Cellular receptors for type beta transforming growth factor. Ligand binding and affinity labeling in human and rodent cell lines

Acidic cellular environments: activation of latent TGF-beta and sensitization of cellular responses to TGF-beta and EGF

Transient (about 2 hr) acidification to approx. pH 5.0 of agar-gelled overlayers containing untransformed NRK-49F or KiMSV-transformed NRK-49F cells in the presence of fetal calf serum or crude 49F-cell conditioned medium, as sources of latent TGF-beta, elicited EGF-dependent colony formation of 49F cells and inhibited spontaneous growth of transformed cells. Pure, active TGF-beta (porcine, type I) had the same effects on these respective cell types, suggesting that the above results were due to activation of latent TGF-beta in the transiently acidic cellular environment. Similar acidifications in the absence of a source of latent TGF-beta enhanced the positive growth response of 49F and AKR-2B cells to EGF and active TGF-beta and also the negative growth response of KiMSV-transformed 49F cells to active TGF-beta. These results are compatible with the idea that acidic cellular environments, particularly in tumor tissues, are conducive to activation of latent TGF-beta, perhaps in conjunction with other activating mechanisms, and to an enhanced response to some growth factors. However, the heterogeneity of cell populations within tumoral masses presents an obstacle to a clear understanding of the consequences of such activation.

Role for carbohydrate structures in TGF-beta 1 latency

Transforming growth factor-beta (TGF-beta) (reviewed in refs 1-3) is a family of molecules that are made up as disulphide-bonded dimers of at least three different types of homologous polypeptides. The active molecules are cleaved from the C termini of precursors. TGF-beta 1, like other forms of TGF-beta, is synthesized and secreted in a latent high relative molecular mass form (L-TGF-beta 1) from which active TGF-beta 1 can be released by transient and probably unphysiological acidification. The latent complex from human platelets contains one dimeric TGF-beta 1 molecules, which is noncovalently associated with a disulphide-bonded complex of one dimeric remnant of the precursor and a single molecule of the so-called TGF-beta 1 binding protein (TGF-beta 1-BP). We report here that enzymatic removal in vitro of the carbohydrate structures in the remnant of the TGF-beta 1 precursor produces biologically active TGF-beta 1 from the latent complex, suggesting that carbohydrate structures are of importance in rendering TGF-beta 1 inactive in the complex in vivo.

Effects of transforming growth factors beta 1 and beta 2 on a mouse clonal, osteoblastlike cell line MC3T3-E1

Transforming growth factors (TGF-beta 1 and TGF-beta 2) are polypeptide growth factors with a wide range of effects on the growth and differentiated function of a variety of cell types. Transforming growth factors of the beta class (TGF-beta) are found in large quantities in bone matrix and are synthesized by osteoblasts. For these reasons, it has been suggested that TGF-beta may play a major role in the regulation of bone cell metabolism. We have studied the effects of porcine TGF-beta 1 and the recently described porcine TGF-beta 2 in a mouse clonal, osteoblastlike cell line MC3T3-E1 that has previously been shown to have many characteristics of osteoblasts. In serum-containing medium, TGF-beta 1 inhibited alkaline phosphatase activity. The inhibition of alkaline phosphatase activity persisted for at least 72 h following a brief (24 h) exposure to TGF-beta 1. TGF-beta 1 also caused a marked change in cell morphology. High doses inhibited collagen synthesis; lower concentrations caused a small increase. Under serum-free conditions, TGF-beta 1 had biphasic effects on alkaline phosphatase activity inhibiting at high but stimulating at low concentrations and had only a slight stimulatory effect on collagen synthesis. Under the experimental conditions used, the effects of TGF-beta 1 on alkaline phosphatase activity and collagen synthesis were independent of effects on cell proliferation. In serum-containing medium, TGF-beta 2 inhibited alkaline phosphatase activity, an effect that was independent of changes in cell proliferation and caused shape changes in an identical fashion to that observed with TGF-beta 1.

The effects of TGF beta on haemopoietic cells

Transforming growth factor beta (TGF beta) suppresses the growth of differentiation inducible, murine IL-3-dependent multipotential cell lines but has no growth inhibitory effect upon an IL-3-independent (leukaemic) cell line arising from one of them, nor on IL-3-dependent cell lines that are unable to undergo differentiation. TGF beta inhibits in vitro colony formation by normal multipotential haemopoietic progenitor cells. Bipotential progenitors recruited by GM-CSF are, however, more resistant to the inhibitory effects of TGF beta, whereas progenitors recruited by the lineage restricted factor, M-CSF, are sensitive to the inhibitory effects. These data indicate that responsiveness to TGF beta is differentiation linked and studies with the cell lines suggest that response (or lack of response is not determined solely by levels of expression of TGF beta receptors. Furthermore, the effects of TGF beta 2 on haemopoietic progenitors are very similar to those induced by TGF beta.

Characterization of activin A binding sites on the human leukemia cell line K562

Recombinant activin A was radioiodinated to a high specific activity with maintenance of bioactivity using the Bolton-Hunter method. The human leukemia cell line K562, known to differentiate in response to activin A, was found to possess high affinity [125I]BH-activin A receptors (Kd approximately 0.13 nM) with a low number of receptors per cell (approximately 600 per cell). This receptor was found to be specific as FSH, LH, GnRH, and TGF-beta 1 do not compete for binding. This is the first description of binding sites for this protein hormone on K562 cells.

Growth factors modulate junctional cell-to-cell communication

The epidermal growth factor (EGF) and the platelet-derived growth factor (PDGF) inhibit gap junctional communication in the mammalian cell lines NRK and BalbC 3T3: cell-to-cell transfer of a 400-dalton tracer molecule is reduced and junctional conductance is reduced. The inhibition of cell-to-cell transfer is reversible and dose dependent; half-maximal effects are obtained at 10(-9) and 10(-11) M concentrations of EGF and PDGF, respectively. The response of junctional conductance is detectable within 2 min of EGF application and reaches a maximum within 10 min. It is among the earliest cellular responses to this growth factor and may be significant in the regulation of growth. The response is lacking in EGF receptor-deficient NIH 3T3 cells. The transforming factor beta (TGF beta) enhances junctional communication in BalbC 3T3: cell-to-cell transfer is increased over a period of 8 hr. But in NRK cells, where it upregulates EGF receptors, TGF beta reduces junctional communication synergistically with EGF.

The effects of type beta transforming growth factor on proliferation and epidermal growth factor receptor expression in a human glioblastoma cell line

Type beta transforming growth factor (B-TGF) is a potent growth inhibitor to many human tumor cell lines. Very little is known about the mechanism for this growth inhibitory action of B-TGF. We here report the effect of B-TGF on proliferation and epidermal growth factor receptor (R-EGF) expression in a human glioblastoma cell line named T-MG1. B-TGF inhibit the soft agar growth of T-MG1 cells. Maximum inhibition was 70%, achieved with 0.5 units B-TGF. B-TGF had no effect on monolayer growth of T-MG1 cells. T-MG1 cells contained abundant R-EGF, which could be divided into two subpopulations, one high affinity and one low affinity population of R-EGF. Treatment with B-TGF caused an initial decrease (0-6 h) in EGF-binding, followed by an increase in EGF-binding which reached maximum after 24 h exposure to B-TGF. Since addition of EGF to agar cultures gave no additional increase in inhibition by B-TGF and EGF alone had no inhibitory effect, we believe that binding of EGF to its receptor is not part of the pathway mediating the inhibitory effect of B-TGF. All neoplastic cells have lost some measure of growth control and the cellular elements involved are growth factors, growth factor receptors and oncogenes. T-MG1 cells contain abundant R-EGF and this may partly explain their malignant nature (malignant nature is here defined as ability to proliferate in agarose). Type alpha transforming growth factors, which in some cancer cells act as uncontrolled autocrine growth factors, were not found in protein extracts from T-MG1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Bifunctional activity of transforming growth factor type beta on the growth of NRK-49F cells, normal and transformed by Kirsten murine sarcoma virus

Transformation of rat NRK-49F cells (49F) by Kirsten murine sarcoma virus (Ki-MSV) renders these cells (Ki-49F cells) capable of autonomous anchorage independent (AI) growth. As compared to nontransformed 49F cells, the transformation by Ki-MSV does not modify the cell response to transforming growth factor-beta (TGF-beta) in monolayer conditions, but alters it in A I growth conditions. The growth of nontransformed or Ki-MSV-transformed adherent 49F cells is slowed down by porcine TGF-beta, and this effect is reversed by epidermal growth factor (EGF). This decrease in the cell growth rate, induced by TGF-beta, does not affect the cloning efficiency of untransformed and transformed adherent 49F cells. Contrarily, porcine TGF-beta decreases the A I cloning efficiency of Ki-49F cells in agar-gelled medium; this effect is only partly reversed by EGF, which does not synergise with TGF-beta to enhance the A I growth as in the case of untransformed 49F cells. Media conditioned by 49F cells, Ki-49F cells, and chicken embryo fibroblasts contain a latent TGF-beta whose capacity to promote the A I growth of 49F cells and to inhibit that of Ki-49F cells is unmasked by acidification. The same situation exists concerning TGF-beta from human platelets. Neutral extracts are inefficient in both tests of promotion and inhibition of A I growth and contain an acid-activable component with an apparent molecular weight of 600 kd. In acid extracts, a 5-9 kd apparent molecular weight component is responsible for the A I growth enhancement of 49F cells and the A I growth inhibition of Ki-49F cells. Further purification by reverse phase chromatography shows that both activities strictly coelute at the same point (32%) of an acetonitrile gradient. These results indicate that TGF-beta is present in physiological conditions as a latent form which requires activation for inhibiting the A I growth of transformed cells as well as for enhancing that of 49F cells.

Transforming growth factor beta (TGF-beta) induces fibrosis in a fetal wound model

The adult cellular response to tissue injury is characterized by acute inflammation followed eventually by fibroblast proliferation and collagen synthesis. Fetal tissue responses to injury differ markedly from those of the adult; an early acute inflammatory response is absent, few fibroblasts participate, and no collagen is deposited. The object of the present study was to analyze the effects of transforming growth factor beta (TGF-beta), an important regulatory molecule in adult healing events, on the fetal tissue response following wounding. Fetal cellular and extracellular matrix responses to injury were evaluated by placing subcutaneous wound implants containing TGF-beta (0.01 to 10 ng) in fetal rabbits at 24 days gestation (term = 31 days). Histologic responses one to seven days later were compared with fetal and adult control implants without TGF-beta. The histology of the adult implant was characterized by an early acute inflammatory response: by day 7 fibroblasts and collagen were predominant. In contrast, control implants removed from fetal rabbits had no histologic evidence of acute inflammation or fibroblast penetration and no collagen was deposited. When implants containing 1.0 ng TGF-beta were removed from fetal rabbits at seven days, a grossly fibrotic reaction was observed: histology confirmed marked fibroblast penetration with collagen deposition. Fetal implants containing 0.01 ng or 10 ng TGF-beta showed few fibroblasts but had increased numbers of inflammatory cells compared with controls. These observations demonstrate that the fetal response becomes adultlike with fibroblast proliferation and collagen accumulation when TGF-beta is added, thus documenting the responsiveness of the fetal system to adult repair signals.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta s are equipotent growth inhibitors of interleukin-1-induced thymocyte proliferation

The effects of two forms of transforming growth factor-beta, TGF-beta 1 and TGF-beta 2, upon the proliferative response of murine thymocytes were investigated in this study. TGF-beta 1 and TGF-beta 2 were found to be equipotent growth inhibitors of interleukin-1 (IL-1)- and phytohemagglutinin (PHA)-stimulated thymocytes when added at the initiation of the cultures. These factors suppressed the proliferative response in a dose-dependent fashion between 0.4 and 100 pM. The proliferative response was maximally inhibited (90% inhibition) at 100 pM. The half-maximal inhibitory dose (ID50) was 6 and 4 pM for TGF-beta 1 and TGF-beta 2, respectively. These factors were less effective or ineffective at suppressing the proliferation of thymocytes which had been prestimulated for 24 to 48 hr by IL-1 and PHA. Neither factor inhibited interleukin-2 (IL-2)-dependent thymocyte proliferation or the proliferation of an IL-2-dependent cytotoxic T cell line (CTL-L), suggesting that the anti-proliferative actions of these factors was by inhibition of cellular events triggered by IL-1. Furthermore, anti-TGF-beta 1 antibodies did neutralize the biological actions of TGF-beta 1 and these antibodies did block the binding of 125I-labeled TGF-beta 1 to cell surface receptors showing that the inhibitory action is mediated through specific receptors for TGF-beta 1 on thymocytes. These antibodies, however, did not neutralize the anti-proliferative action of TGF-beta 2. Although TGF-beta 1 and TGF-beta 2 exhibit very similar biological activities, these molecules are antigenically different and, therefore, have different tertiary structures.

Differential expression of platelet-derived growth factor and transforming growth factor genes in small- and non-small-cell human lung carcinoma lines

We have investigated a panel of human lung cancer cell lines representing the major groups of lung cancer, i.e., small-cell carcinoma (SCC) and the group of non-SCC, consisting of squamous-cell carcinoma (SQC), adenocarcinoma (ADC) and large-cell carcinoma (LCC), for their expression of certain growth factor genes. Messenger RNA from each cell line was hybridized with probes for platelet-derived growth factor (PDGF) A- and B-chains, insulin-like growth factor (IGF)-I and -II, transforming growth factor (TGF)-alpha and -beta, epidermal growth factor (EGF) as well as a probe for the EGF receptor. All non-SCC cell lines examined showed expression of the PDGF A-chain gene. The PDGF beta-chain and TGF-beta genes were expressed in all non-SCC cell lines but one, H-125 (ADC). TGF-alpha gene expression was demonstrated in the SQC cell line U-1752, in both ADC cell lines (H-23 and H-125) and in one of the 3 LCC cell lines, U-1810. IGF-II was only transcribed in the LCC cell line U-1810. The EGF-receptor was detected in all non-SCC cell lines but one, H-661 (LCC). Neither IGF-I nor EGF transcripts could be seen in any of the 10 cell lines examined. In contrast to the non-SCC cell lines, the 4 SCC lines were constantly negative for the probes employed in this study. The frequent and heterogeneous expression of growth factor transcripts in all non-SCC studied, but not SCC-cell lines, may contribute to the difference in biological behaviour observed in vivo and in vitro between the 2 major lung cancer entities.

Absence of TGF-beta receptors and growth inhibitory responses in retinoblastoma cells

The responses of retinoblastoma tumor cells and normal retinal cells to various growth inhibitory factors were examined. Whereas fetal retinal cells were highly sensitive to the antimitogenic effects of transforming growth factor beta 1 (TGF-beta 1), retinoblastoma tumor cell lines were all resistant to this factor. Binding assays and affinity labeling of these cells with radioiodinated TGF-beta 1 revealed that the cells did not have TGF-beta receptors. The retinoblastoma cells lacked the three affinity-labeled proteins of 65, 95, and 300 kilodaltons typically seen in human cell lines and thus differed from normal retinal cells and from other types of neuroectodermal tumors that display the normal pattern of receptors. Loss of TGF-beta receptors, which is a rare event among tumor cells, may represent one mechanism through which these cells escape from negative control and form retinoblastomas.

TGF-beta inhibits growth factor-induced DNA synthesis in hamster fibroblasts without affecting the early mitogenic events

Transforming growth factor beta (TGF-beta) was found to inhibit (IC50 = 0.1 ng/ml) alpha-thrombin or FGF-induced mitogenicity in G0-arrested Chinese hamster lung fibroblasts. Growth factor-stimulated cells became rapidly insensitive to TGF-beta addition during their progression through G0/G1 suggesting that an early step of the mitogenic response was the target of TGF-beta action. Surprisingly, none of the well characterized early mitogenic events commonly triggered by growth factors was found to be affected by TGF-beta addition. These responses included: phosphoinositide breakdown, activation of protein kinase C as determined by EGF receptor down-modulation, subsequent rises in pHi, c-fos, and c-myc mRNA levels, ribosomal protein S6 phosphorylation, the increase in RNA and protein synthesis, induction of ornithine decarboxylase. Only the induction of thymidine kinase, a marker of entry in the S phase, was found to be repressed by TGF-beta, with maximal inhibition when TGF-beta was added early in G1. These results indicate that the inhibitory action of TGF-beta does not affect the growth factors signalling pathways but touches an early event different from those so far analyzed.

A nuclear factor 1 binding site mediates the transcriptional activation of a type I collagen promoter by transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) increases the steady-state RNA levels of several fibroblast extracellular matrix proteins. Using DNA transfection, we show that TGF-beta stimulates the activity of the mouse alpha 2(l) collagen promoter 5- to 10-fold in mouse NIH 3T3 and rat osteosarcoma cells. Deletion analysis indicates that a segment of this promoter between -350 and -300, overlapping a nuclear factor 1 (NF1) binding site, is needed for TGF-beta stimulation. A 3 bp substitution mutation abolishing NF1 binding to this site inhibits TGF-beta activation. Insertion of this NF1 binding site 5' to the SV40 early promoter makes the promoter TGF-beta inducible, but the 3 bp substitution does not. Similarly, when the NF1 binding site at the replication origin of adenovirus 2 and 5 is inserted 5' to the SV40 promoter, the promoter responds to TGF-beta. Therefore an NF1 binding site mediates the transcriptional activation of the mouse alpha 2(l) collagen promoter by TGF-beta.

Transforming growth factor beta and inhibition of hepatocellular proliferation

Transforming growth factor beta (TGF beta) is a recently characterized polypeptide that elicits diverse biologic actions in a wide range of cell types in vitro. TGF beta is a bifunctional growth regulator of fibroblasts with either growth stimulation or growth inhibition but inhibits the growth of most epithelial cells. In addition, TGF beta can either block or induce the differentiation of certain cells. TGF beta reversibly inhibits DNA synthesis in normal adult rat hepatocytes and in cells isolated from regenerating liver 12 h and 18 h after partial hepatectomy. However, at 3 h and 6 h after hepatectomy there is a decrease in sensitivity of hepatocytes to growth inhibition by TGF beta. Recent data from other laboratories indicate that TGF beta expression increases substantially in liver after partial hepatectomy and that administration of purified TGF beta in vivo inhibits DNA synthesis in regenerating rat liver. Together with our observations, these findings suggest that TGF beta may play a central role as a negative paracrine growth regulator in adult rat liver.

Effect of transforming growth factor-beta on human chorionic gonadotropin induced testosterone production by cultured rat testicular cells

The potential role of transforming growth factor-beta (TGF-beta) as an intragonadal regulator in the testis was investigated by studying the effect of TGF-beta on testosterone (T) production by neonatal rat testis cells in primary cultures. After 3 days of preincubation in serum-free medium, testis cells were treated with hormones for 3 additional days. Human chorionic gonadotropin (hCG) treatment (0.3-30 ng/ml) of testis cells elicited a dose-dependent increase of T levels with maximum values greater than 9-fold over baseline. Although TGF-beta alone did not affect T levels, a dose-dependent inhibition of hCG-stimulated T production was observed when cells were cotreated with TGF-beta. Maximal inhibition was greater than 85%, and the IC50 value was 5 ng/ml (2 x 10(-10) M; n = 5 experiments). This inhibitory effect was evident 48 h after the initiation of treatment and could be reversed 1 day after the cessation of TGF-beta exposure of cells. TGF-beta also reduced forskolin and (Bu)2cAMP-induced T production (greater than 85% decrease), indicating that TGF-beta can inhibit steroidogenesis distal to the formation of cAMP. The conversion of exogenously added androgen precursors (progesterone (P) and 17 alpha-hydroxyprogesterone) to T by hCG-stimulated cells was suppressed by the addition of TGF-beta. In contrast, endogenous P accumulation did not change in cultures treated with TGF-beta. Because TGF-beta-like activity has been found in the testis, the observed inhibitory effect of TGF-beta suggests a potential intratesticular regulatory role of this growth factor.

Inhibition of the proliferative response of human B lymphocytes to B cell growth factor by transforming growth factor-beta

The effects of transforming growth factor-beta (TGF-beta) on the proliferative response of human B cells to the low molecular weight B cell growth factor (BCGF) have been investigated in this study. It was found that TGF-beta, at picomolar concentrations, strongly inhibited the BCGF-induced proliferation of anti-mu chain or Staphylococcus aureus Cowan I-activated human B cells and also of a BCGF-dependent cell line derived from a human lymphocytic nodular lymphoma. This inhibitory effect was detected in normal and serum-free culture conditions. The suppression was greatly reduced when TGF-beta was added to the culture one day after BCGF and could be reverted by removing TGF-beta from the culture medium. Since TGF-beta has been detected in supernatants from activated T cells, this factor may represent an important regulatory molecule in the feedback control of B cell activation.

Type beta transforming growth factor (TGF beta) regulation of alkaline phosphatase expression and other phenotype-related mRNAs in osteoblastic rat osteosarcoma cells

TGF beta 1 from porcine platelets increased alkaline phosphatase (AP) activity in the rat osteoblastic cell line ROS 17/2.8 about three-fold. This effect was dose-dependent with an ED50 of about approximately 0.2 ng/ml and was larger during logarithmic growth than at confluence. TGF beta 1 inhibited cell growth by about 30% with similar dose dependence. Thirty min exposure to TGF beta 1 was sufficient to increase AP activity 3 days later by about two-fold but did not affect cell growth, suggesting dissociation between effects on proliferation and differentiation. The rise in AP activity started 6 h after TGF beta 1 addition and was blocked by cycloheximide and actinomycin D. TGF beta 1 also increased AP mRNA by two- to three-fold and this effect was not blocked by cycloheximide. The half-life of AP mRNA, estimated following the addition of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole was about ten h in both control and TGF beta 1-treated cells. The mRNAs for type I procollagen and osteonectin were also increased by TGF beta 1 but fibronectin mRNA was decreased. TGF beta 2 effects on AP and cell growth were similar to those of TGF beta 1, except for lack of activity following transient exposure. At saturating concentrations, TGF beta 2 (2 ng/ml) or dexamethasone (10(-7) M), which has similar effects on these cells, did not further augment the effects of TGF beta 1 (at 2 ng/ml). Above findings suggest that TGF beta promotes osteoblastic differentiation in rat osteosarcoma cells at least in part by acting at the pretranslational level.

Transforming growth factor type beta in normal human urine

TGF beta has been identified in normal human urine specimens from five individuals studied for five consecutive days. The peptide was extracted from urine using Sepralyte C1 beads. Detectable levels of [125I]TGF beta competing activity as measured by radioreceptor assay was found in about half of the specimens studied. The protein isolated from urine using C1 Sepralyte beads was further purified using Biogel P-60 column chromatography. Fractions were tested for TGF beta and EGF competing activity using radioreceptor assays. TGF beta and EGF extracted from urine are clearly separated by column chromatography. Two distinct EGF peaks and a single TGF beta peak were observed. Fractions having [125I]TGF beta competing activity were pooled and further purified using reverse-phase HPLC. HPLC fractions having [125I]TGF beta competing activity were tested for bioactivity using a soft agar assay. The fractions were capable of stimulating soft agar growth of AKR-2B (clone 84A) cells and cross reacted with a TGF beta antibody in a radioimmunoassay. The presence of TGF beta in normal human urine was also demonstrated by immunoblotting. These results also suggest that C1 bead extraction of urine specimens can be used as a rapid first step in purification of TGF beta.

Reciprocal effects of epidermal growth factor and transforming growth factor beta on the anchorage-dependent and -independent growth of A431 epidermoid carcinoma cells

The effects of epidermal growth factor (EGF) and transforming growth factor beta (TGF beta) on the growth of A431 epidermoid carcinoma cells were studied. Whereas the monolayer growth of A431 cells was inhibited by EGF, it was stimulated by TGF beta. Contrary to the effects on the monolayer growth, EGF stimulated the soft agar growth of A431 cells. The stimulatory effects of TGF beta on the anchorage-dependent growth were antagonized by EGF and those of EGF on anchorage-independent growth were antagonized by TGF beta. These results suggest that both factors not only convey the proliferative signals to A431 cells but also induce phenotypic changes, resulting in a preference for either anchorage-dependent or anchorage-independent growth. Moreover, as the stimulatory effects of EGF on the soft agar growth of A431 cells paralleled its reported stimulatory effects on their in vivo growth, it is also suggested that in vivo responses of cells to certain growth factors may correlate better with their responses in soft agar culture than with those in monolayer culture.

Two forms of transforming growth factor-beta distinguished by multipotential haematopoietic progenitor cells

Type-beta transforming growth factors (TGF-beta s) are polypeptides that act hormonally to control proliferation and differentiation of many cell types. Two distinct homodimeric TGF-beta polypeptides, TGF-beta 1 and TGF-beta 2 have been identified which show approximately 70% amino-acid sequence similarity. Despite their structural differences, TGF-beta 1 and TGF-beta 2 are equally potent at inhibiting epithelial cell proliferation and adipogenic differentiation. The recent immunohistochemical localization of high levels of TGF-beta in the bone marrow and haematopoietic progenitors of the fetal liver has raised the possibility that TGF-beta s might be involved in the regulation of haematopoiesis. Here we show that TGF-beta 1, but not TGF-beta 2, is a potent inhibitor of haematopoietic progenitor cell proliferation. TGF-beta 1 inhibited colony formation by murine factor-dependent haematopoietic progenitor cells in response to interleukin-3 (IL-3) or granulocyte-macrophage colony stimulating factor (GM-CSF), as well as colony formation by marrow progenitor cells responding to CSF-1 (M-CSF). The progenitor cell lines examined were approximately 100-fold more sensitive to TGF-beta 1 than TGF-beta 2, and displayed type-I TGF-beta receptors with affinity approximately 20-fold higher for TGF-beta 1 than TGF-beta 2. These results identify TGF-beta 1 as a novel regulator of haematopoiesis that acts through type-I TGF-beta receptors to modulate proliferation of progenitor cells in response to haematopoietic growth factors.

Transforming growth factor beta levels in rat wound chambers

Exogenous TGF-beta accelerates healing in both normal and doxorubicin-treated rats, but whether it plays an intrinsic role in the natural healing process is unknown. Subcutaneous wound chambers in 16 F344 rats were aspirated from postwounding Day 3 through Day 16 for TGF-beta levels and cytology. A soft agar assay and a competitive radioreceptor binding assay were used to determine TGF-beta levels. Papanicolau staining and differential cell counts were used to determine cytology. Results were similar using either method for the determination of TGF-beta levels. With the sensitive radioreceptor assay, low TGF-beta levels on postwounding Day 4, mean 2.6 ng/ml, rose to a peak mean level of 20.4 ng/ml on Day 7 and fell significantly from peak level to a level of 5.4 ng/ml of Day 16. All TGF-beta levels for postwounding Days 6 through 14 were significantly increased over the baseline TGF-beta levels of Days 4 and 5 (P less than 0.05). Day 16 TGF-beta levels were not different from baseline. Cytologic changes were characterized by a liner decrease in total neutrophil count over the exam period and a concurrent linear increase in total lymphocyte and macrophage counts. TGF-beta levels changed in a bell-shaped temporal sequence during healing, apparently unrelated to percentage lymphocyte, macrophage, or neutrophil count. Peak TGF-beta levels occurred during the fibroblast proliferation and collagen synthesis phase of healing. This study presents the first evidence that TGF-beta is present in a healing wound and suggests that it may be an intrinsic mediator of the healing process.

Growth factors modify the epidermal growth factor receptor through multiple pathways

Previous results have shown that tumor promoters modify the properties of the epidermal growth factor (EGF) receptor through the activation of protein kinase C. Diacylglycerol-generating factors such as platelet-derived growth factor (PDGF) and p28sis should activate protein kinase C and alter EGF receptor properties in a similar manner. To test directly the involvement of protein kinase C in the action of media from v-sis-transformed cells on the EGF receptor, Swiss 3T3 cells were first extensively treated with various concentrations of the tumor-promoter phorbol dibutyrate (PDBu) This treatment reduced levels of active protein kinase C in the cells, making them less responsive to subsequent rechallenge with the tumor promoter. The results demonstrate that there are at least two components to the action of media from v-sis transformed cells on EGF binding: a labile factor that confers protein kinase C independence and a stable factor that appears to be dependent on protein kinase C. The action of the first factor cannot be mimicked by transforming growth factor-beta or EGF in either the presence or absence of PDGF. The action of the second factor is similar to that of PDGF. These findings indicate that heterologous regulation of the EGF receptor can occur through both protein kinase C-dependent and -independent pathways.

The transforming growth factor-beta system, a complex pattern of cross-reactive ligands and receptors

A new homodimer form of transforming growth factor-beta (TGF-beta), TGF-beta 2, has been identified in porcine blood platelets. TGF-beta 2 is homologous to ordinary TGF-beta (TGF-beta 1), which is also present in platelets. TGF-beta 1.2, a heterodimer containing one TGF-beta 1 chain and one TGF-beta 2 chain, has also been isolated. TGF-beta 1 and TGF-beta 2 interact differently with a family of receptors in target cells. A 280 kd receptor displays high affinity for both TGF-beta 1 and TGF-beta 2. Occupancy of this receptor by TGF-beta 1 or TGF-beta 2 correlates with the ability of these TGF-beta s to inhibit cell proliferation. In contrast, 65 kd and 85 kd receptors have high affinity for TGF-beta 1 but lower affinity for TGF-beta 2. The existence of distinct forms of TGF-beta that interact differently with a family of TGF-beta receptors could provide flexibility to the regulation of tissue growth and differentiation by the TGF-beta system.

Evidence that transforming growth factor-beta is a hormonally regulated negative growth factor in human breast cancer cells

The hormone-dependent human breast cancer cell line MCF-7 secretes transforming growth factor-beta (TGF-beta), which can be detected in the culture medium in a biologically active form. These polypeptides compete with human platelet-derived TGF-beta for binding to its receptor, are biologically active in TGF-beta-specific growth assays, and are recognized and inactivated by TGF-beta-specific antibodies. Secretion of active TGF-beta is induced 8 to 27-fold under treatment of MCF-7 cells with growth inhibitory concentrations of antiestrogens. Antiestrogen-induced TGF-beta from MCF-7 cells inhibits the growth of an estrogen receptor-negative human breast cancer cell line in coculture experiments; growth inhibition is reversed with anti-TGF-beta antibodies. We conclude that in MCF-7 cells, TGF-beta is a hormonally regulated growth inhibitor with possible autocrine and paracrine functions in breast cancer cells.

Mouse Balb/c3T3 cell mutant with low epidermal growth factor receptor activity: induction of stable anchorage-independent growth by transforming growth factor beta

A mutant clone (MO-5) was originally isolated as a clone resistant to Na+/K+ ionophoric antibiotic monensin from mouse Balb/c3T3 cells. MO-5 was found to show low receptor-endocytosis activity for epidermal growth factor (EGF): binding activity for EGF in MO-5 was less than one tenth of that in Balb/c3T3. Anchorage-independent growth of MO-5 was compared to that of Balb/c3T3 when assayed by colony formation capacity in soft agar. Coadministration of EGF and TGF-beta efficiently enhanced anchorage-independent growth of normal rat kidney (NRK) cells, but neither factor alone was competent to promote the anchorage-independent growth. The frequency of colonies appearing in soft agar of MO-5 or Balb/c3T3 was significantly enhanced by TGF-beta while EGF did not further enhance that of MO-5 or Balb/c3T3. Colonies of Balb/c3T3 formed in soft agar in the presence of TGF-beta showed low colony formation capacity in soft agar in the absence of TGF-beta. Colonies of MO-5 formed by TGF-beta in soft agar, however, showed high colony formation capacity in soft agar in the absence of TGF-beta. Pretreatment of MO-5 with TGF-beta induced secretion of TGF-beta-like activity from the cells, while the treatment of Balb/c3T3 did not induce the secretion of a significant amount of TGF-beta-like activity. The loss of EGF-receptor activity in the stable expression and maintenance of the "transformed" phenotype in MO-5 is discussed.

Isolation and characterization of mink lung epithelial cell mutants resistant to transforming growth factor beta

Mink lung epithelial cells resistant to growth inhibition by transforming growth factor beta (TGF-beta) have been isolated by chemical mutagenesis and growth in the presence of platelet extracts enriched in TGF-beta. Several resistant clones were isolated, at least one of which stably retained its resistance to TGF-beta when grown in the absence of the factor. The cells of this clone were similar to the parent cells in morphology and growth properties. However, unlike the parent cells, the resistant cells did not show any of the following responses to TGF-beta: inhibition of DNA synthesis and proliferation; morphological changes involving increased cell spreading; or stimulation of synthesis of a 48-kilodalton secreted protein. The resistant cells do, however, retain a functional TGF-beta receptor. The TGF-beta resistant cell lines may be useful in genetic studies designed to identify the biochemical events required for inhibition of epithelial cell growth by this factor.

Transforming growth factor beta regulation of cell proliferation

Two types of transforming growth factors (TGF) have been purified and well characterized, TGF alpha and TGF beta. TGF alpha is a 5.6 kD single chain molecule that shows sequence homology to epidermal growth factor (EGF), binds to the EGF receptor, and has biological effects very similar to those of EGF. TGF beta is different from TGF alpha in its molecular structure and biological activity, and has its own specific cell surface receptor. TGF beta is a 25 kD homodimer of 12.5 kD subunits that shows no sequence homology to TGF alpha. TGF beta is a highly ubiquitous molecule produced by a variety of cell types in an inactive form. Most cells have receptors for TGF beta, suggesting that a major regulatory step in TGF beta action is through activation of the inactive form. Growth stimulatory effects with TGF beta have been observed so far only in fibroblastic cells. In at least one circumstance, there is evidence that the stimulatory effects of TGF beta in fibroblastic cells is indirect through induction of c-sis and autocrine stimulation by platelet-derived growth factor (PDGF)-like material. TGF beta inhibits in vitro proliferation of most cell types tested, including normal epithelial cells. Thus TGF beta is primarily a growth inhibitor and not a classical growth factor. Increased autocrine stimulation by endogenous TGF beta in fibroblastic cells or decreased inhibitory effects in epithelial cells (or other cells normally inhibited by TGF beta) could lead to an increased proliferative potential and thereby contribute to the neoplastic phenotype.