Paracrine effects of bombesin/gastrin-releasing peptide and other growth factors on pulmonary neuroendocrine cells in vitro

Pulmonary neuroendocrine cells (PNEC) are numerous in the fetus where they have been implicated to have a role in fetal lung development. We assessed the effects of putative growth factors, gastrin releasing peptide (GRP), cholecystokinin (CCK), gastrin (GN), serotonin (5-HT), and epidermal growth factor (EGF), some of which are produced by PNEC, either alone or in combination, on cultured fetal rabbit PNEC from 20, 24, and 28 day fetuses. GRP increased the total protein of the cultures over a 7 day period in an age-dependent manner, with greatest effect in cultures from the 24 day fetus, no effect with the 28 day fetus, and an inhibitory effect on 20 day cultures. This was accompanied by an increase in PNEC, which could be blocked by treatment of the cultures with a monoclonal antibody to GRP (2A11). There was no increase in ³H-thymidine labeling of PNEC in GRP treated cultures but an increase in numbers of cells partially stained for 5-HT, suggesting the induction of a precursor cell. Other growth factors had neither an inhibitory nor a stimulatory effect either alone or in combination with GRP. Preliminary studies with ¹²⁵I-GRP receptor localization suggests that the GRP receptor is mostly expressed on pulmonary fibroblasts, and less on epithelial cells, so that the role for GRP in fetal lung development, at least in the rabbit, is probably indirect, acting via a paracrine mechanism. © 1993 Wiley-Liss, Inc.     

Platelet-derived growth factor and growth-related genes in rat lung. I. Developmental expression

The autocrine, paracrine, or systemic growth factors responsible for fetal lung cell growth are not completely defined. The progression-type insulin-like growth factors and epidermal growth factor, or transforming growth factor-alpha acting through the epidermal growth factor receptor, appear to act on the developing lung epithelium. The competence factors that facilitate the actions of progression factors during lung growth are unknown. Fetal rat lung cells in vitro synthesize a platelet-derived growth factor (PDGF)-like polypeptide, which we have hypothesized may play a paracrine role in normal lung development. Slot blot and Northern blot analyses of fetal rat lung mRNA have been used to determine if there is a relationship between expression of message for PDGF-A or PDGF-B chains, or their cognate receptors, and periods of maximal growth during late fetal rat lung development. Whole lung mRNA was extracted on 18, 19, 20, 21, and 22 days of gestation (term = 22 days). The peak of DNA synthesis, as assessed by expression of message for DNA polymerase alpha, histone 3, and the proto-oncogenes c-fos and c-myc, which are stimulated by binding of growth factors including PDGF, occurred during the canalicular stage of lung development on days 19 and 20 of gestation. Expression of message for PDGF-A and PDGF-B chains was low during the pseudoglandular stage on day 18, peaked during the canalicular stage on days 19 and 20, then fell again during the saccular stage at days 21 and 22 of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)     

The monoclonal HBA-71 antibody modulates proliferation of thymocytes and Ewing's sarcoma cells by interfering with the action of insulin-like growth factor I.

The monoclonal HBA-71 antibody recognizes a Ewing's sarcoma associated antigen, which is also highly expressed on the cell surface of human cortical thymocytes and islets of Langerhans among normal tissues. The antibody was found to inhibit partially the growth of ES tumor cell lines and to trigger proliferation in thymocyte cultures. The influence of growth factors and the effect of the HBA-71 antibody was further investigated in the present study. The growth of ES tumor cells was demonstrated to be dependent on the presence of insulin-like growth factor I or insulin. The HBA-71 antibody (25 micrograms/ml) enhanced the growth stimulatory effect of IGF-I under serum-free conditions. The expression of the HBA-71 epitope is modulated positively by IGF-I and insulin and negatively by dexamethasone and human growth hormone in ES/PNET tumor cells and thymocytes. IGF-I either alone or in combination with HBA-71 stimulated the proliferation of thymocytes under serum-free conditions whereas in complete medium, IGF-I stimulated thymidine incorporation and the HBA-71 antibody either alone or in the presence of IGF-I showed inhibitory activity most likely due to down-regulation of the receptor. These data demonstrate the important role of IGF-I in the growth of ES/PNET tumor cells as well in the proliferative activity of HBA-71 positive normal thymocytes. The biological activity of IGF-I in malignant thymocytes, pancreas tumors, fetal muscle, brain, granulosa and Sertoli cells has been documented in the literature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Urokinase and the mechanism of osteoblastic metastases by prostate cancer

We have examined the pathogenesis of osteoblastic metastases by attempting to identify growth factors for cells of the osteoblast phenotype which are produced by prostatic cancer tissue. In initial studies, surgical specimens of human prostate cancer (CA) and benign prostatic hyperplasia (BPH) tissue were employed as a source of prostatic tissue, and mitogenic activity for osteoblastic cells was assessed in primary cultures of fetal calvarial cells and in osteosarcoma cells. These studies identified the presence of acid stable peptide mitogens for osteoblasts in both CA and BPH. To pursue these findings, the prostate cancer cell line PC-3 was employed. Biochemical analysis of serum-free conditioned PC-3 medium, using mainly reverse-phase high pressure liquid chromatography, disclosed the presence of a mitogen for osteoblastic cells with a molecular weight of approximately 15 kDa. Amino acid sequencing indicated that this was an amino-terminal fragment of urokinase (UK). Further studies demonstrated abundant plasminogen activator activity in PC-3 conditioned medium and substantial messenger RNA encoding UK in PC-3 cells. High molecular weight (HMW) UK but not low molecular weight (LMW) UK was mitogenic and increased cell numbers in osteoblastic cultures but not in control fibroblast cultures. Specific, competitive binding of HMW but not LMW UK to osteoblastic cells was observed. These studies indicated that the mitogenic activity of UK indeed resides in the amino-terminal region. This was confirmed by demonstrating mitogenic activity for osteoblastic cells using a peptide containing the ‘growth factor domain’ of UK. In summary, these studies have shown that an amino-terminal fragment of UK produced by PC-3 cells has growth factor activity for cells of the osteoblast phenotype. UK fragments may therefore be of importance in the pathogenesis of osteoblastic metastases produced by prostatic cancer cells.     

Expression of insulin-like growth factor in the placenta of intrauterine growth-retarded human fetuses

Many cases of intrauterine growth retardation (IUGR) are the result of placental and fetal tissue insufficiency. Insulin-like growth factor-I (IGF-I) is known to play a role in placental and fetal growth. An immunocytochemical study was performed to localize IGF-I peptides in human placenta and umbilical cords of normal (n = 3) and IUGR (n = 3) fetuses. The peripartum fetal conditions were evaluated as well. Immunoreactive IGF-I was detected in the cytotrophoblast, syncytiotrophoblast, amnion, endothelial cells of fetal capillaries and in the decidua in both normal and IUGR placental tissue. A more robust immunostaining and increased numbers of positively stained cells were found in the decidua of IUGR placenta (p < 0.001). Intense immunostaining was also found in endothelial cells, smooth muscle cells and fibroblasts of the umbilical vein. IGF-I immunoreactivity was also present in stroma (Hofbauer cells and/or fibroblasts) of IUGR villi. Our results indicate that expression of IGF-I is high in specific sites in placenta and umbilical cords, which indicates a paracrine and/or endocrine function. The increased expression of IGF-I in placenta of IUGR fetuses indicates its involvement in restoring normal growth by means of a positive feed-back mechanism.     

Overexpression of insulin-like growth factor-1 (IGF-I) receptor and the invasiveness of cultured keloid fibroblasts

Keloid is a dermal fibroproliferative tissue of unknown etiology. Protein tyrosine kinases (PTKs) play an important role in the regulation of cell growth and differentiation. Activation of PTK cascades in keloid fibroblasts is thought to be closely linked to abnormal cell proliferation and migration. We determined the expression profile of PTK genes in normal skin and keloid fibroblasts using the homology cloning method with a degenerated primer. Eight PTK genes were expressed among a total of 46 receptor-type clones. The most abundant type of PTK receptors was the platelet-derived growth factor receptor in both fibroblasts. However, insulin-like growth factor-I receptor (IGF-IR) was overexpressed only in keloid-derived fibroblasts (9 of 24). Immunohistochemical analysis confirmed the high expression of IGF-IR in keloid fibroblasts, but not in normal fibroblasts. To examine the functional properties of the IGF-I/IGF-IR pathway, we investigated cell proliferation and invasion activities of both types of fibroblasts. The mitogenic effect of IGF-I on both fibroblasts was very weak compared with serum stimulation. In contrast, the invasive activity of keloid fibroblasts was markedly increased in the presence of IGF-I, and inhibited by a neutralizing antibody against IGF-IR. Our results indicate the involvement of activated IGF-I/IGF-IR in the pathogenesis of keloid by enhancing the invasive activity of fibroblasts.     

Identification of pneumocin, a developmentally regulated apical membrane glycoprotein in rat lung type II and Clara cells

Pneumocin (Mr, 165 kD) is a recently identified apical membrane surface sialoglycoprotein marker of type II pneumocytes. A murine monoclonal IgG1 subclass-producing clone 4A (4A mAb), which was developed against the purified pneumocin, and recognized pneumocin on Western blots of adult rat lung homogenates, was used to study expression of the glycoprotein in developing rat lungs. Pneumocin localized to apical membranes of late fetal, neonatal, and adult rat type II pneumocytes as well as Clara cells in situ, by immunofluorescence and immunoelectron microscopy. Faint immunofluorescence was observed in 17-d fetal lungs. However, 19-d fetal lungs showed intense immunofluorescence with the antibody. On immunoelectron microscopy, apical membranes of 19-d fetal and adult rat lung type II cells were labeled by 4A mAb, but type I cells were not stained. On Western blots, amounts of pneumocin increased up to the fourth day after birth, when near-adult levels were attained. Lower molecular weight forms (Mr, 80 to 90 kD) were recognized in 17-d fetal lung. These bands decreased in amount with a corresponding increase in the 165-kD band that was typically observed in adult lungs. Immunoglobulins that were eluted from polyvinylidene difluoride strips containing the 165-kD band recognized the Mr 80 to 90 kD bands and 50-kD component, suggesting that fetal forms of the protein shared an epitope in common with the adult pneumocin. Reactivity of the glycoprotein with 4A mAb was destroyed by enzymatic digestion with trypsin and staphylococcal V8 protease. These data demonstrate that pneumocin is a developmentally regulated apical membrane marker of differentiated type II and Clara cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanical stretch promotes fetal type II epithelial cell differentiation via shedding of HB-EGF and TGF-α

The mechanisms by which mechanical forces promote fetal lung development are not fully understood. Here, we investigated differentiation of fetal type II epithelial cells via the epidermal growth factor receptor (EGFR) in response to mechanical strain. First, we showed that incubation of embryonic day (E) 19 fetal type II cells with recombinant heparin-binding EGF-like growth factor (HB-EGF) or transforming growth factor (TGF)-α, but not with amphiregulin (AR), betacellulin (BTC) or epiregulin (EPR), increased fetal type II cell differentiation, as measured by surfactant protein B/C mRNA and protein levels. Next, we demonstrated that 5% cyclic stretch of E19 monolayers transfected with plasmid encoding alkaline phosphatase (AP)-tagged ligands shed mature HB-EGF and TGF-α into the supernatant and promoted type II cell differentiation. Release of these ligands was also observed in E19 cells subjected to higher degrees of cyclic strain, but not in cells exposed to continuous stretch. Interestingly, the addition of fibroblasts to type II cell cultures did not enhance release of HB-EGF. Whereas HB-EGF shedding was also detected in E18 cells exposed to 5% cyclic stretch, release of this ligand after 2.5% sustained stretch was restricted to cells isolated on E18 of gestation. In addition, mechanical stretch released EGF, AR and BTC. We conclude that mechanical stretch promotes fetal type II cell differentiation via ectodomain shedding of HB-EGF and TGF-α. The magnitude of shedding varied depending on gestational age, ligand, and strain protocol. These studies provide novel mechanistic information potentially relevant to fetal lung development and to mechanical ventilation-induced lung injury.     

Interstitial pulmonary macrophages produce platelet-derived growth factor that stimulates rat lung fibroblast proliferation in vitro.

Alveolar macrophages from humans and several animal species produce factors in vitro that modulate fibroblast growth and have been proposed as mediators of interstitial pulmonary fibrosis. Pulmonary interstitial macrophages (IMs) have not been studied previously in this regard. Pulmonary IMs were isolated from prelavaged rat lungs by enzymatic digestion of tissue and subsequent differential adherence of cells to culture dishes. The ability of IMs to release modulators of fibroblast growth into the culture medium was assessed by measuring [3H]thymidine incorporation into DNA and/or nuclear labeling of early-passage rat lung fibroblasts exposed to medium conditioned by IMs. The percentages of nuclei labeled in fibroblast cultures exposed to interstitial macrophage-conditioned medium (IMCM) alone did not significantly differ from that observed in controls, but fibroblasts exposed to IMCM supplemented with 2% platelet-poor plasma showed a 2.6-fold increase in labeling, indicating that IMCM contains predominantly "competence" growth factor activity. Similar results were obtained using purified human platelet-derived growth factor (PDGF). The level of growth factor activity released by IMs increased in cells that had phagocytized iron spheres during the culture period. In addition, fractionation of IMCM by high-performance liquid chromatography demonstrated most of the growth factor activity at a relative molecular mass of about 35 kd. Subsequent quantitative analysis of the fractions by an enzyme immunoassay for PDGF demonstrated that IMCM contains a homologue of human PDGF. These results show that IMs are capable of producing a PDGF-like growth factor for autologous fibroblasts and that release of this factor is enhanced by exposure to an insoluble inorganic particle. Because PDGF is a potent growth factor for fibroblasts and is released by IMs, it is essential to ask in future studies whether this or similar macrophage products play a significant role in mediating fibroblast proliferation in vivo.     

Nuclear pockets and clefts in the lymphoid cell population of bone marrow and blood of children with acute lymphoblastic leukemia

Demineralized extracts of bone matrix and conditioned media from cultured fetal rat calvaria have been reported to contain growth stimulatory activity for bone cells. To investigate the potential role of these local bone growth factors in the development of bone metastases, we chose the Walker 256 carcinosarcoma, a rat mammary tumor which causes osteolytic bone metastases and hypercalcemia. 45Ca-labeled, 19-day fetal Sprague-Dawley rat calvaria were cultured for 96 hours in BGJb medium. Walker cells from ascites tumors or cultures were grown in unconditioned media or in conditioned media harvested from the bone cultures, in the presence of 10% fetal calf serum. Media were changed every 2 days, cells were counted daily for 5 days, and 3H-thymidine uptake into acid insoluble residues was measured. The growth of tumor cells was 5-6-fold greater in conditioned media than in unconditioned media and the effect was dose dependent. Cells cultured in conditioned media demonstrated a approximately 3-fold enhancement of 3H-thymidine incorporation. Generation of growth stimulatory activity correlated with the extent of bone resorption, measured by release of 45Ca from the fetal parietal bones (r = 0.85; P less than 0.001). Conditioned media from bones cultured with 10(-7) M prostaglandin E2 (PGE2) contained greater amounts of growth stimulatory activity than untreated conditioned media, but PGE2 itself did not stimulate tumor cell growth. Addition of 3.5 mM PO4 to bone cultures blocked bone resorption and the generation of growth factors. Growth stimulatory activity was stable to heat (56 C for 30 minutes) and trypsin digestion, with an apparent molecular weight of less than 17,000 daltons by high-performance liquid chromatography. Conditioned medium also stimulated the growth of 13762 rat mammary adenocarcinoma cells, MB-MDA-231 human breast carcinoma cells, TE-85 osteosarcoma cells, a murine fibrosarcoma and rat embryonic fibroblasts, with the most potent effects noted for Walker tumor cells, the TE-85 osteosarcoma, and human breast carcinoma lines. These results suggest a mechanism by which bone resorption could promote the development of skeletal metastasis.     

Anti-bombesin monoclonal antibodies modulate fetal mouse lung growth and maturation in utero and in organ cultures

Fetal pulmonary neuroendocrine cells (PNECs) contain abundant gastrin-releasing peptide (GRP, mammalian bombesin-like peptide [BLP]). Previously, addition of bombesin resulted in increased fetal lung growth and maturation in utero and in organ cultures. A monoclonal antibody (mAb) to bombesin (2A11) blocked baseline automaturation of lung organ cultures in serum-free medium. In the present study, we analyze lung development following daily in utero administration of 2A11 from gestational days 15–18. Fetal lung treated with 2A11 and then harvested on day 18 demonstrated a dose-dependent decrease in surfactant phospholipid synthesis compared to controls treated with MOPC, an unreactive mAb. However, 2A11-treated fetal lung harvested on day 17 showed paradoxical increases in ³H-choline incorporation into saturated phosphatidylcholine, ³H-thymidine incorporation into DNA, and relative numbers of differentiated type II pneumocytes. In serum-containing day 17 lung organ cultures, 2A11 stimulated choline and thymidine incorporation. Since epidermal growth factor (EGF) is the only agent besides bombesin known to stimulate both fetal lung growth and maturation, we added EGF to serum-free cultures and reconstituted the stimulatory effects. A murine EGF receptor mAb (ERA) blocked 2A11-induced lung growth and maturation in serum-containing cultures, and this effect was overcome by adding EGF. In vivo, ERA also blocked stimulatory effects of 2A11 in fetal lung on day 17. These observations suggest that EGF receptor up-regulation may maintain lung growth and maturation if BLP levels are diminished on day 17. Nonetheless, BLPs appear to be involved in lung maturation on day 18, supporting a role for PNECs in normal lung development. © 1993 Wiley-Liss, Inc.     

Neuraminidase-1, a subunit of the cell surface elastin receptor, desialylates and functionally inactivates adjacent receptors interacting with the mitogenic growth factors PDGF-BB and IGF-2

We recently established that the elastin-binding protein, which is identical to the spliced variant of beta-galactosidase, forms a cell surface-targeted complex with two proteins considered "classic lysosomal enzymes": protective protein/cathepsin A and neuraminidase-1 (Neu1). We also found that cell surface-residing Neu1 can desialylate neighboring microfibrillar glycoproteins and facilitate the deposition of insoluble elastin, which contributes to the maintenance of cellular quiescence. Here we provide evidence that cell surface-residing Neu1 contributes to a novel mechanism that limits cellular proliferation by desialylating cell membrane-residing sialoglycoproteins that directly propagate mitogenic signals. We demonstrated that treatment of cultured human aortic smooth muscle cells (SMCs) with either a sialidase inhibitor or an antibody that blocks Neu1 activity induced significant up-regulation in SMC proliferation in response to fetal bovine serum. Conversely, treatment with Clostridium perfringens neuraminidase (which is highly homologous to Neu1) decreased SMC proliferation, even in cultures that did not deposit elastin. Further, we found that pretreatment of aortic SMCs with exogenous neuraminidase abolished their mitogenic responses to recombinant platelet-derived growth factor (PDGF)-BB and insulin-like growth factor (IGF)-2 and that sialidosis fibroblasts (which are exclusively deficient in Neu1) were more responsive to PDGF-BB and IGF-2 compared with normal fibroblasts. Furthermore, we provide direct evidence that neuraminidase caused the desialylation of both PDGF and IGF-1 receptors and diminished the intracellular signals induced by the mitogenic ligands PDGF-BB and IGF-2.     

Vascular, glial and neuronal effects of vascular endothelial growth factor in mesencephalic explant cultures

Vascular endothelial growth factor is a highly conserved, heparin-binding protein which mediates a number of critical developmental processes in both vertebrates and invertebrates, including angiogenesis, vasculogenesis and hematopoiesis. We employed an organotypic rat explant model (produced from embryonic day 17 fetuses) to assess the effects of vascular endothelial growth factor on brain microvasculature in general and the ventral midbrain specifically. Immunohistochemistry using antisera to rat endothelial cell antigen and laminin demonstrated a robust, dose-dependent effect of vascular endothelial growth factor, resulting in increased vessel neogenesis, branching and lumen size by three days in vitro. This effect was blocked by addition of an anti-vascular endothelial growth factor antibody. At higher doses of vascular endothelial growth factor, the effect was attenuated, though a statistically significant increase in both astrocyte, and neuronal density was observed using antisera to glial and neuronal markers. Tyrosine hydroxylase-immunoreactive (i.e. dopaminergic) neurons, particularly, exhibited increased survival in response to vascular endothelial growth factor application. Vascular endothelial growth factor had a mitogenic effect on endothelial cells and astrocytes, but not dopaminergic neurons, as demonstrated by the addition of [³H]thymidine to the cultures 2 h after the cultures were established. Similarly, results of a radioreceptor assay indicated that specific vascular endothelial growth factor binding sites were present on blood vessels and astrocytes, and were up-regulated by exposure to vascular endothelial growth factor.

We conclude that, in explants of the ventral mesencephalon, exogenously applied vascular endothelial growth factor is mitogenic for endothelial cells and astrocytes, and promotes growth/survival of neurons in general and dopaminergic neurons in particular.     

Basement membrane matrix modifies cytokine interactions between lung cancer cells and fibroblasts.

OBJECTIVE: Proliferation of fibroblasts (desmoplastic reaction) in the lung adenocarcinomas is an important phenomenon that correlates with metastases and poor prognosis. Because basement membranes are often involved in the desmoplastic areas and many cytokines have binding capacity to basement membrane molecules, we hypothesized that basement membrane modify the paracrine effects between cancer cells and fibroblasts via the fibrogenic cytokines and this hypothesis was experimentally investigated. METHODS: The effects of conditioned media derived from ten lung carcinoma cell lines and normal airway epithelial cells on DNA synthesis of fetal lung fibroblasts were determined. We focused on fibroblast growth factor 2 (FGF-2) as the candidate paracrine cytokines and examined their diffusion through an experimental basement membrane matrix model, Matrigel. RESULTS: All the conditioned media promoted DNA synthesis of fetal lung fibroblasts. Detection by ELISA methods and the neutralizing antibodies suggested that FGF-2 was one of the responsible factors for the growth promotion. Diffusion of FGF-2 across the polycarbonate membrane was suppressed by coating with Matrigel. When FGF-2-secreting A549 cells were covered with Matrigel, FGF-2 was stored in Matrigel and its diffusion into the culture media was significantly reduced. Binding of FGF-2 to Matrigel was completely blocked by a basic protein, protamine sulfate. In the presence of protamine sulfate in Matrigel overlaid on A549 cells, diffusion of FGF-2 increased 7-fold as much as that without overlaid Matrigel. CONCLUSION: These results suggest that the basement membrane acts as a barrier to the diffusion and a reservoir of cytokines secreted by cancer cells, and that the subsequent degradation of the basement membrane by cancer cells could release the stored cytokines and promote growth of fibroblasts.