Inactivation of sestrin 2 induces TGF-beta signaling and partially rescues pulmonary emphysema in a mouse model of COPD

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality worldwide. Cigarette smoking has been identified as one of the major risk factors and several predisposing genetic factors have been implicated in the pathogenesis of COPD, including a single nucleotide polymorphism (SNP) in the latent transforming growth factor (TGF)-beta binding protein 4 (Ltbp4)-encoding gene. Consistent with this finding, mice with a null mutation of the short splice variant of Ltbp4 (Ltbp4S) develop pulmonary emphysema that is reminiscent of COPD. Here, we report that the mutational inactivation of the antioxidant protein sestrin 2 (sesn2) partially rescues the emphysema phenotype of Ltbp4S mice and is associated with activation of the TGF-beta and mammalian target of rapamycin (mTOR) signal transduction pathways. The results suggest that sesn2 could be clinically relevant to patients with COPD who might benefit from antagonists of sestrin function.

Transcription factor GATA-6 is expressed in quiescent myofibroblasts in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) (histopathology of usual interstitial pneumonia [UIP]) is a progressive disease with poor prognosis. Characteristic features of IPF/UIP include fibroblastic foci, which are patchy lesions of focal, disarranged myofibroblasts. GATA-6 is a transcription factor linked with cell differentiation. Its role in the development of IPF has not previously been investigated. We hypothesized that GATA-6 participates in the differentiation of fibroblasts into myofibroblasts in IPF/UIP lungs. The expression patterns of GATA-6, the mesenchymal marker alpha-smooth muscle actin (alpha-SMA), and markers for proliferation (Ki67) and apoptosis (caspase-3) were analyzed in human IPF/UIP tissue samples. The effects of GATA-6 overexpression and silencing were studied in cell cultures. The results show that the alpha-SMA-positive fibroblastic foci in IPF/UIP lungs are positive for GATA-6, but negative for Ki67 and caspase-3. Cultured human IPF/UIP fibroblasts expressed GATA-6 mRNA, whereas cells from the normal adult lung did not. In cultured A549 lung epithelial cells, the induction of GATA-6 by transforming growth factor-beta1 resulted in simultaneous expression of alpha-SMA and decrease of E-cadherin. The inhibition of GATA-6 expression in fibroblasts showed that GATA-6 mediates the alpha-SMA-inducing signal of transforming growth factor-beta1. In conclusion, the hallmark of IPF/UIP histopathology, the fibroblast focus, consists of differentiated, quiescent cells that prominently express GATA-6.

Latent transforming growth factor-beta-binding protein-4 regulates transforming growth factor-beta1 bioavailability for activation by fibrogenic lung fibroblasts in response to bleomycin

Recent evidence suggests that subsets of lung fibroblasts differentially contribute to fibrogenic progression. We have previously shown that a subset of rat lung fibroblasts with fibrogenic characteristics [Thy-1 (-) fibroblasts] responds to stimuli (bleomycin, interleukin-4, etc) with increased latent transforming growth factor (TGF)-beta activation, whereas non-fibrogenic Thy-1-expressing [Thy-1 (+)] fibroblasts do not. Activation of latent TGF-beta1 by interstitial lung fibroblasts is critical for fibrogenic responses. To better understand the susceptibility of fibrogenic fibroblasts to the stimulation of TGF-beta activation, we examined the role of latent TGF-beta-binding proteins (LTBPs), key regulators of TGF-beta bioavailability and activation, in TGF-beta1 activation by these fibroblasts. Treatment of fibroblasts with bleomycin up-regulated LTBP-4 mRNA, protein, and soluble LTBP-4-bound large latent TGF-beta1 complexes in Thy-1 (-) fibroblasts to significantly higher levels than in Thy-1 (+) fibroblasts. Bleomycin-induced TGF-beta1 activation required LTBP-4, since lung fibroblasts deficient in LTBP-4 did not activate TGF-beta1. Expression of LTBP-4 restored TGF-beta1 activation in response to bleomycin, but expression either of LTBP-4 lacking the TGF-beta-binding site or only the TGF-beta-binding domain did not. Bleomycin treatment of mice increased LTBP-4 expression in the lung. Thy-1 knockout mice had increased levels of both LTBP-4 expression and TGF-beta activation, as well as enhanced Smad3 phosphorylation compared with wild-type mice. Together, these data identify a critical role for LTBP-4 in the regulation of latent TGF-beta1 activation in bleomycin-induced lung fibrosis.

Latent TGF-beta binding proteins (LTBPs)-1 and -3 coordinate proliferation and osteogenic differentiation of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) possess the capability to differentiate into bone forming cells, osteoblasts, and thus represent a new therapeutic tool in regenerative medicine. Transforming growth factor (TGF)-beta is abundantly present in bone tissue where it regulates osteoblast and osteoclast functions in a complex manner. Latent TGF-beta binding protein (LTBP)-1 mediates the extracellular matrix (ECM) targeting and accumulation of most TGF-beta in the bone. We describe here an important regulatory role for LTBP-3 in TGF-beta activation and autocrine growth control in MSCs. LTBP-3 knockdown via siRNA mediated silencing resulted in reduced cell proliferation and reduced osteogenic differentiation. When MSCs were induced to undergo differentiation, LTBP-3 levels became downregulated in parallel with reduced TGF-beta activation. These changes coincided with the matrix maturation phase of osteogenic differentiation. The mechanism of LTBP-3 is most likely via TGF-beta activation in the early proliferative phase of the differentiation process. Later, when TGF-beta activity would inhibit further maturation and mineralization, LTBP-3 expression becomes downregulated and LTBP-1 containing large latent TGF-beta1 complexes accumulate into the ECM. These complexes represent readily available targets for osteoclast mediated release and activation of TGF-beta in bone tissue. Our results provide evidence that LTBP isoforms can differentially regulate TGF-beta activation and ECM accumulation during osteogenic differentiation.

Transforming growth factor-beta activation in the lung: focus on fibrosis and reactive oxygen species

Transforming growth factor-betas (TGF-beta) regulate a wide variety of cellular functions in normal development and are involved in both tissue homeostasis and disease pathogenesis. The regulation of the TGF-beta family of growth factors is unique because they are targeted to the extracellular matrix in a biologically inactive form. The release from pericellular matrices and the activation of TGF-beta are important mechanisms in several pathophysiologic conditions. Reactive oxygen species (ROS) can activate TGF-beta either directly or indirectly via the activation of proteases. In addition, TGF-beta itself induces ROS production as part of its signal-transduction pathway. The lung is a unique organ, because its structures act as boundaries between gaseous and aqueous phases, allowing the utilization of inhaled oxygen. However, this renders pulmonary tissues vulnerable to the toxic effects of inhaled air. The oxidant pathways are especially relevant in the lung, where TGF-beta is known to have a role in tissue repair and connective tissue turnover. In pulmonary fibrosis, TGF-beta activation is considered as a hallmark of disease progression. More recently, the oxidative effects of cigarette smoking have been found to activate TGF-beta in chronic obstructive pulmonary disease (COPD), a disease consisting of emphysema, airway fibrosis, and focal lung fibrosis.

Gremlin-mediated decrease in bone morphogenetic protein signaling promotes pulmonary fibrosis

RATIONALE

Members of the transforming growth factor (TGF)-beta superfamily, including TGF-betas and bone morphogenetic proteins (BMPs), are essential for the maintenance of tissue homeostasis and regeneration after injury. We have observed that the BMP antagonist, gremlin, is highly up-regulated in idiopathic pulmonary fibrosis (IPF).

OBJECTIVES

To investigate the role of gremlin in the regulation of BMP signaling in pulmonary fibrosis.

METHODS

Progressive asbestos-induced fibrosis in the mouse was used as a model of human IPF. TGF-beta and BMP expression and signaling activities were measured from murine and human fibrotic lungs. The mechanism of gremlin induction was analyzed in cultured lung epithelial cells. In addition, the possible therapeutic role of gremlin inhibition was tested by administration of BMP-7 to mice after asbestos exposure.

MEASUREMENTS AND MAIN RESULTS

Gremlin mRNA levels were up-regulated in the asbestos-exposed mouse lungs, which is in agreement with the human IPF biopsy data. Down-regulation of BMP signaling was demonstrated by reduced levels of Smad1/5/8 and enhanced Smad2 phosphorylation in asbestos-treated lungs. Accordingly, analyses of cultured human bronchial epithelial cells indicated that asbestos-induced gremlin expression could be prevented by inhibitors of the TGF-beta receptor and also by inhibitors of the mitogen-activated protein kinase kinase/extracellular signal-regulated protein kinase pathways. BMP-7 treatment significantly reduced hydroxyproline contents in the asbestos-treated mice.

CONCLUSIONS

The TGF-beta and BMP signaling balance is important for lung regenerative events and is significantly perturbed in pulmonary fibrosis. Rescue of BMP signaling activity may represent a potential beneficial strategy for treating human pulmonary fibrosis.

Bone morphogenetic protein-4 inhibitor gremlin is overexpressed in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF), ie, usual interstitial pneumonia in histopathology, is a disease characterized by tissue destruction and active areas of fibroproliferation in the lung. Gremlin (Drm), a member of the cysteine knot family of bone morphogenetic protein (BMP) inhibitors, functions to antagonize BMP-4-mediated signals during lung development. We describe here consistent overexpression of gremlin in the lung interstitium of IPF patients. Quantitative real-time reverse transcriptase-polymerase chain reaction analyses revealed considerably higher levels of gremlin mRNA in lung biopsies from IPF patients, the highest level being 35-fold higher compared to controls. Lung fibroblasts isolated from IPF patients also expressed elevated levels of gremlin, which was associated with impaired responsiveness to endogenous and exogenous BMP-4. Transforming growth factor-beta-induced epithelial-to-mesenchymal transition of A549 lung epithelial cells in culture was also associated with induction of gremlin mRNA expression. In addition, A549 cells transfected to overexpress gremlin were more susceptible to transforming growth factor-beta-induced epithelial-to-mesenchymal transition. Gremlin-mediated inhibition of BMP-4 signaling pathways is likely to enhance the fibrotic response and reduce epithelial regeneration in the lung. The overexpression of this developmental gene in IPF may be a key event in the persistence of myofibroblasts in the lung interstitium and provides a potential target for therapeutic intervention.

Activation of Smad signaling enhances collagenase-3 (MMP-13) expression and invasion of head and neck squamous carcinoma cells

Squamous cell carcinoma (SCC) cells of the head and neck specifically express collagenase-3 (matrix metalloproteinase-13 (MMP-13)), the expression of which correlates with their invasion capacity. Transforming growth factor-beta (TGF-beta) enhances MMP-13 and collagenase-1 (MMP-1) expression and invasion of SCC cells via p38 mitogen-activated protein kinase. Here, we have examined the role of Smad signaling in regulating MMP-13 expression and in invasion of head and neck SCC cells. Treatment with TGF-beta resulted in activation of Smad2 and Smad3 in SCC cells, but had no effect on their proliferation or viability. Basal activation of Smad3 and p38 was noted in SCC cells without exogenous TGF-beta stimulation, and adenoviral delivery of Smad7 and dominant-negative Smad3 inhibited p38 activation in these cells. Adenoviral overexpression of Smad3 augmented the upregulatory effect of TGF-beta on MMP-13 expression by SCC cells. Disruption of Smad signaling by adenoviral expression of kinase-defective TGF-beta type I receptor (activin-receptor-like kinase-5), Smad7, and dominant-negative Smad3 potently suppressed the basal and TGF-beta-induced expression of MMP-13 and MMP-1 in SCC cells, and inhibited their basal and TGF-beta-induced invasion through Matrigel and type I collagen. Adenoviral overexpression of Smad7 in cutaneous and oral SCC cells significantly inhibited their implantation in skin of SCID mice and growth of xenografts in vivo, as compared to LacZ adenovirus-transduced control cells. Together, these results show that Smad signaling plays an important role in promoting the invasive phenotype of human head and neck SCC cells by upregulating their collagenase expression.

Sequential deposition of latent TGF-β binding proteins (LTBPs) during formation of the extracellular matrix in human lung fibroblasts

Latent TGF-beta binding proteins (LTBPs) mediate the targeting of latent TGF-beta complexes into ECM structures, which is important for TGF-beta activation and functions. LTBPs-1, -3 and -4 associate with and regulate the bioavailability of TGF-betas. We investigated whether LTBP-3 and -4 are associated with pericellular fibrillar structures of human lung fibroblast ECM, and which of their domains are important for this function. Immunoblotting analyses of isolated insoluble matrices as well as immunofluorescence analyses and confocal microscopy indicated that both LTBP-3 and -4 get assembled into the ECM. Interestingly, LTBP-4 was not detected until 7-10 days of culture and LTBP-3 until 14 days of culture. This was a major difference from the deposition kinetics of LTBP-1, which was detected already within 2 days of culture. Expression analyses by real time RT-PCR indicated that the slow appearance of LTBP-3 and -4 was due to the low expression levels soon after subculture. Recombinant N-terminal fragments of LTBP-3 and -4 bound readily to fibroblast ECM. The C-terminal domain of LTBP-4, but not of LTBP-3, also associated with the matrix structures. The levels of ECM-associated latent complexes of TGF-beta1 increased in parallel with the increased production and deposition of the LTBPs. The amount of active TGF-beta in the conditioned medium decreased during extended culture. Our results suggest that ECM is an important site of deposition also for LTBP-3 and -4 and that the temporal and spatial targeting of the TGF-beta complexes are associated with ECM maturation.

Induction of human LTBP-3 promoter activity by TGF-beta1 is mediated by Smad3/4 and AP-1 binding elements

Latent TGF-beta binding proteins (LTBPs) are extracellular matrix glycoproteins, which are essential for the targeting and activation of TGF-betas. LTBP-3 regulates the bioavailability of TGF-beta especially in the bone. To understand the regulation of LTBP-3 expression, we have isolated and characterized the promoter region of human LTBP-3 gene. The GC-rich TATA-less promoter contained several transcription initiation sites and putative binding sites for multiple sequence specific transcription factors including Sp1, AP-1, c-Ets, MZF-1, Runx1 and members of the GATA-family. Reporter gene analyses of the promoter indicated that it was more active in MG-63 than in Saos-2 osteosarcoma cells, suggesting that it is regulated as the endogenous gene. TGF-beta1 stimulated the transcriptional activity of LTBP-3 promoter in MG-63 cells, while certain other bone-derived growth factors and hormones were ineffective. TGF-beta1 increased LTBP-3 mRNA levels accordingly. Analyses of deletion constructs of the promoter and mutational deletion of specific transcription factor binding sites indicated that Smad3/4 and AP-1 binding sites mediated the TGF-beta1 response. The involvement of AP-1 activity was further indicated by decreased TGF-beta responsiveness of the LTBP-3 promoter in the presence of a MEK/Erk signaling pathway inhibitor. Our results suggest an important new role for TGF-beta1 in the regulation of its binding protein, LTBP-3.

TGF-β activation by traction?

Transforming growth factor (TGF)-betas are powerful cytokines that are secreted as inactive (latent) precursors into the extracellular space. To exert their pleiotropic functions, latent TGF-betas require activation. This requisite restricts TGF-beta signaling to tissues that express TGF-beta-activating proteins such as the adhesion molecule alphavbeta6 integrin. Recent work has uncovered the molecular mechanism by which alphavbeta6 integrin activates latent TGF-beta. Latent-TGF-beta-binding protein 1 has been identified as being the major component of this process, and the integrin-interacting region has been mapped to a poorly conserved sequence stretch called the hinge region.

Disruption of LTBP-4 function reduces TGF-beta activation and enhances BMP-4 signaling in the lung

Disruption of latent TGF-β binding protein (LTBP)–4 expression in the mouse leads to abnormal lung development and colorectal cancer. Lung fibroblasts from these mice produced decreased amounts of active TGF-β, whereas secretion of latent TGF-β was significantly increased. Expression and secretion of TGF-β2 and -β3 increased considerably. These results suggested that TGF-β activation but not secretion would be severely impaired in LTBP-4 −/− fibroblasts. Microarrays revealed increased expression of bone morphogenic protein (BMP)–4 and decreased expression of its inhibitor gremlin. This finding was accompanied by enhanced expression of BMP-4 target genes, inhibitors of differentiation 1 and 2, and increased deposition of fibronectin-rich extracellular matrix. Accordingly, increased expression of BMP-4 and decreased expression of gremlin were observed in mouse lung. Transfection of LTBP-4 rescued the −/− fibroblast phenotype, while LTBP-1 was inefficient. Treatment with active TGF-β1 rescued BMP-4 and gremlin expression to wild-type levels. Our results indicate that the lack of LTBP-4–mediated targeting and activation of TGF-β1 leads to enhanced BMP-4 signaling in mouse lung.

Expression of latent TGF-beta binding protein LTBP-1 is hormonally regulated in normal and transformed human lung fibroblasts

Latent transforming growth factor-beta binding proteins (LTBPs), participate in the secretion, targeting and activation of transforming growth factor-beta (TGF-beta) isoforms. Besides the regulation of the bioavailability of TGF-betas, LTBPs are secreted as free forms and they associate with extracellular fibrillar structures. The current study was carried out to understand hormonal regulation of LTBP-1 expression in normal and SV-40 virus transformed human lung fibroblasts. LTBP-1 protein and mRNA expression were analysed by immunoblotting and Northern hybridisation. Basal expression levels of LTBP-1 were significantly reduced in the transformed cells. Retinoic acid (RA) as well as 9-cis-RA increased LTBP-1 expression in both cell lines, probably through post-transcriptional mechanisms. Dexamethasone induced LTBP-1 protein and mRNA levels in both cell lines. The effect was much more prominent in transformed cells and involved both transcriptional and post-transcriptional events. Vitamin D, estradiol and tamoxifen had only negligible effects on LTBP-1 expression. TGF-beta1 increased its own expression as well as LTBP-1 levels in both cell lines, but the response was clearly of lower magnitude in transformed cells. This may reflect insensitivity to TGF-beta1, which is a common feature for malignant cells. Our results indicate that LTBP-1 expression is under the regulation of RA and corticoids in lung fibroblasts. The responses to these hormonal modulators may either be lost or enhanced in transformed cells, which likely contributes to malignant growth.

Disruption of the gene encoding the latent transforming growth factor-beta binding protein 4 (LTBP-4) causes abnormal lung development, cardiomyopathy, and colorectal cancer

Transforming growth factor-betas (TGF-betas) are multifunctional growth factors that are secreted as inactive (latent) precursors in large protein complexes. These complexes include the latency-associated propeptide (LAP) and a latent transforming growth factor-beta binding protein (LTBP). Four isoforms of LTBPs (LTBP-1-LTBP-4) have been cloned and are believed to be structural components of connective tissue microfibrils and local regulators of TGF-beta tissue deposition and signaling. By using a gene trap strategy that selects for integrations into genes induced transiently during early mouse development, we have disrupted the mouse homolog of the human LTBP-4 gene. Mice homozygous for the disrupted allele develop severe pulmonary emphysema, cardiomyopathy, and colorectal cancer. These highly tissue-specific abnormalities are associated with profound defects in the elastic fiber structure and with a reduced deposition of TGF-beta in the extracellular space. As a consequence, epithelial cells have reduced levels of phosphorylated Smad2 proteins, overexpress c-myc, and undergo uncontrolled proliferation. This phenotype supports the predicted dual role of LTBP-4 as a structural component of the extracellular matrix and as a local regulator of TGF-beta tissue deposition and signaling.

Novel non-TGF-β-binding splice variant of LTBP-4 in human cells and tissues provides means to decrease TGF-β deposition

Small latent TGF-β consists of latency associated peptide (LAP) bound to the 25 kDa TGF-β by noncovalent interactions. Small latent TGF-β is secreted from cells and deposited into the extracellular matrix as covalent complexes with its binding proteins, LTBPs. Four LTBPs have been molecularly cloned and their structures contain repetitive sequences. The 3rd 8-Cys repeats of LTBP-1, -3 and -4 are able to associate with small latent TGF-β. We analyzed by RT-PCR the expression of LTBPs 1-4 in a panel of cultured human cell lines including fibroblasts of different origin, endothelial cells and immortalized keratinocytes. LTBPs were expressed in an overlapping manner, but differences in their expression levels were detected. SV-40 transformed human embryonic lung fibroblasts contained less of the mRNAs for the LTBPs, suggesting that malignant transformation leads to decrease in LTBP expression. A novel alternatively spliced form of LTBP-4 lacking the 3rd 8-Cys repeat (LTBP-4Δ8-Cys3rd) was identified. LTBP-4Δ8-Cys3rd does not bind TGF-β and it was found to be expressed in the same tissues as the full length LTBP-4. The exon-intron structure of LTBP-4 around the 3rd 8-Cys repeat was similar to those of LTBP-2 and -3. LTBP-4Δ8-Cys3rd was produced by alternative splicing over two exons. In addition, HL-60 promyelocytic leukemia cells expressed a splice variant lacking only one exon of this region. The expression of the non-TGF-β-binding variant of LTBP-4 may be important for the regulation of TGF-β deposition in tissues. Since LTBPs are a part of the extracellular matrix microfibrils, the LTBP-4Δ8-Cys3rd protein may also be involved in various structural functions not related to TGF-β signaling.

Latency, activation, and binding proteins of TGF-beta

The TGF-beta superfamily of growth factors consists of an increasing number of different polypeptide modulators of cell growth, differentiation, and morphogenesis. Three mammalian isoforms have been molecularly cloned. Numerous ways to regulate the expression of the TGF-beta genes have been identified. TGF-betas are, for example, subject to regulation by retinoids, steroid hormones, and vitamin D. A characteristic feature in the biology of TGF-betas is that they are usually secreted from cells in latent forms. The large latent complex consists of the small latent complex (TGF-beta and its propeptide) and a high molecular weight protease resistant binding protein, latent TGF-beta binding protein (LTBP). LTBPs are required for the proper folding and secretion of TGF-beta. TGF-beta is not just secreted from cultured cells but is deposited via LTBPs to the pericellular space, namely to the extracellular matrix. Release of these complexes and activation by proteases is under tight regulation and provides a means to rapidly increase local concentrations of TGF-beta. Biological events, where enhanced or focal proteolysis and activation of latent TGF-beta takes place, include cell invasion, tissue remodeling, and wound healing.

1alpha,25-dihydroxyvitamin D3 and its analogues down-regulate cell invasion-associated proteases in cultured malignant cells

Vitamin D and its derivatives (deltanoids) are potent regulators of cell proliferation and differentiation. Targeted production of proteolytic enzymes like serine proteases and metalloproteinases is an important part of the invasive process of cancer cells. Treatment with 1 alpha25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] decreases the invasive properties of breast carcinoma cells. Here we have analyzed the effects of 1alpha,25(OH)2D3 and its synthetic analogues on the secretion and cell surface association of the components of the plasminogen activator (PA) system and on the secretion of certain matrix metalloproteinases (MMPs) and their inhibitors in MDA-MB-231 breast carcinoma cells. Deltanoids were able to decrease the secretion of urokinase PA and tissue-type PA activity in a dose-dependent manner and to increase PA inhibitor 1 secretion, leading to reduced total PA activity. CB1093 was the most potent analogue, effective at concentrations several logarithms lower than 1alpha,25(OH)2D3. Transient transfection of different urokinase PA promoter reporter constructs to HT-1080 fibrosarcoma indicator cells indicated that vitamin D-responsive sequences were located between nucleotides -2350 and -1870 in the 5' region of the promoter. Treatment of MDA-MB-231 cells with 1alpha,25(OH)2D3 or other deltanoids also resulted in decreased MMP-9 levels in association with increased tissue inhibitor of MMP 1 activity. Membrane-type 1-MMP expression or proteolytic processing were not appreciably affected by deltanoids. Vitamin D and its analogues caused a decrease in Matrigel invasion assays of MDA-MB-231 cells. Cancer cell invasion is associated with coordinated secretion of proteolytic enzymes and their inhibitors. Vitamin D and its derivatives can evidently influence invasive processes by two means: (a) decreasing the expression and activity of cell invasion-associated serine proteases and metalloproteinases; and (b) inducing their inhibitors.

Vitamin D3 regulation of transforming growth factor-beta system in epithelial and fibroblastic cells--relationships to plasminogen activation

Vitamin D3 and its analogs are potent regulators of growth and differentiation of various cell types. A mechanism of action of vitamin D3 and other steroid hormones is to enhance the secretion of transforming growth factor-beta (TGF-beta) in target cells. In epidermal keratinocytes, vitamin D3 induced the expression of both TGF-beta 1 and TGF-beta 2 with minor changes in mRNA levels, while in BT-20 breast carcinoma cells the increase in TGF-beta activity was preceded by an induction of mRNA. In both cell systems, the absolute amounts of active TGF-beta increased, and in keratinocytes the proportion of active TGF-beta was also enhanced. A concomitant enhancement of secretion of the latent TGF-beta-binding protein by vitamin D3 was observed in BT-20 cells. Retinoic acid, which is known to interfere with vitamin D3 signaling, slightly decreased the levels of secreted TGF-beta 1 protein in BT-20 cells, but did not significantly affect the vitamin D3-induced increase. In addition to regulation of the TGF-beta system, vitamin D3 decreases pericellular plasminogen activator activity in keratinocytes. Plasmin-mediated proteolytic events are involved in the release from pericellular space and activation of TGF-beta. We analyzed vitamin D3 regulation of fibroblast growth and the secretion of PA activity. Vitamin D3 inhibited fibroblast growth in a concentration-dependent manner and downregulated plasminogen activator activity as in keratinocytes. In fibroblasts, vitamin D3 did not induce notable alterations in TGF-beta 1 or latent TGF-beta-binding protein secretion, suggesting divergent growth inhibitory mechanisms. Our results indicate that vitamin D3 and its analogs are potent regulators of the TGF-beta and plasminogen activator systems in cells of epithelial and mesenchymal origin.

Transforming growth factor-beta system and its regulation by members of the steroid-thyroid hormone superfamily

TGF-beta s and their receptors are expressed ubiquitously, and they act as key regulators of many aspects of cell growth, differentiation, and function. Steroid action on target tissues is often associated with increase in TGF-beta isoforms. Regulation of TGF-beta expression and activation is crucial for normal development and growth control. The loss of responsiveness of different tumor cells to the antiproliferative effects of TGF-beta is a common feature in carcinogenesis. Multiple changes are required for the cells to gain complete resistance to TGF-beta growth inhibition (Fynan and Reiss, 1993; Kimchi et al., 1988; Samuel et al., 1992). Although many tumor cells are not growth inhibited by TGF-beta, they respond to TGF-beta treatment by changes in the expression of matrix components and enhanced proteolytic activity (KeskiOja et al., 1988). Agents that induce TGF-beta production in target tissues can have a chemopreventive or chemotherapeutic value for the management of epithelial malignancies. Conversely, data supporting a positive role for TGF-beta in established tumor progression are beginning to emerge (Arteaga et al., 1993a,b; Barrett-Lee et al., 1990; Arrick et al., 1992 ; E. A. Thompson et al., 1991). In later stages of tumor development, cell proliferation is often not inhibited by TGF-beta, and tumor cells secrete large amounts of this growth factor (Fynan and Reiss, 1993). In vivo TGF-beta secreted by tumor or stromal cells can influence host responses such as a natural killer cell function and thus indirctly support tumor cell viability (Arteaga et al., 1993b). TGF-beta may also affect tumor growth indirectly by stromal effects and promotion of angiogenesis. TGF-beta may also be involved in the progression of breast tumors from the steroid-sensitive to steroid-insensitive state (King et al., 1989). Understanding of the net effect of TGF-beta in different stages of tumor development is critical for the evaluation of its therapeutic value in cancer treatment.

1,25-Dihydroxyvitamin D3 enhances the expression of transforming growth factor beta 1 and its latent form binding protein in cultured breast carcinoma cells

Transforming growth factor beta s (TGF-beta s) are a family of polypeptide growth factors that regulate cellular growth, phenotype, and differentiation. TGF-beta s are synthesized as latent high molecular weight complexes that include the NH2-terminal remnant of the TGF-beta precursor (latency-associated protein) and, frequently, latent TGF-beta binding protein. After activation, TGF-beta s act as local mediators of hormonal responses in target tissues. TGF-beta functions as a negative growth regulator for both breast cancer cells and normal mammary epithelial cells. Vitamin D3 is growth inhibitory for the estrogen receptor-negative breast cancer cell line BT-20 and regulates TGF-beta expression in cultured keratinocytes. We studied here the effects of vitamin D3 and its analogues on TGF-beta expression and activity in BT-20 cells. It was found that vitamin D3 enhanced both TGF-beta 1 mRNA and secretion of the protein in a time- and dose-dependent manner. Analyses of the vitamin D3 responses in the presence of cycloheximide or actinomycin D indicated that the TGF-beta 1 mRNA induction was dependent on both protein and RNA synthesis. The amounts of latent TGF-beta binding protein were also increased in the conditioned medium but not in the pericellular matrix of vitamin D3-treated cultures. The amounts of active TGF-beta were enhanced in vitamin D3-treated cultures as well, suggesting autocrine or paracrine functions for the secreted growth factor. Some analogues of vitamin D3 (EB 1089, MC 903, and KH 1060) that are known to be potent inhibitors of breast cancer cell growth both in vitro and in vivo had similar or more pronounced inducing effects on TGF-beta 1 mRNA levels. The present results indicate that vitamin D3 and its analogues are potent inducers of both active and latent forms of TGF-beta 1 in BT-20 breast carcinoma cells and provide evidence for coordinated regulation of latent TGF-beta binding protein and TGF-beta 1.

Vitamin D3 and calcipotriol decrease extracellular plasminogen activator activity in cultured keratinocytes

Vitamin D3, 1 alpha,25(OH)2D3, and its metabolites regulate the growth and differentiation of several cell types. Vitamin D3 and its analogue, calcipotriol (MC 903), inhibit the proliferation of cultured human and mouse keratinocytes and induce keratinocyte differentiation. Calcipotriol is effective in the treatment of psoriasis in which increased plasminogen activator activity has been reported. We analyzed therefore the effects of calcipotriol and vitamin D3 on the production of plasminogen activator (PA) activity in human keratinocytes and a mouse keratinocyte cell line. Caseinolysis-in-agarose assays indicated that vitamin D3 decreases total PA activity in both keratinocyte culture systems. Zymographic analyses of the medium indicated that the secreted activator was of the urokinase type (u-PA). A decrease was observed also in extracellular matrix and membrane-associated u-PA activity of vitamin D3 and calcipotriol treated cells. Immunoblotting analysis of the conditioned medium from human keratinocytes revealed a decrease in the u-PA protein levels. Accordingly, Northern hybridization analysis of the respective mRNAs indicated a rapid decrease in urokinase mRNA levels. Calcipotriol decreased u-PA activity also in the presence of inducers of u-PA activity like transforming growth factor-beta, epidermal growth factor, and phorbol-12-myristate-13-acetate. Calcipotriol also caused a decrease in tissue type PA (t-PA) activity of the keratinocytes. Most t-PA activity was associated with the extracellular matrices and cell membranes as revealed by zymographic analysis. Paradoxically, the secretion and deposition of the matrix of plasminogen activator inhibitor type 1 decreased in calcipotriol-treated cells. The results indicate that a major effect of vitamin D3 on cultured keratinocytes is a decrease of plasminogen activator activity.