Phenotypic transformation of normal rat kidney cells by transforming growth factor beta is not paralleled by enhanced production of a platelet-derived growth factor

TGF-β transactivates EGFR and facilitates breast cancer migration and invasion through canonical Smad3 and ERK/Sp1 signaling pathways

Transforming growth factor-beta (TGF-β) functions as a potent proliferation inhibitor and apoptosis inducer in the early stages of breast cancer, yet promotes cancer aggressiveness in the advanced stages. The dual effect of TGF-β on cancer development is known as TGF-β paradox, and the remarkable functional conversion of TGF-β is a pivotal and controversial phenomenon that has been widely investigated for decades. This phenomenon may be attributed to the cross talk between TGF-β signaling and other pathways, including EGF receptor (EGFR) signaling during cancer progression. However, the underlying mechanism by which TGF-β shifts its role from a tumor suppressor to a cancer promoter remains elusive. In this study, TGF-β is positively correlated with EGFR expression in breast cancer tissues, and a functional linkage is observed between TGF-β signaling and EGFR transactivation in breast cancer cell lines. TGF-β promotes the migration and invasion abilities of breast cancer cells, along with the increase in EGFR expression. EGFR is also essential for TGF-β-induced enhancement of these abilities of breast cancer cells. Canonical Smad3 signaling and ERK/Sp1 signaling pathways mediate TGF-β-induced EGFR upregulation. Hence, our study provided insights into a novel mechanism by which TGF-β supports breast cancer progression.

Pertussis toxin sensitive G-proteins are not involved in the mitogenic signaling pathway of insulin-like growth factor-I in normal rat kidney epithelial (NRKE) cells

There is controversy as to whether or not a pertussis toxin sensitive G-protein is involved in the signaling pathway of insulin-like growth factor-I. We have used normal rat kidney epithelial (NRKE) cells to ask whether or not a pertussis toxin sensitive G-protein was involved in IGF-I stimulated DNA synthesis. NRKE cells express both IGF and IGF-II/M6P receptors and respond to IGF-I with increased thymidine incorporation into DNA. Under many circumstances incubation of cells/cell membranes with GTP analogues will inhibit binding of ligands that are linked to a G-protein-receptor pathway. However, when NRKE membrane preparations were incubated with 125I-IGF-I or 125I-IGF-II in the presence or absence of GTP gamma S, ATP and GTP, binding of the radioligands was not affected by the GTP-analogue. IGF-I and factors from serum of hypophysectomized rats (HRS) stimulated [3H]thymidine incorporation into DNA of NRKE cells. Under serum-free conditions in the presence of EGF (2 ng/ml) and PDGF (1 ng/ml) pertussis toxin over a wide range of doses had no effect upon IGF-I stimulated [3H]thymidine incorporation into DNA of NRKE cells. In addition, PT at a dose of 100 ng/ml had no effect on IGF-I(0.2-50 ng/ml) stimulated DNA synthesis of NRKE cells. However, PT at doses of 5, 50, 500, 5000 and 50,000 ng/ml was capable to ADP-ribosylate a 40 kDa protein in NRKE cell plasma membrane preparations corresponding to known PT-sensitive G-proteins. We conclude, that (1) PT-sensitive G-proteins and both IGF-I and IGF-II/M6P receptors are present in NRKE cell plasma membrane preparations, and most importantly, that (2) PT-sensitive G-proteins are not involved in the mitogenic signaling pathway of IGF-I in NRKE cells.

Immunohistochemical observations on the kinetics of macrophages and myofibroblasts in rat renal interstitial fibrosis induced by cis-diamminedichloroplatinum

It has been speculated elsewhere that growth factors produced by macrophages in response to tissue damage induce a modulation of pre-existing fibroblasts into myofibroblasts, leading to fibrosis. The development of these cells in cis-diamminedichloroplatinum (CDDP)-induced rat renal interstitial fibrosis was observed immunohistochemically. In the cortico-medullary junction, nuclear changes and epithelial necrosis of the proximal renal tubule (mainly the P3 segment) were seen on days 1 and 4 after a single dose (6 mg/kg body weight) of CDDP, and regenerating epithelium appeared on day 7. Gradually developing fibrosis was observed around the affected tubules on days 14 and 28. The increase in fibrosis was confirmed by histometrical analysis. The number of ED-1 (primary antibody) positive macrophages reached a peak in the affected cortico-medullary junction on day 7 and this was accompanied by an increase in muscle actin-positive myofibroblasts. On days 14 and 28, macrophages had declined in number, but the number of muscle actin-positive myofibroblasts in the fibrotic area was still high as compared with control values. Cytoplasmic myofilaments were observed in myofibroblasts by electron microscopy. These findings suggest that the myofibroblasts participate in renal interstitial fibrosis in the rat, and that their appearance may be related to macrophage infiltration in response to tubular injury, at least in the early stages of fibrosis.

Lysophosphatidic acid and bradykinin have opposite effects on phenotypic transformation of normal rat kidney cells

The bioactive lipid lysophosphatidic acid is besides a strong mitogen for quiescent fibroblasts, a potent inducer of phenotypic transformation of normal rat kidney cells. The lysophosphatidic acid induced loss of density-arrest is strongly inhibited by bradykinin. Although their effects on normal rat kidney cell proliferation are opposite, bradykinin mimics many of the intracellular effects induced upon lysophosphatidic acid receptor activation, including phosphoinositide turnover, Ca(2+)-mobilization and arachidonic acid release. Bradykinin does not counteract the lysophosphatidic acid induced reduction of cAMP levels in normal rat kidney cells. However, bradykinin inhibits the lysophosphatidic acid and other growth factor induced phenotypic transformation through the induction of a so far uncharacterized prostaglandin G/H synthase product. The growth inhibitory effect of bradykinin is limited to density-arrested cells, while upon prolonged treatment bradykinin itself is capable to induce the loss of density-dependent growth control. It is concluded that bradykinin is a bifunctional regulator of normal rat kidney cell proliferation and that its inhibitory effects are mediated via the induction of a prostaglandin derivative.

Bradykinin-induced growth inhibition of normal rat kidney (NRK) cells is paralleled by a decrease in epidermal-growth-factor receptor expression

Normal rat kidney fibroblasts, grown to density arrest in the presence of epidermal growth factor (EGF), can be induced to undergo phenotypic transformation by treatment with transforming growth factor beta or retinoic acid. Here we show that bradykinin blocks this growth-stimulus-induced loss of density-dependent growth arrest by a specific receptor-mediated mechanism. The effects of bradykinin are specific, and are not mimicked by other phosphoinositide-mobilizing agents such as prostaglandin F2 alpha. Northern-blot analysis and receptor-binding studies demonstrate that bradykinin also inhibits the retinoic acid-induced increase in EGF receptor levels in these cells. These studies provide additional evidence that EGF receptor levels modulate EGF-induced expression of the transformed phenotype in these cells.

Differential effects of PDGF isoforms on proliferation of normal rat kidney cells

The effects of the PDGF isoforms AA, AB and BB have been studied on the proliferation of normal rat kidney cells, a non-tumorigenic fibroblast cell line which contains both type alpha and type beta PDGF receptors. On monolayer cells made quiescent by serum deprivation, PDGF-AA is a relatively poor mitogen compared to PDGF-AB and PDGF-BB. When these cells are made density-arrested following continuous incubation with epidermal growth factor, however, they can be restimulated to proliferate by all three PDGF isoforms with similar activity when added at sufficiently high concentration, resulting in phenotypic cellular transformation. Binding of radiolabelled isoforms to confluent NRK monolayers obeys the predictions of an induced receptor dimerisation model, and increases in the order AA < AB < BB. Upon preincubation of the cells with PDGF-AA, the dose-response curve for mitogenic activity of PDGF-AB is shifted to higher concentrations, indicating that PDGF-AA can partly antagonize the growth stimulating activity of PDGF-AB, as has also been observed in ligand binding studies. This observation has subsequently been confirmed using fluorescence cytometric analysis. PDGF-AB is highly active in inducing anchorage-independent proliferation of NRK cells, but in all such assays PDGF-AA is at least as potent as PDGF-BB. Intriguingly, PDGF-BB is almost devoid of activity in inducing soft agar growth of these cells, in contrast to PDGF-AA. When compared to substrate-attached cells, enhanced expression of the type alpha PDGF receptor was observed under anchorage-independent conditions. These results show that the relative potency of the three PDGF isoforms to stimulate proliferation of NRK cells is different for quiescent cells in monolayer, density-arrested cells and anchorage-independent cells. Moreover it is shown that the biological activity of PDGFs can be impaired by the additional presence of other isoforms.