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

Ki-67, TGF-β1, and elastin content are significantly altered in lip carcinogenesis

Epithelial changes observed in actinic cheilitis (AC) and lower lip squamous cell carcinoma (LLSCC) have been studied using different markers in order to observe diagnostic and prognostic factors for both lesions. The aim of the present study was to analyze Ki-67, TGF-β1, and elastin content in AC and LLSCC to determine the possible role of these proteins in lip carcinogenesis. Medical records of 29 cases of AC and 53 cases of LLSCC were analyzed. Lesions were classified according histological pattern and submitted to immunostaining for Ki-67, TGF-β1, and elastin. Different percentages of Ki-67-positive cells were found in AC depending on the degree of epithelial dysplasia (p < 0.01). An association was also found between the percentage of Ki-67-positive cells and tumor grade in LLSCC (p < 0.01). An inverse correlation was found between Ki-67 and TGF-β1 in AC and LLSCC (p < 0.01). Elastosis was thinner and more discontinuous in LLSCC in comparison to AC, and this difference in the elastin immunolabeling pattern was statistically significant between groups (p < 0.01). The present findings indicate that changes in Ki-67 and TGF-β1 content contribute to lip carcinogenesis. Furthermore, elastin content reflects changes in the extracellular matrix in both AC and LLSCC.

Regulation of epithelial proliferation by TGF-beta

The closely related mammalian TGF-betas (TGF-beta 1, TGF-beta 2 and TGF-beta 3) are potent inhibitors of proliferation of many cell types in vitro. TGF-beta 1 has been demonstrated to be growth inhibitory in vivo for epithelial, endothelial, myeloid and lymphoid cells. Utilizing skin keratinocytes as a model system for studying the mechanism of TGF-beta 1-induced growth inhibition, it has been demonstrated that TGF-beta 1 rapidly inhibits transcription of the c-myc gene. Antisense c-myc oligonucleotides inhibit proliferation of keratinocytes as effectively as does TGF-beta 1, indicating that TGF-beta 1 suppression of c-myc expression is an important component of this growth inhibition. Studies utilizing DNA tumour virus transforming gene constructs have shown that the retinoblastoma gene product, pRb, or a related protein, is needed for TGF-beta 1 suppression of c-myc transcription. Thus, TGF-beta 1 may act through a tumour suppressor gene product, pRb, to suppress transcription of a proto-oncogene, c-myc, and subsequently inhibit cell proliferation.

Cell-type-specific activation of PAK2 by transforming growth factor beta independent of Smad2 and Smad3

Transforming growth factor beta (TGF-beta) causes growth arrest in epithelial cells and proliferation and morphological transformation in fibroblasts. Despite the ability of TGF-beta to induce various cellular phenotypes, few discernible differences in TGF-beta signaling between cell types have been reported, with the only well-characterized pathway (the Smad cascade) seemingly under identical control. We determined that TGF-beta receptor signaling activates the STE20 homolog PAK2 in mammalian cells. PAK2 activation occurs in fibroblast but not epithelial cell cultures and is independent of Smad2 and/or Smad3. Furthermore, we show that TGF-beta-stimulated PAK2 activity is regulated by Rac1 and Cdc42 and dominant negative PAK2 or morpholino antisense oligonucleotides to PAK2 prevent the morphological alteration observed following TGF-beta addition. Thus, PAK2 represents a novel Smad-independent pathway that differentiates TGF-beta signaling in fibroblast (growth-stimulated) and epithelial cell (growth-inhibited) cultures.

Endocervical cancer is associated with an increase in the ligands and receptors for transforming growth factor-beta and a contrasting decrease in p27(Kip1)

OBJECTIVE

The aim of this study was to investigate the relationship between the expression of the TGF-beta ligands and TGF-beta receptors to the expression of p27(Kip1), a TGF-beta-regulated gene, in endocervical cancer.

METHODS

To examine the expression of TGF-beta and p27(Kip1) in malignant transformation of the uterine endocervix, a panel of 23 formalin-fixed and paraffin-embedded human cervical specimens, including 8 with benign endocervical glands, 8 with cervical adenocarcinoma in situ, and 7 with cervical adenocarcinomas, was used. Tissues were immunostained with polyclonal antibodies that react specifically with TGF-beta 1, TGF-beta 2, TGF-beta 3, TGF-beta RI, TGF-beta RII, and p27(Kip1).

RESULTS

Immunostaining for TGF-beta 1, TGF-beta 2, TGF-beta 3, TGF-beta RI, TGF-beta RII, and p27(Kip1) was detected in normal endocervix, with the TGF-betas showing weak cytoplasmic staining, while p27(Kip1) showed strong nuclear staining. Expression of TGF-beta increased significantly upon neoplastic transformation with the TGF-beta ligands and receptors showing strong cytoplasmic staining in adenocarcinoma in situ compared to normal endocervix. Interestingly, expression of TGF-beta was lower in adenocarcinoma than in adenocarcinoma in situ, but still significantly higher than in normal endocervix. TGF-beta 2 and TGF-beta 3 showed higher levels of immunostaining than TGF-beta 1 in adenocarcinomas. In contrast, p27(Kip1) protein expression decreased with progressive malignancy, with lower p27(Kip1) protein levels detected in adenocarcinoma than in adenocarcinoma in situ, while normal endocervix showed the highest level of p27(Kip1) protein expression.

CONCLUSION

Elevated expression of the TGF-beta ligands and receptors is found in both cervical adenocarcinoma in situ and adenocarcinoma compared to normal endocervix. In contrast, a progressive decrease in p27(Kip1) occurs upon neoplastic transformation of the normal endocervix to cervical adenocarcinoma. These results suggest that neoplastic transformation of the endocervix may be related to dysregulation of TGF-beta and p27(Kip1) seen as an elevation of TGF-beta and a reduction of p27(Kip1) expression that may lead to loss of cell cycle control.

Transforming growth factor beta(1) selectively inhibits the cyclic AMP-dependent proliferation of primary thyroid epithelial cells by preventing the association of cyclin D3-cdk4 with nuclear p27(kip1)

Dog thyroid epithelial cells in primary culture constitute a physiologically relevant model of positive control of DNA synthesis initiation and G0-S prereplicative phase progression by cAMP as a second messenger for thyrotropin (thyroid-stimulating hormone [TSH]). As previously shown in this system, the cAMP-dependent mitogenic pathway differs from growth factor cascades as it stimulates the accumulation of p27(kip1) but not cyclins D. Nevertheless, TSH induces the nuclear translocations and assembly of cyclin D3 and cdk4, which are essential in cAMP-dependent mitogenesis. Here we demonstrate that transforming growth factor beta(1) (TGFbeta(1)) selectively inhibits the cAMP-dependent cell cycle in mid-G1 and various cell cycle regulatory events, but it weakly affects the stimulation of DNA synthesis by epidermal growth factor (EGF), hepatocyte growth factor, serum, and phorbol esters. EGF+serum and TSH did not interfere importantly with TGFbeta receptor signaling, because they did not affect the TGFbeta-induced nuclear translocation of Smad 2 and 3. TGFbeta inhibited the phosphorylation of Rb, p107, and p130 induced by TSH, but it weakly affected the phosphorylation state of Rb-related proteins in EGF+serum-treated cells. TGFbeta did not inhibit c-myc expression. In TSH-stimulated cells, TGFbeta did not affect the expression of cyclin D3, cdk4, and p27(kip1), nor the induced formation of cyclin D3-cdk4 complexes, but it prevented the TSH-induced relocalization of p27(kip1) from cdk2 to cyclin D3-cdk4. It prevented the nuclear translocations of cdk4 and cyclin D3 without altering the assembly of cyclin D3-cdk4 complexes probably formed in the cytoplasm, where they were prevented from sequestering nuclear p27(kip1) away from cdk2. This study dissociates the assembly of cyclin D3-cdk4 complexes from their nuclear localization and association with p27(kip1). It provides a new mechanism of regulation of proliferation by TGFbeta, which points out the subcellular location of cyclin D-cdk4 complexes as a crucial factor integrating mitogenic and antimitogenic regulations in an epithelial cell in primary culture.

Effects of EGF and TGFbeta1 on c-myc gene expression and DNA synthesis in embryonic hamster palate mesenchymal cells

Previous work has shown that cell proliferation is a major contributor to the early palate morphogenesis in mammals. The present study was undertaken to examine the effect of EGF, TGFbeta1 and their combination on proliferation (measured by DNA synthesis) and on the expression of a growth related proto-oncogene, c-myc, in embryonic hamster palate mesenchymal cells (HPMC). Vertically developing hamster palatal shelves were dissected on day 11 of gestation, and trypsinized, and primary cultures were grown in DMEM + 10% serum at 37 degrees C and 5% CO2. Following appropriate growth factor treatment of HPMC, DNA synthesis was measured by scintillation counting and extracted RNA was subjected to Northern blot analysis. In serum-starved, pre-confuent cultures treated with EGF (20 ng/ml), DNA synthesis was stimulated in the presence of 2.5% serum. In contrast, treatment of HPMC with TGFbeta1 (10 ng/ml) in the presence or absence of EGF/serum for 24 hr, or HPMC pre-treatment with TGFbeta1 (30 min) followed by EGF/serum (24 hr), resulted in an arrest of DNA synthesis. Northern blot analysis of RNA extracted from HPMC showed that as serum-starved, growth-arrested cells progressed through G0 to G1 phase of the cell cycle, following EGF treatment, c-myc was expressed by 1 hr and declined thereafter. In contrast, TGFbeta1 did not support expression of c-myc. Following pre- or co-treatment with TGFbeta1, the EGF +/- serum-induced expression of c-myc was seen between 1 and 6 hr. It appears that EGF-induced expression of c-myc may be involved in advancing the HPMC in G1, and thus may contribute to the onset of DNA synthesis in HPMC. Since co- or pre-treatment with TGFbeta1 did not inhibit EGF/serum induced expression of c-myc, it is possible that growth arresting effect of TGFbeta1 may not be exerted directly through inhibition or blockage of c-myc expression.

TGFbeta1 induces a cell-cycle-dependent increase in motility of epithelial cells

We have previously shown that addition of type 1 transforming growth factor-beta (TGFbeta1) to an exponentially growing population of mink lung CCl64 cells increases their average intermitotic time from 14.4 to 20.3 hours, predominantly by extending G1 from 7.5 to 13.5 hours. Here we have used the DRIMAPS system (digitally recorded interference microscopy with automatic phase-shifting) for obtaining data on cellular mass distribution, cell motility and morphology. We found no significant change in the cells' rate of mass increase following TGFbeta1 treatment, which implies that the treated cells attained a higher mass during their extended cell cycle and this was confirmed by direct measurement of cell size. However, the cells showed a dramatic motile response to treatment: TGFbeta1-treated cells had a significantly higher time-averaged speed of 36.2 microm hour-1 compared to 14.5 microm hour-1 for the control cells. The time course of the response was gradual, reaching a maximum mean speed of 52.6 microm hour-1 after 15 hours exposure. We found that the gradual onset of the response was probably not due to a slow accumulation of a secondary factor but because cells were dividing throughout the experiment and most of the response to TGFbeta1 occurred only after the first cell division in its presence. Thus, taking only those cells that had not yet divided, the time-averaged speed of treated cells (26.1 micrometer hour-1) was only moderately higher than that of untreated cells (14.9 micrometer hour-1) whereas, for those cells that had divided, the difference in speed between treated cells (45.1 micrometer hour-1) and untreated cells (14.1 microm hour-1) was much greater. Increased speed was a consequence of enhanced protrusion and retraction of the cell margin coupled with an increase in cell polarity. TGFbeta1 also increased the mean spreading of the cells, measured as area-to-mass ratio, from 3.2 to 4.4 micrometer2 pg-1, and the intracellular mass distribution became more asymmetric. The observations indicate that a G2 signal may be necessary to reach maximal motility in the presence of TGFbeta1.

Transforming growth factor-beta 1 induces apoptosis through down-regulation of c-myc gene and overexpression of p27Kip1 protein in cervical carcinoma

Transforming growth factor-beta 1 (TGF-beta 1) is known to be a potent growth inhibitor for many cell types, including most epithelial cells. In skin keratinocytes, TGF-beta 1 has been shown to inhibit growth and to rapidly reduce c-myc expression. However, the molecular mechanism of TGF-beta 1 action on cell growth of cervical carcinoma has not yet been elucidated. We thus assessed the effect of TGF-beta 1 on the growth of cervical carcinoma cell lines. Two cervical squamous carcinoma cell lines, CUMC-3 and CUMC-6, were incubated with varying concentrations of TGF-beta 1, and growth inhibition was evaluated with tetrazolium-based colorimetric assay. After culture in TGF-beta 1 for 24 h, inhibition of growth was detected in a dose-dependent manner at concentrations of 0.1-10 ng/ml in both cell lines. This effect of TGF-beta 1 on cultured carcinoma cells was associated with apoptotic process including oligonucleosomal ladder DNA and apoptotic body formations. Northern blot analysis revealed c-myc mRNA expression was suppressed by 10 ng/ml of TGF-beta 1 following 3 h of treatment in both cell lines. Western blot analysis showed that the level of p27Kip1 protein was increased after TGF-beta 1 treatment in both cell lines. These results suggest that the mechanisms by which TGF-beta 1 inhibits the growth of cervical carcinoma are complex and may include effects on down-regulation of c-myc gene, and overexpression of p27Kip1 protein.

Secretion of ribonucleases by normal and immortalized cells grown in serum-free culture conditions

The requirement of serum in cell culture is a major limitation for studies on secreted ribonucleases (RNases) because serum contains a high amount of ribonucleolytic activity. Defined culture condition is thus of interest to improve our knowledge of the RNase biology. We report here that cells from three different types and origins, Chinese hamster lung fibroblasts, bovine smooth muscle cells, and human endothelium-derived EA.hy926 cells, proliferate consistently in the presence of a basal medium supplemented with bovine serum albumin, high-density lipoproteins, basic fibroblast growth factor, insulin, and transferrin. Using a new quantitative radio-RNase inhibitor assay, two distinct ribonucleolytic assays, and a radioimmunoassay against angiogenin, it is shown that RNases became apparent in media conditioned by cell monolayers. Both the hamster lung fibroblast and the EA.hy926 cell lines secreted larger amounts of RNase inhibitor-interacting factors and RNase activity than normal smooth muscle cells. The serum-free medium represents an alternative way to grow these cells and allows investigation of biosynthesis and functions of RNases in culture. It should be useful to identify and quantitate unambiguously specific members of the RNase family secreted by normal versus tumor cells in culture.

Cyclin A expression is under negative transcriptional control during the cell cycle

Transcription of the gene coding for cyclin A, a protein required for S-phase transit, is cell cycle regulated and is restricted to proliferating cells. To further explore transcriptional regulation linked to cell division cycle control, a genomic clone containing 5' flanking sequences of the murine cyclin A gene was isolated. When it was fused to a luciferase reporter gene, it was shown to function as a proliferation-regulated promoter in NIH 3T3 cells. Transcription of the mouse cyclin A gene is negatively regulated by arrest of cell proliferation. A mutation of a GC-rich sequence conserved between mice and humans is sufficient to relieve transcriptional repression, resulting in a promoter with constitutively high activity. In agreement with this result, in vivo footprinting reveals a protection of the cell cycle-responsive element in G0/early G1 cells which is not observed at later stages of the cell cycle. Moreover, the footprint is present in dimethyl sulfoxide-induced differentiating and not in proliferating Friend erythroleukemia cells. Conversely, two other sites, which in vitro bind ATF-1 and NF-Y, respectively, are constitutively occupied throughout cell cycle progression.

Transforming growth factor beta 1 inhibits mitogen-activated protein kinase induced by basic fibroblast growth factor in smooth muscle cells

Stimulation of smooth muscle cells with basic fibroblast growth factor (bFGF) results in the activation of the mitogen-activated protein kinase (MAP kinase) cascade and leads to cell proliferation. We show that transforming growth factor beta 1 (TGF-beta 1), at concentrations that completely inhibited bFGF-induced mitogenic activity, decreased bFGF-induced MAP kinase activity. Under these conditions, tyrosine and threonine phosphorylations of MAP kinase were differentially affected depending on the time period of TGF-beta 1 pretreatment. After a short (30 min) TGF-beta 1 pretreatment, the bFGF-mediated increase in phosphorylation of p42mapk on threonine was inhibited, with no effect on the level of phosphotyrosine or decrease in the electrophoretic mobility of p42mapk. This suggests that TGF-beta 1 inhibited MAP kinase activity through the action of a serine/threonine phosphatase. In contrast, a longer TGF-beta 1 pretreatment (4 h) partly inhibited the bFGF-induced MAP kinase mobility shift and correlated with the inhibition of phosphorylation on both threonine and tyrosine, suggesting that long-term TGF-beta 1 treatment prevented activation of the MAP kinase cascade or directly blocked MAP kinase. The ability of long-term (4 h) but not short-term (30 min) TGF-beta 1 pretreatment to inhibit MAP kinase activity was completely dependent on protein synthesis and suggests that TGF-beta 1 inhibits MAP kinase activity by two distinct mechanisms. These findings provide a molecular basis for the growth-inhibitory action TGF-beta 1 on bFGF-induced mitogenic activity.

Transforming growth factor-beta1 modulates p107 function in myeloid cells: correlation with cell cycle progression

Transforming growth factor-beta1 (TGF-beta1) is a potent inhibitor of hematopoietic cell growth. Here we report that TGF-beta1 signals inhibition of IL-3-dependent 32D-123 murine myeloid cell growth by modulating the activities of cyclin E and cyclin-dependent kinase 2 (cdk2) proteins and their complex formation in the G1 phase of the cell cycle. Whereas the cyclin E protein was hyperphosphorylated in TGF-beta1 treated cells, TGF-beta1 decreased both the phosphorylation of cdk2 and the kinase activity of the cyclin E-cdk2 complex. Decreased cyclin E-cdk2 kinase activity correlated with decreased phosphorylation of the retinoblastoma-related protein p107. In support of these observations, transient overexpression of p107 inhibited the proliferation of the myeloid cells, and expression of antisense oligodeoxynucleotides to p107 mRNA blocked TGF-beta1 inhibition of myeloid cell growth. Furthermore, as reported previously, in 32D-123 TGF-beta1 treated cells, c-Myc protein expression was decreased. TGF-beta1 increased the binding of p107 to the transcription factor E2F, leading to decreased c-Myc protein levels. p107 inhibited E2F transactivation activity and was also found to bind the c-Myc protein, suggesting p107 negative regulation of c-Myc protein function. These studies demonstrate the modulation of p107 function by TGF-beta1 and suggest a novel mechanism by which TGF-beta1 blocks cell cycle progression in myeloid cells.

TGF-beta isoforms fail to modulate inositol phosphates and cAMP in normal and tumour-derived human oral keratinocytes

This study examined inositol phosphate and cAMP regulation by TGF-beta 1, -beta 2 and -beta 3 in normal and tumour-derived human oral keratinocytes. Previous findings indicated that the cell lines expressed TGF-beta cell surface receptors and had a range of response to exogenous TGF-beta 1, -beta 2 and -beta 3 from being refractory to the ligand to marked inhibition. Basal levels of inositol phosphates broadly reflected the differentiation status of the cells as demonstrated by involucrin expression, but did not correlate with responsiveness to TGF-beta 1, as measured previously by thymidine incorporation. Treatment of cells with bradykinin or serum caused up-regulation of inositol phosphate levels; by contrast, TGF-beta 1, -beta 2 and -beta 3 failed to modulate inositol phosphates. In two tumour-derived cell lines, the TGF-beta isoforms had no effect on cAMP levels, despite a significant increase in cAMP using a potent agonist of adenylate cyclase (forskolin). Furthermore, the cAMP analogue, dibutyryl cAMP, failed to mimic the inhibitory or refractory responses of TGF-beta in these cells lines. The results demonstrate that in normal and tumour-derived human oral keratinocytes, TGF-beta signal transduction is not mediated by inositol phosphates or cAMP.

Immunohistochemical evaluation of TGF-beta and extracellular matrix proteins expression in rat squamous cell carcinomas

OBJECTIVE

The aim of this study was to establish a possible association between the degree of differentiation of squamous cell carcinomas (SCC) derived from rat oral tissues treated in vivo with carcinogen 4NQO, and the expression of TGF-beta on epithelial cells and the distribution of extracellular matrix proteins (laminin-collagen type IV).

MATERIALS AND METHODS

A parent tumor showing a spectrum of differentiation was used to establish clonal subpopulations that formed differentiated SCC and undifferentiated (spindle cell phenotype) tumours following transplantation to athymic mice.

RESULTS

Immunohistological findings revealed the absence of TGF-beta staining on epithelial cells and extracellular matrix proteins in spindle cell tumours. In contrast, staining of SCC revealed a significant number of TGF-beta positive cells and the presence of extracellular matrix proteins.

CONCLUSIONS

The findings suggested that there is a positive correlation between histological differentiation, TGF-beta expression and the elaboration of extracellular matrix proteins.

TGF-beta and phorbol esters inhibit mitogenesis utilizing parallel protein kinase C-dependent pathways

Transforming growth factor (TGF)-beta mediates matrix production in both mesangial and vascular smooth muscle cells. Both TGF-beta and phorbol-12-myristate-13-acetate (PMA) exert both positive and negative effects on mitogenesis in these as well as other cell types. Phorbol esters act through stimulation of protein kinase C (PKC) and are among the most potent tumor promoters known. The present study was conducted to determine if the growth inhibitory effect of TGF-beta parallels that of the phorbol esters and whether this effect of TGF-beta is dependent on activation of PKC. We show that, in vascular smooth muscle cells stimulated to divide by the addition of the serum component basic fibroblast growth factor (bFGF), TGF-beta1 inhibits mitogenesis in a dose-dependent manner, by a maximum of 79% when applied at a concentration of 1 ng/ml. Furthermore, the inhibitory effect on mitogenesis of either TGF-beta1 or PMA, when added four hours after bFGF, are 71% and 84% respectively. Both TGF-beta1 and PMA cause translocation of celllular PKC with similar time courses, while neither PKC-alpha nor PKC-betaII are increased in quantity in response to TGF-beta1. In addition, down-regulation of PKC by 24 hours incubation with PMA abolishes TGF-beta's inhibitory effect in bFGF-stimulated cells. We conclude that (i) the signaling pathway utilized by TGF-beta resulting in inhibition of mitogenesis parallels that of PMA, and (ii) the inhibitory effect of TGF-beta1 on bFGF-induced mitogenesis is partially due to activation of PKC. These data suggest that TGF-beta may be an endogenous activator of the growth-inhibitory pathway of PKC, and, since cellular differentiated functions generally occur when the cells are proliferation-inhibited, PKC may be a modulator of extracellular matrix deposition.

Initiation of growth inhibition by TGF beta 1 is unlikely to occur in G1

Type beta transforming growth factors represent a family of polypeptides that modulate growth and differentiation. They exert their effect on target cells through interaction with multiple cell surface receptors. Transforming growth factor-beta 1 has a strong inhibitory action on cell division in mink lung CC164 cells, a process that is initiated by immediate induction of junB and phosphorylation of nuclear protein followed by a reduced expression of cdk4. However, its signal transduction pathways are still unresolved. In this study we report a detailed analysis of cell kinetic events following addition of transforming growth factor-beta 1 to mink lung CCL64 cells. We show that transforming growth factor-beta 1 reduces [3H]thymidine incorporation after a delay of 8 hours, which reaches its nadir at 16 hours. The reduced growth rate is maintained for at least 48 hours as shown by flow cytometric analysis of DNA content. Using time-lapse video microscopy it was shown that control cells double on average every 14.4 hours, whereas the transforming growth factor-beta 1-treated cells have a doubling time of on average 20.3 hours. The difference in intermitotic time is a consequence of a prolonged G1 phase (a shift from 7.5 to 13.5 hours on average). However, changes in intermitotic times occur only after cells have undergone division in the presence of transforming growth factor-beta 1 and treated cells finish the ongoing cell cycle exactly like control cells. From these findings we conclude that transforming growth factor-beta 1 may change cell cycle parameters by interfering with cellular events prior to G1.(ABSTRACT TRUNCATED AT 250 WORDS)

TGF beta 1 inhibits branching morphogenesis and N-myc expression in lung bud organ cultures

Lung buds isolated from 11.5 days post coitum mouse embryos survive and undergo branching morphogenesis in culture. This organ culture system was used to examine the role of TGF beta 1 and N-myc expression in lung branching morphogenesis. By 24 hours, TGF beta 1 reversibly inhibited branching morphogenesis in a concentration-dependent manner. N-myc is known to be expressed during embryonic development in epithelial cells involved in branching morphogenesis and homozygous null N-myc mice have defects in lung development. In the present study, TGF beta 1 was shown to inhibit the steady-state level of N-myc RNA 3- to 4-fold at 14 and 48 hours of treatment as measured by northern blot and RNase protection analysis. Suppression of N-myc expression in epithelium was confirmed by in situ hybridization. Since inhibition of N-myc occurred prior to the observed changes in morphology and previous genetic studies have demonstrated and important role for N-myc in lung development, a model is proposed in which TGF beta 1 inhibits tracheobronchial development by inhibiting expression of N-myc.

Close correlation between the dephosphorylation of p53 and growth suppression by transforming growth factor-beta 1 in nasopharyngeal carcinoma cells transduced with adenovirus early region genes

The mechanism of growth inhibition by transforming growth factor (TGF)-beta 1 was investigated. We examined the growth inhibitory effects of TGF-beta 1 on human nasopharyngeal carcinoma (KB) cells which constitutively expressed p53. TGF-beta 1 suppressed the DNA synthesis of KB cells in a dose-dependent manner. It had minimal effect on adenovirus-2-transduced KB cells expressing either adenovirus early region 1B (E1B) or 1A (E1A) product, which respectively binds to p53 or Rb product and inhibits its function, and no growth inhibition at all was observed with KB cells expressing both E1B and E1A products. Dephosphorylation of the p53 was promoted by TGF-beta 1 stimulation in KB cells, but not in E1B-producing KB cells, which sequestrate the function of p53. The growth inhibition of KB cells by TGF-beta 1 was significantly reduced by treatment with okadaic acid. These results suggest that p53 transduces the antiproliferative signal of TGF-beta 1 possibly through its dephosphorylation.

Transforming growth factor-beta inhibits rat intestinal cell growth by regulating cell cycle specific gene expression

Transforming growth factor-beta 1 (TGF-beta 1) inhibits the growth of intestinal cells, but the mechanisms involved are unknown. Using a rat intestinal crypt cell line (IEC-6), we determined the site of action in the cell cycle that TGF-beta 1 acts to suppress proliferation. We also examined the effect of TGF-beta 1 on the expression of proliferation-associated "immediate early" genes (zif268, jun-B, c-myc) during the early G1 phase and the cdc2 gene during the transition from the G1 phase to the S phase of the cell cycle. Cell cycle progression was determined by incorporation of 3H-thymidine, and gene expression was analyzed by Northern blot analysis. We found that TGF-beta 1 acts to inhibit proliferation of rat intestinal crypt cells by blocking cell cycle progression at the middle G1 phase. The genes activated during G1 can be divided into TGF-beta 1 insensitive (zif268, jun-B, and c-myc) and TGF-beta 1 sensitive (the cdc2 gene). TGF-beta 1 suppresses the induction of the cdc2 gene during the G1/S transition without inhibiting the activation of immediate early genes during the early G1 phase.

General inhibition by transforming growth factor beta 1 of thyrotropin and cAMP responses in human thyroid cells in primary culture

Transforming growth factor beta 1 (TGF beta 1) mRNA has previously been identified in human thyroid cells and this agent has been shown to inhibit DNA synthesis in thyroid cells of some other species. In normal human thyroid cells in primary culture, TGF beta 1 inhibited inconstantly the low basal DNA synthesis and strongly the stimulation of DNA synthesis by epidermal growth factor (EGF) and serum, and by thyroid-stimulating hormone (TSH) acting through cAMP. This inhibition, by TGF beta 1, of the TSH and cAMP-dependent DNA synthesis was associated with an inhibition of PCNA (proliferating cell nuclear antigen) synthesis. TGF beta 1 almost completely abolished the cAMP induced stimulation of iodide uptake and thyroperoxidase synthesis. It thus, like EGF, also acts as a dedifferentiating agent. Investigation of the pattern of protein synthesis by two-dimensional gel electrophoresis revealed that while TGF beta 1, by itself, increased the synthesis of only one protein, a tropomyosin isoform, it inhibited most of the effects of cAMP on protein synthesis (35 out of 45 cAMP-regulated proteins were affected). It also reversed the effect of cAMP on the morphology of the thyrocytes. The fact that TGF beta 1 did not affect the increase in cAMP provoked by TSH in human thyroid cells while inhibiting most of the effects of dibutyryl cAMP in these cells suggests an action at a step distal to cAMP generation.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor beta 1-induced delay of cell cycle progression and its association with growth-related gene expression in mouse fibroblasts

TGF beta-induced cell cycle progression is relatively slower than that induced by EGF or PDGF-BB. Further, TGF beta delays EGF or PDGF-induced 5-phase entry in C3H 10T1/2 mouse fibroblasts. In accordance with this delay, the induction of mRNA level of 'immediate early genes' such as c-myc, c-fos, c-jun and junB by TGF beta has slower kinetics compared with those of EGF. TGF beta induces c-sis gene, suggesting possible involvement of secondary growth stimulation by PDGF-like proteins. However, anti-PDGF-AB antibody, which was inhibitory to FDGF-BB-induced [3H]thymidine incorporation, did not block TGF beta-induced DNA synthesis. These results first demonstrate that the delay of cell cycle progression by TGF beta is closely associated with the altered regulation of growth-related gene expression in fibroblasts.

IPG (inositolphosphate glycan) as a cellular signal for TGF-beta 1 modulation of chondrocyte cell cycle

The knowledge of transforming growth factor (TGF)-beta receptors has greatly progressed in the recent years. TGF-beta receptors type I and II have been implicated in the modulation of cell proliferation, whereas type III (betaglycan) may act as a component presenting TGF-beta to its signaling receptors. In addition, four other proteins that bind TGF-beta 1 or TGF-beta 2 have been recently identified in some cell lines, three being anchored to the membrane through a glycosylphosphatidylinositol (GPI). Despite this knowledge, the molecular mechanism of signal transduction through the TGF-beta receptors remain an enigma. TGF-beta family does not signal via any of the classical pathways. As GPI anchors of membrane proteins have been implicated in the transduction of some hormonal effects, we investigated the putative role of GPI in signaling the TGF-beta effects on the proliferation of rabbit articular chondrocytes (RAC). We previously showed that TGF-beta 1 increased DNA replication rate of RAC, with a recruitment of cells in G2/M followed by a subsequent mitosis wave. Here, we find that the factor causes specific GPI hydrolysis, with correlated increase of inositolphosphate glycan (IPG). This effect was specifically inhibited by antibodies that bind TGF-beta 1. Using [3H]-inositol labeling and Triton X-114 extraction, we demonstrate that a hydrophobic material from the membrane is cleaved by treatment of cell cultures with phosphatidylinositol specific phospholipase C (PI-PLC) or by exposure to TGF-beta, supporting that a PI-anchored molecule gives rise to IPG by TGF-beta-induced hydrolysis. The biological relevance of this hydrolysis was demonstrated by the enhancing effect of purified IPG on the DNA synthesis rate, which mimicked the TGF-beta action. These results demonstrate that IPG could be an early messenger in the cellular signaling that mediates the effect of TGF-beta on RAC growth.

Role of proteoglycans and cytoskeleton in the effects of TGF-beta 1 on renal proximal tubule cells

Transforming growth factor-beta (TGF-beta) is a critical cell regulatory protein which influences cell growth, cell differentiation and cell chemotaxis. TGF-beta 1 has been previously shown to promote a migratory and adherent transformation of monolayers of renal proximal tubule cells in primary culture to form solid clusters of cells. To better understand the cellular basis of this TGF-beta 1 effect, these studies evaluated the influence of TGF-beta 1 on the synthesis of proteoglycans and on cytoskeleton rearrangement in rabbit renal proximal tubule cells in primary culture, and their role in this transformation effect of TGF-beta 1. Biosynthetic labeling of proteoglycans with 35S sulfate and enzyme digestion studies demonstrated that TGF-beta 1 promoted the synthesis of heparan sulfate proteoglycans in these cells. The importance of proteoglycan synthesis induced by TGF-beta 1 in this migration and aggregation process was demonstrated with the use of two chemically-dissimilar proteoglycan synthesis inhibitors: xyloside and galactosamine. Both compounds inhibited TGF-beta 1 stimulation of proteoglycan synthesis and diminished TGF-beta 1 promoted transformation of proximal tubule cells as assessed by quantitative morphometry. Further experiments evaluated the influence of TGF-beta 1 on actin microfilaments with the use of rhodamine conjugated phalloidin staining and immunofluorescent microscopy, and demonstrated that TGF-beta 1 provoked a dramatic rearrangement of actin microfilaments into stress fibers. The use of actin microfilament disrupting agents, cytochalasin B and D, attenuated the stress fiber formation promoted by TGF-beta 1 and inhibited the TGF-beta 1-induced morphologic transformation of these cells. Further studies evaluated these effects on the rate of DNA synthesis in these cells, as assessed with 3H-thymidine incorporation. Proteoglycan synthesis inhibitors significantly diminished the maximal proliferative response of these epithelial cells to epidermal growth factor (EGF). In contrast, actin microfilament disaggregation with cytochalasin B or D did not change the rate of DNA synthesis in response to EGF but did attenuate the antiproliferative effect of TGF-beta 1 on EGF-induced DNA synthesis cells. These studies demonstrate that the TGF-beta 1 promoted synthesis cells. These studies demonstrate that the TGF-beta 1 promoted an increase in the production of proteoglycans and a higher ordered structure of the cytoskeleton. Both effects were instrumental in the adhesive migratory response of proximal tubule cells to TGF-beta 1 as well as the DNA synthesis rate response to both EGF and TGF-beta 1.

Growth inhibition of human pancreatic carcinoma cells by transforming growth factor beta-1

Pancreatic cancer is an extremely aggressive malignancy. The factors allowing human pancreatic cancer cells to escape normal growth constraints are not known. However, it has been proposed that certain cancer cells may obtain a growth advantage as the result of a lack of responsiveness to negative growth regulators such as transforming growth factor-beta 1 (TGF-beta 1). We now show that two established pancreatic carcinoma cell lines, COLO 357 and PANC-I, are sensitive to growth inhibition by TGF-beta 1. The growth of COLO 357 cells is inhibited by 50% when incubated in the presence of TGF-beta 1 (5 ng/ml) under low serum conditions (0.5%). PANC-I cells are growth inhibited by 25% under the same conditions. In COLO 357 cells, but not PANC-I cells, TGF-beta 1 also causes a marked alteration in cell morphology. In both cell lines, TGF-beta 1 induces TGF-beta 1 mRNA levels in a time and dose-dependent manner. However, TGF-beta 1 does not increase the amount of TGF-beta 2 or TGF-beta 3 mRNA in these cells. In spite of its growth inhibitory effects, TGF-beta 1 fails to suppress c-myc mRNA levels. These findings suggest that TGF-beta 1 inhibits the growth of human pancreatic cancer cells and point to a significant dysfunction in the ability of TGF-beta 1 to suppress c-myc expression in these cells.

Transforming growth factor-beta: signal transduction via protein kinase C in cultured embryonic vascular smooth muscle cells

Transforming growth factor-beta (TGF-beta), an ubiquitous regulatory peptide, has diverse effects on the differentiation and behavior of vascular smooth muscle cells (VSMC). However, the molecular mechanism through which TGF-alpha exerts its effects remains obscure. We investigated the phosphoinositide/protein kinase C [PKC] signaling pathway in the action of TGF-beta on cultured embryonic avian VSMC of differing lineage: a) thoracic aorta, derived from the neural crest; and b) abdominal aorta, derived from mesenchyme. The second messenger responsible for activation of PKC is sn-1,2-diacylglycerol [DAG]; TGF-beta increased the mass amounts of DAG in the membranes of neural crest-derived VSMC concurrent with translocation of PKC from the soluble to the membrane fraction, but TGF-beta had no effect on the DAG or PKC of mesenchyme-derived VSMC. TGF-beta potentiated the growth of platelet-derived growth factor (PDGF)-treated, neural crest-derived VSMC; but abolished PDGF-induced growth of mesenchymal cells. It is concluded that molecular and functional responses of VSMC to TGF-beta are heterogeneous and are functions of the embryonic lineage of the VSMC.

Transforming growth factor-beta 1 inhibitory effect of platelet-derived growth factor-induced signal transduction on human bone marrow fibroblasts: possible involvement of protein phosphatases

Transforming growth factor-beta 1 (TGF-beta 1) is a potent growth inhibitor for many cell types. On fibroblasts, TGF-beta 1 has been shown to inhibit human platelet-derived growth factor (PDGF)-induced mitogenicity. The mechanism implicated in this growth inhibition is unknown. In this work, we show on human bone marrow fibroblasts that TGF-beta 1, which inhibited PDGF-BB mitogenicity, was able to block PDGF-BB-induced early events such as polyphosphoinositide (PtdIns 4,5-P2, PtdIns 4-P, and PtdIns) breakdown and Ins 1,4,5-P3 formation. No significant modification by TGF-beta 1 of PDGF-BB binding (n1 = 200,000 vs. n2 = 195,000 sites per cell with TGF-beta 1; Kd1 = Kd2 = 0.5 x 10(-9) M) and of internalization kinetics was observed. In addition, TGF-beta 1 was shown to inhibit PDGF-BB receptor autophosphorylation either in intact cells or in partially isolated membranes and to partially inhibit PDGF-R tyrosine kinase activity. Since a dephosphorylation mechanism through protein phosphatases could be implicated, we used okadaic acid, a potent inhibitor of type 1 and 2A serine/threonine phosphatases and showed that okadaic acid restored PDGF-receptor autophosphorylation on tyrosine residues. Based on these data, we suggest that an alternative regulatory mechanism of PDGF tyrosine phosphorylation seems to involve serine/threonine phosphatase activation.

TGF beta inhibits rat thyroid cell proliferation without alterations in the expression of TSH-induced cell cycle-related genes

Transforming growth factor beta (TGF beta) is a secreted polypeptide factor that is thought to play a major role in the regulation of proliferation of many cell types and various differentiation processes. TGF beta acts on thyroid cells by inhibiting cell proliferation and expression of differentiation markers, such as thyroglobulin production and iodide uptake. Exponentially growing thyroid cells cultures accumulate mostly in G0/G1 after exposure to TGF beta for 48 hours. TGF beta inhibits the TSH induced transition of quiescent thyroid cell from the G0 to the S phase. These effects on the thyroid cell growth, however, are not mediated by changes in the TSH-induced cell cycle-related genes expression; both immediate early and progression genes expression is unaffected by the TGF beta treatment.

Inhibition of DNA synthesis by TGF-beta 1 coincides with inhibition of phosphorylation and cytoplasmic translocation of p53 protein

Immunostaining demonstrated that p53 protein was localized in the cytoplasm of growing MCF-7 cells and in the nuclei of cells that were growth arrested by serum starvation. Serum stimulation of the arrested cells induced marked increases in DNA synthesis and p53 phosphorylation, and translocation of the protein from the nucleus to the cytoplasm at 20 h after the stimulation. This increase in the DNA synthesis that was significantly inhibited by TGF-beta 1 was coincident with the inhibition of phosphorylation and cytoplasmic translocation of the p53 protein.

Cadmium's action on NRK-49F cells to produce responses induced also by TGFβ is not due to cadmium induced TGFβ production or activation

Transforming growth factor beta (TGF beta) is a multifunctional regulator of cell growth that has either a stimulatory or inhibitory effect on cell proliferation, depending on TGF beta concentration and on cell type, history and culture conditions. Cadmium mimics some of the effects of TGF beta in cultured cells. In this study the effects of Cd2+ and TGF beta on EGF-induced DNA synthesis in a clonal subpopulation (N1) of NRK-49F cells were compared. It was found that TGF beta 1 and cadmium both inhibit EGF-induced DNA synthesis and cell proliferation in a dose-dependent fashion, but that neither inhibits EGF-induced myc oncogene accumulation. TGF beta 1 and cadmium added at the same time as EGF or several hours after EGF addition showed similar inhibitory effects on EGF-induced [3H]Tdr incorporation, indicating that the inhibitory effect of TGF beta 1 and cadmium on EGF-induced DNA synthesis does not involve early G1 events. Rather, they occur in late G1, at the G1/S boundary or during S phase. Because of the similarities in nature and timing of the Cd2+ and TGF beta responses, the possibility that Cd2+ acts through stimulation of TGF beta production and/or activation was explored. It is shown in this paper however that TGF beta neutralizing antibody blocks the effects of TGF beta 1, but not the cadmium effects, on EGF-induced DNA synthesis, suggesting that cadmium is not functioning through activation or preinduction of TGF beta.

Signal transduction by bFGF, but not TGF beta 1, involves arachidonic acid metabolism in endothelial cells

We investigated the stimulation of early cellular events resulting from the interaction of the growth factor basic FGF (bFGF) and of the growth inhibitor transforming growth factor beta-type 1 (TGF beta 1), with their specific receptors on bovine endothelial cells. At mitogenic concentrations, bFGF stimulated the rapid release of arachidonic acid and its metabolites from (3H)-arachidonic acid labeled cells. When arachidonic acid metabolism was stimulated by addition of the calcium ionophore A23187, the effect of bFGF was amplified. Nordihydroguaïaretic acid, an inhibitor of the lipoxygenase pathway of arachidonic acid metabolism, decreased the mitogenic effect of bFGF, whereas indomethacin, an inhibitor of the cyclooxygenase pathway, was ineffective. These findings suggest that metabolism of arachidonic acid to lipoxygenase products may be necessary for the mitogenic effect of bFGF. Basic FGF did not stimulate the production of inositol phosphates from cells labelled with myo-(2-3H)-inositol nor did it induce calcium mobilization, as measured by fura-2 fluorescence, indicating that bFGF does not activate phosphoinositide-specific phospholipase C in endothelial cells, but rather, that bFGF-induced arachidonic acid metabolism is mediated by another phospholipase. TGF beta 1, which inhibits basal and bFGF-induced endothelial cell growth, had no effect on arachidonic acid metabolism and inositol phosphate formation and did not prevent bFGF-induced arachidonic acid metabolism. These results suggest that the inhibitory action of TGF beta 1 on endothelial cell growth occurs through different mechanisms.

Early gene responses to transforming growth factor-beta in cells lacking growth-suppressive RB function

The growth-suppressive function of the retinoblastoma susceptibility gene product, RB, has been implicated in the mediation of growth inhibition and negative regulation of certain proliferation related genes by transforming growth factor-beta 1 (TGF-beta 1). Early gene responses to TGF-beta 1 were examined in order to determine their dependence on the cell cycle and on the growth-suppressive function of RB. TGF-beta 1, which rapidly elevates the steady-state level of junB and PAI-1 mRNAs and decreases that of c-myc mRNA, induces these responses in S-phase populations of Mv1Lu lung epithelial cells containing RB in a phosphorylated state. Since in this state RB is presumed to lack growth-suppressive activity, the response to TGF-beta 1 was also examined in DU145 human prostate carcinoma cells whose mutant RB product lacks growth-suppressive function. In these cells, TGF-beta 1 also decreases c-myc expression at the transcription initiation level. These results suggests that the c-myc, junB, and PAI-1 responses to TGF-beta 1 are not restricted to the G1 phase of the cell cycle and that down-regulation of c-myc expression by TGF-beta 1 can occur through a mechanism independent from the growth-suppressive function of RB.

Early gene responses to transforming growth factor-beta in cells lacking growth-suppressive RB function

The growth-suppressive function of the retinoblastoma susceptibility gene product, RB, has been implicated in the mediation of growth inhibition and negative regulation of certain proliferation related genes by transforming growth factor-beta 1 (TGF-beta 1). Early gene responses to TGF-beta 1 were examined in order to determine their dependence on the cell cycle and on the growth-suppressive function of RB. TGF-beta 1, which rapidly elevates the steady-state level of junB and PAI-1 mRNAs and decreases that of c-myc mRNA, induces these responses in S-phase populations of Mv1Lu lung epithelial cells containing RB in a phosphorylated state. Since in this state RB is presumed to lack growth-suppressive activity, the response to TGF-beta 1 was also examined in DU145 human prostate carcinoma cells whose mutant RB product lacks growth-suppressive function. In these cells, TGF-beta 1 also decreases c-myc expression at the transcription initiation level. These results suggests that the c-myc, junB, and PAI-1 responses to TGF-beta 1 are not restricted to the G1 phase of the cell cycle and that down-regulation of c-myc expression by TGF-beta 1 can occur through a mechanism independent from the growth-suppressive function of RB.

Transforming growth factor beta 1, a potent chemoattractant for human neutrophils, bypasses classic signal-transduction pathways

Transforming growth factor beta 1 (TGF-beta 1), a homodimeric polypeptide (Mr 25,000), derives from inflammatory cells and acts as a chemoattractant for monocytes and fibroblasts. We report here that TGF-beta 1 is also the most potent chemoattractant yet described for human peripheral blood neutrophils. Recombinant TGF-beta 1 elicited dose-dependent directed migration of neutrophils under agarose that was inhibited in the presence of a neutralizing antibody to TGF-beta 1. Maximal chemotaxis was evoked by TGF-beta 1 at femtomolar concentrations, whereas conventional chemoattractants act at nanomolar concentrations: on a molar basis, TGF-beta 1 was 150,000 times more potent than fMet-Leu-Phe. In contrast, TGF-beta 1 provoked neither exocytosis nor the production of superoxide by neutrophils. We further analyzed the mechanism by which TGF-beta 1 elicits chemotaxis (GTPase activity, [Ca2+], and actin polymerization). In contrast to the conventional chemoattractant fMet-Leu-Phe, TGF-beta neither activated classic heterotrimeric guanine nucleotide-binding proteins nor provoked global mobilization of intracellular Ca2+. Chemoattraction by both fMet-Leu-Phe and TGF-beta 1 was inhibited by cycloheximide and actinomycin D. Moreover, chemotaxis in response to TGF-beta 1 was associated with the polymerization of actin. The selectivity and potency of TGF-beta 1 as a chemoattractant suggest that it elicits directed cell migration by means of a pathway that depends not on classic intracellular signals but on protein synthesis.

Transforming growth factor-beta (TGF-beta) isoforms in rat liver regeneration: messenger RNA expression and activation of latent TGF-beta

Expression of transforming growth factor-beta s (TGF-beta s) 1-3 was studied in normal liver and during liver regeneration after partial hepatectomy in the rat to determine whether each of these isoforms might be involved in hepatocyte growth in vivo. Expression of the mRNAs for all three TGF-beta isoforms increases in the regenerating liver. In addition, the levels of expression of the mRNAs for several extracellular matrix proteins, including fibronectin, vitronectin, laminin, and collagen, also increase in the regenerating liver. Immunohistochemical staining analysis shows a similar distribution of all three TGF-beta s in normal and regenerating liver; however, in both tissues, the level of expression of TGF-beta 1 is 8- to 10-fold higher than that of TGF-beta 2 as determined by sandwich enzyme-linked immunosorbent assay. Expression of all three TGF-beta mRNAs is restricted to liver nonparenchymal cells. Although hepatocytes from normal and regenerating livers do not synthesize TGF-beta, they are sensitive to inhibition of growth by all three TGF-beta isoforms. Hepatocytes from regenerating livers are capable of activating latent TGF-beta 1 complexes in vitro, whereas normal hepatocytes are not. The different TGF-beta isoforms may function in an inhibitory paracrine mechanism that is activated during liver regeneration and may also regulate the synthesis of extracellular matrix components in the regenerating liver.

Effects of transforming growth factor-beta 1 on growth of aortic smooth muscle cells. Influences of interaction with growth factors, cell state, cell phenotype, and cell cycle

Transforming growth factor (TGF)-beta 1 may have different effects on cell proliferation depending on many conditions. This paper clarifies the effects of various conditions on the effect of TGF-beta 1 on proliferation of cultured rabbit aortic smooth muscle cells (SMC) and also the time of its action during the cell cycle. TGF-beta 1 at 10-10,000 pg/ml inhibited DNA synthesis of SMC in the G0 stage derived from normal media or atheromatous intima stimulated by either platelet-derived growth factor (PDGF), fibroblast growth factor, SMC-derived growth factor, or fetal bovine serum (FBS). TGF-beta 1 also inhibited the growth of SMC in the growing state stimulated by either PDGF or FBS. TGF-beta 1 was effective only when added to the culture within 2 h after stimulation of the G0 state SMC with PDGF. It also inhibited increase in transcription of the c-myc protooncogene on stimulation of SMC with PDGF. These data suggest that TGF-beta 1 inhibited proliferation of SMC irrespective of the cell phenotype, growth conditions, and growth factors present and that it exerted this inhibitory effect during the time of the G0/G1 transition.

From growth arrest to growth suppression

Since the introduction of the cell cycle concept two approaches to study growth regulation of cells have been proposed. One claims that cells are naturally quiescent, requiring a stimulatory encouter with growth factors for induction of cell division. The other considers cellular multiplication as the natural steady-state; cessation of multiplication is thus a restriction imposed on the system. In the latter case emphasis is mainly on the signals involved in arrest of multiplication. This Prospect focuses on specific events occurring in mammalian cells at growth arrest, senescence, and terminal differentiation, specifically emphasizing the growth inhibitory factors, tumor suppressor genes, and other signals for growth suppression.

Phosphorylation of nuclear protein is an early event in TGF beta 1 action

Transforming growth factor beta (TGF beta) is a family of polypeptides that modulate growth and differentiation. TGF beta exerts its effects on target cells through interaction with specific cell surface receptors, but the signal transduction pathways are as yet largely unresolved. In this study we report that the growth inhibitory action of TGF beta on mink lung CCl 64 cells is associated with a rapid and transient phosphorylation of a number of nuclear proteins. In parallel, a transient expression of the immediate early gene jun B is observed. The expression of jun B can be inhibited by the protein kinase inhibitor H7 and can be augmented by the phosphatase inhibitor okadaic acid. Thus, protein phosphorylation can be a possible mechanism through which TGF beta 1 initiates early genomic responses.

Transforming growth factor beta 1 inhibition of p34cdc2 phosphorylation and histone H1 kinase activity is associated with G1/S-phase growth arrest

Transforming growth factor beta 1 (TGF beta 1) is a potent inhibitor of epithelial cell proliferation. We present data which indicate that epithelial cell proliferation is inhibited when TGF beta 1 is added throughout the prereplicative G1 phase. Cultures become reversibly blocked in late G1 at the G1/S-phase boundary. The inhibitory effects of TGF beta 1 on cell growth occur in the presence of the RNA synthesis inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole. Associated with this inhibitory effect is a decrease in the phosphorylation and histone H1 kinase activity of the p34cdc2 protein kinase. These data suggest that TGF beta 1 growth inhibition in epithelial cells involves the regulation of p34cdc2 activity at the G1/S transition.

Transforming growth factor beta 1 inhibition of p34cdc2 phosphorylation and histone H1 kinase activity is associated with G1/S-phase growth arrest

Transforming growth factor beta 1 (TGF beta 1) is a potent inhibitor of epithelial cell proliferation. We present data which indicate that epithelial cell proliferation is inhibited when TGF beta 1 is added throughout the prereplicative G1 phase. Cultures become reversibly blocked in late G1 at the G1/S-phase boundary. The inhibitory effects of TGF beta 1 on cell growth occur in the presence of the RNA synthesis inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole. Associated with this inhibitory effect is a decrease in the phosphorylation and histone H1 kinase activity of the p34cdc2 protein kinase. These data suggest that TGF beta 1 growth inhibition in epithelial cells involves the regulation of p34cdc2 activity at the G1/S transition.

TGF-beta: problems and prospects

TGF-beta research is proceeding at an exponential pace. Studies in this area have become increasingly relevant to many areas of cell regulation, continually providing new surprises and findings. One may confidently predict that TGF-beta will be one of the key molecules in future attempts to establish an integrated view of the processes whereby cells coordinate their own and mutual functions. We have seen only the beginning, and this minireview is only a glimpse.

Sensitivity of the cell cycle to TGF beta 1 does not correlate with transformation of a rat liver epithelial cell line

The effects of TGF beta 1 on cell cycle events in a rat liver derived epithelial cell line (BL9) and in two in vitro transformants of this line were studied by flow cytometry. Using either ethidium bromide staining or the incorporation of bromodeoxyuridine to evaluate DNA synthesis it was shown that TGF beta 1 prevented the entry of G0/G1 phase BL9 cells into S phase. TGF beta 1 did not exert its inhibitory effect(s) on DNA synthesis by the modulation of early events in the cell cycle. The tumorigenic transformed BL9 cell lines gave contrasting responses to the effects of TGF beta 1. DNA synthesis in a BL9 cell line derived by transfection with an active N-ras oncogene was unaffected by TFG beta 1 and thus appeared refractory to its growth controlling effects. On the other hand cells from a BL9 cell line derived by in vitro transformation with activated aflatoxin B1 retained their sensitivity to the effects of TGF beta 1. Thus the loss of the inhibitory effect of TGF beta 1 on DNA synthesis is not obligatory for the malignant transformation of rat liver epithelial cells.