoids should be useful agents for experimental studies of both cancer prevention and treatment, as well as for investigation of the mechanism of action of retinoids in the control of cell differentiation.

Animals↗
PubMed1981

Structural components and characteristics of Reichert's membrane, an extra-embryonic basement membrane.

This paper presents an analysis of mouse and rat Reichert's membrane, a thick basement membrane formed between the trophoblast and parietal endoderm cells of early mammalian embryos. When analyzed by polyacrylamide gel electrophoresis. Reichert's membranes from rat and mouse conceptuses appear simple and consist primarily of collagen and 4 noncollagenous glycoproteins of approximate Mr = 415,000, 245,000, 170,000, and 50,000. The proteins at 415,000 and 245,000 are similar in molecular weight to laminin and are immunoprecipitated by anti-laminin antiserum. The protein at 170,000 is co-precipitated with laminin and represents a novel form of a laminin-like protein, whereas the protein at 50,000 is unrelated to laminin. Using metabolic labeling experiments, it is shown that parietal endoderm cells synthesize these components and incorporate them into the matrix in organ cultures but do not degrade Reichert's membrane in the conditions used over a 6-day culture period. Evidence is presented that the high molecular weight collagenase-sensitive proteins (greater than 420,000) observed on polyacrylamide gel electrophoresis are due to lysyl oxidase-derived cross-links between Reichert's membrane components.

Animals↗
PubMed1981

Obligatory separation of hormone binding and biological response curves in systems dependent upon secondary mediators of hormone action.

A mathematical model is presented that describes the effects of hormone concentration on receptor saturation and biological response in systems dependent upon the generation of a secondary mediator such as cyclic AMP. The analysis makes the following assumptions: (i) the binding of hormone to its receptor is a reversible, second-order reaction; (ii) the concentration of mediator that is generated is directly proportional to the number of membrane binding sites occupied by hormone; and (iii) the binding of the mediator with its intracellular receptor to generate an effector complex is also second-order and results in a proportionate biological response. It follows from this treatment that the hormone concentration required for half-maximal biological response is formally lower than that required for half-maximal receptor saturation and that the difference between these two concentrations will depend upon the ratio of total mediator generated at full receptor occupancy to the dissociation constant of the mediator with its receptor. Without invoking concepts of negative cooperativity, this model offers a simple explanation for discrepancies between receptor occupancy and biological response curves that are often observed. Moreover, the mathematical form of the predicted biological response curves conforms to the shape of the response curves observed experimentally in a wide variety of systems.

Animals↗
PubMed1980

A comparative study of eight cell lines derived from human testicular teratocarcinoma.

Eight independent cell lines, derived from human testicular germ-cell tumors, were examined for the expression of various markers. These included major histocompatibility and embryonic antigens, chorionic gonadotropin, alpha fetoprotein, alkaline phosphatase, plasminogen activator, and infectivity by SV40. No line consisted primarily of choriocarcinoma or yolk sac cells, but several contained cells resembling murine embryonal carcinoma; some of these lines formed tumors with the distinctive features of embryonal carcinoma when injected into immunosuppressed animals. It is proposed that human embryonal carcinoma cells, unlike those of the mouse, correspond to a preblastocyst stage of development.

Alkaline Phosphatase↗
PubMed1980

Hormonal induction of differentiation in teratocarcinoma stem cells: generation of parietal endoderm by retinoic acid and dibutyryl cAMP.

It has previously been shown that retinoic acid induces multiple phenotypic changes in cultures of F9 teratocarcinoma stem cells. In this paper we demonstrate that these retinoid-generated cells can be converted to yet another cell type by compounds that elevate cAMP concentrations. The phenotype of the new cell type is characterized by the synthesis of plasminogen activator, laminin and type IV collagen, and by very low levels of alkaline phosphatase and lactate dehydrogenase. The secretion of plasminogen activator and type IV collagen, and low levels of alkaline phosphatase and lactate dehydrogenase, have been previously shown to be properties of parietal endoderm, an extraembryonic cell which is generated early in mouse embryonesis. We show here that parietal endoderm also synthesizes laminin. The cell type generated by retinoic acid and dibutyryl cAMP treatment is therefore indistinguishable from definitive parietal endoderm. Analysis of the final phenotype indicates that it is not dependent upon the continued presence of either compound, and that cAMP agents are active only on cells that have been treated with retinoic acid.

Animals↗