Embryonal carcinoma cell growth and differentiation. Production of and response to molecules with transforming growth factor activity

Transforming growth factors are known to induce anchorage-independent growth of non-transformed cells, and are released by a variety of cells, including MSV-transformed cells. This study demonstrates that the differentiated cells derived from F9 and PC-13 embryonal carcinoma cells, but not the parental cells themselves, respond by increased growth to several factors released by MSV-transformed cells, including partially purified sarcoma growth factor. The chemical properties of the growth-promoting activity are shown to match the chemical properties of the transforming growth factors released by MSV-transformed cells. Furthermore, F9 and PC-13 embryonal carcinoma cells, which do not respond to factors released by MSV-transformed cells, are shown to release factors with transforming growth factor activity. Based on the close relationship between mouse embryonal carcinoma cells and cells of early mouse embryos, it is suggested that molecules with transforming growth factor activity may play a role during the early stages of mammalian development.     

Cellular responsiveness to growth factors correlates with a cell's ability to express the transformed phenotype

Five random subclones of the rat fibroblast line F2408 vary in their frequency of transformation by the unrelated Kirsten murine sarcoma virus and Abelson murine leukemia virus. The same pattern of sensitivity is displayed when the cells are induced to anchorage-independent growth (transformed) by epidermal, platelet-derived, and sarcoma growth factors, or by whole serum. Our results demonstrate that a growth factor's ability to render cells anchorage independent is not unique to transforming growth factors, but common to many growth factors; anchorage-independent growth is a function of the total growth factor concentration in the medium; cells vary in their inherent responsiveness to growth-factor-induced anchorage-independent growth; and cells resistant to growth-factor-induced anchorage-independent growth are also resistant to transformation by a variety of tumor viruses. We conclude that the way a cell responds to growth factors plays a central role in the expression of the transformed phenotype.     

Prostatropin and acidic FGF also support proliferation of an EGF-dependent keratinocyte cell line

Despite the relevance of epithelial cells to the biology of cancer, considerably less is known about the capacity of specific growth factors to control the proliferation of these cells compared to information available on fibroblastic cells. Epidermal growth factor is the most widely recognized mitogen for epithelial cells. We demonstrate that prostatropin and acidic fibroblast growth factor, structurally similar molecules, are potent growth factors for the mouse keratinocyte cell line Balb/MK. This indicates that these growth factors in addition to epidermal growth factor may be of physiological relevance to epidermal cell proliferation.     

The role of growth factors in self-renewal and differentiation of haemopoietic stem cells

Haemopoietic stem cells in vivo proliferate and develop in association with stromal cells of the bone marrow. Proliferation and differentiation of haemopoietic stem cells also occurs in vitro, either in association with stromal cells or in response to soluble growth factors. Many of the growth factors that promote growth and development of haemopoietic cells in vitro have now been molecularly cloned and purified to homogeneity and various techniques have been described that allow enrichment (to near homogeneity) of multipotential stem cells. This in turn, has facilitated studies at the mechanistic level regarding the role of such growth factors in self-renewal and differentiation of stem cells and their relevance in stromal-cell mediated haemopoiesis. Our studies have shown that at least some multipotential cells express receptors for most, if not all, of the haemopoietic cell growth factors already characterized and that to elicit a response, several growth factors often need to be present at the same time. Furthermore, lineage development reflects the stimuli to which the cells are exposed, that is, some stimuli promote differentiation and development of multipotential cells into multiple cell lineages, whereas others promote development of multipotential cell into only one cell lineage. We suggest that, in the bone marrow environment, the stromal cells produce or sequester different types of growth factors, leading to the formation of microenvironments that direct cells along certain lineages. Furthermore, a model system has been used to show the possibility that the self-renewal probability of multipotential cells can also be modulated by the range and concentrations of growth factors present in the environment. This suggests that discrete microenvironments, preferentially promoting self-renewal rather than differentiation of multipotential cells, may also be provided by marrow stromal cells and sequestered growth factors.     

Stimulation of cell growth and inhibition of prostacyclin production by heparin in human umbilical vein endothelial cells

We characterized human umbilical vein (HUV) endothelial cells as to cell growth and prostacyclin production to get a better understanding of the properties of endothelial cells. Endothelial cell growth supplement (ECGS) and basic fibroblast growth factor (FGF) stimulated HUV endothelial cell growth. Heparin further enhanced the cell growth stimulated by ECGS, but not the cell growth stimulated by FGF or in the absence of these growth factors. In the presence of ECGS, the prostacyclin-producing capacity of the cells was inhibited by heparin. However, in the presence of FGF of in the absence of growth factors, heparin did not inhibit prostacyclin production. Therefore, it is likely that there is a specific correlation between heparin and growth factors for endothelial cells in the blood vessel to maintain nonthrombogenicity properly. Heparin-treated cultures may not be suitable for some examinations of prostacyclin production by vascular endothelial cells.     

Differential responsiveness of myc- and ras-transfected cells to growth factors: selective stimulation of myc-transfected cells by epidermal growth factor.

To identify functional relationships between oncogenes and growth factors, we compared the effects of transfected myc and ras oncogenes on the responsiveness of Fischer rat 3T3 cells to three growth factors: epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and transforming growth factor-beta (TGF-beta). Control cells did not grow in soft agar under any conditions. ras-Transfected cells grew in soft agar under all conditions tested and were insensitive to the stimulatory effects of exogenous growth factors. These cells secreted elevated levels of both EGF-like factors and TGF-beta, suggesting that the lack of responsiveness of these cells to exogenous growth factors arose from autocrine stimulation. myc-Transfected cells displayed conditional anchorage-independent growth: they formed numerous colonies in soft agar in the presence of EGF but relatively few colonies in the presence of PDGF or TGF-beta. Secretion of EGF-like factors and TGF-beta by these cells was not elevated above that of control cells. These results suggest a model for the mechanism of cooperation between myc and ras oncogenes in which ras-like genes induce growth factor production, while myc-like genes increase the responsiveness of cells to these factors.     

Identification and characterization of polypeptide growth factors secreted by murine embryonal carcinoma cells

Undifferentiated P19 and PC13 murine embryonal carcinoma (EC) cells have been analyzed for their ability to secrete polypeptide growth factors. This has been carried out by a combination of specific bioassays and the use of biochemical and immunological detection methods. Both P19 and PC13 EC cells secrete a platelet-derived growth factor (PDGF)-like growth factor, a type beta transforming growth factor, and insulin-like growth factors. In addition, PC13 EC cells secrete a heparin-binding growth factor functionally related to fibroblast growth factor, while P19 EC cells secrete transforming growth factor-alpha. This is the first demonstration for secretion of transforming growth factor-alpha by an equivalent of early embryonic cells. The possible paracrine growth stimulating effects of these growth factors have been tested on differentiated derivatives of P19 EC cells, corresponding to all three germ layers. The differences in growth factor production by various embryonal carcinoma cells are discussed in relation to the developmental origin of these cell lines.     

Polyomavirus middle tumor antigen increases responsiveness to growth factors.

The middle tumor antigen (mT) of polyomavirus is unable to transform a clone of NIH 3T3 cells to anchorage independence (L. Raptis and J.B. Bolen, J. Virol. 63:753-758, 1989). However, this oncogene increased the responsiveness of these cells to the growth factors (alpha-like and beta-type transforming growth factors) produced by cells possessing the whole transforming region of polyomavirus. This resulted in the growth of NIH 3T3 cells, expressing mT under control of the dexamethasone-regulatable mouse mammary tumor virus promoter, in agar medium supplemented with these growth factors upon addition of the inducer. Therefore, mT, a transforming oncogene, is able to enhance the responsiveness of established cells to growth factors, a property previously attributed primarily to myc and other establishment type oncogenes.     

Role of colony-stimulating factors in the biology of acute myelogenous leukemia

A high proportion of acute myeloid leukemias (AML) recently investigated for their capacity to synthesize biologically active bioregulatory molecules was found to accumulate messenger (m) RNA and to produce membrane-bound or -secreted forms of stimulating factors for granulocyte, macrophage and mixed granulocyte-macrophage colony growth. Blast cells have also been found to secrete interleukin 1, tumor necrosis factor-alpha, interleukin 6, and to express receptors for various growth factors as well. However, growth factors like interleukin 2 and interleukin 3 have not been identified as AML products, and several other factors including interleukin 4, interleukin 5, etc. need further evaluation. Responsiveness of clonogenic leukemic cells to exogenous growth-promoting factors in vitro suggests a possible role of these biomolecules in the course of these disorders. Important evidence for the crucial role of growth factors, at least in some subtypes of AML, has been provided by demonstrating constitutive growth factor production by leukemic cells and their autonomous in vitro growth which is dependent on autocrine secretion of a specific growth factor. The concert of mechanisms providing stimulatory and inhibitory signals for hematopoiesis, which is adapted to the various physiological requirements of the organism, may have multiple defects in AML. This leads to successive steps of malfunctioning of cells, which finally express a fully malignant phenotype. In addition, these derangements also lead to defects in accessory cells on the level of mediator communication. However, there is evidence for autonomous growth promotion of AML blast by constitutive production of growth factors active in an autocrine fashion (GM-CSF, G-CSF, interleukin 6) and by recruitment of accessory cells to increase CSF supply (GM-CSF, G-CSF) via molecules such as interleukin 1 and TNF-alpha in a paracrine fashion. Molecular analysis of transformed hematopoietic cells has revealed changes of the genome, e.g., insertion of viral genetic information or cytogenetic fractures at DNA sites controlling growth factor gene activation. These events appear to be crucial in the induction of uncontrolled growth factor expression promoting oncogenic transformation of hematopoietic progenitor cells.     

Effects of growth stimulatory factors on mitogenicity and c-myc expression in poorly differentiated and well differentiated human colon carcinoma cells

We demonstrate the differential sensitivity of poorly differentiated and well differentiated human colon carcinoma cells to nutrients alone or to nutrients and polypeptide growth factors under completely serum-free conditions. 3H-Thymidine incorporation into trichloroacetic acid precipitable material and autoradiographic analysis indicated that nutrient replenishment alone was sufficient to initiate DNA synthesis in quiescent poorly differentiated cells, whereas defined polypeptide growth factors produced no additional effect. In contrast, well differentiated cells were mitogenically stimulated to a much greater extent by growth factors (epidermal growth factor + insulin + transferrin), than by nutrient replenishment alone. Expression of the c-myc protooncogene was increased approximately 5-fold after growth factor addition to the well differentiated cells. Maximal expression of c-myc occurred at 4 h post stimulation. In contrast, nutrients resulted in only a slight up-regulation of c-myc (1.8-fold) at approximately 90 min after addition. Addition of nutrients and/or growth factors to the poorly differentiated colon carcinoma cells resulted in an initial decline in c-myc expression (90 min), presumably due to removal of endogenous growth stimulators. Expression of c-myc returned to baseline levels by 24 h after additions. The results indicate that differential sensitivity to polypeptide growth factors is related to differentiation status in this model system and suggest that the insensitivity of poorly differentiated cells to exogenous growth factors may be due to a greater production of autocrine growth stimulators.     

Phenotypic transformation of normal rat kidney cells in a growth-factor-defined medium: induction by a neuroblastoma-derived transforming growth factor independently of the EGF receptor

Polypeptide growth factor activity in serum can be destroyed by treatment with dithiothreitol. When such growth-factor-inactivated serum is used as a supplement of culture media instead of regular serum, normal rat kidney (NRK) cells become quiescent unless defined polypeptide growth factors like insulin and epidermal growth factor (EGF) are added. On this basis a growth-factor-defined medium has been developed for NRK cells, which permits cell proliferation as rapidly as in media supplemented with serum, even at low cell densities. Moreover, cells can be serially passaged in this medium. NRK cells can be induced to grow in semisolid media when incubated with transforming growth factors. The growth-factor-defined medium permits soft agar growth experiments of NRK cells, without interference from polypeptide growth factors in serum. Using this assay system we have shown that EGF alone is unable to induce any degree of anchorage-independent growth in NRK cells. However, a recently identified transforming growth factor from mouse neuroblastoma cells which does not compete with EGF for receptor binding is able to induce progressively growing colonies of NRK cells in soft agar, even without additional EGF.     

Growth of fetal rat gastro-intestinal epithelial cells is region-specifically controlled by growth factors and substrata in primary culture

The mammalian gastro-intestinal tract can be divided into three parts: esophagus and forestomach, glandular stomach, and intestine. We have previously reported primary culture systems for duodenal and glandular stomach epithelial cells in which the cells express tissue-specific marker proteins. However, the effects of growth factors and substrata on cell growth have not been fully investigated. In this study a primary culture system was established for forestomach epithelial cells and the mechanism by which the growth of gastro-intestinal epithelial cells is controlled in primary culture was examined. Forestomach, glandular stomach and duodenal epithelial cells proliferated rapidly in culture, increasing their numbers about 30-, 20-and 10-fold, respectively, in the first 5 days. Scanning electron microscopy showed that these three types of epithelial cells exhibited region-specific morphologies in culture. Results on the effects of growth factors and substrata on the proliferation of the epithelial cells revealed that the culture conditions required to induce maximal epithelial growth differed. Forestomach and glandular stomach epithelial cells required similar combinations of growth factors to proliferate, and these were quite different from those required for duodenal epithelial cells. Glandular stomach and duodenal epithelial cells could proliferate in a serum-free condition while forestomach epithelial cells could not. Thus, glandular stomach epithelial cells exhibited intermediate characteristics between forestomach and duodenal epithelial cells regarding their growth factor requirement. Glandular stomach and duodenal epithelial cells could not proliferate on plastic without collagen substrata while forestomach epithelial cells could. Duodenal epithelial cells proliferated faster on collagen gels than on collagen films, and forestomach epithelial cells faster on collagen films than on collagen gels. Glandular stomach epithelial cells proliferated similarly on both substrata. Thus again, glandular stomach epithelial cells exhibited intermediate characteristics between forestomach and duodenal epithelial cells regarding their substratum dependency. We conclude that the growth of gastro-intestinal epithelial cells is affected by both growth factors and substrata, and that glandular stomach epithelial cells exhibit intermediate characteristics between forestomach and duodenal epithelial cells in responding to these factors. These results suggest that a head-to-tail gradient exists in the gastro-intestinal tract which controls the epithelial response to growth factors and substrata.     

Conditional responsiveness of a chemically transformed cell line to growth factor stimulated DNA synthesis

BP3T3, a clonal benzo(a)pyrene-transformed BALB/c-3T3 cell line, is conditionally responsive to growth factor stimulation. Density arrested cell populations deprived of growth factors by pretreatment with 0.5% platelet-poor plasma synthesized DNA both in response to ng/ml concentrations of PDGF, EGF, and somatomedin C, and in response to insulin, plasma, and serum. The above agents acted singly to induce DNA synthesis, but synergism is suggested because a higher percentage of cells were stimulated to enter the S phase when the growth factors were added in combination. Desensitization to growth factors occurred when cultures were pretreated with the high concentration of growth factors present in 10% serum (or plasma). In desensitized cultures none of the above agents, added singly or in combination, stimulated DNA synthesis. This effect appears to be global because pretreatment with one growth factor (e.g., insulin) inhibited the action of another (e.g., PDGF). Cell density appears to play a critical role in regulating DNA synthesis. Unlike nontransformed BALB/c-3T3 cells whose density is regulated by the serum concentration, the density of BP3T3 cells reached a plateau when cultures were grown in a serum (or plasma) concentration of 3% or greater. Such density arrested cultures were growth factor unresponsive; however, the cells rapidly responded to growth factors by synthesizing DNA and replicating when reseeded at a lower cell density. Thus the growth of BP3T3 cells is regulated by both growth factors and cell density.     

Gut hormones with activity to modulate cellular growth

Recent progress in cancer research revealed that gut hormones have the activity to regulate the cellular growth of cancer cells. Gastrin, cholecystokinin and vasoactive intestinal peptide were demonstrated to stimulate the growth of gastric cancer cells, pancreatic cancer cells and colon cancer cells, respectively. Accordingly, it is possible to assume that these gut hormones may play an important role in the progression of these cancers. Further studies will be required to clarify the role of gut hormones as physiological growth factors in gastrointestinal tissues. The other aspect of gut hormones related with cellular growth is their role as autocrine growth factors. Gastrin-releasing peptide (GRP) is classified as a gut hormone with the structural similarity with amphibian bombesin. Several reported findings indicate that GRP functions as an autocrine growth factor for human small cell lung carcinoma; a monoclonal antibody for GRP is now applied for the therapy of this cancer. It is important to find out other gut hormones functioning as autocrine growth factors.     

Mouse embryonic stem cells and preimplantation embryos require signaling through the phosphatidylinositol 3-kinase pathway to suppress apoptosis

Whereas most mammalian cells require extracellular signals to suppress apoptosis, preimplantation embryos can survive and develop to the blastocyst stage in defined medium without added serum or growth factors. Since cells of these embryos are capable of undergoing apoptosis, it has been suggested that their lack of dependence upon exogenous growth factors results from the production of endogenous growth factors that suppress apoptosis by an autocrine signaling mechanism. In the present study, we have examined the growth factor requirements and intracellular signaling pathways that suppress apoptosis in both mouse preimplantation embryos and embryonic stem (ES) cells, which are derived from the blastocyst inner cell mass. Cultured ES cells, in contrast to intact embryos, required serum growth factors to prevent apoptosis. Suppression of ES cell apoptosis by serum growth factors required the phosphatidylinositol 3-kinase (PI 3-kinase) signaling pathway, since apoptosis was rapidly induced by inhibition of PI 3-kinase with LY294002. In contrast, inhibition of MEK/ERK signaling with U0126 or of mTOR with rapamycin had no detectable effect on ES cell survival. Thus, like most mammalian cells, the survival of ES cells is mediated by growth factor stimulation of PI 3-kinase signaling. Treatment with LY294002 (but not with U0126 or rapamycin) similarly induced apoptosis of mouse blastocysts in serum-free medium, indicating that intact preimplantation embryos are also dependent upon PI 3-kinase signaling for survival. These results demonstrate that PI 3-kinase signaling is required to suppress apoptosis of both ES cells and intact preimplantation embryos, consistent with the hypothesis that survival of preimplantation embryos is maintained by endogenous growth factors that stimulate the PI 3-kinase pathway.     

In vitro survival and proliferation of porcine primordial germ cells

Primordial germ cells (PGC) collected from the genital ridge of Day 25 porcine embryos were cultured on STO feeder cells in medium with or without supplemented growth factors. The effects on porcine PGC proliferation of leukemia inhibitory factor (LIF), LIF + stem cell factor (SCF) or LIF + SCF + basic fibroblast growth factor (bFGF), growth factors shown to be essential for in vitro survival and proliferation of murine PGC, were tested. After histochemical staining, both freshly collected and cultured PGC expressed alkaline phosphatase activity. With or without supplemented growth factors, porcine PGC survived and proliferated in culture for at least 5 d. None of the growth factors tested markedly enhanced in vitro growth of porcine PGC. These results suggest that growth factors provided by either the STO feeder layer or the cultured PGC themselves are sufficient to support in vitro survival and proliferation of porcine PGC. With the support of STO cells, addition of growth factors shown to be essential for the in vitro growth of murine PGC is not required for survival and proliferation of cultured porcine PGC.     

The role of polypeptide growth factors in phenotypic transformation of normal rat kidney cells

A serum-free assay has been established for studying the role of polypeptide growth factors in inducing loss of density-dependent inhibition of growth of normal rat kidney (NRK) cells. The process has been characterized by measuring the time course of [3H]thymidine incorporation into confluent, quiescent NRK cultures stimulated by defined polypeptide growth factors, in combination with cell counting studies, increases in DNA content, and cell cycle analysis by means of a fluorescence-activated cell sorter. It is shown that none of the growth factors tested (epidermal growth factor, platelet-derived growth factor, transforming growth factor-beta, and retinoic acid) is able to induce loss of density-dependent inhibition of growth by itself, but strong synergism was observed when combinations of growth factors were tested. None of the above factors was found to be essential, however, since any combination of three of the above four growth factors strongly induced the process. Strong parallels were observed between the growth factor requirements for inducing loss of density-dependent inhibition of growth under serum-free conditions and the requirements for induction of anchorage-independent proliferation under growth factor-defined assay conditions. This indicates that most likely the same cellular processes underlie these two aspects of phenotypic transformation, although data indicate that anchorage-independent proliferation may be a more restricted property of phenotypic transformation than loss of density dependence of proliferation. It is concluded that phenotypic transformation of NRK cells does not require specific polypeptide growth factors, but reflects the ability of these cells to respond to multiple growth factors.