Growth control in cultured mouse fibroblasts: induction of the pleiotypic and mitogenic responses by a purified growth factor

Fibroblast growth factors as tissue repair and regeneration therapeutics

Cell communication is central to the integration of cell function required for the development and homeostasis of multicellular animals. Proteins are an important currency of cell communication, acting locally (auto-, juxta-, or paracrine) or systemically (endocrine). The fibroblast growth factor (FGF) family contributes to the regulation of virtually all aspects of development and organogenesis, and after birth to tissue maintenance, as well as particular aspects of organism physiology. In the West, oncology has been the focus of translation of FGF research, whereas in China and to an extent Japan a major focus has been to use FGFs in repair and regeneration settings. These differences have their roots in research history and aims. The Chinese drive into biotechnology and the delivery of engineered clinical grade FGFs by a major Chinese research group were important enablers in this respect. The Chinese language clinical literature is not widely accessible. To put this into context, we provide the essential molecular and functional background to the FGF communication system covering FGF ligands, the heparan sulfate and Klotho co-receptors and FGF receptor (FGFR) tyrosine kinases. We then summarise a selection of clinical reports that demonstrate the efficacy of engineered recombinant FGF ligands in treating a wide range of conditions that require tissue repair/regeneration. Alongside, the functional reasons why application of exogenous FGF ligands does not lead to cancers are described. Together, this highlights that the FGF ligands represent a major opportunity for clinical translation that has been largely overlooked in the West.

Molecular and cellular mechanisms of development underlying congenital diseases

In the last several decades, developmental biology has clarified the molecular mechanisms of embryogenesis and organogenesis. In particular, it has demonstrated that the “tool-kit genes” essential for regulating developmental processes are not only highly conserved among species, but are also used as systems at various times and places in an organism to control distinct developmental events. Therefore, mutations in many of these tool-kit genes may cause congenital diseases involving morphological abnormalities. This link between genes and abnormal morphological phenotypes underscores the importance of understanding how cells behave and contribute to morphogenesis as a result of gene function. Recent improvements in live imaging and in quantitative analyses of cellular dynamics will advance our understanding of the cellular pathogenesis of congenital diseases associated with aberrant morphologies. In these studies, it is critical to select an appropriate model organism for the particular phenomenon of interest.

Humanized medium (h7H) allows long-term primary follicular thyroid cultures from human normal thyroid, benign neoplasm, and cancer

CONTEXT

Mechanisms of thyroid physiology and cancer are principally studied in follicular cell lines. However, human thyroid cancer lines were found to be heavily contaminated by other sources, and only one supposedly normal-thyroid cell line, immortalized with SV40 antigen, is available. In primary culture, human follicular cultures lose their phenotype after passage. We hypothesized that the loss of the thyroid phenotype could be related to culture conditions in which human cells are grown in medium optimized for rodent culture, including hormones with marked differences in its affinity for the relevant rodent/human receptor.

OBJECTIVE

The objective of the study was to define conditions that allow the proliferation of primary human follicular thyrocytes for many passages without losing phenotype.

METHODS

Concentrations of hormones, transferrin, iodine, oligoelements, antioxidants, metabolites, and ethanol were adjusted within normal homeostatic human serum ranges. Single cultures were identified by short tandem repeats. Human-rodent interspecies contamination was assessed.

RESULTS

We defined an humanized 7 homeostatic additives medium enabling growth of human thyroid cultures for more than 20 passages maintaining thyrocyte phenotype. Thyrocytes proliferated and were grouped as follicle-like structures; expressed Na+/I- symporter, pendrin, cytokeratins, thyroglobulin, and thyroperoxidase showed iodine-uptake and secreted thyroglobulin and free T3. Using these conditions, we generated a bank of thyroid tumors in culture from normal thyroids, Grave's hyperplasias, benign neoplasms (goiter, adenomas), and carcinomas.

CONCLUSIONS

Using appropriate culture conditions is essential for phenotype maintenance in human thyrocytes. The bank of thyroid tumors in culture generated under humanized humanized 7 homeostatic additives culture conditions will provide a much-needed tool to compare similarly growing cells from normal vs pathological origins and thus to elucidate the molecular basis of thyroid disease.

Pharmacokinetic properties of 2nd-generation fibroblast growth factor-1 mutants for therapeutic application

Fibroblast growth factor-1 (FGF-1) is an angiogenic factor with therapeutic potential for the treatment of ischemic disease. FGF-1 has low intrinsic thermostability and is characteristically formulated with heparin as a stabilizing agent. Heparin, however, adds a number of undesirable properties that negatively impact safety and cost. Mutations that increase the thermostability of FGF-1 may obviate the need for heparin in formulation and may prove to be useful “2nd-generation” forms for therapeutic use. We report a pharmacokinetic (PK) study in rabbits of human FGF-1 in the presence and absence of heparin, as well as three mutant forms having differential effects upon thermostability, buried reactive thiols, and heparin affinity. The results support the hypothesis that heparan sulfate proteoglycan (HSPG) in the vasculature of liver, kidney and spleen serves as the principle peripheral compartment in the distribution kinetics. The addition of heparin to FGF-1 is shown to increase endocrine-like properties of distribution. Mutant forms of FGF-1 that enhance thermostability or eliminate buried reactive thiols demonstrate a shorter distribution half-life, a longer elimination half-life, and a longer mean residence time (MRT) in comparison to wild-type FGF-1. The results show how such mutations can produce useful 2nd-generation forms with tailored PK profiles for specific therapeutic application.

FGF-18, a novel member of the fibroblast growth factor family, stimulates hepatic and intestinal proliferation

The fibroblast growth factors (FGFs) play key roles in controlling tissue growth, morphogenesis, and repair in animals. We have cloned a novel member of the FGF family, designated FGF-18, that is expressed primarily in the lungs and kidneys and at lower levels in the heart, testes, spleen, skeletal muscle, and brain. Sequence comparison indicates that FGF-18 is highly conserved between humans and mice and is most homologous to FGF-8 among the FGF family members. FGF-18 has a typical signal sequence and was glycosylated and secreted when it was transfected into 293-EBNA cells. Recombinant murine FGF-18 protein (rMuFGF-18) stimulated proliferation in the fibroblast cell line NIH 3T3 in vitro in a heparan sulfate-dependent manner. To examine its biological activity in vivo, rMuFGF-18 was injected into normal mice and ectopically overexpressed in transgenic mice by using a liver-specific promoter. Injection of rMuFGF-18 induced proliferation in a wide variety of tissues, including tissues of both epithelial and mesenchymal origin. The two tissues which appeared to be the primary targets of FGF-18 were the liver and small intestine, both of which exhibited histologic evidence of proliferation and showed significant gains in organ weight following 7 (sometimes 3) days of FGF-18 treatment. Transgenic mice that overexpressed FGF-18 in the liver also exhibited an increase in liver weight and hepatocellular proliferation. These results suggest that FGF-18 is a pleiotropic growth factor that stimulates proliferation in a number of tissues, most notably the liver and small intestine.

Late signals are required for the stimulation of DNA synthesis in rat mammary fibroblasts by growth factors

Maximal stimulation of DNA synthesis in quiescent rat mammary (Rama) 27 fibroblasts is elicited by epidermal growth factor (EGF) or basic fibroblast growth factor (bFGF) 18 h after the initial addition of the growth factors-the 'lag' period. At maximally-stimulating concentrations, EGF and bFGF are interchangeable 9 h after their initial addition. When the initial concentration of growth factor is below that required to elicit a maximal response, it is possible to increase the level of DNA synthesis by increasing the concentration of growth factor 9 h after its initial addition. When the initial concentration of growth factor is high, substitution by a lower concentration of growth factor after 9 h allows a greater proportion of cells to synthesize DNA than would be expected from a continuous low dose of growth factor. Similar results are obtained when both the growth factor and its concentration are changed 9 h after the initial addition of growth factor. However, when EGF at a low concentration is substituted for a high concentration of EGF or bFGF the resulting increase in the levels of DNA synthesis is greater when EGF rather than bFGF is added for a second time. The half-life of the growth-stimulatory signals delivered by EGF and by bFGF 9 h after their initial addition is 1-2 h. These results suggest that to stimulate DNA synthesis: (i) EGF or bFGF must deliver a signal(s) continuously; (ii) the initial signals produced by EGF and bFGF are equivalent; (iii) the signals produced between 9-18 h by EGF may be different to those produced by bFGF.

Role of growth factors in cutaneous wound healing: a review

The well-orchestrated, complex series of events resulting in the repair of cutaneous wounds are, at least in part, regulated by polypeptide growth factors. This review provides a detailed overview of the known functions, interactions, and mechanisms of action of growth factors in the context of the overall repair process in cutaneous wounds. An overview of the cellular and molecular events involved in soft tissue repair is initially presented, followed by a review of widely studied growth factors and a discussion of commonly utilized preclinical animal models. The article concludes with a summary of the preliminary results from human clinical trials evaluating the effects of growth factors in the healing of chronic skin ulcers. Throughout, the interactions among the growth factors in the wound-healing process are emphasized.

Autoradiographic studies of rat astroglial cell proliferation in vitro with and without treatment with basic fibroblast growth factor

Using specific autoradiographic methods, cell cycle parameters of untreated and basic fibroblast growth factor (bFGF)-treated astroglial cells from newborn rats grown in primary culture were directly measured. The mode of proliferation was also analysed. In untreated cultures, S phase duration (Ts = 6.9-13.1 h) and cell cycle time (Tc = 10-18 h) can be modified by about a factor of 2 depending on the culture conditions (serum-supplemented or defined medium, thyroid hormone concentration). However, growth fraction (GF = 0.15) and the ratio Ts/Tc remain stable. With increasing days in vitro (DIV) (DIV 7-DIV 20), Ts (7.8-10.6 h) and Tc (10-21 h) are prolonged and GF (0.14-0.06) decreases, probably due to cell maturation. In general, astroglial cells proliferate exponentially with a GF < 1, but stop proliferating about 30-36 h after the last feeding, probably caused by exhaustion of the medium. However, after refeeding they continue to proliferate. As opposed to in vivo, no transition of non-proliferating cells into the GF occurs. After addition of bFGF, GF increases (e.g. GF at DIV 7 = 0.43), but Ts and Tc are not influenced at DIV 7 and 12. At DIV 20, bFGF additionally shortens Ts and Tc, thereby producing values of Ts, Tc and GF like 'younger' cultures. However, the revitalizing effect on 'mature' cells is only transitory. In general, bFGF leads to a single re-entry of G0 cells into the GF. Thereafter, bFGF does not affect the mode of proliferation.

Relationship of growth factors and differentiation in normal and neoplastic development of the mammary gland

The different mammary cell lines described herein appear to be representative of the cell types found in both normal glands and benign tumors of rats and humans. The epithelial cell lines can differentiate to both alveolar-like and myoepithelial-like cells in culture. The epithelial cell lines and particularly those cell lines representing intermediate stages in the myoepithelial differentiation pathway are candidates for the epithelial stem cells found in rat and possibly in human terminal ductal structures. The systemic mammatrophic hormones that are thought to control the growth of the mammary gland in vivo have little or no stimulatory effect alone on the growth of normal and neoplastic rat mammary cells in culture. The pituitary growth factors (fibroblast growth factor [FGF] and pituitary-derived mammary growth factor [PMGF],) and the growth factors released from the different cell lines, (stromal prostaglandin E2 [PGE2] and myoepithelial transforming growth factor alpha [TGF-alpha]) are much more potent mitogenic agents for the mammary cell lines. The ability of FGF and epidermal growth factor (EGF) -related molecules to simulate growth of the different mammary cell types in culture correlates with the presence of their high-affinity receptors. Thus these growth factors are promising candidates for some of the primary effectors of mammary growth in vivo. Malignant mammary epithelial cells have a greatly reduced rate of growth compared to their normal and benign counterparts. They also fail to differentiate or to respond to PMGF but can still respond to PGE2 and TGF-alpha. In addition, highly malignant variants appear capable of adapting to a new growth environment in vivo. This suggests that simple molecular explanations based solely on the autostimulation of cell growth may not be sufficient to explain some of the properties of the slowly growing, highly malignant cells.

Fibroblast Growth Factor Enhances Long-term Potentiation in the Hippocampal Slice

Recently we reported that perfusion of hippocampal slices with epidermal growth factor (EGF) lead to enhancement of potentiated responses after tetanic stimulation. In the present study we report that basic fibroblast growth factor (FGF) can also lead to an enhancement of potentiated responses. FGF is a mitogen for several cell types and exhibits neurotrophic effects on neurons of the central nervous system (CNS). Rat hippocampal slices were perfused with FGF at a concentration of 10-9 M. During extra- and intracellular recordings in the CA1-region, the addition of FGF to the perfusing medium produced no change in evoked responses if single pulse or paired pulse stimulation was used. Furthermore FGF had no influence on the resting membrane potential and input resistance. However, after tetanic stimulation, FGF-treated slices showed an increase in the magnitude of potentiation compared to control slices. Taken together with the EGF data these results support the hypothesis that growth factors like FGF with neurotrophic potential on CNS-neurons can influence synaptic efficacy. Furthermore these results show that factors which are able to modulate developmental plasticity and regenerative plasticity can also modulate synaptic plasticity.

Stem cells and the development of mammary cancers in experimental rats and in humans

Evidence based on immunocytochemical staining and ultrastructure suggests that morphological gradations between epithelial and myoepithelial cells, and possibly between epithelial cells and alveolar-like cells occur in terminal ductal structures of rat and human mammary glands. The benign carcinogen-induced rat and benign human mammary tumors can contain epithelial, myoepithelial-like and alveolar-like cells, whereas the malignant counterparts mainly contain only epithelial-like cells. Clonal epithelial cell lines from normal rat mammary glands, benign tumors, and SV40-transformed human mammary glands can differentiate to either myoepithelial-like or alveolar-like cells. In those of the rat, the differentiation processes occur in steps: intermediate cells along the myoepithelial-like pathway resemble intermediates in terminal ductal structures in vivo, and can also generate certain well-differentiated mesenchymal elements of the original tumours. Differentiation of the benign rat cells to alveolar-like cells with mammatrophic hormones and retinoids in vitro leads to a reduction in their tumor-forming ability in vivo. Cell lines from malignant rat mammary tumors of increasing metastatic potential and from human ductal carcinomas largely fail to yield myoepithelial-like or alveolar-like cells and are relatively slow-growing. Growth of the rat mammary epithelial cells in culture is stimulated by a pituitary-derived mammatrophic growth factor (PMGF), prostaglandin E2, and alpha-transforming growth factor; the response of the malignant cell lines to PMGF is reduced. It is suggested that stem cells exist in the rat and human glands that are capable of differentiating to the other major cell types of the mammary parenchyma, and that during the carcinogenic process they generate genetically unstable cells which lose their ability to differentiate and attempt to maximise their intrinsically slow growth rate.

Cell kinetic studies of chick brain cells in culture: an autoradiographic study with [3H]- and [14C]-thymidine

Labelling index, S-phase duration and cell-cycle time of proliferating brain cells from 6-day-old chick embryos in culture were investigated autoradiographically after labelling with [3H]- and/or [14C]-thymidine. The dissociated cells were cultured in the absence or in the presence of brain extract from 8-day-old chick embryos. Cultures contained essentially two cell types, which could be easily distinguished by the size of their nuclei: small nuclei identified as belonging to precursor cells of neurons and large nuclei corresponding to astroglial cells. The labelling index of astroglial cells (16.4%) was about 2 times higher than that of the neuronal cells (9.9%). Under the influence of brain extract the labelling index of neuroblasts was nearly doubled while that of the astroglial cells remained nearly unchanged. From double-labelling experiments with [3H]- and [14C]-thymidine, the same S-phase duration of about 7 hr was found for both cell types cultured with or without brain extract. A cell-cycle duration of 39 hr for neuronal and of 29 hr for astroglial cells was found. The cycle times remained constant under the influence of brain extract. From the measured data mentioned above, a growth fraction of 50% (neuroblasts) and 68% (astroglial cells) was calculated in control cultures without brain extract. After addition of brain extract, the growth fraction increased for both cell types (neuroblasts: 92%; astroglial cells: 80%). The results demonstrate that more cells proliferate in the presence of brain extract, but the durations of the S-phase and the cell cycle remain unchanged.

Post-transcriptional control of the onset of DNA synthesis by an insulin-like growth factor

The control of eucaryotic cell proliferation is governed largely by a series of regulatory events which occur in the G1 phase of the cell cycle. When stimulated to proliferate, quiescent (G0) 3T3 fibroblasts require transcription, rapid translation, and three growth factors for the growth state transition. We examined exponentially growing 3T3 cells to relate the requirements for G1 transit to those necessary for the transition from the G0 to the S phase. Cycling cells in the G1 phase required transcription, rapid translation, and a single growth factor (insulin-like growth factor [IGF] I) to initiate DNA synthesis. IGF I acted post-transcriptionally at a late G1 step. All cells in the G1 phase entered the S phase on schedule if either insulin (hyperphysiological concentration) or IGF I (subnanomolar concentration) was provided as the sole growth factor. In medium lacking all growth factors, only cells within 2 to 3 h of the S phase were able to initiate DNA synthesis. Similarly, cells within 2 to 3 h of the S phase were less dependent on transcription and translation for entry into the S phase. Cells responded very differently to inhibited translation than to growth factor deprivation. Cells in the early and mid-G1 phases did not progress toward the S phase during transcriptional or translational inhibition, and during translational inhibition they actually regressed from the S phase. In the absence of growth factors, however, these cells continued progressing toward the S phase, but still required IGF at a terminal step before initiating DNA synthesis. We conclude that a suboptimal condition causes cells to either progress or regress in the cell cycle rather than freezing them at their initial position. By using synchronized cultures, we also show that in contrast to earlier events, this final, IGF-dependent step did not require new transcription. This result is in contrast to findings that other growth factors induce new transcription. We examined the requirements for G1 transit by using a chemically transformed 3T3 cell line (BPA31 cells) which has lost some but not all ability to regulate its growth. Early- and mid-G1-phase BPA31 cells required transcription and translation to initiate DNA synthesis, although they did not regress from the S phase during translational inhibition. However, these cells did not need IGF for entry into the S phase.

The role of increased proteolysis in the atrophy and arrest of proliferation in serum-deprived fibroblasts

When cultured fibroblasts are deprived of serum, the degradation of long-lived proteins and RNA increases, the cells stop proliferating, and they decrease in size. To determine the role of the increased protein catabolism in these responses, we studied the effects of inhibitors of intralysosomal proteolysis in Balb/c 3T3 cells. When these cells were placed in serum-deficient medium (0.5% serum), the rate of degradation of long-lived proteins increased about twofold within 30 min. This increase was reduced by 50-70% with inhibitors of lysosomal thiol proteases (Ep475 and leupeptin) or agents that raise intralysosomal pH (chloroquine and NH4Cl). By contrast, these compounds had little or no effect on protein degradation in cells growing in 10% serum. Thus, in accord with prior studies, lysosomes appear to be the site of the increased proteolysis after serum deprivation. When 3T3 cells were deprived of serum for 24-48 hours, the rate of protein synthesis and the content of protein and RNA and cell volume decreased two- to fourfold. The protease inhibitor, Ep475, reduced this decrease in the rate of protein synthesis and the loss of cell protein and RNA. Cells deprived of serum and treated with Ep475 for 24-48 hours had about twice the rate of protein synthesis and two- to fourfold higher levels of protein and RNA than control cells deprived of serum. The Ep475-treated cells were also about 30% larger than the untreated cells. Thus, the protease-inhibitor prevented much of the atrophy induced by serum deprivation. The serum-deprived fibroblasts also stopped proliferating and accumulated in the G1 phase of the cell cycle. The cells treated with Ep475 accumulated in G1 in a manner identical to untreated serum-deprived cells. Other agents which inhibited protein breakdown in serum-deprived cells also did not prevent the arrest of cell proliferation. Thus the enhancement of proteolysis during serum deprivation appears necessary for the decrease in size and protein synthesis, but probably not for the cessation of cell proliferation. When cells deprived of serum in the presence or absence of Ep475 were stimulated to proliferate by the readdition of serum, the larger Ep475-treated cells began DNA synthesis 1-2 hours later than the smaller untreated cells. Thus, after treatment with Ep475, the rate of cell cycle transit following serum stimulation was not proportional to the cell's size, protein, or RNA content, or rate of protein synthesis.

Post-transcriptional control of the onset of DNA synthesis by an insulin-like growth factor

The control of eucaryotic cell proliferation is governed largely by a series of regulatory events which occur in the G1 phase of the cell cycle. When stimulated to proliferate, quiescent (G0) 3T3 fibroblasts require transcription, rapid translation, and three growth factors for the growth state transition. We examined exponentially growing 3T3 cells to relate the requirements for G1 transit to those necessary for the transition from the G0 to the S phase. Cycling cells in the G1 phase required transcription, rapid translation, and a single growth factor (insulin-like growth factor [IGF] I) to initiate DNA synthesis. IGF I acted post-transcriptionally at a late G1 step. All cells in the G1 phase entered the S phase on schedule if either insulin (hyperphysiological concentration) or IGF I (subnanomolar concentration) was provided as the sole growth factor. In medium lacking all growth factors, only cells within 2 to 3 h of the S phase were able to initiate DNA synthesis. Similarly, cells within 2 to 3 h of the S phase were less dependent on transcription and translation for entry into the S phase. Cells responded very differently to inhibited translation than to growth factor deprivation. Cells in the early and mid-G1 phases did not progress toward the S phase during transcriptional or translational inhibition, and during translational inhibition they actually regressed from the S phase. In the absence of growth factors, however, these cells continued progressing toward the S phase, but still required IGF at a terminal step before initiating DNA synthesis. We conclude that a suboptimal condition causes cells to either progress or regress in the cell cycle rather than freezing them at their initial position. By using synchronized cultures, we also show that in contrast to earlier events, this final, IGF-dependent step did not require new transcription. This result is in contrast to findings that other growth factors induce new transcription. We examined the requirements for G1 transit by using a chemically transformed 3T3 cell line (BPA31 cells) which has lost some but not all ability to regulate its growth. Early- and mid-G1-phase BPA31 cells required transcription and translation to initiate DNA synthesis, although they did not regress from the S phase during translational inhibition. However, these cells did not need IGF for entry into the S phase.

Different growth factors stimulate cell division of rat mammary epithelial, myoepithelial, and stromal cell lines in culture

A number of single-cell-cloned cell lines have been used to examine the growth-promoting effects of putative mammotrophic agents on the various cell types in normal and neoplastic rat mammary glands. A partially purified novel pituitary-derived growth factor stimulates only cuboidal epithelial cells to divide whereas fibroblast growth factor (FGF) stimulates the growth of stromal and myoepithelial-like cells. Epidermal growth factor (EGF) has a widespread but variable growth-stimulating action, but prolactin and growth hormone are essentially inactive when added alone at a concentration of 5 micrograms/ml. Phosphoethanolamine stimulates the growth of one epithelial cell line and a derivative myoepithelial-like cell line, but is inactive on the other cell lines tested. The use of defined cloned cell lines provides a direct and reproducible assay for the identification and purification of inducers of mammary growth.

Brain and pituitary fibroblast growth factor activities behave identically on three independent high performance liquid chromatography systems

Fibroblast Growth Factors obtained from bovine brain and pituitary glands were compared. They were shown to behave identically on three high performance liquid chromatographic systems, which separate proteins by the independent criteria of size, charge and hydrophobicity. They also migrated similarly on electrophoresis in polyacrylamide gels in the presence of sodium dodecyl sulphate with an apparent molecular weight of 12,000. It was concluded that the two factors were very similar, or identical. They were active at promoting DNA synthesis in rat mammary fibroblasts (Rama 27) at a concentration of 0.1 ng/ml.

Growth factors and their action in vivo and in vitro

The molecular nature and mechanism of action of several of the growth factors including epidermal growth factor, fibroblast growth factor and platelet-derived growth factor is reviewed. The ectopic production of growth factors may be important in the growth development of certain tumours. In addition, attention is directed to the importance of the extracellular matrix in controlling cell proliferation and differentiation.

Induction of differentiation in a rat mammary epithelial stem cell line by dimethyl sulphoxide and mammotrophic hormones

Rama 25 is a clonal epithelial cell line derived from a dimethylbenzanthracene-induced rat mammary adenocarcinoma. In the presence of the mammotrophic hormones, insulin, hydrocortisone, estrogen and prolactin, Rama 25 produces small amounts of casein and forms domes at a low rate. The rates of both these processes can be greatly increased by the addition of dimethyl sulphoxide or hexamethylenebisacetamide which are also known to induce the differentiation of Friend erythroleukemia cells. Other compounds which stimulate the differentiation of Rama 25 cells include linoleic acid and 6-thioguanine. The intracellular pathways triggering changes in the two markers of differentiation are partially separable using different combinations of hormones, prolactin and hydrocortisone being the most important for the production of casein and the formation of domes respectively. The kinetics of differentiation, as judged by the appearance of these two markers, are characterised by two phases, a fixed period of 8 h (lag phase), the length of which is independent of the dimethyl sulphoxide concentration and a second phase where their rates are dependent on the concentration of dimethyl sulphoxide. Rama 25 cells do not become committed to differentiate during this lag phase but increasing numbers of cells do so after this period. We suggest that the differentiation processes occur in two stages. The first stage, involving the inducer, commits Rama 25 cells to a new differentiated state. The second stage, involving the hormones, modulates the expression of different markers of this state. Both casein production and dome formation can be blocked by inhibitors of DNA synthesis and show reciprocal changes with the rates of cellular DNA synthesis. Thus, in its hormonal and DNA synthetic requirements for differentiation, Rama 25 cells appear to resemble some of the mammary epithelial cells of mature virgin rats.

Growth-related changes in specific mRNAs of cultured mouse cells

A cDNA plasmid library has been constructed from the poly(A)+ RNA present in BALB/c3T3 cells after serum stimulation. Of 3,500 clones tested, approximately 0.5% contained inserts corresponding to mRNAs present at higher levels in serum-stimulated BALB/c 3T3 cell cultures than in quiescent cultures. Most of these RNA species increased 2- to 5-fold, and the kinetics of increase for various RNAs differed. One clone (28H6) hybridized to a 1-kilobase RNA species that is present at barely detectable levels in resting cells but is increased at least 15- to 20-fold after serum stimulation, reaching a maximal level coincident with the onset of DNA synthesis. This RNA was at a high level in proliferating cells but decreased rapidly as cells reached confluence. 28H6 RNA was also increased in resting cells infected with simian virus 40 or stimulated with platelet-derived growth factor.

In vitro evidence from tissue cultures to prove existence of rabbit and human renotropic growth factor

When synchronized primary rabbit kidney monolayer cell cultures were incubated with a medium that contained uninephrectomized rabbit serum, the incorporation of tritiated thymidine into DNA was much greater than that with a medium that contained normal rabbit serum. The maximal growth-stimulating activity of uninephrectomized rabbit serum on thymidine incorporation into confluent monolayer cultures and sparsely cultured cells was increased approximately two- and fivefold, respectively, above that of normal serum. We conclude that uninephrectomized sera contain a growth-stimulating factor. Similarly, sera from a uninephrectomized human kidney donor and a cancer patient stimulated primary human kidney cell cultures to incorporate tritiated thymidine at levels far beyond those with their prenephrectomized sera. The maximal growth-stimulating activities of uninephrectomized human sera with confluent monolayer cultures and sparsely cultured cells were approximately six- and 13-fold, respectively, above those with the prenephrectomized sera. Thus, the maximal growth-stimulating activity in uninephrectomized human sera was much greater than that in uninephrectomized rabbit sera. Differences in the maximal growth-stimulating activities may be due to differences in the relative number of cell types, for example, epithelial versus fibroblast, present in these kidney cell cultures. By the use of primary cultured cells from other organs such as rabbit skin and human prostate and primary kidney cultures from three species (rabbit, human, and hamster), the growth-stimulating factor in uninephrectomized sera showed organ specificity, that is, renotropic and species specificity in this in vitro assay system.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of wound healing, using brain extract with fibroblast growth factor (FGF) activity. II. Histological and morphometric examination of cells and capillaries

Reported in this paper are studies by which evidence was produced to increased formation of granulation tissue in rats, aged two and six months, seven days after repeated localised administration of brain extract from cattle with FGF activity (fibroblast growth factor). Such increased formation of granulation tissue was attributable to the formation in the same granulation tissue of larger amounts of capillaries, which actually provided conditions for better blood supply. The above increase was associated with stimulation of the synthetic function of fibroblasts and myofibroblasts in the granulation tissue. Comprehensive morphometric tests, including differential counting, appeared to show that additional effects had to be assumed, in particular on macrophages and lymphocytes. Such increase in angiogenesis seemed to suggest that in the in vivo model studied FGF proved to be, first of all, a factor of angiogenesis rather than a factor of fibroblast growth. The above results, as obtained from rats which differed in age, exhibited a certain variation in response to FGF. This seems to underline the importance of age-dependent examination also in the context of pharmacological studies.

Platelet-derived growth factor-modulated proteins: constitutive synthesis by a transformed cell line

Platelet-derived growth factor (PDGF) initiates replication of density-arrested BALB/c-3T3 mouse cells by rendering them "competent" to respond to factors contained in plasma. Treatment of quiescent cells with PDGF rapidly stimulates the preferential synthesis of several cytoplasmic proteins (molecular weights 29,000 to 70,000). Four of these proteins were noted within 1.5 hr of PDGF addition and one (pI) within 40 min. Inhibitors of RNA synthesis prevented the synthesis of these proteins. Both the synthesis of pI and the stimulation of DNA synthesis displayed a similar dose response to PDGF concentration. Pituitary fibroblast growth factor, which also induces competence, stimulated pI and pII synthesis. Plasma, epidermal growth factor, or insulin, which do not induce competence, did not stimulate selective synthesis of these proteins. A transformed variant of BALB/c-3T3 cells, which has retained the growth requirement for plasma factors but lost the requirement for PDGF, synthesizes these PDGF-modulated proteins constitutively.

Glucocorticoids inhibit the stimulatory effect of epidermal growth factor on the initiation of DNA synthesis

Confluent, quiescent Swiss 3T3 cells in culture can be stimulated to initiate DNA synthesis and divide by addition of growth factors to the culture medium. Here we show that hydrocortisone and other steroids which have glucocorticoid activity inhibit the stimulation of these cells by epidermal growth factor (EGF) in contrast to their reported enhancement of stimulation by fibroblast growth factor (FGF). Binding studies using [3H]-triamcinolone acetonide show that Swiss 3T3 cells contain a single class of glucocorticoid receptor of uniform affinity (KD = 2.0 nM), and about 34,000 receptor sites per cell. Those steroids which displace bound [3H]-triamcinolone acetonide are also effective in inhibiting the stimulation of DNA synthesis by EGF in the presence or absence of insulin, and the concentration of triamcinolone acetonide required for one-half maximal biological effect is in the same range as the KD. A similar concentration is required for one-half maximal enhancement of the effect of FGF. These results suggest that both the inhibitory and stimulatory effects of glucocorticoids may be mediated via these receptors, the different effects thus being due to differences in the intracellular events triggered by each growth factor.

Two growth factors and two hormones regulate initiation of DNA synthesis in cultured mouse cells through different pathways of events

Epidermal growth factor (EGF) as well as prostaglandin F2 alpha (PGF2 alpha), when added to quiescent, confluent Swiss 3T3 cells, stimulate the initiation of DNA synthesis, which occurs with apparent first-order kinetics after a lag phase of 14-15 hr. These two growth factors appear to stimulate similar events; insulin enhances and hydrocortisone can inhibit the stimulatory effect of either. Here we show that the addition of EGF and PGF2 alpha together, however, results in a synergistic effect seen at the end of the lag phase, but only when EGF and PGF2 alpha are added within 6 hr of each other. Addition of one growth factor 10 or 15 hr after the other delayed the synergy for 15 hr after the addition of the second growth factor. Insulin further increased the rate of entry into the s phage stimulated by EGF and PGF2 alpha together, whereas hydrocortisone inhibited the stimulatory effect observed with either EGF or PGF2 alpha alone. These results suggest that, in spite of the common events responsible for the interactions with the two hormones, EGF and PGF2 alpha must have differences in their sequences of events that initiate DNA synthesis.

Antagonism in action between mouse or human interferon and platelet growth factor

Human leukocyte and mouse fibroblast interferons abolished the mitogenic effect of human or bovine platelet growth factor (PGF) on human or mouse cells. Conversely, the antiviral and anticellular activity of both forms of interferon was inhibited by PGF in the homologous and in certain heterologous cell systems.

The stimulation of the initiation of DNA synthesis by fibroblast growth factor in Swiss 3T3 cells: interactions with hormones during the pre-replicative phase

Fibroblast Growth Factor (FGF) stimulates quiescent Swiss 3T3 cells to initiate DNA synthesis and divide. Cells begin to enter the S-phase after a lag of 13--15 hr, and the rate of initiation of DNA synthesis in the population can be quantified by a first order rate constant, k. A subsaturating concentration of FGF may establish the lag phase, while the value of k is dependent on the FGF concentration present during the second half of the lag phase. Insulin and hydrocortisone enhance the effect of FGF by increasing k without changing the lag phase, and they can act when added at any time after FGF. Prostaglandin E1 (PGE1) causes a decrease in k and a lengthening of the lag phase, and acts only when added during the first 8 hr. None of these agents stimulate DNA synthesis in the absence of FGF.

Epidermal thinning: evaluation of commercial corticosteroids

Epidermal thinning of mouse tail skin was compared for commercial preparations of clobetasol propionate (Dermovate), clobetasone butyrate (Eumovate), fluocinonide (Metosyn), and hydrocortisone butyrate (Locoid). The thickness measurements were ranked with those for hydrocortisone (1%), betamethasone valerate (Betnovate), triamcinolone acetonide (Ledercort), fluocinolone acetonide (Synlar), and prednisolone stearoylglycolate (Sinistrone) obtained in a previous study (Spearman and Jarrett, 1975). All steroids caused epidermal thinning, except clobetasone butyrate. Some cream and ointment vehicles were also assayed. Epidermal thickening was caused by the cream and ointment vehicles used for Eumovate and also by the cream employed for Locoid formulation.

Induction by lithium ion of multiplication of mouse mammary epithelium in culture

Lithium ion at concentrations between 2 and 20 mM simulated the stimulatory effects of insulin on the uptake of alpha-aminoisobutyric acid, synthesis of RNA and DNA, and cell multiplication in mouse mammary gland explants cultured in a chemically defined synthetic medium. Other monovalent cations were virtually ineffective. In most instances the stimulatory effect of lithium ion was somewhat smaller than and additive to that of insulin. However, lithium ion was incapable of substituting for the action of insulin in augmenting milk protein synthesis in mammary explants cultured with other lactogenic hormones, prolactin, and glucocorticoid. The observed similarities of the responses of mammary cells to lithium and insulin suggest that possible importance of cation(s) in the regulation of mammary cell proliferation, which may be a common basis for the action of the two agents. On the other hand, the observed inability of lithium to mimic the lactogenic effect of insulin indicates a specific function of the hormone in the functional differentiation of mammary cells.

The role of glucocorticoid hormones as biological amplifiers

Recent research in hormone action has been aimed at studying single effects in well-defined systems. As exemplified in several chapters of this book, it has been possible to deduce a general mechanism of action of the glucocorticoids using this approach. Most hormones, and the glucocorticoids in particular, do not act as independent agents in the intact animal. Although the best known example of how glucocorticoids interact with other hormones is the amplification of the effect of those whose action is mediated by cAMP, these steroids also augment the effects of a variety of other hormones and effectors. Such interactions are of interest in clinical medicine as well, since glucocorticoid hormones are used in combination with other drugs in a number of conditions, including the treatment of asthma, allergies, and certain kinds of shock and cancer. Neither the biochemical nor the pharmacologic basis for the effects of the glucocorticoids is known. In some cases the actions of other hormones are not observed unless the tissue has first been exposed to glucocorticoids. In these instances the glucocorticoids are said to exert a "permissive effect," since they allow a process to proceed at a maximal rate even though the steroid itself has no effect on this process. There is no doubt that such examples exist, as documented above: thus the concept of a "permissive effect" does have utility. The term fails to describe the more general role the glucocorticoids play, since in many instances the steroid also has a direct effect on the process itself, or optimizes a process in which the primary effector is not as yet known. Because of these cases, and because the historically more general usage first proposed by INGLE [1] seems to have been forgotten, use of the term "permissive effect" has been avoided in this chapter. An ultimate goal in glucocorticoid hormone research is to identify the mechanisms involved in the amplification effect these hormones exert. Now that the actions of these hormones and of the hormones they interact with are being defined, such work is within the realm of feasibility.

Specificity of the inhibition of DNA synthesis by extracts from cloned normal, sarcoma-virus-transformed and revertant 3T3 cells

Extracts containing tissue-specific DNA-inhibitory activity were prepared from normal FL (Swiss) and BALBc3T3 cells, from these cells transformed with sarcoma virus and from revertants cloned from the transformed cell lines. By testing all extracts on all cell lines we found that (1) production of and susceptibility to the inhibitors were decreased in transformed BALB/c cells (2) specificity varied with expression of the transforming genome, as an extract from a given cell line inhibited the growth of its cell of origin, e.g. revertant, more than normal or transformed cells, and (3) there was also a DNA-synthesis stimulator.

Hydrocortisone stimulation of human mammary epithelial cells

Rapid proliferation of mammary epithelial cells derived from biopsy specimens of human fibroadenomas was observed when medium was supplemented with ten percent fetal bovine serum and hydrocortisone (5 microgram per ml-1). Hydrocortisone in combination with FBS also led to a 2.5-fold increase in cell cluster attachment and subsequent colony formation. A similar effect was not observed with human serum. In contrast to fibroblast cell systems, insulin did not significantly alter cell growth. The results show that a mitogenic response to glucocorticoids by mammary epithelium may depend on the presence of factors in sera.

Effect of serum on cells cultured from human mammary tumors

Clusters of cells derived from biopsy specimens of human mammary ductal carcinomas form two morphologically distinct epithelial colonies in culture, designated as E and E'. The proportion of E' cell clusters that attached and formed colonies ranged from 0.3 to 13.0% with different tumors. Attachment was independent of tumor grade. Microscopic observations revealed that the survival of E' cell colonies was limited to approximately 10 days with rapid cell degeneration commencing about 7 days. A comparison of sera showed that colony formation by cells from malignant tumors during the 1st week of culture was maximum in the presence of fetal bovine serum. Human serum alone was 70 to 100% less effective in promoting E' colonies. The most significant finding was that human serum from normal donors inhibited E' colony development in the presence of FBS. Although human serum was less effective than FBS in promoting colony formation by clusters of E cells, an inhibition was not observed. Inhibitory activity could not be attributed to either antagonistic hormones or the source of human serum. These results demonstrate that normal human serum contains a factor(s) that exhibits an inhibitory activity specific for human epithelial cells (E') derived from malignant tumors.

The effect of chondrocyte growth factor on membrane transport by articular chondrocytes in monolayer culture

Chondrocyte growth factor (CGF), a contaminant of pituitary glycoprotein hormones, stimulates growth of cultured lapine articular chondrocytes while depressing SO4-proteoglycan synthesis. To study its effect on membrane transport, NIH-bTSH and two other preparations with comparable CGF activity were employed. In early log phase (36 hr) cultures CGF (64 microgram/ml) did not alter thymidine (dThd) uptake during the first 5 min. By 15 min however, TCA-precipitable dThd was 4-fold greater than in controls while the TCA-soluble fraction remained the same. CGF increased deoxy-glucose (DG) uptake in 36-hr old cultures. At 66 hr, CGF reduced DG transport. The transport of cycloleucine (CL) and aminoisobutyric acid (AIB) was reduced by CGF in 36 and 66-hr old cultures. There was a dose dependency between CGF concentration, the lowered uptake of DG, CL and AIB, and cell protein content. The effect of CGF on DG transport and dThd incorporation into DNA was not immediate but required prior exposure of the cells to CGF. CGF did not alter DG transport in rabbit or mouse fibrocytes or Chang liver cells. This and the reported finding that pituitary fibroblast growth factor (FGF), increases amino acid transport in other cells suggests that the biological specificity of CGF may not be identical to that of FGF.

Factors involved in the modulation of cell proliferation in vivo and in vitro: the role of fibroblast and epidermal growth factors in the proliferative response of mammalian cells

The control of proliferation of mesoderm-derived cells by EGF and FGF has been examined taking, as an example, the vascular endothelium. The mechanisms by which cell proliferation can be brought to a stop in vivo and in vitro have been reviewed.

The regulation by fibroblast growth factor of early transport changes in quiescent 3T3 cells

This study involves the use of fibroblast growth factor (FGF) as a substitute for exogenous serum to examine the early transport changes which occur when quiescent 3T3 cells re-initiate active growth. FGF, in nanogram amounts, together with insulin and dexamethasone, can induce mitogenesis and mitosis in 3T3 cells GO-arrested by holding in growth medium containing 0.8% calf serum. In terms of quiescent cell transport activity enhancement, FGF is 300,000-fold more effective than fresh serum, on a protein basis. In addition, very short exposure of serum-depleted cells to FGF indicates that a distinct temporal or time sequence exists in the transport system activation process. For example, uptake of alpha-aminoisobutyric acid (AIB) and uridine are stimulated very rapidly, whereas hypoxanthine uptake does not respond until much later. Closer analysis shows that AIB uptake is maximally enhanced within zero to two minutes after FGF addition to cells. Finally, the stimulatory effect of FGF on transport system activities is specific in terms of the proliferative state of the cells to which it is added, and in terms of the uptake systems which respond to it.

Temporal sequence of hormonal interactions during the prereplicative phase of quiescent cultured 3T3 fibroblasts

After addition of prostaglandin F2alpha (PGF2alpha) and insulin to quiescent cultured 3T3 fibroblasts a constant lag phase of 15 hr occurs before an increased rate of cellular exit from G1 is observed. The latter process follows first order kinetics, which can be quantified by a rate constant k. The temporal relationship of the interactions of PGF2 alpha, insulin, and hydrocortisone to produce alterations in the rate of exit from G1 was investigated. PGF2alpha establishes a constant lag phase and produces alterations in the rate constant k. These two effects can be partially separated by adding two concentrations of PGF2alpha at different times. Insulin fails to establish the lag phase but can stimulate the effect of PGF2alpha when added at any time after PGF2alpha. Hydrocortisone reduces the value of k when added between 0 and 3 hr after PGF2alpha. These results show that the lag phase can beseparated into temporal regions during which hormones can interact to produce changes in the rate of cellular exit from G1.

Differential effects of inhibitors of cell division upon the growth stimulating activities of insulin and serum in nutritionally depleted human and mouse cells

Cultured mouse and human cells were arrested in their growth by artificially depriving them of phosphate. The quiescent cells could be stimulated to synthesize DNA and to divide by addition to the growth medium of insulin, dialyzed serum and/or the full concentration of phosphate. In order to gain insight into mechanisms by which insulin and serum stimulate growth, the inhibitory effects of antimitotic agents were examined. Of the inhibitors tested, vinblastine and cytocalasin B abolished the growth promoting activity of insulin, while colchicine inhibited the activity of both serum and insulin. The present results suggest that insulin-stimulated growth is meciated by a different path way than serum-stimulated growth and is sensitive to mechanisms that occur at various times prior to insulin addition.