Ectopic production of heparin-binding growth factors and receptors for basic fibroblast growth factor by rat mammary epithelial cell lines derived from malignant metastatic tumours

An in vitro model of epithelial cell growth stimulation in the rodent mammary gland

Mouse mammary epithelial cell cultures previously described bring about extensive proliferation and a cell population with the appropriate markers for luminal ductal epithelial cells, and also the ability to form normal tissue after implantation into mice. This success may result from a culture environment that resembles certain aspects of the environment in the mammary gland. Mouse mammary epithelial cells, whose proliferation is limited when plated alone, can be stimulated to multiply by contact with lethally irradiated cells of the LA7 rat mammary tumour line. Most of the proliferative stimulus is imparted by direct cell contact between LA7 and mouse mammary cells. Junctions, including adherens junctions, form among all cells in the culture, much as junctions form in the mammary gland. LA7 cells secrete TGFalpha and bFGF, factors found in the mammary gland, and factors to which mouse mammary cells respond in culture. Mouse mammary cells express keratins 8 and 18, markers for luminal cells of the mammary duct. LA7 cells express keratin 14 and vimentin, markers for myoepithelial cells. These facts, taken together, fit a model of cell replacement in an epithelial tissue and also imitate the relationship between luminal ductal cells and myoepithelial cells in the mammary gland. This method of culturing cells is useful, not only for in vitro-in vivo carcinogenesis studies, but also for the study of mechanisms by which growth signals are imparted from one cell to another.

Estrogen mitogenic action. I. Demonstration of estrogen-dependent MTW9/PL2 carcinogen-induced rat mammary tumor cell growth in serum-supplemented culture and technical implications

The MTW9/PL cell line was established by our laboratory in culture from the carcinogen-induced hormone-responsive MT-W9A rat mammary tumor of a Wistar-Furth (W/Fu) rat. This tumor formed estrogen, androgen, and progesterone responsive tumors in W/Fu rats (Sirbasku, D. A., Cancer Res. 38:1154-1165; 1978). It was later used to derive the MTW9/PL2 cell population which was also estrogen-responsive in vivo (Danielpour, D., et al., In Vitro Cell. Dev. Biol. 24:42-52; 1988). In the study presented here, we describe serum-supplemented culture conditions in which the MTW9/PL2 cells demonstrate > or = 80-fold steroid hormone growth responses. All sera used were steroid hormone-depleted by charcoal-dextran treatment at 34 degrees C. The studies were done with horse serum as well as serum from other mammalian species. The growth of the MTW9/PL2 cells was biphasic in response to hormone-depleted serum. Concentrations of < or = 5% (v/v) promoted optimum growth. Above this concentration, serum was inhibitory. Concentrations > or = 40% (v/v) inhibited growth altogether. Addition of 1.0 x 10(-13)-1.0 x 10(-8) M 17beta,-estradiol (E2) reversed the inhibition completely. At 1.0 x 10(-8) M, estrone, estriol and diethylstilbestrol promoted growth as well as E2. Testosterone and dihydrotestosterone promoted growth only at > or = 10(-7) M. Progesterone was effective only at > or = 10(-6) M. Cortisol was ineffective. Labeled-hormone-binding analysis and Western immunoblotting documented that MTW9/PL2 cells had estrogen and progesterone receptors but not androgen or cortisol receptors. Estrogen treatment of MTW9/PL2 cells induced a concentration and time dependent increase in progesterone receptors. We conclude (1) the MTW9/PL2 population is the first highly steroid hormone-responsive rat mammary tumor cell line to be established in culture from a carcinogen-induced tumor, and (2) sera from a number of species including horse, rat and human contain an inhibitor which mediates estrogen sensitive MTW9/PL2 cell growth in culture.

Expression and localization of members of the fibroblast growth factor family in the bovine mammary gland

The goal of the study was to examine the expression and localization of members of the fibroblast growth factor family in the bovine mammary gland during different developmental and functional stages. Mammary tissue was obtained from German Brown Swiss cows (n = 23) during defined stages of mammogenesis (before and during pregnancy), lactogenesis, peak and late lactation, and involution. Extracted mRNA was analyzed by reverse transcription polymerase chain reaction and RNase protection assay. The tissue content of fibroblast growth factor-1 and fibroblast growth factor-2 was determined by radioimmunoassay, and the localization of fibroblast growth factor-2 was determined by immunohistochemistry. The highest mRNA concentration for fibroblast growth factor-1, -2, and -7 and their receptors was detected in the glands of virgin heifers or primigravid heifers during involution; less abundant fibroblast growth factor mRNA was detected during lactogenesis and galactopoiesis. Tissue protein concentrations of fibroblast growth factor-1 and fibroblast growth factor-2 showed similar tendencies. Immunoreactive fibroblast growth factor-2 was observed during mammogenesis and involution in endothelial cells, ductal epithelial cells, myoepithelial cells, and some alveolar cells. After positive staining, fibroblast growth factor-2 could only be observed in endothelial and myoepithelial cells during lactogenesis and could only be observed in myoepithelial cells during galactopoiesis. Expression, tissue concentration, and distinct localization suggest that fibroblast growth factors may be important in the local regulation of the bovine mammary gland.

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.

Fibroblast growth factors and their receptors

Fibroblast growth factors (FGFs) represent a group of polypeptide mitogens eliciting a wide variety of responses depending upon the target cell type. The knowledge of the cell surface receptors mediating the effects of FGFs has recently expanded remarkably. The complexity of the FGF family and the FGF-induced responses is reflected in the diversity and redundancy of the FGF receptors. In this review, a number of biochemical characteristics and biological properties of the FGF family and its receptors are described and their expression both in normal tissues and in tumours is discussed. Finally we speculate on the targetting of growth inhibition agents to tumours through FGF receptors.

Stem cells in breast epithelia

The rodent and human nonpregnant mammary glands contain epithelial, intermediate and myoepithelial cells which have all been isolated as cell lines in vitro. Transforming growth factor-alpha (TGF alpha) and basic fibroblast growth factor (bFGF) are produced by myoepithelial cells and can stimulate the growth of intermediate stem cells in vitro. Epithelial and intermediate cells behave like stem cells in vitro, since they can differentiate into alveolar-like an myoepithelial cells. The myoepithelial differentiation pathway is associated with the early expression of a calcium-binding regulatory protein called p9Ka and the protease, Cathepsin D. Myoepithelial cells are also present in benign lesions but not in malignant mammary carcinomas of rats or humans, whose resultant cell lines fail to differentiate completely along the myoepithelial cell pathway. Loss of the myoepithelial cell in some invasive carcinomas may be compensated, at least in part, by changes in malignant cells. Over-expression of TGF alpha and/or erbB receptors may reduce the requirement for TGF alpha, whilst ectopic production of bFGF and its receptors and p9Ka/Cathespin D may assist in tumorigenesis and in metastasis, respectively. Thus compensation for, or retention of, molecules potentially involved in the differentiation of mammary cells may be a mechanism by which malignancy progresses in some human invasive carcinomas.

Interaction of heparan sulfate from mammary cells with acidic fibroblast growth factor (FGF) and basic FGF. Regulation of the activity of basic FGF by high and low affinity binding sites in heparan sulfate

We have determined the relationship between the binding sites for acidic fibroblast growth factor (aFGF) and basic FGF (bFGF) in heparan sulfate (HS) prepared from a panel of mammary cell lines and the ability of the HS to activate aFGF and bFGF in DNA synthesis assays. The ka of the HS for aFGF fell into three groups, whereas the kd (0.0015-0.016 s-1) and the Kd (0.4-8.6 microM) formed a continuum. bFGF possessed a high affinity binding site (Kd 22-30 nM) with a fast ka (320,000-550,000 M-1 s-1), termed "fast/high," and a lower affinity site (Kd 47-320 nM) with a slower ka (35,000-150,000 M-1 s-1), termed "slow/low." Most of the species of HS possessed the latter binding site, which was able to activate bFGF in HS-deficient fibroblasts. However, the HS from the culture medium of the mammary fibroblasts and the myoepithelial-like cells possessed both a fast/high and a slow/low binding site and could not activate bFGF, although it could potentiate the growth-stimulatory activity of aFGF. Treatment of the HS possessing two binding sites for bFGF with heparitinase 1 released oligosaccharides that were able to restore the activity of bFGF in HS-deficient fibroblasts.

Elevated expression of calcium-binding protein p9Ka is associated with increasing malignant characteristics of rat prostate carcinoma cells

Northern and Western blotting techniques were used to study expression of the mRNA and corresponding protein product of the S100-related calcium-binding molecule p9Ka in 6 different metastatic cell lines of the Dunning R3327 rat prostate cancer model. In cells with the lowest metastatic capability (G cells), p9Ka mRNA was barely detectable. In 2 weakly metastatic cell lines (AT-1 and AT-2), p9Ka transcript amounts were, respectively, 6.29 +/- 0.74 and 5.55 +/- 1.11 times that detected in the G cells. In 3 highly metastatic cell lines (AT-3, MAT-LyLu and MAT-Lu), the amounts of p9Ka mRNA were, respectively, 12.85 +/- 2.82, 13.06 +/- 1.69 and 11.62 +/- 1.81 times that expressed in the G cells. Western blot analyses detected no p9Ka protein in the G cells. The amounts of p9Ka protein expressed by tumour cells of intermediate metastatic capability (AT-1 and AT-2) were 3.4 +/- 1.3 microg and 3.3 +/- 1.4 microg, respectively, per 1 x 10(6) cells. The amounts of p9Ka protein expressed by the tumour cells of highest metastatic capability (AT-3, MAT-LyLu and MAT-Lu) were 8.3 +/- 1.1 microg, 8.7 +/- 1.6 microg and 9.6 +/- 1.7 microg, respectively, per 1 x 10(6) cells. Our data reveal a direct association between the elevated expression of mRNA and the p9Ka protein amounts and the increased metastatic capability of individual prostatic cancer cell lines. We suggest that calcium-binding protein p9Ka may play an important role in the metastatic behaviour of rat prostate cancer.

Invasion of human colorectal carcinoma cells is promoted by endogenous basic fibroblast growth factor

The growth-stimulatory and invasion-promoting effects of basic fibroblast growth factor (bFGF) were examined in 2 series of related human colon carcinoma cell lines (HCT116A, HCT116B and 20-10-1 as well as and LS180, LS174T and ARK1A) that exhibit different invasive potentials. The invasive cell lines 20-10-1 and ARK1A grew more rapidly than their non-invasive counterparts; exogenously added bFGF stimulated the proliferation of all the cells. When extracts of the cells were fractionated on columns of heparin-Sepharose, bFGF-like activity was found in extracts from each cell line. The amount of bFGF-like growth-stimulatory activity was greater in the more invasive cells: the invasive cells 20-10-1 contained 35-fold more activity than the non-invasive HCT116A cells, and the ARK1A cells contained 15-fold more activity than LS180 cells. Relatively small amounts of bFGF-like activity were recovered from medium conditioned by the invasive cells. The bFGF-like growth-stimulatory activity from the cell extracts was neutralised by an antibody to bFGF, and immunoblotting revealed the presence of an 18 kDa immunoreactive polypeptide, consistent with the presence of bFGF in the cell extracts. Exogenously added bFGF caused the usually non-invasive HCT116A cells to invade collagen gels. The HCT116B and 20-10-1 cells that were naturally invasive in a collagen gel assay also showed increased levels of invasiveness in the presence of bFGF, but an antibody that neutralised the activity of bFGF reduced the constitutive invasiveness of these cells. Our results suggest a causal relationship between the endogenous production of bFGF and the invasive potential of human colon carcinoma cells.

Acidic and basic fibroblast growth factor mRNA and protein in mouse mammary glands

Previous studies suggest that members of the fibroblast growth factor (FGF) family are mitogenic to mammary epithelium. In order to determine expression of acidic and basic FGF (aFGF and bFGF) during mammary development, mice were euthanized as virgins, early pregnant, mid-pregnant, late-pregnant, or during early lactation. Mammary expression of both aFGF and bFGF mRNA increased through pregnancy. Acidic FGF mRNA continued to increase during early lactation, but basic FGF message level decreased drastically during early lactation. Western blots probed with anti-aFGF showed four immunoreactive bands approx 30, 48, 52, and 55-kDa in size. The 30-, 48-, and 55-kDa bands for aFGF were expressed at low levels during virgin and early pregnant stages but were more prominent during the later stages. The 52-kDa band was high during the virgin and early pregnant stages and low in mid-pregnancy through early lactation. Blots probed with anti-bFGF showed two bands approx 30 and 50 kDa in size. Both bands increased through early-pregnancy, but during late-pregnancy there was a decrease in immunoreactive protein levels, which remained low during early lactation. Experiments to determine where FGF mRNAs are produced in the mammary gland suggest that both FGFs may be produced in the stroma, leading to the hypothesis that aFGF and bFGF are stromally produced growth factors and probably act on the epithelial component of the gland in a paracrine fashion.

Effect on tumorigenicity and metastasis of transfection of a diploid benign rat mammary epithelial cell line with DNA corresponding to the mRNA for basic fibroblast growth factor

To examine the potential role of fibroblast growth factors (FGF) in tumorigenesis and metastasis, plasmid constructs containing the human basic FGF (bFGF) gene, with or without fusion to a secretory signal peptide (IgbFGF), were transfected into the diploid rat mammary epithelial cell line Rama 37. All transfectants possessed multiple copies of the transfected cDNA, which was expressed as the corresponding mRNA and the protein. The amount of bFGF protein was usually greater than the bFGF growth-stimulatory activity that could be recovered from the transfected cells. Nevertheless, the amount of bFGF growth-stimulatory activity secreted by the IgbFGF transfectants (0.08-0.8 ng/ml/24 hr) was sufficient to induce growth in responsive cells. However, the transfectants themselves were refractory to stimulation by exogenously added bFGF, despite possessing a small number of high-affinity receptors for bFGF. When the bFGF or the IgbFGF transfectants were inoculated into the mammary fat pads of syngeneic rats, the tumour incidence was low (0-50%). However, when cells cultured from these tumours were inoculated into the fat pad of syngeneic rats, the tumour incidence was 100%. Tumours were in all cases benign and no metastases were observed. Our results suggest that the role of bFGF in metastasis is not simply one of autocrine/paracrine stimulation of cell growth and that other events may also be required.

Growth factors and their receptors in neoplastic mammary glands

Control of the growth of mammary glands is largely exerted in vivo by systemic hormones and locally-produced growth factors, whereas malignant tumours gradually lose the ability to respond to both types of control in vivo. However, the systemic hormones have little direct effect on stimulating the growth of rat or human mammary cell lines in vitro. Estrogens are thought to work by stimulating locally-produced growth factors and/or their receptors, eg transferrin, TGF alpha and IGF-1, and prolactin by a contaminating pituitary mammary growth factor (PMGF). Mammary stem cells intermediate between epithelial and myoepithelial cells are thought to be retained in malignant carcinomas, whereas the TGF alpha and bFGF-producing myoepithelial cells are lost. Hormonal autonomy of carcinomas may develop by overproduction of the locally-produced growth factors, their receptors (including related receptors, eg c-erbB-2) and/or by stem cells differentiating sufficiently to utilise normal control mechanisms, eg refractivity to PMGF and autocrine/paracrine response to bFGF. The failure of the stem cells to differentiate completely to myoepithelial cells in carcinomas greatly reduces the heparan sulphate proteoglycan sink used to sequester to bFGF in normal glands and also removes the possibility of eliminating cells by terminal differentiation, both processes possibly contributing to the uncontrolled growth of the malignant breast cell.

Fibroblast growth factors and their receptors: an information network controlling tissue growth, morphogenesis and repair

The stimulation of cellular metabolism by the nine fibroblast growth factors (FGFs) is mediated by a dual-receptor system. This comprises a family of four receptor tyrosine kinases (FGFR) and heparan sulphate proteoglycans (HSPG). The stimulation of cell division by FGFs has an obligate requirement for both partners of the dual-receptor system. The binding of the nine FGFs to the FGFRs is marked by a pattern of overlapping specificity despite alternative splicing events generating a large number of FGFR proteins. Thus many of the FGFR isoforms bind several FGFs. It is likely that each FGF requires a different pattern of sulphation within the heparan sulphate chains for binding. Therefore, the HSPG receptors may provide additional specificity, allowing a cell to fine tune its response to the FGFs present in the extracellular milieu. The HSPG receptors also control the availability of FGFs and hence regulate the transport of FGFs within a tissue. FGF-stimulated cell division would appear to have a mandatory requirement for the FGFs to be translocated to the nucleus via the cytosol after interacting with the dual-receptor system. The consequences of the potential direct action of FGFs in stimulating cell division are examined in the light of current models of signal transduction.