Characterization of transforming growth factors produced by the insulin-independent teratoma-derived cell line 1246-3A

Inhibition of tumorigenicity of the teratoma PC cell line by transfection with antisense cDNA for PC cell-derived growth factor (PCDGF, epithelin/granulin precursor)

The PC cell line is a highly tumorigenic, insulin-independent, teratoma-derived cell line isolated from the nontumorigenic, insulin-dependent 1246 cell line. Studies of the PC cell growth properties have led to the purification of an 88-kDa secreted glycoprotein called PC cell-derived growth factor (PCDGF), which has been shown to stimulate the growth of PC cells as well as 3T3 fibroblasts. Sequencing of PCDGF cDNA demonstrated its identity to the precursor of a family of 6-kDa double-cysteine-rich polypeptides called epithelins or granulins (epithelin/granulin precursor). Since PCDGF was isolated from highly tumorigenic cells, its level of expression was examined in PC cells as well as in nontumorigenic and moderately tumorigenic cells from which PC cells were derived. Northern blot and Western blot analyses indicate that the levels of PCDGF mRNA and protein were very low in the nontumorigenic cells and increased in tumorigenic cell lines in a positive correlation with their tumorigenic properties. Experiments were performed to determine whether the autocrine production of PCDGF was involved in the tumorigenicity of PC cells. For this purpose, we examined the in vivo growth properties in syngeneic C3H mice of PC cells where PCDGF expression had been inhibited by transfection of antisense PCDGF cDNA. The results show that inhibition of PCDGF expression resulted in a dramatic inhibition of tumorigenicity of the transfected cells when compared with empty-vector control cells. These data demonstrate the importance in tumor formation of overexpression of the novel growth factor PCDGF.

Immunolocalization of alpha-transforming growth factor in the developing rat mammary gland in vivo, rat mammary cells in vitro and in human breast diseases

Immunoreactive alpha-transforming growth factor (alpha-TGF) was shown by immunocytochemistry to be present in the rat mammary gland at various stages of development, the staining being most intense in mature myoepithelial cells. Alpha-TGF was also detected in the secretions of the mammary glands of pregnant and lactating rats. alpha-TGF in the extracts of rat mammary glands at each stage of development, and in several rat mammary cell lines and in culture medium in which they had been grown, was shown by Western blotting to consist primarily of a protein of molecular weight 50 kDa. The amount of this protein was greater in the mammary gland of the lactating rat than in resting or involuting glands. alpha-TGF was also found in some, but not all, human breast carcinomas, and in benign hyperplastic breast diseases.

Impaired epidermal growth factor production in genetically obese ob/ob mice

Epidermal growth factor (EGF) is a potent inhibitor of adipose differentiation in vitro and delays adipose tissue development in vivo. Here we show that in the homozygous male obese mice the level of EGF in the submaxillary gland and plasma is significantly lower than in the glands and plasma of age-matched control littermates. This EGF deficiency in ob/ob mice was observed as early as 5 wk of age when obesity had just become apparent and was also found in adult mice. The level of prepro-EGF mRNA expression in the submaxillary gland was also lower in obese mice than in control littermates. However, the level of kidney prepro-EGF mRNA was the same in mice with both phenotypes, suggesting that the regulation of prepro-EGF mRNA expression is different in both tissues. These results indicate that genetic obesity in mice is accompanied by a decrease in the production of EGF.

Nucleotide sequence of the C-terminal region of the mouse epidermal growth factor receptor and expression in teratoma-derived cell lines with increased tumorigenic properties

The isolation of a cDNA corresponding to a portion (amino acid 943 to 1073) of the cytoplasmic domain of the mouse EGF receptor surrounding the auto phosphorylation sites was obtained by using the reverse transcriptase polymerase chain reaction (RT-PCR) approach. Deduced amino acid sequence of mouse EGF receptor (EGFr) shows a 92% and 76% homology to corresponding regions in the human and the chicken EGFr, respectively. This cDNA was used to develop a sensitive RNase protection assay to investigate EGF receptor mRNA expression in mouse C3H teratoma derived cell lines with increased tumorigenic properties which display a progressive decrease of EGF binding and response. The results show that increased tumorigenicity was not accompanied by a change in EGF receptor mRNA expression. Moreover, they indicate that the RNase protection assay developed using the probe described here is a sensitive approach to investigate EGF receptor expression in murine cells.

Fibroblast growth factor inhibits proliferation of a highly tumorigenic insulin-independent teratoma-derived cell line

The present paper examines the effect of basic fibroblast growth factor (bFGF) on the proliferation of teratoma-derived cell lines having increased tumorigenic properties isolated from the non-tumorigenic adipogenic cell line 1246. Although FGF is a mitogen for the non tumorigenic 1246 cells and for the moderately tumorigenic 1246-3A cells derived from the 1246 cells, bFGF inhibits the proliferation and DNA synthesis of the highly tumorigenic PC cells starting at concentration as low as 30 pg/ml. The inhibitory effect of FGF on PC cell growth is irreversible as demonstrated by the inability of the cells to resume proliferation once FGF is removed from the culture medium. Comparison of 125I-bFGF binding to the three cell lines was performed. Based on the Scatchard analysis of the binding data, PC cells display only low affinity class of FGF binding sites whereas 1246 and 1246-3A cells presented also high affinity binding sites. The inhibitory effect of FGF on PC cells did not go through activation of a PKC mediated pathway, which is also known to inhibit PC cell proliferation, since FGF inhibition of PC cell growth was still apparent after PKC down regulation. FGF was still able to transiently stimulate the expression of mRNA for early growth associated genes as demonstrated by c-myc and c-fos expression, although it inhibited cell proliferation on PC cells. Our data demonstrate that the highly tumorigenic teratoma cells acquire an inhibitory response for a factor which is growth stimulatory to non-tumorigenic and moderately tumorigenic cells from which they are derived.

Decreased transforming growth factor-beta response and binding in insulin-independent teratoma-derived cell lines with increased tumorigenic properties

The mouse C3H teratoma-derived cell line 1246 is an adipogenic cell line which stringently requires insulin to proliferate and differentiate in defined medium. From this cell line an insulin-independent cell line called 1246-3A was isolated. It was found that, in contrast to 1246 cells, 1246-3A cells had lost the ability to differentiate and became tumorigenic when injected at a density of 10(6) cells/mouse into syngeneic host C3H mice. In addition, they produce in their culture medium transforming growth factor alpha- and beta-like polypeptides which stimulate their proliferation. Highly tumorigenic insulin-independent cell lines able to give rise to tumor when injected at a density of 10(4) cells/mouse were isolated by using an in vitro-in vivo shuttle technique. The highly tumorigenic cell lines have lost the response to TGF-beta 1. The binding of TGF-beta 1 to the nontumorigenic parent cell line or to cells displaying increased tumorigenic properties was investigated. The data presented here indicate that the increased tumorigenicity is accompanied by a progressive decrease of specific binding of TGF-beta 1 to the cells. However, the decreased number of cell surface TGF-beta 1 binding sites in the highly tumorigenic cells did not correlate with an increase in the secretion of TGF-beta protein by the tumorigenic cells, as all of TGF-beta produced by the cells was in a latent form. Affinity cross-linking experiments indicated that the 1246 cell line displayed several TGF-beta cross-linked molecular species (MW 140, 92, and 70 kDa). Increase of tumorigenicity was accompanied by a marked decrease in the intensity of the cross-linked bands, particularly of the 92 and 70 kDa species.